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Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

Hemi-acetal formation creates a new asymmetric carbon atom at carbon

atom number one (C-1) and hence two stereoisomers called anomers are

formed. The new asymmetric carbon atom is called anomeric carbon. It is (C-

1) for aldoses and (C-2) for ketoses. In the D-series when the OH-group of the

anomeric carbon is present to the right in Fischer projection formula, it is given

the “-form”, and when present to the left it is given “-form”. In the L-series

the “-form” will have the anomeric (OH) to the left while “-form” will have

that (OH) to the right.

HO H H OH HO H H OH
C C C C

O O O O

CH OH CH OH CH OH CH OH
2
2
2
2
-L-Anomer -D-Anomer -D-Anomer -L-Anomer
D-Glucopyranose
L-Glucopyranose

Hudson found that the configuration of the anomeric carbon atom could be

determined from the optical rotation. The -compound is that having the

highest positive rotation and the -compound with the lowest negative rotation.

Important notes: Pyranose, Furanose, Anomers

• Aldoses→a six membered ring “pyranose ring”.

• Ketoses→a five membered ring “furanose ring”.

• Remember the 2 formulae of “Haworth” [β and α].

• Hemiacetal formation → a new asym. (C) at (C-1) → two stereoisomers called

anomers are formed [β and α].

• The new asym.(C) atom, anomeric carbon, (C-1) for aldoses and (C-2) for

ketoses.

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