2',5'-NUCLEOTIDE ANALOGS AS ANTIVIRAL AGENTS

Abstract: There is provided the use of a nucleotide analog of formula (I) wherein R1 represents (i) a hydrogen atom, (ii) a 2' or 3'-P-thionucleotidyl residue conjugated at its 5' position with an acyl group, (iii) a phosphoryl group, a P-thiophosphoryl group, a PO2R<2>H group optionally esterified with a linear or branched, cyclic or acyclic aliphatic hydroxy alkyl group having from 1 to 6 carbon atoms or with a lipophilic moiety or (iv) an acyl group; R<2> represents a C1-C6 alkyl group or hydrogen atom, and the pharmaceutically acceptable salts thereof, in the manufacture of a medicament for use as an antiviral, antitumour, immunomodulatory, interferon-enhancing or interferon-inducing agent. Some compounds of formula (I) are new. A process for their preparation and pharmaceutical compositions comprising them are also provided.

Description: 2' ,5'-NUCLEOTIDE ANALOGS AS ANTIVIRAL AGENTS. The present invention relates ' to the use of nucleotide analogs having 2' ,5' unusual internucleotide linkage as antivirals, antitumors, immunomodulators, enhancers of interferons or interferon inducers, to new diribonucleotide analogs and to a stereoselective route for their preparation. The recent literature describes the "2-5A system" as the main mechanism by which inte.rferon promotes an antiviral state and carries on its activity resulting in the degra¬ dation of viral mRNA and therefore in the inhibition of protein synthesis. Interferon seems to provide a membrane-mediated signal to a healthy cell with risk of viral infection. Such a signal leads to a level increase of the enzyme 2-5A Synthetase that is activated after infection by the ds RNA formed during the virus life cycle or introduced by the virus itself. This enzyme generates 2' ,5'-oligoadenylates (2-5A) from ATP and these unusual oligonucleotides activate a 2-5A-dependent endonuclease, responsible for the degradation of single strand RNA and hence for the inhibition of protein synthesis. 2',5'-Oligoadenylates (2-5A) are oligoribonucleotides where 3 to 15 adenosine units are linked by phosphate moieties unusually between the position 2' and 5' , besides they have a triphosphate capping at the 5'end. Moreover 2-5A system seems to be involved in cell regulation and differentiation. In any case the level of 2-5A has a fundamental importance and the regulation is obtained through a formation-degradation balance. While the formation is provided by 2-5A Synthetase, 2-5A are degraded by the specific enzyme 2'-Phosphodiesterase (2'-PDE) that starts its action at the 2'end of the oligo er chain and gives 5'-AMP and 5'-ATP (B. LEBLEU AND J. Content, in "Interferon 4" (I. Gresser ed. ) pp. 47-94, Academic Press - New York, 1982). Selectivity of action of the 2-5A system for the inhibition of viral translation respect to the cellular one is thought to be due to the localization of the system activity within the cell, the stimulation by ds RNA being restricted to the particular area where it appears. From this picture a known therapeutic approach for an antiviral action is the utilization of exogenous 2-5A analogs, chemically modified in order to attain a more intense activation of endoribonuclease L through metabolic resistance of the analog to 2'-phosphodiesterase action (P.F. Torrence, K. Lesiak, J. Imai, M.I. Johnston and H. Sawai, in "Nucleosides, Nucleotides and their Biological Applications", J.L. Rideout, D.W. Henry, L.M. Beacham III, eds. pp. 67-115, Academic Press - New York, 1983). This approach suffers from two disadvantages: the high number of charges in the molecules renders the problem of penetration more difficult to be solved and, more importantly, activation of endoribonuclease by exogenous agents could be devoid of any specificity of antiviral action. The object of the present invention is to provide compounds that increase the level of endogenous 2-5A by acting on the formation-degradation balance through the inhibition of the 2'-phosphodiesterase (2'-PDE) . In such a way the alteration will still depend on the activation • of 2-5A synthetase by infectious particles keeping the localization of action within particular region of the cell and hence maintaining selectivity against viral agents. Moreover the less charged or even compounds of the present invention render the obstacle of cell penetration easier to be overcome. The present invention relates to the use of nucleotide analogs having 2' ,5' unusual internucleotide linkage as antivirals, antitumors, immunomodulators, -enhancers of interferons or interferon inducers having the formula I •■ • . ■ herein R x represents (i) a hydrogen atom, (ii) a 2' or 3' -P-thionucleotidyl residue conjugated at its 5' position with an acyl group, (iii) a phoshoryl group, a P-thiophosphoryl group, a P0 2 R 2 H group optionally esterified with a linear or branched, cyclic or acyclic aliphatic hydroxy alkyl group having from 1 to 6 carbon atoms or with a lipophilic moiety or (iv) an acyl group; R 2 represents a C x -C 6 alkyl group or hydrogen atom,- and the pharmaceutically acceptable salts thereof. In another aspect the present invention provides a compound of the formula I' I' wherein R_ is as above defined and R 3 has the same meanings of i above defined but not hydrogen atom, P-thiophosphoryl or phosphoryl group. In the present specification, the definition C a .-C β alkyl group encompasses linar cr r_τ±eά r ac^lir rr c-jrli- aiy-yl <j—-— r fr-r etaiple πεthyl, ethyl, jrcpyl, n-tu yl, s-cut-yl, i-^rc yi, tεrt-faΛyl, aτyl, c cl hexyl, ry-it ^ -ii yl . v m R3 cr R 1 χfcμLt≤fci.1 a P-1±iα^1e tidyl re- be, h=y are prefetctiLy a resid-ε. Preferred lipophilic moieties are cholesteryl group or glycerol esterified with saturated on unsaturated long chain fatty acids having from 6 to 20 carbon atoms. Such fatty acids are preferably palmitic or miristic. The C x -C 6 alkyl phosphonyl group which R_ and R 3 may represent is preferably methylphosphonyl group. The acyl group which R 3 or Ra. may represent is preferably the residue of (i) an aliphatic carboxylic acid with linear or branched, acyclic or cyclic skeleton having from 1 to 20 carbon atoms for example 6 to 16 carbon atoms, preferably octanoic, cyclohexylacetic or palmitic acid; (ii) a difunctional acid, more preferably oxalic, carbonic, phosphoric, thiophosporic, malonic or succinic acid, in which the other acidic moiety is esterified with a Ci-Cβ hydroxy alkyl group or with a lipophilic moieity as defined above; (iii) carboxylic acid endowed with positive charged part at physiological pH and with or without lipophilic group, preferably non-α aminoacids, more preferably B-aminopropionic and 3- or 6-aminocaproic acids, or α-aminoacids of basic nature, more preferably lysine, or a short peptide chain, for example of two to six, preferably two to four, amino acid residues, and containing at least one basic residue like lysine. In the case of the basic cC-amino acid or the short peptide chain, the terminal £-amino group is optionally protected. Preferred terminal nitrogen atom protecting groups include for yl, acetyl, trifluoroacetyl, propionyl, benzoyl; benzyloxycarbonyl (Z), 4-nitrobenzyloxycarbonyl, 4-methoxybenzyloxycarbonyl, 2,4-dichlorobenzyloxycarbonyl, 2-bromobenzyloxycarbonyl, 9-fluorenylmethoxycarbonyl (F oc) , 3,5-dimethoxy-α, ' α'-dimethylbenzyloxycarbonyl (Ddz) t-butoxycarbonyl, 1-methylcyclobutoxycarbonyl, adamtanyloxycarbonyl, isobornyloxycarbonyl; trityl, benzyl, methyl and isopropyl groups. Preferred peptidic chain are Lys-Gly and Lys-Phe, optionally protected by benzyloxycarbonyl group. Salts of compounds according to the invention with pharmacuetically acceptable acids or bases are included. Such acid addition salts can be derived from a variety of inorganic and organic acids as sulphuric, phosphoric, hydrochloric, hydrobromic, hydroiodic, nitric, sulphamic, citric, lactic, pyruvic, oxalic, maleic, succinic, tartaric, cinnamic, acetic, trifluoroacetic, benzoic, salicyclic, gluconic, ascorbic and related acids. Such base addition salts can be derived from a variety of inorganic and organic bases as sodium hydroxide, potassium hydroxide, diethylamine, triethylamine and dicyclohexylamine. It is to be noted that when the phosphorothioate moiety is under the form of a salt, the partial or whole negative charge may be located on the oxygen atom or on the sulphur atom or in equilibrium between them. It is also to be noted that, owing to the presence of the asymmetric phosphorous atoms, the compounds of the invention may be diastereomer mixture or pure diastereomer having S„ or -p configuration. Preferably, at least one of the phosphorothioate groups is of the Sj, configuration, more preferably the phosphorotiate group adjacent to the 2'/3' terminal adenylate mojety is of the Sj, configuration. In the following table I the most preferred compounds according to the present invention are shown. TABLE 1 where = 0 il CH 3 (CH 2 ) 6 -C CH, The invention further provides a process for preparing a compound of the formula I' as above defined which comprises introducing the desired R 3 group at the 5' position of an appropiately protected compound of the formula II II wherein Z represents hydrogen or a protective group such as an acyl group, preferably a benzoyl group; X represents any of the protective groups generally used for the hydroxyl group like ^ acyl, trityl, tetrahydropyranyl, ethoxytetrahydropyranyl, allyloxycarbonyl, p-nitrophenylethylcarbonyl, p-nitrophenylethylsulphonyl, tert.butyldimethylsilyl, 1,3-tetraisopropyldisiloxyl, the last two being the preferred ones; Y represents hydrogen or just a negative charge (that is diester moiety under salt form) or an usual protecting group of the phosphate function like for example O-chloro- phenyl, methyl, trichloroethyl, allyl, p-nitrophenylethyl, β-cyanoethyl, unprotected and hence diester form being the preferred one, and then removing the protecting groups. The preparation of the compounds of the formula I' wherein R 3 is a 2' or 3' P-thionucleotidyl residue conjugated at its 5' position with an acyl group may be carried out from 2' , 5' phosphorothioate trimers. SCHEME As shown in scheme 1, the 2', 5' -phosphorothioate trimers are obtained by allowing the 2' -hydrogenphosphonate of a properly protected adenosine like compound 2 to react with a properly protected 2', 5' -diadenqsyl phosphorothioate like for example compound 7 where base amino groups can be conveniently unprotected as well as the phos ' phorothioate moiety. In this process the only necessary protections are for the hydroxyl groups other than the 5'-hydroxyl group that has to be involved in the esterification. The coupling reaction is performed by adding a hindered acyl chloride as condensing agent, preferably pivaloyl chloride or adamantoyl chloride in a solvent like pyridine. The process is completed by thio-oxidation performed with elemental sulphur, better a suspension of suphur in pyridine or other known thiooxidizing agents. If the configuration of the starting dimer phosphorothioate is S p; the trimer is obtained in high yield (85% in the example) as a mixture of diastereomers ^, , S v and S- p , S.p with a ratio 2:8, that is with a marked prevalence of the last one. These diastereoisomers can be separated by silica-gel column chromatography and independently converted to the protected intermediate trimers by conjugation of the 5' position, after detritylation, with an appropriate group, like a phosphoric or carboxylic acid, as described hereinbelow for the dinucleotides. The final compounds are obtained by deprotection with known methodologies like for example treatment with hydrazine in pyridine/acetic acid for debenzoylation, treatment with an acid like trifluoroacetic acid in methylene chloride for detritylation and treatment with tetrabutylammonium fluoride in tetrahydrofuran and pyridine for desilylation. The preparation of the compounds of the formula I' wherein R 3 is a P0 2 R 2 H or a P-thiophosphoryl group esterified with a lipophilic moiety is outlined in Scheme 2 as an example of the process. A proper dimer with available 5'-hydroxyl group and with N 6 -protected or N 6 -unprotected bases, like for example 5 or 7 is made to react with 3-H-phosphonate of cholesterol 21 obtained from cholesterol by reaction with a suitable phosphorylation mixture such as PC1 3 , triazole and N-met- hylmorpholine. The coupling between the nucle'otidic dimer 5 or 7 and cholesterol 3-Hτphosphonate 21 can be performed by using a hindered acyl halide like adamantoyl chloride as activacting agent followed by thiooxidation with a proper reagent like for example elemental sulphur. By this process the base-deprotected dinucleotide 7 directly gives the (3-cholesteryl)thiophosphoryl derivative 23, while the base-protected dinucleotide 5 gives the inter¬ mediate 22 that in turn can be deprotected to 23 by basic treatment like ammonia in pyridine. Desilylation of the intermediate 23 for example by treatment with tetra¬ butylammonium fluoride affords the final compound 24, 5'-0-[ (3-cholesteryl)thiophosphoryl] adenosyl(2'—>5' )thiophosphoryladenosine. Analogously a proper dinucleotide with available 5'-hy¬ droxyl group like 7 can be coupled with the H-phosphonate of 1,2-dipalmitoylglycerol 26 that can be obtained from 1,2-dipalmitoylglycerol in analogous manner as 21. The coupling can be performed by adding a condensing agent, for example a hindered acyl chloride preferably pivaloyl chloride or adamantoyl chloride in pyridine, and can be followed by oxidation with a I_ solution to get the pho¬ sphate moiety or by oxidation with a proper sulphur con¬ taining reagent, like for example elemental sulphur, to get the phosphorothioate moiety like in the dipalmitoyl- thiophosphatidyl derivative 27. The last intermediate can be desilylated by known procedures, like using tetra¬ butylammonium fluoride, to give 5'-0-[ (1,2-dipa- lmitoylglyceryl)thiophosphoryl]adenosyl(2'—>5' ) thiop- hosphoryladenosine (28) as final compound. A proper dinucleotide with available 5'-hydroxyl group. like 7, can also be made to react with an alkyl- phosphonylating mixture like for example a mixture compo¬ sed by methylphosphonyldichlόride, triazole, triethylamine and pyridine to afford the methylphosphonyl derivative 29. This intermediate can undergo a proper desilylating tre¬ atment, like with tetrabutylammonium fluoride * , to give the final product 30, namely 5,'-O-methylphosphonyladenosyl (2'—>5' )thiophosphoryladenosine. T- ' O preparation of the compounds of the formula I' wherein R-, represents an acyl moieties is illustrated in scheme 3 and can be performed on either base-protected oligonucleo- ι-.Lde (like 5) or base-unprotected oligonucleotide (like 7 or 11) using for example a DCC-mediated esterification. As an example cholesterol or other cholesteryϊ derivatives can be properly functionalized by preesterification with a dicarboxylic linker like succinic acid to intermediate 31 that can be made to react with the P-thio-dinucleotide 7 in the presence of a condensing reagent like dicyclohexylcarbodiimide (DCC) with dimethyl- a inopyridine and/or hydroxybenzotriazole at least in catalytic amount in pyridine or other proper solvent like methylene chloride at a temperature between -30°C and 50°C preferably at room temperature and during a period lasting at least 30 minutes to 48 hours preferably 24 hours. Afterward evaporation of the solvent and dissolution of the residue in a chlorinated solvent like methylene chloride causes the formed dicyclohexylurea to be insoluble and filtration provides its elimination. Aqueous washing of the organic solution and evaporation of the solvent at atmospheric or reduced pressure give rise' to a crude product 32 that can either be purified by column chromatography or directly undergo desilylation procedure to the final product 37, namely 5'-0-[ (3-cholesteryl) succinyl]adenosyl(2'—> 5' )-S^-thiophosphoryladenosine. An analogous DCC-mediated esterifying procedure can be applied to a base unprotected thiophosphoryl dinucleotide like 11 for the conjugation with simple carboxylic acid having linear or branched skeleton containing or not also 14 SCHEME? 