801992-26-7Relevant academic research and scientific papers
Serine and threonine Schiff base esters react with β-anomeric peracetates in the presence of BF3·Et2O to produce β-glycosides
Keyari, Charles M.,Polt, Robin
, p. 181 - 206 (2011/04/23)
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. Copyright Taylor & Francis Group, LLC.
