METHYLENE PHOSPHONATE NUCLEOSIDE ANALOGS AND OLIGONUCLEOTIDE ANALOGS MADE THEREFROM

Abstract: Oligonucleotide analogs and nucleoside analogs as well as methods for their synthesis are described. The nucleoside analogs are useful as antiviral agents and as agents to treat tumors or infectious agents. The oligonucleotides are useful in diagnostic and therapeutic applications.

Description: ME HY^EWg PBQgPBQNATP NUCI^QSSPE ANALOGS ANP Q IGQKPC E TIDE ANALQgS HAPE THEREFROM Field of the Invention This invention relates to methylene phosphonate nucleosides which exhibit antiviral and antitumor activity and oligonucleotides derived from methylene phosphonate nucleoside monomers that have enhanced nuclease stability. The invention also relates to processes for preparing the compounds, their derivatives and oligonucleotides containing one or more 5' methylene phosphonate internuσleotide linkages. The oligonucleotides are resistant to nuclease degradation and are useful for diagnostic and therapeutic applications. Background Art Antisense and triple helix oligonucleotides are synthetic oligonucleotides which bind complementary nucleic acids (i.e. sense strand RNA or duplex DNA sequences) via hydrogen bonding, thereby inhibiting expression of these sequences. Therapeutic intervention at the nucleic acid level using oligonucleotides offers a number of advantages. Inhibition of gene expression is ore efficient than inhibition of the protein encoded by the gene since transcription of a single DNA sequence gives rise to multiple copies of mRNA which, in turn, are translated into many protein molecules. Oligonucleotides have been used to inhibit gene expression in a variety of systems. There are several reviews that discuss this topic (1-4). In addition, the use of oligonucleotides in sequence-specific recognition of double stranded DNA (5,6) as well as potential chemotherapeutic agents (7) has been reviewed. An important feature of the antisense oligomeric probes is the design of the backbone of the administered oligomer. Specifically, the backbone should contain internucleoside linkages that are stable in vitro and should be structured such that the oligomer is resistant to endogenous nucleases, such as nucleases that attack the phosphodiester linkage (8). At the same time, the oligomer must also retain its ability to hybridize to the target DNA or RNA. In order to ensure these properties, a number of modified oligonucleotides have been constructed which contain alternate internucleoside linkages. Several of these oligonucleotides are described in Uhlmann, E. and Peyman, A., Chemical Reviews (1990) 9fi:543-584. Among these are methylphosphonates (wherein one of the phosphorous-linked oxygens has been replaced by methyl); phosphorothioates (8,9) (wherein sulphur replaces one of these oxygens) and various amidates (wherein NHg or an organic amine derivative, such as morpholidates or piperazidates , replace an oxygen). These substitutions confer enhanced stability, for the most part, but suffer from the drawback that they result in a chiral phosphorous in the linkage, thus leading to the formation of 2 n diastereomers where n is the number of modified diester linkages in the oligomer. The presence of these multiple diastereomers considerably weakens the capability of the modified oligonucleotide to hybridize to target sequences. Some of these substitutions also retain the ability to support a negative charge and the presence of charged groups decreases the ability of the compounds to penetrate cell membranes. There are numerous other disadvantages associated with these modified linkages, depending on the precise nature of the linkage. Phosphorodithioate modified backbones have been made (9,10). These modified oligonucleotides are nuclease resistant and are diastereomerically pure. However, these modifications further reduce the affinity of the oligonucleotide for its intended target (10c). A variety of modified nonionic (11) oligonucleotides including methylphosphonate, phosphoroamidate, and phosphotriesters generally are either composed of a mixture of diastereomers, have a low affinity for intended targets, or both. A deoxyoligonucleotide comprised from nucleotide monomers that contain a methylene (-CH p -) group substituted for the 5 / -oxygen can be resistant to nucleases, especially those that leave a 3'-phosphate moiety after cleavage of the internucleotidic bond. This results from the fact that the requisite P-C bond can not be cleaved under normal physiological conditions. Additionally, a single diastereomerically pure deoxyoligonucleotide could be prepared, as the internucleotide phosphorous linkages would be achiral. we refer to the nucleotides containing a methylene (-CH -) group substituted for the 5'-oxygen as 5'-methylene phosphonates. The preparation of ribo (i.e. 2'-OH) 5'-methylene phosphonates is well documented in the literature (12). Uridine (13-15), adenosine (13-15), and guanosine (16) 5'-methylene phosphonates have been prepared. A number of analogues of adenosine 5'-methylene phosphonate have been prepared (17-23). In addition, ribavirin 5'-methylene phosphonate (24), as well as a ribo 5'-methylene phosphonate containing thiazole-4-carboxamide as the base, has been prepared (25). Ribo compounds having a 3'-methylene phosphonate have also been prepared (26-28). There are very few reports of 2'-deoxy 5'-methylene phosphonates in the literature, and these are all related to thymidine. Only the syntheses of 5'-methylene phosphonates of thymidine (29), 3'-azidothymidine (AZT) (30,31), and 2'-deoxy-5-fluoro-uridine (32) have been reported. There have been no reports on the syntheses of 5'-methylene phosphonates derived from 2'-deoxyadenosine, 2'-deoxycytidine, or 2'-deoxyguanosine. There also have been no reports on the synthesis of 5' methylene phosphonate nucleosides having 5-iodouracil, 2-aminopurine or 2,6-diaminopurine as the base. The 5-iodouridine 5' methylene phosphonate compound would be made in an analogous manner to that used to synthesize the 5' methylene phosphonate derived from thymidine as described for compounds 33 and 37 below. The 2-aminopurine and 2 ,6-diaminopurine nucleoside 5' methylene phosphonates would be made in an analogous manner to that used to synthesize the 5' methylene phosphonate derived from deoxyadenosine as described for compounds 36 and 40 below. Several ribo 5'-methylene phosphonate dimers have been synthesized. These include UpCH ^ U and UpCH ^ A (33,34). Several ribo 3'-methylene phosphonate dimers (33), as well as a trimer (28) have been synthesized. These ribo dimers and trimer were prepared using the diester method of oligonucleotide synthesis (35,36). This method suffers from low product yields, and difficulties in purification of the final product (35,36). The method is generally not useful in the preparation of longer oligonucleotides. Recently, a ribo oligonucleotide 10-mer consisting of 5'-methylene phosphonates, ApA pCHoA) * , was prepared enzymatically using polynucleotide phosphorylase (37). This technique, however, cannot be used for the preparation of oligonucleotides having a defined sequence of mixed bases. Only one 2'-deoxy dimer, TpCHoT, and one 2'-deoxy trimer, TpCH-TpCH-T, have been reported in the literature (29). Only the 5'-methylene phosphonate derived from thymidine was used in the dimer and trimer. No mixed base 2'-deoxy 5'-methylene phosphonate dimers or longer mixed base, 2'-deoxy 5'-methylene phosphonate oligonucleotides have been reported. Additionally, no 2'-deoxy 5'-methylene phosphonate oligonucleotides longer than a 3-mer of any kind have been reported. However, recently the synthesis of oligodeoxynucleotides containing 5'-methylene phosphonates of 2'-deoxy-4'-carbocyclic nucleosides has been reported w. Frick and S.W. Schneller, Meetings Abstract, Conference on Nucleic Acid Therapeutics. January 13-17, 1991, Clearwater Beach, Florida, p 63). Disclosure of the Invention The present invention is directed to (i) onomeric 5'-methylene phosphonate nucleoside analogs, their tautomers, isomers and salts and (ii) modified oligonucleotides including dimers, trimers and tetramers wherein the modification comprises replacing at least one phosphodiester linkage, -0P(0)0 ' 0-, of the oligonucleotide with a 5'-methylene phosphonate type linkage of the formula -OPXYCHg-, wherein X is O or S and Y is OR 4 , N(R 4 ' or SR 4^ wherein each R 4 is independently H, methyl, ethyl, propyl, isopropyl, butyl, phenyl, alkyl (4-18C) or substituted alkyl (1-18C). other preferred alkyl and substituted alkyl groups are hexyl, nonyl, oleyl and methoxyethyl. Methods for synthesis of the modified oligonucleotides using the monomers are also disclosed. The modified oligonucleotides may be represented as shown in general structural formula I: and include stereoisomers and salts thereof, wherein X and Y are as defined above, W is independently 0 or CH«, each B is independently a purine or pyri idine base or modified form each Z is independently a noninterfering substituent, preferably hydrogen, PO^- or a protecting group; each R is independently hydrogen, hydroxyl, 0- allyl, S-allyl, O-methyl, S-methyl or fluorine; and n is an integer between 1 and 30 with the proviso that (i) at least one W is CH 2 , (ii) when B is thymine and n is 1 or 2 then not all R 5 are H, (iii) when B is adenine and n is an integer from 1 to 9 then not all R^ are OH, (iv) when B is uracil and n is 1 then not all R^ are OH and (v) when n is 1 and the 5' B is uracil and the 3' B is adenine then not all R J are OH. Modified forms of bases as defined herein are base analogs such as 5- methylcytosine or derivatives of bases such as N 2 - isobutyrylguanine or N 4 -benzoylcytosine that contain standard blocking groups or other deriviates. Bases such as adenine, guanine, cytosine, thymine and uracil as well as modified forms (base analogs) such as 5-methylcytosine , aziridinylcytosine , 8-hydroxy-N 6 -methyladenine , pseudoisocytosine, 5- propynyluracil and 5-propynylcytosine are preferred. Preferred protecting groups are H-phosphonate, methylphosphonate, MMT, DMT, methylphosphoramidite and β- σyanoethylphosphoramidite. The oligonucleotides can be synthesized from appropriate derivatives of monomers of formula (II): II and their salts, zwitterions, solvates and tautomers, which can be present as diastereoisomers, wherein B, X and Y have the meanings defined above; R 5 is hydrogen, hydroxyl, fluorine, O-benzyl, O-t-butyldimethylsilyl , O- DMT and O-MMT; and R' is hydrogen, O-allyl, S-allyl, O- methyl, S-methyl or fluorine or both R 6 and R , when taken together with the carbon atom to which each is attached, form a 2', 3' epoxide group or a carbon-carbon double bond which gives a 2' 3' dideoxydidehydro sugar analog. Also included are monomers and their isomers of compounds containing a double bond at the C5' methylene carbon as shown in Tables 2 and 5 below. Any hydroxyl group can be coupled to a standard protecting group. Preferred bases include guanine, adenine, cytosine, thymine, uracil, inosine, xanthine, hypoxanthine, 5-iodouracil, 5-iodocytosine, 5- ethyluracil, 5-propynyluracil , 5-fluorouracil , 5- trifluoromethyluracil, 5-bromovinyluracil, 5- propynylcytosine, 5-methylcytosine, 8-hydroxy-N 6 -methyladenine, aziridinylcytosine, 2-aminopurine, 2,6-diaminopurine, 6-chloropurine, 3- deazaguanine, 7-deazaadenine, 8-bromoadenine, 7- deazaguanine, 3-deazaadenine, and 6-hydroxylaminopurine, 6-thiopurine or other base analogs or altered forms can be utilized. Unless specifically indicated, bases are linked to the sugar moiety at conventional positions such as N9 of adenine, guanine and other purines or the Nl of cytosine, thymine, uracil and other pyrimidines. Stereoisomers of the monomers include α-anoraers of the base residue. Dideoxy and dideoxyarafluoro monomers can be prepared essentially by a previously disclosed method using appropriate compounds disclosed herein (56) . 