IMPROVED PROCESS FOR THE SYNTHESIS OF OLIGOMERIC COMPOUNDS

Abstract: Synthetic processes are provided wherein oligomeric compounds are prepared having phosphodiester, phosphorothioate, and phosphorodithioate covalent linkages. Also provided are synthetic intermediates useful in such processes.

Description: IMPROVED PROCESS FOR THE SYNTHESIS OF OLIGOMERIC COMPOUNDS FIELD OF THE INVENTION This invention relates to methods for the preparation of oligomeric compounds having phosphite, phosphodiester, phosphorothioate, or phosphorodithioate linkages, and to intermediates useful in their preparation. BACKGROUND OF THE INVENTION Oligonucleotides and their analogs have been developed and used in molecular biology in certain procedures as probes, primers, linkers, adapters, and gene fragments. Modifications to oligonucleotides used in these procedures include labeling with nonisotopic labels, e.g. fluorescein, biotin, digoxigenin, alkaline phosphatase, or other reporter molecules . Other modifications have been made to the ribose phosphate backbone to increase the nuclease stability of the resulting analog. These modifications include use of methyl phosphonate, phosphoro¬ thioate, and phosphorodithioate linkages, and 2 ' -0-methyl ribose sugar units. Further modifications include those made to modulate uptake and cellular distribution. With the success of these compounds for both diagnostic and therapeutic uses, there exists an ongoing demand for improved oligonucleotides and their analogs. It is well known that most of the bodily states in multicellular organisms, including most disease states, are effected by proteins. Such proteins, either acting directly or through their enzymatic or other functions, contribute in major proportion to many diseases and regulatory functions in animals and man. For disease states, classical therapeutics has generally focused upon interactions with such proteins in efforts to moderate their disease-causing or disease-potentiating functions. In newer therapeutic approaches, modulation of the actual production of such proteins is desired. By interfering with the production of proteins, the maximum therapeutic effect may be obtained with minimal side effects. It is a general object of such therapeutic approaches to interfere with or otherwise modulate gene expression, which would lead to undesired protein formation. One method for inhibiting specific gene expression is with the use of oligonucleotides, especially oligonucleotides which are complementary to a specific target messenger RNA (mRNA) sequence. Several oligonucleotides are currently undergoing clinical trials for such use. Phosphorothioate oligonucleotides are presently being used as antisense agents in human clinical trials for various disease states, including use as antiviral agents. Transcription factors interact with double- stranded DNA during regulation of transcription. Oligonucleotides can serve as competitive inhibitors of transcription factors to modulate their action. Several recent reports describe such interactions (see Bielinska, A., et. al., Science, 1990, 250, 997-1000; and Wu, H., et. al., Gene, 1990, 89 , 203-209). In addition to such use as both indirect and direct regulators of proteins, oligonucleotides and their analogs also have found use in diagnostic tests. Such diagnostic tests can be performed using biological fluids, tissues, intact cells or isolated cellular components. As with gene expression inhibition, diagnostic applications utilize the ability of oligonucleotides and their analogs to hybridize with a complementary strand of nucleic acid. Hybridization is the sequence specific hydrogen bonding of oligomeric compounds via Watson-Crick and/or Hoogsteen base pairs to RNA or DNA. The bases of such base pairs are said to be complementary to one another. Oligonucleotides and their analogs are also widely used as research reagents . They are useful for understanding the function of many other biological molecules as well as in the preparation of other biological molecules. For example, the use of oligonucleotides and their analogs as primers in PCR reactions has given rise to an expanding commercial industry. PCR has become a mainstay of commercial and research laboratories, and applications of PCR have multiplied. For example, PCR technology now finds use in the fields of forensics, paleontology, evolutionary studies and genetic counseling. Commercialization has led to the development of kits which assist non-molecular biology-trained personnel in applying PCR. Oligonucleotides and their analogs, both natural and synthetic, are employed as primers in such PCR technology. Oligonucleotides and their analogs are also used in other laboratory procedures. Several of these uses are described in common laboratory manuals such as Molecular Cloning, A Laboratory Manual , Second Ed., J. Sambrook, et al . , Eds., Cold Spring Harbor Laboratory Press, 1989; and Current Protocols In Molecular Biology, F. M. Ausubel, et al . , Eds., Current Publications, 1993. Such uses include as synthetic oligonucleotide probes, in screening expression libraries with antibodies and oligomeric compounds, DNA sequencing, in vi tro amplification of DNA by the polymerase chain reaction, and in site-directed mutagenesis of cloned DNA. See Book 2 of Molecular Cloning, A Laboratory Manual , supra . See also "DNA-protein interactions and The Polymerase Chain Reaction" in Vol. 2 of Current Protocols In Molecular Biology, supra . Oligonucleotides and their analogs can be synthesized to have customized properties that can be tailored for desired uses. Thus a number of chemical modifications have been introduced into oligomeric compounds to increase their usefulness in diagnostics, as research reagents and as therapeutic entities. Such modifications include those designed to increase binding to a target strand (i.e. increase their melting temperatures, Tm) , to assist in identification of the oligonucleotide or an oligonucleotide-target complex, to increase cell penetration, to stabilize against nucleases and other enzymes that degrade or interfere with the structure or activity of the oligonucleotides and their analogs, to provide a mode of disruption (terminating event) once sequence-specifically bound to a target, and to improve the pharmacokinetic properties of the oligonucleotide. The chemical literature discloses numerous processes for coupling nucleosides through phosphorous- containing covalent linkages to produce oligonucleotides of defined sequence. One of the most popular processes is the phosphoramidite technique ( see, e . g. , Advances in the Synthesis of Oligonucleotides by the Phosphoramidite Approach, Beaucage, S.L.; Iyer, R.P., Tetrahedron , 1992, 48, 2223-2311 and references cited therein), wherein a nucleoside or oligonucleotide having a free hydroxyl group is reacted with a protected cyanoethyl phosphoramidite monomer in the presence of a weak acid to form a phosphite- linked structure. Oxidation of the phosphite linkage followed by hydrolysis of the cyanoethyl group yields the desired phosphodiester or phosphorothioate linkage. The phosphoramidite technique, however, has significant disadvantages. For example, cyanoethyl phosphoramidite monomers are quite expensive. Although considerable quantities of monomer go unreacted in a typical phosphoramidite coupling, unreacted monomer can be recovered, if at all, only with great difficulty. Another disadvantage of using a 3 _ eliminating cyanoethoxy group is formation of acrylonitrile upon removal of the phosphorus protecting group. Acrylonitrile is a highly toxic agent as well as a suspected carcinogen ( See 1994-1995 Aldrich Chemical Company Catalog, at page 32). Acrylonitrile is also suspected of forming cyclic structures with thymidine resulting in oligomeric compounds having decreased hybridization ability. These modified oligomeric compounds are undesirable because they are difficult to separate from the desired oligomeric compound. Consequently, there remains a need in the art for synthetic methods that will overcome these problems. Several processes are known for the solid phase synthesis of oligonucleotide compounds. These are generally disclosed in the following United States Patents: No. 4,458,066; issued July 3, 1984; No. 4,500,707, issued Feb. 19, 1985; and No. 5,132,418, issued July 21, 1992. Additionally, a process for the preparation of oligonucleotides using phosphoramidite intermediates is disclosed in United States Patent, serial number 4,973,679, issued Nov. 27, 1990. A process for the preparation of phosphoramidites is disclosed in United States Patent, serial number 4,415,732, issued Nov. 15, 1983. Phosphoramidite nucleoside compounds are disclosed in United States Patent, serial number 4,668,777, issued May 26, 1987. A process for the preparation of oligonucleotides using a β-eliminating phosphorus protecting group is disclosed in United States Patent, serial number Re. 34,069, issued Sep. 15, 1992. A process for the preparation of oligonucleotides using a β-eliminating or allylic phosphorus protecting group is disclosed in United States Patent, serial number 5,026,838, issued Jun. 25, 1991. SUMMARY OF THE INVENTION It is an object of the present invention to provide methods for the preparation of oligomeric compounds having phosphite, phosphodiester, phosphorothioate, or phosphorodithioate containing covalent linkages. It is a further object of the present invention to provide synthetic intermediates useful in such processes. Other objects will be apparent to those skilled in the art. These objects are satisfied by the present invention, which provides methods for the preparation of oligomeric compounds having phosphite, phosphodiester, phosphorothioate, or phosphorodithioate containing covalent linkages . In one aspect of the present invention, methods are provided for the preparation of oligomeric compounds comprising a moiety having the Formula IX: IX wherein: Z is CN, -Si(R 9 ) 3 , halogen, N0 2 , alkaryl, sulfoxyl, sulfonyl, thio, substituted sulfoxyl, substituted sulfonyl, or substituted thio, wherein the substituents are selected from the group consisting of alkyl, aryl, or alkaryl; each R 9 is, independently, alkyl having 1 to about 10 carbon atoms, or aryl having 6 to about 10 carbon atoms; X, is 0 or S; comprising the steps of: (a) providing a compound having the Formula II: II wherein: each Rι, is, independently, H, -OH, -F, or -0-X 3 -D; X 3 is alkyl having from 1 to 10 carbons; D is H, amino, protected amino, alkyl substituted amino, imidazole, or (-0-X 3 ) p , where p is 1 to about 10; each X 2 is O or S; R 3 and R 3a are each hydrogen, a hydroxyl protecting group, or a linker connected to a solid support; each B, independently, is a naturally occurring or non-naturally occurring nucleobase or a protected naturally occurring or non-naturally occurring nucleobase; n is 0 to about 50; each Q is a phosphorus protecting group, preferably -X,H or -X,-CH 2 -CH=CH-CH 2 -Z; R 5 is -N(R 6 ) , or a heterocycloalkyl or heterocycloalkenyl ring containing from 4 to 7 atoms, and having up to 3 heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen; R 6 is straight or branched chain alkyl having from 1 to 10 carbons; (b) reacting the compound of Formula II with a compound having the Formula III: III wherein R 3a is hydrogen; and R 2 is a hydroxyl protecting group, or a linker connected to a solid support, provided that R 2 and R 3 are not both simultaneously a linker connected to a solid support; to form the oligomeric compound. Some preferred embodiments of the methods of the invention further comprise the step of oxidizing the oligomeric compound. In some preferred embodiments, the methods of the invention further comprise transforming the oxidized oligomeric compound to form a further compound having the Formula III, where n is increased by 1. Preferably, the methods of the invention comprise a capping step, either prior to or after the oxidation step. Other preferred embodiments of the invention further comprise the step of cleaving the oligomeric compound to produce a compound having the Formula I: In some preferred embodiments of the invention, Z is CN. In other preferred embodiments of the invention, each R 6 is isopropyl . In preferred embodiments, X : and X 2 can each independently be 0 or S . In some preferred embodiments the compound of Formula II is obtained by reaction of a compound having the Formula V: V with a compound having the Formula VI (R s ) 2 P-X r CH 2 -CH=CH-CH 2 -Z VI in the presence of an acid. Preferably, R 5 is N,N-diisopropylamino. Also provided in accordance with the invention are novel compounds having the Formula VII: A-X r CH 2 -CH=CH-CH 2 -Z VII wherein: A is (R 7 )(R 8 )P-; R 8 is R 5 , or has the Formula X: wherein: each R,, is, independently, H, -OH, -F, -O-X 3 -D; X 3 is alkyl having from 1 to 10 carbons; D is H, amino, protected amino, alkyl substituted amino, imidazole, or (-0-X 3 ) p , where p is 1 to about 10; 4 each X 2 is 0 or S; R 5 is -N(R 6 ) 2 , or a heterocycloalkyl or heterocycloalkenyl ring containing from 4 to 7 atoms, and having up to 3 heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen; each Q is a phosphorus protecting group, preferably -X^ or -X,-CH 2 -CH=CH-CH 2 -Z; m is 0 to about 50; each B, independently, is a naturally occurring or non-naturally occurring nucleobase or a protected naturally occurring or non-naturally occurring nucleobase; and R 7 is R 5 , or has the Formula VIII: VIII wherein: R 3 is hydrogen, a hydroxyl protecting group, or a linker connected to a solid support; and n is 0 to about 50; with the proviso that the sum of m and n do not exceed 50; and Z is CN, -Si(R 9 ) 3 , halogen, N0 2 , alkaryl, sulfoxyl, sulfonyl, thio, substituted sulfoxyl, substituted sulfonyl, or substituted thio, wherein the substituents are selected from the group consisting of alkyl, aryl, or alkaryl; each R 9 is, independently, alkyl having 1 to about 10 carbon atoms, or aryl having 6 to about 10 carbon atoms; In some preferred embodiments of the compounds of the invention Z is C . In other preferred embodiments Z is Si(R 9 ) 3 . In further preferred embodiments A