Classification of Natural Products

Lec 2
Natural products can be arranged for study under
the following headings:
1. Alphabetical

2. Taxonomic

3. Morphological

4. Pharmacological or therapeutic

5. Chemical or Biogenetic

6. Chemo-taxonomical

7. Serotaxonomical
 1.
§ Alphabetical classification is the simplest way of classification of any disconnected
items.
§ Crude drugs are arranged in alphabetical order of their Latin and/or English names
(common names) or sometimes local language names (vernacular names).
§ Some of the pharmacopoeias, dictionaries and reference books which classify crude
drugs according to this system are as follows:

1. Indian Pharmacopoeia
2. British Pharmacopoeia
3. British Herbal Pharmacopoeia
4. United States Pharmacopoeia and National Formulary
5. British Pharmaceutical Codex
6. European Pharmacopoeia
§ Merits
1. It is easy and quick to use. (No technical person is required for handling the
system).
2. There is no repetition of entries and is devoid of confusion.
3. In this system location, tracing and addition of drug entries is easy.

§ Demerits
1. There is no relationship between previous and successive drug entries.
2. This type of classification does not help in distinguishing the drugs of plant,
animal or mineral sources.

Examples: Acacia, Benzoin, Cinchona, Dill, Ergot, Fennel, Gentian, Hyoscyamus,

Ipecacuanha, Jalap, Kurchi, Liquorice, Mints, Nux vomica, Opium, Podophyllum,
Quassia, Rauwolfia, Senna, Vasaka, Wool fat, Yellow bees wax, Zeodary.
 2.
§ Inthis system the drugs are arranged according to taxonomical studies. The drugs
are arranged according to their kingdom, subkingdom, division, class, order, family,
genus and species.
Merits
1. Taxonomical classification is helpful for studying evolutionary developments.
2. It allows for a precise and ordered arrangement and accommodates any drug
without ambiguity.

Demerits
1. This system also does not
correlate in between the
chemical constituents and
biological activity of the drugs.
 3.
Drugs are arranged according to their morphological or external characters of the
plant parts or animal parts, i.e. which part of the plant is used as a drug and including
organised and unorganised:

§ Organised drugs (cellular): obtained from the direct parts of the plants and
containing cellular tissues. e.g. leaves (digitalis, Senna and belladonna), flowers
(clove, saffron), fruits (cardamom), seeds (Physostigma), herbs (vinca) and
entire organisms, woods, barks, rhizomes and roots.
§ Unorganised drugs (Acellular): prepared from plants by some intermediate
physical processes such as incision, drying or extraction with a solvent and not
containing any cellular plant tissues. e.g. dried latex (opium) extracts, gums,
resins, oils, fats and waxes.
§ Merits: more convenient for practical study especially when the chemical nature of
the drug is not clearly understood.
§ Demerits: 1. The main drawback of morphological classification is that there is no
corelation of chemical constituents with the therapeutic actions.
2. Repetition of drugs or plants occurs.
4.
§ This classification involves the grouping of drugs according to the
pharmacological action of their most important constituent or their
therapeutic use.

§ This classification is more relevant and is a mostly followed method.

§ Drugs like digitalis, squill and strophanthus having cardiotonic action are
grouped irrespective of their parts used or phylogenetic relationship or the
nature of phytoconstituents they contain.
Merits
This system of classification can be used
for suggesting substitutes of drugs, if
they are not available at a particular place
or point of time.

Demerits
Drugs having different action on the body
get classified separately in more than one
group that causes ambiguity and
confusion.
Cinchona is antimalarial drug because of
presence of quinine but can be put under
the group of drug affecting heart because
of antiarrhythmic action of quinidine.
 5.

§ Here, the crude drugs are divided into

different groups according to the
chemical nature of their most
important constituent present in the
plant to which the pharmacological/
therapeutic activity of drug is
attributed.

§ Irrespectiveof the morphological or

taxonomical characters, the drugs with
similar chemical constituents are
grouped into the same group.
§ Advantage: it is a popular approach for phytochemical studies.

§ Disadvantage: ambiguities arise when particular natural products possess a number

of compounds belonging to different groups of compounds.

§ Example:

Certain drugs are found to contain alkaloids and glycosides (Cinchona), Fixed oil and
volatile oil (Nutmeg) of equal importance together and hence it is difficult to
categorize them properly.
6.

