Furanose and Pyranose Forms of D-Ribose
D-Ribose exists in both furanose (5-membered ring) and pyranose (6-membered ring) forms. Each form can have an α or β anomer depending on the orientation of the hydroxyl group at the anomeric carbon (C1):
Furanose Forms:
α-D-Ribofuranose:
OH
/ \
H-C-C-OH
| | |
H C C OH
| |
O H
β-D-Ribofuranose:
OH
/ \
OH-C-C-C-OH
| | |
H C C OH
| |
O H
Pyranose Forms:
α-D-Ribopyranose:
OH
/ \
H-C / \ O
/ \ /
OH C C-OH
/ \ /
H C
\ /
O
β-D-Ribopyranose:
OH
/ \
OH-C-C \ O
| | /
H C C-OH
| \ /
O H
In the furanose forms, the anomeric carbon (C1) is bound to oxygen, forming a ring. In the pyranose forms, the anomeric carbon is bound to oxygen and another carbon, forming a larger ring. The α and β anomers differ in the orientation of the hydroxyl group at the anomeric carbon.