L-galactose

D (+) Galactose is a constituent of numerous polysaccharides It is best obtained by acid hydrolysis of lactose (milk sugar) a disaccharide of d glucose and d galactose L (—) Galactose also occurs naturally and can be prepared by hydrolysis of flaxseed gum and agar The principal source of d (+) mannose is hydrolysis of the polysaccharide of the ivory nut a large nut like seed obtained from a South American palm... 

L-Monosaccharides do exist in nature, serving a few relatively specialized roles. L-Galactose is a constituent of certain polysaccharides, and L-arabinose is a constituent of bacterial cell walls. 

Deoxy-L-galactose (L-fucose) is common, and has only been found as the a- or )3-pyranoside. The rare D-fucose has, however, been found both as a-pyranoside, in the LPS frorn Pseudomonas cepacia serotypes B and E, and as a-furanoside, in the cell-wall antigen from Eubacterium saburreum L 452 and the O-antigens from different strains of Psuedomonas syrin-gae The a-furanoside, as in 3, has a cis relationship between the aglycon and OH-2. The corresponding P form has not yet been found. 6-Deoxy-o-and -L-talose are components of the extracellular polysaccharides from some strains of Butyrivibrio fibrisolvens and of the LPS from some strains of E. coli respectively. 

L-Galactose is probably not produced from L-glycerose, since the latter inhibits glycolysis and, even so, reaction with dihydroxyacetone phosphate in the presence of aldolase yields L-sorbose 1-phosphate which, on stereochemical grounds, is also an unlikely precursor. A more plausible route is direct conversion from D-galactose (XXI) by complete reversal of stereo-... 

By analogy with the biosynthesis of L-ascorbic acid and with other oxidation-reduction enzyme systems, it seems likely that D-galactose is oxidized to D-galacturonic acid (XXIII) on reduction at Cl, this yields L-galactonic acid (XXIV), the 1,5-lactone (XXV) of which, on reduction at Cl, would give L-galactose (XXII). 

Deoxy-L-galactose (L-fucose) HO H H HO HaC—C—C—C—C-—CHO H HO HO H plant gums seaweeds blood polysaccharides sea-urchin eggs frog-spawn mucin... 

Schwarz, V., and Golberg, L., Galactose-l-phosphate in galactose cataract. Biochim. et Biophys. Acta 18, 310-311 (1955). 

Deoxy-L-galactose 19, 3-amino-2,3-dideoxy-L-xylo-hexose 20 and L-diginose 21 are synthesized conveniently from the aldehyde 18 (35). 

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