35 R=CH 3 (CH 2 ) 14 - 38 R=CH 3 (CH 2 ) 6 - as as example __ examples 39 R= _XH 2 - 40 R=CH 3 (CH 2 ) 14 - cyclic or aromatic structures; palmitic, octanoic and cyclohexylacetic acids being described examples. The above described procedure ' gives in these cases intermediates 33, 34 and 36, that can be desilylated by tetrabutylammonium fluoride to 5'-O-octanoyladenosyl ( 2'—>5' )-Sjp-thiophosphoryladenosine (38), 5'-O-cyclohexyl acetyladenosyK2'—>5' )-S^-thiophosphoryladenosine (39) , and 5'-O-palmitoyladenosyl(2'—>5' )-Sp-thiophosphorylade- nosine (40) respectively. The same esterification proce- dure can be performed on a base-protected P-thiooligonucleotide like 5 obtaining in this case a base-protected intermediate like 35 that successively has to undergo selective deacylation at the base without concomitant lysis of the ester bond just formed. This can be done by reaction with aqueous hydrazine in pyridine-acetic acid obtaining for example intermediate 36 from 35. Aminoacyl and peptidyl derivatives are synthetically analogous cases. Conjugation through esterification of the nucleotidic 5'-hydroxyl group with an aminoacid shows to be a process feasible in the same manner as above explained for lipophilic derivative, as outlined in scheme 4, both in the case of α- or non-α-aminoacid. Besides the optional α-aminogroup, it is necessary to have free amino groups in other positions of the acyl moiety like B, * , δ or ε position for our purposes as above explained, and if present the α-aminogroup in the final product can be free or remain protected, for example by benzyloxycarbonyl group. For these reasons the selected examples for the process outlined in scheme 4 are esterifications with β-aminopropionic acid, with ε-aminohexanoic acid and N- a-benzyloxycarbonyllysine where during the process the non-α aminogroup can be conveniently and temporarily protected with t.butoxycarbonyl group as non-limiting example. So aminoacylation of the 5'-hydroxyl group of 2' ,5'-P-thio oligonucleotide can be accomplished on either base-protected or base-unprotected nucleotidic substrates. SCHEME 4- PREPARATION OF AMINOACYL DERIVATIVES like respectively 5 and 7. In the first case the esterification step is followed by selective base deprotection, effected by hydrazine treatment as above mentioned, to convert compounds of type 41 to compounds of type 42. In any case the esterification procedure using aminoprotected aminoacids can be performed * as described above by using dicyclohexylcarbodiimide with dimethylaminopyridine and/or hydroxybenzotriazole or other similar activating agents in a dry polar organic solvent like pyridine or methylene chloride at a temperature between -30°C and 50°C preferably at room temperature for a period lasting at least 30 minutes to 96 hours depending on the case testing the reaction mixture by TLC. Replacement of pyridine with a solvent like methylene chloride is useful to allow to filter off most of the formed dicyclohexylurea. In any case usual work-up gives a crude compound that can be either used for the subsequent step or purified by column chromatography. So the esterification step and the hydrazine treatment for base deprotection can be made either in this order or in the reverse order to give as example the protected β-aminopropionyl derivative 42a, the protected ε-aminohexanoyl derivative 42b, and the protected N^-benzyloxycarbonyllysyl derivative 42c. The deprotection steps, namely the t.butoxycarbonyl group removal for example by trifluoroacetic acid treatment and the desilylation performed for example by tetrabutyl¬ ammonium fluoride treatment, have necessarily to follow in this order and not in the reverse one to give 5'-0-(β- aminopropionyl)adenosyl(2'—>5' )-Sy-thiophosphoryladeno- sine (43a), 5'-0-(ε-ami o ex noyl)adenosγl(2 , —>5')-S*.,- thiophosphoryladenosine (43b), and 5'-O-[(N^-benzyloxy- carbonyl)lysy1]adenosyl(2'—>5' ) -S_.-thiophosphoryladeno- sine (43c) respectively as final compounds. Similarly an oligopeptide chain can also be conjugated to an oligonucleotide as appears in these examples through the formation of an ester bond. As shown by the examples outlines in scheme 5, ester-type conjugation can be effected either on base-protected or base-unprotected nucleotidic substrates also' in this case. Two possible routes are exemplified in scheme 5. Elongation of the peptidic chain can be either done before conjugation with the oligonucleotide (like in route A) o'r after the coupling of the carboxy-terminal aminoacid (like in route B) and adding sequentially the other aminoacids using the known methodologies for peptide synthesis. In the last case what is new and it is here proved is the fact that these methodologies for peptidic chain elongation are largely compatible with the unprotected base amino group and with the unprotected phosphorothioate moiety present in the substrate along the whole synthesis. So it shows to be a simple and versatile synthetic methodology for the target molecule here exemplified and for similar ones, also having the advantage of the possibility to diversify the synthetic process for the aminoacid sequence in the last steps. This process is also object of this patent. Analogously to the coupling with a single aminoacid the esterification between a nucleotidic 5' hydroxyl group and a peptide can be performed by treatment with dicyclohexyl- carbodiimide or other carbodiimides in the presence of catalyst like dimethylaminopyridine or hyd- roxybenzotriazole as above explained. Such treatment can give for example base-protected peptidyl conjugates like 44 abd 45 (from 5) or directly base-unprotected peptidyl conjugates like 46 and 47 (from 7). In the first case base debenzoylation to the last compounds can be effected by treatment with aqueous hydrazine as above described. As outlined in scheme 5 the same peptidylester intermediates 46 and 47 can be obtained as examples through the route B that involve a first aminoacid conjugation even starting from base-unprotected P-thio-(2' ,5' )oligonucleotide like 7 to give a monoaminoacyl intermediate like 48, as a further example of the case already illustrated in scheme 4. 19 Subsequent butoxycarbonyl removal by trifluoroacetic acid treatment give an intermediate like 49 in which an amino group is available for peptidic chain elongation. So peptidic bond for example with dicyclόhexylcarbodiimide in the presence of hydroxybenzotriazole in methylene chloride giving for example a peptidic product like 47 in a selective manner although the presence of unprotected base amino groups and an unprotected phosphorothioate moiety. In any case the final deprotection treatments like t.butoxycarbonyl group removal by trifluoroacetic acid and desylalation by tetrabutylammonium fluoride in the necessary order as above mentioned provide the final compounds, namely 5'-0-[ (N^-benzyloxycarbonyD-L-lysyl- glycyl]adenosyl(2'—>5' )-S^-thiophosphoryladenosine (50) and 5'-0-[(N β -benzyloxycarbonyl)-L-lysγl- L-ρhenylalanyl]adenosyl(2'—>5' )-Sj,-thiophosphoryladenosi- ne (51) as representative examples. SCHEME 5 The nucleotides of the formula I wherein R 1 represents hydrogen atom a p-thiophosphoryl or a phosphoryl group and the starting compounds of the formula II are known compounds or may be prepared according to known methods, see for example WO 89/03683. Also the scientific paper "High stereoselectivity in the formation of the inter-ribonucleotide phosphorothioate bond", of C. Battistini et al, presented at the " -*- International Round Table-Nucleosides, Nucleotides and their Biological Applications" (July 30-August 3, 1990, Uppsala - Sweden), describes the preparation of the final known dimers of the formula I on the protected dimers of the formula II starting from properly protected adenosine analogs one having free the 2' hydroxyl group and the other having the 2' and 3' positions protected and the 5'-hydroxyl group available for substitution. As an example 6-N-benzoyl-5'-0-dimethoxytrityl-3'- O-t.butyldimethylsilyladenosine 1, is made to react with a P (III) phosphorylating agent, like phosphorus trichloride or better what is obtained by mixing phosphorus trichloride, triazole, N-methylmorpholine in dichloromethane. The resulting 2'-H-phosphonate 2 is coupled with a 2', 3'-0, 0-diprotected nucleoside like 6-N-benzoyl-2' , 3'-0-O-bis-t.butyldimethylsilyl adenosine 3 by adding a condensing agent, for example a hindered acyl chloride, preferably pivaloyl chloride or adamantoyl chloride in pyridine. This coupling procedure has to be followed by an oxidation stage performed with elemental sulphur (S β ) or better a suspension of sulphur in pyridine, or other thiooxidizing agent. This process gives high yield of the 2', 5'-phosphorothioate dimer 4 as a mixture of diastereomers, differing for the phosphorus configuration, in a ratio 8:2, where S„ means a configuration S at the phosphorus atom and R-p means a configuration R at the phosphorus atom. These diastereomers can be separated by silica-gel column chromatography and they can independently be deprotected by known methodologies either completely to the final dimers S^-15 and R.p-15, oi partially to proper intermediates useful for further conjugation to the 5'-position. As a matter of fact compounds S.p-4 or Rp-4 can be detritylated by acids at the position 5' of the first ribose to have the corresponding S.p or R.p form of the benzoylated dimer 5 ready for further reactions at the first 5' position. Alternatively, debenzoylation of 4 can afford dimers of type 6, whose detritylation gives debenzoylated dimers 7 (S-p or R„) , with only the first 5' position available for further synthetic operations. By this methodology the S^-stereo- selectivity of the coupling can be modulated by the nature of the protecting groups at the first 5' and 3' positions and the second 3' and 2' positions (first and second being referred to the conventional way of reading a molecule of this type, from the 5' and to the 2', 3' end). This is shown by two other examples, one being the coupling of the above mentioned 2'-H-phosphonate 2 with a different 5' component (8) having the tetraisopropyldisiloxane moiety as protecting group for both the positions 2' and 3' . The coupling reaction and the thiooxidations stage, performed as mentioned above, gives the protected 2' , 5'-phosphorothioate dimer 9, again with S^-stereoselectivity, namely with an S & to „ ratio of 7:3. Analogously the process has been applied by using 6-N-benzoyl-3' , 5'-0-(tetraisopropyldisiloxane- 1,3-diyl) adenosine 12 as 2' component. Its phosphorylation, performed as mentioned above, gives the corresponding H-phosphonate derivative 13, whose coupling with δ-N-benzoyl-2' , 3'-0-{tetraisopropyldisiloxane-l,3- diyl) adenosine (8) and subsequent thiooxidation affords the 2' , 5'-phosphorothioate dimer 14 with a complete S^,- stereoselectivity. A complete deprotection of the dimer 14 by using well known methodologies gives the final dimer (S p ,)-P-thioadenylyl(2' , 5' )adenosine S^-15. Conveniently intermediate 9 (S„ or R„) has been partially deprotected by acid-promoted detritylation to the corresponding derivative 10 fS^ or ^.) having the 5' position the only free hydroxyl group, as a useful intermediate. Synthetically useful also is the debenzoylated analog 11 (either in S p or R^ configuration) easily obtainable from 10. All the partially deprotected dinucleotide analogs, benzoylated or not, mentioned in the examples (5, 7, 10, 11) are key intermediate for further synthetic modifications aiming to 5'-elongation or conjugation, but they can also be conveniently converted to the final 2', 5'-phosphorothioate dimers S^-15 and R^-15 by known methodologies. 