This document discusses chemotaxonomy of medicinal plants. It defines chemotaxonomy as the approach of using chemical characteristics of plants to develop plant classifications or solve taxonomic problems. Primary metabolites like carbohydrates and secondary metabolites like alkaloids, glycosides, and terpenoids are important for chemotaxonomy. The distribution and types of these compounds provide insights into the phylogenetic relationships between plant taxa. Chemotaxonomic studies analyze qualitative and quantitative chemical variation within and between plant parts to better understand plant relationships.

1. Chemotaxonomy of Medicinal plant
CHEMOTAXONOMY:
Definition:-The approach of taxonomy in which chemical nature of plants are used
in developing classification or in solving taxonomical problems is called
chemotaxonomy ,chemosystematics, chemical taxonomy ,chemical plant taxonomy or
plant chemo taxonomy are the common names of chemotaxonomy. It gives the close
relationship between chemical constituents of plants and their taxonomical
status. Chemotaxonomy establishes relationship between the position of the plant
and exact understanding of biological evaluation and natural relation ship.
Depending upon chemical evidence, plants are classified accurately as alkaloids,
flavonoids, carotenoids, polysaccharides, terpenoids, fatty acids (proteins).
Purpose of chemotaxonomy:Chemotaxonomy has been used in all levels of
classification. Chemical evidences have been used in all the groups of the plant
kingdom starting from simple organism like fungi and bacteria up to the most
highly advanced and specialized group of Angiosperms. 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. o Chemical characters and their use in taxonomy: - Naik
divided the chemical characters into 3 categories. 1. Directly visible
characters:-Starch grains, raphides, silica ,gypsum ,etc 2. chemical test
characters:-phenolic ,betalins, oil fats, waxes ,alkaloids 3. Proteins o On the
other hand in 1987 some authors divided the natural chemicals plants products
into 2 groups on the basis of molecular weight. 1. Low molecular weight
compounds:- That is a molecular weight of 1000 or less than 1000 called as
Micromolecules. Ex:-Amino acids, alkaloids, fatty acids, terpenoids, flavonoids.
2. High molecular weight compounds:- with a molecular weight of more than 1000
called as Macromoecules. Ex:-proteins, DNA, RNA complex , Polysaccharides.
History of Chemotaxonomy: • The concept of classification of plant based on
chemical character is not new. it is started in 15th &16th centuries by
anatomist Newmann, Grew & James petitver. They recognized similar chemicals or
medicinal effects of umbelliferous plants. (carminative)
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2. Chemotaxonomy of Medicinal plant
• • • • • • Greshoff in 1909, suggested that chemical characters should be
included in natural classification. Baker and Smith in 1920, worked on single
genus Eucalyptus (176)-collected morphological and chemical data and finally
concluded on the morphological basis the feather contended leaves having more
pinene in their volatile oil. Mc Nair in 1935, says that ‘more closely related
taxas produce more similar chemical products’. Beale and coworkers in 1940,
surveyed 32 species of Tulip for anthocyanin contents and distribution of group
of compounds in genus as a taxonomic characters. Conden et.al. in 1944, develop
paper chromatography. Bat & smith in 1948, showed that paper chromatography
applied to analysis of plant pigments.
Clasification of Chemotaxonomy: based on the taxonomical and chemical knowledge:
Descriptive taxonomy Dynamic taxonomy Serotaxonomy Descriptive taxonomy deals
with the classification of plant and secondary metabolite and other products
like sugar & amino acid. It is also concerned with evolutionary change, chemical
convergence and divergence in the plant. Dyanamic taxonomy is based on
biosynthetic pathway. Serotaxonomy or semantics is based on pathway of specific
proteins and amino acids sequencing in proteins. It is further classified as;
1. 2. 3. DNA- primary semantics RNA-secondary semantics Proteins-tertiary
semantics
Principle of chemotaxonomy
Chemical classification of plants is based on their chemical constitutions; i.e.
on their molecular characteristics. The same type of metabolites can be the
product of two quite different pathways. Different plants sometimes contain
secondary constituents belonging to different classes of compound but
biosynthetically appear to be same.
