Synthesis and separation of diastereomers of uridine 2′,3′-cyclic boranophosphate

The first boron-containing 2′,3′-cyclic phosphate-modified analogue, uridine 2′,3′-cyclic boranophosphate (2′,3′-cyclic-UMPB), was synthesized. 5′-O-Protected uridine was cyclophosphorylated by diphenyl H-phosphonate to yield uridine 2′,3′-cyclic H-phosphonate, which upon silylation followed by boronation and subsequent acid treatment gave 2′,3′-cyclic-UMPB in high yield. The two diastereomers of 2′,3′-cyclic-UMPB were separated by HPLC. An alternative method for synthesis of uridine 2′,3′-cyclic phosphorothioate (2′,3′-cyclic-UMPS) via H-phosphonate was also described.