2'-deoxy-5'-methylene phosphonate oligonucleotides of length 2-30 bases or more of mixed base composition can be synthesized according to the methods disclosed herein. These oligodeoxynucleotides are prepared using the phosphotriester method (38) from suitably protected 2'-deoxy 5'-methylene phosphonate nucleotide monomers. We prepared 5'-methylene phosphonates in both a protected form that was suitable for oligonucleotide synthesis, as well as in a completely deprotected form. Some of the 5'-methylene phosphonates that were prepared were derived from 2'-deoxycytidine and 2'-deoxyguanosine. The monomers described herein are suitable for solid phase oligonucleotide synthesis by triester chemistry. For example, compounds 87-90 in Table 6 which are derived from corresponding precursors 60, 62, 64 and 66 in Table 5 may be utilized in solid phase synthesis using described methods. Previous methods utilized diester chemistry which is more difficult and generates low yields of product. Oligonucleotides containing 2'-deoxy-2'-fluoro-ribonucleotides are of interest because the conformation of the sugar closely resembles that of RNA and consequently these oligonucleotides have a -higher affinity to DNA than normal oligodeoxyribonucleotides (M. Ikehara, Heterocycles 1984, 21, 75). The oligonucleotide analogs may be used as conventional probes or primers for various diagnostic assays. Synthesis of oligonucleotides containing a covalent crosslinking aziridinylcytosine residue is disclosed in commonly assigned co-pending U.S. application serial no. 640,654, synthesis of oligonucleotides containing a region of inverted polarity is disclosed in commonly assigned co-pending PCT application serial no. PCT/US90/06128, synthesis of oligonucleotides containing improved base analogs, such as 8-hydroxy-N°-methyladenine and pseudoisocytosine, for triple helix formation are disclosed in commonly assigned co-pending U.S. application serial no. 643,382 and synthesis of oligonucleotides containing noninterfering substituents at either the 5' or 3' ends of oligonucleotides is disclosed in commonly assigned co-pending U.S. application serial no. 482,943. All documents cited herein are incorporated herein by reference. 5' methylene phosphonate nucleoside having N 4 -etheno-5-methylcytosine (aziridinylcytosine) as the base can be prepared from the thymidine 5' methylene phosphonate (compound 37 below) by transient silyl protection, formation of the appropriate triazolide, removal of silyl protecting groups and then reaction with aziridine in DMF using the procedures described in pending PCT application serial no. PCT/US90/03680. The free 5'-methylene phosphonate nucleosides present enzymatically nonhydrolysable isosteres of mononucleotides. As such they can be converted intracellularly by cellular kinases to the corresponding nucleoside phosphono triphosphates, incorporated into DNA by polymerases and thus interfere with cellular metabolism. The inhibitory effects of nucleoside and nucleotide analogs often exert their effects through interaction with DNA or RNA polymerase enzymes. Nucleoside phosphonates can exhibit activity against viruses, tumors, parasites such as malaria parasites, trypanosomes and yeasts or other infectious agents. For example, several acyclic methylene phosphonates such as the methylene phosphonates derived from ganciclovir, and acyclovir are potent antivirals (39-42). The analogs disclosed herein are isosteric with the methylene phosphonates disclosed herein. A similar class of methylene phosphonate compounds has been shown to have both antiviral activity and activity against the DNA polymerase enzyme of the malaria parasite Plasmodium falciparum (54). Other nucleoside phosphonates have been described in PCT publication no. WO 84/04748. The compounds of the present invention can thus be used to treat cancers or tumors, especially those caused by viruses in addition to their use as agents to treat various pathogenic agents. Nucleoside analogs have also been used to treat tumors or malignant cells (55). 5 Physiologically acceptable salts, zwitterions and solvates of the compounds of this invention are prepared by methods known in the art. The salts include amine or ammonium salts and salts of physiologically acceptable metals, particularly Li + , K + , Na + , Ca ++ and , ° Mg ++ , and are novel compounds and comprise a further aspect of the invention. Metal salts can be prepared by reacting a metal hydroxide with a compound of the invention. Examples of metal salts which can be prepared in this way are salts containing Li + , Na + , and K + . A 5 less soluble metal sale can be precipitated from a solution of a more soluble salt by addition of a suitable metal compound. Acid salts can be prepared by reacting a compound of the invention with an acid such as HCl, HBr, HpSO * , or an organic sulphonic acid. 0 Nucleoside monomer compounds possess antiviral activity and can be used in the control or prevention of viral infections, e.g. of herpes simplex viral or HCMV infections. The in vitro activity of the compounds of formula I and their tautomers in inhibiting herpes 5 simplex virus type 2 (HSV-2) can be demonstrated by means of plaque reduction or cytopathic effects assays. Host VERO or human fibroblast cells are infected with virus stock containing a known number of infectious virions in the presence of various concentrations of compound. 0 Plaques in the cell monolayer are then counted and compared to untreated controls and to acyclovir treated controls. The degree of cytopathic effects inhibition or titer reduction at each concentration of compound is expressed as a percentage of the control titer (100%). *5 The EC50 value, namely the concentration of compound which inhibits viral activity or titer by 50%, is then calculated. The results that are obtained with representative compounds show that virus titer reductions occur. Compound numbers 38 and 39 as described in Table 3 were tested for antiviral activity against the human herpesviruses HSV-1 (strain 377), HSV-2 (strain MS) and HCMV (strain AD169) in vitro. Efficacy was assayed by measuring reduction of cytopathic effects in primary human foreskin fibroblasts. Compound 38 was administered to cells in tissue culture as the monosodium, hydrogentriethylammonium salt and compound 39 was used as the disodium salt. Both compounds were administered to cells immediately prior to infection of cells on microtiter wells. CPE reduction was determined at 72 h post infection for HSV or at 14 d post infection for HCMV. Compound 38 was found to have an EC of 28.3 μg/mL for HCMV, >100 μg/mL for HSV-1 and HSV-2 and compound 39 was found to have an EC C Q of >100 μg/mL for HCMV, HSV-1 and HSV-2. The compounds disclosed herein can be used as medicaments in the form of pharmaceutical preparations which contain them in association with a compatible pharmaceutical carrier material. This can be an organic or inorganic carrier suitable for enteral, e.g. oral, or parenteral administration. Examples of such carriers are water, gelatin, gum arabic, lactose, starch, magnesium stearate, talc, vegetable oils, polyalkylene glycols and petroleum jelly. The pharmaceutical preparations can be made up in a solid form, e.g. as tablets, dragees, suppositories or capsules, or in a liquid form, e.g. as solutions, suspensions or emulsions; they can be subjected to standard pharmaceutical operations, e.g. sterilization and/or may contain adjuvants, e.g. preserving, stabilizing, wetting or emulsifying agents, salts for varying the osmotic pressure or buffers. The compounds may also be formulated in a manner suitable for administration as an aerosol. They may also contain other therapeutically valuable substances. The compounds disclosed herein and their tautomers can be administered for the control or prevention of viral infection, such as herpes simplex viral infections, to warmblooded animals in need of such treatment. The disclosed compounds and their tautomers can be administered to adult humans in a daily dosage of from about 1 to 1000 mg, preferably about 5 to 500 mg. The daily dosage can be administered as a single dose or in divided doses. The above dosage range is given by way of example only and can be varied upwards or downwards depending on factors such as the particular compound being administered, the route of administration, the severity of the indication being treated and the condition of the patient. Experimental Section General. Flash chromatography refers to the procedure of still et. al (43). Drying refers to drying over NagSO^ filtration, and concentration. All reactions requiring dry solvents were run under a dry argon atmosphere. The following six tables show structures for compounds 1 through 120. Table 1 For tables 1-6; G = guanine; C = cytosine; A = adenine; T = thymine; G Ib = N 2 -isobutyrylguanine; C° z = N -benzoylcytosine; A = N -benzoyladenine; T = N^-benzylthymine; Bn = benzyl; DMT = 4,4'-dimethoxytrityl; TBS = t-butyldimethylsilyl; +HTEA = hydrogentriethylammonium; A D "' = N°- dimethoxytrityladenine, U = uracil and Me = methyl. Table 2 For definition of abbreviations, see Table 1. Table 3 10 15 For definition of abbreviations, see Table 1. 20 25 30 35 Table 4 or definition of abbreviations, see Table 1, Tab 5 For definition of abbreviations, see Table 1, Table 6 For definition of abbreviations, see Table 1. N t -Isobutyryl-2'-deoxyguanosme (1). The acylation by transient protection method of R. A. Jones (44) was used. To a stirred mixture of 4.28 g (15.0 mmol) of 2'-deoxyguanosine monohydrate (that was first concentrated from dry pyridine) in 150 mL of dry pyridine that was cooled on an ice water bath was added 9.75 mL (76.8 mmol, 5.12 equiv) of chlorotrimethylsilane dropwise, over several minutes. After 30 min., 12.8 mL (76.9 mmol, 5.13 equiv.) of isobutyric anhydride was added dropwise, over several minutes. ' " The ' ice bath was removed and stirring was continued for 2 h. The reaction mixture was then cooled on an ice water bath, and 30 mL of cold H2O was added to the reaction. After 15 min., 30 mL of concentrated aqueous ammonia was added. The reaction was stirred for 30 min. , and then concentrated. The residue was taken up in 100 mL of H^O and extracted with Et«0. The title compound was either crystallized from the aqueous layer, or was isolated by flash column chromatography. N 2 -Isobutyryl-5'-O-(4,4'-di*ethoxytrityl)-2'- deoxyguanosine (2). The tritylation procedure of Jones (45) was modified such that no DMAP was used. To 3.37 g (10.0 mmol) of N 2 -isobutyryl-2'-deoxyguanosine (that was first concentrated from dry pyridine) in 50 mL of dry pyridine, was added 4.06 g (12.0 mmol, 1.20 equiv.) of 4,4'-dimethoxytrityl chloride. The reaction was stirred for 15 h, and then concentrated. The residue was partitioned between CH Cl- and 0.5% aq. NaHCOg, shaken, and separated. The organic layer was washed with 0.5% aq. NaHCO, and dried. The crude product was purified by flash chromatography. N*-Benzoyl-2'-deoxycytidine (3). This compound was prepared from 2'-deoxycytidine monohydrate by the same procedure used for the preparation of N 2 -isobutyryl-2'-deoxyguanosine except that 9.0 mL (77.5 mmol, 5.17 equiv.) of benzoyi chloride was used instead of isobutyric anhydride. N^-Benzoyl-5'-o-(4,4'-dimethoxytrityl)-2'-deoxycytidine (4). This compound was prepared from N -benzoyl-2'- deoxycytidine by the same procedure used for the preparation of N 2 -isobutyryl-5'-0-(4,4'-dimethoxytrityl) -2'-deoxyguanosine. N 6 -Benzoyl-2'-deoxyadenosine (5). This compound was prepared from 2'-deoxyadenosine monohydrate by the same procedure used for the preparation of N 4 -benzoyl-2'-deoxycytidine. N°-Benzoyl-5'-O-(4,4*-dimethoxytrityl)-2'-deoxyadenosine (6). This compound was prepared from N°-benzoyl- 2'-deoxyadenosine by the same procedure used for the preparation of N 2 -isobutyryl-5'-0-(4,4'-dimethoxytrityl) -2'-deoxyguanosine. 