Synthesis of penicillamine- and cysteine-containing nucleoamino acids as potential antivirals and aminopeptidase B inhibitors

Nucleoamino acids, wherein D- and L-penicillamine and D-and L-cysteine are attached to uridine or thymidine through a carboxylic ester linkage, have been synthesized and evaluated as antivirals and aminopeptidase B (AP-B) inhibitors. The coupling of the α-amino-β-mercapto acids, N,S-protected as N-formylthiazolidines, to 2′,3′-O-isopropylideneuridine, 3′-O-acetylthymidine, 5′-O-tritylthymidine, and thymidine was achieved via the mixed anhydride formed from N,N-bis-(2-oxooxazolidin-3-yl)phosphorodiamidic chloride and the corresponding protected amino acid in the presence of 4-(dimethylamino)pyridine. Treatment of the protected compounds with 1 mol dm–3-HCl in refluxing MeOH, under argon, afforded the corresponding deprotected nucleoamino acids free of racemization. Neither the compounds herein described nor D-penicillamine showed anti-HIV-1 activity in MT-4 cells or antiviral activity against some other viruses at concentrations below the cytotoxicity threshold. Penicillamine and cysteine monoesters were equipotent with the corresponding free amino acid in inhibiting AP-B with an IC50 in the 10–4 mol dm–3 range, while the bis-(α-amino-β-mercaptoacyl)thymidine derivatives were approximately twice as potent as the monoesters.