PYRIDINE - PIPERIDINE ALKALOIDS

Lec.( 2 )


PYRIDINE - PIPERIDINE ALKALOIDS

On reduction, the tertiary base, pyridine, is converted into the secondary base, piperidine .These two nuclei form the basis of this group, which is sometirnel divided into three subgroups :

(I) Derivatives of piperidine ,includinglobeline from lobelia.

(2) Derivatives of nicotinic acid , including arecoline from areca .

(3) Derivatives ofboth pyridine and pynolidine,including nicotine fromtobacco .

The important alkaloidaldrugs and their alkaloids that are classified inthis group are areca, arecolinehydrobromide , lobelia ,lobeline and nicotine.

Biosynthesis of Pyridine-PiperidineAlkaloids
,
Tracer studics have shown that ornithine is incorporated
into nicotine by tobacco plants.
This incorporationresuitsi n a symmetric labeling pattern of nicotine .
Nicotine is primarily a product of root metabolism, but the formation of small amounts , as well as subsequent reactions such as the demethylation of nicotine , can occur in the leaves of plants .

Areca
Areca , areca nut , or betel nut is the dried , ripe seed ofAreca catechu L.
Areca contains several alkaloids that arereduced pyridine derivatives .
ducedpyridinen derivatives. Among them arearecoline, arecaidine,guvacine,andguvacoline . The total alkaloid content can reach0.45%.
Arecoline,t he most abundant and physiologically
most active alkaloid, is a liquid occurringto the extent of about 0.2% .
Areca also containstannin(abourl -15%) , lipids , volatile oils,
and gum. Areca is classified as an anthelmintic in veterinary practice and is employed as a vermicide and taeniafuge.

Lobelia
Lobelia or Indian tobacco consists of the dried leaves and ropsofLobeliainflataL. The drug contains 14 alkaloids, of which lobelineis the major and most important. a pungent volatile oil, resin, lipids, and gum.
Lobeline occursacolorless crystals that are slightly soluble
in water but readily soluble in hot alcohol.Lobeline produces similar, but weaker, pharmacologic effects to those of nicotine on the peripheral circulation; neuromuscular junctions,
and the central nervous system. For this reason, lobeline sulfate was formerly incorporated in tablets or lozenges that were intended to aid inbreaking the tobacco habit (smokingdeterrent) .
The majority of controlled studies showed thatLobeline had only a placebo effect on decreasing thephysical craving for cigarettes,so these products were removed from the market.

Nicotine
Nicotine is a pyridinealkaloidobtained from the dried
Leaves of the tobacco plantNicotianatabacum L. (Fam. Solanaceae).
Nicotinei s colorless to pale yellow very hygroscopic, oily ,volatileliquid with an unpleasant. pungent odor and a sharp, burning, persistent taste .
Nicotine is a ganglionic( nicotinic ) cholinergic – receptor agonist with
Complex pharmacologic actions that include effects mediated by binding to rcceptors in autonomic ganglia , the adrenal medulla , the neuromuscular junction, and the brain . Chronic use of nicotine may result in psychologic and physical dependence . As a temporary aid for the cessation of cigarettesmoking , the drug is available in transdermal system , and it also available bound to an ion exchange resin in a chewing gum base . These alternative sources of nicotine help reduce the withdrawal symptoms associated with nicotine addiction.


Dr. Saad Ali Ihsan
Professor of Medicinal & Aromatic Plants