2. What is Chemotaxonomy?
• Taxnomy is the theory and practice of classification.
• This system of classification relies on the chemical similarity of a taxon, i.e.it is
based on the existence of relationship between constituents in various plants.
• It is the latest system of classification that gives more scope for understanding the
relationship between chemical constituents, their biosynthesis and their possible
action.
“Study of the chemical variation in a diversity of organisms, and their
relationships.”
3. Purpose of chemotaxonomy
The evidence is used in classification of plants into 2 main purposes.
1. To improve the existing system of plants differentiation.
2. To develop the present day knowledge of natural relationship of plants.
• Three broad categories of compounds are used in chemotaxonomy:
primary metabolites
secondary metabolites
semantices
Primary metabolites, are parts of vital metabolic pathways, most of them are of
universal occurrence and is utilized by the plant itself for growth and development.
Eg: Starch, chlorophyll, aleurone grain, citric acid, aconitic acid, etc.
Secondary metabolites present in plant, is used for protection and defence.
Eg: Glycoside, alkaloid, volatile oil, flavonoid and plant phenol.
4. • The phenolics, alkaloids, terpenoids and non-protein amino acids, are the four
important and widely exploited groups of compounds utilized for chemotaxonomic
classification.
• These groups of compounds exhibit a wide variation in chemical diversity,
distribution and Function.
5. What are Phenols?
• Phenols probably constitute the largest group of plant secondary metabolites.
• Widespread in Nature, and to be found in most classes of natural compounds
having aromatic moieties, they range from simple structures with one
aromatic ring to highly complex polymeric substances such as tannins and
lignins.
• Phenols are important constituents of some medicinal plants and in the food
industry they are utilized as colouring agents, flavourings, aromatizers and
antioxidants.
6. Main Phenolic Classes
(1) Simple phenolic compounds
(2) Tannins
(3) Coumarins and their glycosides
(4) Anthraquinones and their glycosides
(5) Naphthoquinones
(6) Flavone and related flavonoid glycosides
(7) Anthocyanidins and anthocyanins
(8) Lignans and lignin
7. Phenols as markers in chemotaxonomy
• Phenols are among the most widespread class of metabolites in nature, and
their distribution is almost ubiquitous.
• But compounds which have restricted occurrence may have
chemotaxonomic evidence.
It is estimated that 100,000 to 200,000 secondary metabolites exist and some
20% of the carbon fixed by photosynthesis is channeled into the
phenylpropanoid pathway, thus generating the majority of the natural
occurring phenolics.
Most commonly occurred phenolic compound is mono or Dihydroxy
derivatives of benzoic and cinnamic acid.
8. E.g.
(1) Ellagic acid
• Ellagic acid is absent in fern, gymnosperm and monocotyledon,
but it is infrequently found in dicotyledon family.
It is useful chemotaxonomic marker in subfamily Rosoidae (tribe-kerrieae)-
belongs to family Rosaceae.
• Out of seven tribes in Rosoideae, only Kerrieae does not contain ellagic acid.
Because of this the tribe Kerrieae was removed from sub-family Rosoideae.
9. (2) 4-hydroxy benzoic acid
• 4-hydroxy benzoic acid and 4-hydroxy phenyl acetic acid have been
reported in 8 genera of family Saxifragaceae,
but in case of Astilbe genus, 4-hydroxy phenyl acetic acid is replaced
by 2-hydroxy phenyl acetic acid.
• Therefore in genus Astilbe 2-hydroxy phenyl acetic acid is the marker.
10. Coumarin derivatives are common volatile constituent responsible for odour in many
plants.
The hydroxylated derivatives are having restricted distribution which can be utilized
as chemotaxonomic markers.
eg.
(3) Umbelliferone occurs widely in Umbelliferae while in Compositae it is
characteristic of genus Hieracium (hawkweed).
11. • Flavonoids are largest group of phenolic compounds. They are mostly found in the vacuole of higher
plant and absent in lower plant.
Different classes of flavanoids:
· Flavones
· Flavanone
· Isoflavanone
· Isoflavonoids
· Anthocyanidin
· Chalcone
All flavonoids have common biosynthetic origin and therefore it posses the same
basic structural element,
e.g. 2-phenylchromone skeleton.
They may be present in many classes depending on degree of oxidation of pyran ring which may be
open and cyclize into furan ring, e.g. 2-phenyl benzo pyrilium : anthocyanin &
2-phenylchromone: flavone, flavanol, isoflavone.
