Stereocontrolled Synthesis of the <scp>d</scp>- and <scp>l</scp>-<i>glycero</i>-β-<scp>d</scp>-<i>manno</i>-Heptopyranosides and Their 6-Deoxy Analogues. Synthesis of Methyl α-<scp>l</scp>-<i>Rhamno</i>-pyranosyl-(1→3)-<scp>d</scp>-<i>glycero</i>-β-<scp>d</scp>-<i>manno</i>-heptopyranosyl- (1→3)-6-deoxy-<i>glycero</i>-β-<scp>d</scp>-<i>manno</i>-heptopyranosyl-(1→4)-α-<scp>l</scp>- <i>rhamno</i>-pyranoside, a Tetrasaccharide Subunit of the Lipopolysaccharide from <i>Plesimonas shigelloides</i>
作者:David Crich、Abhisek Banerjee
DOI:10.1021/ja061594u
日期:2006.6.1
The synthesis of D-and L-glycero-alpha-manno-thioheptopyranosides, protected with 4,6-O-alkylidenetype acetals is described. In glycosylations carried out with preactivation with the 1-benzenesulfinylpiperidine/trifluoromethanesulfonic anhydride couple, both the D-and L-glycero series exhibit excellent, beta-selectivity with a range of glycosyl acceptors. In contrast, a 4,7-O-alkylidene acetal was found not to afford, beta-selectivity. With a 4,6-O-[1-cyano-2-(2-iodophenyl) ethylidene] acetal protected thioglycoside, excellent, beta-selectivity was obtained in glycosylation reactions, and subsequent treatment with tributyltin hydride and azoisobutyronitrile brought about clean fragmentation to the 6-deoxy-glycero-beta-D-manno-heptopyranosides. This chemistry was applied to the stereocontrolled synthesis of methyl alpha-L-rhamno-pyranosyl-(1 -> 3)-D-glycero-beta- D-manno-heptopyranosyl-(1 -> 3)-6-deoxy-glycero-beta-D-manno-heptopyranosyl-(1 -> 4)-alpha-L-rhamno-pyranoside, a component of the lipopolysaccharide from Plesimonas shigelloides.