is H or -P(R 5 ) 2 . In some preferred embodiments R 3 is -N(CH(CH 3 ) 2 ) 2 , and other preferred embodiments R 7 has the Formula VII . Preferably, n is 1 to 30, with 1 to about 20 being more preferred. In some preferred embodiments n is 0. In more preferred embodiments, Z is CN, X ] is O, and A is H; or Z is CN; X ± is S; and A is H. In other preferred embodiments Z is CN, X { is 0, and each R 6 is isopropyl. In further preferred embodiments Z is CN, X ! is S, and each R 6 is isopropyl. In particularly preferred embodiments, the compounds of the invention have the Formula IV: IV wherein R 2 is preferably a linker connected to a solid support, or hydrogen. In preferred embodiments m and n are each 0; or Z is CN , and X, is 0 . The present invention also provides products produced by the methods of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS The present invention provides methods for the preparation of oligomeric compounds having phosphite, phosphodiester, phosphorothioate, or phosphorodithioate linkages, and to intermediates useful in their preparation, In some preferred embodiments of the invention, methods are provided for the preparation of an oligomeric compound comprising a moiety having the Formula IX: IX wherein: Z is CN, -Si(R 9 ) 3 , halogen, N0 2 , alkaryl, sulfoxyl, sulfonyl, thio, substituted sulfoxyl, substituted sulfonyl, or substituted thio, wherein the substituents are selected from the group consisting of alkyl, aryl, or alkaryl; each R 9 is, independently, alkyl having 1 to about 10 carbon atoms, or aryl having 6 to about 10 carbon atoms; X x is 0 or S; comprising the steps of: (a) providing a compound having the Formula II: II wherein: each R 2 , is, independently, H, -OH, -F, or -0-X 3 -D; X 3 is alkyl having from 1 to 10 carbons; D is H, amino, protected amino, alkyl substituted amino, imidazole, or (-0-X 3 ) p , where p is 1 to about 10; each X 2 is 0 or S; R 3 and R 3a are each hydrogen, a hydroxyl protecting group, or a linker connected to a solid support; each B, independently, is a naturally occurring or non-naturally occurring nucleobase or a protected naturally occurring or non-naturally occurring nucleobase; n is 0 to about 50; each Q is a phosphorus protecting group, preferably -X,H or -X,-CH 2 -CH=CH-CH 2 -Z; R 5 is -N(R 5 ) 2 , or a heterocycloalkyl or heterocycloalkenyl ring containing from 4 to 7 atoms, and having up to 3 heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen; R 6 is straight or branched chain alkyl having from 1 to 10 carbons; (b) reacting the compound of Formula II with a compound having the Formula III: III wherein R 3a is hydrogen; and R 2 is a hydroxyl protecting group, or a linker connected to a solid support, provided that R 2 and R 3 are not both simultaneously a linker connected to a solid support; to form the oligomeric compound. The methods of the present invention are useful for the preparation of oligomeric compounds containing monomeric subunits that are joined by a variety of linkages, including phosphite, phosphodiester, phosphorothioate, and/or phosphorodithioate linkages. As used herein, the term "oligomeric compound" is used to refer to compounds containing a plurality of monomer subunits that are joined by phosphite, phosphodiester, phosphorothioate, and/or phosphorodithioate linkages. Oligomeric compounds include oligonucleotides, their analogs, and synthetic oligonucleotides. Monomer or higher order synthons having Formulas II or III above include both native (i.e., naturally occurring) and synthetic (e.g., modified native of totally synthetic) nucleosides. In preferred embodiments, compounds of Formula II and Formula III are reacted to produce compounds of Formula IV. Methods for coupling compounds of Formula II and Formula III of the invention include both solution phase and solid phase chemistries. Representative solution phase techniques are described in United States Patent No. 5,210,264, which is assigned to the assignee of the present invention. In preferred embodiments, the methods of the present invention are employed for use in iterative solid phase oligonucleotide synthetic regimes. Representative solid phase techniques are those typically employed for DNA and RNA synthesis utilizing standard phosphoramidite chemistry, ( see, e . g. , Protocols For Oligonucleotides And Analogs, Agrawal, S., ed., Humana Press, Totowa, NJ, 1993). A preferred synthetic solid phase synthesis utilizes phos¬ phoramidites as activated phosphate compounds. In this technique, a phosphoramidite monomer is reacted with a free hydroxyl on the growing oligomer chain to produce an intermediate phosphite compound, which is subsequently oxidized to the P v state using standard methods. This technique is commonly used for the synthesis of several types of linkages including phosphodiester, phosphorothioate, and phosphorodithioate linkages. Typically, the first step in such a process is attachment of a first monomer or higher order subunit containing a protected 5 '-hydroxyl to a solid support, usually through a linker, using standard methods and procedures known in the art. The support-bound monomer or higher order first synthon is then treated to remove the 5'- protecting group, to form a compound of Formula III wherein R 2 is a linker connected to a solid support. Typically, this is accomplished by treatment with acid. The solid support bound monomer is then reacted with a compound of Formula II to form a compound of Formula IV, which has a phosphite or thiophosphite linkage of Formula IX. In preferred embodiments, synthons of Formula II and Formula III are reacted under anhydrous conditions in the presence of an activating agent such as, for example, lH-tetrazole, 5-(4- nitrophenyl)-lH-tetrazole, or diisopropyla ino tetrazolide. In preferred embodiments, phosphite or thiophosphite compounds containing a linkage of Formula IX are oxidized as shown below to produce compounds having a linkage of Formula XI, where X l and X 2 can each be 0 or S: IX XI Choice of oxidizing agent will determine whether the linkage of Formula IX is oxidized to a phosphotriester, thiophosphotriester, or a dithiophosphotriester linkage. It is generally preferable to perform a capping step, either prior to or after oxidation of the phosphite triester, thiophosphite triester, or dithiophosphite triester. Such a capping step is generally known to provide benefits in the prevention of shortened oligomer chains, by blocking chains that have not reacted in the coupling cycle. One representative reagent used for capping is acetic anhydride. Other suitable capping reagents and methodologies can be found in United States Patent 4,816,571, issued March 28, 1989. Treatment with an acid removes the 5 '-hydroxyl protecting group, and thus transforms the solid support bound oligomer into a further compound of Formula III wherein R 3a is hydrogen, which can then participate in the next synthetic iteration; i.e., which can then be reacted with a further compound of Formula II. This process is repeated until an oligomer of desired length is produced. The completed oligomer is then cleaved from the solid support. The cleavage step, which can precede or follow deprotection of protected functional groups, will yield a compound having the Formula I wherein R 2 is hydrogen. During cleavage, the linkages between monomeric subunits are converted from phosphotriester, thiophosphotriester, or dithiophosphotriester linkages to phosphodiester, phosphorothioate, or phosphorodithioate linkages. This conversion is effected through the loss of an oxygen or sulfur protecting group of Formula Z-CH 2 -CH=CH-CH 2 - . Depending upon the species Z, it is believed that the loss of an oxygen or sulfur protecting group occurs via either a δ-elimination mechanism, or a δ-fragmentation mechanism. While not wishing to be bound by a particular theory, it is believed that the loss of the oxygen or sulfur protecting group where Z is a non-silyl electron withdrawing group occurs via a δ-elimination mechanism, illustrated in Scheme I below: VII In this mechanism, a base first abstracts an acidic proton from the carbon atom adjacent to electron withdrawing group Z. The resonant movement of electrons as depicted in Scheme I above is believed to cause the loss of the oxygen or sulfur protecting group via a δ-elimination, thereby forming a phosphodiester, phosphoro¬ thioate, or phosphorodithioate linkage. The other product of the deprotection is a 1-substituted-l,3-butadiene, having electron withdrawing substituent Z at the 1-position. Substituent Z can be an electron withdrawing group selected such that it facilitates the abstraction of a proton from the adjacent carbon atom by resonance, inductive, or other electron withdrawing mechanisms. Accordingly, Z can be any of a variety of electron withdrawing substituents, provided that it does not otherwise interfere with the methods of the invention. Preferred non-silyl electron withdrawing Z groups include CN, halogens, N0 2 , alkaryl groups, sulfoxyl groups, sulfonyl groups, thio groups, substituted sulfoxyl groups, substituted sulfonyl groups, or substituted thio groups, wherein the substituents are selected from the group consisting of alkyl, aryl, or alkaryl. In more preferred embodiments Z is cyano. Z can also be a trisubstituted silyl moiety, wherein the substituents are alkyl, aryl or both. While not wishing to be bound by a particular theory, it is believed that the loss of the oxygen or sulfur protecting group, where Z is such a trisubstituted silyl moiety, occurs via a δ-fragmentation mechanism, illustrated in Scheme II below: In this scheme, a nucleophile attacks the silyl silicon atom, and the resonant movement of electrons as depicted in Scheme II above is believed to cause the loss of the oxygen or sulfur protecting group via a δ-fragmentation mechanism, thereby forming a phosphodiester, phosphorothioate, or phosphorodithioate linkage. The other products of the deprotection are 1, 3-butadiene, and Nu-Si(R 3 ) 3 . A wide variety of bases can be used to initiate the δ-elimination of the oxygen or sulfur protecting group. These include aqueous ammonium hydroxide, aqueous methylamine, or DBU ( 1,8-diazabicyclo[5.4.0]undec-7-ene) . A wide variety of nucleophiles can be used to initiate the δ-fragmentation of the oxygen or sulfur protecting group. These include ammonium hydroxide, fluoride ion, alkyl amines, aqueous bases, and alkyl amines in combination with ammonium hydroxide. The resulting products include phosphate, phosphorothioate, and phosphorodithioate containing compounds . Contact with fluoride ion preferably is effected in a solvent such as tetrahydrofuran, acetonitrile, dimethoxyethane, or water. Fluoride ion preferably is provided in the form of one or more salts selected from tetraalkylammonium fluorides (e.g., tetrabutylammonium fluoride (TBAF)), potassium fluoride, or cesium fluoride. Preferably, conditions for removal of the oxygen or sulfur protecting group via δ-elimination or δ-fragmentation also effect cleavage of the oligomeric compound from the solid support. The methods of the present invention are applicable to the synthesis of a wide variety of oligomeric compounds which contain phosphite, phosphodiester, phosphorothioate, or phosphorodithioate linkages. As used herein, the term "oligomeric compound" denotes a polymeric compound containing two or more monomeric subunits joined by such phosphite, phosphodiester, phosphorothioate, or phosphorodithioate linkages. During the synthetic cycle it is advantageous to protect any preexisting internucleoside linkages present in the synthons represented by Formula II and Formula III. Accordingly, substitiuent Q can be any of the wide variety of phosphate protecting groups that are used to protect phosphous linkages such as phosphodiester, phosphodiester, phosphorothioate, or phosphorodithioate linkages. In preferred embodiments of the invention Q is XjH or -X 1 -CH 2 -CH=CH-CH 2 -Z . Examples of other phosphorus protective groups include cyanoethyl groups and diphenyl ethyl- silylethyl (DPSE) groups. Additional representative protective groups are disclosed in Beaucage, et al . , Tetrahedron 1992, 48, 2223-2311, and also in Beaucage, et - 21 - al . , Tetrahedron 1993, 49 , 6123-6194, the disclosures of which are incorportated herein by reference in their entirety. In preferred embodiments, the methods of the invention are used for the preparation of oligonucleotides and their analogs. As used herein, the term "oligonuclotide analog" means compounds that can contain both naturally occurring (i.e. "natural") and non-naturally occurring ("synthetic") moieties, for example, nucleosidic subunits containing modified sugar and/or nucleobase portions. Such oligonucleotide analogs are typically structurally distinguishable from, yet functionally interchangeable with, naturally occurring or synthetic wild type oligonucleotides. Thus, oligonucleotide analogs include all such structures which function effectively to mimic the structure and/or function of a desired RNA or DNA strand, for example, by hybridizing to a target. The term synthetic nucleoside, for the purpose of the present invention, refers to a modified nucleoside. Representative modifications include modification of a heterocyclic base portion of a nucleoside to give a non-naturally occurring nucleobase, a sugar portion of a nucleoside, or both simultaneously. Representative nucleobases include adenine, guanine, cytosine, uridine, and thymine, as well as other non-naturally occurring and natural nucleobases such as xanthine, hypoxanthine, 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine, 2-propyl and other alkyl derivatives of adenine and guanine, 5-halo uracil and cytosine, 6-azo uracil, cytosine and thymine, 5-uracil (pseudo uracil), 4-thiouracil, 8-halo, oxa, amino, thiol, thioalkyl, hydroxyl and other 8-substituted adenines and guanines, 5-trifluoromethyl and other 5-substituted uracils and cytosines, 7-methylguanine. Further naturally and non naturally occurring nucleobases include those disclosed in U.S. Patent No. 3,687,808 (Merigan, et al . ) , in chapter 15 by Sanghvi, in Antisense Research and Applica