TMSOTf-promoted glycosidation of 1-C-(2-thiazolyl)-α-D-galactopyranosyl acetate (α)-2 and 1-C-(2-thiazolyl)-α-D-mannofuranosyl acetate 7 donors with 1 equiv of primary 3 and secondary 5 sugar alcohols acceptors gave exclusively the corresponding α-D-ketodisaccharides 4a, 8a, 11a, and 12a in 60-73% yield. On the other hand glycosidation of the 1-C-(2-thiazolyl)-α-D-glucopyranosyl acetate 6 with the primary alcohol 3 under the above conditions afforded a mixture of α- and β-D-ketodisaccharides 9a and 10a in ca. 1:1 ratio. The important role of the thiazole ring for the easy glycosidation of these ketol acetates was pointed out by comparison with ketoses bearing a methyl, carboxymethyl, and 2-furyl group. Application of the thiazolyl-to-formyl deblocking reaction sequence to the thiazolylketodisaccharides gave the corresponding aldehydes which in turn were converted into alcohols and esters by reduction and oxidation, respectively.
Thiazolylketol acetates as glycosyl donors. Stereoselective synthesis of alpha-linked ketodisaccharides
DONDONI, Alessandro;MARRA, Alberto;
1996
Abstract
TMSOTf-promoted glycosidation of 1-C-(2-thiazolyl)-α-D-galactopyranosyl acetate (α)-2 and 1-C-(2-thiazolyl)-α-D-mannofuranosyl acetate 7 donors with 1 equiv of primary 3 and secondary 5 sugar alcohols acceptors gave exclusively the corresponding α-D-ketodisaccharides 4a, 8a, 11a, and 12a in 60-73% yield. On the other hand glycosidation of the 1-C-(2-thiazolyl)-α-D-glucopyranosyl acetate 6 with the primary alcohol 3 under the above conditions afforded a mixture of α- and β-D-ketodisaccharides 9a and 10a in ca. 1:1 ratio. The important role of the thiazole ring for the easy glycosidation of these ketol acetates was pointed out by comparison with ketoses bearing a methyl, carboxymethyl, and 2-furyl group. Application of the thiazolyl-to-formyl deblocking reaction sequence to the thiazolylketodisaccharides gave the corresponding aldehydes which in turn were converted into alcohols and esters by reduction and oxidation, respectively.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.