3:6-Anhydro-l-galactose in Agar

Abstract

IN continuation of our former communication¹ we are now able to confirm that the substance (X) derived from agar is a derivative of 3: 6-anhydro-l-galactose as recently advanced by Hands and Peat². 3: 6-Anhydro-β-methyl-d-galactoside, m.p. 118°, [α]²⁰⁰D = −113° in water has now been synthesized from the crystalline triacetyl 6-p-toluenesulphonyl α-d-galactosyl-1-bromide ([α]D = +157°) of Ohle and Thiel³ by treatment with silver carbonate and methyl alcohol followed by deacylation with sodium hydroxide. Methylation of this substance yielded quantitatively crystalline 2: 4-dimethyl 3: 6-anhydro-β-methyl-d-galactoside, m.p. 82°, [α]²⁰⁰D = −77° in water, −86° in chloroform, which is undoubtedly the enantiomorph of (X), since the properties are the same but the sign of the rotation is reversed (mixed m.p. 65°). We have obtained further confirmation of this point by the preparation of the anilides of the dimethyl anhydro sugars, 2: 4-dimethyl 3: 6-anhydro-d-galactose anilide having m.p. 118°, whilst the corresponding derivative from agar had m.p. 117° strongly depressed on admixture with the d-anilide. Furthermore, the properties and stability of the lactones produced on oxidation are in agreement with these findings, so that the substance (X) must be regarded as 2: 4-dimethyl 3: 6-anhydro-β-methyl-l-galactoside.