tion, Ed. S. T. Crooke and B. Lebleu, CRC Press, 1993, in Englisch et al . , Angewandte Chemie, International Edition, 1991, 30, 613-722 (see especially pages 622 and 623, and in the Concise Encyclopedia of Polymer Science and Engineering, J.I. Kroschwitz Ed., John Wiley & Sons, 1990, pages 858-859, Cook, P.D., Anti-Cancer Drug Design, 1991, 6, 585-607. The term 'nucleosidic base' is further intended to include heterocyclic compounds that can serve as like nucleosidic bases including certain 'universal bases' that are not nucleosidic bases in the most classical sense but serve as nucleosidic bases. Especially mentioned as a universal base is 3-nitropyrrole. Representative 2' sugar modifications (position R : ) amenable to the present invention include fluoro, O-alkyl, O-alkylamino, O-alkylalkoxy, protected O-alkylamino, O-alkylaminoalkyl, 0-alkyl imidazole, and polyethers of the formula (O-alkyl) m , where m is 1 to about 10. Preferred among these polyethers are linear and cyclic polyethylene glycols (PEGs), and (PEG)-containing groups, such as crown ethers and those which are disclosed by Ouchi, et al . , Drug Design and Discovery 1992, 9 , 93, Ravasio, et al . , J. Org. Chem. 1991, 56, 4329, and Delgardo et . al . , Cri tical Reviews in Therapeutic Drug Carrier Systems 1992, 9 , 249. Further sugar modifications are disclosed in Cook, P.D., supra . Fluoro, O-alkyl, O-alkylamino, 0-alkyl imidazole, 0- alkylaminoalkyl, and alkyl amino substitution is described in United States Patent Application serial number 08/398,901, filed March 6, 1995, entitled Oligomeric Compounds having Pyrimidine Nucleotide(s) with 2' and 5' Substitutions . Sugars having O-substitutions on the ribosyl ring are also amenable to the present invention. Representative substitutions for ring 0 include S, CH 2 , CHF, and CF 2 , see, e.g., Secrist, et al . , Abstract 21 , Program & Abstracts, Tenth International Roundtable, Nucl eosides, Nucleotides and their Biological Applications, Park City, Utah, Sept. 16-20, 1992. As used herein, the term "alkyl" includes but is not limited to straight chain, branch chain, and alicyclic hydrocarbon groups . Alkyl groups of the present invention may be substituted. Representative alkyl substituents are disclosed in United States Patent No. 5,212,295, at column 12, lines 41-50. As used herein, the term "aralkyl" denotes alkyl groups which bear aryl groups, for example, benzyl groups. The term "alkaryl" denotes aryl groups which bear alkyl groups, for example, methylphenyl groups. "Aryl" groups are aromatic cyclic compounds including but not limited to phenyl, naphthyl, anthracyl, phenanthryl, pyrenyl, and xylyl . As used herein, the term "heterocycloalkyl" denotes an alkyl ring system having one or more heteroatoms (i.e., non-carbon atoms) . Preferred heterocycloalkyl groups include, for example, morpholino groups. As used herein, the term "heterocycloalkenyl" denotes a ring system having one or more double bonds, and one or more heteroatoms. Preferred heterocycloalkenyl groups include, for example, pyrrolidino groups. In some preferred embodiments of the invention R 2 , R 3 or R 3a can be a linker connected to a solid support. Solid supports are substrates which are capable of serving as the solid phase in solid phase synthetic methodologies, such as those described in Caruthers U.S. Patents Nos. 4,415,732; 4,458,066; 4,500,707; 4,668,777; 4,973,679; and 5,132,418; and Koster U.S. Patents Nos. 4,725,677 and Re. 34,069. Linkers are known in the art as short molecules which serve to connect a solid support to functional groups (e.g., hydroxyl groups) of initial synthon molecules in solid phase synthetic techniques. Suitable linkers are disclosed in, for example, Oligonucleotides And Analogues A Practical Approach, Ekstein, F. Ed., IRL Press, N.Y, 1991, Chapter 1, pages 1-23. Solid supports according to the invention include those generally known in the art to be suitable for use in solid phase methodologies, including, for example, controlled pore glass (CPG), oxalyl-controlled pore glass ( see, e . g. , Alul, et al . , Nucleic Acids Research 1991, 19 , 1527), TentaGel Support -- an aminopolyethyleneglycol derivatized support ( see, e . g. , Wright, et al . , Tetrahedron Letters 1993, 34 , 3373) and Poros -- a copolymer of polystyrene/divinylbenzene. In some preferred embodiments of the invention R 2 , R 3 or R 3a can be a hydroxyl protecting group. A wide variety of hydroxyl protecting groups can be employed in the methods of the invention. Preferably, the protecting group is stable under basic conditions but can be removed under acidic conditions. In general, protecting groups render chemical functionalities inert to specific reaction conditions, and can be appended to and removed from such functionalities in a molecule without substantially damaging the remainder of the molecule. Representative hydroxyl protecting groups are disclosed by Beaucage, et al . , Tetrahedron 1992, 48, 2223-2311, and also in Greene and Wuts, Protective Groups in Organic Synthesis, Chapter 2, 2d ed, John Wiley & Sons, New York, 1991. Preferred protecting groups used for R 2 , R 3 and R 3a include dimethoxytrityl (DMT), monomethoxytrityl, 9-phenylxanthen-9-yl (Pixyl) and 9-(p- ethoxyphenyl)xanthen-9-yl (Mox) . The R 2 or R 3 group can be removed from oligomeric compounds of the invention by techniques well known in the art to form the free hydroxyl. For example, dimethoxytrityl protecting groups can be removed by protic acids such as formic acid, dichloroacetic acid, trichloroacetic acid, p-toluene sulphonic acid or with Lewis acids such as for example zinc bromide. See for example, Greene and Wuts, supra . In some preferred embodiments of the invention amino groups are appended to alkyl or other groups, such as, for example, 2 '-alkoxy groups (e.g., where R : is alkoxy). Such amino groups are also commonly present in naturally occurring and non-naturally occurring nucleobases. It is generally preferred that these amino groups be in protected form during the synthesis of oligomeric compounds of the invention. Representative amino protecting groups suitable for these purposes are discussed in Greene and Wuts, Protective Groups in Organic Synthesis, Chapter 7, 2d ed, John Wiley & Sons, New York, 1991. Generally, as used herein, the term "protected" when used in connection with a molecular moiety such as "nucleobase" indicates that the molecular moiety contains one or more functionalities protected by protecting groups . Sulfurizing agents used during oxidation to form phosphorothioate and phosphorodithioate linkages include Beaucage reagent ( see e . g. Iyer, R.P., et . al . , J. Chem . Soc , 1990, 112, 1253-1254, and Iyer, R.P., et . al . , J. Org. Chem . , 1990, 55 , 4693-4699); tetraethylthiuram disulfide (see e. g. , Vu, H., Hirschbein, B.L., Tetrahedron Lett . , 1991, 32, 3005-3008); dibenzoyl tetrasulfide ( see e . g. , Rao, M.V., et . al . , Tetrahedron Lett . , 1992, 33, 4839-4842); di(phenylacetyl)disulfide ( see e . g. , Kamer, P.C.J., Tetrahedron Lett . , 1989, 30, 6757-6760); sulfur, sulfur in combination with ligands like triaryl, trialkyl, triaralkyl, or trialkaryl phosphines. Useful oxidizing agents used to form the phosphodiester or phosphorothioate linkages include iodine/tetrahydrofuran/ water/pyridine or hydrogen peroxide/water or tert-butyl hydroperoxide or any peracid like m-chloroperbenzoic acid. In the case of sulfurization the reaction is performed under anhydrous conditions with the exclusion of air, in particular oxygen whereas in the case of oxidation the reaction can be performed under aqueous conditions . Oligonucleotides or oligonucleotide analogs according to the present invention hybridizable to a specific target preferably comprise from about 5 to about 50 monomer subunits. It is more preferred that such compounds comprise from about 10 to about 30 monomer subunits, with 15 to 25 monomer subunits being particularly preferrred. When used as "building blocks" in assembling larger oligomeric compounds (i.e., as synthons of Formula II), smaller oligomeric compounds are preferred. Libraries of dimeric, trimeric, or higher order compounds of general Formula II can be prepared for use as synthons in the methods of the invention. The use of small sequences synthesized via solution phase chemistries in automated synthesis of larger oligonucleotides enhances the coupling efficiency and the purity of the final oligonucloetides . See for example: Miura, K . , et al . , Chem . Pharm . Bull . , 1987, 35 , 833-836; Kumar, G., and Poonian, M.S., J. Org. Chem. , 1984, 49 , 4905- 4912; Bannwarth, W., Hel vetica Chimica Acta , 1985, 68, 1907- 1913; Wolter, A., et al . , nucl eosides and nucl eotides , 1986, 5, 65-77. It will also be appreciated that the use of dimeric and longer synthons (i.e., where n in the compounds of Formula II is gretater than 1) provides the additional benefit of reducing the production of shorter (failure) sequences within which one or more nucleotides are absent. It is aprticularly advantageous to reduce the nu er of contaminating sequences wherein a single nucleotide is absent ("n-l ers") , as these are often diffricult to separate from the desired oligonucleotide. In one aspect of the invention, the compounds of the invention are used to modulate RNA or DNA, which code for a protein whose formation or activity it is desired to modulate. The targeting portion of the composition to be employed is, thus, selected to be complementary to the preselected portion of DNA or RNA, that is to be hybridizable to that portion. In preferred embodiments of the methods of the invention, the compound of Formula II is prepared by reaction of a protected nucleoside having Formula V: and a phosphine compound of Formula VI VI in the presence of an acid. Suitable acids include those known in the art to be useful for coupling of phosphoramidites, including, for example, diisopropylam onium tetrazolide. Compounds of Formula VI are preferably prepared by reacting an alcohol having the formula HOCH 2 CH=CHCH 2 Z with phosphorus trichloride, and reacting the resultant product, Cl 2 PX,CH 2 CH=CHCH 2 Z, with at least two equivalents of an amine having the formula [(R 6 ) 2 N] 2 NH. Each of the R 6 groups can be the same or different, and are preferably alkyl having 1 to about 10 carbon atoms, more preferably 1 to 6 carbon atoms, with 3 carbon atoms, and particularly isopropyl groups, being especially preferred. j and X 2 can each independently be O or S . Thus, compounds having chiral phosphorus linkages are contemplated by the present invention. See Stec, W.J., and Lesnikowski, Z.J., in Methods in Molecular Biology Vol . 20 : Protocols for Oligonucleotides and Analogs, S. Agrawal, Ed., Humana Press, Totowa, N.J. (1993), at Chapter 14. See also Stec, W.J. et al . , Nucleic Acids Research, Vol. 19, No. 21, 5883-5888 (1991); and European Patent Application EP 0 506 242 Al. Also provided in preferred embodiments of the invention are compounds having the general Formula VII: A-X r CH 2 -CH - CH-CH 2 -Z VI I wherein Xi, A, and Z are as defined above. The oligomeric compounds of the invention can be used in diagnostics, therapeutics and as research reagents and kits. They can be used in pharmaceutical compositions by including a suitable pharmaceutically acceptable diluent or carrier. They further can be used for treating organisms having a disease characterized by the undesired production of a protein. The organism should be contacted with an oligonucleotide having a sequence that is capable of specifically hybridizing with a strand of nucleic acid coding for the undesirable protein. Treatments of this type can be practiced on a variety of organisms ranging from unicellular prokaryotic and eukaryotic organisms to multicellular eukaryotic organisms. Any organism that utilizes DNA-RNA transcription or RNA-protein translation as a fundamental part of its hereditary, metabolic or cellular control is susceptible to therapeutic and/or prophylactic treatment in accordance with the invention. Seemingly diverse organisms such as bacteria, yeast, protozoa, algae, all plants and all higher animal forms, including warm- blooded animals, can be treated. Further, each cell of multicellular eukaryotes can be treated, as they include both DNA-RNA transcription and RNA-protein translation as integral parts of their cellular activity. Furthermore, many of the organelles ( e . g. , mitochondria and chloroplasts) of eukaryotic cells also include transcription and translation mechanisms. Thus, single cells, cellular populations or organelles can also be included within the definition of organisms that can be treated with therapeutic or diagnostic oligonucleotides . As will be recognized, the steps of the methods of the present invention need not be performed any particular number of times or in any particular sequence. Additional objects, advantages, and novel features of this invention will become apparent to those skilled in the art upon examination of the following examples thereof, which are intended to be illustrative and not intended to be limiting. EXAMPLE 1 l-Chloro-2-butene-4-ol 2-Butene-l, -diol (600 g, 6.81 mol) was added to a 5-liter three-necked round bottomed flask equipped with a condenser, a pressure equalizing addition funnel and a mechanical stirrer. To this was added anhydrous ether (1400 mL) and pyridine (604.9 L, 7.49 mol). The reaction flask was cooled to 0 'C and thionyl chloride (545.6 mL, 7.49 mol) was added dropwise over a period of 2.5 hours. After the addition was complete, the reaction mixture was allowed to warm to room temperature and stirred overnight. The reaction mixture was then poured into 500 mL of ice water and extracted with ether (2 x 400 mL) . The combined ether extracts were washed with saturated sodium bicarbonate followed by brine and dried (Na 2 SO / ) . Concentration of the dried extracts gave the title compound which was used in the next step without further purification. EXAMPLE 2 4-Cyano-2-butene-l-ol l-Chloro-2-butene-4-ol (230 g, 2.14 mol) was dissolved in anhydrous acetonitrile (1250 mL) and added to a 3 L round bottomed flask under an atmosphere of argon. Potassium cyanide (825 g, 12.5 mol) was added all at once and the reaction was stirred at room temperature for 3 hours. Nal (16 g, 0.054 mol) was added and the reaction mixture was stirred overnight at room temperature. The reaction mixture was filtered and the solid washed with ethyl acetate (800 mL) . Concentration of the filtrate in vacuo afforded an oil which was triturated with ether (750 mL) . This mixture was filtered and the clear filtrate concentrated. The crude product was distilled using a short path to give the title compound, bp 89-91 'C at 0.2 mm Hg. IR (neat) cm "1 : 3400, 2900, 2250, 1650. EXAMPLE 3 4-Cyano-2-butenyl-N / N,N' ,N'-tetraisopropylphosphorodiamidite A 500 mL three-necked flask equipped with a magnetic stirrer, a glass stopper and an inlet for argon is assembled under an atmosphere of argon. All the glassware is dried in an oven at 120 "C for 1 hour. Anhydrous ether (150 L) and phosphorous trichloride (67.5 mmol) is added to the flask. 