Flavonoids help regulate cellular activity and fight off free radicals that cause oxidative stress on your body. It has been reported that flavonoids are important for human health because of their antioxidant, antibacterial, antiviral, and anti‐inflammatory activities.

1. STEREOCHEMISTRY OF
FLAVONOIDSPRESENTED BY-
ANUP KUMAR RAY
M.Pharm. (Pharmacognosy)
IIT-BHU.

2. CONTENTS
• INTRODUCTION
• BASIC CHEMISTRY
• STEREOCHEMICAL EXAMPLE
• ENZYMATIC STEREOSELECTIVITY TABLE
• STEREOCHEMISTRY RELATED TO
BIOLOGICAL ACTIVITY

3. INTRODUCTION
•Flavonoids are phenolic substances isolated from a wide range
of vascular plants, and more than 8150 different flavonoids
have been reported.
•Flavonoids are located inside the cells or on the surface of
various plant organs and have various functions in plants.
•They act in plants as antioxidants, antimicrobials,
photoreceptors, visual attractors, feeding repellents, and for
light screening.

4. Cont..
•Many studies have shown that flavonoids exhibit biological and
pharmacological activities, including antioxidant, cytotoxic,
anticancer, antiviral, antibacterial, cardioprotective,
hepatoprotective, neuroprotective, antimalarial, antileishmanial,
antitrypanosomal and antiamebial properties.
•These biological and pharmacological properties are usually
attributed to their free radical scavenging efficacies, metal
complexion capabilities, and their ability to bind to proteins with a
high degree of specificity.

5. BASIC CHEMISTRY
•The term “flavonoid” is generally used to describe a broad collection of
natural products that include a C6-C3-C6 carbon framework, or more
specifically a phenylbenzopyran functionality.
•Depending on the position of the linkage of the aromatic ring to the
benzopyrano (chromano) moiety, this group of natural products may be
divided into three classes:
1) The flavonoids (2-phenylbenzopyrans)
2) The isoflavonoids (3-benzopyrans) , and
3) The neoflavonoids (4-benzopyrans) .

6. Cont..
These groups usually share a common chalcone precursor, and
therefore are biogenetically and structurally related.

7. Cont..
1) Flavonoids [2-Phenylbenzopyrans]
Based on the degree of oxidation and saturation
present in the heterocyclic C-ring, the flavonoids may
be divided into the following groups:

9. Cont..
2) Isoflavonoids (3-benzopyrans)
The isoflavonoids are a distinctive subclass of the
flavonoids. These compounds possess a 3-
phenylchroman skeleton that is biogenetically derived
by 1,2-aryl migration in a 2-phenylchroman precursor.
Isoflavonoids are subdivided into the following
groups:

11. Cont..
3) Neoflavonoids (4-benzopyrans)
The neoflavonoids are structurally and
biogenetically closely related to the flavonoids and
the isoflavonoids and comprise the 4-
arylcoumarins (4-aryl-2H-1- benzopyran-2-ones),
3,4-dihydro-4-arylcoumarins, and neoflavenes.

13. 4) Minor Flavonoids
Natural products such as chalcones and aurones also contain a C6-
C3-C6 backbone and are considered to be minor flavonoids.
These groups of compounds include the 2′-hydroxychalcones,
2′-OH-dihydrochalcones, 2′-OH-retro-chalcone,
aurones (2-benzylidenecoumaranone), and auronols.

15. STEREOCHEMICAL EXAMPLES
•α- and β-Hydroxydihydrochalcones
•Dihydroflavonols
•Flavan-3-ols and Flavan-3,4-diols

18. ENZYMATIC
STEREOSELECTIVITY
TABLE

20. STEREOCHEMISTRY
RELATED TO
BIOLOGICAL ACTIVITY

21. Eg. - Catechin
The Asian native Centaurea maculosa (spotted
knapweed) has displaced native weeds and crops
throughout the western United States. Contributing to
the invasiveness of this exotic is the secretion of the
phytotoxic trans-flavan-3-ol (-)-catechin from its
roots.

22. Both enantiomers of catechin are present in root exudates
of C. maculosa; however, only (-)-catechin had
allelopathic (phytotoxic) activity.
Interestingly,(+)-catechin (but not (-)-catechin) displayed
antibacterial activity against several root pathogens, which
suggests that secretion of a racemic mixture may
simultaneously protect C. maculosa roots against
microbial pathogens and weaken roots of neighboring

23. THANK YOU