HEXOSES. 211 



According to NEUBERG and to REWALD J the pentose obtained from a 

 pancreas nucleoprotein and the pentose isolated by NEUBERG and BRAHN 

 from inosinic acid is identical with Z-xylose. 



Ribose. This pentose has been prepared synthetically by E. FISCHER. 

 The phenylhydrazone melts at 154-155 C, the p-bromphenylhydrazone 

 at 164-165 C. The osazone is identical with arabinosazone. On oxida- 

 tion it yields an optically inactive trioxyglutaric acid, which melts at 170- 

 171 C. d-ribose is, according to LEVENE and JACOBS, the pentose of 

 inosinic acid, guanylic acid and yeast nucleic acid. According to these 

 workers the pentose exists in these nucleic acids in a glucoside-like com- 

 bination with the purine bases, as so-called nucleosides. It must be 

 remarked that NEUBERG adheres to his claim that Z-xylose exists at 

 least in the pancreas. 2 



Hexoses (C 6 Hi 2 O 6 ). 



The most important and best-known simple sugars belong to this 

 group, and most of the other bodies which have been considered as car- 

 bohydrates in the past are anhydrides of this group. Certain hexoses, 

 such as glucose and fructose, either occur in nature already formed 

 or are produced by the hydrolytic splitting of other more complicated 

 carbohydrates or glucosides. Others, such as mannose or galactose, 

 are formed by the hydrolytic cleavage of other natural products, while 

 some, on the contrary, such as gulose, talose, and others, are obtained 

 only by artificial means. 



All hexoses, as also their anhydrides, yield levulinic acid, CsHsOs, 

 besides formic acid and humus substances on boiling with dilute min- 

 eral acids. Oxymethyl furfurol, CeHeOs, occurs here as an intermediary 

 step and this then quantitatively decomposes into levulinic acid and 

 formic acid. 3 Some of the hexoses, as above stated, are fermentable 

 with yeast. 



Some hexoses are aldoses, while others are ketoses. Belonging to the 

 first group we have MANNOSE, GLUCOSE, and GALACTOSE, and to the other 

 FRUCTOSE, and also SORBINOSE. 



The most important syntheses of the carbohydrates have been made 

 by E. FISCHER and his pupils, chiefly within the members of the hexose 

 group. " A short summary of the syntheses of hexoses will be given. 



' 1 Tollens and Miither, Ber. d. d. chem. Gesellsch., 37; Bertrand, Bull. soc. chim. 

 (3), 5; Neuberg, Ber. d. d. chem. Gesellsch., 35; Neuberg and Brahn, Biochem. Zeitchr., 

 5; Rewald, Ber. d. d. chem. Gesellsch., 42 (1909). 



2 E. Fischer, Ber. d. d. chem. Gesellsch, 24, Levene and Jacobs, ibid, 42, 2102, 2469 

 2474, 3247 (1909); 43, 3147 (1910); Neuberg, ibid., 42, 2806 (1909); 43, 3501 (1910). 



3 Kiermeyer, Chem. Zeitung., 1895; v. Ekenstein and Blanksma, Ber. d. d. chem. 

 Gesellsch., 43, 2355 (1910). 



