New syntheses of D-tagatose and of 1,5-anhydro-D-tagatose from D-galactose derivatives.
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 alpha configuration. Reduction of 9/10 with NaBH4 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.
Barili
P L
PL
Dipartimento di Chimica Bioorganica, Universitá di Pisa, Italy.
Berti
G
G
Catelani
G
G
D'Andrea
F
F
Miarelli
L
L
D000080:Acetals / Q000138:chemical synthesis; D005690:Galactose / Q000031:analogs & derivatives* / Q000737:chemistry; D005697:Galactosides / Q000737:chemistry; D006601:Hexoses / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013402:Sugar Alcohols / Q000737:chemistry* / Q000592:standards
C096719:1,5-anhydrotagatose; D000080:Acetals; D005697:Galactosides; D006601:Hexoses; D013402:Sugar Alcohols; C030192:tagatose; D005690:Galactose