Synthesis, in Vitro Antiviral Evaluation, and Stability Studies of Novel α-Borano-Nucleotide Analogues of 9-[2-(Phosphonomethoxy)ethyl]adenine and (R)-9-[2-(Phosphonomethoxy)propyl]adenine

We describe here the synthesis of 9-[2-(Boranophosphonomethoxy)ethyl]adenine (6a) and (R)-9-[2-(Boranophosphonomethoxy)propyl]adenine (6b), the first α-boranophosphonate nucleosides in which a borane (BH3) group substitutes one nonbridging oxygen atom of the α-phosphonate moiety. H-phosphinates 5a and 5b and α-boranophosphonates 6a and 6b were evaluated for their in vitro activity against human immunodeficiency virus (HIV) infected cells and against a panel of DNA or RNA viruses. Compounds 5a, 5b, 6a, and 6b exhibited no significant antiviral activity in vitro and cytotoxicity. To measure the chemical and enzymatic stabilities of the target compounds 6a and 6b, kinetic data of decomposition for derivatives 5a, 5b, 6a, 6b, and standard compounds were studied at 37 °C in several media. The α-Boranophosphonates 6a and 6b were metabolized in culture medium into H-phosphinates 5a and 5b, with half-live values of 5.3 h for 6a and 1.3 h for 6b.