Application of Indole in Drug Synthesis, Chemistry tutorial


Indole is basically the parent of a very large number of alkaloids and medicinally significant compounds. The indole ring system is found in Indomethacin (that is, anti-inflammatory agent) vinca alkaloids, employed in the treatment of different cancers, reserpine (that is, an antihypertensive agent), serotonin (a neurotransmitter) and tryptophan (a necessary amino acid) to state but few.


Indomethacin is a non-steroidal anti-inflammatory drug (NSAID) discovered in the year 1963. It is a non-selective inhibitor of cyclooxygenase 1 and 2 (COX1 and COX2) enzymes which participate in the biosynthesis of prostaglandins from arachidonic acid. Prostaglandins are hormone-like molecules which encompass a broad variety of effects, some of which lead to fever, pain and inflammation. It is generally utilized to reduce fever, pain, stiffness and swelling.  It is marketed under numerous trade names, comprising: Indocid, Indocin, Indochron E-R and Indocin-SR.

Indomethacin can be synthesized by employing the Fischer indole synthesis (figure shown below).

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Fig: Synthesis of Indomethacin

Vinca Alkaloids:

Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Biochemically derived from the tryptophan, serotonin is mainly found in the gastrointestinal (GI) tract, platelets, and in the central nervous system (CNS) of animals comprising humans. This is a well-known contributor to feelings of well-being; thus it is as well termed as a 'happiness hormone' in spite of not being a hormone.  

Around 80% of the human body's total serotonin is positioned in the enterochromaffin cells in the gut, where it is employed to regulate the intestinal movements. The remainder is synthesized in serotonergic neurons in the CNS where it consists of different functions. Such comprise the regulation of mood, appetite, sleep and also muscle contraction. Serotonin as well consists of some cognitive functions, comprising memory and learning. Modulation of serotonin at synapses is thought to be a main action of some classes of pharmacological antidepressants.

Tryptophan (L-Trp or D-Trp; sold for medical utilization as Tryptan) is one of the 20 standard amino acids, and also an essential amino acid in the human diet. This is encoded in the standard genetic code as the codon UGG. Only the L-stereoisomer of tryptophan is employed in structural or enzyme proteins, however the D-stereoisomer is occasionally found in naturally produced peptides (for illustration, the marine venom peptide contryphan). The unique structural characteristic of tryptophan is that it consists of an indole functional group. This is a necessary amino acid as illustrated by its growth effects on rats.

For most of the organisms (comprising humans), tryptophan is a necessary amino acid. This signifies that it can't be synthesized by the organism and thus should be part of its diet. Amino acids, comprising tryptophan, act as building blocks in the protein biosynthesis. Moreover, tryptophan functions as a biochemical precursor for the following compounds.

Serotonin (that is, a neurotransmitter), synthesized through tryptophan hydroxylase. Serotonin, in turn, can be transformed to melatonin (a neurohormone), through N-acetyltransferase and 5-hydroxyindole-O-methyltransferase activities. 

Niacin is synthesized from tryptophan through kynurenine and quinolinic acids as key biosynthetic intermediates. 

Auxin (that is, a phytohormone) whenever sieve tube elements experience apoptosis tryptophan is transformed to auxins. 

The disorders fructose malabsorption and lactose intolerance cause improper absorption of tryptophan in the intestine, reduced levels of tryptophan in the blood and depression.

Other applications of Indole:

The other Indoles of biological significance comprise tryptophan which is the precursor of two hormones; serotonin, a vasoconstrictor and melatonin (figure shown below), which is comprised in the control of circadian rhythm. In addition, the amino acid tryptophan is a necessary component of proteins and anxin (Indole-3-acetic acid) is a plant hormone which co-ordinates many growth and behavioral processed in the life of a plant. Others comprise, ergot alkaloids, reserpine and vinca alkaloids.

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Fig: Important Derivatives of Indole

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