5'-O-(4,4*-Dimethoxytrityl)-thymidine (7). This compound was prepared from thymidine by the same procedure used for the preparation of N 2 -isobutyryl-5'-0-(4,4'- dimethoxytrityl)-2'-deoxyguanosine. 3'-O'-t-Butyldimethylsilyl-N 2 -isobutyryl-2'- deoxyguanosine (8). To a stirred solution of 2.00 g (3.13 mmol) of N 2 -isobutyryl-5'-0-(4,4'- dimethoxytrityl)-2'-deoxyguanosine and 1.54 g (22.6 mmol, 7.22 equiv.) of imidazole in 12.5 mL of dry DMF was added 1.16 g (7.70 mmol, 2.46 equiv.) of t-butyldimethylsilyl chloride. The reaction was stirred at room temperature for 3.5 h and then concentrated. The residue was partitioned between CH 2 C1 2 and H 2 0, shaken, and separated. The organics were washed with H 2 0 and concentrated (not dried). The crude residue was then stirred in 100 mL of 80% aq. HOAc for 1.5 h and then concentrated. The residue was partitioned between CH 2 C1 2 and H 2 0, shaken, and separated. The organics were washed with sat. aq. NaHCO j , H 2 0, and dried. The crude product was purified by flash chromatography on a 40 mm column using one column volume of 2% TEA in CH 2 C1 2 , then one column volume of 2% TEA and 2% MeOH in CH 2 C1 2 , and then 2% TEA and 4% MeOH in CH 2 C1 2 . The product was concentrated from toluene affording 1.18 g (83.7% yield). 3*-0-t-Butyldimethylsilyl-N*-benzoyl-2'-deoxycytidine (9). This compound was prepared from 29.09g (45.90 mmol) of N 4 -benzoyl-5'-O-(4,4'-dimethoxytrityl)-2'-deoxycytidine by the same procedure used for the preparation of 3'- 0-t-butyldimethylsilyl-N 2 -isobutyryl-2'-deoxyguanosine. Column chromatography of the crude material afforded 15.29 g (74.8% yield) of product. 3 *-O-t-Butyldimethylsilyl-N^-benzoyl-2'-deoxyadenosine (10). This compound was prepared from N°-benzoyl- 5'-0-(4,4'-dimethoxytrityl)-2'-deoxyadenosine by the same procedure used for the preparation of 3'-0-t- butyldιmethylsιlyl-N t -ιsobutyryl-2'-deoxyguanosine. 3'-0-t-Butyldimethylsilylthymidine (11). This compound was prepared from 5'-0-(4,4'-dimethoxytrityl)-thymidine by the same procedure used for the preparation of 3'- 0-t-butyldιmethylsιlyl-N t -ιsobutyryl-2'-deoxyguanosine. 3'-0,N 3 -Dibenzylthymidine (12). To a stirred solution of 2.18 g of 5'-0-(4,4'-dimethoxytrityl)-thymidine (4.00 mmol) in 52 L of dry DMF was carefully added 2.00 g of a 60% oil dispersion of NaH. The reaction was stirred at room temperature for 5 min. To the mixture was added 4.77 mL (40.1 mmol, 10.0 equiv.) of benzyl bromide dropwise, over several minutes. After 1 h, the reaction was cooled on an ice-water bath. Then, 12 mL of sat. aq. NaHCO, was carefully added (vigorous hydrogen gas evolution) dropwise, over several minutes. The mixture was stirred for 10 min, and then concentrated. The residue was then stirred in 100 mL of 80% aq. HOAc at room temperature for 1.5 h, and then concentrated. The crude residue was partitioned between CH 2 C1 2 and H 2 0, shaken, and separated. The organic layer was washed with sat. aq. NaHCO j , H 2 0, and then dried. The crude product was purified by flash chromatography on a 50 mm column using two column volumes of CH C1 , two column volumes of 1% MeOH in CH 2 C1 2 , and then 2.5% MeOH in CH 2 C1 2 as eluents. This afforded 1.49 g of product (88.2% yield) as a colorless solid. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-β-D- ribo-hex-5-enofuranosyl)-N 2 -isobutyrylguanine]-6'- phosphonate (13). Literature methods (39) were adapted for the preparation of the title compound. To a solution of 106 mg of 3'-0-t-butyldimethylsilyl-N 2 -isobutyryl- 2'-deoxyguanosine (0.236 mmol) and 294 mg of dicyclohexylcarbodiimide DCC (1.42 mmol, 6.02 equiv.) in 1.3 mL of dry DMSO was added 11.3 mg of methylphosphonic acid (0.118 mmol, 0.50 equiv.). The reaction was stirred at room temperature. After 18 h, dry pyridine (0.080 mL) and then 120 mg (0.236 mmol, 1.00 equiv.) of diphenyl [ (triphenylphosphoranylidene)methyl]phosphonate (46) were added. Another 0.80 mL of dry DMSO was added. The reaction was stirred at room temperature. After 27 h, the reaction was diluted with CH«C1 , washed with 2 x 2 2' H 2 0, and dried. The crude material was flashed on a 25 mm column using one column volume of CH 2 C1 2 , then one column volume of 3% MeOH in CH 2 C1 2 , and then 6% MeOH in CH 2 C1 2 as eluents. The product containing fractions were combined and concentrated. The product was purified again purified by flash chromatography on a 25 mm column using one column volume of 12.5% EtOAc in CH 2 C1 2 , then one column volume of 25% EtOAc in CH 2 C1 2 , and then 50% EtOAc in CH 2 C1 2 as eluents. This procedure afforded 9.4 mg (6.0% yield) of product. Diphenyl [9-3-0-t-Butyldimethylsilyl-2,5,6,trideoxy-β-D- ribohexofuranosyl)-N-isobutyrylguanine]-6'-phosphonate (14). To a solution of 9.4 mg (0.0138 mmol) of diphenyl [ -(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo-hex- 5-enofuranosyl)-N^ 7-i.sobutyrylguanme]-6'-phosphonate in 20 mL of MeOH was added a catalytic amount of 10% Pd on carbon. The mixture was hydrogenated at 260 psi of H 2 (in a Parr reaction vessel) for 3 h. The mixture was filtered through Celite and concentrated. The crude product was purified by flash chromatography on a 15 mm column using one column volume of CH 2 C1 , then one column volume of 12.5% EtOAc in CH 2 C1 2 , then one column volume of 25% EtOAc in CH 2 C1 2 , and then 50% EtOAc in CH 2 C1 2 as eluents. This procedure afforded 2.0 mg (21.3% yield) of product. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-β-D- ribo-hex-5-enofuranosyl)-IP-benzoylcytosine]-6'- phosphonate (15). This compound was prepared from 9.87 g (22.15 mmol) of 3'-0-t-butyldimethylsilyl-N 4 -benzoyl-2'-deoxycytidine by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-b-D-ribo-hex- 5-enofuranosyl)-N 2 -isobutyrylguanosine]-6'-phosphonate. Chromatography of the residue on silica gel afforded 9.42 g (63.2% yield) of product. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-β-D- ribohexofuranosyl)-JP-benzoylcytosine]-6'-phosphonate (16). This compound was prepared from 9.00 g (13.36 mmol) of diphenyl [1-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo-hex- 5-enofuranosyl)-N^-benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribohexo furanosyl)-N 2 -isobutyrylguanosine]-6'-phosphonate. Chromatography of the residue on silica gel afforded 4.08 g (55.4% yield) of product. Diphenyl [9-(3-o-t-Butyldimethylsilyl-2,5,6-trideoxy-β-D- ribo-hex-5-enofuranosyl)-N -benzoyladenine]-6'- phosphonate (17). This compound is prepared from 3'-0-t-butyldimethylsilyl-N°-benzoyl-2'-deoxyadenosine by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo-hex- 5-enofuranosyl)-N 2 -isobutyrylguanosine]-6'-phosphonate. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-β-D- ribohexofuranosyl)-N^-benzoyladenine]-6'-phosphonate (18). This compound is prepared from diphenyl [9-(3- O-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo-hex-5 -enofuranosyl)-N 6 -benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo- hexofuranosyl)-N^ 7-i .sobutyrylguanosme]-6'-phosphonate. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxγ-β- D-ribo-hex-5-enofuranosyl)-thymine]-6'-phosphonate (19) . This compound is prepared from 3'-0-t-butyldimethylsilyl- thymidine by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy- β-D-ribo-hex-5-enofuranosyl)-N 2 -isobutyrylguanosine]-6'- phosphonate. Diphenyl [l-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-β-D- ribohexofuranosyl)-thymine]-6'-phosphonate (20). This compound is prepared from diphenyl [l-(3-0-t- butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo-hex-5- enofuranosyl)-thymine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribohexo furanosyl)-N 2 -isobutyrylguanosine]-6'-phosphonate. Diphenyl [l-(3-0-benzyl-2,5,6-trideoxy-β-D-ribo-hex-5- enofuranosyl)-N^-benzylthymine]-6'-phosphonate (21). The title compound was prepared by modification of related known procedures (13,19). To a stirred solution • 3 of 300 mg of 3'-0,N J -dibenzylthymidine (0.710 mmol) and 874 mg of (4.24 mmol, 5.97 equiv.) of dicyclohexylcarbodiimide (DCC) , in 2.37 mL of DMSO was added 0.356 mL of a 1.0 M solution (0.356 mmol, 0.50 equiv.) of orthophosphoric acid (Aldrich) in DMSO. The reaction was stirred at room temperature. After 19 h, 0.237 mL of dry pyridine was added, followed by 412 mg (0.710 mmol, 1.0 equiv.) of diphenyl [(triphenylphosphoranylidene)methyl]phosphonate. The reaction was stirred for 31 h. The reaction mixture was partitioned between CH 2 C1 2 and H 2 0, shaken and separated. The organic layer was washed with H 2 0 and dried. The residue was purified by flash chromatography on a 25 mm column using one column volume of CH 2 C1 2 , one column volume of 5% EtOAc in CH 2 C1 2 , and then 10% EtOAc in CH 2 C1 2 as eluents. This afforded 334 mg (80.5% yield) of product. Diphenyl [1-(3-O-benzyl-2,5,6-trideoxy-β-D- ribohexofuranosyl)-N^-benzylthymine]-6 '-phosphonate (22). To a stirred solution of 334 mg (0.513 mmol) of diphenyl [1-(3-0-benzyl-2,5,6-trideoxy-β-D-ribo-hex-5- enofuranosyl)-N^-benzylthymine]-6'-phosphonate in 7.7 mL of dry Et 2 0 was added 307 mg (1.03 mmol, 2.01 equiv.) of 2,4,6-tri-isopropylbenzenesulphonyl hydrazide (47), followed by 0.143 mL of dry TEA. The reaction was refluxed for 14 h. The mixture was partitioned between Et-O and sat. aq. NaHCO,, shaken, and separated. The organic layer was washed with H«0 and dried. The residue was purified by flash chromatography on a 25 mm column using one column volume of CH 2 C1 2 , one column volume of 5% EtOAc in CH 2 C1 2 , and then 10% EtOAc in CH 2 C1 2 as eluents. This afforded 244 mg (72.8% yield) of product. Dimethyl[1-(3-0-benzy-2,5,6-trideoxy-β-D- ribohexofuranosyl)-N^-benzylthymine]-6'-phosphonate (23). Commercially available CsF (100 mg) was flame dried while under vacuum, and allowed to cool to room temperature. To the dried solid was added 3.00 mL of dry MeOH, followed by 143 mg (0.219 mmol) of diphenyl • 3 [1-(3-0-benzyl-2 ,5,6-trideoxy-β-D-πbohexofuranosyl)-N°- benzylthymine]-6'-phosphonate. The reaction was stirred for 20 h, and then concentrated. The residue was partitioned between CH 2 C1 2 and H 2 0, shaken, and separated. The organics were washed with H 2 0 and dried. The residue was purified on a 25 mm column using one column volume of CH 2 C1 2 , one column volume of 2.5% MeOH in CH 2 C1 2 , and then 5% MeOH in CH 2 C1 2 as eluents. This procedure afforded 85.9 mg (74.0% yield) of product. Dimethyl [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl)- N^-benzylthy ine]-6'-phosphonate (24). Known literature methods (48) were adapted to remove the benzyl protecting group from the 3'-oxygen. Dimethyl [l-(3-0-benzyl- 2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 3 -benzylthymine]- 6'-phosphonate (3.0 mg, 0.00567 mmol) was added to a 4.4% solution of HC0 2 H in MeOH (prepared from 96% HC0 2 H) followed by a catalytic amount of 10% Pd on carbon. The reaction was stirred at room temperature for 19 h. The reaction was then filtered through Celite and concentrated. This procedure afforded 2.0 mg (80.6% yield) of product as a colorless solid. Dibenzyl [1-(3-0-benzyl-2,5,6-trideoxy-β-D- rilx>hexofuranosyl)-N -benzylthymine]-6'-phosphonate (25). This procedure was based on a related procedure (25). To a solution of 416 mg (0.638 mmol) of diphenyl • 2 [l-(3-0-benzyl-2 ,5 ,6-trideoxy-β-D-ribohexofuranosyl)-N" 3 - benzylthymine]-6'-phosphonate in 3.0 mL of benzyl alcohol, was added 2.0 L of a solution prepared by the addition of 200 mg of NaH to 16.7 mL of benzyl alcohol. After 1 h, the reaction mixture was diluted with 50 mL of Et 2 0. Excess gaseous C0 2 was bubbled into the mixture. A gel like mixture formed which was dissolved in EtOAc. This solution was concentrated onto silica gel. The silica gel was loaded onto a previously equilibrated 25 mm column and eluted with one column volume of CH 2 C1 2 , then one column volume of 10% EtOAc in CH 2 C1 2 , and then 20% EtOAc in CH 2 C1 2 as eluents. This afforded 127 mg (29.3% yield) of product. Diphenyl [9-(2,5,6-trideoxy-β-D-ribohexofuranoxyl)- N 2 -isobutyrylguanine]-6'-phosphonate (26). This reaction is based on a similar procedure by Barton et al (30). To 5.00 mmol of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribohexo furanosyl)-N -isobutyrylguanine]-6'-phosphonate in 100 mL of dry THF is added 5.5 mL (5.5 mmol, 1.1 equiv.) of a 1.00 M solution of tetrabutylammonium fluoride (TBAF) in THF. The reaction is stirred at room temperature for 1 h. Then 20 mL of MeOH is added. The reaction is stirred for 5 min., and then concentrated. The residue is purified by flash chromatography. Diphenyl [l-(2,5,6-trideoxy-β-D-ribohexof ranosyl)- N 4 -benzoylcytosine]-6'-phosphonate (27). This compound is prepared from diphenyl [l-(3-0-t-butyldimethylsilyl- 2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 4 -benzoylcytosine] -6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N 2 -isobutyrylguanine]-6'-phosphonate. Diphenyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)- N 6 -benzoyladenine]-6'-phosphonate (28). This compound is prepared from diphenyl [9-(3-0-t-butyldimethylsilyl- 2,5,6-trideoxy-β-D-ribohexofuranosyl)-N^-benzoyladenine]- 6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N 2 -isobutyrylguanine]-6'-phosphonate. Diphenyl [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl)- thymine]-6'-phosphonate (29). This compound is prepared from diphenyl [l-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy β-D-ribohexofuranosyl)-thymine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonate. Di ethyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)- N 2 -isobutyrylguanine]-6'-phosphonate (30). This compound is prepared from diphenyl [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N -isobutyrylguanine]-6'-phosphonate and CsF in MeOH by the same procedure used for the preparation of dimethyl [l-(3-0-benzyl-2,5,6-trideoxy- β-D-ribo-hexofuranosyl)-N 3 -benzylthymine]-6'-phosphonate. After the aqueous extraction and drying, the crude product is purified by flash chromatography. Dimethyl [1-(2,5,6-trideoxy-B-D-ribohexofuranosyl)- IP-benzoylcytosine]-6 *-phosphonate (31). This compound is prepared from diphenyl [l-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N 4 -benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of dimethyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonate. Dimethyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)- N^-benzoyladenine)-6'-phosphonate (32). This compound is prepared from diphenyl [9-(2 ,5,6-trideoxy-β- D-ribohexofuranosyl)-N°-benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of dimethyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonate. Dimethyl [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl) -thymine]-6'-phosphonate (33). This compound is prepared from diphenyl [l-(2,5,6-trideoxy-β-D- ribohexofuranosyl-thymine]-6'-phosphonate by the same procedure used for the preparation of dimethyl (9-(2,5,6- trideoxy-β-D-ribohexofuranosyl)-N -isobutyrylganine]-6'- phosphonate. [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonic acid (34). This reaction is based on a similar procedure by Barton et al (30). To a stirred, ice-cooled mixture of dimethyl [9-(2,5 ,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonate in 150 mL of CH 2 C1 2 is added 1.98 mL (15.0 mmol, 3.0 equiv.) of bromotrimethy1- silane dropwise, over several minutes. The reaction is stirred for 30 min., and then the ice bath is removed. After stirring for an additional 10 h, 20 mL of MeOH is added. The reaction is stirred for 5 min. , and then concentrated. The product is used without further purification. [1-(2,5,6-Trideoxy-β-ribohexofuranosyl)-IP-benzoy1 cytosine]-6'-phosphonic acid (35). This compound is prepared from dimethyl [l-(2,5,6-trideoxy-β-D- ribohexofuranosyl)- N^-benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of [9-(2,5,6- trideoxy-β-D-ribohexofuranosyl)-N -isobutyrylguanine3 -6'-phosphonic acid. [9-(2,5,6-Trideoxy-β-D-ribohexof ranosyl)-N 6 - benzoyladenine]-6'-phosphonic acid (36). This compound is prepared from dimethyl [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N -benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonic acid. [1-(2,5,6-Trideoxy-β-D-ribohexofuranosyl)-thymine]-6'- phosphonic acid (37). This compound was prepared from dimethyl [1-(2 ,5 ,6-trideoxy-β-D-ribohexofuranosyl)- thymine]-6'-phosphonate by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D- πbohexof uranosyl ) -N^-isobutyrylguanme ] -6 ' -phosphonic acid. [9-(2,5,6-Trideoxy-β-D-ribohexofuranosyl)-guanine]-6'- phosphonic acid (38). The entire crude [9-(2,5,6- trideoxy-β-D-ribohexofuranosyl)-N 2 ~isobutyrylguanine]-6'- phosphonic acid, from above, is heated in 150 mL of concentrated aqueous ammonia at 55©c for 18 h, and then concentrated. [1-(2,5,6-Trideoxy-β-D-ribohexof ranosyl)-cytosine]-6'- phosphonic acid (39). This compound is prepared from [1-(2 ,5,6-trideoxy-β-D-ribohexofuranosyl)-N - benzoylcytosine]-6'-phosphonic acid by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-guanine]-6'-phosphonic acid. [9-(2,5 ,6-Trideoxy-β-D-ribohexofuranosyl)-adenine]-6'- phosphonic acid (40). This compound is prepared from [9-(2 ,5 ,6-trideoxy-β-D-ribohexofuranosyl)-N - benzoyladenine]-6'-phosphonic acid by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-guanine]-6'-phosphonic acid. Diphenyl [9-(3-θ-[4,4'-Dimethoxytrityl]-2,5,6- trideoxy-β-D-ribohexofuranosyl)-N 2 -isobutyrylguanine]-6'- phosphonate (41). To 5.00 mmol of diphenyl [9-(2,5 ,6-trideoxy-β-D-ribohexofuranosyl) -\V 7— isobutyrylguanine]-6'-phosphonate (that is first concentrated from dry pyridine) in 30 mL of dry pyridine, is added 2.03 g (6.0 mmol, 1.20 equiv.) of 4,4'-dimethoxytrityl chloride. The reaction is stirred for 15 h, and then concentrated. The residue is partitioned between CH 2 C1 2 and 0.5% aq. NaHCO- j , shaken, and separated. The organic layer is washed with 0.5% aq. NaHCOg and dried. The crude product is purified by flash chromatography. Diphenyl [1-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy-β- D-ribohexofuranosyl)-N*-benzoylcytosine]-6'-phosphonate (42). This compound is prepared from diphenyl [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 4 - benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-[4,4'- p dimethoxytrityl]-2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 4 - -isobutyrylguanine]-6'-phosphonate. Diphenyl [9-(3-θ-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy-β- D-ribohexofuranosyl)-N°-benzoyladenine]-6'-phosphonate (43). This compound is prepared from diphenyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-N°- benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-[4,4'- p dimethoxytrityl]-2,5 ,6-trideoxy-β-D-ribohexofuranosyl)-N c -isobutyrylguanine]-6'-phosphonate. Diphenyl [1-(3-θ-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy- β - D-ribohexofuranosyl)-thymine]-6'-phosphonate (44). This compound is prepared from diphenyl [l-(2,5,6-trideoxy-β- D-ribohexofuranosyl)-thymine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-[4,4'-dimethoxytrityl]-2,5,6-trideoxy-β-D- ribohexof ranosyl)-N -isobutyrylguanine]-6'-phosphonate. Monophenyl [9-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxγ- β-D-ribohexof ranosyl)-N -isobutyrylguanine]-6'- phosphonate hydrogentriethylammonium salt (45). A mixture of 3.00 mmol of diphenyl [9-(3-0-[4,4'- dimethoxytrityl]-2,5,6-trideoxy-β-D-ribohexofuranosyl) -N 2 -isobutyrylguanine]-6'-phosphonate is stirred in 100 mL of concentrated aqueous ammonia at room temperature. The reaction is monitored by TLC. After ca. 1 h, the mixture is concentrated. The product is purified by flash chromatography. Monophenyl [1-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy- β-D-ribohexofuranosyl)-ϊr-benzoylcytosine]-6 '-phosphonate hydrogentriethylammonium salt (46). This compound is prepared from diphenyl [l-(3-0-[4,4'-dimethoxytrityl]- 2,5,6-trideoxy-β-D-ribohexofuranosyl) -ϊr- benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of monophenyl [9-(3,-0-[4,4'- p dimethoxytrityl]-2,5,6-trideoxy-β-D-ribohexofuranosyl)-N fc isobutyrylguanine]-6'-phosphonate hydrogentriethylammonium salt. Monophenyl [9-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy- β-D-ribohexofuranosyl)-N ® -benzoyladenine]-6'-phosphonate hydrogentriethylammonium salt (47). This compound is prepared from diphenyl [9-(3-0-[4,4'-dimethoxytrityl]- 2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 6 - -benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of monophenyl [9-(3-0-[4,4'~ dimethoxytrityl]-2,5,6-trideoxy-β-D-ribohexofuranosyl)- N 2 -isobutyrylguanine]-6'-phosphonate hydrogentriethyl¬ ammonium salt. Monophenyl [1-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy -β-D-ribohexofuranosyl)-thymine]-6'-phosphonate hydrogentriethylammonium salt ( 8). This compound is prepared from diphenyl [l-(3-0-[4,4'-dimethoxytrityl]- 2,5,6- trideoxy-β-D-ribohexofuranosyl)-thymine]- 6'-phosphonate by the same procedure used for the preparation of monophenyl [9-(3-0-[4,4'-dimethoxytrityl]- 2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonate hydrogen¬ triethylammonium salt. 9-(2-Deoxy-2-fluoro-β-D-arabinofuranosyl)-N 2 - isobutyrylguanine (49). This compound is prepared from 9_(2-deoxy-2-fluoro-β-D-arabino uranosyl)-guanine (49, 57) by the same procedure used for the preparation of p , N fc -ιsobutyryl-2 ' -deoxyguanosine . 9- [ 2-Deoxy-5-0- (4 ,4' -dimethoxytrityl ) -2-f luoro-β-D-arabin ofuranosyl]-N ?-isobutyrylguanine (50). This compound is prepared from 9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)- by the same procedure used for the preparation of N 2 -isobutyryl-5'-0-( 4 , 4 '-dimethoxytrityl )- 2 ' -deoxyguanosine . 1-(2-Deoxy-2-fluoro-β-D-arabinof ranosyl)-N*- benzoylcytosine (51). This compound is prepared from 1-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-cytosine (50) by the same procedure used for the preparation of N*-benzoyl-2'-deoxycytidine. 1-[2-Deoxy-5-0-(4,4'-dimethoxytrityl)-2-fluoro-β-D- arabinofuranosyl]-N -benzoylcytosine (52). This compound is prepared from l-(2-deoxy-2-fluoro-β-D- arabinofuranosyl)-N 4 -benzoylcytosine by the same procedure used for the preparation of N 4 -benzyol-5'- 0-(4,4'-dimethoxytrityl)-2'-deoxycytidine. 9-(2-Deoxy-2-fluoro-β-D-arabinofuranosyl) -Vr- benzoyladenine (53). This compound is prepared from 9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-adenine (49) by the same procedure used for the preparation of N 6 -benzoy1-2'-deoxyadenosine. 9-[2-Deoxy-5-0-(4,4'-dimethoxytrityl)-2-fluoro-β-D- arabinofuranosyl]-N°-benzoyladenine (54). This compound is prepared from 9-(2-deoxy-2-fluoro-β-D-arabino- furanosyl)-N°-benzoyladenine by the same procedure used for the preparation of N°-benzoyl-5'-0- (4,4'-dimethoxytrityl)-2'-deoxyadenosine. 