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HEXOSES: 211
According to Neitberg and to Rewald1
the pentose obtained from a
pancreas nucleoprotein and the pentose isolated by Neuberg and Bkahn
from inosinic acid is identical with /-xylose.
Ribose. This pentose has been prepared synthetically by E. Fischer.
The phenylhydrazone melts at 154-155° C, the p-bromphenylhydr:iz<>n<-
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 /-xylose exists at
least in the pancreas.2
Hexoses (C0H12O6).
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 gulcse, talose, and others, are obtained
only by artificial means.
All hexoses, as also their anhydrides, yield levulinic acid, C5H8O3,
besides formic acid and humus substances on boiling with dilute min-
eral acids. Oxymethyl furfurol, CqHqO^, 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).
1
Kiermeyer, Chem. Zeitung., 1895; v. Ekenstein and Blanksma, Ber. d. d. chem.
Gesellsch., 43, 2355 (1910).
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