12. • Flavone & flavanols and their glycosides are universally distributed but some of
the substitution patterns are restricted to certain family, having chemotaxonomic
importance.
E.g. 6-o-substituted flavonoids in family : Laminaceae,Rutaceae,Asteraceae
5-deoxy flavone in family : Fabaceae
2-o-substitueted flavonols in family : Laminaceae, Solanaceae
• Anthocyanidins, water soluble pigments responsible for red, pink, purple, blue, violet
colours to flower and fruit.
These pigments occur as glycoside anthocyanidins and their aglycone anthocyanidins.
These are rare in gymnosperm but mostly occurs in angiosperm. Except in
Caryophyllales.
13. Research studies :
• Alston (1967) documented hybridization between the species of Baptisia by using chromatographic patterns of
flavonoids
• Dahlgren (1980,1981) used flavonoids in clarifying certain relationship while suggesting his famous system of
angiosperm classification
• Psilotum contains biflavonyls and this brings it closer to lycopods than leptosporangiate ferns
• Ellagic acid .a polyphenol,is confined to woody dicots and not found in monocots
• Analysis of leaf flavonoids if Liliaceae, Juncaceae, Cyperaceae, Gramineae(Williams,1976) suggest that all these
families have arisen from Liliaceous ancestors.
• Williams et al.,(1983) identified six ornamental species of Fuchsia on the basis of their leaf flavonoids.
• Eucryphia of the family Eucryphiaceae can easily be distinguished based on their glycosides
• Species of Spirodella ,unidentifiable on morphological grounds,can distinguish on flavonoids
• Thymol and derivatives in Calea nelsonii (Martinez et al.,1987)
• Salicylalcohol and its glycosides in Populus and Salix (Julkunen-Tiitto, 1985 a,b)
• 2-hydroxy-6-methoxybenzoic acid (Potesilova et al., 1987)
• Syringic and protocatechuic acid as markers within family Gentianaceae (Daniel and Sabnis,1978)
• Phenolic acids within genus Sarcocaulon (Groenewald et al., 1986)
• Long chain alkylphenols in Hepaticeae and Phycpphyceae provide evolutionary indicators among Algea and lower
terrestrial green plants( Asakawa et al., 1987)
14. Research studies :
Flavonoids as chemotaxonomic markers in the genus Drosera.
-The pattern of major phenolic compounds ;the composition of flavonoids and
ellagic acid derivatives in 10 Drosera species belonging to 7 different subgenera
and/or sections of the genus have been investigated for chemotaxonomic
allocation.
Phenolic compounds as chemical markers of low taxonomic levels in the family Poaceae
Syringic and protocatechuic acid as systematic markers in family Gentianceae (Daniel and Sabnis; 1978)
Research on Presence of long chain alkylphenols in both Hepaticeae and Phycophyceae provide
evolutionary indicators among algea and terrestrial green plants (Asakawa et al.,1987)
- Research articles
A chemotaxonomic study of practically all the species of the genus Aloe has showed that flavonoids occur as
major compounds in 31 out of a total of 380 species investigated.
- Journal of medicinal plant studies ; ISSN 2320-3862
15. Summary
• With the advancement of analytical techniques, today so many groups of
plants are there in which phytochemical data has contributed to extensive
taxonomic improvements.
• The presence or absence of a particular phytochemical in a plant along
with the knowledge of its biochemical synthetic pathways can be used to
assign its taxonomic position.
16. Thank you
References :
• Trease and Evans – Pharmacognosy – 16th Edition
• Textbook of Pharmacognosy & Phytochemistry – Biren & Seth – Chemotaxanomic Classification
• Pubchem open chemistry database - pubchem.ncbi.nlm.nih.gov – Chemical structures
• Plant taxonomy – 2nd Edition , by Sharma –pg122
• Methods in plant biochemistry –by P M Dey – Chemotaxonomic importance –pg 34
• Journal of medicinal plant studies – Chemotaxonomy – A Tool for plant classification – Ram Singh
• Phenolic compounds as chemical markers of low taxonomic levels in the family Poaceae
(V. Míka1, V. Kubáň2, B. Klejdus2, V. Odstrčilová1, P. Nerušil1)
• A chemotaxonomic survey of flavonoids and simple phenols in leaves of the Ericaceae
(J. B. Harborne & Christine a. Williams)
• Chemotaxonomy of medicinal plants – Anukul -Scribd
