L-3-O-BENZYL-ALPHA-D-ARABINO-HEXO-PYRANOS-2-ULOSYL BROMIDE - A CONVENIENTLY ACCESSIBLE GLYCOSYL DONOR FOR THE EXPEDIENT CONSTRUCTION OF DIANTENNARY BETA-D-MANNOSIDES BRANCHED AT O-3 AND O-6

A concise practical, large scale-adaptable six-step sequence has been developed for the transformation of diacetone-glucose into -benzoyl-3- O-benzyl-alpha-D-arabino-hexo-pyranos-2 -ulosyl bromide (7), a most us eful indirect beta-D-mannosyl donor as its blocking group pattern allo ws the construction of biologically relevant beta-D-mannosides branche d at O-3 and O-6. The broad utility of this new ulosyl bromide 7 resid es in its high anomeric reactivity, and in the ease and uniformity wit h which beta-stereocontrol can be achieved over both, glycosidations a nd carbonyl reduction of the beta-ulosides formed: Koenigs-Knorr condi tions exclusively provide beta-glycosiduloses, hydride reduction of th eir carbonyl functions proceeds with high stereoselectivities (> 20:1) in favor of the beta-D-mannosides, These preparatively auspicious pro perties are materialized in an efficient, straightforward synthesis of alpha-D-Manp-(1 --> 6)-[alpha-D-Manp-(1 --> 3)]-beta-D-Manp-(1 --> O) -Octyl, the 3,6-O-branched core-mannotrioside carrying an octyl spacer instead of the chitobiosyl unit. (C) 1998 Elsevier Science Ltd.