Pharmacognosy - medicinal plants (herbs)

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Theme XVIII: Heterocycles

Heterocyclic compounds with condensed nucleus. Indole, tryptophan, indole-3-acetic acid.

Characteristics of heterocyclic compounds with condensed nucleus. Indole and derivatives. Tryptophan and indole-3-acetic acid. Biological significance.


Among the heterocyclic with condensed nucleus the indole plays an important biological role.


Its ring is a fusion of a benzene ring with another pyrrole and this structure facilitates electrophilic substitution reactions.

There are numerous derivatives of indole with great biological importance. One of these derivatives is tryptophan, which is an essential amino acid present in most proteins and other derivative is the indole-3-acetic acid or  indolylacetic acid.


It is an essential amino acid that is not synthesized by mammals, so must be obtained through the diet. Vitamin B3 is metabolized from this substance and its lack determines the sickness known as pellagra. It also has a great significance in the formation of a universal transmitter involved in oxidation-reduction reactions of the organisms and in the biosynthesis of fatty acids, among other functions.


Indole-3-acetic acid

Auxins are organic substances that applied in small amounts cause significant physiological effects on plants, i.e. they act as plant hormones in growth of stems, root formation, size of leaves, branches among other effects. The indole-3-acetic acid is called "auxin" to belong to this group of hormonal substances.

Indole-3-acetic acid

This acid is synthesized in the growing parts of plants and circulate throughout all tissues. Most part is synthesized in apical buds.

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