Biologically Active Mesomeric Betaines and Alkaloids, Derived from 3- Hydroxypyridine, Pyridin-N-oxide, Nicotinic Acid and Picolinic Acid: Three Types of Conjugation and Their Consequences

Betainic pyridinium alkaloids and analogs are members of the four major classes of heterocyclic mesomeric betaines, i.e. conjugated (CMB), cross-conjugated (CCMB), pseudo-cross-conjugated heterocyclic mesomeric betaines (PCCMB), and conjugated Nylides and thus offer the possibility of detailed comparisons of the types of conjugation. The chemistry of these systems is surveyed.