Asymmetric syntheses of the methyl 3-deoxy-3-amino-glycosides of d-glycero-l-gulo-heptose, d-glycero-d-galacto-heptose, d-glycero-l-allo-heptose and d-glycero-d-allo-heptose

The methyl glycosides of 3-deoxy-3-amino-d-glycero-l-gulo-heptose, 3-deoxy-3-amino-d-glycero-d-galacto-heptose, 3-deoxy-3-amino-d-glycero-l-allo-heptose and 3-deoxy-3-amino-d-glycero-d-allo-heptose were prepared from the corresponding d-aldopentoses via a seven step synthetic sequence. The doubly diastereoselective conjugate additions of the requisite antipode of lithium N-benzyl-N-(α-methylbenzyl)amide to four diastereoisomeric d-aldopentose-derived α,β-unsaturated esters and in situ enolate oxidation with the requisite antipode of camphorsulfonyloxaziridine (CSO) were used as the key, stereodefining steps. Sequential protection of the C(2)-hydroxyl group within the resultant α-hydroxy-β-amino esters and partial reduction of the ester functionality furnished the corresponding β-amino aldehydes. Subsequent N- and O-deprotection gave the target compounds (as the corresponding methyl pyranosides and/or methyl furanosides) in good yields and high diastereoisomeric purity.