Amines in Natural Products

Study Notes

Natural products are often named by combining the name of the organism from which they are isolated and a chemical part name.
These compounds are all amines, so their names end in '-ine'.
Natural products are made in nature from amino acids.

Pyrrolidine alkaloids are made from the amino acid ornithine.
Pyrrolidine is a simple five-membered cyclic amine, and pyrrolidine alkaloids contain this ring somewhere in their structure.
Examples of pyrrolidine alkaloids include nicotine, atropine, hygrine, and tropinone.
Ornithine is an amino acid not usually found in proteins, but most organisms use it, often in the excretion of toxic substances.
When dead animals decay, the decarboxylation of ornithine leads to putrescine, which smells revolting and is known as the 'smell of death'.

The biosynthesis of pyrrolidine alkaloids involves a pyridoxal-catalysed decarboxylation of ornithine, which follows the normal sequence up to a point.
The CO2H group as well as the amino group is lost from ornithine, and the rest of the molecule makes the pyrrolidine ring.
The three-carbon side-chain in hygrine comes from acetate, or rather from acetyl CoA, and the N-methyl group comes from SAM.

Benzyl isoquinoline alkaloids are made from tyrosine.
These alkaloids have a benzyl group attached to position 2 of an isoquinoline ring.
They are usually oxygenated on the benzene ring, and many are found in opium poppies (Papaver somniferum).
Papaverine is an ideal example of a benzyl isoquinoline alkaloid.

Terpenes are volatile constituents of plant resins and essential oils.
They are all aliphatic compounds with a scattering of double bonds and rings, few functional groups, and an abundance of methyl groups.
Examples of terpenes include pinene, camphor, humulene, and phytol.
Terpenes are made from a C5 precursor, and the favourite candidate is isoprene (2-methylbuta-1,3-diene).

The first step in the biosynthesis of terpenes is the Claisen ester condensation of two molecules of acetyl CoA, one acting as an enol and the other as an electrophilic acylating agent to give acetoacetyl CoA.

Natural products come from secondary metabolism.
Primary metabolism involves the 'big four'—nucleic acids, proteins, carbohydrates, and lipids.
Secondary metabolism involves the exploration of compounds produced by plants, microorganisms, fungi, insects, mammals, and every other type of living thing.
Without some kind of classification, the task of description would be hopeless, so a biosynthetic classification is used, grouping substances not by species but by methods of biological synthesis.