Galactose 3,8-anhydro-2-0-methyl

D. Horton and J. S. Jewell, Synthesis of l,6-anhydro- 3-D-talopyranose from derivatives of D-galactose and D-mannose, Carbohydr. Res., 5 (1967) 149-160 G. J. F. Chittenden, Oxidation of some derivatives of D-galactose with methyl sulphoxide-acid anhydride mixtures a route to derivatives of D-glucose and D-talose, ibid., 15 (1970) 101-109. 

Sarmentose Sedoheptulose Sedoheptulosan Solatriose 2.6- Dideoxy-3-0-methyl-D-xy/o-hexose D-a/froHept-2-ulose 2.7- Anhydro P-D-a/fro-hept-2-ulopyranose a-L-Rhamnopyranosyl-(1 ->2)-[P-D-glucopyranosyl-(1->3)]-D-galactose... 

The product retains, however, the configuration of D-galactose and is in fact methyl trimethyl-D-galactopyranoside (LII). The intermediate formation of a 1,3-anhydro ring is postulated. 

For the properties of the methyl derivatives of 3,6-anhydro-L-galactose see Advances in Carbohydrate Chemistry, 2, 77 (1946).)... 

L-Gulose readily forms an anhydride, and in a study on alginic acid, methylated L-guloses were isolated as their anhydrides.88 Other anhydro sugars, such as 3,6-anhydro-L-galactose and its 2-methyl ether, may be found in algae (see, for example, Ref. 412), and, under certain circumstances, 2,3,6-tri-O-methyl-D-galactose may form an anhydride.571... 

Neighboring-group participation by the vicinal, trans-acetoxyl group (see p. 125) serves to explain the abnormal behavior of methyl 4-0-acetyl-2,3-anhydro-6-0-benzyl- or -trityl-a-D-gulopyranoside with hydrogen chloride in acetone, or with 80% aqueous acetic acid, which give D-galactose, instead of the D-idose, derivatives.67 In the same way, 2-0-acetyl-3,4-anhydro-D-altropyranosides yield D-man-nosides, not D-idosides.9 6z(see p. 125). 

Hands and Peat,8 and Percival, Somerville and Forbes9 isolated from methylated agar a compound which was found to be a derivative of 3,6-anhydro-L-galactose. The components of agar and their relative amounts will be described in some detail in the following sections. 

Jones and Peat23 separated methylated agar into an acidic and a neutral fraction by precipitation methods. From the hydrolyzate of the acidic fraction they isolated 2,4,6-trimethyl-D-galacto e, 2,3,4,6-tetra-methyl-D-galactose, and 3,6-anhydro-2,5-dimethyl-L-galactonic acid (XII, as the crystalline amide of m. p. 173°). The structure assignment of XII was made on the following basis. The rotation of its amide, [a]D —75.7°... 

Percival and Thomson44 obtained a mixture of disaocharide esters from which, on hydrolysis and derivatization, they isolated 2,3,4,6-tetramethyl-D-galactose anilide and a mixture of methylated acids. From these acids they obtained 3,6-anhydro-2,5-dimethyl-L-galactonic acid, the structure of which was determined by almost the same means as those employed by Jones and Peat.23 On methanolysis of hexamethylagarobiose, Araki28 isolated 3,6-anhydro-2,5-dimethyl-L-galactose dimethyl acetal (XIII),... 

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