C. Niacin
Synonyms Nicotinic Acid; Pellagra Preventive Factor (or P.P. Factor); Vitamin B3; Akotin; Daskil; Nicacid; Niacor; Nicangin; Nicobid; Nicolar; Niconacid; Nico-Span; Wampocap. The term ‘niacin’ has also been applied to nicotinamide.
Biological Sources It is widely distributed in nature; and appreciable quantities are found in fish, yeast, liver, and cereal grains.
Chemical Structure
3-Pyridinecarboxylic acid; (C6H5NO2).
Preparation It may be prepared by the oxidation of nicotine** as given below.
3. It is a nonhygroscopic substance and fairly stable in air.
4. It shows uvmax : 263 nm; and pH 2-7 of a saturated solution.
5. Solubility: 1 g dissolves in 60 ml water; freely soluble in boiling water and ethanol; soluble in
propylene glycol; and insoluble in ether.
Identification Test
1. Niacin Sodium Salt Sesquihydrate (C6H4NNaO2.1½H2O) (Synonym: Direktan): It is obtained
as either white crystals or crystalline powder, which is stable in air. Its solubility profile are as
follows: 1 g dissolves in ~ 1.4 ml of water, in 60 ml ethanol, in 10 ml glycerol; and insoluble in
ether. The pH of aqueous solution is ~ 7.
2. N-Oxide Derivative (Oxiniacic Acid): It is obtained as needles mp 254-255°C (dec.) and uvmax
(0.1 N.H2SO4):220, 260 nm (€ 22400, 10200).
Uses
1. It is used as antihyperlipoproteinemic agent.
2. It is a vital vitamin (enzyme cofactor).
Biosynthesis of Nicotine, Anabasine and Niacin Interestingly, plants such as Nicotiana make use of an altogether different pathway employing glyceraldehyde 3-phosphate and L-aspartic acid precursors as given under. Thus, the dibasic acid quinonilic acid features in the aforesaid pathway which upon decarboxylation gives rise to nicotinic acid.
It is pertinent to mention here that the formation of nicotine caused by a pyrrolidine ring derived from ornithine, quite possibly as the N-methyl-∆1-pyrrolinium cation gets hooked on to the pyridine ring present in nicotinic acid thereby displacing the carboxyl function during the course of reactions as depicted in (B). Further, a dihydronicotinic acid intermediate is most likely to be engaged permitting decarboxylation to the enamine 1,2-dihydropyridine. It, therefore, allows an aldol-type interaction with the N-methylpyrrolinium cation, and ultimately undergoes dehydrogenation of the dihydropyridine ring reversed to a pyridine ring yields nicotine. In this fashion, nornicotine is derived by the oxidative demethylation of nicotine.
Finally, anabasine is generated from nicotinic acid and lysine via the ∆1-piperidinium cation in an effectively analogous sequence as shown in (C) below.
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* Sadykov and Timbekov, J. Appl. Chem., USSR, 29, 148 (1956).
** MeElvain, S.M., Org. Synth. Coll.Vol I, 385 (1941).
