B-1 Proposed biosynthetic pathways for production of several pyridine alkaloids

FIGURE XVII.B-1 Proposed biosynthetic pathways for production of several pyridine alkaloids (17B05). 

Myosmine can be formed from nornicotine by enzymatic dehydrogenation (2332, 17B24). 

Cotinine and 2,3 -bipyridyl and their derivatives represent the major oxidized alkaloids in tobacco. Cotinine is synthesized from nicotine via enzymatic oxidation or autooxidation (1157, 17B03). 2,3 -Bipyridyl is formed by oxidation of anat-abine. Frankenburg et al. (1221a, 1222-1224) were the first to identify 2,3 -bipyridyl as a fermentation product along with 

3-acylpyridine. Other oxidized alkaloids identified in green and cured tobacco are nicotyrine, nicotinic acid, nicotinamide, and nicotine-fV-oxides. Enzell et al. (1149a) found that these oxidation products of tobacco alkaloids tend to increase in yield during curing and storage of tobacco. 

Pyrimidines play a central role in cellular regulation and metabolism. They are substrates for DNA and RNA biosynthesis, regulators of biosynthesis of some amino acids, and cofactors in the biosynthesis of phospholipids, glycolipids, sugars, and polysaccharides (17B45). Pyrimidine biosynthesis is very complicated and involves formic acid, glutamate, and aspartate as starting materials in a series of enzymatic reactions to eventually form orotic acid. Orotic acid, or uracil- 

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