Galactose ether

The structure of compound A was established in part by converting it to known compounds Treat ment of A with excess methyl iodide in the presence of silver oxide followed by hydrolysis with dilute hydrochlonc acid gave a tnmethyl ether of D galactose Companng this trimethyl ether with known trimethyl ethers of D galactose allowed the structure of compound A to be deduced... 

How many tnmethyl ethers of D galactose are there Which one is the same as the product derived from compound A" ... 

Gal = galactose Glc=glucose Ara=arabinose Rhm = rhamnose DiMe = dimethyl (ether). 

A mixture of 10 g. of D-galactose, 10 ml. of ethyl acetoaeetate, 10 ml. of ethanol, and 5 g. of zinc chloride is heated on a steam bath during 75 minutes. The mixture is cooled, 45 ml. of water is added, and the solution is extracted with two 30-ml. portions of benzene. The aqueous layer is then extracted with nine 15-ml. portions of ethyl acetate. The united extracts are washed successively with an aqueous solution of sodium bisulfite and with an aqueous solution of sodium bicarbonate, dried with anhydrous sodium sulfate, filtered, and the filtrate evaporated to dryness, affording 4.5 g. of a sirup. This is saponified with 12.5 ml. of 10% sodium hydroxide solution, and then acidified (to Congo Red) with phosphoric acid. The aqueous solution is extracted with successive 30-ml. portions of ethyl acetate, and these are dried with anhydrous sodium sulfate, and individually evaporated to dryness. Extracts after the fourth yield a solid product m. p., 130°. Recrystallized from petroleum ether plus acetic acid, the compound has m. p. 132-134° yield, variable, ca. 2%.54... 

Maher, George G., The Methyl Ethers of the Aldopentoses and of Rhamnose and Fucose, X, 257-272 Maher, George G., The Methyl Ethers of D-Galactose, X, 273-282 McColloch, R. J. See Kertesz, Z. I. McDonald, Emma J., The Polyfructo-sans and Difructose Anhydrides, II, 253-277... 

The novel type of disaccharide IX, consisting of a unit of n-galactose joined to a unit of L-arabinose, was obtained by autohydrolysis of gum arabic. The structure of this disaccharide was proved by the fact that methylation yielded the heptamethyl ether X and this gave on hydrolysis 2,3,4,6-tetramethyl-D-galactose (XI) and 2,4-dimethyl-L-arabinose (XII). 

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... 

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