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3. Chemotaxonomy of Medicinal plant
Chemotaxonomic studies include the investigation of the pattern of compound
occurring in the plant and preferentially in all various individual parts of
plant such as the bark , wood, leaves , root, cuticles and seed. Such integrated
investigations are necessary in order to obtain really convincing evidence for
the relationship of plants. Before any important conclusions are drawn about the
presence or absence of a particular compound adequate sampling of a large number
of members of the species at different stages of development and growing in
different environment should be made.
Different stages of Chemotaxonomic investigation:
1. 2. 3. 4. Choice of group, taxonomic survey and sound sampling modification of
suitable chemical techniques Analysis of all material interpretation of data and
its comparison from all other sources
According to the interest of investigation the relative stages may vary (for
taxonomy, phylogenetic & chemistry) Sound sampling: an understanding of natural
variation within a group and phylogenies are helpful in good sampling. The
collection of plant sample done: By the help of professional plant collector
From national garden and national herbarium From professional plant sellers
Personal travel & collection Modification of suitable chemical techniques:
Depending upon the choice of investigator, what class of material is likely to
exhibit useful variation at the taxonomic level. Intraspecific chemical
variation Qualitative and quantitative variation between different parts of same
plant Variation due to Seasonal and environmental fluctuation Analysis of the
material: qualitative and quantitative analysis is done by phytochemical
screening, electrophoresis, chromatography, finger print, and spectroscopy. All
the spectra obtained from different technique should be analyses.
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4. Chemotaxonomy of Medicinal plant
Interpretation and comparison of data: All the data obtained from chemistry,
phylogenetic and taxonomy is interpreted & depending upon the evidence the
classification of plant should be reconsidered. If only a minor change occurs in
the match of chemical and other variation then the classification is essentially
confirmed.
Three broad categories of compounds are used in Chemotaxonomy:- .
1. Primary metabolites 2. Secondary metabolites, 3. 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. Example; starch, chlorophyll, aleurone grain, citric acid, aconitic
acid, etc. CARBOHYDRATES IN CHEMOTAXONOMY: Carbohydrates are universal
constituents of living organism and widely distributed in the plant. Thus,
carbohydrate is having little chemotaxonomic significance, but some of the rare
sugars having chemotaxonomic significance. Eg. • • • • 6-Deoxy hexose;
2, 6-Dideoxy hexose; Gentiobiose & Gentianose; Polyols and polysaccharides,
6-Deoxy hexose: It occurs in the form of methyl ether that is restricted to
certain family. So the presence or absence of such sugars is help in the study
of phylogenetic relationship. Ex. L-thevetose and D-digitalose are used as
cardiotonic. 2, 6-Dideoxy hexose: Cardinolides containing D-digitoxose, L-
oleandrose, D-cyamarose sugars are particularly abundant in family apocynaceae
and asclepiadaceae (both are group of unrelated family). Gentiobiose and
gentianose: These are uncommon sugar in amygdalin, characteristic of family
rosaceae and gentianaceae respectively. Polyols: Among monosaccharide
derivatives eg. D-sorbitol, D-mannitol and mesoxylitol; D-sorbitol occurs
naturally in fruits of various rosaceae family. The presence or absence of these
sugar alcohol in rosaceae can be utilized to identify subfamily. It is reported
that sorbitol is present in all species belong to subfamily of rosaceae like
spiraeoidae, pomoidae, prunoidae, and rosoidae, but in species of ulmaria genus
belong to
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5. Chemotaxonomy of Medicinal plant
rosoidae, sorbitol is absent. So, the absence of this chemotaxonomy marker
confirms the removal of ulmaria from spiraeoidae to rosoidae. Polysaccharides:
It is condensation of large number of monosaccharide molecules. That is
universal in the energy storage forms eg. Starch, dextran, fructan, cellulose,
and inulin. Among these polysaccharides inulin is characteristic of family
compositae, while the fructan is present in family graminae. Thus,
polysaccharide is also utilized in confirming phylogenetic relationship. Eg.
