Efficient chemoenzymatic synthesis of ADP-D-glycero-beta-D-manno-heptose and a mechanistic study of ADP-L-glycero-D-manno-heptose 6-epimerase.

[reaction: see text] A chemoenzymatic synthesis of ADP-D-glycero-beta-D-manno-heptose (ADP-D,D-Hep) is described in which D,D-Hep 7-phosphate is converted to ADP-D,D-Hep by two biosynthetic enzymes. This strategy allows access to the 6''-deuterated analogue, which upon incubation with the epimerase showed complete retention of the isotopic label at the 6''-position. This provides evidence for a direct oxidation mechanism in which the hydride initially transferred to the NADP+ cofactor is subsequently returned to the same carbon in a nonstereospecific manner.