Glycal Glycosylation and 2-Nitroglycal Concatenation, a Powerful Combination for Mucin Core Structure Synthesis

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• 作者：Jü ; rgen Geiger ; B. Gopal Reddy ; Gottfried A. Winterfeld ; R. Weber ; M. Przybylski ; R. R. Schmidt
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：June 8, 2007
• 年：2007
• 卷：72
• 期：12
• 页码：4367 - 4377
• 全文大小：317K
• 年卷期：v.72,no.12(June 8, 2007)
• ISSN：1520-6904

文摘

A 3,4-O-unprotected galactal derivative having bulky 6-O-TIPS protection (compound 2) could beregioselectively 3-O-glycosylated with O-(galactopyranosyl) trichloroacetimidates; depending on theprotecting group pattern stereoselectively - and -linked disaccharides were obtained. With O-(2-azido-2-deoxyglucopyransyl) trichloroacetimidate as donor (compound 10A), glycosylation of 2 and of a 6-O-unprotected galactal derivative led in acetonitrile as solvent exclusively to a (1-3)- and a (1-6)-linked disaccharide, respectively. Nitration of the galactal moieties of the saccharides followed by Michael-type addition of serine and threonine derivatives (7a,b) installed the -galacto-configuration, thus readilyfurnishing O-glycosyl amino acid building blocks for the incorporation of core 1, core 2, core 3, core 6,and core 8 structures into glycopeptides. 2-Nitrogalactal and 2-nitroglucal derivatives could be alsosuccessfully employed in glycoside bond formation via Michael-type addition in a reiterative manner,affording the corresponding core 5, core 7, and core 6 building blocks. In this approach, highlystereoselective glycoside bond formations were based exclusively on Michael-type addition to the nitro-enol ether moiety of the 2-nitroglycals. Hence, 2-nitroglycals are versatile intermediates for base-catalyzedglycoside bond formation.