Xylose sulfur-containing

It is precisely to the production of meatlike flavors that the great majority of patents based on the Maillard reaction have been directed. Mos of them indicate cysteine or cystine as the essential sulfur-containing compound. Other patents claim alternative sources for sulfur, e.g., derivatives of mercaptoacetaldehyde (36), mercaptoalkylamines (37), S-acetylmercaptosuccinic acid (38), 2-thienvltetrasulfide (39), "a sulfide" (40), and hydrogen sulfide (heated with aqueous xylose without any amino acid) (41). 

A synthesis of 4,5-dithio-L-xylose, a thio sugar in which the competition between sulfur-containing furanose and pyranose rings could be studied, has not yet been successful. Periodate scission of 3,4-0-isopropylidene-l,2-dithio-l,2-(thiocarbonyl)-D-glucitol led to an aldehyde which could not be isolated in pure form. ... 

Relatively pure xylan isolated from the holocellulose of aspen (Populus) wood is said to contain 85% of xylose residues.78 One of the characteristic properties of xylan is its ease of hydrolysis. Because it hydrolyzes much more readily than cellulose, mild acid treatment may be employed to bring about preferential hydrolysis of xylan from plant material. Xylose is ordinarily prepared in the laboratory by direct sulfuric acid hydrolysis of the native xylan in ground corn cobs.74 Hydrolysis in hydrochloric acid proceeds rapidly, but decomposition to furfural also occurs to some extent.76 A commercial method for the production of D-xylose from cottonseed hulls76 and straw77 and from corn cobs17 78 has been described. 

Cold barium hydroxide quantitatively removes the sulfite group from 25 and 26. The 5-amino-5-deoxy-D-xylose so liberated exists mainly in the form 17. Only in alkaline solution is it relatively stable toward acids it is extremely sensitive. Compound 17 accordingly behaves fundamentally differently from all other monosaccharides. In neutral solution (obtained by neutralization of its solution in barium hydroxide with carbon dioxide), the Amadori rearrangement product (22) is formed on standing at room temperature. With hydrochloric acid, 22 is likewise formed as the major product, together with 3-pyridinol (21). Free 17 cannot be isolated in pure form the product obtained contains 16 and 22 in proportions that vary with the pH of the evaporated solution. The impurities are lowest at pH 9.6. It is reported that, from the evaporated solution of 17, a 96 % yield of 25 can be recovered, but it should be mentioned that 16 and 22 also react with sulfurous acid to form 25 and 29. Thin-layer chromatograms (silica gel with p-dioxane—water) always show, besides 17, spots for the secondarily formed 16 and 22. 

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