292
D. J. BELL
CH 2 OH
1
c=o
I
H—C—OH
1
H—C—OH
1
CH 2 OH
(XIV)
D-Erythropentulose
[D-Ribulose, -Arabinulose]
HCHO
1
-C—H
1
1
-C—H
1
-C—OH
1
CH 2 OH
(XVII)
D-Lyxose
HCH 3
1
1
c=o
1
1
-C—H
1
1
-C—H
j
CH 3
(XV)
CH 2 OH
1
c=o
1
HO—C—H
1
H—C—OH
1
CH 2 OH
CHO
1
H—C—OH
1
HO—C—H
1
H—C—OH
1
CH 2 OH
(XVI)
D-Xylose
(XVIII)
D-Threopentulose
[D-Xylulose, -Lyxulose]
(XVIII) is D-threopentulose (cf. IV). In common use, however, are
such names as D-xylulose for (XVIII), which occurs, in small concentrations, as an intermediary metabolite (6). All these sugars can be
shown experimentally to possess at C-4, the highest-numbered asymmetric center, the configuration of D-glyceraldehyde; all except D-lyxose
(XVII) have been found in natural environments either as the free
sugars or as compounds from which the free sugar may be obtained by
hydrolysis. L-Enantiomorphs of arabinose (XIX) and of xylulose
(L-threopentulose) (7) (XX) are the only members of the L-family of
pentoses so far found in nature.
CHO
I
H—C—OH
HO—C—H
HO—C—H
CH 2 OH
(XIX)
CH 2 OH
I
c=o
I
H—C—OH
HO—C—H
CH 2 OH
(XX)
3. 2-Deoxy-O-ribose
The monosaccharides so far described fulfill the historic condition
that their elementary formula is Cx (H 2 0)x, which means that every
carbon atom in the chain bears a covalently linked oxygen atom either
in the form of hydroxyl or of carbonyl. Natural sugars are known which
possess typical properties but have one or more carbon atoms in the