25 BIOLOGICAL ACTIVITY Th compounds object of this patent can be useful as an- tivirals, antitu orals and/or immunomodulators and/or po¬ tentiating agent of interferon (IFN) action. As a representative example we mention the case of comp¬ ound S-p-15 that shows activity especially providing a way of increasing penetration into the cells like for example the use of liposomes as carrying agents. Indeed "in vi¬ tro" tests on partially trypsinized cells or per eabilized cells show a 50% inhibiting dose of 150-200 uM against herpes simplex virus type I (HSV-1), strain (see table 1). TABLE 1 - Effect pf S^-15 on the replication of HSV-1 (strain HF) on Hep2 cells, permeabilized by Tween 80 (average values of four experiments) Sjp-lS concentration aa % inhibition 400 uM 80 200 μM 60 100 uM 20 The same compound (Ss,-15) shows a marked potentiating ac- tion towards interferon (IFN); in fact it potentiates IFN 4 times on normal cells (Hep2, monolayer) and 8 times on partially trypsinized cells (suspension) against Semliki Forest virus (SFV). The maximum rolered dose of S^-15 for Hep2 cells is 400 UM- Other examples of "in vitro" activity against enveloped DNA viruses like HSV-1 are given by the lipophilic derivatives like the cholesterylsuccinylderivative of the Ss, dinucleotide 37 and the palmitoyl derivative of the S P dinucleotide 40 showing MIC (minimum inhibitory concentration) of 25 μM and 12.5 uM respectively. These compounds are also active against RNA viruses both enveloped and non-enveloped. As a matter of fact compound 37 has a MIC of 12.5 μM against HRS virus (human respiratory syncytial virus) , that is a paramixovirus and also 12.5 μM against SFV (Semliki Forest virus) belonging to the family togaviridae; both being examples of enveloped RNA viruses. The same compound has activity against enteroviruses like Coxsackie B, a non-enveloped RNA virus, with a MIC of 25 μM, evaluating the cytopathic effect. Also the palmitoyl derivative 40 is an example of wide spectrum antiviral showing a MIC of 12.5 μM against HSV-1; 10 μM against HRS; 37 μM against SFV; 12.5 μM against Cox B (Coxackie B virus); 7 μM against Col SK (encephalomyocarditis Columbia SK virus) that is a non-enveloped RNA virus, by evaluation of the cytopathic effect. Compound 40 also showed an activity against retroviruses like MoSV (Moloney sarcoma virus) with ID 5σ 12.5 μM for foci formation. Table 2 summarizes the activity data of the example compounds 37 and 40. 27 For example the dipalmitoylphosphatidyl derivative 28 shows a MIC of 6.2 μM against the cytopathic effect of HRS (human respiratory syncytial) ' virus. As other examples of activity against RNA viruses we mention the activity of 3-aminoρropionyldinucleotide 2' ,5'-s^-phosphorotioate 43a against Coxsackie B virus and Columbia SK virus with MIC.37 μM and 50 μM respectively. Also α-aminoacyl derivatives are endowed with antiviral activity as exemplifies by the α-carbobenzoxylysyl derivative with the phosphorothioate moiety having the R configuration (R-p-43c) that inhibits the cytopathic effect by HRS virus with a MIC of 50 μM and by Coxsackie B virus with a MIC of 37 μM. On the other end the isomer with S ∑ , configuration at the phosphorothioate moiety, namely Sp-43c inhibits the cytopathic effect due to Columbia SK virus at 75 μM concentration. The compounds of the invention are useful in methods of treatment of the human or animal body by therapy. They have antiviral activity and can be used against RNA viruses in humans and other mammals. They show also antitumor and immunomodulating activity and can therefore be used as anticancer agents and immunomodulators. For these purposes, they can be formulated into oral dosage forms such as tablets, capsules and the like. The present invention provides a pharmaceutical composition comprising as active ingredient a compound of formula (I) or a pharmaceutically acceptable base addition salt thereof, together with a pharmaceutically acceptable carrier or diluent. The compounds can be administered alone or by combining them with a conventional carrier or diluent, such as magnesium carbonate, magnesium stearate, talc, sugar, lactose, pectin, dextrin, starch gelatin, tragacanth, methyl cellulose, sodium carboxymethyl cellulose, low melting wax, cocoa butter, and the like. Flavoring agents, solubilizers, lubrificants, suspending agents, binders, tablet-disintegrating agents and the like may be employed. The compounds may be encapsulated with or 28 without other carriers. In all cases the proportion of active ingredients in said compositions both solid and liquid will be at least sufficient to impart antiviral activity thereto on oral administration. The compounds may also be injected parenterally, in which case they are used * in the form of a sterile solution containing other solutes, for example, enough saline or glucose to make the solution isotonic. Typically, a dose of 20-2000 mg of a compound of the invention may be administered per day to a human under treatment. The compounds can be administered as an aerosol with particles small enough to reach the lower respiratory tract (mass median aerosol diameter = 1-2 μ) , and can be delivered via an oxygen hood or tent for treatment of severe lower respiratory tract infections due to respiratory syncytial virus or to other paramyxo or to myxoviruses. The following preparations and examples illustrate the invention without limiting it. In these examples whether more ribose rings are present in the molecule, NMR data are given indicating with A, B, C, ... respectively the first, second, third .. ribose ring going from the 3' end to the 5' end of the oligonucleotide molecule, i.e. from the right bottom to the left top of the structure as drawn on the schemes. Preparation 1 N s -Benzoyl-3'-O-(t.butyldimethylsilyl)-5'-O-(dimethoxytry- tyl)-adenosine-2'-(hydrogenphosphonate) , triethylammonium salt (2) 1,2,4-Triazole (8.76 g, 126.8 mmol) was added to a stirred solution of phosphorus trichloride (3.32 ml, 38 mmol) and N-methyl-morpholine (42 ml, 380 mmol) in anhydrous methylene chloride (300 ml), at room temperature. After 30 minutes the reaction mixture was cooled to a 0°C and N 6 -Benzoyl-3'-O-(t.butyldimethylsilyl)-5'-0-(dimethoxy trityl)-adenosine ( 1 ) (6 g, 7.62 mmol), (dried by coevaporation with acetonitrile) in anhydrous methylene chloride (40 ml) was added- dropwise over 20 minutes, stirred for 10 minutes, poured into 1.0 M aqueous triethyl ammonium hydrogen carbonate (TEAB, pH 8.5), shaken and separated. The aqueous phase was extracted with methylene chloride and the combined organic phase was dried (Na 2 S0 4 ) and concentrated. Purification by silica gel column chromatography (eluent: methylene chloride/methanol/ triethylamine 90:10:0.2) followed by TEAB extraction gave the title compound (2) (6.53 g, 90% yield). 1 H-NMR (200 MHz, CDC1 3 ): 6 = 9.1 (bs, 1H, NHCO) ; 8.74, 8.37 (two s, 2H, adenine H's): 8.0-6.7 (m, 18 H, aromatic H's); 6.89 (d, J = 626.9 Hz, 1H, PH) ; 6.32 (d, J = 5.7 Hz, 1H, HI'); 5.39 (ddd, J = 10.3, 5.7, 4.3 Hz, 1H, H2'); 4.61 (dd, J = 4.3, 4.0 Hz, 1H, H3' ) ; 4.25 (dt, J = 4.0, 4.4 Hz, 1H, H4'); 3.76 (s, 6H, 2 QCH„) ; 3.43, 3.28 (two dd, J = 10.5, 4.4 Hz, 2H, CH 2 -5'); 0.86 (s, 9H, SiC(CH 3 ) 3 ); 0.13, 0.05 (two s, 6H, 2 SiCH 3 ); + triethylammonium signals. 3i P NMR (81 MHz, DMSO-d 6 ): δ = 1.86 (two d, J = 10.3, 626.9 Hz) (H 3 P0 4 as external reference) FAB-MS : m/z 852 ( [M+H] " *) . Preparation 2 (R P ) and (S ^ )-N g -Benzoyl-3'-0-(t.butyldimethylsilyl)-5'-O- (dimethoxytrityl)-P-thioaden iyl-(2'—>5' )-N s -benzoyl-2' ,- 3'-O-(di-t.butyldimethylsilyl)-adenosine, triethylammonium salt (4) N 6 -Benzoyl-3'-O-(t.butyldimethylsilyl)-5'-O-(dimethoxytri- tyl)adenosine-2'-(hydrogenphosphonate) (2) , triethylam¬ monium salt (6.36 g, 6.67 mmol) and N β -benzoyl-2' , 3'-0-(di-t.butyldimethylsilyl)-adenosine (3 (4.0 g, 6.67 0 mmol) were first coevaporated three times with anhydrous pyridine, then dissolved in anhydrous pyridine (50 ml). Pivaloyl chloride (2.05 ml, 16.67 mmol) was added and the resulting solution was stirred at room temperature for 45 minutes. Sulfur (2.4 g) and after 3 hours triethylamine 5 (30 ml) were added. The reaction mixture was stirred at room temperature for 30 minutes, then the solvent was evaporated. The residue was diluted with water and extracted with methylene chlo¬ ride. The combined extracts were dried (Na 2 SO « ) and con- o centrated. Purification and separation of the diastereoisomers (_4) were accomplished by silica gel column chromatography (eluent: methylene chloride/methanol/triethylamine 90:3: 0.2). 5 The high Rf (1.87 g; TLC: Rf 0.33, methylene chloride/ methanol/triethylamine, 90:5:0.2) and low Rf (7.51 g; TLC: Rf 0.28, methylene chloride/methanol/triethylamine, 90:5: 0.2) diastereomers gave a combined yield Of 9.38 g (90%) as white solids. High Rf diastereomer (4-R P ) : ^H-NMR (200 MHz, DMSO-d β ) : 5 = 11.12, 11.11 (two s, 2H, 2 NHCOPh); 9.03, 8.69, 8.63, 8. ' 61 (four s, 4H, adenine H's); 8.0-6.7 (m, 23H, aromatic H's); 6.36 . (d, J = 4.5 Hz, 1H, Hl'B); 6.06 (d, J = 7.5 Hz, 1H, Hl'A); 5.55 (m, 1H, H2'B); 4.9-5.0 (m, 2H, H3'B + H2'A); 4.35 (d, J = * 4.6 Hz, 1H, H3'A); 4.04 ( , 1H, H4'B) .3.95 (m, 1H, H4'A); 3.8-3.6 (m, 2H, CH a OP); 3.66 (s, 6H, 2 OCH 3 ); 3.3-3.0 (m, 2H, CH 2 -5'A); 0.88, 0.81, 0.59 (three s, 27H, 3 SiC(CH 3 ) 3 ); 0.16, 0.12, 0.05, -0.14, -0.54 (5s, 18H, 6 SiCH 3 ); + triethylammonium signals. FAB-MS : m/z 1463.6 {[M-H]-). - Low Rf diastereomer (4-Sg) : H-NMR (200 MHz, DMSO-d β ) : δ = 8.92, 8.69, 8.65, 8.63 (four s, 4H, adenine H's); 8.1-6.7 (m, 23H, aromatic H's); 6.37 (d, J = 4.0 Hz, 1H, Hl'B); 6.06 (d, J = 7.5 Hz, 1H, Hl'A); 5.55 (m, 1H, H2'B); 4.93 (m, 2H, H2'A + H'B) ; 4.47 (d, J = 4.4 Hz, 1H, H3'A); 4.1-3.8 (m, 4H, H4'A + H4'B + CH 2 OP); 3.68 (s, 6H, 2 OCH 3 ) ; 3.4-3.30 (m, 2H, CH 2 -5'A); 0.88, 0.79, 0.62 (three s, 27H, 3 SiC(CH 3 ) 3 ); 0.14, 0.09, 0.07, -0.12, -0.48 (five s, 18H, 6 SiCH 3 ); + triethylam¬ monium signals. FAB-MS : m/z 1463.5 ([M-H]"). Preparation 3 3'-O-(t.Butyldimethylsilyl)-5'-O-(dimethoxytrityl)-(S P )-P- thioadenylyl-(2'—>5' )-2' .3'-Q-(di-t.butyldimethylsilyl)- adenosine, triethylammonium salt (6_) A suspension of N 6 -benzoyl-3'-0-(t.butyldimethylsilyl)-5'- -O-(dimethoxytrityl)-(S- * )-P-thioadenylyl-(2'—>5' )-N 6 -ben- zoyl-2' ,3'-0-(di-t.butyldimethylsilyl)-adenosine, tri- ethyalammonium salt (4_) (3 g, 1.914 mmol) in 30% ammonium hydroxide (300 ml) and pyridine (30 ml) was stirred at room temperature for 48 hours. The reaction mixture was concentrated and purified by silica gel column chromato¬ graphy (eluent: methylene chloride/methanol/triethylamine, 90:10:0.2) to give the title compound (6) (2.34 g, 90% yield). ^H-NMR (200 MHz, DMSO-d 6 ): δ = 8.68, 8.28, 8.19, 8.15 ( four s , 4H, adenine H' s ) ; 7 . 4-6.7 (m, 13H, aifomatic H' s ) ; 6 .33 (d, J = 4. 6 Hz , 1H, Hl'B ) ; 6. 10 (d, J = 4. 9 Hz , 1H, Hl' A) ; 5.56 (m, 1H, H2 'B) ; 4.86 (m, 1H, H2 ' A) ; 4. 57 (m, 1H, H3 'B) ; 4. 3-4.1 (m, 4H, H4 ' A + H4 ' B + CH 2 OP) ; 3 .73 (s, 6H, 2 OCH 3 ); 3.5-3.2 (m, 2H, CH 2 0-DMT) ; 0.89, 0.85, 0.77 (3s, 27H, Si-C(CH 3 ) 3 ); 0.18, 0.10, 0.07, 0.04 (four s, 18H, 6 SiCH 3 ) ; + triethylammonium signals. FAB-MS (sodium salt): m/z 1255.4 ([M-Na]-). Preparation 4 3'-O-(t.Butyldimethylsilyl)-P-thioadenyl-(2'—>5 f )-2' ,3'- -0-(di-t.butyldimethylsilyl)-adenosine, triethylammonium salt (7) A solution of trifluoroacetic acid (1.8 ml) in methylene chloride (60 ml) was added to a solution of 3'-0-(t.butyl- dimethylsilyl)-5'-O-(dimethoxytrityl)-(S P )-P-thioadenylyl- (2'—>5' )-2' ,3'-0-(di-t.butyldimethylsilyl)-adenosine, triethylammonium salt (6_) (2.34 g, 1.72 mmol) in methylene chloride (120 ml), at 0°C. After 5 minutes the reaction mixture was poured into IN aqueous triethylammonium hydro- gencarbonate (200 ml). The organic phase was separated and the aqueous phase was extracted three times with methylene chloride. The combined extracts were dried (Na 2 SO„) and concentrated. The residue was purified by silica gel co¬ lumn chromatography (eluent: methylene chloride/methanol/ triethylamine, 90:10:0.2) to give the title compound (7) (1.72 g, 95% yield). ^H-NMR (200 MHz, DMSO-d 6 ): δ = 8.45, 8.26, 8.09, 8.03 ( four s, 4H, adenine H's); 1.22, 1.20 (two bs, 4H, 2 NH 2 ); 6.06 (d, J = 6.4 Hz, 1H, Hl'B); 5.87 (d, J = 7.6 Hz, 1H, Hl'A); 5.48 ( , 1H, CH 2 OH) ; 5.31 (m, 1H, H2'B); 4.79 (dd, J = 4.5, 7.6 Hz, 1H, H2'A); 4.57 (m y 1H, H3'B); 4.47 (d, J = 4.5 Hz, 1H, H3'A); 3.92 (m, 1H, H4'A); 3.9-3.8 (m, 2H, H4'B + CH(H)OP); 3.7-3.6 (m, 1H, CH(H)OP) ; 3.6-3.4 (m, 2H, CH 2 OH); 0.88, 0.87, 0.59 (thre s, 27H, 3 SiC(CH 3 ) 3 ); 0.17, 0.05, -0.13, -0.5 (four s, 18H, 6 SiCH 3 ) Preparation 5 (Sp) and (Rp)-N e -Benzoyl-3'-Q-(t.butyldimethylsilyl)-5'-O- (dimethoxytrityl)-P-thio-adenylyl-(2'-->5' )-N β -benzoyl-2 ! ,3' -disiloxanediyl)-adenosine, triethylammonium salt (9_) N s -Benzoyl-3'-0-(t. utyldimethylsilyl)-5'-O-(dimethoxy- trityl)-adenosine-2'-(hydrogenphosphonate) , triethylammo- nium salt ( 2 ) (3.8 g, 4.0 mmol) and N β -benzoyl-2' ,3'-O- (1,1,3,3-tetraisopropyl-l,3-disiloxanediyl)-adenosine ( & ) (2.45 g, 4.0 mmol) were rendered anhydrous by evaporation of added dry pyridine and dissolved in the same solvent (35 ml) and then pivaloyl chloride (12.9 ml, 10.0 mmol) was added dropwise. After 30 minutes at room temperature sulfur (10 eq) was added and the mixture was stirred for 2.5 hours. The reaction mixture was quenched by adding triethylamine (5 ml), evaporated under reduced pressure and the residue was dissolved in ethyl acetate. The organic layer was washed with water and evaporated under vacuum. Purification and separation of the diastereomers Rp and Sp (9) were accomplished by two successive chromatographies on silica gel performing a linear gradient from ethyl acetate to ethyl acetate/methanol 90:5. The high Rf(Rp) (1.0 g, 18%, TLC Rf 0.47, ethyl acetate/ methanol 90:5) and the low Rf(Sp) (2.5 g, 42%, TLC Rf 0.33 ethyl acetate/methanol 95:5) diastereomers (9_) gave a combined yield of 3.5 g (60%) as white solids. I-Sp: "-H-NMR (200 MHz, DMSO-d β ): δ = 11.14, 11.19 (two s, 2H, 2 NHCOPh); 8.89, 8.71, 8.64 (three s, 4H, adenine H's); 8.0-6.7 (m, 23H, aromatic H's); 6.36 (d, J = 4.0 Hz, IH, Hl'B); 6.10 (d, J = 6.4 Hz, IH, Hl'A); 5.53 (m, IH, H2'B); 5.13 (dd, J = 4.8, 6.4 Hz, IH, H2'B); 4.94 (m, IH, H3'B); 4.76 (m, IH, H3'A); 4.2-3.7 (m, 4H, H4'A + H4 * 'B + CH 2 OP) ; 3.68 (s, 6H, 2 OCH 3 ); 3.3-3.0 (m, 2H, CH 2 ODMT) ; 1.2-0.8 (m, 37H, SiC(CH 3 ) 3 + 4 Si-CH(CH 3 ) 2 ) ; 0.10, 0.06 (two s, 6H, 2 SiCH 3 ) FAB-MS: m/z 1477.9 ([M-H] " ). 