Glycosidase Inhibitors: Synthesis of Enantiomerically Pure Aza-Sugars from Schiff Base Amino Esters via Tandem Reduction-Alkenylation and Osmylation
作者:Robin Polt、Dalibor Sames、Jason Chruma
DOI:10.1021/jo9820115
日期:1999.8.1
Nitrogen-in-the-ring "aza-sugars" have been synthesized in enantiomerically pure form from the amino acid L-alanine in excellent overall yield. The O'Donnell's Schiff base of L-alanine methyl ester 9a was converted to ate-sugar L-fuco-1-deoxy-nojirimycin, 18, and to the epimer L-gulo-1-deoxy-nojirimycin, 20, in eight steps. The overall yields were 20 and 29%, respectively. The methodology for the efficient generation of silyl- and benzyl-protected (E)-3-lithio-2-propen-1-ols, and the use of these alkenyllithiums with iBu(5)Al(2)H as nucleophiles in the three-selective tandem reduction-alkenylation of the Schiff base esters is described. Osmium-catalyzed cis-oxygenation of the resulting olefin products was selective for the galacto (fuco) amino polyols in all cases for the acyclic olefins, and was gulo-selective for the cyclic D-4,5-dihydropyridine pivalate, 17c. TEMPO-NaOCl was selective for oxidation of the primary position of the acyclic Schiff bases, and allowed for minimal protection/deprotection of the intermediates. The resulting N-benzhydryl heterocycles were easily deprotected with H-2-Pd at atmospheric pressure.