4-Cyanobutene-l-ol (50 mmol) in ether (50 L) is added to the reaction flask slowly with stirring at 0 "C (ice bath) using a pressure-equalized addition funnel. After the addition is complete, the ice bath is removed and the reaction is stirred for three hours at room temperature. The reaction mixture is then transferred to a 500 mL flask and concentrated under reduced pressure. To the product in anhydrous ether (200 mL) is added diisopropylamine (57.7 mL) at 0 'C under argon. After the addition is complete, stirring is continued at room temperature for 16 hours. The reaction mixture is filtered and concentrated to afford the title compound. EXAMPLE 4 Preparation of protected phosphoramidite monomers A. 5'-O-DMT-thymidine-3'-O-(4-cyano-2-butenyl N,N-diisopropylphosphoramidite) A 250 L two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an atmosphere of argon. All the glassware is dried at 120 'C for 1 hour. 5'-O-DMT-thymidine (7 mmol) and 5-(4- nitrophenyl)-lH-tetrazole (5.6 mmol) and anhydrous acetonitrile (50 mL) is added to the flask. To this stirred mixture at room temperature is added a solution of 4-cyano- 2-butenyl-N,N,N' ,N'-tetraisopropylphosphorodiamidite (10.5 mmol) in acetonitrile (50 mL) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL) , washed once with cold saturated sodium bicarbonate solution, brine and dried (MgSO/ . The dried solution is concentrated under reduced pressure and purified by silica gel flash column chromatography to give the title compound. B. N2-Isobutyryl-5'-O-DMT-2'-deoxyguanosine-3'- 0-(4-cyano-2-butenyl N,N-diisopropylphosphoramidite) A 250 L two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an argon atmosphere. All the glassware is dried at 120 "C for 1 hour. The flask is charged with N2-isobutyryl- 5 '-0-DMT-2 '-deoxyguanosine (5 mmol) and diisopropyl ammonium tetrazolide (4 mmol) . Anhydrous acetonitrile (50 L) is added. To this stirred mixture at room temperature is added a solution of 4-cyano-2-butenyl-N,N,N' ,N'-tetraisopropyl- phosphorodiamidite (7.5 mmol) in acetonitrile (50 mL) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL) , washed once with cold saturated sodium bicarbonate solution, brine and dried (MgS0 ) . The dried solution is concentrated under reduced pressure to afford the product which is purified by silica gel flash column chromatography. C. N6-Benzoyl-5'-O-DMT-2'-deoxyadenosine-3'-O- (4-cyano-2-butenyl N,N-diisopropylphosphoramidite) A 250 mL two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an atmosphere of argon. All the glassware is dried at 120 'C for 1 hour. The flask is charged with N6-benzoyl-5 ' - O-DMT-2 '-deoxyadenosine (5 mmol) and diisopropyla monium tetrazolide (4 mmol) . Anhydrous acetonitrile (50 mL) is added. To this stirred mixture at room temperature is added a solution of 4-cyano-2-butenyl-N,N,N' ,N'-tetraisopropyl- phosphorodia idite (6 mmol) in acetonitrile (50 L) . After stirring for two hours, the reaction mixture is filtered and concentrated to a residue which is purified by silica gel flash column chromatography to give the title compound. D. N4-Benzoyl-5'-0-DMT-2'-deoxycytidine-3'-0- (4-cyano-2-butenyl N,N-diisopropylphosphoramidite) A 250 L two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an atmosphere of argon. All the glassware is dried at 120 "C for 1 hour. The flask is charged with N4-benzoyl-5'- 0-DMT-2 '-deoxycytidine (5 mmol) and diisopropylammonium tetrazolide (4 mmol). Anhydrous acetonitrile (50 mL) is added. To this stirred mixture at room temperature is added a solution of 4-cyano-2-butenyl-N,N,N' ,N'-tetraisopropyl- phosphorodiamidite (7.5 mmol) in acetonitrile (50 mL) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL) , washed once with cold saturated sodium bicarbonate solution, brine and dried (MgSO- . The dried solution is concentrated under reduced pressure to afford the product which is purified by silica gel flash column chromatography. Example 5 Coupling Procedures A. Synthesis of T-T phosphorothioate dimer 100 milligram (4 mmole) of 5'-O-DMT-thymidine bonded to CPG (controlled pore glass) through an ester linkage is transferred to a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with dichloromethane and then with acetonitrile. Then, a 0.2 M solution of 5 '-O-DMT-thymidine- 3 '-0-(4-cyano-2-butenyl N,N-diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 24 hours at 65 'C. The aqueous solution is filtered, concentrated under reduced pressure to give the phosphorothioate dimer of T-T. B. Synthesis of C-T phosphorothioate dimer 5 '-O-DMT-thymidine (100 mg, 4 mmole) bonded to CPG (controlled pore glass) through an ester linkage is transferred to a glass reactor, and a CH 2 CH1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5'- hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N4-Benzoyl-5 '-0-DMT-2 '- deoxycytidine-3 '-0-(4-cyano-2-butenyl N,N-diisopropyl- phosphoramidite) in acetonitrile and a 0.4 M solution of 1H- tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes . The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl groups. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 24 hours at 65 "C. The aqueous solution is filtered, concentrated under reduced pressure to give the phosphorothioate dimer of dC-T. C. Synthesis of T-T phosphodiester dimer 5 '-O-DMT-thymidine (100 mg, 4 mmole) bonded to CPG through an ester linkage is transferred to a glass reactor, and a CH 2 CH1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5 'hydroxyl group. The product is washed with CH 2 CH1 2 and then with acetonitrile. Then, a 0.2 M solution of 5 '-O-DMT-thymidine-3 '-0-(4-cyano-2-butenyl N,N-diisoproρylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then 0.1 M iodine in water/pyridine/THF (2:20:80, v/v/v) is added and reacted at room temperature for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8, v/v/v), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl groups. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 24 hours at 65 'C. The aqueous solution is filtered, concentrated under reduced pressure to give the T-T phosphodiester dimer. D. Synthesis of 5'-TTTTTTT-3' phosphorothioate heptamer 5 '-O-DMT-thymidine (50 mg, 2 mmole) bonded to CPG through an ester linkage transferred to a glass reactor, and a CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5'-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5'-O-DMT-thymidine- 3 '-O-(4-cyano-2-butenyl N,N-diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8, v/v/v), and N- ethyl imidazole/THF is added to cap the unreacted 5'- hydroxyl groups. The product is washed with acetonitrile. This complete cycle is repeated five more times to get the completely protected thymidine heptamer. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes at room temperature. The aqueous solution is filtered and concentrated under reduced pressure to give the phosphorothioate heptamer of TTTTTTT. E. Synthesis of 5'-d(GACT)-3' phosphorothioate tetramer 5'-O-DMT-thymidine (50 mg, 2 mmole) bonded to CPG through an ester linkage is taken in a glass reactor, and a CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-O-DMT-thymidine- 3 '-0-(4-cyano-2-butenyl N,N-diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/ THF (1:1:8, v/v/v), and N- methyl imidazole/THF is added to cap the unreacted 5'- hydroxyl groups. The product is washed with acetonitrile. A CH 2 C1 2 solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl groups. The product is washed with acetonitrile. Then, a 0.2 M solution of N4-benzoyl-5 '-O-DMT-2 '-deoxycytidine-3 ' -0- (4-cyano-2-butenyl N,N-diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8, V/V/V), and N- ethyl imidazole/THF is added to cap the unreacted 5'- hydroxyl groups. The product is washed with acetonitrile. A CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N6- benzoyl-5 '-0-DMT-2 '-deoxyadenosine-3 '-O-(4-cyano-2-butenyl N,N-diisopropylphosphoramidite) in anhydrous acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/ THF (1:1:8, v/v/v), and N- ethyl imidazole/THF is added to cap the unreacted 5'- hydroxyl groups. The product is washed with acetonitrile. A dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N2-isobutyryl-5 '-O-DMT-2 '-deoxyguanosine-3 '-0- { 4-cyano-2-butenyl N,N-diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5'-hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes at room temperature and then incubated at 55 'C for 24 hour. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate tetramer of 5'-dG-dA-dC- T-3' . EXAMPLE 6 l-Tri_methylsilylthioxy-4-cyano-2-butene To a stirred mixture of l-cyano-2,3-butadiene (0.1 mol) and trimethylsilylthiol (0.1 mol) in anhydrous ether (300 ml) under argon, is added a catalytic amount of rhodium acetate at room temperature. After 24 hours the reaction mixture is filtered and concentrated to give the title compound. EXAMPLE 7 4-Cyano-2-buteny1-N,N ,N' ,N'-tetraisopropylthiophosphoro- diamidite A 500 mL three-necked flask equipped with a magnetic stirrer, a glass stopper and an inlet for argon is assembled, after drying in an oven at 120 'C for 1 hour. The flask is purged with argon while cooling and an atmosphere of argon is maintained inside the flask. Anhydrous ether (150 L) and phosphorous trichloride (67.5 mmol) is added to the flask. l-Trimethylsilyl-4-cyano-2- butene (50 mmol) in ether (50 L) is slowly added to the reaction flask with stirring at 0 'C (ice bath) using a pressure-equalized addition funnel. After the addition is complete, the ice bath is removed and the reaction is stirred for three hours at room temperature. The reaction mixture is then transferred to a 500 mL flask and concentrated under reduced pressure. To the resulting residue in anhydrous ether (200 mL) is added diisopropylamine (57.7 mL) at 0 * C under argon. After the addition is complete, stirring is continued at room temperature for 16 hours. The reaction mixture is filtered and concentrated and the resulting residue purified by silica gel column chromatography to afford the title compound. EXAMPLE 8 Preparation of protected phosphorothioamidite monomers A. 5'-O-DMT-thymidine-3'-0-(4-cyano-2-butenyl N,N-diisopropylthiophosphoramidite) A 250 mL two-necked flask equipped with a magnetic stirrer, a glass stopper and an inlet for argon is assembled, after drying in an oven at 120 * C for 1 hour. The flask is purged with argon while cooling and an atmosphere of argon is maintained inside the flask. 5'-0- DMT-thymidine (7 mmol) and 5-(4-nitrophenyl)-lH-tetrazole (5.6 mmol) and anhydrous acetonitrile (50 mL) is added to the flask. To this stirred mixture at room temperature is added a solution of 4-cyano-2-butenyl-N,N,N' ,N'- tetraisopropylthiophosphorodiamidite (10.5 mmol) in acetonitrile (50 L) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL), washed once with cold aqueous solution of saturated sodium bicarbonate, brine and dried (MgS0 4 ) . The dried solution is filtered and the filtrate is concentrated under reduced pressure and purified by silica gel flash column chromatography to give the title compound. B. N2-Isobutyryl-5'-0-DMT-2'-deoxyguanosine-3'- 0-(4-cyano-2-butenyl N,N-diisopropylthiophosphoramidite) . A 250 L two-necked flask equipped with a magnetic stirrer, a glass stopper and an inlet for argon is assembled, after drying in an oven at 120 'C for 1 hour. The flask is purged with argon while cooling and an atmosphere of argon is maintained inside the flask. The flask is charged with N2-isobutyryl-5 '-0-DMT-2 '- deoxyguanosine (5 mmol) and diisopropyl ammonium tetrazolide (4 mmol). Anhydrous acetonitrile (50 mL) is added. To this stirred mixture at room temperature is added a solution of 4-cyano-2-butenyl-N,N,N' ,N'-tetraisopropylthio- phosphorodiamidite (7.5 mmol) in acetonitrile (50 mL) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL) , washed once with cold saturated sodium bicarbonate solution, brine and dried (MgS0 4 ) . The dried solution is filtered and the resulting filtrate is concentrated under reduced pressure. The resulting residue is purified by silica gel flash column chromatography to give the title compound. C. N6-Benzoyl-5'-O-DMT-2'-deoxyadenosine-3'-0- (4-cyano-2-buteny-l-N,N-diisopropylthiophosphoramidite) A 250 L two-necked flask equipped with a magnetic stirrer, a glass stopper and an inlet for argon is assembled, after drying in an oven at 120 'C for 1 hour. The flask is purged with argon while cooling and an atmosphere of argon is maintained inside the flask. The flask is charged with N6-benzoyl-5 '-0-DMT-2 ' -deoxyadenosine (5 mmol) and diisopropylammonium tetrazolide (4 mmol). Anhydrous acetonitrile (50 mL) is added. To this stirred mixture at room temperature is added a solution of 4-cyano- 2-butenyl-N,N,N' ,N'-tetraisopropylthiophosphorodiamidite (6 mmol) in acetonitrile (50 mL) . After stirring for two hours, the reaction mixture is filtered and concentrated to a residue which is purified by silica gel flash column chromatography to give the title compound. D. N4-Benzoyl-5'-O-DMT-2 '-deoxycytidine-3'-0- (4-cyano-2-butenyl N,N-diisopropylthiophosphoramidite) . A 250 L two-necked flask equipped with a magnetic stirrer, a glass stopper and an inlet for argon is assembled, after drying in an oven at 120 * C for 1 hour. The flask is purged with argon while cooling and an atmosphere of argon is maintained inside the flask. The flask is charged with N4-benzoyl-5 '-O-DMT-2 '-deoxycytidine (5 mmol) and diisopropylammonium tetrazolide (4 mmol) . Anhydrous acetonitrile (50 mL) is added. To this stirred mixture at room temperature is added a solution of 4-cyano- 2-butenyl-N,N,N' ,N'-tetraisopropylthiophosphorodiamidite (7.5 mmol) in acetonitrile (50 L) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL) , washed once with cold saturated sodium bicarbonate solution and then brine. The organic layer is dried (MgS0 4 ), filtered, and the filtrate concentrated under reduced pressure. The resulting residue is purified by silica gel flash column chromatography to give the title compound. Example 9 Coupling Procedures A. Synthesis of T-T phosphorodithioate dimer 100 milligram (4 mmole) of 5 '-O-DMT-thymidine bonded to CPG (controlled pore glass) through an ester linkage (commercially available) is transferred to a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with dichloromethane and then with acetonitrile. A 0.2 M solution of 5 '-O-DMT-thymidine- 3 '-0-(4-cyano-2-butenyl N,N-diisopropylthiophosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap any unreacted 5 '-hydroxyl groups. The product is washed with acetonitrile. The CPG containing the compound is treated with 30% aqueous ammonium hydroxide solution for 24 hours at 65 "C. The aqueous solution is filtered, concentrated under reduced pressure to give the phosphorodithioate T-T dimer. ■ B. Synthesis of C-T phosphorodithioate dimer 5 '-O-DMT-thymidine (100 mg, 4 mmole) bonded to CPG through an ester linkage is transferred to a glass reactor, and a CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5 '-hydroxyl groups. The product is washed with acetonitrile. Then, a 0.2 M solution of N4-benzoyl-5 '-0-DMT-2 '-deoxycytidine-3 '-0-(4-cyano-2- butenyl N,N-diisopropylthiophosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl groups. