3,4-O-Isopropylidene-D-lyxo-hexopyranosid-2-ulose derivatives, obtained by oxidation of 3,4,6-protected D-galactopyranosides, can be alkylated in their anionic 2,6-pyranose forms to produce bis-glycosides containing the 2,5-dioxabicyclo[2.2.2]octane ring system. The 1-benzyl-2- methyl bis-glycoside 4b, when subjected to catalytic hydrogenolysis, produces the methyl D-lyxo-hexopyranos-2-uloside 10, existing as an 8:2 mixture of 1,5-pyranose anomers 9. Computational and NMR evidence is presented in favour of the hypothesis that the major anomer has the alfa configuration. Reduction of 9/10 with NaBH 4 gives methyl 3,4-O-isopropylidene-beta-D-tagatopyranoside, that can be hydrolyzed to D-tagatose. A simple synthesis of 1,5-anhydro-D-tagatose, starting from 1,5-anhydro-D-galactitol, is also presented. All new compounds were fully characterized by elemental analysis and by 1H and 13C NMR spectroscopy.
NEW SYNTHESES OF D-TAGATOSE AND OF 1,5-ANHYDRO-D-TAGATOSE FROM D-GALACTOSE DERIVATIVES
CATELANI, GIORGIO;D'ANDREA, FELICIA;
1995-01-01
Abstract
3,4-O-Isopropylidene-D-lyxo-hexopyranosid-2-ulose derivatives, obtained by oxidation of 3,4,6-protected D-galactopyranosides, can be alkylated in their anionic 2,6-pyranose forms to produce bis-glycosides containing the 2,5-dioxabicyclo[2.2.2]octane ring system. The 1-benzyl-2- methyl bis-glycoside 4b, when subjected to catalytic hydrogenolysis, produces the methyl D-lyxo-hexopyranos-2-uloside 10, existing as an 8:2 mixture of 1,5-pyranose anomers 9. Computational and NMR evidence is presented in favour of the hypothesis that the major anomer has the alfa configuration. Reduction of 9/10 with NaBH 4 gives methyl 3,4-O-isopropylidene-beta-D-tagatopyranoside, that can be hydrolyzed to D-tagatose. A simple synthesis of 1,5-anhydro-D-tagatose, starting from 1,5-anhydro-D-galactitol, is also presented. All new compounds were fully characterized by elemental analysis and by 1H and 13C NMR spectroscopy.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
