Synthetic routes to nucleoside analogs of N-substituted 1,3-thiazolidines

Nucleoside analogs, namely 6-benzamido-9-(3-benzoyl-4(R))-methoxycarbonyl-2,2-dimethyl-thiazolidin-5(S)-yl)-9H-purine (7) and 6-chloro-9-[(3-benzoyl-2,2-dimethylthiazolidin-4(R)-yl)methyl]-9H-purine (8), were obtained from 3-benzoyl-5(S)-benzoyloxy-4(R)-methoxycarbonyl-2,2-dimethylthiazolidine (23) and 3-benzoyl-4(R)-hydroxymethyl-2,2-dimethylthiazolidine (24), respectively, the former, by treatment with 6-benzamidochloromercuripurine and titanium tetrachloride in 1,2-dichloroethane and the latter, by treatment with 6-chloropurine, triphenylphosphine, and diethyl azodicarboxylate in tetrahydrofuran. Compound 23 was obtained from 3-benzoyl-4(R)-methoxycarbonyl-2,2-dimethylthiazolidine (13) by treatment with benzoyl peroxide in refluxing benzene whereas compound 24 was obtained from 13 by borohydride reduction. The stereochemistry of the isomeric sulfoxides 18a and 18b, obtained from 13 by treatment with m-chloroperbenzoic acid, was assigned by means of 1Hmr spectroscopy. Reaction of the sulfoxides 18a and ...