SYNTHESIS, PROPERTIES, AND REACTIONS OF α- AND β-D-GLUCOPYRANOSYL ESTERS OF SOME TRIPEPTIDES

Article abstract of DOI:10.1016/S0008-6215(00)85517-2

The 2,3,4,6-tetra-O-benzyl-1-O-(N-benzyloxycarbonyltripeptidyl)-D-glucopyranoses 1, 8, and 13 were synthesised from 2,3,4,6-tetra-O-benzyl-α-D-glucopyranose and the active esters of the appropriate N-protected tripeptides (Gly-Gly-Gly-, L-Phe-Gly-Gly-, and Gly-Gly-L-Phe-) in the presence of imidazole; the anomeric mixtures were resolved and the α and β anomers characterised.The β anomer of 13, containing the L and D enantiomers (ratio ca. 3:1) of Gly-Gly-Phe- as the aglycon, could be resolved by column chromatography into the pure isomeric forms.Catalytic hydrogenolysis of the β anomers, in the presence and absence of a strong acid, yielded the free 1-esters 2β, 9β, and 14β, which were characterised as the mono-oxalate or trifluoroacetate salts and as free bases.Similarly, the α anomers afforded 2α, 9α, and 14α, whereas omission of the strong acid led to accompanying 1 --> 2 acyl migration, to give the 2-O-acyl derivatives.All of the compounds prepared were converted into the N-acetyl and/or peracetylated derivatives.The 1-esters 2β and 9β, both in the charged and uncharged form, and the trifluoroacetate salt of 14β, are susceptible to cleavage by β-D-glucosidase; the enzyme had no effect on the uncharged form of 14β.This difference between 14β and its salt is discussed in conformational terms.