Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
Date (from‐to) : 1996 -1998
Author : HASHIMOTO Shun-ichi; KITAGAKI Shinji; NAKAMURA Seiichi; NAKAJIMA Makoto
Due to the rapidly recognized biological significance of saccharide residues of carbohydrate-containing biomolecules, the rational design and development of stereocontrolled glycosidation reactions are of growing importance not only in carbohydrate chemistry but also in medicinal chemistry.
As part of a program to develop novel and efficient glycosidation methods capitalizing on the phosphorus-containing leaving groups, we have now found that glycosyl donors incorporating diethyl phosphite exhibit not only excellent shelf-stabilities but also the following distinct advantages in the glycosidation reactions. (1) Coupling of benzyl-protected glycopyranosyl diethyl phosphites with a variety of acceptor alcohols can be effected by the aid of BF_3-OEt_2 as a promoter even at -78゚C to exhibit the highest 1,2-trans-beta-selectivity known to date for glycosidations with a non-participating group on O-2. (2) TMSOTf-mediated glycosidation of glycosyl phosphites bearing participating groups at C-2 constitutes an extremely mild and general method for the stereocontrolled construction of 1,2-trans-beta-glycosidic linkages. (3) A direct method for the construction of 2-deoxy-beta-glycosidic linkages has been developed by using 2-deoxyglycopyranosyl diethyl phosphites in the presence of a catalytic amount of TMSOTf, wherein glycosidations of 2-deoxy-D-gluco- and 2-deoxy-L-rhamnopyranosyl donors with primary alcohols have been found to exhibit the highest beta-selectivity known to date. (4) A direct glycosidation for the stereocontrolled construction of 1 , 2-cis-beta-mannnosides, a long-standing and formidable problem, has been achieved by exploiting 4,6-O-benzylidene-protected mannopyranosyl diethyl phosphites in the presence ofTMSOTf, though the method is limited to primary alcohols. (5) A highly stereocontrolled 1,2-cis-alpha-glycosidation under conditions mild enough for acid-labile alcohols has been developed by using benzyl-protected glycopyranosyl diethyl phosphites as glycosyl donors in the presence of 2,6-di-tert-butylpyridinium iodide and tetrabutylammonium iodide.