SYNTHESIS OF CARBON-BRIDGED N-ACETYL-C-LACTOSAMINE AND DERIVATIVES

4-C-Formyl-2-azidoglucopyranoside 12a, required for N-acetyl-C-lactosa mine synthesis as electrophile, was obtained from thexyldimethylsilyl 2-azido-2-deoxy-glucopyranoside 3 via readily available 4-O-unprotecte d 6a and then 4-C-methylene derivative 8a in overall seven steps. Alte rnatively, regioselective silylation of 3 with tert-butyldimethylsilyl chloride gave 4-O-unprotected 6b which was transformed by a similar r eaction sequence into 12a. In order to circumvent a Wittig reaction, 6 a was transformed into triflate 13 the reaction of which with 4-C-cyan o derivative 14 followed by reduction with DIBAH and base-catalyzed is omerization also afforded 12a. Reaction of 12a with 1-C-lithiated 2-ph enylsulfinyl-D-galactal 15 as nucleophile furnished C-disaccharide int ermediates 16a and 16b as diastereoisomers. Ensuing removal of the phe nylsulfinyl group with Raney nickel and diastereospecific 2b-hydrogen and 3b-hydroxy transfer afforded beta(1-->4)-connected N-acetyl-C-lact osamines 19a and 19b; their structures were deduced from derivatives 2 0a, b and 21a, b on the basis of H-1-NMR data. Hydrogenolytic O-debenz ylation of 19b afforded hydroxymethylene-bridged N-acetyl-C-lactosamin e 2b'.