RESUMEN
D-Allose and its derivatives play important roles in the field of health care and food nutrition. Pure and well-defined D-allose derivatives can facilitate the elucidation of their structure-activity relationship as an essential step for drug design. The Lattrell-Dax epimerization, refers to the triflate inversion using nitrite reagent, is known as valuable method for the synthesis of rare D-allose derivatives. Here, the influence of protecting group patterns on the transformation efficiency of D-glucose derivatives into synthetically useful D-alloses and D-allosamines via the Lattrell-Dax epimerization was studied. For C3 epimerization of D-glucose derivatives bearing O2-acyl group, an anomeric configuration-dependent acyl migration from O2 to O3 was found. In addition, a neighbouring group participation effect-mediated S1 nucleophilic substitution of the D-glucosamine bearing C2 trichloroacetamido (TCA) group in the Lattrell-Dax epimerization was dependent upon anomeric configuration. Thus, the effect of anomeric configuration on the Lattrell-Dax epimerization of D-glucose suggests that β-D-glucosides with low steric hindrance at C2 should be better substrates for the synthesis of D-allose derivatives. Significantly, the efficient synthesis of the orthogonally protected D-allose 13 and D-allosamine 18 will serve well for further assembly of complex glycans.
RESUMEN
The pharmacological activities of natural glycosides are closely related to the polyfunctional sugar moieties. Modification of active natural products by glycosylation can change the stereochemical configuration, improve the solubility, tune up the activities and change pharmacokinetic properties for higher efficacy and better selectivity. Compared with the common D-glucose, D-allose, a C-3 epimer of D-glucose rarely exists in nature, but it plays an important role in food, health, medicine, and so on. It is not easily metabolized in the living organisms, but can be used as a safe and low-calorie sweetener. The natural allopyranosides are absolute conjugation forms which are same as other glucopyranosides and rhamno-pyranosides with a broad array of biological activities. This article summarizes the major progresses made in phytochemistry and biological activity studies of these compounds. Structure-activity relationship analyses of partial anti-tumor and anti-diabetic allopyranosides were performed regarding the data reported in the literatures. These insights may provide a theoretical and experimental reference for the discovery of new drug and drug design based on allopyranosides.