We report synthesis, in vitro antiviral activity, and stability studies in biological media of original boranophosphonate isosteres of AZT and d4T monophophates. A convenient route for the synthesis of 3′-Azido-3′-deoxythymidine-5′-boranophosphonate 8 and 2′, 3′- Didehydro-3′-dideoxythymidine-5′-boranophosphonate 12 is described. H-phosphinates 7 and 11, and α-boranophosphonates 8 and 12 exhibited no significant in vitro activity ...