A convenient access to the 1,5-anhydro forms of d-tagatose, l-rhamnulose and d-xylulose via 2-hydroxyglycal esters

Zemplén methanolysis or a three-step protocol comprising hydroxylaminolysis, de-O-acetylation and deoximination smoothly and efficiently convert the benzoylated 2-hydroxy-d-glycals of d-galactose, l-rhamnose and d-xylose into their configurationally related 1,5-anhydro-ketoses, thereby providing convenient access to the 1,5-anhydro forms of d-tagatose, l-rhamnulose and d-xylulose. Invariably obtained as amorphous solids, they are best characterized through their highly crystalline oximes.

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3,4,6-Tri-O-acetyl-1,5-anhydro-d-tagatose E-oxime[α]D23=-44.3 (c 0.5, CHCl3)Source of chirality: d-galactose

1,5-Anhydro-d-tagatose E-oxime[α]D20=-12.8 (c 1, MeOH)Source of chirality: d-galactose

(6S)-4-Acetoxy-6-acetoxymethyl-2H-pyran-3(6H)-one[α]D20=-42.7 (c 1.2, CHCl3)Source of chirality: d-galactoseAbsolute configuration: (6S)

1,5-Anhydro-d-tagatose[α]D21=-7.9 (c 0.9, H2O)Source of chirality: d-galactose

1,5-Anhydro-d-tagatose diethyldithioacetal[α]D20=-57 (c 1.1, MeOH)Source of chirality: d-galactose

3,4,6-Tri-O-acetyl-1,5-anhydro-d-tagatose diethyldithioacetal[α]D23=+15.7 (c 1, CHCl3)Source of chirality: d-galactose

3,4-Di-O-benzoyl-1,5-anhydro-l-rhamnulose E-oxime[α]D21=+123 (c 0.5, CHCl3)Source of chirality: l-rhamnose

3,4-Di-O-benzoyl-1,5-anhydro-l-rhamnulose[α]D21=+109.9 (c 1.1, CHCl3)Source of chirality: l-rhamnose

(6S)-4-Benzoyloxy-6-methyl-2H-pyran-3(6H)-one[α]D21=-10.5 (c 1.2, CHCl3)Source of chirality: l-rhamnose

(2S)-5,5-Dimethoxy-2-methyl-tetrahydropyran-4-one[α]D20=+154.6 (c 1.3, CHCl3)Source of chirality: l-rhamnose

3,4-Di-O-acetyl-1,5-anhydro-d-threo-pent-2-ulose E-oxime[α]D22=-58.3 (c 0.3, CHCl3)Source of chirality: d-xylose

3,4-Di-O-benzoyl-1,5-anhydro-d-threo-pent-2-ulose E-oxime[α]D23=-111 (c 0.6, CHCl3)Source of chirality: d-xylose

1,5-Anhydro-d-threo-pent-2-ulose E-oxime[α]D20=+14.8 (c 1, H2O)Source of chirality: d-xylose

3,4-Di-O-benzoyl-1,5-anhydro-d-pentulose[α]D20=-117 (c 0.6, CHCl3)Source of chirality: d-xylose

3,4-Di-O-benzoyl-1,5-anhydro-d-pentulose monohydrate[α]D20=-131 (c 0.7, CHCl3)Source of chirality: d-xylose

1,5-Anhydro-d-threo-pentulose diethyldithioacetal[α]D20=-79.3 (c 1.1, MeOH)Source of chirality: d-xylose

3,4-Di-O-benzoyl-1,5-anhydro-d-threo-pentulose diethyldithioacetal[α]D20=-121.4 (c 0.8, CHCl3)Source of chirality: d-xylose

3,4,6-Tri-O-acetyl-1,5-anhydro-d-psicose E-oxime[α]D20=+27.2 (c 0.84, CHCl3)Source of chirality: d-allose

3,4,6-Tri-O-acetyl-1,5-anhydro-d-sorbose E-oxime[α]D20=-15.1 (c 0.6, CHCl3)Source of chirality: d-glucose

3,6-Di-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-1,5-anhydro-d-fructose E-oxime[α]D21=-22.3 (c 0.3, CHCl3)Source of chirality: cellobiose