TOTAL SYNTHESIS OF (-GALACTOSTATIN - AN ILLUSTRATION OF THE UTILITY OF THE THIAZOLE-ALDEHYDE SYNTHESIS())

The natural aza sugar (+)-galactostatin (+)-1 has been prepared from D -serine by sequential installation of chiral 1C and 2C units employing thiazole-based reagents. Thus, the D-serine-derived methyl ester 3 wa s transformed by 2-thiazolyllithium (4) into the thiazolyl amino keton e 5 which, via syn stereoselective carbonyl reduction and thiazolyl-to -formyl conversion, gave the first key intermediate, the alpha-hydroxy beta-amino aldehyde 10. The olefination of this compound by [(2-thiaz olyl)-methylene]triphenylphosphorane (14) followed by osmium tetroxide cis dihydroxylation of the resulting alkene E-16 and cleavage of the thiazole ring produced the second key intermediate, the amino- and hyd roxyl-protected 5-deoxy-5-amino- D-galactose 20. The removal of all pr otecting groups of this compound afforded the target aza sugar (+)-1 i n 17.3% overall yield from 3.