9-Rp: H-NMR (200 MHz, DMSO-d 6 ): δ = 11.2-11.1 (m, 2H, 2 NHCO0) ; 8.9-8.6 (m, 4H, adenine H's); 8.1-6.7 (m, 23H, aromatic H's); 6.34 (d, J = 4.2 Hz, IH, Hl'B); 6.12 (d, J = 5.5 Hz, IH, Hl'A); 5.51 (m, IH, H2'B); 5.12 (m, IH, H2 » A); 4.92 (m, IH, H3'B); 4.67 (m, IH, H3'A); 4.1-4.0 (m, 4H, H4'A + H4'B + CH 2 OP); 1.3-0.8 (m, 37H, 4 SiCH(CH 3 ) 2 + SiC(CH 3 ) 3 ); 0.13, 0.10 (two s, 6H, 2 SiCH 3 ) FAB-MS: m/z 1477.7 ([M-H] " ). Preparation 6 N β -Benzoyl-3' ,5'-O-(1,1,3,3-tetraisopropyl-1,3-disiloxane¬ diyl)-adenosine-2'-(hydrogenphosphonate) , triethylammonium salt (13) 1,2,4-Triazole (11.5 g, 167.5 mmol) was added to a stirred solution of phosphorus trichloride (4.36 ml, 50 mmol) and N-methyl morpholine (53.7 ml, 500 mmol) in anhydrous methylene chloride (500 ml) at room temperature. After 30 minutes the reaction mixture was cooled to 0 β C and N 6 -benzoyl-3' ,5'-O-(1,1,3,3-tetraisopropyl-1,3-disiloxane- diyl)adenosine (6.13 g, 10 mmol), (dried by evaporation with pyridine) anhydorus methylene chloride (130 ml) was added dropwise over 20 minutes, then kept stirring for 10 minutes more. The reaction mixture was quenched by adding IM aqueous 35 triethylammonium hydrogen carbonate (400 ml), then shaken and separated. The aqueous phase was washed with methylene chloride and the combined organic layer was dried (Na 2 S0 4 ) and evaporated under reduced pressure. Purification of the crude was performed by silica gel colum chromatography (eluent: ethyl acetate/methanol/triethylamine 10:1:0.2) to obtain 7.5 g (96% yield).of the title compound. Preparation 7 N β -Benzoyl-3' ,5'-O-(1,1,3,3-tetraisopropyl-l,3-disiloxa- nediyl)-(S P )-P-thio-adenylyl-(2'-->5' )-N β -benzoyl-2' ,3'-O- -(1,1,3,3-tetraisopropyl-l,3-disiloxanediyl)-adenosine, triethylammonium salt (14) N 6 -Benzoyl-3' ,5'-O-(1,1,3,3-tetraisopropyl-l,3-disiloxane- diyl)-adenosine-2'-(hydrogenphosphonate), triethylammonium salt (.13) (2-3 g, 2.96 mmol) and N β -benzoyl-2' ,3'-0-(l,l, 3,3-tetraisopropyl-l,3-disiloxanediyl)adenosine (8!) (1.9 g, 2.96 mmol) were rendered anhydrous by evaporation of added dry pyridine and dissolved in 20 ml of the same solvent. Pivaloyl chloride (0.91 ml, 7.4 mmol) was then added dropwise stirring the reaction mixture under anhydrous N 2 atmosphere. 30 Minutes later sulfur (10 eq) was added and the mixture kept under stirring over night. The reaction was quenched by adding triethylamine (15 ml), evaporated under reduced pressure and the residue was dissolved in methylene chloride. The organic layer was washed several times with water, dried over sodium solf te and evaporated under vacuum. Purification performed by silica gel column chromatography (linear gradient from ethyl acetate to ethyl acetate/metha nol 95:5) gave the title compound as white solid (2.7 g, 63% yield). Preparation 8 6 -benzoyl-3'-O-(t.butyldimethylsilyl)-(S τ> )-P-thio-adenyl- yl-(2'—>5' )-N s -benzoyl-2' ,3'-O-(1.1.3,3-tetraisopropyl- -1,3-disiloxanediyl)adenosine, triethylammonium salt (10) Trifluoroacetic acid (2.5 ml) was added dropwise to an ice cooled solution of N β -benzoyl-3'-0-(t.butyldimethylsilyl)- -5'-O-dimethoxy-trityl-( s 9 )-P-thio-adenylyl-(2'—>5' )-N 6 - -benzoyl-2' ,3'-O-(1,1,3,3-tetraisopropyl-l,3-disiloxanedi¬ yl)adenosine, triethylammonium salt (9) (1.94 g, 1.23 mmol) in methylene chloride (100 ml). After 30 minutes at 0°C the reaction was finished and 1.0 N aqueous triethyl¬ ammonium hydrogen carbonate (100 ml) was added. The organic layer was washed 3 times with water, dried (Na 2 S0 4 ) and evaporated at reduced pressure. The residue was purified by silica gel column chromato¬ graphy (ethyl acetate/methanol 95:5) obtaining the title compound (10) as white foam (1.49 g, 95% yield). X H-NMR (200 MHz, DMS0-d 6 ): 6 = 11.19, 11.11 (two s, 2H, 2 NHCOPh); 8.85, 8.71, 8.65, 8.63 (four s, 4H, adenine H's); 8.0-7.5 (m, 10H, aromatic H's); 6.19 (d, J = 6.5 Hz, IH, Hl'B); 6.07 (d, J = 6.2 Hz, IH, Hl'A); 5.43 (m, IH, H2'B); 5.07 (dd, J = 4.6, 6.2 Hz, IH, H2'A); 4.71 (m, IH, H3'A); 4.56 (m, IH, H3'B); 4.06 (m, IH, H4'A); 3.95 (m, IH, H4'B); 4.0-3.4 (m, 4H, CH 2 OH + CH 2 OP) ; 1.2-0.7 (m, 37H, Si-C(CH 3 ) 3 + 4 Si-CH(CH 3 ) 2 ); 0.15 (s, 6H, 2 SiCH 3 ) FAB-MS: m/z 1175.6 ([M-H] " ). Preparation 9 3'-O-(t.butyldimethylsilyl)-(S„)-P-thio-adenylyl-(2'—>5 « ) -2' ,3'-O-(1,1,3,3-tetraisopropyl-1,3-disiloxanediyl)adeno- sine, triethylammonium salt (11) N 6 -benzoyl-3'-O-(t.butyldimethylsilyl)-(Sy)-P-thio-adenyl¬ yl-(2'—>5' )-N 6 -benzoyl-2' ,3'-O-{1,1,3,3-tetraisopropyl- 1,3-disiloxanediyl)adenosine triethylammonium salt (10) (0.5 g, 0.38 mmol) was dissolved in hydrazine buffer (15 ml, 0.5M hydrazine in pyridine/acetic acid 3:2) and the reaction mixture was kept • at room temperature for 16 hours. The solution was cooled to 0°C, acetylacetone was added (1.57 ml, 2 molar eq. relative to hydrazine), the solution was evaporated in vacuum, and the? residue was partitioned between water and methylene chloride. The organic layer was washed with water, dried (Na 2 S0 4 ), evaporated under reduced pressure and coevaporated with toluene. The crude was purified by silica gel column chromatography eluteing with a linear gradient of methylene chloride/methanol from 85:15 to 70:30 to obtain the title compound 11 (200 mg, 65% yield). X H-NMR (400 MHz, DMS0-d 6 ): δ = 8.48, 8.26, 8.12, 8.05 (four s, 4H, adenine H's); 7.29, 7.22 (two bs, 4H, 2 NH 2 ); 6.06 (d, J = 6.4 Hz, IH, Hl'B); 5.93 (d, J = 6.7 Hz, IH, Hl'A); 5.47 (bs, IH, CH 2 0H) ; 5.28 (ddd, J = 4.5, 6.4, 10.0 Hz, IH, H2'B); 5.02 (dd, J = 4.8, 6.7 Hz, IH, H2'A); 4.73 (dd, J = 2.5, 4.8 Hz, IH, H3'A); 4.56 (dd, J = 2.9, 4.5 Hz, IH, H3'B); 4.01 (m, IH, H4'A); 3.92 (m, IH, H4'B); 3.90 (m, IH, CH(H)OP); 3.7-3.4 (m, 3H, CH(H)OP + CH 2 OH) ; 1.2-0.9 (m, 28H, 4 SiCH(CH 3 ) 2 ); 0.88 (s, 9H, SiC(CH 3 ) 3 ); 0.14 (s, 6H, 2 SiCH 3 ) FAB-MS: m/z 991 ([M+H] * ) Preparation 10 3'-O-(t.Butyldimethylsilyl)-(Rp)-P-thioadenylyl-(2'—>5' )- 2' ,3'-Q-(di-t.butyldimethylsilyl)adenosine, triethylammo¬ nium salt (7) A suspension of N s -benzoyl-5'-0-(dimethoxytrityl)-3'-0-(t. butyldimethylsil yl)-(Rp)-P-thioadenylyl-(2'-->5' )-N β -ben- zoyl-2' ,3'-0-(di-t.butyldimethylsilyl)adenosine, triethyl¬ ammonium salt (4_) (1 g, 0.638 mmol) in 30% ammonium hydroxide (120 ml) and pyridine (10 ml) was stirred at room temperature for 48 hours. The reaction mixture was concentrated and the residue, dissolved in methylene chloride (50 ml), was added a solution of trifluoroacetic (0.6 ml) in methylene chloride (10 ml), at 0°C. After 5 minutes the reaction mixture was poured into IN aqueous triethylammonium hydrogen carbonate 100 ml). The orgnic phase was separated and the aqueous phase was. extracted 3 times with methylene chloride. The combined extracts were dried (Na 2 S0 4 ) and concentrated. The residue was purified by silica gel column chromatography (eluent: methylene chloride/methanol/ triethylamine 90:10:0.2) to give the title compound H) (572 g, 85% yield over the two steps). ^-H-NMR (200 MHz, DMS0-d 6 ) : δ = 8.53, 8.28, 8.09, 8.03 (four s, 4H, adenine H's); 7.20 (bs, 4H, 2 NH 2 ) ; 6.06 (d, J = 6.06 Hz, IH, Hl'B); 5.86 (d, J = 7.6 Hz, IH, Hl'A); 5.48 (m, IH, CH 2 0H) ; 5.33 (ddd, J = 4.8, 6.6, 12.1 Hz, IH, H2'B); 4.82 (dd, J = 4.4, 7.6 Hz, IH, H2'A); 4.59 (dd, J = 2.3, 4.8 HZ, IH, H3'B); 4.30 (d, J = 4.4 Hz, IH, H3 » A); 3.93 (m, IH, H4'B); 3.79 (m, IH, H4'A); 3.7-3.2 (m, 4H, CH 2 QH + CH 2 0P); 0.89, 0.87, 0.59 (three s, 27H, 3 SiC(CH 3 ) 3 ); 0.18, 0.03, -0.13, -0.53 (four s, 18H, 6 SiCH a ) ; + triethylammonium signals. Preparation 11 3'-O-(t.butyldimethylsilyl)-(S- ^ )-P-thioadenylyl-(2'—>5' )- -2' ,3'-0-(di-t.butyldimethylsilyl)adenosine ammonium salt ( D To a mixture of N 6 -benzoyl-3'-0-(t.butyldimethylsilyl)-(Sp) -P-thioadenylyl-{2'->5' )-N 6 -benzoyl-2' ,3'-0-(di-t.butyldi¬ methylsilyl)-adenosine (5_) (2 g, 1.6 mmol) and 30% NH..OH (200 ml) pyridine was added obtaining a complete dissolut- ion. The solution was stirred at 40°C for a few hours, then was evaporated under vacuum and the residue was purified by silica gel chromatography eluting with methy¬ lene chloride/methanol as gradient from 80:20 to 70:30 giving the title compound (7) (1.6 g, 90% yield). TLC on silica gel: £ 0.33 eluting with methylene chloride /methanol/ mmonia 75:15:0.5. The product showed the same analitical data as those reported in preparation 10. ri'eparation 12 (Sp) and (R ^ )-N β -benzoyl-3'-0-(t.butyldimethylsilyl)-5'-0- (dimethoxytrityl)-P-thioadenylyl-(2'—>5' )-3' -Q-(t.butyl¬ dimethylsilyl-(S ^ )-P-thioadenylyl-(2'—>5' )-2' .3'-0-(di-t. butyl dimethylsilyl)adenosine, triethylammonium salt (16 and 17 ) N 6 -Benzoyl-3'-0-(t.butyldimethylsilyl)-5'-0-(dimethoxytri- tyl)adenosine-2'-(hydrogenphosphonate) , triethylammonium salt (2) (360 mg, 0.379 mmol) and 3'-0-(t.butyldime- thylsilyl-(S r )-P-thioadenylyl-(2'—>5' )-2' ,3'-O-(di-t.but- yl-di ethylsilyDadenosine, triethylammonium salt (7) (400 g, 0.379 mmol) were first coevaporated 3 times with anhydrous pyridine, then dissolved in the same solvent (10 ml). Adamantoyl chloride (271 g, 1.36 mmol) was added and the resulting solution was stirred at room temperature for 1 hour. Sulfur (150 mg) and after 3 hours triethylamine (3 ml) were added. The reaction mixture was stirred at room temperature for 30 minutes, then the solvent was evapo- rated. The residue was diluted with water and extracted with methylene chloride. The combined extracts were dried (Na 2 S0 4 ) and concentrated. Purification and separation of the diastereomers (^6 and 17) was accomplished by silica gel column chromatography (eluent: methylene chlo- ride/methanol/triethylamine 90:10:0.2). The high Rf (492 mg; TLC: Rf0.35, methylene chloride/ methanol/triethylamine, 80:20:0.2) and low Rf (123 mg; TLC: Rf0.30, methylene chloride/methanol/triethylamine, 80:20:0.2) diastereomers gave a combined yield of 650 mg (85% yield) as white solids. High Rf diastereomer (S I .,S S .) (16): ^-H-NMR (400 MHz, DMSO-d β ): δ = 8.64, 8.61, 8.52, 8.25, 8.24 (five s, 6H, adenine H's); 8.1-6.7 (m, 18H, aromatic H's); 6.31 (d, J = 4.1. Hz, IH, Hl'B); 6.08 (d, J = 5.4 Hz, IH, Hl'C); 5.87 (d, J =' 7.6 Hz, IH, Hl'A); 5.48 (m, IH, H2'B); 5.18 (m, IH, H2'C); 4.86 (m, IH, H3'B); 4.82 (dd, J = 4.4, 7.6 Hz, IH, H2'A); 4.57 (m, IH, H3'C); 4.43 (m, IH, H3'A); 4.03 (m, IH, H4'B); 4.0-3.6 (m, 6H, H4'C + H4Α+2 CH 2 OP); 3.5-3.3 (m,.2H, CH 2 ODMT) ; 0.94, 0.92, 0.84, 0.74 (four s, 36 H, 4 SiC(CH 3 ) 3 ); 0.24, 0.20, 0.15, 0.11, 0.09, -0.05 (six s, 24H, 8 SiCH 3 ); + triethylammonium signals. 31 P-NMR (81 MHz, CDC1 3 ) : δ 58.52, 57.70 (85% H 3 P0 4 as ex¬ ternal reference). FAB-MS: m/z 1819.8 ([M-H] " ) Low Rf diastereomer (R B ,,S I .) (17) : ^- R (400 MHz, DMSO-d β ): δ = 8.65, 8.63, 8.53, 8.24 (four s, 6H, adenine H's); 8.1-6.8 (m, 18H, aromatic H's); 6.32 (d, J = 4.5. Hz, IH, Hl'B); 6.08 (d, J = 6.0 Hz, IH, Hl'C); 5.88 (d, J = 7.9 Hz, IH, Hl'A); 5.53 (m, IH, H2'B); 5.20 (m, IH, H2'C); 4.88 (t, J = 5.1 Hz, IH, H3'B); 4.82 (dd, J = 4.4, 7.9 Hz, IH, H2'A); 4.60 (m, IH, H3'C); 4.43 (m, IH, H3'A); 4.01 (m, IH, H4'B); 4.0-3.6 (m, 6H, H4'C + H4'A + 2 CH 2 OP); 3.68 (s, 6H, 2 OCH 3 ); 3.3-3.0 (m, 2H CH 2 ODMT); 0.86, 0.83, 0.73, 0.58 (four S, 36 H, 4 Si-C(CH 3 ) 3 ); 0.14, 0.11, 0.05, 0.03, 0.02, -0.17, -0.52 (seven s, 24H, 8 SiCH 3 ); + triethylammonium signals. FAB-MS: m/z 1819.5 ([M-H] " ) Example 1 ( S P )-P-thioadenylyl- ( 2'-->5' )-adenosine. sodium salt (15) A 30% ammonia solution in water (19 ml) was added to a solution of N 6 -benzoyl-3' ,5'-0-(1,1,3,3-tetraisopropyl-1,3 -disiloxanediyl)-(Sp)-P-thio-adenylyl-(2'—>5 f )-N β -benzoyl -2' ,3'-0-(1,1,3,3-tetraisopropyl-l,3-disiloxanediyl)adeno¬ sine, triethylammonium salt (L4) (0.20 g, 0.138 mmol) in dioxane (10 ml). The reaction mixture was kept stirring in a sealed vassel at 50°C for 4 hours then evaporated under reduced pressure. The residue, dissolved in pyridine/ dioxane 1:4 (10 ml) was added with tetrabutylammonium fluoride (trihydrate) (435 mg, 1.38 mmol) and stirred overnight. The reaction mixture was quenched with water, and washed with methylene chloride. The aqueous phase was evaporated under reduced pressure. The crude was purified by reverse phase colomn chromatography performing a linear gradient using water/acetonitrile (from pure water to 85:15). The fractions containing the wished product were collected and passed through a column of Dowex 50 -X8, sodium cation strong exchanger. The aqueous solution was lyophilized to obtain 70 mg (80% yield) of title compound as sodium salt. HPLC analysis : RT 7.0 min [A: 0.2M ammonium acetate, B = methanol, 3-20%, 10 min, hold 20% B]; Column: Watman Partisphere 5C18 (110x4.7 mm). X H-NMR (200 MHz, DMSO-d β ) : δ = 8.41, 8.27, 8.12, 8.08 (four s, 4H, adenine H's); 7.11, 7.08 (two bs, 4H, 2 NH 2 ); 6.02 (d, J = 5.9 Hz, IH, Hl'B); 5.87 (d, J = 6.2 Hz, IH, Hl'A); 5.12 (ddd, J = 4.6, 5.9, 10.0 Hz, IH, H2'B); 4.52 (dd, J = 5.1, 6.2 Hz, IH, H2'A); .4.41 (dd, J = 4.1, 4.6 Hz, IH, H3'B); 4.15 (dd, J = 2.9, 5.1 Hz, IH, H3'A); 3.88 (m, 2H, H4'A + H4'B); 3.9-3.7 (m, 2H, CH 2 OP) ; 3.63 (dd, J = 3.0, 12.2 Hz, IH, CH(H)OH); 3.51 (dd, J = 4.1, 12.2 Hz, IH, CH(H)OH) : P-NMR (81 MHz, D 2 0) : δ 56.25 (85% H 3 P0 4 as external reference) FAB-MS: m/z 635 ([M+H] ). F- ample 2 {S-p)-P-Thioadenylyl-(2'—>5' )-adenosine, sodium salt (15) A IN tetrabutylammonium fluoride solution in tetrahydro¬ furan (2.5 ml) was added to a solution of 3'-0-(t.butyldi- methylsilyl)-(S * ,)-P-thioadenylyl-(2'—>5' )-2' ,3'-0-(di-t. butyldimethylsilyl)adenosine, triethylammonium salt ( ) (380 mg, 0.36 mmol) in tetrahydrofuran/pyridine (10 ml, 4:1). The reaction mixture was stirred at room temperature for 3 hours, then concentrated and diluted with water. The aqueous phase was extracted 3 times with methylene chloride then concentrated. The residue was purified by reverse phase chromatography on RP8 column (eluent: stepwise gradient of methanol from 0 to 20% in water) and passed through a column of Dowex-50 -X8, a* form. Evaporation of the solvent gave the title compound 15 (205 mg, 90% yield) as a white solid. Analytical data are the same as reported in example 1. Example 3 (Rp)-P-thioadenylyl-(2'—>5' )adenosine sodium salt (15 Rp) A IN tetrabutylammonium fluoride solution in tetrahydro furan (1 ml) was added to a solution of 3'-O-(t.butyldime¬ thylsilyl)-(Rp)-P-thioadenylyl-(2'—>5' )-2' ,3'-O-(di-t.bu¬ tyl dimethylsilyl)adenosine, triethylammonium salt (7) (120 mg, 0.114 mmol) in tetrahydrofuran/pyridine (6 ml 4:1). The reaction mixture was stirred for 3 hours, then concentrated and diluted with water. The aqueous phase was extracted 3 times with methylene chloride then concentrat¬ ed. The residue was purified by reverse phase chromatogra¬ phy on RP8 (eluent: stepwise gradient of methanol from 0 to 20% in water) and passed through a column of Dowex 50W-X8, Na"" form. Evaporation of the solvent gave the title compound (15-Rp) (61 mg, 85% yield) as a white solid. HPLC analysis : RT 6.5 min [A = 0.2M ammonium acetate, B = methanol, 3-20% B, 10 min, hold 20% B] X H-NMR (200 MHz, DMSO-d 6 )-: δ = 8.42, 8.29, 8.12, 8.11 (four s, 4H, adenine H's); 7.15, 7.08 (2bs, 4H, 2 NH 2 ); 6.02 (d, J = 6.0 Hz, IH, Hl'B); 5.89 (d, J = 6.1 Hz, IH, Hl'A); 5.11 (ddd, J = 5.9, 6.0, 11.4 Hz, 1Η, H2'B); 4.55 (dd, J = 5.3, 6.1 Hz, IH, H2'A); 4.43 (dd, J = 3.1, 5.9 Hz, IH, H3'B); 4.14 (dd, J = 3.2, 5.3 Hz, IH, H3'A); 4.0-3.9 (m, 2H, H4'A + H4'B); 3.9-3.7 (m, 2H, CH 2 OP); 3.7-3.5 (m, 2H, CH 2 OH) 3: P-NMR (81 MHz, D 2 0) : δ 57.69 (85% H 3 P0 4 as external reference) Example 4 Cholesterol-3-hydrogenphosphonate triethylammonium salt ( 21 ) 1,2,4-Triazole (3.04 g, 44 mmol) was added to a stirred solution of phosphorus trichloride (1.1 ml, 12.8 mmol) and N-methylmorpholine (14.1 ml, 128 mmol) in dry methylene chloride (100 ml) at room temperature. After 30 minutes the reaction mixture was cooled to 0°C and cholesterol (20) (1 g, 2.6 mmol, dried by coevaporation from pyridine) in dry methylene chloride (20 ml) was added dropwise during 30 minutes. The mixture was stirred for 45 minutes, poured into IM aqueous triethylammonium bicarbonate at pH 8.5 (100 ml), shaken and separated. The aqueous layer was extracted with methylene chloride (4 x 75 ml) and the combined organic extracts were dried (Na 2 S0 4 ) and evapora¬ ted under vacuum. The residue was purified by silica gel column chromatography eluting with methylene chloride/ methanol/triethylamine in gradient 95:5:0.5 to 85:15:0.5, obtaining the title compound (21) (1.15 g, 77% yield). X H NMR (400 MHZ, CD 3 OD) ; δ= 6,79 (d, J= 613.6 Hz, IH, PH) 5.37 (m, IH, H6); 3.96 (m, IH, H3); 2.37 (m, 2H, CH 2 -4) 1.03 (s,3H, CHa-19); 0.95 (d, J= 6.7 Hz, 3H, CH 3 -21) 0.89, 0.88 (two d, J= 6.7 Hz, 6H, CH 3 -26 + CH 3 -27); 0.72 (s, 3H, CH 3 -18) + triethylammonium signals. FAB-MS: m/z 449 ([M-H]-). Example 5 5'-Q-(cholester-3-yl-P-thiophosphoryl)-3'-O-(t. utyldime¬ thylsilyl-(Sp)-P-thioadenylyl-(2'-->5' )-2' ,3'-Q-(di-t.bu¬ tyldimethylsilyl)adenosine triethylammonium salt (23) Cholesterol-3-hydrogenphosphonate triethylammonium salt (21) (350 mg, 0.63 mmol) and 3'-O-(t.butyldimethylsilyl)- -(S,.)