Page 37 - PG 504-theoretical notes-phyto-1-2024-2025..

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

➢ D-and L-sugar pairs: (enantiomers) → mirror images: Identical chemical

properties. Differ in sign of rotation, i.e., (+), (-); e.g., D-Glucose and L-Glucose.

Any sugar pairs, not mirror images → (diastereoisomers): Differ widely in both

physical and chemical properties. Have different names, e.g. D-Allose , D-mannose.

Aldohexoses: C6, four chiral carbons, sixteen stereoisomers

L-series can be obtained from L-glycaraldehyde by same ascending.

Important Notes:

1) Prefixes D and L represent the absolute configuration of the asymmetric

carbon atom irrespective to their optical rotation.

2) Optical rotation is indicated by symbols: d (+) or l (-).

3) There is no simple relation between configuration and optical rotation.

4) The L-series can be obtained from L-glycaraldehyde by ascending method.

5) D-Sugars occur in nature more than L-sugars.

6) When sugar molecule contains more than one asymmetric carbon, it is the farthest
asymmetric carbon from the reducing group which defines the configuration.

7) D-lactic acid is found in living muscles; and sour milk.

8) In some cases, one form of a molecule is beneficial, and the enantiomer is a

poison (e.g., thalidomide).

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