§ 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.
There are certain types of chemical constituents that characterize certain
classes of plants.
§ Example: Tropane alkaloids generally occur in most of the members of
Solanaceae.
 7.
§ The serotaxonomy can be explained as the study about the application or the utility
of serology in solving the taxonomical problems.
§ Serology can be defined as the study of the antigen–antibody reaction. Antigens are
those substances which can stimulate the formation of the antibody.
§ Antibodies are highly specific protein molecule produced by plasma cells in the
immune system.
§ Protein are carriers of the taxonomical information and commonly used as antigen
in serotaxonomy.
§ It determines the degree of similarity between species, genera, family, etc., by
comparing the reaction with antigens from various plant taxa with antibodies
present against a given taxon.
§ Serology helps in comparing nonmorphological characteristics, which helps in the
taxonomical data.
§ The concept that plants can be classified on the basis of their chemical

constituents is not new; for example, early workers classified the algae into

green, brown and red forms, but it is only during the last 40 years that

modern techniques of isolation and characterization have led to the chemical

screening of many thousands of plant samples.

§ The living organism may be considered a biosynthetic laboratory for:

1. Chemical compounds: ( carbohydrate , proteins , fats) that are utilized as

food by humans.

2. Other Constituents:
a. Inert Constituents (Pharmaceutical active constituents )
b. Active Constituents

Inert Constituents: The chemical compounds, though present in plant and

animal kingdom, which do not possess any definite therapeutic values as such
but are useful as an adjunct either in the formulation of a ‘drug’ or in surgery
are collectively known as inert constituents.
§ Examples:

(a) Plant Drugs:

Microcrystalline forms of cellulose are used as combination binder-
Cellulose disintegrants in tabletting. Colloidal cellulose particles aid in
stabilization and emulsification of liquid.
Lignin To precipitate proteins, and to stablise asphalt emulsions.
Suberin Esters of higher monohydric alcohols and fatty acids.
Starch As pharmaceutic aid i.e.; tablet filler, binder and disintegrant.
Colouring Matters For colouring food products and pharmaceuticals

(b) Animal Drugs:

For coating “enteric pills” that are unaffected in the stomach but
Keratin
dissolved by the alkaline into intestinal secretions
Active Constituents: The chemical entities that are solely responsible for existing
pharmacological, microbial or in a broader-sense therapeutic activities are usually
termed as active constituents. Most drugs like: alkaloids, glycosides, steroids,
terpenoids, bitter principles are the bonafide members of this particular category.

The presence of these secondary plant products (active constituents) are governed
by two school of thoughts, namely:
(a) Superfluous Metabolites: substances that have no value as such and perhaps
their presence are due to the lack of exceretory mechanism in them.

(a)Characteristic Survival Substances: substances which exert a positive survival

value on the plant wherein they are actually present. They offer more or less a
‘natural defence- mechanism’ whereby these host plants are survived from
destruction owing to their astringent, odorous and unpalatable features.
Examples: Poisonous alkaloidal containing plants or astringent containing shrubs.
§ The secondary active constituents of plant drugs are influenced by 3

principle factors:

1. Genetic Composition (or Heredity)

2. Ontogeny (stage of development or aging of the plant).

3. Environment.
1. Genetic Composition (or Heredity) effect: induces both quantitative and
qualitative changes.

Plants of the same genus origin that resemble one another closely inform and
structure, may be quite different in genetic composition. This often results
distinct differences in chemical composition, particularly with references to
secondary constituents. Such plants are said to belong to different chemical
races,

e.g. Papaver somniferum contains alkaloid morphine, while

Papaver rhoeas has no morphine alkaloid content.

2. Ontogeny: The age of a medicinal plant has a direct impact on the
concentration of the ‘active constituent’. It is, however, not always true that
older the plant greater would be the active principal.
The cannabidiol alkaloid content of Cannabis sativa reaches a peak early in the
growing season then begins to decline, when this decline occur, the
concentration of tetrahydrocannabinol alkaloid begins to increase and
continues increasing until the plant approach maturity.
In the opium poppy, Papaver somniferum, the morphine contents of the
capsules are highest within 2-3 weeks after flowering and if these poppy is
harvested early, codeine will be predominate.
On the other hand, if harvesting was delayed the morphine decomposed.
3. Environmental factors :
There are a number of environmental factors which may afford considerable
changes in active plant constituents, for instance: composition of soil (mineral
contents); climate (dry, humid, cold); and lastly the methods of cultivation
(using modified strains, manual and mechanical cultivation).

For a specific instance, it may be recalled that a soil rich-in-nitrogen content

evidently gives rise to a relatively higher yield of alkaloids in the medicinal
plants; whereas a soil not so abundant in nitrogen content and grown in
comparatively dry zones may yield an enhanced quantum of volatile oil.