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The promising antiviral properties of 3'-fluoro-3'-deoxyadenosine and 4',4'-difluoro-4'-deoxy-5'-noraristeromycin prompted the synthesis of the corresponding 3'-fluoro derivatives of 5'-noraristeromycin. These target compounds, which were prepared from the same readily accessible cyclopentenol, were found to be inactive when subjected to 31 viral assays. The results have some implications on the mechanism of antiviral action of 5'-noraristeromycin and provide guidance for future geminal-difluoro analog design.

The potent antiviral potential of 5'-amino-5'-deoxy-5'-noraristeromycin (2) is limited by associated toxicity. To seek derivatives of 2 that circumvent this undesirable property, three amino substituted derivatives (acetyl, 3; formyl, 4; and methyl, 5) of 2 have been prepared in 4-7 steps from the same intermediate, (1S,4R)-4-(6-chloropurin-9-yl)cyclopent-2-en-1-ol (6). Key steps involved an improved Pd(0)-catalyzed allylic azidation and a novel Pd(0)-catalyzed allylic amidation. The three target compounds were evaluated against a large number of viruses and found to be inactive except for a very weak effect of 5 on human cytomegalovirus, varicella zoster virus, and Epstein-Barr virus. There was also no noteworthy cytotoxicity associated with the new derivatives. Thus, these results indicate variation of the cyclopentyl amine of 2 does not offer a means to improve upon its antiviral potential.

5′-Noraristeromycin ( 1 ) and its enantiomer ( 2 ) have been found to possess a wide range of antiviral effects. In the search for analogues of 1 and 2 with improved activity, the synthesis of both enantiomers of 5′-mercapto-5′-deoxy-5′-noraristeromycin ( Figure 1 , Scheme 1 , Scheme 2 and 7 ) has been accomplished. While (+)- 7 was inactive, (−)- Figure 1 , Scheme 1 , Scheme 2 did show marginal activity against vaccinia virus, but not any other virus.

5′-Fluoro-5′-deoxyaristeromycin ( 2 ) has been prepared via a Mitsunobu coupling of (1 S ,2 S ,3 R ,4 S )-2,3-(cyclopentylidenedioxy)-4-fluoromethylcyclopentan-1-ol with N 6 -bis-boc protected adenine. This procedure is adaptable to preparing a number of 5′-fluoro-5′-deoxycarbocyclic nucleoside analogs with diversity in the heterocyclic base. Antiviral analysis found promising activity for 2 toward measles but no other viruses. No cytotoxicity was observed for 2 .

Using the observation that the side effects of aristeromycin (carbocyclic adenosine) were reduced by removing the methylene at the center in aristeromycin where phosphorylation occurs, derivatives of carbocyclic oxetanocin A (4a), oxetanocin G (4b), and 2-aminooxetanocin A (16) lacking the 3'-methylene have been prepared in racemic form. The only viruses for which an appreciable inhibitory effect of the compounds (minimum inhibitory concentration ranging from 1 to 40 microg/mL) was noted were herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV). However, when directly compared for their antiviral potency against HSV-1 with their parents oxetanocin A and oxetanocin G, compounds 4a and 4b proved clearly less active.

A synthetic route to (1 S ,2 S ,3 R ,5 S )-3-(6-amino-9 H -purin-9-yl)-5-fluorocyclopentane-1,2-diol (that is, the 4′-fluoro derivative of 4′-deoxy-5′-noraristeromycin, 3 ) is described via a fluorinated cyclopentanol, which is in contrast to existing schemes where fluorination occurred once the purine ring was present. Compound 3 was assayed versus a number of viruses. A favorable response was observed towards measles (IC 50 of 1.2 μg/mL in the neutral red assay and 14 μg/mL by the visual assay) but this was accompanied by cytotoxicity in the CV-1 host cells (21–36 μg/mL). Among the viruses unaffected by 3 were human cytomegalovirus and the poxviruses (vaccinia and cowpox), which are three viruses that were inhibited by the 4′,4′-difluoro analog of 3 (that is, 2 ).

The biological versatility of aristeromycin (carbocyclic adenosine) is limited by accompanying cytotoxicity caused ostensibly by the intracellular formation of its 5‘-nucleotide derivatives. Aristeromycin derivatives that offered steric interference to this transformation at the C-5‘ center were sought. This paper describes the facile stereospecific synthesis, where necessary, of such C-5‘-methylated aristeromycin derivatives.

5'-norcarbocyclic nucleosides have been found to possess a variety of meaningful biological properties. Derivatives of these compounds possessing substituents at the hydroxyl and heterocyclic ring bearing carbon atoms have not been described. As entries into these compounds, the 4'- and 1'-methyl derivatives of 5'-noraristeromycin (2 and 3) have been prepared from a common cyclopentyl precursor 8. The synthetic methods developed are adaptable to 5'-norcarbanucleosides possessing a variety of heterocyclic bases and in the l-like configuration. In turn, the products from such syntheses will lend themselves to a number of structural and biochemical investigations relevant to carbanucleosides in general. Compounds 2 and 3 lack antiviral properties and were not cytotoxic.

To begin an exploration of the structural parameters responsible for the activity of (+)-5'-noraristeromycin toward hepatitis B virus (HBV), three derivatives varied at the C-4' position have been prepared and evaluated. The syntheses began with a Mitsunobu coupling reaction of an appropriate cyclopentanol with 6-chloropurine. The products of these reactions were synthetically altered by standard ammonolysis and deprotection procedures to give the desired products. Evaluation of the new derivatives indicated that removal of the C-4' hydroxyl of (+)-5'-noraristeromycin increased its potency toward HBV by approximately 10-fold.

To evaluate analogues of the antiviral agent (R)-9-(3,4-dihydroxybutyl)guanine in which the side-chain C-3 hydroxyl oxygen is part of a five-membered ring, carbocyclic 3′-oxa-2′,3′-dideoxyguanosine (4) and carbocyclic 3′-oxa-2′,3′-dideoxy-7-deazaguanosine (5) have been synthesized in 17 and 14 steps, respectively, from 5-O- acetyl -1,2-O- isopropylidene -α- d - xylofuranose . Compounds 4 and 5 and their 6-chloro precursors were evaluated against a wide variety of DNA and RNA viruses. Only 4 showed any marginal activity and this was limited to HSV-1 and HSV-2. Even though 4 was less potent towards these latter two viruses than acyclovir, its mechanism and target of action is proposed to resemble that of acyclovir. The only toxicity observed for these compounds was observed in the cell growth assay with human embryonic lung cells.