Efficient chemical synthesis of both anomers of ADP L-glycero- and D-glycero-D-manno-heptopyranose

A series of anomeric phosphates and ADP-activated L-glycero- and D-glycero-D-manno-heptopyranoses has been prepared in high overall yields, which provided model compounds and substrates in the elucidation of biosynthetic pathways and glycosyl transfer reactions of nucleotide-activated bacterial heptoses. The alpha-anomers of the heptosyl phosphates were obtained in high yield and selectivity using the phosphoramidite procedure, whereas the beta-phosphates were formed preferentially employing acylation of reducing heptoses with diphenyl phosphorochloridate. An efficient route to the formation of the nucleotide diphosphate sugars was elaborated by coupling of the O-acetylated phosphates with AMP-morpholidate followed by alkaline deprotection to furnish ADP-L- and D-glycero-alpha-D-manno-heptose in 84 and 89% yield, respectively. Deacetylation of the O-acetylated beta-configured ADP heptoses was conducted at strictly controlled conditions (-28 degrees C at pH 10.5) to suppress formation of cyclic heptose-1,2-phosphodiesters with concomitant release of AMP. Isolation of the unstable beta-configured ADP-heptoses by anion-exchange chromatography and gel-filtration afforded ADP L- and D-glycero-beta-D-manno-heptose in high yields.