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 24 hours at 65 "C. The aqueous solution is filtered, concentrated under reduced pressure to give the phosphorodithioate dimer of dC- T. C- Synthesis of T-T phosphorothioate dimer 5 '-O-DMT-thymidine (100 mg, 4 mmole) bonded to CPG through an ester linkage is transferred to a glass reactor, and a CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5 '-hydroxyl group. The product is washed with CH 2 C1 2 and then with acetonitrile. A 0.2 M solution of 5 '-0-DMT-thymidine-3 '-0-(4-cyano-2-butenyl N,N- diisopropylthiophosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then 0.1 M iodine in water/pyridine/THF (2:20:80, v/v/v) is added and reacted at room temperature for 5 minutes . The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8, v/v/v), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl groups. The product is washed with acetonitrile. The CPG containing the compound is treated with 30% aqueous ammonium hydroxide solution for 24 hours at 65 "C. The aqueous solution is filtered, concentrated under reduced pressure to give the T-T phosphorothioate dimer. D. Synthesis of 5'-TTTTTTT-3 ' phosphorodithioate heptamer 5 '-O-DMT-thymidine (50 mg, 2 mmole) bonded to CPG through an ester linkage is transferred to a glass reactor, and a CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5 '-hydroxyl groups. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-0- DMT-thymidine-3 '-0-(4-cyano-2-butenyl N,N- diisopropylthiophosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes . The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8, v/v/v), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl groups. The product is washed with acetonitrile. This complete cycle is repeated five more times to get the completely protected thymidine heptamer. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes at room temperature. The aqueous solution is filtered and concentrated under reduced pressure to give the phosphorothioate heptamer of TTTTTTT. E. Synthesis of 5 '-d(GACT)-3' phosphorodithioate tetramer 5 '-O-DMT-thymidine (50 mg, 2 mmole) bonded to CPG through an ester linkage is taken in a glass reactor, and a CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-O-DMT-thymidine- 3 '-0-(4-cyano-2-butenyl N,N-diisopropylthiophosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulf rization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/ lutidine/ THF (1:1:8, v/v/v), and N- methyl imidazole/THF is added to cap the unreacted 5'- hydroxyl groups. The product is washed with acetonitrile. A CH 2 C1 2 solution of 2% dichloroacetic acid (volume/ volume) is added to deprotect the 5 '-hydroxyl groups. The product is washed with acetonitrile. Then, a 0.2 M solution of N4-benzoyl-5 '-O-DMT-2 '-deoxycytidine-3 '-0- ( -cyano-2-butenyl N,N-diisopropylthiophosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8, V/V/V) , and N- methyl imidazole/THF is added to cap the unreacted 5'- hydroxyl groups. The product is washed with acetonitrile. A CH 2 C1 2 solution of 2% dichloroacetic acid (v/v) is added to deprotect the 5'-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N6- benzoyl-5 '-O-DMT-2 '-deoxyadenosine-3 '-0-(4-cyano-2-buteny 1 N,N-diisopropylthiophosphoramidite) in anhydrous acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/ THF (1:1:8, v/v/v), and N- methyl imidazole/THF is added to cap the unreacted 5'- hydroxyl groups. The product is washed with acetonitrile. A dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N2-isobutyryl-5 '-O-DMT-2 '-deoxyguanosine-3 '- 0-(4-cyano-2-but enyl N,N-diisopropylthiophosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 24 hours at 65 'C. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate tetramer of 5'- dG-dA-dC-T-3' . EXAMPLE 10 Standard Deprotection Procedures A. Deprotection using NH^OH A homothymidine phosphorothioate dodecamer was synthesized as per the procedures of Example 5(D). The dodecamer was treated with saturated NH^OH for 24 hours at 65 "C to afford the completely deprotected product as determined by mass spectroscopy. B. Deprotection using CH 3 NH Z A homothy idine phosphorothioate dodecamer was synthesized as per the procedures of Example 5(D) . The dodecamer was treated with CH 3 NH 2 at 55 * C to afford the completely deprotected product as determined by mass spectroscopy. EXAMPLE 11 Synthesis of a Phosphorothioate Homo T 20 er 5 ' -O-DMT-thymidine bonded to CPG (controlled pore glass) through an ester linkage (commercially available) is transferred to a glass reactor. The CPG bound 5 ' -O-DMT- thymidine was washed with acetonitrile for 30 seconds followed by dichloromethane for 30 seconds. The CPG bound 5 ' -O-DMT-thymidine was treated with dichloroacetic acid (3%) in dichloromethane for 2 minutes followed by washing with acetonitrile for 3 minutes . The resulting detritylated thymidine bonded to CPG was reacted simultaneously with equal volumes of 5 ' -O-DMT- thymidine-3 '-0-( 4-cyano-2-butenyl N,N-diisopropylphosphor- amidite) (0.2 M) in acetonitrile and lH-tetrazole (0.4 M) in acetonitrile at room temperature for 5 minutes . The reagents are drained away and this step was repeated for an additional 5 minutes. The resulting T-T dimer bonded to CPG was washed with acetonitrile for 30 seconds and oxidized with Beaucage reagent (0.5 M) in acetonitrile for 3 minutes. This sulfurization step was repeated for an additional 3 minutes. The CPG was washed with acetonitrile for 30 seconds followed by treatment with equal volumes of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF for 1 minute to cap any unreacted sites. The above process of washing, detritylating, reacting with a monomer subunit, oxidizing and capping was repeated 18 times to synthesize the 20 mer homo thymidine phosphorothioate oligomeric compound. The CPG bound 20 mer was treated with 30% aqueous ammonium hydroxide solution for 2 hours at room temperature. The aqueous solution was filtered, concentrated under reduced pressure to give the phosphorothioate homo T 20 mer. The synthesis was run on a 1 μmole scale and the overall coupling efficiency was found to be greater than 99% as determined by spectrophotometric quantitation of released p,p'-dimethoxytriphenylmethyl cation. EXAMPLE 12 Synthesis of a Phosphorothioate Mixed Sequence 20 mer (GCC-CAA-GCT-GGC-ATC-CGT-CA) Following the procedures of Example 11, the mixed sequence 20 mer (GCC-CAA-GCT-GGC-ATC-CGT-CA) was synthesized using the protected monomer subunits of Example 4 (a,b,c, and d), 5 '-O-DMT-thymidine-3 '-0-(4-cyano-2-butenyl N,N- diisopropylphosphoramidite) , N2-isobutyryl-5 '-O-DMT-2 '- deoxyguanosine-3 '-0-(4-cyano-2-butenyl N,N- diisopropylphosphoramidite) , N6-benzoyl-5 '-O-DMT-2 '- deoxyadenosine-3 '-O-(4-cyano-2-butenyl N,N- diisopropylphosphoramidite) , N4-Benzoyl-5 '-O-DMT-2 '-deoxy- cytidine-3 '-0-(4-cyano-2-butenyl N,N-diisopropylphosphorami- dite) . The synthesis was carried out on a 1 μmole scale and the 20 mer was deprotected with aqueous NH 4 0H at room temperature for 1 hour followed by heating to 60 "C for 20 hours . The crude oligomer was purified by reverse-phase HPLC. The product was further characterized by capillary gel electrophoresis. EXAMPLE 13 Synthesis of a Silyl-containing Nucleosides The synthesis of representative silyl-containing nucleosides of the invention is depicted below in Scheme 3: Commercially available 1-acetoxy-l, 3-butadiene (compound 1) is first reacted with (R 9 ) 3 Si-H in the presence of Rh 2 Cl 2 (CO) to produce compound 2. The hydroxyl group is deprotected using K 2 C0 3 in methanol to produce compound 3. Compound 3 is then reacted with PC1 3 in ether at 0°C to produce compound 4, which is further reacted with isopropylamine in ether to produce compound 5. Compound 5 is then reacted with a 5 '-DMT nucleoside 6 in the presence of tetrazole in CH 2 C1 2 at room temperature to yield synthon 7. EXAMPLE 14 Preparation of 1, 1, l-triphenyl-4-acetoxy-l-sila-2-butene A solution of 1-acetoxy-l,3-butadiene (0.1 mol), triphenylsilane (0.1 mol), and Rh 2 Cl 2 (C0) 4 (194.5 mg, 0.625 mol) in 100 mL of toluene was stirred at room temperature under argon for 3 days . The reaction mixture is treated with decolorizing charcoal, and the mixture boiled briefly. After cooling, the reaction mixture is filtered through Celite. Concentration of the solution will afford the title compound. Example 15 Preparation of 1, 1, l-triphenyl-l-sila-2-butene-4-ol. The crude acetoxy compound from Example 14 is dissolved in 250 mL methanol, and 25.0 g of potassium carbonate is added all at once. After stirring for 2 hours, the reaction mixture is filtered and concentrated. The concentrated residue is partitioned between 200/200 mL water/ethyl acetate. The organic layer is removed, washed with brine, dried and concentrated. The crude material is purified by flash chromatography using silica gel to afford the pure product. Example 16 Preparation of 1,1,l-triphenyl-l-sila-2-butenyl-N,N- diisopropylbisphosphoramidite A 500 mL three-necked flask equipped with a magnetic stirrer, a glass stopper and an inlet for argon is assembled under argon atmosphere. All glassware are dried in an oven at 120 °C for 1 hour. The reaction flask is charged with anhydrous ether (150 mL) and phosphorous trichloride (67.5 mmol). 1, 1, l-triphenyl-l-sila-2-butene-4- ol (50 mmol) in ether (50 L) is added to the reaction flask slowly with stirring at 0 °C (ice cooling) using pressure- equalized addition funnel. After addition is complete, ice bath is removed and the reaction is stirred for three hours. The reaction mixture then is transferred to a 500 mL flask and concentrated under reduced pressure. To this product in anhydrous ether (200 mL) is added diisopropylamine (57.7 L) at 0 °C under argon. After the addition is complete, stirring is continued at room temperature for 16 hours (overnight) . The reaction mixture is filtered and concentrated to afford the title compound. Example 17 Preparation of Protected Phosphoramidite Monomers A. 5'-0-( ,4'-dimethoxytrityl)thymidine-3'-0- ( l,l,l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) . A 250 L two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an argon atmosphere. All glassware are dried at 120 °C for 1 hour. The flask is charged with 5'-0-(4,4'- dimethoxytrityl)thymidine (7 mmol) and 5-(4-nitrophenyl)-1H- tetrazole (5.6 mmol). Anhydrous acetonitrile (50 mL) is added. To this stirred mixture under argon at room temperature is added a solution of 1, 1, l-triphenyl-l-sila-2- butenyl N,N-diiεopropylphosphoramidite (10.5 mmol) in acetonitrile (50 L) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 L) , washed once with cold saturated sodium bicarbonate solution, brine and dried (MgS0 4 ) . The dried solution is concentrated under reduced pressure to afford a viscous foamy liquid. The crude product is purified by flash chromatography using silica gel to afford the product. Triethylamine (1%) is used throughout the purification. B. N 2 -Isobutyryl-5'-0-(4,4 '-dimethoxytrityl)-2'- deoxyguanosine-3'- 0-(1,1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoraπtidite) . A 250 mL two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an argon atmosphere. All glassware are dried at 120 °C for 1 hour. The flask is charged with N 2 -Isobutyryl-5 '-0- (4,4 '-dimethoxytrityl)-2 '-deoxyguanosine (5 mmol) and diisopropyl ammonium tetrazolide (4 mmol). Anhydrous acetonitrile (50 mL) is added. To this stirred mixture under argon at room temperature is added a solution of 1,1, l-triphenyl-l-sila-2-butenyl-N,N-diisopropyl- phosphoramidite (7.5 mmol) in acetonitrile (50 mL) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL) , washed once with cold saturated sodium bicarbonate solution, brine and dried (MgS0 4 ) . The dried solution is concentrated under reduced pressure to afford the product which is purified by flash chromatography using silica gel. Triethylamine (1%) is used throughout the purification. C. N 6 -Benzoyl-5'-0-(4,4 '-dimethoxytrityl)-2'- deoxyadenosine-3'-0-( 1,1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) . A 250 mL two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an argon