1-[2-Deoxy-5-0-(4,4'-dimethoxytrityl)-2-fluoro-β-D- arabinofuranosyl]-thymine (55). This compound was prepared from 2.90 g (11.1 mmol) of 1-(2-deoxy-2-fluoro- β-D-arabinofuranosyl)-thymine (51) by the same procedure used for the preparation of 5'-0-(4,4'-dimethoxytrityl)- thymidine. Chromatography of the residue on silica gel afforded 6.98 g (89.4% yield) of product. 9-(3-0-t-Butyldimethylsilyl-2-deoxy-2-fluoro-β-D- arabinofuranosyl)-N-isobutyrylguanine (56). This compound is prepared from 9-[2-deoxy-5-0-(4,4'- p dimethoxytrityl)-2-fluoro-β-D-arabinofuranosyl]-N *4* - isobutyrylguanine by the same procedure used for the preparation of 3'-0-t-butyldimethylsilyl- p N -ιsobutyryl-2'-deoxyguanosine. 1-(3-0-t-Butyldimethylsilyl-2-deoxy-2-fluoro-β-D- arabinofuranosyl)-N -benzoylcytosine (57). This compound is prepared from l-[2-deoxy-5-0-(4,4'-dimethoxytrityl) -2-fluoro-β-D-arabinofuranosyl]-N *" -benzoylcytosine by the same procedure used for the preparation of 3'-O-t-butyldimethylsilyl-N^-benzoyl-2'-deoxycytidine. 9-(3-0-t-Butyldimethylsilyl-2-deoxy-2-fluoro-β-D- arabinofuranosyl)-N°-benzoyladenine (58). This compound is prepared from 9-[2-deoxy-5-0-(4,4'-dimethoxytrityl)- 2-fluoro-β-D-arabinofuranosyl]-N 6 -benzoyladenine by the same procedure used for the preparation of 3'-0-t-butyldimethylsilyl-N 6 -benzoyl-2'-deoxyadenosine. 1-(3-0-t-Butyldimethylsilyl-2-deoxy-2-fluoro-β-D- arabinofuranosyl)-thymine (59). This compound was prepared from 6.28 g (11.16 mmol) of l-[2-deoxy-5-0- (4,4'-dimethoxytrityl)-2-fluoro-β-D- arabinofuranosyl]-thymine by the same procedure used for the preparation of 3'-0-t-butyldimethylsilylthymidine. Column chromatography of the crude residue afforded 3.59 g (85.9% yield) of product. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy- 2-fluoro-β-D-arabino-hex-5-enofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonate (60). This compound is prepared from 9-(3-0-t-butyldimethylsilyl-2-deoxy- -2-fluoro-β-D-arabinofuranosyl)-N 2 -isobutyrylguanine by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo-hex- 5-enofuranosyl)-N 2 -isobutyrylguanosine]-6'-phosphonate. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-2- fluoro-β-D-arabinohexofuranosyl)-N 2 -isobutyrylguanine]-6' -phosphonate (61). This compound is prepared from diphenyl [9-(3-o-t-butyldimethylsilyl-2,5,6-trideoxy- p 2-fluoro-β-D-arabιno-hex-5-enofuranosyl)-N 6 — isobutyrylguanine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-t- butyldimethylsilyl-2,5,6-trideoxy-β-D-ribohexofuranosyl)- p . N fc -isobutyrylguanine]-6'-phosphonate. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5 ,6-trideoxy- 2-fluoro-β-D-arabino-hex-5-enofuranosyl)-N*- benzoylcytosine]-6'-phosphonate (62). This compound is prepared from l-(3-0-t-butyldimethylsilyl-2-deoxy-2- fluoro-β-D-arabinofuranosyl)-N^-benzoylcytosine by the same procedure used for the preparation of diphenyl [1-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-β-D-ribo-hex- 5-enofuranosyl)-N -benzoylcytosine]-6'-phosphonate. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-N*-benzoylcytosine]-6' -phosphonate (63). This compound is prepared from diphenyl [1-(3-0-t-butyldimethylsilyl-2 ,5,6-trideoxy- 2-fluoro-β-D-arabino-hex-5-enofuranosyl)-N*- benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [l-(3-0-t- butyldimethylsilyl-2,5,6-trideoxy-β-D-ribohexofuranosyl)- N 4 -benzoylcytosine]-6'-phosphonate. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy- 2-fluoro-β-D-arabino-hex-5-enofuranosyl) -Vr- benzoyladenine3-6'-phosphonate (64). This compound is prepared from 9-(3-0-t-butyldimethylsilyl-2-deoxy-2- fluoro-β-D-arabinofuranosyl)-N°-benzoyladenine by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl-2 ,5 ,6-trideoxy-β-D-ribo-hex- 5-enofuranosyl)-N°-benzoyladenine]-6'-phosphonate. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-2- fluoro-β-D-arabinohexofuranosyl)-N°-benzoyladenine]-6'- phosphonate (65). This compound is prepared from diphenyl [9-(3-0-t-butyldimethylsilyl-2 ,5 ,6-trideoxy-2- fluoro-β-D-arabino-hex-5-enofuranosyl)-N°-benzoyladenine] -6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-t-butyldimethylsilyl- 2,5,6-trideoxy-β-D-ribohexofuranosyl)-N°-benzoyladenine]- 6'-phosphonate. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-2- fluoro-β-D-arabino-hex-5-enofuranosyl)-thymine]-6'- phosphonate (66). This compound was prepared from 3.12 g (8.33 mmol) of l-(3-0-t-butyldimethylsilyl-2- deoxy-2-fluoro-β-D-arabinofuranosyl)-thymine by the same procedure used for the preparation of diphenyl [l-(3-0-t- butyldimethylsilyl- 2,5,6-trideoxy-β-D-ribo-hex-5-enofuranosyl)-thymine]-6'- phosphonate. Column chromatography of the crude residue afforded 1.19 g (70.4% yield) of product. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-2- fluoro-β-D-arabinohexofuranosyl)-thymine]-6'-phosphonate (67). This compound was prepared from 1.69 g (2.80 mmol) of diphenyl [1-(3-0-t-butyldimethylsilyl-2,5 ,6-trideoxy-2-fluoro-β-D- arabino-hex-5-enofuranosyl)-thymine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [1-(3-0-t-butyldimethylsilyl-2 ,5 ,6-trideoxy-β-D- ribohexofuranosyl)-thymine]-6'-phosphonate. Column chromatography of the crude residue afforded 249 mg (27.6% yield) of product. Diphenyl [9-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N -isobutyrylguanine -6'- phosphonate (68). This compound is prepared from diphenyl [9-(3-0-t-butyldimethylsilyl-2 ,5 ,6-trideoxy -2-fluoro-β-D-arabinohexofuranosyl)-N 2 -isobutyrylguanine] -6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N 2 -isobutyrylguanine]-6'-phosphonate. Diphenyl [l-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N -benzoylcytosine]-6'-phosphonate (69). This compound is prepared from diphenyl [1-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N 4 -benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl) -N 4 -benzoylcytosine]-6'-phosphonate. Diphenyl [9-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N°-benzoyladenine3-6'-phosphonate (70). This compound is prepared from diphenyl [9-(3-0-t-butyldimethylsilyl-2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N°-benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)- -N 1* '-benzoyladenine]-6'-phosphonate. Diphenyl [1-(2,5,6-trideoxy-2-fluoro-β-D arabinohexofuranosyl)-thymine3-6'-phosphonate (71). This compound is prepared from diphenyl [l-(3-0-t- butyldimethylsilyl-2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-thymine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-thymine]-6'- phosphonate. Dimethyl [9-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N 2 -isobutyrylguanine]-6'- phosphonate (72). This compound is prepared from diphenyl [9-(2,5 ,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N 2 -isobutyrylguanine]-6'- phosphonate by the same procedure used for the preparation of dimethyl [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N -isobutyrylguanine3-6'-phosphonate. Dimethyl [1-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N 4 -benzoylcytosine3-6'-phosphonate (73). This compound is prepared from diphenyl [1-(2,5,6-trιdeoxy-2-fluoro-β-D-arabinohexofuranosyl) -N4 - benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of dimethyl [l-(2,5,6-trideoxy -β-D-ribohexofuranosyl)-N^-benzoylcytosine]-6'- phosphonate. Dimethyl [9-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N 6 -benzoyladenine]-6'-phosphonate (74). This compound is prepared from diphenyl [9-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)-N°- benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of dimethyl [9-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N°-benzoyladenine]-6'-phosphonate. Dimethyl [1-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-thymine]-6'-phosphonate (75). This compound is prepared from diphenyl [l-(2,5,6-trideσxy- 2-fluoro-β-D-arabinohexofuranosyl)-thymine]-6'- phosphonate by the same procedure used for the preparation of dimethyl [1-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-thymine]-6'-phosphonate. [9-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)-N fc - isobutyrylguanine]-6'-phosphonic acid (76). This compound is prepared from dimethyl [9-(2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-N 2 -isobutyrylguanine]- 6'-phosphonate by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl) -N c 7-ι .sobutyr lguani .ne]-6'-phosphoni .c acid. A [1-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)-lr- benzoylcytosine]-6'-phosphonic acid (77). This compound is prepared from dimethyl [l-(2,5,6-trideoxy-2-fluoro- β-D-arabinohexofuranosyl)-N 4 -benzoylcytosine]-6'- phosphonate by the same procedure used for the preparation of [l-(2,5,6-trideoxy-β-D- ribohexofuranosyl)-N 4 -benzoylcytosine]-6'-phosphonic acid. [9-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)-N 6 - benzoyladenine]-6'-phosphonic acid (78). This compound is prepared from dimethyl [9-(2,5,6-trideoxy-2-fluoro- β-D-arabinohexofuranosyl)-N°-benzoyladenine]-6'- phosphonate by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl) -N°-benzoyladenine]-6'-phosphonic aci . [l-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- thymine]-6'-phosphonic acid (79). This compound is prepared from dimethyl [l-(2,5,6-trideoxy-2-fluoro-β- D-arabinohexofuranosyl)-thymine]-6'-phosphonate by the same procedure used for the preparation of [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-thymine]- 6'-phosphonic acid. [9-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- guanine3-6'-phosphonic acid (80). This compound is prepared from [9-(2,5,6-trideoxy-2-fluoro-β-D- p arabinohexofuranosyl)-N'-isobutyrylguanme]-6'-phosphonic acid by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-guanine]-6'- phosphonic acid. [1-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexof ranosyl)- cytosine]-6'-phosphonic acid (81). This compound is prepared from [l-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N 4 -benzoylcytosine]-6'-phosphonic acid by the same procedure used for the preparation of [1-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-cytosine]-6'- phosphonic acid. [9-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- adenine]-6'-phosphonic acid (82). This compound is prepared from [9-(2,5,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N 6 -benzoyladenine]-6'-phosphonic acid by the same procedure used for the preparation of [9-(2,5,6-trideoxy-β-D-ribohexofuranosyl)-adenine]-6'- phosphonic acid. Diphenyl [9-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy -2-fluoro-β-D-arabinohexofuranosyl)-N 2 -isobutyrylguanine] -6'-phosphonate (83). This compound is prepared from diphenyl [9-(2 ,5 ,6-trideoxy-2-fluoro-β-D- -arabinohexofuranosyl)-N 2 -isobutyrylguanine]-6'- phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-[4, '-dimethoxytrityl] -2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 2 - isobutyrylguanine]-6'-phosphonate. Diphenyl [1-(3-0-[4,4'-Dimethosytrityl]-2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-IP-benzoylcytosine]-6' -phosphonate (84). This compound is prepared from diphenyl [1-(2 ,5 ,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N -benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [1-(3-0-[4,4'-dimethoxytrityl]-2,5 ,6-trideoxy-β -D-ribohexofuranosyl)-N -benzoylcytosine]-6'-phosphonate. Diphenyl [9-(3-0-[4,4'-Dimethoxytrityl3-2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-N°-benzoyladenine3-6'- phosphonate (85). This compound is prepared from diphenyl [9-(2,5 ,6-trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-N°-benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [9-(3-0-[4 ,4'-dimethoxytrityl]-2,5,6-trideoxy-β -D-ribohexofuranosyl)-N°-benzoyladenine]-6'-phosphonate. Diphenyl [1-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy-2- -fluoro-β-D-arabinohexof ranosyl)-thymine]-6'-phosphonate (86). This compound is prepared from diphenyl [1-(2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- thymine]-6'-phosphonate by the same procedure used for the preparation of diphenyl [l-(3-0-[4,4'- di ethoxytrityl]-2,5,6-trideoxy-β-D-ribohexofuranosyl)- thymine]-6'-phosphonate. Monophenyl [9-(3-O-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy- p 2-fluoro-β-D-arabinohexofuranosyl)-N c -isobutyrylguanιne3- 6'-phosphonate hydrogentriethylammonium salt (87). This compound is prepared from diphenyl [9-(3-0-[4,4'~ dimethoxytrityl]- p 2,5,6-tπdeoxy-2-fluoro-β-D-arabmohexofuranosyl)-N 4 — isobutyrylguanine]-6'-phosphonate by the same procedure used for the preparation of monophenyl [9-(3-0-[4,4'- p dimethoxytrityl]-2,5,6-trιdeoxy-β-D-ribohexofuranosyl)-N -isobutyrylguanine]-6'-phosphonate hydrogentriethylammonium salt. Monophenyl [1-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-IP-benzoylcytosine3-6' -phosphonate hydrogentriethylammonium salt (88). This compound is prepared from diphenyl [l-(3-0-[4,4'~ dimethoxytrityl] -2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)-N 4 - benzoylcytosine]-6'-phosphonate by the same procedure used for the preparation of monophenyl [l-(3-0-[4,4'~ dimethoxytrityl]-2,5,6-trideoxy-β-D-ribohexofuranosyl)-N 4 -benzoylcytosine]-6'-phosphonate hydrogentriethylammonium salt. Monophenyl [9-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-N^-benzoyladenine3-6'- phosphonate hydrogentriethylammonium salt (89). This compound is prepared from diphenyl [9-(3-0-[4,4'- dimethoxytrityl]- 2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)-N 6 - benzoyladenine]-6'-phosphonate by the same procedure used for the preparation of monophenyl [9-(3-0-[4,4'- dimethoxytrityl]-2,5 ,6-trideoxy-β-D-ribohexofuranosyl)-N 6 -benzoyladenine]-6'-phosphonate hydrogentriethylammonium salt. Monophenyl [1-(3-0-[4,4'-Dimethoxytrityl]-2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-thymine3-6'- phosphonate hydrogentriethylammonium salt (90). This compound is prepared from diphenyl [l-(3-0-[4,4'~ dimethoxytrityl] -2,5,6-trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- thymine]-6'-phosphonate by the same procedure used for the preparation of monophenyl [l-(3-o-[4,4'~ dimethoxytrityl]-2,5,6-trideoxy-β-D-ribohexofuranosyl)- thymine]-6'-phosphonate hydrogentriethylammonium salt. Synthesis of oligonucleotides. Oligonucleotides are synthesized from the 5'-end to the 3'-end. The phosphotriester method of oligonucleotide synthesis described by Sproat and Gait is used (38). Appropriately protected 3'-0-(4,4'-dimethoxytrityl)-nucleosides having a free 5'-hydroxyl group are required for the solid phase synthesis (52). These nucleosides are affixed to a long chain- aikyi*amiτιe controlled pore glass (LCAA/CPG) via a succinate linker using standard methods (38). The 3'-0-DMT group on the support bound nucleoside is cleaved with 3% (v/v) dichloroacetic acid in 1,2-dichloroethane (DCE) . After washing with DCE, and then pyridine, coupling of the appropriate monophenyl nucleoside-6'-phosphonate as its hydrogentriethylammonium salt is effected with the coupling agent l-mesitylenesulphonyl-3-nitro-l,2,4-triazole (MSNT) and 1-methylimidazole (NMI) in pyridine. This coupling is allowed to occur from 15-45 minutes. The support is then washed with pyridine. The oligo containing support is then treated with an Ac 2 0/lutidine/DMAP capping solution. The capping agent and its use is described by Atkinson and Smith (53). After capping, the support is washed with first DCE, pyridine, and then DCE again. Then the cycle is repeated (ie. deprotection, coupling, capping). After the last coupling step, the fully protected oligonucleotide is cleaved from the support and fully deprotected using a mixture of pyridine-2-carbaldoxime and tetramethylguanidine in dioxane/water (38). This deprotection is allowed to occur at 37°C for 20 h. After drying in vacuo, the oligonucleotide is purified by either HPLC or polyacrylamide gel electrophoresis (PAGE). Diphenyl [9-(3-o-t-Butyldimethylsilyl-2,5,6-trideoxy -β-D-ribohexofuranosyl)-N 2 -isobutyrylguanine3-6'- phosphonate (14). Another procedure for the preparation of the title compound follows. A solution of 2.70 g (3.97 mmol) of diphenyl [9-(3-0-t-butyldimethylsilyl- 2,5,6-trideoxy-B-D-ribo-hex-5-enofuranosyl)-N 7" * - isobutyrylguanine]-6'-phosphonate was reduced with 2,4,6-tri-isopropylbenzenesulphonyl hydrazide and triethylamine as in the preparation of compound 22. After extractive workup, the crude product was used in the next step without further purification. Dimethyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy -β-D-ribohexofuranosyl)-N2-isobutyrylguanine3-6'- phosphonate (91). The entire crude compound 14 from above was treated with CsF and MeOH as in the preparation of compound 23. After workup, the product was purified by flash chromatography and afforded 476 mg (21.5% yield) of product. Monomethyl [9-(2,5,6-Trideoxy-β-D-ribohexofuranosyl) -guanine3-6'-phosphonate sodium salt (92). A solution of 288 mg (0.516 mmol) of compound 91 in 8.5 mL of 0.5 N NaOH solution of MeOH/H 2 0 4:1 was heated at 8O0C for 1.5 h. The volatiles were rotovapped off. To the mixture was added 5.70 mL of H«0, and this mixture was neutralized to pH = 7.0 with 1 N aqueous HCl. The aqueous mixture was extracted with Et 2 0 several times. The aqueous layer was concentrated. The residue was purified by reverse phase HPLC on a C18 column using CH 3 CN/H 2 0 as eluents. This afforded 148 mg (75.2% yield) of product. [9-(2,5,6-Trideoxy-β-D-ribohexofuranosyl)-guanine -6'- phosphonate disodium salt (93). To 60.0 mg (0.157 mmol) of compound 92 in 25 mM tris and 1 mM MgCl 2 was added 1 unit of phosphodiesterase (from Crotalus duriss, that was purchased from Boehringer Mannheim as a 50% w/v solution in glycerol) . The pH of the solution was kept between 8.5 and 9.5 during the course of the reaction by adding solid tris to the reaction. After 17 h, the phosphodiesterase was removed on a size exclusion column (Centriprep-10 column, purchased from Amicon). The product was purified on a reverse phase C18 column using a combination of 100 mM triethylammonium acetate (TEAA) and CHgCN as eluants. The product was azeotroped from EtOH/H 2 0 several times to remove excess TEAA. The triethylammonium counter ion was exchanged for Na + on a Bio-Rad Poly-Prep cation exchange column (AG 50W-x8 resin, Na + form). The product was desalted by reverse phase HPLC on a C18 column using CH 3 CN/H 0. This afforded 38.2 mg (63.9% yield) of product. [9-(2,5,6-Trideoxy-β-D-ribohexofuranosyl)-guanine]-6'- phosphonate monosodium inonohydrogentriethylammonium salt (119). The procedure for the preparation of compound 93 was used except that the cation exchange column was not treated with enough aqueous NaOH before the phosphonate was loaded onto the column. The resulting acidic resin caused some depurination, and only partial exchange of Na + for hydrogentriethylammonium cation. The resulting mixture was separated on a reverse phase C18 column using CH 3 CN/H 2 0 as eluents. This afforded 14.1 mg (19.2% yield) of product as the monohydrogentriethylammonium salt. Dimethyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy- β-D-ribohexofuranosyl)-BT-benzoylcytosine3-6'-phosphonate (94). This compound was prepared from 3.88 g (5.74 mmol) of compound 16 by the same procedure used for the preparation of compound 91. Purification of the product by silica gel chromatography afforded 700 mg (22.1 % yield) of product. Monomethyl [1-(2,5,6-Trideoxy-β-D-ribohexofuranosyl) -cytosine -6'-phosphonate sodium salt (95). This compound was prepared from 500 mg (0.906 mmol) of compound 94 by the same procedure used for the preparation of compound 92. Purification by HPLC on a C18 column using CH^CN/HgO afforded 336 mg ( > 100% yield) that contained only the product and less than one equivalent of benzoic acid by H NMR. [1-(2,5,6-Trideoxy-β-D-ribohexofuranosyl)-cytosine3-6'- phosphonate disodium salt (96). This compound was prepared from 100 mg (0.293 mmol) of compound 95 by the same procedure used for the preparation of compound 93. This procedure afforded 61.3 mg (59.9% yield) of product. Dimethyl [1-(3-0-t-Butyldimethylsilyl-2 ,5,6-trideoxy-2- fluoro-β-D-arabinohexofuranosyl)-thymine3-6'-phosphonate (97). This compound was prepared from 1.14 g (1.88 mmol) of compound 67 by the same procedure used for the preparation of compound 91. Column chromatography of the crude residue on silica gel afforded 249 mg (27.6% yield) of product. Monomethyl [1-(2,5,6-Trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-thymine]-6'-phosphonate sodium salt (98). This compound was prepared from 220 mg (0.458 mmol) of compound 97 by the same procedure used for the preparation of compound 92. HPLC purification afforded 90.0 mg (40.9% yield) of product. [1-(2,5,6-Trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- thymine]-6'-phosphonate disodium salt (99). This compound was prepared from 80.0 mg (0.214 mmol) of compound 98 by the same procedure used for the preparation of compound 93. This procedure afforded 18.1 mg (22.1% yield) of product. 1-[2-Deoxy-δ-O-(4,4'-dimethoxytrityl)-2-fluoro-β-D- arabinofuranosyl3-uracil (100). This compound was prepared from 4.00 g (17.2 mmol) of l-(2-deoxy-2- fluoro-β-D-arabinofuranosyl)-uracil (5lb) by the same procedure used for the preparation of compound 55. Column chromatography of the crude residue afforded 6.60 g (69.9% yield) of product. 1-(3-0-t-Butyldimethylsilyl-2-deoxy-2-fluoro-β-D-arabino furanosyl)-uracil (101). This compound was prepared from 5.60 g (10.2 mmol) of compound 100 by the same procedure used for the preparation of compound 59. Column chromatography of the crude residue afforded 2.70 g (73.4% yield) of product. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy -2-fluoro-β-D-arabino-hex-5-enofuranosyl)-uracil3-6'- phosphonate (102). This compound was prepared from 3.50 g (9.71 mmol) of compound 101 by the same procedure used for the preparation of compound 66. Column chromatography of the crude residue afforded 4.02 g (70.3% yield) of product. Diphenyl [1-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy- 2-fluoro-β-D-arabinohexofuranosyl)-uracil]-6'-phosphonate (103). This compound was prepared from 3.80 g (6.46 mmol) of compound 102 by the same procedure used for the preparation of compound 67. Column chromatography of the crude residue afforded 1.20 g (31.4% yield) of product. Monomethyl [1-(2,5,6-Trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-uracil]-6'-phosphonate sodium salt (105). A solution of 350 mg (0.592 mmol) of compound 103 in 0.5 N NaOH in MeOH/H 2 θ 4:1 was heated at 80oc for 1.5 h. The volatiles were removed on a rotovap. The mixture was diluted with H 2 0, cooled on ice, " neutralized with 1 N aqueous HCl, and then extracted with Et 2 0. The aqueous layer was concentrated and the product purified by reverse phase HPLC on a C18 column using CH 3 CN/H 2 0 as eluents. This afforded 97.6 mg (45.8% yield) of product. [1-(2,5,6-Trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- uracil3-6'-phosphonate disodium salt (106). This compound was prepared from 89.6 mg (0.249 mmol) of compound 105 by the same procedure used for the preparation of compound 99. This procedure afforded 28.9 mg (31.5% yield) of product. Diphenyl [1-(3-o-t-Butyldimethylsilyl-2,5 ,6-trideoxy-2- fluoro-β-D-arabinohexofuranosyl)-cytosine3-6'-phosphonate (107). To an ice-cooled mixture of 758 mg (1.28 mmol) of compound 103, 5.20 mL of TEA, and 523 mg of 1,2,4-triazole in 17.3 mL of dry CH 3 