The 2,3,4,6-tetra-O-acetyl-b-D-glucopyranosyl auxiliary is effective in directing bromopropargyloxy additions to the olefinic bonds of vinylogous esters/carbonates; in the presence of AIBN and 1-ethylpiperidinium hypophosphite, the adducts undergo highly stereoselective reductive radical cyclisations in which quaternary carbon stereogenic centres are generated.
A460 7 0 D (E) -1 -(2',3',4',6'-Tetra-~-acetyl-~-~-glucopyranosyloxy) buta-l,3-diene ( I c), its 3-methyl derivative (1 d), its 2,3-dimethyl derivative (1 e), its (32) -4-acetoxy-3-(t-butyldimethylsilyloxy) derivative ( I f ) , its 3 -(t-butyldimethylsilyloxy) derivative (1 g), and its (32) -3-(t-butyldimethylsilyloxy) -2,4-dimethyl derivative (1 h) have been prepared and their diastereofacial reactivities towards N-phenylmaleimide and tetracyanoethylene assessed. With the former dienophile in benzene at ambient temperature, the dienes (Ic, d, f, g) gave ca. 87: 13 mixtures of the cycloadduct pairs (2c) and (3c), (2d) and (3d), (2f) and (3f), and (2g) and (39); however, the dienes (le, h) afforded only the cycloadducts (2e, h). With
The extracellular polysaccharides produced by Cryptococczrs lazrrenlii have been isolated and shown to consist of (A) a n acidic polysaccharide containing D-mannose, D-xylose, and D-glucuronic acid; ( B ) a neutral polysaccharide containing D-glucose only.Preliminary structural studies on the acidic material suggest that it consists of a mannosecontaining backbone with xylose and glucuronic acid as end groups, \vhile the glucan contains 1 -,3 3, 1 --t 4, 1 --t 2, and (or) 1 --t 6 linked residues. INTRODUCTION l/Iucli is l t n o~~~n about the origin of sugars fouiid in ho~~~opolysaccharides (1-11). On the other halid the origin of sugars in heteropolysaccharides has not been investigated to any great extent (12, 13).As part of a program for iiivestigatiiig the biosynthesis of monosaccliarides found in heteropolysaccl~arides, we have studied the extracellular polysaccharide produced by the yeast orgallisill Cryptococc~ls lar~rentii.This organism, 1;indly supplied by the United States Department of Agriculture, Peoria, Illinois, was chosen because it produced high yields of polysaccharides froin a wide variety of sugar substances.Cryfltococc~~s laz~rentii \\.as grown 011 an unbuffered casaiiiiiio acids -salts medium n~i t h glucose as the main carbon source (14). An acidic and a neutral polysaccharide were isolated by the follo\\~ing procedure, which was considered unlil
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.