Synthesis of 2-methyl-[2-acetamido-4- O-acetyl-6- O-benzyl-3 O-(2-butenyl)-1,2-dideoxy-α- d-glucopyrano]-[2,1- d]-2-oxazoline a versatile intermediate for the synthesis of complex oligosaccharides of bacterial cell-wall, human milk, and blood-group substances

Abstract

2-Methyl-[2-acetamido-4- O-acetyl-6- O-benzyl-3- O (2-butenyl)-1,2-dideoxy-α- d-glucopyrano]-[2,1- d]-2-oxazoline ( 2), a glycosylating agent in which the three hydroxyl groups are blocked with protecting groups of differing “persistence”, is of utility in the synthesis of oligosaccharides containing highly branched 2-acetamido-2 deoxy- d-glucosyl residues, and it was synthesized in a ten-step sequence from 2-acetamido-2-deoxy- d-glucose via allyl 2-acetamido-4,6- O-benzylidene-2-deoxy-β- d-glucopyranoside ( 3)- Alkylation of 3 with 2-butenyl (crotyl) bromide, hydrolysis of the benzylidene acetal group, benzylation of the 6-hydroxyl group, and acetylation of the 4-hydroxyl group afforded allyl 2-acetamido-4- O-acetyl-6- O-benzyl-3- O-(2-butenyl)-2-deoxy-β- d-glucopyranoside ( 10). Treatment or 10 with chlorotris(triphenylphosphine)rhodium( l) gave mainly the corresponding 1-propenyl β-glycoside, which was converted into oxazoline 2 by the action of mercuric chloride-mercuric oxide in acetonitrile. Glycosylation of benzyl 2-acetamido-3,6-di- O-benzyl-2-deoxy-α- d-glucopyranoside with 2, and subsequent O-deacetylation at O-4′ gave a glycosyl acceptor, benzyl 2-acetamido-4- O-[2-acetamido-6- O-benzyl-3- O-(2-butenyl)-2-deoxy-β- d-glucopyranosyl]-3,6-di- O-benzyl-2-deoxy-α- d-glucopyranoside.