CN was added 230 microliters of P0C1 3 dropwise over five minutes. After 15 minutes, the ice bath was removed, and stirring was continued for an additional hour. The reaction was concentrated, partitioned between CH 2 C1 2 and H 2 0, shaken, and separated. The organic layer was dried (Na 2 SO^), filtered, and concentrated. The residue was concentrated once from dry CH 3 CN, and then taken up in 38 mL of dry CH 3 CN. The reaction was saturated with anhydrous NH 3 , and the flask was tightly stoppered. After 65 h, the reaction was concentrated. The residue was taken up in CH 2 C1 2 , washed with H 2 0, dried (Na 2 S0 * ) , filtered, and concentrated. Column chromatography of the crude product on silica gel afforded 410 mg (54.5% yield) of product. Monophenyl [1-(2,5,6-Trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-cytosine -6'-phosphonate sodium salt (108). A solution of 350 mg (0.596 mmol) of compound 107 in 20 mL of 0.5 N NaOH in dioxane/H 2 0 1:1 was heated at 80oc for 1.5 h. The volatiles were removed on a rotovap. The mixture was diluted with H 2 0, cooled on ice, neutralized with 1 N aqueous HCl, and extracted with Et 2 0. The aqueous layer was concentrated to give crude product. The monophenyl phosphonate was purified as the hydrogentriethylammonium salt in the next step. Monophenyl[1-(2,5,6-Trideoxy-2-fluoro-β-D-arabinohexo furanosyl)-cytosine3-6'-phosphonate hydrogentriethylammonium salt (120). The entire crude compound 108 from above was purified by reverse phase HPLC on a C18 column using 100 mM aqueous triethylammonium acetate (pH = 6.5) and CH 3 CN as eluents. This afforded 227 mg (76.2% yield from compound 107) of product. [1-(2,5,6-Trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- cytosine3-6'-phosphonate disodium salt (109). This compound was prepared from 180 mg (0.360 mmol) of compound 120 by the same procedure used for the preparation of compound 106. This procedure afforded 81.8 mg (61.9% yield) of product. 9-[2-Deoxy-5-0-(4,4'-dimethoxytrityl)-2-fluoro-β-D- arabinofuranosyl3-N°-(4,4'-dimethoxytrityl)-adenine (110). To 2.70 g (10.03 mmol) of 9-(2-deoxy-2- fluoro-β-D-arabinofuranosyl)-adenine* 9 in 65 mL of dry pyridine was added 8.98 g (26.6 mmol) of 4 ,4'-dimethoxytrityl chloride. The reaction was stirred at room temperature for 63 h and then concentrated. The residue was taken up in CH 2 C1 2 , washed with 0.5% aqueous NaHC0 3 , dried (Na 2 S0 4 ) , filtered, and concentrated. Column chromatography of the crude product on silica gel afforded 5.71 g (63.4% yield) of product. 9-(3-0-t-Butyldimethylsilyl-2-deoxy-2-fluoro-β-D-arabino furanosyl)-adenine (111). This compound was prepared from 5.46 g (6.25 mmol) of compound 110 by the same procedure used for the preparation of compound 101. The product was not purified by chromatography, but was precipitated from CH 2 C1 2 with hexanes affording 1.87 g (77.9% yield) of product. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy-2 -fluoro-β-D-arabino-hex-5-enofuranosyl)-adenine]-6'- phosphonate (112). This compound was prepared from 1.67 g (4.35 mmol) of compound 111 by the same procedure used for the preparation of compound 102. Column chromatography of the crude product on silica gel afforded 1.49 g (56.0% yield) of product. Diphenyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy -2-fluoro-β-D-arabinohexofuranosyl)-adenine3-6'- phosphonate (113). This compound was prepared from 1.11 g (1.82 mmol) of compound 112 by the same procedure used for the preparation of compound 103. Column chromatography of the crude product on silica gel afforded 133 mg (11.9% yield) of product. Monophenyl [9-(2,5,6-Trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-adenine]-6'-phosphonate sodium salt (114). This compound is prepared from compound 113 by the same procedure used for the preparation of compound 108. [9-(2,5,6-Trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- adenine3-6'-phosphonate disodium salt (115). This compound is prepared from compound 114 by the same procedure used for the preparation of compound 109. Dimethyl [9-(3-0-t-Butyldimethylsilyl-2,5,6-trideoxy -2-fluoro-β-D-arabinohexofuranosyl)-N -isobutyrylguanine] -6'-phosphonate (116). This compound is prepared from compound 61 by the same procedure used for the preparation of compound 91. Monomethyl [9-(2,5,6-Trideoxy-2-fluoro-β-D- arabinohexofuranosyl)-guanine3-6'-phosphonate sodium salt (117). This compound is prepared from compound 116 by the same procedure used for the preparation of compound 92. [9-(2,5,6-Trideoxy-2-fluoro-β-D-arabinohexofuranosyl)- guanine]-6'-phosphonate disodium salt (118). This compound is prepared from compound 117 by the same procedure used for the preparation of compound 93. References 1. Stein, C. A.; and Cohen, J. S. Cancer Res., 1988, 48, 2659-2688. 2. van der Krol, A. R. ; Mol, J. N. M. ; and Stuitje, A. R. BioTechniques, 1988, 6, 958-976. 3. Weintraub, H. M. Scientific American, January, 1990, 40-46. 4. J. Goodchild in "Oligodeoxynucleotides: Antisense Inhibitors of Gene Expression," chapter 3, J. S. Cohen (ed.), 1989, CRC Press, Inc. Boca Raton, Florida. 5. P.B. Dervan in "Oligodeosynucleotides: Antisense Inhibitors of Gene Expression," chapter 9, J. S. Cohen (ed.), 1989, CRC Press, Inc. Boca Raton, Florida. 6. P. B. Dervan in "Nucleic Acids and Molecular Biology," volume 2, pp 49-64, F. Eckstein and D. M. J. Li1ley (eds.), 1988, Springer-Verlag, Berlin. 7. Zon, G. Pharmaceutical Res., 1988, 5, 539-549. 8. C. A. Stein and J. S. Cohen in "Oligodeoxynucleotides: Antisense Inhibitors of Gene Expression," chapter 5, J. S. Cohen (ed.), 1989, CRC Press, Inc. Boca Raton, Florida. 9. M. H. Carruthers in "Oligodeoxynucleotides: Antisense Inhibitors of Gene Expression," chapter 1 , J . S. Cohen (ed.), 1989, CRC Press, Inc. Boca Raton, Florida. 10. a. Grandas, A.; Marshall, W. S.; Nielsen, J. ; and Carruthers, M. H. Tetrahedron Lett., 1989, 30, 543-546. b. Brill, . K. -D. Tang, J. -Y. ; Ma, Y. -X.; and Carruthers, M. H. J. Amer. Chem. Soc; 1989, 111, 2321-2322. c. Carruthers, M. H. ; Beaton, G.; Brill, W. K. -D.; Cummins, L. ; Ma, Y. -X.; Marshall, W. S.; Nielsen, J. ; Sasmor, H. ; and Yau, E. "Synthesis and Biological Studies with Dithioate DNA." Presented at the 9th International Round Table: Nucleosides, Nucleotides, and their Biological Applications; July 30-August 3, 1990, Uppsala, Sweden. 11. P. S. Miller in "Oligodeoxynucleotides: Antisense Inhibitors of Gene Expression," chapter 4, J. S. Cohen (ed.), 1989, CRC Press, Inc. Boca Raton, Florida. 12. Engel, R. Chem. Rev., 1977, 77, 349-367. 13. Jones, G. H.; and Moffatt, J. G. J. Amer. Chem. Soc, 1968, 90, 5337-5338. 14. Padyukova, N. S.; Karpeisky, M. Y.; Kolobushkina, L. I.; and Mikhailov, s. N. Tetrahedron Lett., 1987, 28, 3623-3626. 15. Mikhailov, s. N. ; Padyukova, N. S.; Karpeiskii, M. Y.; Kolobushkina, L. I.; and Beigelman, L. N. Collect. Czech. Chem. Commun. , 1989, 54, 1055-1067. 16. Martin, J. C. ; and Verheyden, J. P. H. Nucleosides and Nucleotides, 1988, 7, 365-374. 17. Hampton, A.; Perini, F. ; and Harper, P. J. Biochemistry, 1973, 12, 1730-1736. 18. Hampton, A.; Sasaki, T. ; and Paul, B. J. Amer. Chem. SOC, 1973, 95, 4404-4414. 19. Montgomery, J. A.; Laseter, A. G. ; and Hewson, K. J. Het. Chem., 1974, 11, 211-218. 20. Hampton, A.; Sasaki, T. ; Perini, F.; Slotin, L. A. ; and Kappler, F. J. Med. Chem., 1976, 19, 1029-1033. 21. Hampton, A.; Slotin, L. A.; Kappler, F.; Sasaki, T. ; and Perini, F. J. Med. Chem., 1976, 19, 1371-1377. 22. Kappler, F.; Hai, T. T. ; and Hampton, A. J. Med. Chem., 1986, 29, 318-322. 23. Kappler, F.; Hai, T. T.; Cotter, R. J. ; Hyver, K. J. ; and Hampton, A. J. Med. Chem., 1986, 29, 1030-1038. 24. Fuertes, M. ; Witkowski, J. T.; Streeter, D. G.; and Robins, R. K. J. Med. Chem., 1974, 17, 642-645. 25. Marquez, V. E. ; Tseng, C. K. H. ; Gebeyehu, G.; Cooney, D. A.; Ahluwalia, G. S.; Kelley, J. A.; Dalai, M. ; Fuller, R. W. ; Wilson, Y. A.; and Johns, D. G. J. Med. Chem., 1986, 29, 1726-1731. 26. Albrecht, J. P.; Jones, G. H.; and Moffatt, J. G. Tetrahedron, 1984, 40, 79-85. 27. Albrecht, H. P.; Jones, G. H. ; and Moffatt, J. Amer. Chem. Soc, 1970, 92, 5511-5513. 28. Mazur, A.; Tropp, B. E.,* and Engel, R. Tetrahedron, 1984, 40, 3949-3956. 29. Cozzone, R. J. ; and Kaptein, R. FEBS Lett., 1983, 155, 55-60. 30. Barton, D. H. R. ; Gero, S. D.; Quicklet-Sire, B.; and Samadi, M. Tetrahedron Lett., 1989, 30, 4969-4972. 31. Tanaka, H. ; Fukui, M. ; Haraguchi, K. ; Masaki, M. ; and Miyasaka, T. Tetrahedron Lett., 1989, 30, 2567-2570. 32. Montgomery, J. A.; Thomas, H. J. ; Kisliuk, R. L. ; and Gaumont, Y. J. Med. Chem., 1979, 22, 109-111. 33. Jones, G. H.; Albrecht, H. P.; Damodaran, N. P.; and Moffatt, J. G. J. Amer. Chem. Soc, 1970, 92, 5510-5511. 34. Griffin, J. H. ; Schechter, A. N. ; and Cohen, J. S. Annals New York Academy of Sciences, 1973, 222, 693-708. 35. B. E. Kaplan and K. Itakura in "Synthesis and Applications of DNA and RNA," chapter 2, S. A. Narang (ed.), 1987, Academic Press, Orlando, Florida. 36. a. Crockett, G. C. Aldrichimica Acta, 1983, 16, 47-55. b. Agarwal, K. L.; Yamazaki, A.; Cashion, P. J. and Khorana, H. G. Angew. Chem. Int. Ed. Eng. , 1972, 11, 451-459. 37. Breaker, R. R. ; Gough, G. R. ; and Gilham, P. T. Nucleic Acids Res., 1990, 18, 3085-3086. 38. B. S. Sproat and M. J. Gait in "Oligonucleotide Synthesis: A Practical Approach," chapter 4, M. J. Gait (ed.), 1984, IRL Press, Oxford. 39. Prisbe, E. J. ; Martin, J. C. ; McGee, D. P. C. ; Barker, M. F. ; Smee, D. F. ; Duke, A. E. ; Matthews, T. R. ; and Verheyden, J. P. H. J. Med. Chem., 1986, 29, 671-675. 40. Duke, A. E.; Smee, D. F.; Chernow, M. ; Boehme, R. ; and Matthews, T. R. Antiviral Research, 1986, 6, 299-308. 41. Reist, E. J. ; Sturm, P. A.; Pong, R. Y.; and sidwess, R. W. Nucleosides and Nucleotides, 1989, 8, 919-922. 42. Sidwell, R. w.; Huffman, J. H.; Barnard, D. L. ; and Reist, E. J. Nucleosides and Nucleotides, 1989, 8, 833-836. 43. Still, W. C. ; Hahn, M. ; and Mitra, A. J. Org. Chem., 1978, 43, 2923-2925. 44. R. A. Jones in "Oligonucleotide Synthesis: A Practical Approach," chapter 2, pp. 25-27, M. J. Gait (ed.), 1984, IRL Press Limited, Oxford. 45. R. A. Jones in "Oligonucleotide Synthesis: A Practical Approach," chapter 2, pp. 27-28, M. J. Gait (ed.), 1984, IRL Press Limited, Oxford. 46. Jones, G. H. ; Hamamura, E. K. ; and Moffatt, J. G. Tetrahedron Lett., 1968, 55, 5731-34. 47. Cusack, N. J.; Reese, C. B.; Risius, A. C; and Roozpeikar B. Tetrahedron, 1976, 32, 2157-62. 48. ElAmin, B.; Anantharamaia , G. M. ; Royer, G. P.; and Means, G. E. J. Org. Chem., 1979, 44, 3442-3444. 49. Chu, C. K. ; Matulic-Adamic, J. ; Huang, J. -T.; Chou, T. -C. ; Burchenal, J. H. ; Fox, J. J. ; and Watanabe, K. A. Chem. Pharm. Bull., 1989, 37, 336-339. 50. Watanabe, K. A.; Reichman, U. ; Hirota, K. ; Lopez, C; and Fox, J. J. J. Med. Chem., 1979, 22, 21-24. 51.a. Tann, C. H.; Brodfuehrer, P.R.; Brundidge, S. P.; Sapino, Jr., C. ; and Howell, H. G. J. Org. Chem., 1985, 50, 3644-3647. b. Howell, H. G. ; Brodfuehrer, P. R. ; Brundidge, s. P. ; Benigni, D. A. ; and Sapino, Jr., C. J. Org. Chem., 1988, 53, 85-88. 52. van de Sande, J. H. ; Ramsing, N. B.; Germann, M. W.; Elhorst, W. ; Kalisch, B. W. ; Kitzing, E. V.; Pon, R. T.; Clegg, R. C; and Jovin, T. M. Science, 1988, 241, 551-557. 53. T. Atkinson and M. Smith in "Oligonucleotide Synthesis: A Practical Approach," chapter 3, M. J. Gait (ed.), 1984, IRL Press Limited, Oxford. 54. E. de Vries, et al, Mol. Biochem. Parasitol., 1991, 47, 43-50. 55. W.A. Remers (ed.) Antineoplastic Agents, 1984, Wiley & Sons, New York. 56. R.z. Sterzycki, et al, J. Med. Chem., 1990, 33, 2150-2157. 57. A.D. Borthwick, et al, J. Med. Chem., 1991, 34, 907- 914.