Tropical and subtropical species of grasses accumulate starch in their leaves,
while temperate grasses accumulate fructans.
Secondary metabolites present in plant, is used for protection and defence. Eg.
Glycoside, alkaloid, volatile oil, flavonoid and plant phenol. Glycosides in
chemotaxonomy:
Glycosides are compounds in which one or more sugars are combined with non-sugar
components by glycosidic linkage or by hemiacetal linkage involving oxygen
(Oglycoside). Depending upon the linkage the glycoside may be classified as: •
• • • O-glycoside; eg. Rhein. C-glycoside; eg. Aloin, cascaroside. N-
glycoside; eg. Adenosine. S-glycoside; eg. Sinigrine. Distribution of O-
glycosides is widespread, so it is having little chemotaxonomic value. The
nature of sugar moiety and its position of attachment to aglycone maybe
characteristics of cardiac glycosides. Eg. L-thevetose, D-digitalose,
Dcymarose,L-oleandrose (cardiotonic) C-glycosides, which possess a direct carbon
linkage between sugar and non-sugar are rare in nature. They are found in some
plants containing anthraquinone derivatives eg. Aloin in aloe-liliaceae;
cascaroside in cascara-rhamnaceae. About 25 C-glycosides of flavonoid group are
known more are flavone and few iso-flavone and flavanone, these are plant
phenol, but studied in C-glycosides. S-glycosides are examplified by those
produce isothiocyanate on hydrolysis. These compounds are characteristic of the
family cruciferae, moringaceae, capparaceae. So these family having phylogenetic
relationship.
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6. Chemotaxonomy of Medicinal plant
Cyanogenetic glycoside in chemotaxonomy:
Plant species having ability to produce hydrogen cyanide by enzymatic hydrolysis
are common in family Rosaceae, Passifloraceae, Leguminosae, Gramineae. Different
amino acid like phenyl alanine, tyrosine, valine, leucine, and isoleucine are
precursor for the biosynthesis of cyanogenetic glycosides, but they are
restricted to particular family. Example: Leucine-Leguminosae and sapindaceae.
On the basis of amino acid precursors some conclusion may be derived, at family
level cyanogenetic glycoside amygdaline synthesized from phenyl alanine,
restricted rosaceae, but same compound synthesized from amino acid valine or
isoleucine is restricted to Leguminosae. The accumulation of cyanogenetic
glycoside is also significant in confirming the position of certain family.
Thioglucoside in chemotaxonomy:
These are responsible for the characteristic flavors of various plants or family
brassicaceae and few related family like, Capparidaceae, Tropaeolaceae and
Resedaceae. On the basis of alkyl component of glucosinolate compound, brassica
species can be differentiated eg. Brassica juncea (mustard) from Indian
subcontinent contain 3-butenyl glucosinate and allyl glucosinate while those
from Asiatic country contain only allyl compound. So ancestry of Indian species
is doubtful, because that is hybrid of B. nigra (allyl glucosinate) and B.
compestris (3-butenyl glucosinate).
ALKALOID IN CHEMOTAXONOMY
Alkaloids are compounds, containing heterocyclic nitrogen, basic character and
complex molecular structure. Such compounds are restricted to plant kingdom. o
True alkaloids have a nitrogen-containing nucleus derived from biogenetic amine.
o Proto alkaloids   derived from amino acids, but lack a heterocyclic ring.
Natural protoalkaloids are usually simple amines e.g. ephedrine , mescaline.Some
times they may be precursor of true alkaloids. o Pseudo alkaloids biologically
unrelated to amino acids.Most of them derived from- terpenes, sterols ,
nicotinic acid or purines.
