1. Linear monosaccharides are commonly represented using the Fisher Projection (see also the Monosaccharide Browser at U. Leeds, UK). The projections are usualy made with a vertical carbon chain and the carbonyl group closest to the top. Bonds represented vertically point to the back of the surface and those represented horizontally point to the front. Simple linear sugars can be either Aldehydo or Keto, depending on the position of the carbonyl group.
2. Carbohydrates are classified as either D or L depending on configuration of the highest-numbered asymmetric carbon atom (the asymmetric carbon at the lowest position in the Fisher representation). Since the sugars of the D configuration are more commonly found in nature they will be the only ones represented from now on, being the L the mirror image for each case.
Ex: CHO CHO
| |
H-C-OH HO-C-H
| |
CH2OH CH2OH
D-Glyceraldehyde L-Glyceraldehyde.
3. Each sugar will be linked to the corresponding structure in the Klotho Biochemical Compounds Declarative Database at Washington U. or to a local structure.
4. The cyclic representation of sugars will be made using either Fisher Projections from Klotho or Haworth Projections from CARBLOCKS, a set of locally develloped graphic tools.
5. Sugar cyclization normally leads to the formation of 6-membered rings, designated as Piranoses, or 5-membered rings, designated Furanoses. The cyclization creates of an asymmetric carbon, the anomeric carbon, with two possible configurations designated alpha and beta.
Ex: a) Fisher Projectionb) Haworth Projection
alpha-D-Glucopyranose beta-D-Glucopyranose
Ketoses
CHO
|
H-C-OH
|
CH2OH
D-Glyceraldehyde
________________________________________________________________
CHO CHO
| |
H-C-OH HO-C-H
| |
H-C-OH H-C-OH
| |
CH2OH CH2OH
D-Erythrose D-Threose
________________________________ ________________________________
CHO CHO CHO CHO
| | | |
H-C-OH HO-C-H H-C-OH HO-C-H
| | | |
H-C-OH H-C-OH HO-C-H HO-C-H
| | | |
H-C-OH H-C-OH H-C-OH H-C-OH
| | | |
CH2OH CH2OH CH2OH CH2OH
D-Ribose D-Arabinose D-Xylose D-Lyxose
________________ _________________ _________________ _________________
CHO CHO CHO CHO CHO CHO CHO CHO
| | | | | | | |
H-C-OH HO-C-H H-C-OH HO-C-H H-C-OH HO-C-H H-C-OH HO-C-H
| | | | | | | |
H-C-OH H-C-OH HO-C-H HO-C-H H-C-OH H-C-OH HO-C-H HO-C-H
| | | | | | | |
H-C-OH H-C-OH H-C-OH H-C-OH HO-C-H HO-C-H HO-C-H HO-C-H
| | | | | | | |
H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH
| | | | | | | |
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH
D-Allose D-Altrose D-Glucose D-Mannose D-Gulose D-Idose D-Galactose D-Talose
CH2OH
|
C=O
|
CH2OH
Dihydroxyacetone
CH2OH
|
C=O
|
H-C-OH
|
CH2OH
D-Erythrulose
________________________________
CH2OH CH2OH
| |
C=O C=O
| |
H-C-OH HO-C-H
| |
H-C-OH H-C-OH
| |
CH2OH CH2OH
D-Ribulose D-Xylulose
________________ _________________
CH2OH CH2OH CH2OH CH2OH
| | | |
C=O C=O C=O C=O
| | | |
H-C-OH HO-C-H H-C-OH HO-C-H
| | | |
H-C-OH H-C-OH HO-C-H HO-C-H
| | | |
H-C-OH H-C-OH H-C-OH H-C-OH
| | | |
CH2OH CH2OH CH2OH CH2OH
D-Psicose D-Fructose D-Sorbose D-Tagatose