Nicotinates biological activity, structure

Niacin (Fig. 1) is a collective name for all vitamers having the biological activity associated with nicotinamide (= pyridine-3-carboxamide), including nicotinic acid (= pyridine-3-carboxylic acid) and a variety of pyridine nucleotide structures. 

Nicotinamide and nicotinic acid are both white crystalline substances. Their aqueous solution has a maximal UV absorbance at 263 nm. Both vitamers have the same biological activity as they can be converted into each other. Figure 2 shows the structure of the coenzyme forms NAD+ and NADP+. 

These include nicotinic acetylcholine receptors, neuronal calcium channels, muscle sodium channels, vasopressin receptors, and iV-methyl-D-aspartate (NMDA) receptors. Some general features of the structure, function, and evolution of biologically active peptides isolated from Conus venom are presented. 

Niacin is a generic name for a small family of molecules having niacin biological activity. The most common structures that fall into this category are nicotinic acid and nicotinamide ... 

True alkaloids derive from amino acid and they share a heterocyclic ring with nitrogen. These alkaloids are highly reactive substances with biological activity even in low doses. All true alkaloids have a bitter taste and appear as a white solid, with the exception of nicotine which has a brown liquid. True alkaloids form water-soluble salts. Moreover, most of them are well-defined crystalline substances which unite with acids to form salts. True alkaloids may occur in plants (1) in the free state, (2) as salts and (3) as N-oxides. These alkaloids occur in a limited number of species and families, and are those compounds in which decarboxylated amino acids are condensed with a non-nitrogenous structural moiety. The primary precursors of true alkaloids are such amino acids as L-ornithine, L-lysine, L-phenylalanine/L-tyrosine, L-tryptophan and L-histidine . Examples of true alkaloids include such biologically active alkaloids as cocaine, quinine, dopamine, morphine and usambarensine (Figure 4). A fuller list of examples appears in Table 1. 

The term niacin refers to nicotinic acid (pyridine-3-carboxyhc acid), its amide nicotinamide, and derivatives that show the same biological activity as nicotinamide. A distinction between the two primary vitamin forms has to be considered, however, when considering some aspects of their metabolism and especially their different pharmacological actions at high doses. Structures of both vitamers and the two coenzyme forms containing the nicotinamide moiety are given in Figure 30-23. 

ABT-594, a nicotinic acetylcholine receptor (nAChR) modulator that exhibits potent antinociceptive activity in animal models of pain, was discovered through optimization of a series of compounds that was first identified as part of a program directed toward the discovery of nAChR modulators for Alzheimer s disease. Structure-activity studies on ABT-594 indicate that both the azetidine ring and an appropriately substituted pyridine ring are key structural features contributing to its biological activity, which together with its favorable pharmacokinetic and safety profiles, has led to its advancement to clinical trials for treatment of pain in humans. 

Since the piperidines behave in a specific way and are teratogenic, they also fulfill specific criteria for teratogenesis [23, 24, 38, 70, 85]. The structural characteristics of these piperidines need to be determined and their main differences outlined to be able to find out their mechanism of action, as fetal movement and malpositioning. The birth defects caused by Conium maculatum are the same, and their biological activities occur by a similar mechanism of action [16,52, 65,66,70]. As usual with biological active compounds one use to characterize the toxicity into acute and chronic forms. The peripheral actions of coniine are similar to those of nicotine, but it produces more pronounced paralysis of the central nervous system and of the skeletal muscle nerve [65, 70]. 

Two compounds, nicotinic acid and nicotinamide, have the biological activity of niacin. When nicotinic acid was discovered to be a curative and preventive factor for pellagra, it was already known as a chemical compound, and was therefore never assigned a number among the B vitamins. The name niacin was coined in the USA when it was decided to enrich maize meal with the vitamin to prevent pellagra - it was considered that the name nicotinic acid was not desirable because of the similarity to nicotine. In USA, the term niacin is commonly used to mean specifically nicotinic acid, and nicotinamide is known as niacinamide elsewhere niacin is used as a generic descriptor for both vitamers. Figure 2.16 shows the structures of nicotinic acid, niacin and the nicotinamide nucleotide coenzymes, NAD and NADE... 

Niacin refers to a group of compoimds also known as vitamin B3, presenting similar biological activity, including nicotinamide, nicotinic acid, as well as other pyridine nucleotide structures. In the body, these compounds act as cofactors in oxidation—reduction reactions. To determine the total vitamin B3 content, either an acid or alkaline hydrolysis is necessary. The separation is normally performed by RPLC with fluorescence (322 nm ex., 380 nm em.) or UV detection (254 nm). 

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