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7. Chemotaxonomy of Medicinal plant
Occurrence and Distribution:
Higher plants particularly in the dicotyledons, abundance in the Angiosperms
families Apocynaceae, Papaveraceae, Ranculaceae, Rubiaceae, Rutaceae,
Solanaceae, but less frequent in lower plants and fungi. In plants, alkaloids,
due to their basic nature, generally exist as a salt of organic acid like,
oxalic acid, citric acid, malic acid,, tartaric acid, tannic acid etc. Some
alkaloids like narceine and nicotine are occurring free in nature. A few
alkaloids occur as glycoside of sugars like glucose, rhamnose, and galactose.
E.g. alkaloids of solanum and veratrum groups as amides (Piperine), as esters
(Atropine, Cocaine) of organic acid.
Criteria for using Alkaloids in taxonomy:
Definition of alkaloids Definition of alkaloid plants The type of alkaloids that
can be distinguished Homologous and analogous characters
Definition:
Alkaloids are more or less toxic substances having physiological action. They
are basic in nature, contain heterocyclic nitrogen, and are synthesized in
plants from amino acid and or their intermediate derivatives. They are of
limited distribution in plant kingdom.” But such definition excludes a number of
nitrogen containing plant constituents, which are normally thought as alkaloids.
E.g. Biological amines like Ephedrine ,Hardenine,Betain ,Cholin, Muscarine. All
such alkaloids are separately referred as protoalkaloids or biological amines or
amino alkaloids. But when protoalkaloids and true alkaloids occur in same genus
or family, both are usually classified as alkaloids. Ex. – Hardenine, Mescaline
in cactaceae family. Another group of nitrogen compounds that fall outside our
definition of alkaloids are mono, sesqui,di-terpenes, steroids, nicotinic acid,
purines. These can also be classified according to precursor on which they are
based and collectively called as pseudo alkaloids.E.g . Conessine, Caffeine.
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8. Chemotaxonomy of Medicinal plant
Definition of alkaloid plants:
There is no sharp dividing line between alkaloids containing plants and
alkaloids free plants. From practical point of view, we can define lower limit
as 0.01% of dry weight. Another characteristic of true alkaloid is that it
always contains more than one alkaloid. E.g. Ricinine is only alkaloid in
Ricinus communis and Genitianine only alkaloid in Gentianaceae, that’s why these
two bases have been kept outside the class of true alkaloids.
Type of alkaloids that can be distinguished: –
It has been found that amino acids phenylalanine, ornithine, tryptophan, lysine,
histidine, Anthranilic acid are primary precursors of alkaloids in plants. Each
of this amino acid can be regarded as starting point for synthesis of one or
more types of alkaloids. Therefore we may put the alkaloids into families
corresponding to six amino acids mentioned above. There are also numbers of
alkaloids which can be regarded as hybrids. E.g. Phenylalanine family –
Hardenine, Ephedrine, Anahaline group, Papaverine group, Morphine group.
Tryptophan family - Ajamaline, Yohimbine, vinblastine etc. Ornithine family -
Hygrine, Atropine, Ecgonine etc . Lysine family - Coniine, Anabasine etc.
Homologous and analogous chemical characters:
Two similar substances or even same substance may be isolated from two different
plants and are taxonomically important if the compounds are derived from exactly
same metabolically process. But same compounds or similar compounds are produced
by different metabolic pathways in different plants.
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9. Chemotaxonomy of Medicinal plant
E.g. Anabasine in Nicotiana genus (Solanaceae family) is formed from one
molecule of lysine on the other hand in Leguminosae family two molecules of
lysine are involved. Thus it seems that Anabasine of Solanaceae is not
equivalent (homologous) to that in Leguminosae. Similarly quinine has been
isolated from several unrelated genera. The quinoline alkaloids of cinchona bark
are obviously quite different structurally from yohimbine alkaloids from yohimbe
bark but they are closely related biosynthetically and this points to a close
relation between the plants in which they occur. Generally ornithine and lysine
families of alkaloids are closely related. Therefore, they should be treated as
one unit from chemotaxonomic point of view.