Claims: What is claimed is: 1. A modified oligonucleotide of formula (I): and stereoisomers and salts thereof, wherein: each B is independently a purine or pyrimidine base or modified form; each Z is independently a noninterfering substituent, hydrogen or a protecting group; each R 5 is independently hydrogen, hydroxyl, fluorine, O-methyl, O-allyl, S-methyl or S-allyl; each Y is independently OR 4 , N(R 4 )~ or SR 4 wherein. each R 4 is independently hydrogen, methyl, ethyl, propyl, isopropyl, butyl, phenyl, alkyl (4 - 18C) or substituted alkyl (1-18C); X is selected from oxygen and sulfur; and n is an integer from 1 to 30, with the proviso that (i) at least one W is CH 2 , (ii) when B is thymine and n is 1 or 2 then not all R 5 are H, (iii) when B is adenine and n is an integer from l to 9 then not all are OH, (iv) when B is uracil and n is 1 then not all R 13 are OH and (v) when n is 1 and the 5' B is uracil and the 3' B is adenine then not all R 5 * are OH. 2. The modified oligonucleotide of claim 1 5 wherein Y is 0 " , OH or OR 4 . 3. The modified oligonucleotide of claim 2 wherein X is oxygen. 1° 4. The modified oligonucleotide of claim 3 which is a dimer, trimer or tetramer. 5. The modified oligonucleotide of claim 3 comprising i5 a first nucleotide sequence containing at least three nucleotide residues, said sequence having either 3' to 5' or 5' to 3' polarity, and, coupled thereto, a second nucleotide sequence containing at least one nucleotide residue, said second sequence having 20 polarity inverted from that of the first sequence. 6. The oligonucleotide of claim 3 which is capable of forming a triplex with a target duplex DNA. 25 7. The oligonucleotide of claim 3 which is capable of forming a covalent crosslink with a target duplex DNA. 8. The modified oligonucleotide of claim 3 0 wherein R 5 is hydrogen, hydroxyl or fluorine. 5 9. A compound having the following formula (II): X II and stereoisomers and tautomers thereof, wherein: B is a purine or pyrimidine base or modified form; R" is hydrogen, hydroxyl, fluorine, O-benzyl, O-t-butyldimethylsilyl, O-DMT and 0-MMT; and R' is hydrogen, O-allyl, S-allyl, O-methyl, S-methyl or fluorine or both Rr and R , when taken together with the carbon atom to which each is attached, form a 2', 3' epoxide group or a carbon-carbon double bond; each Y is independently OR 4 , N(R 4 ) 2 or SR 4 wherein, each R 4 is independently hydrogen, methyl, ethyl, propyl, isopropyl, butyl, phenyl, alkyl (4 - 18C) or substituted alkyl (1-18C); X is selected from oxygen and sulfur; and the corresponding salts, zwitterions, and solvates. 10. The compound of claim 9 wherein, R w is hydroxyl, O-DMT or O-t-butyldimethylsilyl; R 7 is hydrogen; X is oxygen; and each Y is independently hydroxyl, O-methyl, 0- ethyl, O-propyl, 0-isopropyl, 0-butyl or O-phenyl, with the proviso that R 5 has the a epimeric configuration corresponding to the 3' hydroxyl of ribose. 11. The compound of claim 10 wherein B is guanine. 12. The compound of claim 10 wherein B is adenine. 13. The compound of claim 10 wherein B is cytosine. 14. The compound of claim 10 wherein B is inosine, uracil, xanthine, hypoxanthme, 5-iodouracil, 5- iodocytosine, 5-ethyluracil , 5-propynyluracil, 5- fluorouracil, 5-trifluororaethyluracil, 5- bromovinyluracil, 5-propynylσytosine, 5-methylcytosine, 8-hydroxy-N°-methyladenine, aziridinylcytosine, 2-aminopurine, 2,6-diaminopurine, 3-deazaguanine, 6- chloropurine, 7-deazaadenine, 8-bromoadenine, 7- deazaguanine, 3-deazaadenine, 6-hydroxylaminopurine and 6-thiopurine. 15. The compound of claim 9 wherein, R 6 and R 7 are both hydrogen; X is oxygen; and each Y is independently hydroxyl, o-methyl, o- ethyl, O-propyl, o-isopropyl, O-butyl or O-phenyl, with the proviso that R° has the epimeric configuration corresponding to the 3' hydroxyl of ribose. 16. The compound of claim 15 wherein B is thymine. 17. The compound of claim 15 wherein B is adenine. 18. The compound of claim 15 wherein B is cytosine, 19. The compound of claim 15 wherein B is inosine. 20. The compound of claim 15 wherein B is guanine, uracil, xanthine, hypoxanthme, 5-iodouracil, 5- iodocytosine, 5-ethyluracil , 5-propynyluracil , 5- fluorouracil , 5-trifluoromethyluracil , 5- bromovinyluracil , 5-propynylcytosine, 5-methylcytosine, 8-hydroxy-N 6 -methyladenine, aziridinylcytosine, 2-aminopurine , 2,6-diaminopurine, 3-deazaguanme, 6- chloropurine, 7-deazaadenine, 8-bromoadenine, 7- deazaguanine, 3-deazaadenine, 6-hydroxylaminopurine or 6- thiopurine. 21. The compound of claim 9 having the formula (III): III and stereoisomers thereof, wherein B, Y and X have any of the meanings given in claim 9 and the corresponding salts and solvates thereof. 22. The compound of claim 9 having the formula (IV): IV and stereoisomers thereof wherein B, Y and X have any of the meanings given in claim 9 and the corresponding salts and solvates thereof. 23. The compound of claim 22 wherein X is oxygen. 24. The compound of claim 23 wherein B is adenine. 25. The compound of claim 23 wherein B is cytosine. 26. The compound of claim 23 wherein B is thymine. 26. The compound of claim 23 wherein B is guanine, uracil, inosine, xanthine, hypoxanthme, 5-iodouracil, 5- iodocytosine, 5-ethyluracil, 5-propynyluracil, 5- fluorouracil, 5-trifluσromethyluracil, 5- bromovinyluracil, 5-propynylcytosine , 5-methylcytosine, 8-hydroxy-N 5 -methyladenine , aziridinylcytosine, 2-aminopurine, 2,6-diaminopurine, 3-deazaguanine,6- chloropurine, 7-deazaadenine, 8-bromoadenine, 7- deazaguanine, 3-deazaadenine, 6-hydroxylaminopurine or 6- thiopurine. 27 . The compound of claim 9 having the formula (V) wherein Y has the meaning defined in claim 9; and B is selected from the group consisting of guanine, adenine, cytosine, thymine, uracil, inosine, xanthine, hypoxanthine, 5-iodouracil, 5-iodocytosine, 5 ethyluracil, 5-propynyluracil, 5-fluorouracil, 5- trifluoromethyluracil, 5-bromovinyluracil, 5- propynylcytosine , 5-methylcytosine, 8-hydroxy-N°-methyladenine, aziridinylσytosine, 2-aminopurine , 2,6-diaminopurine, 3-deazaguanine , 6- chloropurine, 7-deazaadenine , 8-bromoadenine , 7- deazaguanine , 3-deazaadenine, 6-hydroxylaminopurine and 6-thiopurine. 28. The compound of claim 27 wherein B is guanine, 29. The compound of claim 27 wherein B is adenine. 30. The compound of claim 27 wherein B is cytosine. 31. The compound of claim 27 wherein B is thymine. 32. The compound of claim 27 wherein B is uracil. 33. The compound of claim 27 wherein B is inosine. 34. The compound of claim 27 wherein B is xanthine, hypoxanthine, 5-iodouracil, 5-iodocytosine, 5- ethyluracil, 5-propynyluracil, 5-fluorouracil, 5- trifluoromethyluracil , 5-bromovinyluracil, 5- propynylcytosine, 5-methylcytosine, 2-aminopurine, 2,6-diaminopurine, 3-deazaguanine, 6-chloropurine, 7- deazaadenine, 8-bromoadenine, 7-deazaguanine, 3- deazaadenine, 6-hydroxylaminopurine or 6-thiopurine. 35. The compound of claim 9 having the formula (VI): VI wherein Y has the meaning defined in claim 9; and B is selected from the group consisting of guanine, adenine, cytosine, thymine, uracil, xanthine, hypoxanthine, 5-iodouracil, 5-iodocytosine, 5- ethyluracil, 5-propynyluracil, 5-fluorouracil, 5- trifluoromethyluracil, 5-bromovinyluracil, 5- propynylcytosine, 5-methylcytosine, 8-hydroxy-N 6 -methyladenine, aziridinylcytosine, 2-aminopurine, 2,6-diaminopurine, 3-deazaguanine, 6- chloropurine, 7-deazaadenine, 8-bromoadenine, 7- deazaguanine, 3-deazaadenine, 6-hydroxylaminopurine and 6-thiopurine. 36. A compound having the formula (VII) VII and stereoisomers thereof wherein B is a purine or pyrimidine base or a modified form; and R° is t-butyldimethylsilyl. p 37. The compound of claim 36 wherein B is l — isobutyrylguanine, N -benzoylcytosine, N°-benzoyladenine, thymine, uracil or adenine. 38. A compound having the formula (VIII) VIII wherein, B is a purine or pyrimidine base or a modified form; Rr is hydrogen, DMT or TBS; R ° is hydrogen, methyl, phenyl, TBS, alkyl (2- 5 18C) or substituted alkyl (1-18C); and R 1 * is hydrogen, phenyl, +HTEA, Na + , methyl, alkyl (2-18C) or substituted alkyl (1-18C) and the corresponding salts, zwitterions and solvates. ° 39. The compound of claim 38 wherein B is guanine, adenine, cytosine, thymine, uracil, N fc -ιsobutyrylguanme, N 4 -benzoylcytosine or N°-benzoyladenine. 40. A pharmaceutical composition useful for 5 treatment of a viral infection or malignant condition which comprises an effective amount of a compound of claim 1 in combination with a pharmaceutically acceptable carrier. 0 41. A pharmaceutical composition useful for treatment of a viral infection or which comprises an effective amount of a compound of claim 9 in combination with a pharmaceutically acceptable carrier. 42. The composition of claim 9 in unit dosage form. 43. The composition of claim 27 in unit dosage form. 44. A method for treatment of parasitic infection or malignant condition which comprises administering to an individual in need of such treatment an effective amount of a compound of claim 9. 45. A method for treatment of viral infection which comprises administering to an individual in need of such treatment an effective amount of a compound of claim 9. 46. The oligonucleotide of claim 1 which is exonuclease stable by having 2 or more 5' methylene phosphonate linkages at both 5' and 3' terminal internucleotide residues. 47. The modified oligonucleotide of claim 1 wherein each B is independently selected from adenine, guanine, cytosine, 5-methylcytosine, aziridinylcytosine, 8- hydroxy-N°-methyladenine, thymine, uracil, pseudoisocytosine and inosine. 48. A pharmaceutical composition useful for treatment of a tumor or parasitic infection or which comprises an effective amount of a compound of claim 9 in combination with a pharmaceutically acceptable carrier. 49. A pharmaceutical composition useful for treatment of a tumor or parasitic infection which comprises an effective amount of a compound of claim 27 in combination with a pharmaceutically acceptable carrier. 50. The compound of claim 9 having the formula (IX): IX wherein Y has the meaning defined in claim 9; and B is selected from the group consisting of guanine, adenine, cytosine, thymine, uracil, inosine, xanthine, hypoxanthine, 5-iodouracil, 5-iodocytosine, 5- ethyluracil, 5-propynyluracil, 5-fluorouracil, 5- trifluoromethyluracil, 5-bromovinyluracil, 5- propynylcytosine, 5-raethylcytosine, 8-hydroxy-N δ -methyladenine, aziridinylcytosine, 2-aminopurine, 2,6-diaminopurine, 3-deazaguanine, 6- chloropurine, 7-deazaadenine, 8-bromoadenine, 7- deazaguanine, 3-deazaadenine, 6-hydroxylaminopurine and 6-thiopurine. 51. The compound of claim 50 wherein B is guanine. 52. The compound of claim 50 wherein B is adenine. 53. The compound of claim 50 wherein B is cytosine. 54. The compound of claim 50 wherein B is thymine. 55. The compound of claim 50 wherein B is uracil. 56. The compound of claim 50 wherein B is inosine.

Inventors: BISCHOFBERGER NORBERT W, BUHR CHRIS, FROEHLER BRIAN, MATTEUCCI MARK, BISCHOFBERGER, NORBERT, W., BUHR, CHRIS, FROEHLER, BRIAN, MATTEUCCI, MARK
Applicants: GILEAD SCIENCES INC, GILEAD SCIENCES, INC.
Application year: 1992
Main classification: C07H19
IPC codes: A61K31, A61P31, A61P33, A61P35, C07H19, C07H21