ASSIGNMENT: BIOSYNTHESIS OF ALKALOIDS AND GLYCOSIDES
BIOSYNTHESIS OF ALKALOIDS
Alkaloids are naturally occurring organic nitrogen-containing bases. They are secondary metabolites containing nitrogen moiety usually heterocylic in nature. The nitrogen is usually derived from an amino acid commonly; phenylalanine, tyrosine, tryptophan, histidine, ornithine and anthranilic acid. Alkaloids are found primarily in plants and are especially common in certain families of flowering plants and also fungi though a rare source. However, they are an important source of allopathic and homeopathic medicine because of toxicity and controlled dosage.
Some of the various types of alkaloids include;Ornithine derived alkaloids
As shown below; the amino acid, its decarboxylation product, putrescine and proline constitute the basic unit of the tropane, ergotamine, nicotine, necine and stachydrine groups of alkaloids.
Pharmaceutically the tropane group is important. Tropane alkaloids are derived from L-ornithine. The principal alkaloid of medicinal interest in this group are hyoscyamine that is more stable racemate atropine, and hyoscine. T He compounds are esters and are hydrolysed by heating at 60C with baryta water; atropine yields tropic acid and tropine; hyoscine gives tropic acid and oscine formed by enzymatic hydrolysis but the chemical treatment converts it to the more stable geometric isomer.The Tropane class of alkaloids found in solanaceae contains anticholinergic drugs hyoscyamine (racemic mixture is called atropine) and scopolamine.
Lysine derived alkaloids
.Lysine and its associated compounds give rise to a number of alkaloids, some of which are analogues to the ornithine group.The lycopodium alkaloids are also derived from lysine. Although in some cases, such as the quinolizidone jupin alkaloids ,lysine is incorporated via a symmetrical precursor eg. Cadaverine.
Phenylalanine-tyrosine- and dihyroxyphenylalanine-derived alkaloids...