Some alkaloids are restricted to only very certain plants e.g.
Morphine is restricted to P. somniferum Coniine is restricted to Umbeliferous
sp. Strychnine is restricted to strychnos species Accumulation of Isoquinoline
alkaloids in families Fumariaceae and Papaveraceae, indicate that there is close
relationship between two families. Both families accumulate Isoquinoline
alkaloids, and always contain Protopine. There are instances where alkaloid
biosynthesis can be helpful to chemotaxomist for arranging the species within
genus according to their alkaloid content.
Evidences from basic moiety:
Pyridine and Piperidine The parent base pyridine occurs in some plants as
Lobeline obtained from Lobelia inflata family Lobeliaceae. Nicotine obtained
from Nicotiana tobaccum family Solanaceae Anabasine obtained from Nicotiana
gluaca family chenopodiaceae. Anabasine occurs in tobacco, where it is formed
from lysine and nicotinic acid. In the legume and chenopod species where
Anabasine also occurs, it can be synthesized from two molecules of lysine.
Isoquinoline Alkaloids Isoquinoline alkaloids are obtained from following
plants. E.g. Papaverine is obtained from P. somniferum family Papaveraceae
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10. Chemotaxonomy of Medicinal plant
Berberine is obtained from Hydrastis canadensis family Berberidaceae The amino
acid phenylalanine and tyrosine act as precursor for isoquinoline nucleus.
Hydrastine which is found in Berberidaceae and Rannunculaceae. Tropane alkaloids
Among the best-known members of the group are the solanaceae alkaloids, which
are very characteristic of the solanaceae. Atropine and Hyoscyamine serve as
example. In erythroxylum, cocaine alkaloids are found which are same in nucleus
but do not occur in the solanacae. Ornithine is the precursor Indole Alkaloids
Indole alkaloids are found in following plants. Physostigmine obtained from
Physostigma venonsum family Leguminosae. Yohimbine obtained from Rauwolfia
serpentina family Apocyanaceae. Vinblastine obtained from Catharanthus roseus
family Apocyanaeae. Indole alkaloids origination from Phenylalanine as in
Erythria alkaloids (Leguminosae) such as Erysopine. In most cases e.g.
Tryptamine (Loganiaceae), yohimbine (Apocyanaceae) and strychnine (Loganiaceae)
the parent compound is tryptophan.
Plant Phenol in chemotaxonomy:
Most commonly occurred phenolic compound is mono or Dihydroxy derivatives of
benzoic and cinnamic acid. Phenolic compounds having restricted occurrence may
have chemotaxonomic value eg; Trihydroxy derivatives of benzoic acid and
cinnamic acid.
Eg: 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)-rosaceae. 4-hydroxy benzoic acid and 4-
hydroxy phenyl acetic acid have been reported in eight genera of family
saxifragaceae, but in case of Astilbe genus, 4-hydroxy phenyl acetic acid is
replaced by 2-hydroxy phenyl acetic acid.
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11. Chemotaxonomy of Medicinal plant
Coumarin derivatives are common volatile constituent responsible for odour in
many plants. The hydroxylated derivative are having restricted distribution can
be utilized as chemotaxonomic marker eg. Umbelliferone occurs widely in
Umbelliferae while in Compositae it is characteristic of genus Hieracium
(hawkweed). 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-phenyl chromone: flavone,
flavanol, isoflavone.
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 occurs as glycoside anthocynidins and their
aglycones anthocyanidins. These are rare in gymnosperm but mostly occurs in
angiosperm. Except in Caryophyllales.
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