Improved methods for the stereoselective synthesis of mannoheptosyl donors and their glycosides: toward the synthesis of the trisaccharide repeating unit of the Campylobacter jejuni RM1221 capsular polysaccharide
摘要:
In view of the importance of 6-deoxymannoheptosides as structural units in the Campylobacter jejuni RM1221 capsular polysaccharide, the development of effective synthetic protocols for 4-O-6-S-alpha-cyanobenzylidene thio-o-mannoheptapyranoside donors carrying either 3-O-naphthylmethyl or 3-O-acetyl groups is described starting from D-mannose. In particular, tris(phenylthio)methyllithium is found to undergo highly stereoselective addition to a mannose-6-aldehyde in sharp contrast to the vinyl Grignard reagent whose reactions were essentially devoid of selectivity. A brief survey of coupling reactions with the two donors indicted the 3-O-acetyl system to be highly alpha-selective whereas the 3-O-naphthylmethyl congener was highly beta-selective indicating that the presence of the seventh carbon atom in these donors is not detrimental to coupling selectivity in either instance. (C) 2013 Elsevier Ltd. All rights reserved.
Improved methods for the stereoselective synthesis of mannoheptosyl donors and their glycosides: toward the synthesis of the trisaccharide repeating unit of the Campylobacter jejuni RM1221 capsular polysaccharide
摘要:
In view of the importance of 6-deoxymannoheptosides as structural units in the Campylobacter jejuni RM1221 capsular polysaccharide, the development of effective synthetic protocols for 4-O-6-S-alpha-cyanobenzylidene thio-o-mannoheptapyranoside donors carrying either 3-O-naphthylmethyl or 3-O-acetyl groups is described starting from D-mannose. In particular, tris(phenylthio)methyllithium is found to undergo highly stereoselective addition to a mannose-6-aldehyde in sharp contrast to the vinyl Grignard reagent whose reactions were essentially devoid of selectivity. A brief survey of coupling reactions with the two donors indicted the 3-O-acetyl system to be highly alpha-selective whereas the 3-O-naphthylmethyl congener was highly beta-selective indicating that the presence of the seventh carbon atom in these donors is not detrimental to coupling selectivity in either instance. (C) 2013 Elsevier Ltd. All rights reserved.
Improved methods for the stereoselective synthesis of mannoheptosyl donors and their glycosides: toward the synthesis of the trisaccharide repeating unit of the Campylobacter jejuni RM1221 capsular polysaccharide
作者:Sébastien Picard、David Crich
DOI:10.1016/j.tet.2013.04.094
日期:2013.7
In view of the importance of 6-deoxymannoheptosides as structural units in the Campylobacter jejuni RM1221 capsular polysaccharide, the development of effective synthetic protocols for 4-O-6-S-alpha-cyanobenzylidene thio-o-mannoheptapyranoside donors carrying either 3-O-naphthylmethyl or 3-O-acetyl groups is described starting from D-mannose. In particular, tris(phenylthio)methyllithium is found to undergo highly stereoselective addition to a mannose-6-aldehyde in sharp contrast to the vinyl Grignard reagent whose reactions were essentially devoid of selectivity. A brief survey of coupling reactions with the two donors indicted the 3-O-acetyl system to be highly alpha-selective whereas the 3-O-naphthylmethyl congener was highly beta-selective indicating that the presence of the seventh carbon atom in these donors is not detrimental to coupling selectivity in either instance. (C) 2013 Elsevier Ltd. All rights reserved.