Niacin Analogues
Ethyl nicotinate, nicotinic acid N-methylamide, p-picoline p-methyl pyridine) and 3-hydroxymethylpyridine have vitamin activity. The evidence indicates that these compounds are active on the basis of their conversion into nicotinic acid. Pyridyl-3-aldehyde added to the diet was effective in niacin-deficient ducks, but pyridyl-3-carbinol and p-picoline were inactive when fed with the diet. They were active given per, and all three were active upon injection.
Niacin Antagonists
A number of compounds structurally related to niacin act as antagonists in animals and/or in microorganisms. Pyridine-3-sulfonic acid, and 3-acetylpyridine are examples. It is probable that such antagonists are used in the synthesis of DPN or TPN analogues and that these combinations are not physiologically active. Thus the organism is deprived of its normal complement of these coenzymes. In most cases additional niacin overcomes the antagonism. The compound 6-aminonicotinamide produces niacin deficiency symptoms in rats at a level of 15 to 30 mg per kg of diet. The symptoms are prevented by the further addition of 150 to 300 mg of niacinamide per kg of ration. The 6-amino analogue is quite active against some tumors in rats, and this tumor inhibition is reversed by niacin-amide.
