Boranephosphonates. Unraveling chemistry of the P-BH3 functional group

Abstract

Nucleoside boranephosphonates are an important class of nucleotide analogues in which one of the non-bridging oxygen atoms has been replaced by a borane moiety (-BH3). In the presence of iodine nucleoside boranephosphonates react with 1° and 2° amines to afford the corresponding phosphoramidates, while with 3° and heteroaromatic amines, the borane group is modified forming new derivatives with the P-B-N bond system. We investigated mechanistic aspects of these reactions and showed that both of them followed the same initial steps that involved most likely formation of λ3-boranephosphonate as a key, electrophilic intermediate. It reacts further, eventually leading to either the corresponding phosphoramidate diester or the B-ammoniumboranephosphonate derivative, depending on the type of amine used.