Conjugate addition of N-methylhydroxylamine upon (S)-4-(tert-butyldimethylsilyloxymethyl)butenolide 5 proceeded stereospecifically to afford the D-erythro isomer 6. A stereospecific phenylselenylation α to the carbonyl group led to the D-arabino isomer 12, allowing the stereoselective synthesis from L-glutamic acid of the α-D isomer 16 of the title compounds. Conversely, the α-L isomer 16' was obtained from D-glutamic acid. Upon skipping the orientating phenyselenylation step, both α-D-erythro (16) and β-D-erythro (18) isomers were obtained. Contrasting with the significant anti-HIV activity of the β-D-threo isomer, the β-D-erythro nucleoside exhibited no such property but did exhibit anti-VZV activity. On the other hand, the α-D-erythro isomer (16) was devoid of any tested (HIV, HSV, VZV, CMV) antiviral activity and the α-L-isomer 16' was inactive against HIV.