2,6-Disubstituted benzoates as neighboring groups for enhanced diastereoselectivity in beta-galactosylation reactions: synthesis of beta-1,3-linked oligogalactosides related to arabinogalactan proteins.
Arabinogalactan proteins (AGPs) are plant glycoproteins which contain a beta-1,3-linked galactan core. The synthesis of the beta-galactopyranose-1,3-beta-galactopyranose linkage using various 2-O-acyl-protected glycosyl donors has been plagued with poor stereoselectivity and side reactions including orthoester formation and transesterification of the 2-O-acyl group from the donor to the acceptor. We have investigated the use of 2,6-disubstituted benzoyl groups as bulky neighboring groups on the glycosyl donor. A 2,4,6-trimethylbenzoyl group was found to be optimal and enabled the formation of the beta-galactopyranose-1,3-beta-galactopyranose linkage to disarmed ester-protected acceptors, suppressing transesterification and reducing orthoester formation while enhancing the beta-selectivity of galactosylation reactions. A series of beta-1,3-linked oligogalactosides were prepared and elaborated to neoglycoconjugates for the study of AGP biosynthesis and AGP binding proteins.
McGill
Nathan W
NW
School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
Williams
Spencer J
SJ
D001565:Benzoates / Q000737:chemistry*; D002240:Carbohydrate Sequence; D004952:Esters / Q000737:chemistry; D006031:Glycosylation; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009088:Mucoproteins / Q000138:chemical synthesis* / Q000737:chemistry; D009844:Oligosaccharides / Q000138:chemical synthesis* / Q000737:chemistry; D010940:Plant Proteins / Q000138:chemical synthesis / Q000737:chemistry; D013237:Stereoisomerism
D001565:Benzoates; D004952:Esters; D009088:Mucoproteins; D009844:Oligosaccharides; D010940:Plant Proteins; C006619:arabinogalactan proteins