A series of nucleosides were synthesized in which the 4'-hydrogen was substituted with either an azido or a methoxy group. The key steps in the syntheses of the 4'-azido analogues were the stereo- and regioselective addition of iodine azide to a 4'-unsaturated nucleoside precursor followed by an oxidatively assisted displacement of the 5'-iodo group. The 4'-methoxynucleosides were made via epoxidation of 4'-unsaturated nucleosides with in suit epoxide opening by methanol. Reaction-mechanism considerations, empirical conformation rules, NMR-based conformational calculations, and NOE experiments suggest that the 4'-azidonucleosides prefer a 3'-endo (N-type) conformation of the furanose moiety. When evaluated for their inhibitory effect on HIV in A3.01 cell culture, all the 4'-azido-2'-deoxy-beta-D-nucleosides exhibited potent activity. IC50's ranged from 0.80 microM for 4'-azido-2'-deoxyuridine (6c) to 0.003 microM for 4'-azido-2'-deoxyguanosine (6e). Cytotoxicity was detected at 50-1500 times the IC50's in this series. The 4'-methoxy-2'-deoxy-beta-D-nucleosides were 2-3 orders of magnitude less active and less toxic than their azido counterparts. Modifications at the 2'- or 3'-position of the 4'-substituted-2'-deoxynucleosides tended to diminish activity. Further evaluation of 4'-azidothymidine (6a) in H9, PBL, and MT-2 cells infected with HIV demonstrated a similar inhibitory profile to that of AZT. However, 4'-azidothymidine (6a) retained its activity against HIV mutants which were resistant to AZT.

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The practical synthesis of a mixed phenoxy-amidate derivative of PMPA with high oral bioavailability and favorable pharmacokinetics is described. The non-stereoselective synthetic route produces a 1:1 mixture of two diastereomers at phosphorous. Simulated moving bed chromatography using Chiralpak AS enabled kilo-scale isolation of the more potent diastereomer (GS-7340). The GS-7340 phosphorous chiral center was found to be (S) by X-ray crystallography.

New carbocyclic adenosine analogues substituted at the 6'-position with fluorine, hydroxyl, methylene, or hydroxymethyl have been synthesized as potential mechanism-based inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase. The synthetic routes began with a functionalized (+/-)-azidocyclopentane 2, which was elaborated to the adenosine analogue, or with functionalized cyclopentane epoxides 11, 20, and 27, which were opened directly with adenine in the presence of base. The 6' alpha-fluoro, 6' beta-fluoro, and 6'-methylene carbocyclic adenosine analogues were potent inhibitors of AdoHcy hydrolase. None of the compounds displayed significant activity against herpes simplex virus type 1 or type 2, but several demonstrated potent inhibition of vaccinia virus replication.

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