ABSTRACT
A new glycosyl acceptor to be used in sialylation was designed as a 3-hydroxy derivative of 4-methoxyphenyl ß-d-galactopyranoside with 2-O-acetyl group and O-4 and O-6 protected as benzylidene acetal. Two alternative syntheses of this compound were compared. Sialylation of 3-OH group of the glycosyl acceptor with O-chloroacetylated N-trifluoroacetylneuraminic acid phenyl thioglycoside (NIS, TfOH, MeCN, MS 3â¯Å, -40⯰C) was studied in a wide concentration range (5-150â¯mmolâ¯L-1). The outcome of sialylation generally followed the predictions of supramer analysis of solutions of sialyl donor in MeCN, which was performed by polarimetry and static light scattering and revealed two concentration ranges differing in solution structure and the structures of supramers of glycosyl donor. The optimized conditions of sialylation (Câ¯=â¯50â¯mmolâ¯L-1) were used to synthesize protected Neu-α(2-3)-Gal disaccharide (78%, α:ßâ¯=â¯13:1), which was then converted to sialyl-α(2-3)-galactose imidate building block useful for the synthesis of complex sialo-oligosaccharides.
Subject(s)
Galactose/chemical synthesis , Carbohydrate Conformation , Galactose/chemistryABSTRACT
In the present work we report that acetyl groups of per - acetylated aryl glycosides have different reactivity during the acidic deacetylation using HCl/EtOH in CHCl3, which leads to preferential deacetylation at O-3, O-4 and O-6. Thereby, the one-step preparation of 2-O-acetyl aryl glycosides with simple aglycon was accomplished for the first time. It was proved that the found reagent is to be general and unique for the preparation of series of 2-Ð-acetyl aryl glycosides. We have determined the influence of both carbohydrate moiety and the aglycon on the selectivity of deacetylation reaction by kinetic experiments. Using DFT/B3LYP/6-31G(d,p) and semi-empirical ÐÐ1 methods we have found that the highest activation barrier is for 2-Ð-acetyl group. This completely explains the least reactivity of 2-Ð-acetyl group.