Aza-C-disaccharides: Synthesis of 6-deoxygalactonojirimycin β-C(1→3) linked with D-altrofuranosides and D-galactose

Article abstract of DOI:10.1021/jo970151t

Cross-aldolization of 3-O-benzyl-N-(benzyloxycarbonyl)-2,6,7-trideoxy- 2,6-imino-4,5-O-isopropyl-idene-β-D-glycero-L-mannoheptose((-)-12, derive from D-glycero-D-gulo-heptono-1,4-lactone in eight steps) with (+)- (1R,4S,5S,6S)- and (-)-(1S,4R,5R,6R)-6-chloro-5-(phenylseleno)-7- oxabicyclo[2.2.1]heptan-2-one (obtained in one step from the 'naked sugars' (-)- and (+)-7-oxabicyclo[2.2.1]hept-5-en-2-one) were highly stereoselective (lithium enolates, like modes), giving aldols (-)-14 and (+)-16, respectively. Stereoselective methods were developed for the conversion of (- )-14 into methyl 3-deoxy-3-C-[(1'R)-2',6',7'-trideoxy-2',6'-imino-β-D- glycero-L-manno-heptitol-1'-yl]-α- and -β-D-altrofuranoside ((+)-1α,β). The aza-C-disaccharide 1α prefers a anti conformation (bonds C(2')-C(3') and C(1')-C(3) are antiperiplanar) for the β-D-galactoside moiety (³J(H,H) coupling constants, NOEs). Aldol (+)-16 was converted stereoselectively into 3-deoxy-3-C-[(1'S)-2',6'7'-trideoxy-2',6'-iminio-β-D-glycero-L-manno- heptitol-1'-yl]-β-D-galactose trifluoroacetate.