compounds show various pharmacological activities like anticoagulant, anticancer,
anti-Alzheimer, and anti-inflammatory activities (Xu et al. 2015).
The structures of some important coumarins are shown below in Fig. 10.13.
10.4.3 Flavonoids
Among the normally occurring phenolic compounds, flavonoids have taken a
maximum place in the plant kingdom. Out of about 2000 of these known compounds, around 500 compounds are found as a free state (Evans 2009). The most
available flavonoids include flavones, flavonols, and anthocyanins. The flavones
and their derivative are generally yellow in color (Latin flavus, meaning yellow).
These compounds are ubiquitously distributed worldwide but they are mainly
available in young tissues and in the higher plants. They are found in Pteridophyta
(mainly fern and related plants), Gymnosperma (conifer), monocots, and dicots.
Among the dicot families, plants belonging to the families Leguminosae,
Polygonaceae, Rutaceae, Umbelliferae, and Compositae are a rich source of flavonoids. Researches worldwide have reported the medicinal activities of drugs
containing flavonoids. For examples, milk thistle (Silybum marianum belonging to
the family Compositae), liquorice root (G. glabra belonging to the family
Leguminosae), Roman chamomile (Chamaemelum nobile, Buck–wheat
(Fagopyrum esculentum belonging to the family Polygonaceae), and ginkgo (
Ginkgo biloba Linn. belonging to the family Gingkoaceae). Many herbs having
flavonoids have now been incorporated in the British Pharmacopeia (B.P.). For
example, Birch Leaf (Betula pendula), Calendula flower (Calendula officinalis),
Horsetail (Equisetum ramosissimum), Elderflower (Sambucus nigra), Motherwort
(Leonurus cardiac), Lime Flower (Tilia cordata), and passionflower (Passiflora
edulis) are well-known plants. The flavonoid compounds have been shown pharmacological properties like anti-inflammatory, antiallergic, antithrombotic, vasoprotective, antitumor, antifungal, hepatoprotective, and gastric mucosal protective
activities (Table 10.3) (Montanher et al. 2007; Serafini et al. 2010). Flavonoids have
a 15 carbon skeleton arranged as C 6 –C 3 –C 6 in which two phenyl rings are linked by
a three-carbon chain. A carbonyl group is present at one end of a three-carbon
chain. This three-carbon chain may be either open in case of chalcone and dihydrochalcone (simplest naturally occurring flavonoid) or as a part of the heterocyclic
ring and the heterocyclic ring fused with benzene ring forms chroman ring. Flavone
and flavonol are common flavonoids in which B-ring is attached at 2 position of
C-ring, on the other hand, in isoflavone structure, the B-ring is attached to 3
position of C–ring. Flavonoids exist as free molecules or as glycosidic forms
(Fig. 10.14). The glycosidic form of flavonoids is generally O-glycosides and few
are C-glycosides. Chemically, flavonoids are also known as benzo-c-pyrone
derivatives. Biflavonoids are also available in which two flavonoids molecules are
joined through either C–C linkage or C–O linkage. Anthocyanin present in most
plants is responsible to provide red, blue, purple color to the flower. Anthocyanin
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C. C. Kandar
anti-Alzheimer, and anti-inflammatory activities (Xu et al. 2015).
The structures of some important coumarins are shown below in Fig. 10.13.
10.4.3 Flavonoids
Among the normally occurring phenolic compounds, flavonoids have taken a
maximum place in the plant kingdom. Out of about 2000 of these known compounds, around 500 compounds are found as a free state (Evans 2009). The most
available flavonoids include flavones, flavonols, and anthocyanins. The flavones
and their derivative are generally yellow in color (Latin flavus, meaning yellow).
These compounds are ubiquitously distributed worldwide but they are mainly
available in young tissues and in the higher plants. They are found in Pteridophyta
(mainly fern and related plants), Gymnosperma (conifer), monocots, and dicots.
Among the dicot families, plants belonging to the families Leguminosae,
Polygonaceae, Rutaceae, Umbelliferae, and Compositae are a rich source of flavonoids. Researches worldwide have reported the medicinal activities of drugs
containing flavonoids. For examples, milk thistle (Silybum marianum belonging to
the family Compositae), liquorice root (G. glabra belonging to the family
Leguminosae), Roman chamomile (Chamaemelum nobile, Buck–wheat
(Fagopyrum esculentum belonging to the family Polygonaceae), and ginkgo (
Ginkgo biloba Linn. belonging to the family Gingkoaceae). Many herbs having
flavonoids have now been incorporated in the British Pharmacopeia (B.P.). For
example, Birch Leaf (Betula pendula), Calendula flower (Calendula officinalis),
Horsetail (Equisetum ramosissimum), Elderflower (Sambucus nigra), Motherwort
(Leonurus cardiac), Lime Flower (Tilia cordata), and passionflower (Passiflora
edulis) are well-known plants. The flavonoid compounds have been shown pharmacological properties like anti-inflammatory, antiallergic, antithrombotic, vasoprotective, antitumor, antifungal, hepatoprotective, and gastric mucosal protective
activities (Table 10.3) (Montanher et al. 2007; Serafini et al. 2010). Flavonoids have
a 15 carbon skeleton arranged as C 6 –C 3 –C 6 in which two phenyl rings are linked by
a three-carbon chain. A carbonyl group is present at one end of a three-carbon
chain. This three-carbon chain may be either open in case of chalcone and dihydrochalcone (simplest naturally occurring flavonoid) or as a part of the heterocyclic
ring and the heterocyclic ring fused with benzene ring forms chroman ring. Flavone
and flavonol are common flavonoids in which B-ring is attached at 2 position of
C-ring, on the other hand, in isoflavone structure, the B-ring is attached to 3
position of C–ring. Flavonoids exist as free molecules or as glycosidic forms
(Fig. 10.14). The glycosidic form of flavonoids is generally O-glycosides and few
are C-glycosides. Chemically, flavonoids are also known as benzo-c-pyrone
derivatives. Biflavonoids are also available in which two flavonoids molecules are
joined through either C–C linkage or C–O linkage. Anthocyanin present in most
plants is responsible to provide red, blue, purple color to the flower. Anthocyanin
346
C. C. Kandar