atmosphere. All glassware are dried at 120 'C for 1 hour. The flask is charged with N 6 -benzoyl-5 '-0- (4,4 '-dimethoxytrityl)-2 '-deoxyadenosine (5 mmol) and diisopropylammonium tetrazolide (4 mmol). Anhydrous acetonitrile (50 mL) is added. To this stirred mixture under argon at room temperature is added a solution of 1,1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite (6 mmol) in acetonitrile (50 L) . After stirring for two hours, the reaction mixture is filtered and concentrated to afford the product which is purified by flash chromatography using silica gel. Triethylamine (1%) is used throughout the purification. D. N*-Benzoyl-5'-O-(4,4'-dimethoxytrityl)-2'- deoxycytidine-3'-O-(1,1,l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) A 250 mL two-necked flask equipped with a magnetic stirrer, a gas inlet for argon, and a septum is assembled under an argon atmosphere. All glassware are dried at 120°C for 1 hour. The flask is charged with N 4 -benzoyl-5 '-0-(4, 4 '- dimethoxytrityl)-2 '-deoxycytidine (5 mmol) and diisopropylammonium tetrazolide (4 mmol). Anhydrous acetonitrile (50 mL) is added. To this stirred mixture under argon at room temperature is added a solution of 1,1, l-triphenyl-l-sila-2-butenyl N,N- diisopropylphosphoramidite (7.5 mmol) in acetonitrile (50 L) . After stirring for two hours, the reaction mixture is filtered and the filtrate diluted with ethyl acetate (100 mL) , washed once with cold saturated sodium bicarbonate solution, brine and dried (MgSO,,) . The dried solution is concentrated under reduced pressure to afford the product which is purified by flash chromatography using silica gel. Triethylamine (1%) is used throughout the purification. Example 18 Coupling Procedures A. Synthesis of T-T phosphorothioate dimer 100 milligram (4 mmole) of 5 '-0- dimethoxytritylthy idine bonded to CPG (controlled pore glass) through an ester linkage is taken in a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with dichloromethane and then with acetonitrile. Then, a 0.2 M solution of 5 '-O-(4,4 '- dimethoxytrityl)thymidine-3 '-0-(1,1, l-triphenyl-l-sila-2- butenyl-N,N-diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes and then incubated at 55 * C for 12 hours. The aqueous solution is filtered, concentrated under reduced pressure and then treated at room temperature with 1.0 M solution of tetra-Λ-butyl ammonium fluoride in THF to give a phosphorothioate dimer of T-T. B. Synthesis of C-T phosphorothioate dimer 100 milligram (4 mmole) of 5 '-0- Dimethoxytritylthymidine bonded to CPG (controlled pore glass) through an ester linkage is taken in a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N*-Benzoyl-5 '-0-(4,4 '-dimethoxytrityl )-2 '- deoxycytidine-3 '-0-( 1, 1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes . The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes and then incubated at 55 °C for 12 hours. The aqueous solution is filtered, concentrated under reduced pressure and then treated at room temperature with 1.0 M solution of tetra-73-butyl ammonium fluoride in THF to give a phosphorothioate dimer of dC-T. D. Synthesis of 5'-TTTTTTT-3' phosphorothioate heptamer 50 milligram (2 mmole) of 5 '-O- Dimethoxytritylthymidine bonded to CPG (controlled pore glass) through an ester linkage is taken in a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-0-(4,4 '-dimethoxytrityl)thymidine-3 '-0- (1,1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes . The support is washed with acetonitrile and then a solution of acetic anhydride /lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. This complete cycle is repeated five more times to get the completely protected thymidine heptamer. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes at room temperature. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate heptamer of TTTTTTT. E. Synthesis of 5'-d(GACT)-3' phosphorothioate tetramer 50 milligram (2 mmole) of 5 '-0- dimethoxytritylthymidine bonded to CPG (controlled pore glass) through an ester linkage is taken in a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-0-(4,4 '-dimethoxytrityl)thymidine-3 '-0- (1,1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N ή -benzoyl-5'-0-(4,4 '-dimethoxytrityl)-2 '- deoxycytidine-3 '-0-( 1,1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N 6 -benzoyl-5 '-0-( ,4 '-dimethoxytrityl)-2 '- deoxyadenosine-3 '-0-( 1, 1, l-triphenyl-l-sila-2-butenyl-N,N- diisopropylphosphoramidite) in anhydrous acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of N 2 -isobutyryl-5 '-0-(4,4 ' -dimethoxytrityl)- 2 '-deoxyguanosine-3 '-0- (1,1, l-triphenyl-l-sila-2-butenyl- N,N-diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes at room temperature and then incubated at 55 °C for 24 hours. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate tetramer of 5'- dG-dA-dC-T-3' . EXAMPLE 19 3'-O-Levulinylthymidine The title compound was synthesized according a published procedure, see G. Kumar, M. S. Poonian, J. Org. Chem . 1984, 49 , 4905-4912. EXAMPLE 20 3'-0-Levulinyl-N2-isobutyryl-2'-deoxyguanosine 5 '-DMT-N2-isobutyryl-2 '-deoxyguanosine (71.6 g, 0.112 mol) is transferred to a 1000 ml flask and anhydrous dioxane (700 ml) is added and stirred until the solution becomes homogeneous. Then dicyclohexylcarbodiimide (57.8 g, 0.280 mol), levulinic acid (25.9 g, 0.224 mol) and 4- dimethylaminopyridine (0.56 g) are added and vigorously stirred using magentic stirring. After 3 hours, the reaction mixture is filtered, the solid residue washed with ethyl acetate (250 ml). The filterates are combined and concentrated to afford a product. This product is dissolved in dichloromethane (400 ml) and 2.5% DCA in dichloromethane (160 ml) is added and stirred. After 1 hour, the reaction mixture is diluted with dichloromethane (400 ml) and washed with saturated sodium bicarbonate solution. The organic layer is separated, dried and concentrated. The crude product is purified by flash chromatography using silica gel to give the title compound. EXAMPLE 21 Synthesis of T-T phosphorothioate dimer To a stirred solution of 3 '-O-levulinylthymidine (5 mmole) and lH-tetrazole (5 mmole) in anhydrous acetonitrile (25 ml) at room temperature under argon is added a solution of 5 ' -O-(4 ,4 '-dimethoxytrityl)thymidine-3 '- O-(4-diphenylmethylsilyl-2-butenyl N,^-diisopropyl phosphor¬ amidite) (6 mmole) in acetonitrile (20 ml). After stirring for 3 h, the sulfurizing reagent (a mixture of sulfur (200 mmole) /triethylamine (20 mmole) in dichloromethane (75 ml) is added all at once. After 5 hours, the reaction mixture is filtered and concentrated. The crude product is purified by flash chromatography using silica gel and ethylacetate/ hexane as eluents . EXAMPLE 22 Deprotection of 3'-O-levulinyl group 5 '-(0-4,4 '-Dimethoxytrityl)-3 '-(O-levulinyl)- thymidine dimer (35.0 g) is dissolved in an ice-cold solution of hydrazine-hydrate (10.0 g) , pyridine (240 ml) and acetic acid (240 ml). After 10 minutes, ice is added, followed by extraction with dichloromethane. The organic phase is dried over sodium sulfate, filtered and the solvent is removed. The residue is purified by silica gel column chromatography (ethyl acetate/n-hexanes 1:1, then ethyl acetate, 0.1% triethylamine) to afford the desired product. EXAMPLE 23 Synthesis of thymidyl-thymidine dimer amidite Under argon, a solution of IH tetrazole (5 mmol) and 4-cyano-2-butenyl-N, N, N ' , N '-tetraisopropylphosphoro- diamidite (30 mmol) in dry acetonitrile (100 ml) is added to thymidyl-thymidine dimer (20 mmol). After 2 hours, ethyl acetate is added and the solution is extracted with aqueous sodium bicarbonate. The organic phase is dried over sodium sulfate and the solvent is removed under reduced pressure. The residue is purified by column chromatography to afford the desired product. EXAMPLE 24 Synthesis of C-T- phosphorothioate dimer To a stirred solution of 3 '-O-levulinylthymidine (5 mmole) and lH-tetrazole (5 mmole) in anhydrous acetonitrile (25 ml) at room temperature under argon is added a solution of 5 ' -0-(4,4 '-dimethoxytrityl)-2 '- deoxycytidine-3 '-0-(4-diphenylmethylsilyl-2-butenyl N , N- diisopropyl phosphoramidite) (6 mmole) in acetonitrile (20 ml). After stirring for 3 h, the sulfurizing reagent (a mixture of sulfur (200 mmole) /triethylamine (20 mmole) in dichloromethane (75 ml) is added all at once. After 5 hours, the reaction mixture is filtered and concentrated. The crude product is purified by flash chromatography using silica gel and ethylacetate/hexane as eluents. EXAMPLE 25 Deprotection of 3'-O-levulinyl group 5 '-(0-4,4 '-Dimethoxytrityl)-3 '-(O-levulinyl)-2 ' - deoxycytidinyl-thymidine dimer (35.0 g) is dissolved in an ice-cold solution of hydrazine-hydrate (10.0 g) , pyridine (240 ml) and acetic acid (240 ml). After 10 minutes, ice is added, followed by extraction with dichloromethane. The organic phase is dried over sodium sulfate, filtered and the solvent is removed. The residue is purified by silica gel column chromatography (ethyl acetate/n-hexanes 1:1, then ethyl acetate, 0.1% triethylamine) to afford the desired product. EXAMPLE 26 Synthesis of 2'-deoxycytidinyl-thymidine dimer amidite Under argon, a solution of IH tetrazole (5 mmol) and 4-cyano-2-butenyl-N, N, N ', N '-tetraisopropylphosphoro- diamidite (30 mmol) in dry acetonitrile (100 ml) is added to 2 '-deoxycytidinyl-thymidine dimer (20 mmol). After 2 hours, ethyl acetate is added and the solution is extracted with aqueous sodium bicarbonate. The organic phase is dried over sodium sulfate and the solvent is removed under reduced pressure. The residue is purified by column chromatography to afford the desired product. EXAMPLE 27 Synthesis of d(A-G)-phosphorothioate dimer To a stirred solution of 3 '-O-levulinyl-2 '- deoxyguanosine (5 mmole) and lH-tetrazole (5 mmole) in anhydrous acetonitrile (25 ml) at room temperature under argon is added a solution of 5'-0- (4,4 '-dimethoxytrityl) - 2 '-deoxyadenosine-3 ' -O- ( -diphenylmethylsilyl-2-butenyl N, N- diisopropyl phosphoramidite) (6 mmole) in acetonitrile (20 ml). After stirring for 3 h, the sulfurizing reagent (a mixture of sulfur (200 mmole) /triethylamine (20 mmole) in dichloromethane (75 ml) is added all at once. After 5 hours, the reaction mixture is filtered and concentrated. The crude product is purified by flash chromatography using silica gel and ethyl acetate /hexane as eluents . EXAMPLE 28 Deprotection of 3'-O-levulinyl group 5 '-(0-4,4 '-Dimethoxytrityl)-3'-( -levulinyl)-2 ' - deoxyade nosinyl-2 '-deoxyguanosine dimer (35 g) is dissolved in an ice-cold solution of hydrazine-hydrate (10.0 g), pyridine (240 ml) and acetic acid (240 ml). After 10 minutes, ice is added, followed by extraction with dichloromethane. The organic phase is dried over sodium sulfate, filtered and the solvent is removed. The residue is purified by silica gel column chromatography (ethyl acetate/n-hexanes 1:1, then ethyl acetate, 0.1% triethylamine) to afford the desired product. EXAMPLE 29 Synthesis of 2'-deoxyadenosinyl-2 '-deoxyguanosine dimer a idite Under argon, a solution of IH tetrazole (5 mmol) and 4-cyano-2-butenyl-.iV, N, N ' ,W-tetraisopropylphosphoro- diamidite (30 mmol) in dry acetonitrile (100 ml) is added to 2 '-deoxyadenosinyl-2 '-deoxyguanosine dimer (20 mmol). After 2 hours, ethyl acetate is added and the solution is extracted with aqueous sodium bicarbonate. The organic phase is dried over sodium sulfate and the solvent is removed under reduced pressure. The residue is purified by column chromatography to afford the desired product. EXAMPLE 30 Synthesis of 5'-TTTTTTT-3' phosphorothioate heptamer 50 milligram (2 mmole) of 5 '-O-dimethoxy- tritylthymidine bonded to CPG (controlled pore glass) through an ester linkage is taken in a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-0-(4,4 '-dimethoxytrityl)-thymidyl-thymidine- 3 '-0-(4-cyano-2-butenyl N,N-diisσpropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes . This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. This complete cycle is repeated two more times to get the completely protected thymidine heptamer. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes at room temperature and then incubated at 55 °C for 1 hour. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate heptamer of 5 '-TTTTTTT- 3' . EXAMPLE 31 Synthesis of 5'-d(TTCTAGT)-3' phosphorothioate heptamer 50 milligram (2 mmole) of 5'-O-dimethoxy- tritylthymidine bonded to CPG (controlled pore glass) through an ester linkage is taken in a glass reactor, and a dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-0-(4 ,4 '-dimethoxytrityl)-2 '-deoxyadenosinyl- 2 '-deoxyguanosine-3 '-0-(4-cyano-2-butenyl N,N- diisopropylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes . The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes . The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5'-hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 '-0-(4,4 '-dimethoxytrityl)-2 '-deoxy- cytidinyl-thymidine-3 '-0 -(4-cyano-2-butenyl N,N-diiso- propylphosphoramidite) in acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes . The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5'-hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2% dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 5 ' -0-(4, '-dimethoxytrityl)-thymidyl-thymidine -3 '-0-(4-cyano-2-butenyl N,N-diisopropylphosphoramidite) in anhydrous acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/ lutidine/THF (1:1:8), and N- methyl imidazole/THF is added to cap the unreacted 5'- hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30% aqueous ammonium hydroxide solution for 90 minutes at room temperature and then incubated at 55 °C for 24 hour. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate heptamer of 5'- d(TTCTAGT)-3' . EXAMPLE 32 Levulinic anhydride: A solution of 1, 3-dicyclohexylcarbodiιmιde (DCC) (207 g, 1 mol) in diethyl ether (1.2 1) was added to a solution of levulinic acid (232 g, 2 mol) in anhydrous diethyl ether (800 ml) . Within a couple of minutes a colorless precipitate formed and a slight temperature increase in the reaction flask was observed. After stirring for 5 h, the solid (DCU) is removed by filtration and the solvent is removed under reduced pressure. 