PSEUDOSUGARS, 39 - SYNTHESIS OF METHYL 5A'-CARBA-BETA-LACTOSIDE AND N-ACETYL-5A'-CARBA-BETA-LACTOSAMINIDES, AND RELATED 5A'-CARBADISACCHARIDES

Construction of the ether-linked methyl 5a'-carba-beta-lactoside (3) a nd N-acetyl-5a'-carba-beta-lactosaminide (4) were carried out starting from the coupling products 15 and 16, readily obtained by coupling be tween anhydro-4,6-O-benzylidene-5a-carba-D-mannopyranose (7) and the o xide anions generated from methyl 2,3,6-tri-O-benzyl-beta-D-glucopyran oside (8) and methyl ido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosid e (10), respectively. Their 5a-carba-alpha-D-mannopyranose moieties we re transformed into those of 5a-carba-beta-D-galactopyranose by a sequ ence of reaction: Oxidation of the 2'-OH group, epimerization of the C -1' with DBU, selective reduction of the carbonyl group, and epimeriza tion of the C-4' via oxidation and then reduction of 4'-OH or S(N)2 re action of the 4'-mesylate with an acetate anion. Reaction of -O-isopro pylidene-5a-carba-alpha-D-galactopyranose (6), initially expected as t he potential donor, with these oxide anions did not give any ether-lin ked products, rather resulting in elimination reaction of 7. However, coupling of the epoxide 6 with methyl tamido-4-amino-2,4-dideoxy-beta- D-glucopyranosides (19) easily gave rise to imino-linked 5a'-carbadisa ccharide derivative 38, which, after deprotection, gave the imino-link ed congener 5. On the other hand, two biologically interesting carbadi saccharides including methyl N,N'-diacetyl-5a'-carbachitobioside (45) were obtained from the versatile intermediate 24.