-P-thioadenylyl-(2'-->5')-2 * ,3'-O-(di-t.butyldimethyl¬ silyl)-adenosine ( ) (670 mg, 0.69 mmol) were coevaporated twice with dry pyridine and dissolved in the same solvent (9 ml), then pivaloyl chloride (197 mg, 1.64 mmol) was added as condensing reagent under nitrogen atmosphere. The reaction mixture was stirred for 1 hour, then sulphur (201 g, 6.3 mmol) was added and this suspension was stirred for 3 hours, quenched by addition of triethylamine (0.42 ml) and extracted with methylene chloride (3 x 20 ml). The organic layer was dried over Na 2 S0 4 and evaporated. The residue was purified by column flash chromatography eluting with dichloromethane/methanol/triethylamine 94:5:1 to afford the title compound (23) (900 mg, 83% yield). TLC on silica gel: R_ 0.32 eluting with dichloromethane/ methanol/ammonia 9:1:0.5. FAB-MS : m/z 1417.8 ([M-H] " ). Example 6 5'-O-(cholester-3-yl-P-thiophosphoryl)-(Sp)-P-thioadenylyl -(2'—>5' )adenosine sodium salt (24) 5'-0-(cholester--3-yl-P-thiophosphoryl)-3'-O-(t.butyldime¬ thylsilyl)-(S,.)-P-thioadenylyl-(2'~>5' )-2' ,3'-0-(di-t.bu¬ tyldimethylsilyl) adenosine (23) (400 mg, 0.25 mmol) was dissolved in tetrahydrofuran (20 ml). A IM solution of tetrabutylammonium fluoride in tetrahydrofuran (1.5 ml, 1.5 mmol) was added at 0°C. The solution was stirred for 24 hours at room temperature and then quenched with water. The reaction mixture was concentrated under vacuum and extracted with dichloromethane (4 x 10 ml). The combined organic phases were evaporated, the residue was redissol- ved in water/acetonitrile 8:2 and chromatographed by reverse phase on C8 eluting with a gradient of water/ acetonitrile from 8:2 to 1:1. Fractions containing the product were collected and passed through a column of Dowex 50 -X8 Na * form. The aqueous solution * was lyophi¬ lized to give the title compound ( 24 ) (150 mg, 55% yield). TLC on silica gel : R* 0.58 eluting with acetonitrile/ water 9:1. 1 H NMR (400 MHz, DMSO-d 6 ): i.a. δ= 8.42, 8.38, 8.07, 8.06 (four s, 4H, adenine H'S); 7.20 (b.s., 4H. NH-,'! ; 6.02 (dd. J=6.7, 2.6 Hz, IH, Hl'B); 5.85 (dd, J=6.7, 4.4 Hz, IH, Hl'A); 5.1-5.0( m,2H, H2'B+ H6); 4.53 (m, IH, H2'A); 4.37 (m, IH, H3'B); 4.2K , IH, H3'A); 4.07 (m, 2H, H4'B + H4'A); 4.0-3.6 (m, 5H, CH 2 -5'A + CH 2 -5'B + H3). FAB-MS : m/z 1075 ([M-H] " ). Example 7 5'-0-(cholester-3-yl-P-thiophosphoryl)-N e -benzoyl-3'-0-(t. butyldimethylsilyl)-(S P )-P-thioadenylyl-(2'—>5' )-N fi -benzoyl -2' ,3'-O-(di-t.butyldimethylsilyl)adenosine (22) Cholesterol-3-hydrogenphosphonate triethylammonium salt (21) (250 mg, 0.45 mmol) and N 6 -benzoyl-3'-0-(t.butyldime¬ thylsilyl)-(S»)-P-thioadenylyl-(2'—>5' )-N β -benzoyl-2' ,3'- -0-(di-t.butyldimethylsilyl)adenosine (5) (630 mg, 0.49 mmol) were coevaporated twice with dry pyridine and dis¬ solved in the same solvent (6 ml). Then adamantoyl chloride (270 mg, 1.35 mmol) was added as condensing reagent under nitrogen atmosphere. The reaction mixture was stirred for one hour, then sulphur (145 mg, 4.5 mmol) was added, the suspension was stirred for 3 hours, quenched by addition of triethylamine (0.3 ml) and extracted with dichloromethane (3 x 15 ml). The combined organic extracts were dried over Na 2 S0 4 and evaporated. The lesidue was purified by flash chromatography eluting with dichloromethane/ methanol in gradient from 97:3 to 90:10 to afford the title ' compound (22) (600 mg, 72% yield). TLC on silica gel : R , 0.75 eluting with dichloromethane/methanol/triethylamine 9:1:0.5. Example 8 5'-O-(cholester-3-yl-P-thiophosphoryl)-(S P )-P-thioadenylyl -(2'—>5' )adenosine sodium salt (24) from 22 via 23. 5'-0-(cholester-3-yl-P-thiophosphoryl)-N β -benzoyl-3'-0-(t. butyldimethylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )-N 6 -ben- zoyl-2' ,3'-0-(di-t.butyldimethylsilyl)-adenosine (22) (450 mg, 0.24 mmol) was added of 30% ammonia (30 ml) and dis¬ solved with pyridine (28 ml) under stirring. The same treatment described in preparation 11 gave compound ___ that showed the same analitical data as described in example 5. The same procedure described in example 6 was performed obtaining 2_ with 52% overall yield. Compound 24 showed the same analitical data reported in example 6. Example 9 l,2-Dipalmitoyl-sn-glycero-3-hydrogenphosphonate) , trie¬ thylammonium salt (26) [A variation of the procedure described by I. Lindh and J. Stawinski, J. Org. Chem. 1989, 54,13381 1,2,4-Triazole (5.05 g, 73.2 mmol) was added to a stirred solution of phosphorous trichloride (1.9 ml, 21.95 mmol) and N-methyl-morpholine (42 ml, 219.5 mmol) in anhydrous methylene chloride (150 ml), at room temperature. After 30 minutes the reaction mixture was cooled to 0°C and 1,2-Dipalmitoyl-sn-glycerol (25) (2.5 g, 4.39 mmol), (dried by coevaporation with acetonitrile) in anhydrous methylene chloride (20 ml) was added dropwise over 20 minutes, stirred for 10 minutes, poured into 1.0 M aqueous triethylammonium hydrogen carbonate (TEAB, pH 8.5), shaken and separated. The aqueous phase was extracted with methylene chloride and the combined organic phase was dried (Na 2 S0 4 ) and concentrated. Purification by silica gel column chromatography eluting with methylene chloride/methanol/ triethylamine (90:10:0.2) followed by TEAB washing gave the title compound (^6) * (2.70 g, 84% yield) . X H-NMR (200 MHz, CDC1 3 ): δ = 6.91 (d, J = 630 Hz, IH, PH); ' 5.22 (m, IH, CH OCO) ; 4.33 (dd, J = 3.8, 11.9 Hz, IH, CH(H)OCO); 4.14 (dd, J = 6.5, 11.9 Hz, IH, CH(H)OCO) ; 4.01 (dd, J = 5.2, 8.3 Hz, 2H, CH 2 OP0 2 ); 2.27 (m, 4H, OCOCH 2 (CH 2 ) i3 CH 3 ); 1.56 (m, 4H, OCOCH 2 CH 2 (CH 2 ) 12 CH 3 ) ; 1.22 (m, 48H, 2 (CH 2 ) i2 CH 3 ); 0.86 (t, J = 6.8 Hz, 6H, 2 CH 3 ); + triethylammoni -Γ. signals. Example 10 3'-0-(t.butyldimethylsilyl)-( S- )-P-thioadenylyl-(2'—>5' )- 2' ,3 τ -O-(di-t.butyldimethylsilyl)-adenosine, triethylam¬ monium salt (27) l,2-Dipalmitoyl-sn-glycero-3-hydrogenphosphonate, triethyl ammonium salt (2j>) (140 mg, 0.190 mmol) and 3'-0-(t. butyldimethylsilyl)-S p )-P-thioadenylyl-{2'—>5' )-2' ,3'-O- {di-t.butyldimethylsilyl)adenosine, triethylammonium salt (2) (200 mg, 0.190 mmol) were coevaporated three times with anhydrous pyridine, then dissolved in the same solvent (5 ml). Pivaloyl chloride (58.5 μl, 0.475 mmol) was added and the resulting solution was stirred at room temperature for 45 minutes. Sulfur (90 mg) and after 3 hours triethylamine (3 mg) were added. The reaction mixture was stirred at room temperature for 30 minutes, then the solvent was evaporated. The residue was diluted with water and extracted with methylene chloride. The combined extracts were dried (Na 2 S0 4 ) and concentrated. Purification of the residue by silica gel column chromatography eluting with methylene chloride methanol/ triethylamine 90:10:0.2 gave the title compound (22) (290 mg, 85% yield) as a mixture of diastereomers. 1 H- MR (200 MHz, CDCl 3 + D 2 0) ' : δ = 8.27, 8.15 (four s, 4H, adenine H's); 6.35 (d, J = 7.0 Hz, IH, Hl'B); 6.03, 6.00 (two d, J = 5.0 Hz, IH, Hl'A, 2 diastereomers); 5.48 (m, IH, H2'B); 5.24 (m, IH, CH(0C0R)CH 2 0P) ; 4.63 * (d, J = 4.4 Hz, IH, H3'B); 4.37 (m, IH, H2'A); 4.4-3.9 (m,9H, H3'A, H4'B + H4'A + 3 CH 2 OP) ; 2.26 (m, 4H, 2 CH 2 COO) ; 1.55 (m, 4H, 2 CH 2 CH 2 COO); 1.23 (m, 48H, 2 CH 3 (CH 2 ) 12 ); 0.95-0.70 (m, 33H, 2 CH 3 (CH 2 ) 14 + 3 SiC(CH 3 ) 3 ); 0.27, 0.26, 0.22, 0.21, 0.08, 0.04, 0.03, -0.05, -0.20, -0.21 (ten s, 18H, SiCH a 2 diastereomers) ; + triethylammonium signals. FAB-MS: m/z 1602 ( [M+H] * ) . Example 11 5'-O-[1,2-Dipalmitoyl-sn-glycero-3-(R-pSp)-thiophosphoryll- (Sp)-P-thioadenylyl-(2'—>5' )adenosine, sodium salt (28) A IN tetrabutylammonium fluoride solution in tetrahydro¬ furan (0.8 ml) was added to a solution of 5'-0-[l,2-dipal- mitoyl-sn-glycero-3-(RpS p )-thiophosphoryl]-3'-0-(t.butyl- dimethylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )-2' ,3'-O-(di- t.butyldimethylsilyl)adenosine, triethylammonium salt (27) (200 mg, 0.111 mmol) in tetrahydrofuran (3.2 ml), at room temperature. After 4 hours the reaction mixture was diluted with methylene chloride and washed with water, dried (Na 2 S0 4 ) and concentrated. The residue was purified by silica gel column chromatography eluting with methylene chloride/methanol/triethylamine 90:10:1, and passed through a-column of Dowex 50W-X8 resin, Na " * " form to give the title compound (j28) (125 mg, 87% yield). ^H-NMR (400 MHz, DMSO-d 6 + D 2 0) : δ = 8.46, 8.10, 8.07 ( three s , 4H, adenine H' s) ; 6.05 (d, J = 5. 4 Hz , IH, Hl ' B) ; 5. 86 (d, J = 6.7 Hz , IH, Hl ' A) ; 5.10 (m, IH, H2 ' B) ; 5.00 (m, IH, CHOCO) ; 4.53 (m, IH, H3 'B) ; 4.38 (m, IH, H2 ' A) ; 4.2-3 .8 (m, 11H , ChCH 2 OCO , 3 CH 2 OP + H3 ' A + H4 ' B + H4'A); 2.13 ( , 4H, 2 0C0CH 2 ); 1.4-1.1 (m, 52H, 2 0C0CH 2 (CH 2 ) 13 CH 3 ); 0.78 (t, J= 6.0 Hz , 6H, 2 (CH 2 ) T4 CH 3 ) FAB-MS: m/z 1303 { [M+H]*) . ' Example 12 5'-0-( ethylphosphonyl)-3' -0-(t.butyldimethylsilyl)-(S )- P-thioadenylyl-(2'->5' )-2' ,3'-Q-(di-t.butyldimethylsilyl) adenosine, triethylammonium salt (29) Methylphosphorodichloridate (106 mg, 0.8 mmol) was added to a solution of triazole (110 mg, 1.6 mmol) and triethyl amine (445 μl, 3.2 mmol) in dry pyridine (5 ml) and the resulting suspension stirred at 0°C for 15 minutes under nitrogen. A solution of 3'-0-(t.butyldimethylsilyl)-(Sp)- -P-thioadenylyl-(2'->5' )-2' ,3'-O-(di-t.butyldimethylsilyl) adenosine, triethylammonium salt (2) (350 mg, 0.331 mmol) in dry pyridine (9 ml) was added, the mixture stirred at room temperature for 2 hours, poured into 1.0M aqueous triethylammonium hydrogen carbonate (TEAB pH 8.5) and concentrated. Purification by silica gel column chromatography eluting with methylene chloride/methanol/ triethylamine 65:35:1, gave the title compound (^9) (380 mg, 93% yield) . ^H-NMR (200 MHz, DMS0-d β ): δ = 8.51, 8.31, 8.10, 8.06 (four s, 4H, adenine H's); 7.26, 7.17 (two bs, 4H, NH 2 ); 6.10 (d, J = 6.3 Hz, IH, Hl'B); 5.85 (d, J = 7.5 Hz, IH, Hl'A); 5.33 (m, IH, H2'B); 4.83 (dd, J = 7.5, 4.4 Hz, IH, H2'A); 4.63 (dd, J = 4.4, 2.9 Hz, IH, H3'B); 4.42 (d, J = 4.4 Hz, IH, H3'A); 4.01 (m, IH, H4'B); 3.9-3.7 (m, 5H, CH 2 -5'A + CH 2 -5'B + H4'A); 1.03 (d, J = 16.2 Hz, 3H, P-CH 3 ); 0.89, 0.87, 0.60 (three s, 27H, SiC(CH 3 ) 3 ); 0.19, 0.17, 0.04, -0.13, -0.50 (five s, 18H, SiCH 3 ) FAB-MS: m/z 1033 ( [M+HD Example 13 5'-O-(M thylphosphonate)-(S )-P-thioadenylyl-(2'—>5' )ade¬ nosine, sodium salt (30) A IN tetrabutylammonium fluoride solution in tetrahydro- furan (1.05 ml) was added to a solution of 5 1 '-0-(methyl- phosphonate)-3'-O-(t.butyldimethylsilyl)-(Sp)-P-thioade- nylγl-(2'~>5' )-2' ,3'-0-(di-t.butyldimethylsilyl) adeno¬ sine, triethylammonium salt (.29) (175 mg, 0.141 mmol) in tetrahydrofuran/pyridine 4:1 (5 ml). The reaction mixture was stirred for 6 hours, then concentrated and diluted with water. The aqueous phase was extracted 3 times with diethylether then concentrated. The residue was purified by reverse-phase chromatography on RP8 eluting with a stepwise gradient of acetonitrile from 0 to 40% in water and passed through a column of Dowex-50 -X8 resin, Na " " form. Evaporation of the solvent gave the title compound (30) (88 mg, 85% yield) as a white solid. ^H-NMR (200 MHz, DMSO-d 6 + D 2 0) : δ = 8.48, 8.45, 8.11, 8.09 (four s, 4H, adenine H's); 6.07 (d, J = 7.5 Hz, IH, Hl'B); 5.87 (d, J = 6.8 Hz, IH, Hl'A); 5.17 (ddd, J = 4.8, 7.5, 10.0 Hz, IH, H2'B); 4.59 (dd, J = 4.9, 6.8 Hz, IH, H2'A); 4.39 (d, J = 4.8 Hz, IH, H3'B); 4.26 (dd, J = 2.4, 4.9 Hz, IH, H3'A); 4.09 (m, 2H, H4'A + H4'B); 3.8-3.6 (m, 4H, 2 CH 2 0P); 1.00 (d, J = 15.9 Hz, 3H, CH 3 P0) . 