220 g of a semi-solid product (at room temp.) is obtained which is used without further purification in the subsequent reactions. EXAMPLE 33 N 4 -Benzoyl-3 *-O-levulinyl-2 '-deoxycytidine Levulinic anhydride (51.4 g, 240 mmol) was added to a solution of 5'-DMT-N' i -benzoyl-deoxycytιdine (76 g, 120 mmol) in dry pyridine (240 ml) . 4-Dimehtylaminopyridιne (DMAP) (390 mg) was added. After 2h most of the pyridine was removed under vaccum and the remaining dark colored solution was poured on ice/water (ca. 2 kg) which was stirred for several hours. A precipitate formed which was isolated by filtration and rinsed with water (21) and dried in vacuo. To remove more water, the solid was dissolved in CH ^ C1 : (300 ml) . The organic layer was separated, dried over Na_.S0 4 and evaporated. The residue was dissolved in a solution of p-toluenesulfonic acid (21 g) in ethylacetate/methanol (75 ml, 85:15, v/v) . After a few minutes (15-20 mm) the flask content solidified. The finely ground solid was extracted with diethyl ether (total 500 ml ether) . The solid was dissolved in CH 2 C1 2 (1 1) and extracted with aqu. NaHCO, (IM) . A solid (product ') formed during this step which was removed by filtration. The organic layer was dried over Na-SO, and concentrated under vacuum. After ca. 90<- of the solvent is removed more product was isolated by filtration. The solid fractions are combined: 44 g (85 > ) . More product can be recoverd from the CH Cl_ solution. EXAMPLE 34 3' -O-Levulinylthymidine: A solution of 5' -dimethoxytntylthymidme (272.3 g, 500 mmol) in anhydr. pyridme (500 ml) was added to a solution of levulinic anhydride (214 g, 1 mol) in pyridme (500 ml) . Dimethylaminopyridme (DMAP, 1 g) was added. After 5 h, most of the solvent was removed by evaporation, the remammg dark colored oil was poured on ice (2 kg) /NaHCO, (IM, 1 1) and stirred for several hours. The oily/solid precipitate was isolated by filtration and washed several times with water. The solid was dried m vacuo. To remove more water from the product, the solid was dissolved m CH ^ Cl , the aqueous phase was separated, the organic phase dried over Na SO, and evaporated. The finely ground solid was added to a solution of p-toluenesulfonic acid (80 g) ethyl acetate/methanol (85:15, 500 ml) . After 20 mm, the reaction mixture was added to sat. NaHCO, (900 ml) solution (CO _ evolution) . To this mixture, diethyl ether (500 ml) was added. The two layers were separated, and the organic layer was re-extracted with dil. NaHCO solution. The combined aqueous layers were extracted with diethyl ether. For isolation of the product, the aqu. layer was extracted several times with CH-C1_ or CHCl,.The CHCl fractions were combined, dried over Na 2 S0 4 , and concentrated. The residue was recrystalized from ethyl acetate-hexane, yield: 55-60o EXAMPLE 35 N-Benzoyl-3 '-O-levulιnyl-2 '-deoxyadenosine Levulinic anhydride (51.4 g, 240 mmol) was added to a solution of 5'-DMT-N-benzoyl-deoxyadenosme (120 mmol) in dry pyridine (240 ml) . 4-Dimehtylaminopyridme (DMAP) (390 mg) was added. After 2h most of the pyridine was removed under vaccum and the remaining dark colored solution was poured on ice/water (ca. 2 kg) which was stirred for several hours. A precipitate formed which was isolated by filtration and rinsed with water (21) and dried m vacuo. To remove more water, the solid was dissolved CH C1- (300 ml) . The organic layer was separated, dried over Na : S0 4 and evaporated. The residue was dissolved in a solution of p-toluenesulfonic acid (21 g) in ethylacetate/methanol (75 ml, 85:15, v/v) . After a few minutes (15-20 mm) the flask content solidified. The finely ground solid was extracted with diethyl ether (total 500 ml ether) . The solid was dissolved in CH.C1_ (1 1) and extracted with aqu. NaHCO, (IM) . A solid (product !) formed durmg this step which was removed by filtration. The organic layer was dried over Na.SO,, and concentrated under vacuum. The solid fractions are combined: 44 g (85 " ) . EXAMPLE 36 N 2 -Isobutyryl-3 '-O-levulinyl-2 '-deoxyguanosine Levulinic anhydride (51.4 g, 240 mmol) was added to a solution of 5'-DMT-N"-isobutyryl-deoxyguanosιne (120 mmol) in dry pyridine (300 ml) . 4-Dιmehtylaminopyrιdine (DMAP) (390 mg) was added. After 2h most of the pyridme was removed under vaccum and the remaining dark colored solution was poured on ice/water (ca. 2 kg) which was stirred for several hours. A precipitate formed which was isolated by filtration and rmsed with water (21) and dried in vacuo. To remove more water, the solid was dissolved in CH Cl (300 ml) . The organic layer was separated, dried over Na,S0 4 and evaporated. The residue was dissolved n a solution of p-toluenesulfonic acid (21 g) in ethylacetate/methanol (75 ml, 85:15, v/v) . After a few minutes (15-20 mm) the flask content solidified. The finely ground solid was extracted with diethyl ether (total 500 ml ether) . The solid was dissolved CHCl (1 1) and extracted with aqu. NaHCO (IM) . A solid (product ' ) formed during this step which was removed by filtration. The organic layer was dried over Na SO, and concentrated under vacuum The solid fractions are combined to afford the product. EXAMPLE 37 β-Cyanoethyl phosphorodichloridite: This compound was synthesized as per reported procedure; Ogilvie, K. K. Can. J. Chem. 58, 268C (1980) . EXAMPLE 38 5 * -O- (4 ,4 '-dimethoxytrityl) -N 4 -benzoyl-2 '-deoxycytιdm-3 '-yl-O- 2-cyanoethyl-0-3 '-O-levulιnylthymιdιn-5 '-yl phosphorothioate. 5 ' -0- (4, 4 ' -dimethoxytrityl) -W 4 -benzoyl-2 ' - deoxycytidme (41 g, 63 mmol) was coevaporated with dry pyridme (100 ml) then dissolved dry THF (200 ml), some 4A molecular sieves added and the whole set aside for 15 minutes. 2-Cyanoethylphosphorodιchlorιdιte (11.9 g, 69 mmcl) was added to a stirred suspension of 1, 2, 4-trιazole (9.6 g, 138 mmol) and pyrid e (11.2 ml, 138 mmol) m dr THF (300 ml) at -35 C. After 10 mm the above dry solution of 50-O- (4,4'- dimethoxytrityl) -N"-benzoyl-2 ' -deoxycytidme was added dropwise over 30 minutes. After a further 10 mm a solution 3'-0- levulmylthymidme [21.0 g, 62 mmol, previousl/ azeotroped with pyridme (50ml) ] in dry THF (100 ml) was added over 10 mm and after a further 20 mm the mixture allowed to warm to room temperature. After 60 mm Beaucage reagent (40.0 g, 200 πvmol) was added and the products allowed to stir for 15 minutes. Pyridme (20 ml) was added and the reaction mixture filtered. The solid was washed with EtOAc and the combined filtrates concentrated under reduced pressure. A solution of the residue m EtOAc (1000 ml) was washed with saturated aqueous sodium hydrogen carbonate (2 x 300 ml) then dried (Na_SO„) and concentrated m vacuo. The residue was purified by chromatography on silica gel, the appropriate fractions, eluted with EtOAc, were pooled and concentrated under reduced pressure to give the title compound as a colorless glass. EXAMPLE 39 5'-0-{4 ,4 '-dimethoxytrityl) -N 4 -benzoyl-2 '-deoxycytιdm-3 '-yl-O- 2 '-cyanoethyl-O-thymιdιn-5 '-yl phosphorothioate. 5'-0- (4, 4 '-dιmethoxytrιtyl) -W 1 -benzoyl-2 ' - deoxycytιdιn-3' yl-0-2-cyanoethyl-0-3 '-O-levulmylthymιdm-5' -yl phosphorothioate (46.8 g, 42 mmol) was dissolved m an ice-cold solution of hydrazine monohydrate (11.5 ml) in acetic acid- pyrid e (1:2 v/v, pH 5.1, 345 ml) The mixture was allowed to warm toroom temperature and after a total of 30 mm the products were poured mto ice (2000 ml) . The ice was allowed to melt and the formed colorless precipitate collected by filtration. The solid was washed with water then dissolved n CH Cl_ (600 ml) and the solution washed with saturated aqueous sodium hydrogen carbonate (200 ml) , dried (Na SO,) and concentrated m vacuo. The residue was fractionated on silica gel, combination and evaporation of the fractions eluted with EtOAc gave the title compound (61°) as a colorless glass. EXAMPLE 40 4-cyano-2-butenyl-N,N-dnsopropyl phosphoramidite of 5'-0- (4,4' -dimethoxytrityl) -W-benzoyl-2 ' -deoxycytιdιn-3 '-yl-O-2- cyanoethyl-O-thymιdιn-5 ' -yl phosphorothioate. 5' -O- (4, 4 '-dimethoxytrityl) -A^-benzoyl-2 ' - deoxycytιdιn-3 ' -yl-0-2-cyanoethyl-0 thymιdm-5'-yl phosphorothioate (8.54 g, 8.5 mmol) was coevaporated with dry dioxane (30 ml) then redissolved CH 2 C1 ^ (120 ml) and bis (diisopropylam o) -4-cyano-2-butenyloxyphosphme (29.7 mmol) followed by 1-H-tetrazole (0.89 g, 12.8 mmol) added. The mixture was stirred atroom temperature for 1 h, then diluted with CH Cl (200 ml) and extracted with ice-cold saturated aqueous sodium hydrogen carbonate (200 l) . The organic layer was dried (Na ; S0 and concentrated under reduced pressure. A solution of the residue in EtOAc-hexane (7:3 v/v, 30 ml) was passed through a short column of silica gel packed in the same solvent system. The column was washed witn the same solvent and the product containing fractions pooled and concentrated in vacuo to give an oil.. The oil was dissolved in CH Cl ^ (30 ml) and hexane (200 ml) added gradually with swirling. The supernatant was decanted away from the formed colorless oil and the procedure repeated. The residue was dissolved m CH,C1_ (10 ml) and the solution concentrated under reduced pressure to give the title compound. EXAMPLE 41 5'- - (4,4'-dimethoxytrityl) -^-benzoyl-2 '-deoxycytιdιn-3 '-yl-O- 2-cyanoethyl-0-3'-0-levulιnyl-N-benzoyl-2-deoxyadenosιne-5 '-yl phosphorothioate. 5 ' -O- (4, 4 ' -dimethoxytrityl) -W 1 -benzoyl-2 ' - deoxycytidine (41 g, 63 mmol) was coevaporated with dry pyridine (100 ml) then dissolved m dry THF (2C0 ml), some 4A molecular sieves added and the whole set aside for 15 minutes. 2-Cyanoethylphosphorodichloridite (11.9 g, 69 mmol) was added to a stirred suspension of 1, 2, 4-triazole (9.6 g, 138 mmol) and pyridme (11.2 ml, 138 mmol) in dry THF (300 ml) at -35 r C. After 10 mm the above dry solution of 5-0- (4,4- dimethoxytrityl) -N 1 -benzoyl-2'-deoxycytidine was added dropwise over 30 minutes. After a further 10 min a solution 3-0- levulmyl-N-benzoyl-2 ' -deoxyadenosine [62 mmol, previously azeotroped with pyridine (50ml) ] in dry THF (100 ml) was added over 10 min and after a further 20 min the mixture allowed to warm toroom temperature. After 60 mm Beaucage reagent (40.0 g, 200 mmol) was added and the products allowed to stir for 15 minutes. Pyridine (20 ml) was added and the reaction mixture filtered. The solid was washed with EtOAc and the combined filtrates concentrated under reduced pressure. A solution of the residue in EtOAc (1000 ml) was washed with saturated aqueous sodium hydrogen carbonate (2 x 300 ml • then dried (Na ^ SO.,) and concentrated in vacuo. The residue was purified by chromatography on siiica gel, die appropiiaLe IiacLiυns, eiuLeu with EtOAc, were pooled and concentrated under reduced pressure to give the title compound. EXAMPLE 42 5 ' -O- (4 ,4 '-dimethoxytrityl) -N 4 -benzoyl -2 ' -deoxycytidin-3 '-yl-O- 2-cyanoethyl-O-N-benzoyl -2 ' -deoxyadenosιne-5 ' -yl phosphorothioate . 5' -O- (4, '-dimethoxytrityl) -N f -benzoyl-2 ' - deoxycytidm-3 ' -yl-0-2-cyanoethyl-0-3 '-O-levulinyl-N-benzoyl- 2 ' -deoxyadenosme-5 ' -yl phosphorothioate (42 mmol) was dissolved in an ice-cold solution of hydrazine monohydrate (11.5 ml) in acetic acid-pyπdine (1:2 v/v, pH 5.1, 345 ml) The mixture was allowed to warm toroom temperature and after a total of 30 min the products were poured mto ice (2000 ml) . The ice was allowed to melt and the formed colorless precipitate collected by filtration. The solid was washed with water then dissolved m CH : Cl t (600 ml) and the solution washed with saturated aqueous sodium hydrogen carbonate (200 ml), dried (Na SO and concentrated m vacuo. The residue was fractionated on silica gel, combination and evaporation of the fractions eluted with EtOAc gave the title compound. EXAMPLE 43 4-cyano-2-butenyl-N,N-diisopropyl phosphoramidite of 5'-0- (4 ,4 '-dimethoxytrityl) -N" -benzoyl -2 ' -deoxycytidin-3 '-yl-O-2- cyanoethyl- -N-benzoyl-2 ' -deoxyadenosιne-5 ' -yl phosphorothioate. 5 ' -0- (4, 4 '-dimethoxytrityl) - 4 -benzoyl-2 ' - deoxycytidm-3 ' -yl-0-2-cyanoethyl-0-N-benzoyl-2 ' - deoxyadenosine-5 ' -yl phosphorothioate (8.54 g, 8.5 mmol) was coevaporated with dry dioxane (30 ml) then redissolved in CHCl , (120 ml) and bis (diisopropyla ino ) -4-cyano-2- butenyioxyphosphme (29.7 mmol) followed by 1-H-tetrazole (0.89 g, 12.8 mmol) added. The mixture was stirred atroom temperature for 1 h, then diluted with CHCl (200 ml) and extracted with ice-cold saturated aqueous sodium hydrogen carbonate (200 ml) . The organic layer was dried (Na ^ S0 4 ) and concentrated under reduced pressure. A solution of the residue in EtOAc-hexane (7:3 v/v, 30 ml) was passed through a short column of silica gel packed m the same solvent system. The column was washed with the same solvent and the product containing fractions pooled and concentrated in vacuo to give an oil. The oil was dissolved in CHCl ^ (30 ml) and hexane (200 ml) added gradually with swirling. The supernatant was decanted away from the formed colorless oil and the procedure repeated. The residue was dissolved in CHC1 ^ (10 ml) and the solution concentrated under reduced pressure to give the title compound. EXAMPLE 44 5 '-O-(4,4 '-dimethoxytrityl) -N 4 -benzoyl-2 '-deoxycytidιn-3 '-yl- - 2-cyanoethyl-0-3 '-O-levulinyl-N2-isobutyryl-2-deoxyguanosine- 5'-yl phosphorothioate. 5'-0- (4, 4 '-dimethoxytrityl) -AT 1 -benzoyl-2'- deoxycytidine (41 g, 63 mmol) was coevaporated with dry pyridine (100 ml) then dissolved in dry THF (200 ml), some 4A molecular sieves added and the whole set aside for 15 minutes. 