MONOSACCHARIDES
471
Box 12.2
Ring size and anomeric form of common sugars
Sugars exist predominantly in cyclic hemiacetal or hemiketal forms, and whilst both six-membered pyranose and
five-membered furanose structures are encountered, a particular ring size is usually characteristic for any one
sugar, especially when it is found in combination with other entities in natural structures. The most commonly
encountered monosaccharides and their usual anomers are shown here. By convention, the ring form is drawn
with the ring oxygen to the rear and the anomeric carbon furthest right. Also shown are the accepted abbreviations
for these sugars.
O
HO
HO
OH
HO
OH
O
HO
HO
OH
O
HO
HO
HO
O
HO
OH
HO
OH
O
OH
OH
HO
HO
O
HO
HO
OH
HO
OH
OH
OH
OH
O
HO
HO OH
OH
HO
O
HO
OH
HO
OH
β-D-glucose
(β-D-Glc)
α-L-arabinose
(α-L-Ara)
β-D-xylose
(β-D-Xyl)
β-D-galactose
(β-D-Gal)
α-L-rhamnose
(α-L-Rha)
[preferred conformation]
β-D-fructose
(β-D-Fru)
β-D-mannose
(β-D-Mann)
β-D-ribose
(β-D-Rib)
CHO
OH
H
HO
H
H
OH
H
OH
CH 2 OH
CHO
OH
H
OH
H
CH 2 OH
OH
D-(+)-glucose
H
D-(−)-ribose
CH 2 OH
O
HO
H
H
OH
H
OH
CH 2 OH
D-(−)-fructose
CHO
H
HO
HO
H
H
OH
H
CH 2 OH
OH
D-(+)-mannose
CHO
OH
H
HO
H
HO
H
H
CH 2 OH
OH
D-(+)-galactose
CHO
OH
H
HO
H
HO
CH 2 OH
H
L-(+)-arabinose
CHO
OH
H
HO
H
H
CH 2 OH
OH
D-(+)-xylose
L-(−)-rhamnose
CHO
OH
H
H
OH
HO
H
HO
CH 3
H
R
R
R
R
R
R
R
R
R
S
R
R
R
R
R
S
The two anomers are designated α or β by comparison of the chiralities at the anomeric centre and at the highest
numbered chiral centre. If these are the same (RS convention), the anomer is termed β, or α if they are different.
Note that the D and L prefixes are assigned on the basis of the chirality (as depicted in Fischer projections) at the
highest numbered chiral centre and its relationship to D-(R)-(+)-glyceraldehyde or L-(S)-(−)-glyceraldehyde (see
Section 3.4.10).
The stereochemistries of the various substituents may be deduced by considering the implications of the Fischer
projection (see Box 3.16).