Let’s look at an overview of it’s synthesis, are you ready? They are synthesized from amino acids basically; lysine, ornithine, trptophan, tyrosine and aspartic acid. Mevalonic pathway generates much of the carbon skeleton for alkaloids. The biosynthetic pathway leading to the formation of nicotine is of importance. The bitter vitamin nicotinic acid is a precursor of NAD and NADP which are electron carriers in metabolic pathways.
Roles of alkaloids
some are poisonous in nature which makes domestic herbivores to select plants to be eaten to avoid being poisoned. examples are iuphines, larkspur, atropine,caniine etc. They act as defence mechanism for plants.They are used medicinally to induce, modify or alter physiological processes, hence such includes morphine, codeine, atropine, ephedrine etc.Some accolades such as cocaine, nicotine and caffeine are used as stimulants or sedatives.
Mode of action
i. Some attach to nerve receptors and effect neurotransmission
ii. Orders effect physiological processes such as protein synthesis, membrane transport, enzyme activity etc.
Classes of alkaloids
The classes of includes
Pyrrolidine (e.g nicotine)Tropane (e.g atropine, cocaine)Piperidine (e.g caniine)Pyrrolizidine (retrorsine)Quinolizidine (e.g lupinine)Isoquinoline (e.g codeine, morphine)Indole (strycine) ￼
“True alkaloids” contain nitrogen in the
heterocycle and originate from amino acids . Their characteristic examples are
atropine, nicotine, and morphine. This group also includes some that besides the nitrogen heterocycle contain
terpene (e.g. , evonine or peptide fragments ( e.g. ergotamine. The piperidine alkaloid coniine and coniceine may be regarded as true alkaloids (rather than pseudoalkaloids: see below) although they do not originate from amino acids.
2. “Protoalkaloids”, which contain nitrogen (but not the nitrogen heterocycle) and also originate from amino acids. Examples include mescaline , adrenaline and
3. Polyamine alkaloids – derivatives of
putrescine , spermidine , and spermine.
4. Peptide and cyclopeptide alkaloids.
5. Pseudoalkaloids – alkaloid-like compounds that do not originate from amino acids.
This group includes terpene -like and
steroid -like alkaloids, as well as purine -like alkaloids such as caffeine ,
theobromine , theacrine and
theophylline . Some authors classify as pseudoalkaloids such compounds such as
ephedrine and cathinone. Those originate from the amino acid phenylalanine, but acquire their nitrogen atom not from the amino acid but through transamination.
They were once thought to be nitrogenous waste as related to urea and uric acid in mammals, nitrogen storage compounds or growth regulators, but there is little evidence to support the fact of these functions.
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