Synthesis of oligo(α-D-glycosyl phosphate) derivatives by a phosphoramidite method via boranophosphate intermediates

An efficient method for the synthesis of short oligo(α-D-glycosyl boranophosphate) derivatives by using an α-D-glycosyl phosphoramidite as a monomer unit was developed. The synthesis of oligomers was carried out by repeating a cycle consisting of the condensation of the monomer unit with a terminal hydroxy group of carbohydrates, boronation of the resultant phosphite intermediates, and terminal deprotection. The phosphoramidite monomer unit was synthesized from the corresponding glycosyl iodide and methyl N,N-diisopropylphosphonamidate in a highly α-selective manner. Di- and tri(α-D-glycosyl boranophosphate) derivatives obtained by the synthetic cycle were converted into the corresponding H-phosphonate diester derivatives, which were then used to synthesize di- and tri(α-D-glycosyl phosphate) derivatives including a fragment of Leishmania glycocalyx lipophosphoglycans.