Synthesis of normuramic acid carba analog and its glycopeptide derivative resistant to beta-elimination splitting of the side chain

Carba analogs of normuramic acid, i.e., 3-(benzyl 2-acetamido-2,3-dideoxy-4 ,6-O-isopropylidene-alpha -D-glucopyranosid-3-yl)propanoic acid derivatives (nitrile or esters) 3a-3c were prepared by addition of radicals generated from benzyl 2-acetamido-2-deoxy-4,6-O-isopropylidene-3-O-[(methylsulfanyl)t hiocarbonyl]- (2a) or -3-O-(phenoxythiocarbonyl)alpha -D-glucopyranoside (2 b) with Bu3SnH to acrylonitrile or acryl esters. Alkaline hydrolysis of eth yl ester 3c afforded 3-(benzyl 2-acetamido-2,3-dideoxy-4,6-O-isopropylidene -alpha -D-glucopyranosid-3-yl)propanoic acid (5). Coupling of acid 5 with L -2-aminobutanoyl-D-isoglutamine benzyl ester trifluoroacetate and subsequen t deprotection of the intermediate 6 furnished N- [3-(2-acetamido-2, 3-dide oxy-alpha -D-glucopyranosid-3-yl)propanoyl]-L-2-aminobutanoyl-D-isoglutamin e (7).