Serine and threonine Schiff base esters react with β-anomeric peracetates in the presence of BF3·Et2O to produce β-glycosides

Charles M. Keyari, Robin Polt

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

Improved procedures are reported for the glycosylation of L-serine and L-threonine utilizing activated Schiff base glycosyl acceptors, which are less expensive and more efficient alternatives to published methods. L-serine or L-threonine benzyl ester hydrochloride salts were reacted with the diarylketimine bis-(4-methoxyphenyl)-methanimine in CH3CN at rt to form the more nucleophilic Schiff bases 3a and 3b in excellent yield. These Schiff bases exhibited ring-chain tautomerism in CDCl3 as shown by 1H NMR. Schiff bases 3a and 3b, acting as glycosyl acceptors, reacted at rt with simple sugar peracetate donors with BF3·OEt 2 promotion to provide the corresponding L-serine and L-threonine O-linked glycosides in excellent yields and purities. The dipeptide ester Schiff base Ar2C = N-Ser-Val-OCH3 3e also reacted to provide β-glycosides in excellent yields, and without epimerization. With microwave irradiation the reactions were complete in 2 to 5 min. To investigate this reaction further, classical AgOTf-promoted Koenigs-Knorr reaction of D-glucopyranosyl, lactosyl, and maltosyl bromides were examined, providing the β-glycosides with yields ranging from 35% to 68%. The difference in reactivity between α- and β-carbohydrate peracetate donors was remarkable. The less configurationally stable D-xylopyranosyl tetra-acetate (a pentose) showed no selectivity (αvsβ-configuration) toward the Schiff bases.

Original languageEnglish (US)
Pages (from-to)181-206
Number of pages26
JournalJournal of Carbohydrate Chemistry
Volume29
Issue number4
DOIs
StatePublished - May 1 2010

Keywords

  • Glycopeptide
  • Glycoside
  • Glycosylation
  • Lewis acid
  • Schiff base
  • Serine

ASJC Scopus subject areas

  • Biochemistry
  • Organic Chemistry

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