3X P NMR (81 MHz, D 2 0) : δ = 56.18 (P=S) ; 27.77 (P-CH 3 ) (85% H 3 P0 4 as external reference) FAB-MS: m/z 757 ([M + Na] ÷ ); 735 ([M + H] ÷ ) . Example 14 3-O-succinylcholesterol Preparation A: Succinic anhydride (174 mg, 1.74 mmol) was added to a solution of cholesterol (20) (518 mg, 1.34 mmol) in dry toluene (30 ml)containing benzensulfonic acid as catalyst. The solution was refluxed for 45 minutes, neutralized with 2% aqueous sodium bicarbonate and washed with water. The organic phase was dried (Na 2 S0 4 ) and evaporated under vacuum. The residue was purified by silica gel column chromatography eluting with a gradient of ethyl acetate 0 to 20% in cyclohexane to give the title compound (3_1) (500 g, 76.6% yield) . NMR (400 MHz, CDC1 3 ): δ= 8.72 (bs, IH, COOH) ; 5.39 (m, IH, H6); 4.65 (m, IH, H3) ; 2.69 (m, 2H, OCOCH 2 .CH 2 COOH) ; 2.62 (m, 2H, 0C0CH 2 - CH^COOH) ; 2.33 (d, J= 7.9 Hz, 2H, CH 2 -4); 1.03 (s, 3H, CH 3 -19); 0.93 (d, J= 6.7 Hz, 3H, CH 3 -21); 0.88, 0.87 (two d, J= 6.7 Hz, βH, CH 3 -26 + CH 3 -27); 0.69 (s, 3H, CH 3 -18). FAB-MS : m/z 485 ([M-H] " ). Preparation B: Succinic anhydride (255 mg, 2.55 mmol) and dimethylamino- pyridine (90 mg, 0.75 mmol) were added to a solution of cholesterol (2_0) (500 mg, 1.29 mmol) in dry pyridine (30 ml). The solution was heated at 90 β C for 4 hours, then stirred for 18 hours at room temperature, diluted with dichloromethane (60 ml) and washed with water. The organic phase was dried (Na 2 S0 4 ) and evaporated under vacuum with complete elimination of pyridine. The residue was purified by silica gel column chromatography eluting with a gradient from cyclohexane to cyclohexane/ethyl acetate 80:20, to give the title compound (31) (300 mg, 50% yield). The compound showed the same analytical data as in Prepara¬ tion A. Example 15 5'-o-(cholester-3-yloxycarbonylpropanoyl)-3'-Q-(t.butyldi¬ methylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )-2' .3'-o-(di-t. butyldimethylsilyl)adenosine, sodium salt (32) 3-0-Succinylcholesterol (3_1) (400 mg, 0.82 mmόl) and 3'-0- -(t.butyldimethylsilyl)-(JSa )-P-thioadenylyl-(2'—>5' )-2' , 3'-O-(di-t.butyldimethylsilyl)adenosine triethylammonium salt (2) (440 mg, 0.45 mmol) were coevaporated twice with dry pyridine and dissolved in the same solvent (8 ml). Then N,N'-dicyclohexylcarbodiimide (185 mg, 0.9 mmol) and 4-dimethylaminopyridine (14.6 mg, 0.12 mmol) were added to the stirred solution under nitrogen atmosphere. The reaction mixture was stirred for 24 hours at room tempera¬ ture and then evaporated to dryness. The residue was redis- solved in dichloromethane, the insoluble dicyclohexylurea was filtered off and the organic solution was washed with water, dried (Na 2 S0 4 ) and evaporated under reduced pressu¬ re. The residue was purified by silica gel column chromatography using a gradient from dichloromethane to dichloromethane/methanol 70:30, to give the title compound (11) (350 mg, 54% yield). TLC on silica gel : R_ 0.23 eluting with dichloromethane/methanol 8:2. Example 16 5'-O-(cholester-3-yloxycarbonylpropanoyl)-(Sp)-P-thioade¬ nylyl- (2*—>5' )-adenosine, sodium salt (37) 5'-O-(cholester-3-yloxycarbonylpropanoyl)-3'-O-(t.butyldi¬ methylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )-2' ,3'-0-(di-t. butyldimethylsilyl)adenosine, sodium salt (H) (350 mg, 0.24 mmol) was dissolved in tetrahydrofuran (12 ml) and 1 M tetrabutylammonium fluoride in tetrahydrofuran (1.45 ml, 1.45 mmol) was added at 0°C. The solution was stirred for 1 hour at 0°C and 1 hour at room temperature. The reaction mixture was quenched with 1 M aqueous triethylammonium bicarbonate until pH 7 and extracted with dichloromethane (5 x 30 ml). The organic phase was evaporated to dryness and the residue purified by silica gel column chromatogra- phy eluting with dichloromethane/methanol as a gradient from 90:10 to 70:30. All the fractions containing the product were combined and passed through a column of resin Dowex 50W-X8, Na * form. The aqueous solution was lyophi¬ lized to give the title compound (37) (190 mg, 72% yield). 1 H NMR (400 MHz, DMS0-d β ): δ = 8.47, 8.25, 8.12, 8.09 (four s, 4H, Adenine H's); 7.25 (bs, 4H, 2 NH 2 ); 6.08 (d, J= 4.5 Hz, IH, Hl'B); 5.87 (d, J= 6.0 Hz, IH, Hl'A); 5.74, 5.40, 5.22 (three d, J= 4.5 Hz, 3H, 3 OH); 5.31 (m, IH, H6); 5.16 (ddd, J= 4.5, 6.0, 10.0 Hz, IH, H2'B); 4.6-4.5 (m, 2H, H3'B, H2'A ); 4.40 (m, IH, H3) ; 4.3-3.8 (m, 7H, CH^-OP, CH^OCO, H4'A, H4'B, H3'A); 2.50 (m, 2H, OCOCH^CHaCOO) ; 2.21 (m, 2H, 0C0CH2CH 2 C00) ; 0.91 (s, 3H, CH 3 -19); 0.89 (d, J= 6.3 Hz, 3H, CH 3 -21); 0.85, 0.84 (two d, J= 6.3 HZ, 6H, CH 3 -26, CH 3 -27); 0.64 (s, 3H, CH 3 -18). FAB-MS : m/z 1103 ( [M+H] * ) . Example 17 3' -O-(t.butyldimethylsilyl)-5'-O-n-octanoyl-(Sp)-P-thio¬ adenylyl-(2'->5')-2',3'-Q-(l,l,3,3-tetraisopropyl-l,3-di¬ siloxanediyl)adenosine, triethylammonium salt (33) 3-0-(t.butyldimethylsilyl)-(Sp)-P-thioadenylyl-{2'~> 5')- 2' ,3'-O-(1,1,3,3-tetraisopropyl-l,3-disiloxanediyl)adeno¬ sine triethylammonium salt (11) (210 mg, 0.19 mmol) was dried by coevaporation with pyridine and dissolved in the same solvent (18 ml). N' , '-Dicyclohexylcarbodiind.de (80 g, 0.38 mmol), 4-dimethylaminopyridine (12 mg, 0.1 mmol) and octanoic acid (55 mg, 0.38 mmol) were added and the mixture was stirred for 16 hours at room temperature. The mixture was evaporated to dryness, the residue thus obtained was dissolved in a small amount of precooled methylene chloride and insoluble N,N'-dicyclohexylurea was filtered off. Methylene chloride (100 ml) was added and the organic solution was washed with water, dried (Na 2 S0 4 ) and evaporated. The crude was purified by silica gel column chromatography eluting with a linear * gradient of methylene chloride/methanol (85:15 to 80:20). The title compound (H) was obtained as a white foam (200 mg, 85% yield) . ^H-NMR (200 MHz, DMSO-d 6 ) : δ = 8.50, 8.22, 8.11, 8.07 (four s, 4H, adenine H's); 7.30, 7.25 (bs, 4H, 2 NH 2 ); 6.19 (d, J = 4.3 Hz, IH, Hl'B); 5.94 (d, J = 6.2 Hz, IH, Hl'A); 5.29 (ddd, J = 4.3, 4 3, 10.6 Hz, IH, H2'B); 5.05 (dd, J = 4.8, 6.2 Hz, IH, H2'A); 4.89 (m, IH, H3'B); 4.73 (dd, J = 3.2, 4.8 Hz, IH, H3'A); 4.3-3.8 (m, CH 2 OP + COOCH 2 + H4'A + H4'B); 2.32 (m, 2H, CH 2 COO) ; 1.4-0.8 (m, 50H, CH 3 (CH 2 ) S ÷ 4 SiCH(CH 3 ) 2 + SiC(CH 3 ) 3 ); 0.14, 0.13 (two s, 6H, 2 SiCH 3 ) FAB-MS: m/z 1095 ([M+H]*). Example 18 5'-O-n.Octanoyl-(Sp)-P-thioadenylyl-(2'—>5' )adenosine, sodium salt (38) 0.2N Tetrabutylammonium fluoride solution in tetrahydro¬ furan/pyridine 4:1 (6.7 ml) was added to 3'-0-(t.butyl dimethylsilyl)-5'-O-n.octanoyl-(Sp)-P-thioadenylyl-(2'—> 5* )-2' ,3'-O-(1,1,3,3-tetraisopropyl-l,3-disiloxanediyl) adenosine, triethylammonium salt (H) (0.2 g, 0.16 mmol) and the resulting solution was stirred for 1 hour at room temperature. Then the mixture was concentrated and the residue thus obtained was purified by silica gel column chromatography eluting with methylene chloride/methanol 85:15. The fractions containing the pure title compound as triethylammonium salt were concentrated under reduced pressure to afford a white foam that was dissolved in water and a small amount of acetonitrile and passed through a column of Dowex- 50 -X8 resin Na " * form. The aqueous solution was lyophilized to obtained the expected compound (3_8) as sodium salt (97 mg, 78% yield). X H-NMR (400 MHz, DMSO-d β ) : δ = 8.49, 8.25, 8.13, 8.10 (four s, 4H, adenine H's)_; 7.26 (bs, 4H, 2 NH 2 ); 6.07 (d, J = 4.4 Hz, IH, Hl'B); 5.87 (d, J = 6.4 Hz, IH, Hl'A); 5.69 (d, J = 4.8 Hz, IH, OH2'A); 5.41 (bs, IH, OH3'B); 5.23 (bs, IH, OH3'A); 5.21 (ddd, J = 2.8, 4.4, 9.5 Hz, IH, H2'B); 4.53 (m, 2H, H2'A + H3'B); 4.28 (m, IH, CH(H)OCO); 4.15 (m, IH, H3'A); 4.1-3.8 (jn, 5H, CH(H)OCO + H4'A + H4'B + CH 2 OP); 2.20 (t, J = 7.3 Hz, 2H, CH 2 COO) ; 1.4-1.1 (m, 10H, CH 3 (CH 2 ) S CH 2 ) ; 0.81 (t, J = 6.7 Hz, 3H, CH 3 (CH 2 ) 6 ). FAB-MS: m/z 761 ( [M+H] * ) . Example 19 3'-Q-(t.butyldimethylsilyl)-5'-Q-cyclohexylacetyl-(Sp)-P- thioadenylyl-(2'—>5')-2',3'-O-(1,1,3,3-tetraisopropyl-l,3 -disiloxanediyl)adenosine, triethylammonium salt (34) 3'-O-(t.butyldimethylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )- 2' ,3'-O-(1,1,3,3-tetraisopropyl-l,3-disiloxanediyl)adeno¬ sine, triethylammonium salt (11) (270 mg, 0.25 mmol) was dried by coevaporation with pyridine and dissolved in the same solvent (7 ml). N,N'-Dicyclohexylcarbodiimide (103 mg, 0.5 mmol), 4-dimethylaminopyridine (15 mg, 0.125 mmol) and cyclohexylacetic acid (71 mg, 0.5 mmol) were added and the mixture was stirred overnight at room temperature. The mixture was evaporated to dryness, the residue thus obtained was dissolved in a small amount of precooled methylene chloride and insoluble N,N'-dicyclohexylurea was filtered off. Methylene chloride (100 ml) was added, the organic solution was washed with water, dried (Na 2 S0 4 ) and the solvent evaporated. The crude was purified by silica gel column chromatography eluting with a linear gradient of methylene chloride/methanol 90 : 10 to 75 : 25 . The expected compound ( 3_4) was obtained as a white foam ( 217 mg, 70% yield) . FAB-MS : m/z 1093 . 5 ( [M-H] " ) . Example 20 5'-O-Cyclohexylacetyl-(Sp)-P-thioadenylyl-(2'—>5' )adeno¬ sine, sodium salt (39) 0.2M Tetrabutylammonium fluoride solution in tetrahydro¬ furan/pyridine 4:1 (5.25 ml) was added to 3'-0-{t.butyl- dimethylsilyl)-5'-O-cyclohexylacetyl-(Sp)-P-thioadenylyl- (2'—>5' )-2' ,3'-O-(1,1,3,3-tetraisopropyl-l,3-disiloxane¬ diyl)adenosine, triethylammonium salt (34) (170 mg, 0.14 mmol) and the resulting solution was stirred for 1 hour at room temperature. Then the mixture was evaporated to dryness and the residue was purified by silica gel column chromatography eluting with methylene chloride/methanol 90:10 to 75:25. The fractions containing the pure title compound as triethylammonium salt were collected and evaporated. The product obtained as a white foam was dissolved in water/acetonitrile and passed through a column of Dowex-50 -X8 resin, Na "1" form. The aqueous solution was lyophilized to obtain the expected compound (39) as sodium salt (80 mg, 75% yield). X H-NMR (400 MHz, DMSO-d 6 ) : δ = 8.49, 8.25, 8.13, 8.10 (four s, 4H, adenine H's); 7.26 (bs, 4H, 2 NH 2 ); 6.09 (d, J = 4.4 Hz, IH, Hl'B); 5.88 (d, J = 6.0 Hz, IH, Hl'A); 5.23 (ddd, J = 2.8, 4.4, 9.5 Hz, IH, H2'B); 4.54 (m, 2H, H3'B + H2'A); 4.30 (m, IH, CH(H)OCO); 4.17 (dd, J = 2.5, 2.8 Hz, IH, H3'A); 4.1-3.8 (m, 5H, CH(H)OCO + H4'A + H4'B + CH 2 OP); 2.08 (m, 2H, CH 2 COO) ; 1.54 (m, 6H, cyclohexane H's); 1.2-0.8 (m, 5H, cyclohexane H's). FAB-MS: m/z 759 ([M+H]-). Example 21 5'-O-palmitoyl-3' -0-(t.butyldimethylsilyl)-N β -benzoyl-(S„) • -P-thioadenylyl-(2'—>5' )-2' , " 3'-0-(di-t.butyldimethyl¬ silyl)-N β -benzoyl- adenosine triethylammonium salt (35) . To a solution of 3'-0-(t.butyldimethylsilylJ-N β -benzoyl- (Sp)-P-thioadenylyl-(2'—>5' )-2' ,3'-0-(di-t.butyldimethyl¬ silyl)-N β -benzoyl-adenosine triethylammonium salt (5_) (0.8 g, 0.74 mmol) in dry pyridine (20 ml), palmitic acid (0.8 g, 0.89 mmol) is added at room temperature, under vigorous stirring. The resulting solution was cooled at 0°C, and N,N'-dicyclohexylcarbodiimide (0.30 g, 1.4 mmol) was added in one portion. The resulting solution was stirred over¬ night at room temperature and then poured into crushed ice (50 g) , stirred 20 minutes and extracted twice with dichloromethane (2x100 ml).The combined extracts were dried and evaporated under vacuum. Purification by silica gel column chromatography eluting with dichloromethane/ /methanol 90:10, afforded the title compound (3_5) (0.9 g, 93% yield) as a colorless foam. ^H-NMR (200 MHz, DMSO-d 6 ) : δ = 11.13 (bs, 2H, 2 NHCO) ; 8.92, 8.70, 8.62 (three s, 4H, adenine H's); 8.1-7.4 (m, 10 H, aromatic H's); 6.31 (d, J= 4.9 Hz, IH, Hl'B); 6.04 (d, J= 7.1 Hz, IH, Hl'A); 5.48 (m, IH, H2'B); 4.90 (dd, J= 4.4, 7.1 HZ, IH, H2'A); 4.83 (m, IH, H3'B); 4.49 (d, J= 4.4 Hz, IH, H3'A); 4.4-3.6 (m, 6H, H4'A + H4'B + CH^OP + COOCH 2 ) ; 2.17 (t, J= 7.4 Hz, 2H, CH 2 COO) ; 1.4-1.1 (m, 26H, i____) _ 3 ) ; 0.90 (s, 18H, 2 SiC(CH a ) 3 ); 0.82 (t, J= 6.7 Hz, 3H, CH 3 -(CH 2 )- L3 - ); 0.61 (s, 9H, SiC(CH 3 ) 3 ); 0.20, 0.19, 0.07, -0.11, -0,49 (six s, 18H, 6 SiCH„). Example 22 '-O-Palmitoyl-3'-0-(t.butyldimethylsilyl)-(S ^ )-P-thio¬ adenylyl- (2'—>5')-2' ,3'-Q-(di-t.butyldimethylsilyl)- adenosine triethylammonium salt (36) . To a solution of 5'-O-palmitoyl-3'-0-(t.butyldimethyl¬ silyl)-N s - benzoyl-(S s -)-P-thioadenylyl-(2'~>5' )-2' ,3'-0- (di-t.butyldimethyl silyl)-N β -benzoyl-adenosine triethyl¬ ammonium salt (3_5) (0.9 g, 0.69 mmol) in a pyridine-acetic acid mixture 3:2, cooled at 0°C, a 0.5 M hydrazine hydrate solution (3 ml, 1.5 mmol) was added dropwise under stirring. The resulting solution was kept at 0°C for 6 hours, then evaporated to leave a residue which was taken up with dichloromethane (250 ml). The organic solution was washed with water (3x20 ml) ,dried and evaporated under vacuum. The residue was purified by silica gel column cromatography eluting with dichloromethane/methanol/- triethylamine 90:10:0.5, to give the title compound (36) (0.64 g, 84% yield), as a colorless foam. •■ -H-NMR (200 MHz, CDC1 3 ) : δ = 8.68, 8.30, 8.19, 8.08 (four s, 4H, adenine H's); 6.7, 6.2 (two bs, 4H, 2 ____) ; 6.31 (d, J= 4.2 Hz, IH, Hl'B); 6.10 (d, J= 5.1 Hz, IH, Hl'A); 5.50 (m, IH, H2'B); 4.95 (dd, J= 4.6, 5.1 Hz, IH, H2'A); 4.58 (t, J= 4.6 Hz, IH, H3'B); 4.5-4.1 (m, 7H, H3'A + H4'A + H4'B + CH 2 OP + CH- ^ OCO) ; 2.25 (t, J= 7.1 Hz, 2H, CH-aCOO) ; 1.6-1.2 (m, 26H, [____) _ 3 ) f ' 0.94, 0.91 (two s, 18H, 2 SiC(CH3_) 3 ); 0.8 (signal overlapped by triethylammonium signals, 3H, CHa.