2-Cyanoethylphosphorodιchlorιdιte (11.9 g, 69 mmol) was added to a stirred suspension of 1, 2, -trιazole (9.6 g, 11 ti mmol) and pyrid e (11.2 ml, 138 mmol) m dry THF (300 ml) at -35 C. After 10 mm the above dry solution of 5'-0-(4,4'- dimethoxytrityl) -N'-benzoyl-2 '-deoxycytidme was added dropwise over 30 minutes. After a further 10 mm a solution 30-0- levulmyl-N2-ιsobutyryl-2'-deoxyguanoosme [62 mmol, previously azeotroped with pyridme (50ml) ] in dry THF (100 ml) was added over 10 mm and after a further 20 mm the mixture allowed to warm toroom temperature. Alter 60 mm Beaucage reagent ( U.U g, 200 mmol) was added and the products allowed to stir for 15 minutes. Pyridme (20 ml) was added and the reaction mixture filtered. The solid was washed with EtOAc and the combined filtrates concentrated under reduced pressure. A solution of the residue in EtOAc (1000 ml "> was washed with saturated aqueous sodium hydrogen carbonate (2 x 300 ml) then dried (Na SO and concentrated in vacuo. The residue was purified by chromatography on silica gel, the appropriate fractions, eluted with EtOAc, were pooled and concentrated under reduced pressure to give the title compound. EXAMPLE 45 5'-0- (4 ,4 '-dimethoxytrityl) -N -benzoyl-2'-deoxycytιdιn-3 ' -yl-O- 2-cyanoethyl -0-N2 -lsobutyryl -2 ' -deoxyguanosine-5 ' -yl phosphorothioate. 5'-0- (4, 4 ' -dιmethoxytrιtyl) -N , -benzoyl-2 '- deoxycytιdm-3'-yl-0-2-cyanoethyl-0-3'-0-levulιnyl-N2- ιsobutyryl-2 '-deoxyguanosme-5'-yl phosphorothioate (42 mmol) was dissolved in an ice-cold solution of hydrazine monohydrate (11.5 ml) in acetic acid-pyπdme (1:2 v/v, pH 5.1, 345 ml) The mixture was allowed to warm toroom temperature and after a total of 30 mm the products were poured mto ice (2000 ml) . The ice was allowed to melt and the formed colorless precipitate collected by filtration. The solid was washed with water then dissolved CHCl (600 ml) and the solution washed with saturated aqueous sodium hydrogen carbonate (200 ml) , dried (Na S0 4 ) and concentrated m vacuo . The residue was fractionated on silica gel, combination and evaporation of the fractions eluted with EtOAc gave the title compound. EXAMPLE 46 -cyano-2-butenyl-N ,N-dι isopropyl phosphoramidite of 5 ' -0- (4 , 4 ' -dimethoxytrityl ) -N 4 -benzoyl -2 ' -deoxy cytιdιn-3 ' -yl-O-2- cyanoe thyl - 0-N2 - ι s obu tyryl - 2 ' -de oxy guano s me - 5 ' -yl phosphorothioate. 5 * -0- (4, 4 ' -dimethoxytrityl) -W -benzoyl-2 ' - deoxycytιdm-3'-yl-0-2-cyanoetnyl-0 N2-ιsobutyryl-2'- deoxyguanosιne-5' -yl phosphorothioate (8.54 g, 8.5 mmol) was coevaporated with dry dioxane (30 ml) then redissolved m CH Cl t (120 ml) and bis (diisopropylammo) -4-cyano-2- butenyloxyphosphme (29.7 mmol) followed by 1-H-tetrazole (0.89 g, 12.8 mmol) added. The mixture was stirred atroom temperature for 1 h, then diluted with CH Cl ^ (200 il and extracted with ice-cold saturated aqueous sodium hydrogen carbonate (200 ml) . The organic layer was dried (Na SOJ and concentrated under reduced pressure. A solution of the residue in EtOAc-hexane (7:3 v/v, 30 ml) was passed through a short column of silica gel packed in the same solvent system. The column was washed with the same solvent and the product containing fractions pooled and concentrated m vacuo to give an oil.. The oil was dissolved CH ^ C1 (30 ml) and hexane (200 ml) added gradually with swirling. The supernatant was decanted away from the formed colorless oil and the procedure repeated. The residue was dissolved m CH Cl t (10 ml) and the solution concentrated under reduced pressure to give the title compound. EXAMPLE 47 Synthesis of 5 '-d(CTCACGT) -3 '-phosphorothioate heptamer. 50 milligram (2 mmole) of 5'-0- dimethoxytntylthymidine bonded to CPG (controlled pore glass) through an ester linkage is taken m a glass reactor, and a dichloromethane solution of 2/ dichloroacetic acid (volume/volume) is added to deprotect the 5' -hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 4-cyano-2-butenyl-N, N-diisopropyl phosphoramidite of 5' -0- (4, ' -dimethoxytrityl) -ΛT-benzoyl- ' -deoxycytιdιn-3 ' - yl-0-2-cyanoethyl-0-N2-ιsobutyryl-2'-deoxyguanosine-5'-yl phosphorothioate) m acetonitrile and a 0.4 M solution of 1H- tetrazole acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidme/THF (1:1:8), and N- methyl imidazole/THF is added to cap the unreacted 5 ' -hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2 dichloroacetic acid (volume/volume) is added to deprotect the '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 4-cyano-2-butenyl-N, -diisopropyl phosphoramidite of 5' -0- (4, 4 '-dimethoxytrityl) -N'-benzoyl-2 ' -deoxycytidιn-3 '- yl-O-2-cyanoethyl-0-N-benzoyl-2 ' -deoxyadenosιne-5 ' -yl phosphorothioate in acetonitrile and a 0.4 M solution of 1H- tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N- methyl imidazole/THF is added to cap the unreacted 5'-hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2° dichloroacetic acid (volume/volume) is added to deprotect the 5'-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 4-cyano-2-butenyl-N,N-diisopropyl phosphoramidite of 5' -0- (4, 4 ' -dimethoxytrityl) -AT 4 -benzoyl-2 ' -deoxycytιdm-3 ' - yl-0-2-cyanoethyl-0-thymidin-5 ' -yl phosphorothioate in anhydrous acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature tor s minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidine/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 '-hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30'j aqueous ammonium hydroxide solution for 90 minutes at room temperature and then incubated at 55° C for 24 hour. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate heptamer of 5 ' -d (CTCACGT) - 3' . EXAMPLE 48 Synthesis of 5'-d(CTCACGC) -3 ' phosphorothioate heptamer. 50 milligram (2 mmole) of 5'-0-dιmethoxytπtyl-N4- benzoyl-2' -deoxycytidine bonded to CPG (controlled pore glass) through an ester linkage is taken in a glass reactor, and a dichloromethane solution of 2 dichloroacetic acid (volume/volume) is added to deprotect the 5'-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 4-cyano-2-butenyl-N,N-diisopropyl phosphoramidite of 5' -0- (4, 4 ' -dimethoxytrityl) -ΛT'-benzoyl-2 ' -deoxycytidm-3 ' - yl-0-2-cyanoethyl-0-N2-ιsobutyryl-2 ' -deoxyguanosine-5 ' -yl phosphorothioate) m acetonitrile and a 0.4 M solution of 1H- tetrazole m acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydπde/lutidme/THF (1:1:8), and N- methyl lmiαazole/'iHl is added to cap the unreacted ' -hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2 dichloroacetic acid (volume/volume) is added to deprotect the 5 '-hydroxyl group. The product is washed with acetonitrile. Then, a 0.2 M solution of 4-cyano-2-butenyl-N,N-diisopropyl phosphoramidite of 5'-0- (4, 4 '-dimethoxytrityl) -Λ/ * '-benzoyl-2 ' -deoxycytιdm-3 ' - yl-0-2-cyanoethyl-0-N-benzoyl-2 ' -deoxyadenosine-5 ' -yl phosphorothioate m acetonitrile and a 0.4 M solution of 1H- tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent m acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidme/THF (1:1:8), and N- methyl imidazole/THF is added to cap the unreacted 5 ' -hydroxyl group. The product is washed with acetonitrile. A dichloromethane solution of 2o dichloroacetic acid (volume/volume) is added to deprotect the ' -hydroxyl group. The product is washed with acetonitrile. T en, a 0.2 M solution of 4-cyano-2-butenyl-N,N-diisopropyl phosphoramidite of 5' -0- (4, 4-dimethoxytrityl) -ΛT'-benzoyl-2 '-deoxycytιdm-3 ' -yl- 0-2-cyanoethyl-0-thymιdιn-5' -yl phosphorothioate m anhydrous acetonitrile and a 0.4 M solution of lH-tetrazole in acetonitrile is added, and reacted at room temperature for 5 minutes. The product is washed with acetonitrile, and then a 0.05 M solution of Beaucage reagent in acetonitrile is added and reacted at room temperature for 5 minutes. This sulfurization step is repeated one more time for 5 minutes. The support is washed with acetonitrile and then a solution of acetic anhydride/lutidme/THF (1:1:8), and N-methyl imidazole/THF is added to cap the unreacted 5 ' -hydroxyl group. The product is washed with acetonitrile. The carrier containing the compound is treated with 30o aqueous ammonium hydroxide solution tor 90 minutes at room temperature and then incubated at 55° C for 24 hour. The aqueous solution is filtered, concentrated under reduced pressure to give a phosphorothioate heptamer of 5' -d (CTCACGC) - 3' . It is intended that each of the patents, publications, and other published documents mentioned or referred to in this specification be herein incorporated by reference in its entirety. Those skilled in the art will appreciate that numerous changes and modifications may be made to the preferred embodiments of the invention and that such changes and modifications may be made without departing from the spirit of the invention. It is therefore intended that the appended claims cover all such equivalent variations as fall within the true spirit and scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. A method for the preparation of an oligomeric compound comprising a moiety having the Formula IX: IX wherein: Z is CN, halogen, N0 2 , alkaryl, sulfoxyl, sulfonyl, thio, substituted sulfoxyl, substituted sulfonyl, or substituted thio, wherein the substituents are selected from the group consisting of alkyl, aryl, or alkaryl; and comprising the steps of: (a) providing a compound having the Formula II: II wherein: each R l t is, independently, H, -OH, -F, or -O-X 3 -D; X 3 is alkyl having from 1 to 10 carbons; D is H, amino, protected amino, alkyl substituted amino, imidazole, or (-0-X 3 ) p , where p is 1 to about 10; each X 2 is 0 or S ; R 3 and R 3a are each hydrogen, a hydroxyl protecting group, or a linker connected to a solid support; each B, independently, is a naturally occurring or non-naturally occurring nucleobase or a protected naturally occurring or non-naturally occurring nucleobase; n is 0 to about 50; Q is a phosphorus protecting group; R is -N(R 6 ) 2 , or heterocycloalkyl or heterocycloalkenyl ring containing from 4 to 7 atoms, and having up to 3 heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen; R 6 is straight or branched chain alkyl having from 1 to 10 carbons; (b) reacting the compound of Formula II with a compound having the Formula III: III wherein R 3a is hydrogen; and R 2 is a hydroxyl protecting group, or a linker connected to a solid support, provided that R 2 and R 3 are not both simultaneously a linker connected to a solid support; to form the oligomeric compound. The method of claim 1 further comprising the step of oxidizing the oligomeric compound to form a further compound having the Formula III, wherein R 3 is hydrogen, a hydroxyl protecting group, or a linker connected to a solid support; and where is increased by 1. 3. The method of claim 2 further comprising a capping step. 4. The method of claim 3 wherein the capping step is performed subsequent to oxidation. 5. The method of claim 3 wherein the capping step is performed prior to oxidation. 6. The method of claim 3 further comprising the step of cleaving the oligomeric compound to produce a compound having the Formula I: 7. The method of claim 1 wherein Z is CN and Q is XjH or -X ! -CH 2 -CH=CH-CH 2 -Z . 8. The method of claim 7 wherein each R 6 is isopropyl. 9. The method of claim 7 wherein X 2 is 0. 10. The method of claim 9 wherein X, is S. 11. The method of claim 9 wherein X { is 0. 12. The method of claim 7 wherein X 2 is S. 13. The method of claim 12 wherein X x is S. 14. The method of claim 12 wherein X L is 0. 15. The method of claim 1 wherein the compound of Formula II is obtained by reaction of a compound having the Formula V: V with a compound having the Formula VI : (R 5 ) 2 P-X ! -CH 2 -CH=CH-CH 2 -Z VI in the presence of an acid, 16. A compound having the Formula VII: A-X 1 -CH 9 -CH=CH-CH,-Z VII wherein: X j is 0 or S; A is (R 7 )(R 8 )P-; R 8 is R 5 , or has the Formula X: x wherein: each Rj, is, independently, H, -OH, -F, -0-X 3 -D; X 3 is alkyl having from 1 to 10 carbons; D is H, amino, protected amino, alkyl substituted amino, imidazole, or (-0-X ) p , where p is 1 to about 10; each X 2 is 0 or S; R 5 is -N(R 6 ) 2 , or a heterocycloalkyl or heterocycloalkenyl ring containing from 4 to 7 atoms, and having up to 3 heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen; each Q is a phosphorus protecting group; m is 0 to about 50; each B, independently, is a naturally occurring or non-naturally occurring nucleobase or a protected naturally occurring or non-naturally occurring nucleobase; and R 7 is R 5 , or has the Formula VIII: VIII wherein: R 3 is hydrogen, a hydroxyl protecting group, or a linker connected to a solid support; and n is 0 to about 50; with the proviso that the sum of m and n do not exceed 50; and Z is CN, halogen, N0 2 , alkaryl, sulfoxyl, sulfonyl, thio, substituted sulfoxyl, substituted sulfonyl, or substituted thio, wherein the substituents are selected from the group consisting of alkyl, aryl, or alkaryl. 17. The compound of claim 16 wherein Z is CN and Q is XjH or -X 1 -CH 2 -CH=CH-CH 2 -Z. 18. The compound of claim 17 wherein i is 0. 19. The compound of claim 17 wherein X is S. 20. The compound of claim 17 wherein A is H. 21. The compound of claim 17 wherein A is -P(R 5 ) 2 , 22. The compound of claim 20 wherein R 5 is -N(CH(CH 3 ) 2 ) 2 . 23. The compound of claim 16 wherein R 7 has the Formula VII. 24. The compound of claim 23 wherein n is 1 to 30. 25. The compound of claim 23 wherein n is 1 to about 25. 26. The compound of claim 23 wherein n is 0. 27. The compound of claim 17 wherein Z is CN; X } is 0; and A is H. 28. The compound of claim 17 wherein Z is CN; X x is S; and A is H. 29. The compound of claim 17 wherein Z is CN; X } is 0; and each R 6 is isopropyl . 30. The compound of claim 17 wherein Z is CN; X L is S; and each R 6 is isopropyl . 31. The compound of claim 16 having the Formula IV: IV 32. The compound of claim 31 wherein R 2 is a linker connected to a solid support. 33. The compound of claim 31 wherein R 2 is hydrogen. 34. The compound of claim 31 wherein and n are each 0. 35. The compound of claim 31 wherein Z is CN; Q is XjH or -X 1 -CH 2 -CH=CH-CH 2 -Z; and X r is 0. 36. The product produced by the process of claim 3. 37. The method of claim 6 wherein said cleaving step removes from said oligomeric compound a moiety of formula Z-CH 2 -CH=CH-CH 2 - via a δ-elimination mechanism. 38. The method of claim 6 wherein said cleaving step removes from said oligomeric compound a moiety of formula Z- CH 2 -CH=CH-CH 2 - via a δ-fragmentation mechanism.

Inventors: RAVIKUMAR VASULINGA T, RAVIKUMAR, VASULINGA, T.
Applicants: ISIS PHARMACEUTICALS INC, RAVIKUMAR VASULINGA T, ISIS PHARMACEUTICALS, INC., RAVIKUMAR, VASULINGA, T.
Application year: 1996
Main classification: C07H1
IPC codes: C07F9, C07H21, C12N15