AZA-C-DISACCHARIDES - SYNTHESIS OF 6-DEOXYGALACTONOJIRIMYCIN BETA-C(1-]3) LINKED WITH D-ALTROFURANOSIDES AND D-GALACTOSE

Cross-aldolization of 4,5-O-isopropylidene-beta-D-glycero-L-mannohepto se ((-)- 12, derived from D-glycero-D-gulo-heptono-1,4-lactone in eigh t steps with (+)-(1R,4S,5S,6S)- and o-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 stereoselectiv e (lithium enolates, like modes, giving aldols (-)- 14 and (+)- 16, re spectively. Stereoselective methods were developed for the conversion of(-)- 14 into methyl imino-beta-D-glycero-L-manno-heptitol-1'-yl]-alp ha and -beta-D-altro-furanoside ((+)-1 alpha,beta). The aza-C-disaccha ride 1 alpha prefers a anti conformation (bonds C(2')-C(3') and C(1')- C(3) are antiperiplanar) for the beta-D-galactoside moiety ((3)J(H,H) coupling constants, NOEs). Aldol(+)- 16 was converted stereoselectivel y into 3-deoxy-3-C-[(1'S)-2',6',7'-trideoxy -2 D-glycero-L-manno-hepti tol-1'-yl]-beta-D-galactose trifluoroacetate.