-(CH 2 ) x3 ) ); 0.78 (s, 9H, SiC(O ) ; 0.24, 0.21, 0.10, 0.06, - 0.03, - 0.17 (six s, 18H, 6 SiCHa) ; + triethylammonium signals. Example 23 5'-O-Palmitoyl-(Sp)-P-thioadenylyl-(2'—>5' )-adenosine sodium salt (40) . To a solution of 5'-O-palmitoyl-3'-0-(t.butyldimethylsilyl) -(S r> )-P-thioadenylyl-(2'~>5' )-2' ,3'-0-(di-t.butyldimethy¬ lsilyl)-adenosine triethylammonium salt (3_6) (0.60 g, 0.54 mmol) in dry tetrahydrofuran (2 ml), under dry nitrogen atmosphere, a 1 M tetrabutylammonium fluoride solution in tetrahydrofuran (2 ml, 2 mmol) was added at room tempera- ture. After 2 hours, water (10 ml) was added to the mixture, the organic solvent evaporated and the residue taken up with dichloromethane (100 ml). The organic phase was washed with brine (10 ml), dried and evaporated under vacuum. The resulting residue was chromatographed on silica gel. Faster moving by-products were removed by elution with dichloromethane/ methanol 95:5, further elution with dichloromethane/methanol 70:30 led to the pure title compound ( _[) as salt mixture. The pure sodium salt was then obtained by stirring a solution of the above compound in acetone/water 1:1 (60 ml) with Dowex-50 -X8 resin, Na" " form (500 mg) , for 20 minutes and then by passing the solution through a 2x8 cm column of the same resin. Evaporation of organic solvents and lyophilization afforded the title compoud (40_) (315 mg, 67% yield). ""H-NMR (200 MHz, DMSO-d β ) : δ = 8.54, 8.30, 8.19, 8.12 (four s, 4H, adenine H's); 7.7, 7.6 (two bs, 4H, 2 NH a ) ; 6.09 (d, J= 4.3 Hz, IH, Hl'B); 5.87 (d, J= 5.4 Hz, IH, Hl'A); 5.18 (m, IH, H2'B); 4.48 (m, 2H, H2'A + H3'B); 4.3-4.0 (m, 7H, H4'A + H4'B + H3'A + CH a QP + CH ? OCO) ; 2.20 (t, J= 7.1 Hz, 2H, CHsCOO) ; 1.4-1.1 (m, 26H, (CH a )„); 0.83 (t, J= 6.9 Hz, 3H, CH^(CH a ) 14 ). Example 24 5'-O-[N-(t.butoxycarbonyl)- β -alanyl]-3'-O-(t.butyldimethyl silyl)-(Sp -P-thioadenylyl-(2'—>5' )-2' .3'-O-(di-t.butyl¬ dimethylsilyl)adenosine, triethylammonium salt (42a) 3'-0- ( t.Butyldimethylsilyl)-P-thioadenylyl-(2'->5' )-2' ,3'- O-(di-t.butyldimethylsilyl)-adenosine, triethylammonium salt (2) (500 mg, 0.474 mmol) and Boc-β-alanine (180 mg, 0.948 mmol) were coevaporated 3 times with anhydrous pyridine, and dissolved in the same solvent (30 ml). N,N'-Dicyclohexylcarbodilmide (195 mg, 0.948 mmol) and 4-dimethylaminopyridine (11.6 mg, 0.095 mmol) were added and the resulting mixture was stirred at room temperature for 48 hours. The reaction mixture was concentrated, diluted with methylene chloride and washed with water. The organic phase was dried (Na 2 S0 4 ) and concentrated. Purification by silica gel column chromatography eluting with methylene chloride/methanol/ triethylamine 90:5:0.2, gave the title compound (42a) (522 mg, 90% yield). H-NMR (200 MHz, CDC1 3 ): δ = 8.58, 8.28, 8.18, 8.08 (four s, 4H, adenine H's); 6.30 (d, J = 5.0 Hz, IH, Hl'B); 6.07 (d, J = 4.9 Hz, IH, Hl'A); 5.60 (m, IH, H2'B); 4.81 (m, IH, H3'B); 4.60 (m, IH, H2'A); 4.4-4.1 (m, 7H, H3'A + H4'B + H4'A + CH 2 OP + CH 2 OCO); 3.33 (t, J = 6.0 Hz, 2H, CH 2 COO); 2.50 (m, 2H, CH 2 NHCOO) ; 1.41 (s, 9H, COOC(CH 3 ) 3 ); 0.94, 0.91, 0.79 (three s, 27H, 3 SiC(CH 3 ) 3 ); 0.23, 0.20, 0.09, 0.06, -0.03, -0.15 (six s, 18H, 6 SiCH 3 ) + triethyl¬ ammonium signals. FAB-MS: m/z 1126 ( [M+H]-) . Example 25 5'-O-(β-alanyl)-(Sp)-P-thioadenylyl-(2'->5' )adenosine, so¬ dium salt (43a) Trifluoroacetic acid (3 ml) was added to a solution of 5'-0-[N-(t.butoxycarbonyl)- β -alanyl]-3'-0-(t.butyldimethyl silyl)-(Sp)-P-thioadenylyl-(2'—>5' )-2' ,3'-O-(di-t.butyl- dimethylsilyl)adenosine, triethylammonium salt (42a) (470 mg, 0.383 mmol) in methylene chloride (3 ml), containing 1,2-ethanedithiol (0.32 ml) as a carbocation scavenger, at 0°C. After 1 hour the reaction mixture was diluted with methylene chloride and neutralized with IN aqueous triethyammonium hydrogen carbonate. The organic phase was dried (Na 2 S0 4 ) and concentrated. A IN tetrabutyl ammonium fluoride solution in tetrahydrofuran (2.5 ml) was added to the residue dissolved in tetrahydrofuran (10 ml). After 2 hours the reaction mixture was diluted with water and extracted with diethylether. The aqueous phase was concentrated, purified by reverse phase chromatography on RP8 eluting with a stepwise gradient of acetonitrile from 0% to 60% in water and passed through a column of Dowex 50W-X8 resin, Na "1" form. Evaporation of the solvent gave the title compound 43a (182 mg, 70% yield over the 2 steps) . 1 H-NMR (200 MHz, DMSO-d 6 ): δ = 8.44, 8.26, 8.12, 8.08 (four s, 4H, adenine H's); 7.25 (bs, 4H, 2 NH 2 ) ; 6.08 (d, J = 4.4 HZ, IH, Hl'B); 5.84 (d, J = 6.4 Hz,lH, Hl'A); 5.16 (m, IH, H2'B); 4.6-4.4 (m, 2H, H2'A + H3'B); 4.3-3.7 (m, 7H, H3'A + H4'B + H4'A + C00CH 2 + CH 2 OP) ; 2.97 (m, 2H, CH 2 CH 2 NH 3 ~); 2.60 (m, 2H, COCH 2 CH 2 NH 3 -'-) FAB-MS: m/z 684 ( [M+H]-) . Example 26 5'-O-[N-(t.Butoxycarbonyl)-6-aminocaproyl]-3'-O-(t.butyl¬ dimethylsilyl)-(Sp)-P-thiadenylyl-(2'-->5' )-2' ,3'-O-(di-t. butyldimethylsilyl)adenosine, triethylammonium salt (42b) 3'-0-(t.Butyldimethylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )- 2' ,3'-0-(di-t.butyldimethylsilyl)adenosine, triethylammo- nium salt (2) (300 mg, 0.285 mmol) and N-(t.butoxy¬ carbonyl)-6-aminocaproic acid (132 mg, 0.570 mmol) were coevaporated three times with anhydrous pyridine and dissolved in the same solvent (30 ml). N,N'-Dicyclohexyl- carbodiimide (117 mg, 0.570 mmol) and 4-dimethylamino- pyridine (6.9 mg, 0.057 mmol) were added and the resulting mixture was stirred at room temperature for 48 hours. The reaction mixture was concentrated, diluted with methylene chloride and washed with water. The organic phase was dried (Na 2 S0 4 ) and concentrated. Purification of the residue by silica gel column chromatography eluting with methylene chloride/ methanol/triethylamine 90:5:0.2 gave the title compound (42b) (325 mg, 90% yield). 1 H- MR (400 MHz, DMSO-d 6 ) : δ = 8.50, 8.20, 8.10, 8.08 (four s, 4H, adenine H's); 7.07 (bs, 4H, 2 NH-.); 6.60 (bs, IH, CH 2 NHCOO); 6.23 (d, J = 5.0 Hz, IH, Hl'B); 5.91 (d, J = 7.3 Hz, IH, Hl'A); 5.33 (m, IH, H2'B); 4.90 (m, IH, H2'A); 4.86 (m, IH, H3'B); 4.48 (d, J = 4.4 Hz, IH, H3'A); 4.3-3.9 (m, 6H, H4'A + H4'B + COOCH 2 + CH 2 OP) ; 2.85 (m, 2H, CH 2 NHCOO); 2.16 (t, J = 5.6 Hz, 2H, CH 2 COO) ; 1.4-1.0 (m, 6H, COCH 2 (CH 2 ) 3 CH 2 NH); 1.34 (s, 9H, COOC(CH 3 ) 3 ) ) ; 0.89, 0.62 (two s, 27H, 2 SiC(CH 3 ) 3 ); 0.18, 0.07, 0.06, -0.13, -0.46 (five s, 18H, 6 SiCH 3 ) + triethylammonium signals. FAB-MS: m/z 1168 ( [ +H]*) . Example 27 5'-O-(6-Aminocaproyl)-(S F )-P-thioadenylyl-(2'—>5' )adeno¬ sine, sodium salt (43b) Trifluoroacetic acid (2 ml) was added to a solution of 5'-O- [N-(t.butoxycarbonyl)-6-aminocaproyl]-3'-0-(t.butyldimethyl¬ silyl)-(Sp)-P-thioadenylyl-(2'—>5' )-2' ,3'-0-(di-t.butyldime- thyl silyl)adenosine, triethylammonium salt (42b) (260 mg, 0.205 mmol) in methylene chloride (2 ml) containing 1,2-ethanedithiol (0.17 ml) as a carbocation scavenger, at 0 β After 1 hour the reaction mixture was diluted with methylene chloride and neutralized with IN aqueous triethylammonium hydrogen carbonate. The organic phase was dried (Na 2 S0 4 ) and concentrated. A 1 N tetrabutylammonium fluoride solution in tetrahydrofuran (1.3 ml) was added to the residue dissolved i tetrahydrofuran (5.1 ml). After 3 hours the reaction mixture was diluted with water and extracted with diethylether. The aqueous phase was concentrated, purified by reverse-phase chromatography on RP8 eluting with a stepwise gradient of acetonitrile from 0% to 60% in water, and passed through a column of Dowex-50W-X8 resin, Na * form. Evaporation of the solvent gave the title compound 43b (.118 mg, 80% yield over two steps) . H-NMR (400 MHz, DMSO-d 6 , t = 45 β C): δ = 8.45) 8.25, 8.12, 8 (four s, 4H, adenine H's);.7.25 (bs, 4H, 2 NH 2 ); 6.07 (d, J 5.4 Hz, IH, Hl'B); 5.86 (d, J = 6.0 Hz, IH, Hl'A); 5.20 (m, H2'B); 4.52 (m, 2H, H3'B + H2'A); 4.3-3.8 (m, 7H, H3'A + H4' H4'A + COOCH 2 + CH 2 OP) ; 2.74 (m, 2H, CH 2 NH 3 *) ; 2.28 (m, 2H, CH 2 COO); 1.49 ( , 4H, COCH 2 CH 2 CH 2 CH 2 CH 2 NH 3 *) ; 1.26 (m, 2H, COCH 2 CH 2 CH 2 CH 2 CH 2 NH 3 -) . FAB-MS: m/z 726 ( [M+H] * ) . Example 28 5'-O-[N**-(Benzyloxycarbonyl)-N"-(t.butoxycarbonyl)-L-lysyl3- -3'-O-(t.butyldimethylsilyl)-(S P )-P-thioadenylyl-(2'—>5' )- -2' ,3'-Q-(di-t. utyldimethylsilyl)adenosine, triethylammoniu salt (S,-42c) 3'-O-(t.butyldimethylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )- 2' ,3'-(di-1.butyldimethylsilyl)adenosine, triethylammonium salt (2) (500 mg, 0.474 mmol) and 0 --(benzyloxycarbonyl)- -N e -(t.butoxycarbonyl)-L-lysine (360 mg, 0.948 mmol), were coevaporated three times with anhydrous pyridine and dissolv in the same solvent (30 ml). N,N'-Dicyclohexylcarbodiimide ( mg, 0.948 mmol) and 4-dimethyl-aminopyridine (11.6 mg, 0.095 mmol) were added and the resulting mixture was stirred at ro temperature for 48 hours. The reaction mixture was then concentrated, diluted with methylene chloride and washed wit water. The organic phase was dried (Na 2 S0 4 ) and concentrated. Purification of the residue by silica gel column chromatogra eluting with methylene chloride/ methanol/triethylamine (90:5:0.2) gave the title compound (S-g-420) (590 mg, 88% yield) . ---H-NMR (200 MHz, CDC1 3 + D 2 0) : δ = 8.62, 8.29, 8.23, 8.09 (f s, 4H, adenine H's); 7.32 (m, 5H, aromatic H's); 6.34 (d, J 4.6 Hz, IH, Hl'B); 6.08 (d, J = 5.5 Hz, IH, Hl'A); 5.47 (ddd = 4.0, 4.6, 10.7 Hz, IH, H2'B); 5.09 (s, 2H, COOCH 2 Ph) ; 4.85 (m, IH, H3'B); 4.66 (dd, J = 4.8, 5.5 Hz, IH, H2'A); 4.4-4.1 (m, 8H, H3'A + H4 » A + H4'B +' COOCH 2 + CH 2 OP + CHα); 2.96 (m, 2H, (CH 2 ) 3 CH 2 NHCO); 1.42 (s, 9H, COOC(CH 3 ) 3 ); 1.9-1.0 (m, 6H, (CH 2 ) 3 CH 2 NHCO); 0.93, 0.91, 0.76 (three s, 27H, 3 SiCCH 3 ) 3 ); 0.22, 0.18, 0.09, 0.07, -0.05, -0.21 (six s, 8H, 6 SiCH 3 ) + triethylammonium signals. FAB-MS: m/z 1318 ([M+H]-). Example 29 5'-O-[Nα-(benzyloxycarbonyl)-L-lysyl]-(s P )-P-thioadenylyl(2' 5' )adenosine, sodium salt (Sp-43c) Trifluoroacetic acid (2 ml) was added to a solution of 5'-0-[ -(benzyloxycarbonyl)-Nε-(t.butoxycarbonyl)-L-lysyl]-3'-0-(t.b tyldimethylsilyl)-(Sp)-P-thioadenylyl-(2'—>5' )-2' ,3'-O-(di-t. butyldimethylsilyl)adenosine, triethylammonium salt (42c) (50 mg, 0.352 mmol) in methylene chloride (2 ml) containing 1,2-ethanedithiol (0.3 ml) as a carbocation scavenger at 0 β C. After 1 hour the reaction mixture was diluted with methylene chloride and neutralized with IN aqueous triethylammonium hydrogen carbonate. The organic phase was dried (Na 2 S0 4 ) and concentrated. A IN tetrabutylammonium fluoride solution in tetrahydrofuran (2.5 ml) was added to the residue dissolved in tetrahydrofuran (10 ml). After 2 hours the reaction mixture was diluted with water and extracted with diethylether. The aqueous phase was concentrated and the residue purified by reverse-phase chromatography on RP8 elutin with a stepwise gradient of acetonitrile from 0% to 60% in water. The solution was passed through a column of Dowex-5QW-X resin, Na "*" form and evaporation of the solvent gave the title compound (Sτ.-43c) (203 mg, 66% yield over the two steps). ^-H-NMR (200 MHz, DMSO-d s ): δ = 8.42, 8.27, 8.11 (three s, 4H, adenine H's); 7.76 (d, J = 7.0 Hz, IH, NHCO) ; 7.33 (m, 5H, aromatic H's); 7.25 (bs, 4H, 2 NH 2 ) ; 6.08 (d, J = 5.7 Hz, IH, Hl'B); 5.85 (d, J = 5.6 Hz, IH, Hl'A); 5.18 (m, IH, H2'B); 5.0 (s, 2H, COOCH 2 Ph); 4.52 (m, 2H, H3'B + H2'A); 4.3-3.8 (m, H3'A + H4'A + H4'B + COOCH 2 + CH 2 OP + CHα) ; 3.10 (m, 2H, (CH 2 ) 3 CH 2 NH 3 ÷ ); 1.7-1.2 (m,'6H, CH(CH 2 ) 3 CH 2 ) ; 0.92 (t, J = Hz, 3H, CH 3 (CH 2 ) 4 ) . FAB-MS: 875 ([M+H] * ). * Example 30 5'-O-[N**-(benzyloxycarbonyl)-N"-(t.butoxycarbonyl)-L-lysyl] -N β -benzoyl-3'-0-(t.butyldimethylsilyl)-(Rp)-P-thioadenylyl -(2'—>5' )-N β -benzoyl-2' ,3'-O-(di-t.butyldimethylsilyl)- adenosine triethylammonium salt (Rp-41c) . To a solution of N 6 -benzoyl-3'-O-(t.butyldimethylsilyl)- -(Rp)-P-thioadenylyl-(2'~>5' )-N 6 -benzoyl-2' ,3*-O-(di-t.- butyldimethylsilyl)adenosine (R P -5) (500 mg, 0.5 mmol) in dry pyridine, N^-benzyloxycarbonyl-N'-t.butoxycarbonyl-L- lysine (350 mg, 0.98 mmol) was added on stirring at 0°C, followed by 4-dimethylaminopyridine (200 mg, 1.6 mmol). The N,N'-dicyclohexylcarbodilmide (200 mg, 1 mmol) dissolved in dry pyridine (10 ml) was slowly added. The resulting solution was stirred overnight at room temperature. Evaporation of the solvent afforded an oily mixture which was chromatographed on a silica gel column eluting with dichloromethane/ methanol/triethylamine 98:2:0.2, to give the pure title compound (R∑.-41c) (600 mg, 73% yield), as a colorless foam. Example 31 5'-0-[N°--(benzyloxycarbonyl)-N"-(t.butoxycarbonyl)-L-lysyl] -3'-O-(t.butyldimethylsilyl)-(Rp)-P-thioadenylyl- (2'—>5' ) 2' ,3'-O- (t.butyldimethylsilyl)adenosine triethylammonium salt (R»-42c) 5'-O-[N°--(benzyloxycarbonyl)-N"-(t.butoxycarbonyl)-L-lysyl] N β -benzoyl-3'-O-(t.butyldimethylsilyl)-(Rp)-P-thioadenylyl- (2'—>5' )-N 6 -benzoyl-2' ,3'-O-(di-t.butyldimethylsilyl)- adenosine triethylammonium salt (R„-41c) (400 mg, 0.26 mmol), was dissolved in pyridine/acetic acid 3:2 and 0.5 M hydrazine hydrate (6 ml) was added dropwise to the resulting solution cooled at 0°C.The reaction mixture was stirred at 0°C for 3 hours and at room temperature overnight. The reaction mixture was evaporated under vacuum, and the residue taken up with 1 M triethylammonium bicarbonate (30 ml). Extraction with dichloromethane (2x50 ml), washing of the combined organic phases with water, drying and evapo¬ ration under vacuum afforded a crude product which was purified by silica gel column chromatography eluting with dichloromethane/methanol/triethylamine 90:10:0.5. The pure title compound (Rp-42c) was obtained as a colorless foam (280 mg, 73% yield) . X H-NMR (200 MHz, DMSO-d s ) : δ = 8.58, 8.24, 8.10, 8.06 (four s, 4H, adenine H's); 7.64 (d, J= 7.5 Hz, IH, CONHCH) ; 7.32 (m, 5H, aromatic H's); 7.19 (bs, 4H, 2 NH^) ; 6.74 (t, J= 5.6 Hz, IH, NH(CH 2 ) 4 ); 6.21 (d, J= 4.8 Hz, IH, Hl'B); 5.88 (d, J= 7.6 Hz, IH, Hl'A); 5.35 (m, IH, H2'B); 4.99 (s, 2H, CH Ph); 4.86 (d, J= 4.4 Hz, IH, H3'B); 4.82 (dd, J= 4.5, 7.6 Hz, IH, H2'A); 4.33 (d, J= 4.5 Hz, IH, H3'A); 4.2-3.4 (m, 7H, CHα + H4'A + H4'B + CH,OP + CH,OCO) ; 2.9-2.8 (signal overlapped by triethylammonium signals, 2H, CONHCH 2 ) ; 1.33 (s, 9H, COOC(CH 3 _) 3 ); 1.6-1.1 (m, 6H, (CH^ a ); 0.89, 0.87, 0.60 (three s, 27H, 3 SiCfCH^a); 0.19, 0.04, -0.14, -0.53 (four s, 18H, 6 SiCH 3 ) + triethylammonium signals. Example 32 5'-O-[ 0 --(benzyloxycarbonyl)-L-lysyl1-(Rp)-P-thioadenylyl- (2'—>5')- adenosine, (R„-43c) 5'-O-[N* 3 --(benzyloxycarbonyl)-N β -(t.butoxycarbonyl)-L-lysyl]■ -3'-O-(t.butyldimethylsilyl)-(Rp)-P-thioadenylyl-(2'—>5' )- 2' ,3'-O-(t.butyldimethylsilyl)adenosine triethylammonium salt (R-..-42C) (200 mg, 0.13 mmol) was dissolved in dry dichloromethane (20 ml), and the resulting solution was cooled at 0°C under dry nitrogen atmosphere. Then trifluoro- acetic acid (1 ml), was added dropwise and the reaction mixture was stirred for 10 minutes. Water (3 ml) was added, followed by solid sodium bicarbonate to obtain neutraliza¬ tion of the solution. The resulting slurry was treated with dichloromethane (100 ml) and the organic phase was separated, washed with water, dried and evaporated under vacuum. The residue was .dissolved in tetrahydrofuran (9 ml), cooled at -20°C and treated with 1 M tetrabutylammonium fluoride solution in tetrahydrofuran (1 ml, 1 mmol). The resulting reaction mixture was then stirred for 30 minutes at -30°C, and for 20 minutes at room temperature. Water (2 ml) was added, the organic solvent evaporated under vacuum and the residue was taken up with water (50 ml). The aqueous phase was washed with ethyl ether (2x10 ml), and chromato- graphed by reverse phase on Licroprep RP-8 column eluting with water/methanol 65:35 to give the pure title compound (Rp-43c) obtained as a colorless solid after lyophilization (10 mg, 7% yield) . ^H-NMR (400 MHz, DMSO-d β ) δ = 8.43, 8.29, 8.16, 8.14 (four s, 4H, adenine H's); 7.60 (bs, IH, NHCO) ; 7.30 (bs, 7H, 2 NH 2 + H-, * ) ; 7.10 (m, 5H, aromatic H's); 6.10 (d, J- 6.0 Hz, IH, Hl'B); 5.91 (d, J= 5.6 Hz, IH, Hl'A); 5.30 (m, IH, H2'B); 5.05 (s, 2H, CH^Ph) ; 4.57 (t, J= 5.2 Hz, IH, H2'A); 4.48 (t, J= 4.8 Hz, IH, H3'B); 4.3-3.7 (m, 8H, CHα + H4'A + H4'B + CH 2 OP + CH 2 OCO + H3'A); 2.67 (m, 2H, CH a NH„-) ; 1.8-1.2 (m, 6H, (____) _ ) . Example 33 5'-O-[N"--(benzyloxycarbonyl)-N'-(t.butoxycarbonyl)-L-lysyl- glycyl1- N β -benzoyl-3'-O-(t.butyldimethylsilyl)-(S P )-P-thi- oadenylyl-(2'—>5' ) -N β -benzoyl-2' ,3'-Q-(di-t.butyldimethyl¬ silyl)adenosine triethylammonium salt (44) . N 6 -Benzoyl-3'-O-(t.butyldimethylsilyl)-(Sp)-P-thioadenylyl- (2'—>5' ) -N 6 -benzoyl-2' ,3'-0-(di-t.butyldimethylsilyl) adenosine (Sp-5) (1.9 g, 1.8 mmol), was dissolved in pyridine (150 ml),and the resulting solution was cooled at O'-'C. 4-Dimethylaminopyridine (0.20 g, 1.6 mmol) and N,N'- dicyclohexylcarbodiimide (0.45 g 2.2 mmol) were added. The reaction mixture was stirred for 72 hours at room tempe¬ rature, then the solvent was evaporated and the residue partitioned betwen 5% aqueous citric acid and dichloro¬ methane. The aqueous phase was extracted with dichloro¬ methane and the combined organic extracts were washed with 1 M triethylammonium bicarbonate, and then with water, dried (Na 2 S0 4 ) and evaporated under vacuum to give the title compound (^ ) (2.81 g, 93% yield), sufficiently pure to be used for the next step. Example 34 5'-O-[N°--(benzyloxycarbonyl)-N c -(t.butoxycarbonyl)-L-lysyl- glycyl]- 3'-O-(t.butyldimethylsilyl)-(Sp)-P-thioadenylyl- (2'—>5' )-2' ,3'-0- (di-t.butyldimethylsilyl)adenosine tri¬ ethylammonium salt (46). 