Synthesis of C-8 deuterated glycosides of 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) related to chlamydial lipopolysaccharides

Methyl glycosides of Kdo and a (2 --> 8)-linked Kdo disaccharide were prepared which contain a deuterium label at C-8 of the reducing unit. The label was introduced in fair diastereoselectivity upon reduction of an aldehyde group using a chiral borane complex derived from N-benzyloxycarbonyl-(S)-proline which produced the 8-(S)-deuterated derivative as the major isomer. Further coupling with a Kdo bromide gave the alpha-(2 --> 8)-linked disaccharide in good yield. The deprotected disaccharide serves as a model for NMR spectroscopic studies on the side chain conformation of a carbohydrate epitope from the bacterial pathogen Chlamydia.