5'-O-[N°--(benzyloxycarbonyl)-N e -(t.butoxycarbonyl)-L-lysyl- glycyl]- N 6 -benzoyl-3'-O-(t.butyldimethylsilyl)-(Sp)-P-thio- adenylyl-(2'~>5' ) -N 6 -benzoyl-2' ,3'-0-(di-t.butyldimethyl- silyl)adenosine triethylammonium salt (^4) (1.8 g, 1.1 mmol) was dissolved in an ice-cooled 0.5 M solution of hydrazine hydrate in pyridine-acetic acid 3:2 (11 ml). The resulting solution was then stirred overnight at room temperature. Water (30 ml) was added, and the resulting slurry was treated with 1 M triethylammonium bicarbonate until gas evolution stopped and extracted with dichloromethane (5x50 ml). The organic extracts were washed with water (2x10 ml), dried (Na 2 S0 4 ) and evaporated under vacuum. The residue was purified by silica gel column chromatography eluting with dichloromethane/methanol/ triethylamine 86:10:0.6, to give the pure title compound (4_6) (0.9 g, 57% yield) as a color¬ less foam. H-NMR (200 MHz, DMSO-d β ) : δ = 8.50, 8.25, 8.10, 8.09 (four s, 4H, adenine H's); 8.33 (bs, IH, CONHCH 2 CO) ; 7.33 (m, 6H, NHCH + aromatic H's); 7.33, 7.23 (two bs, 4H, 2 H,) ; 6.74 (bs, IH, NH(CH 2 ) 4 ); 6.23 (d, J= 4.3 Hz, IH, Hl'B); 5.89 (d, J= 7.6 Hz, IH, Hl'A); 5.30 (m, IH, H2'B); 5.00 (s, 2H, CH 2 Ph); 4.9-4.8 (m, 2H, H2'A +-H3'B); 4.47 (d, J= 4.4 Hz, IH, H3'A); 4.4-3.7 (m, 9H, H4'A + H4'B + CH 2 OP + CH- a OCO + CHα + CONHCH ? CO) ; 2.9-2.8 (signal overlapped by triethyl¬ ammonium signals, 2H, NHCH a (CH-,)-,) ; 1.34* (s, 9H,' C00C(CH i ) 3 ); 1.6-1.1 (m, 6H, (____) _ ) ; 0.89, 0.87, 0.60 (three s, 27H, 3 SiC(CHa.) 3 ); 0.17, 0.15, -0.14, -0.51 (four s, 18H, 6 SiCHa) + triethylammonium signals. Example 35 5'-O-[N 0 --(benzyloxycarbonyl)-L-lysylqlvcyl]-(S P )-P-thio- adenylyl-(2'—>5' )adenosine (50) . 5'-O-[ β -(benzyloxycarbonyl)-N β -(t.butoxycarbonyl)-L-lysyl- glycyl]-3' -O-(t.butyldimethylsilyl)-(Sp)-P-thioadenylyl- (2'—>5')-2' ,3'-0-(di-t.butyldimethylsilyl)adenosine tri¬ ethylammonium salt (4_6) (150 mg, 0.1 mmol), was dissolved in an ice-cooled 1:1 mixture of trifluoroacetic acid and dichloromethane. The resulting solution was stirred at 0 β C under dry nitrogen atmosphere for 45 minutes. Then it .was diluted with dichloromethane (50 ml), neutralized with solid sodium bicarbonate, and partitioned between water and dichloromethane. Evaporation of the dried organic phase afforded the residue (121 mg) as a slightly yellow foam sufficiently pure for the next step. The above residue was dissolved in dry tetrahydrofuran (30 ml), and treated with a 1 M tetrabutylammonium fluoride solution in tetrahydrofuran (0.8 ml, 0.8 mmol). The resulting solution was stirred for 1.5 hours at room temperature, then 1 M triethylammonium bicarbonate solution (20 ml) was added and after the removal of the organic solvent the aqueous phase was charged on a Dowex-50W-X8 (Na-form) column. The column was eluted with water/acetoni¬ trile 98:2, the proper fraction were combined, evaporated to half volume and chromatographed by reverse phase on a RP-8 column eluting with water/acetonitrile 9:1. Fractions containing the product were combined and lyophilized to give the title compound (5_0) as a colorless solid (40 mg, 38% yield) . X H-NMR (200 MHz, DMS0-d 6 ) : 6 = 8.45, 8.23, 8.12, 8.10 (four s, 4H, adenine H's); 8.30 (bs, IH, CONHCH 2 ); 7.33 (m, 5H, aromatic H's); 7.25 (bs, 8H, 2 NH^ + NHCH + NH 3 -) ; 6.14 (d, J= 2.8 Hz, IH, Hl'B); 5.87 (d, J= 6.3 Hz, IH, Hl'A); 5.10 (m, IH, H2'B); 5.00 (s, 2H, CH ? Ph) ; 4.58 (m, IH, H3'B); 4.50 (m, IH, H"'A); 4.3-3.7 (m, 8H, H3'A + H4'A + H4'B + CHα + CH 2 QP + CH 2 QCO + ); 2.72 (t, J= 7.2 Hz, 2H, CH 2 H 3 -) ; 1.8-1.2 (m, 6H, (CH 2 ) 3 ). FAB-MS: m/z 932 ([M+H] * ). Example 36 5'-O-[N-(t.butoxycarbonyl)-L-phenylalanyl]-3'-O-(t.butyl- dimethyl silyl)-(S-c)-P-thioadenylyl-(2'-->5' )-2' ,3'-Q-(di- t.butyldimethyl silyl)adenosine triethylammonium salt (48) . 3'-O-(t.butyldimethylsilyl)-(Sp)-P-thioadenylyl-{2'~>5' )- 2' ,3'-O- (di-t.butyldimethylsilyl)adenosine triethylammonium salt (2) (1.2 g, 1.2 mmol), was dissolved in dry pyridine (100 ml) and N-(t.butoxycarbonyl)-L-phenylalanine (500 mg, 1.8 mmol) was added. To the resulting solution cooled at 0°C, 4-dimethylaminopyridine (110 mg, 0.9 mmol), and N,N'- dicyclohexylcarbodiimide (370 mg, 1.8 mmol) were added on stirring. The reaction mixture was stirred at room temperature for 96 hours, then the solvent was evaporated and the residue taken up with dichloromethane (100 ml). The organic phase was washed with 5% sodium bicarbonate solution (2x10 ml), and then with water, dried (Na 2 S0 ) and evaporated to dryness. The residue was purified by silica gel column chromatography eluting with dichloromethane/- methanol/triethylamine 80:20:1 to afford the pure title compound (^8_) (1.25 g, 82% yield). TLC on silica gel: R_ 0.66 eluting with dichloromethane/methanol/triethylamine 86:10:0.6. • 71 Example 37 5'-O-(L-phenylalanyl)-3'-O-(t.butyldimethylsilyl)-(Sp)-P- thioadenylyl-(2' —>5' )-2' ,3'-O-(di-t.butyldimethylsilyl)- adenosine (49) . 5'-0-[ -(t.butoxycarbonyl)-L-phenylalanyl]-3'-O-(t.butyl- dimethyl silyl)-(Sp)-P-thioadenylyl-(2'—>5' )-2' ,3'-O-(di- -t.butyldimethyl silyl)adenosine triethylammonium salt (48) (1.5 g, 1.18 mmol), was dissolved in 60 ml of dry dichloro¬ methane and cooled at 0°C. Trifluoroacetic acid (20 ml) was added dropwise under dry nitrogen atmosphere and the resulting solution was stirred at 0°C for 1.5 hours. Then the reaction mixture was neutralized with solid sodium bicarbonate and partitioned between water and dichloro¬ methane. The organic phase was dried (Na 2 S0 4 ) and evaporated leaving as residue the title compound (^9) (1.1 g, 85% yield) as a slight brown foam sufficiently pure to be used for the next step. Example 38 5'-O-[N°-(benzyloxycarbonyl)-N c -(t.butoxycarbonyl)-L-lysyl- phenylalanyl]-3'-O-(t.butyldimethylsilyl)-(S P )-P-thioadenyl- yl-(2'~>5' )-2'-3'-0-(di-t.butyldimethylsilyl)adenosine tri¬ ethylammonium salt (47) . 5'-O-( -phenylalanyl)-3'-O-(t.butyldimethylsilyl)-(Sp)-P- thioadenylyl-(2'~>5' )-2' ,3'-0-(di-t.butyldimethylsilyl)ade- nosine (4_9) (1.1 g, 0.9 mmol), and N^-benzyloxycarbonyl-N*- -t.butoxycarbonyl -L-lysine (456 mg, 1.2 mmol), were coeva¬ porated twice with dry pyridine then dissolved in dry dichloromethane (50 ml), and hydroxybenzotriazole (12 mg, 0.09 mmol) was added. To this ice-cooled solution, N,N'-di- cyclohexylcarbodiimide (247 mg, 1.2 mmol) was added in one portion, under stirring. The resulting solution was stirred at room temperature for 6 hours; some precipitated dicyclo- hexylurea was filtered off, and washed with cold dichloro- 7*2 methane. The filtrate and the washing were combined, washed with 5% sodium bicarbonate solution, and then with brine. Evaporation of the solvent afforded a solid which was dissolved in ethyl acetate/ dichloromethane 90:10. On standing overnight at +5°C a further amount of dicyclohexyl- urea was precipitated. Filtration and evaporation of the filtrate gave rise to a crude material which was purified by column chromatography on silica gel eluting with dichloro¬ methane/ methanol/ triethylamine 90:10:0.5 to give the pure title compound (.42) (1.1 g, 88% yield). H-NMR (400 MHz, DMSO-d β ) : δ - 8.50, 8.26, 8.09, 8.06 (four s, 4H, adenine H's); 8.10 (m, 2H, 2 NH) ; 7.4-7.0 (m, 14H, aromatic H's + 2 NH ) ; 6.70 (bs, IH, NHBoc); 6.22 (d, J= 4.4 Hz, IH, Hl'B); 5.89 (d, J= 7.6 Hz, IH, Hl'A); 5.30 (m, IH, H2'B); 4.97 (s, 2H, COOCH 2 Ph) ; 4.85-4.80 (m, 2H, H3'B + H2'A); 4.47 (m, IH, NHCHCOO) ; 4.44 (d, J= 4.4 Hz, IH, H3'A); 4.34, 4.12 (two m, 2H, C00CH 2 5'B); 4.06 (m, IH, H4'B); 3.90 (m, 3H, CH^OP + H4'A); 3,76 (m, IH, (CH 2 ) 4 CH); 2.83 (m, 2H, CH-∑NHBoc); 1.33 (s, 9H, COOC(CH 3 ) 3 ); 1.6-1.0 (m, 6H, (CH 2, ) 3 -CH 2 -NH) ; 0.88, 0.86, 0.60 (three s, 27H, 3 SiC( C___) 3 ) ; 0.18, 0.17, 0.04, -0.15, -0.40 (five s, 18H, 6 SiCHa) . Example 39 5'-O-[t -(benxyloxycarbonyl)-L-lysyl-L-phenylalanylyl]-(S P )- -P- thioadenylyl-(2'—>5' )-adenosine (51) 5'-O-[N" 3 --(benzyloxycarbonyl)-N β -{t.butoxycarbonyl)-L-lysyl- phenylalanyl]-3'-0-(t.butyldimethylsilyl)-(Sp)-P-thioadenyl- yl-(2'—>5' )-2'-3'-0-(di-t.butyldimethylsilyl)adenosine tri¬ ethylammonium salt (47) (500 mg, 0.358 mmol) was dissolved in dichloromethane (30 ml), and trifluoroacetic acid (6 ml), was added dropwise to this ice-cooled solution under dry nitrogen atmosphere. The reaction mixture was stirred at 0°C for two hours, neutralized with solid sodium bicarbonate, and partitioned between water and dichloromethane. The aqueous phase was extracted with dichloromethane (2x20 ml) and the combined organic extracts were washed with water, dried (Na 2 S0 4 ) and evaporated under vacuum to give a slight brown solid (400 mg, 86% yield). This solid was dissolved in dry tetrahydrofuran (60 ml), and the solution was cooled at -10°C. I M tetrabutylammonium fluoride in tet.rahydrofuran (1.66 ml, 1.66 mmol) was added under dry nitrogen atmosphe¬ re. The reaction mixture was then stirred at -10°C for 6 hours. 0.1 M ammonium acetate (40 ml) was added and the organic solvent evaporated under vacuum at low temperature (0°C). The aqueous residue was washed with ethyl ether (2x10 ml), the washing organic phase back extracted with water, and the combined aqueous phases charged on a RP-8 column. Elution with water/ acetonitrile 40:60 and lyophilization of the proper fraction led to the pure title compound (5_1) (133 mg, 40% yield over the two step) . X H-NMR (400 MHz, DMSO-d 6 ) : δ = 8.47, 8.21, 8.13, 8.11 (four s, 4H, adenine H's); 8.40 (d, J= 8.2, IH, NHCH); 7.70 (bs, 3H, NHV) ; 7.2-7.0 (m, 11H, NHCH + aromatic H's + 2 adenine NH ^ ) ; 6.17 (d, J= 1.6 Hz, IH, Hl'B); 5.88 (d, J= 6.4 Hz, IH, Hl'A); 5.00 (m, 4H, 2 CH 2 Ph) ; 4.77 (m, IH, H3'B); 4.54 (m, IH, H2'A); 4.43 (m, IH, CH(CH 2 ) 4 ); 4.4-3.8 (m, 8H, H4'A + H4'B + H3'A + CHCH 2 Ph- + CH 2 OCO + CH a OP) ; 3.2-2.7 (m, 4H CHCH 2 Ph + CH ? Ha-); 1.7-1.2 (m, 6H, (CH a ) . FAB-MS: m/z 1022 ( [M+H]" " ) .

Claims: CLAIMS 1. Use of a nucleotide analog of the formula I wherein R_ represents (i) a hydrogen atom, (ii) a 2* or 3 1 - P-thionucleotidyl residue conjugated at its 5' position with an acyl group, (iii) a phosphoryl group, a P- thiophosphoryl group, a P0 2 R 2 H group optionally esterified with a linear or branched, cyclic or acyclic aliphatic hydroxy alkyl group having from 1 to 6 carbon atoms or with a lipophilic moiety or (iv) an acyl group; R 2 represents a C_-C Q alkyl group or hydrogen atom, and the pharmaceutically acceptable salts thereof, in the manufacture o2 a medicament for use as an antiviral, antitumour, immunomodulatory, interferon-enhancing or interferon-indueing agent. 2. Use according to claim l wherein, in formula (I), R 1 is a 2-P-thioadenyl residue. 75 3. Use according to claim 1 wherein, in formula (I), R 1 is a P0 2 R 2 H group optionally esterified with a lipophilic moiety selected from a cholesteryl group or glycerol esterified with an unsaturated or saturated long chain fatty acid having from 6 to 20 carbon atoms. 4. Use according to claim 1 wherein, in formula (I), R 1 is a Pθ2R 2 H group in which R 2 is methyl. 5. Use according to claim 1 wherein R^ represents an acyl group which is the residue of one of the following: (i) an aliphatic carboxylic acid with a linear or branched, acyclic or cyclic skeleton of from 1 to 20 carbo atoms; (ii) a difunctional acid in which one acidic moiety is esterified with a C^-Cg hydroxy alkyl group or with a lipophilic moiety; or (iii) a carboxylic acid bearing, at physiological pH, a centre of positive charge. 6. Use according to claim 5 wherein R^ represents an acyl group which is the residue of one of the following: (i) octanoic, cyclohexylacetic or palmitic acid; (ii) oxalic, carbonic, phosphoric, malonic or succinic acid in which one acidic moiety is esterified with a C-^-Cg hydroxy alkyl group or a lipophilic moiety; or (iii) a ,9-aminopropionic acid, a 3- or 6-aminocaproic acid or an -amino acid of a basic nature, or a short peptide chain containing at least one basic residue, the α-amino acid or short peptide chain being optionally protected at the terminal α-amino group. 7. A compound of the formula I 1 wherein R 2 is as defined in claim 1 and R3 is as defined for R_ in any one of claims 1 to 6 with the exception of hydrogen, a P-thiophosphoryl and a phosphoryl group; or a pharmaceutically acceptable salt thereof. 8. A pharmaceutical composition which comprises a compound of the formula I 1 as defined in claim 7 and a pharmaceutically acceptable diluent or carrier. 9. A process for preparing a compound of the formula I' as defined in claim 7, which process comprises introducing the desired R3 group at the 5' position of an appropriately protected compound of the formula II wherein Z represents hydrogen or a protecting group, X represents a protecting group for the hydroxyl group; and Y represents hydrogen, a negative charge or protecting group for the phosphate function; and then removing the protecting groups. 10. A compound as claimed in claim 7 for use as an antiviral, antitumour, immunomodulatory, interferon- enhancing or interferon-inducing agent.

Inventors: BATTISTINI CARLO, BRASCA MARIA GABRIELLA, ERMOLI ANTONELLA, FUSTINONI SILVIA, GIORDANI ANTONIO, BATTISTINI, CARLO, BRASCA, MARIA, GABRIELLA, ERMOLI, ANTONELLA, FUSTINONI, SILVIA, GIORDANI, ANTONIO
Applicants: ERBA CARLO SPA, FARMITALIA CARLO ERBA S.R.L.
Application year: 1992
Main classification: A61K31
IPC codes: A61K31, A61P31, C07H21