CHEMICAL ECOLOGY OF ALKALOIDS EXEMPLIFIED WITH THE PYRROLIZIDINE

摘要

Within secondary metabolites, alkaloids represent a diverse group with more than 12 000 structures elucidated.' According to Pelletier, they are defined as cyclic compounds containing nitrogen in a negative oxidation state that are limited in distribution among living organisms.2 Though this group encompasses a vast array of unrelated structures, most exhibit substantial biological activities, particularly pharmacological effects on vertebrates.3 Most alkaloids are easily resorbed, and due to their nitrogenous structure many of them interfere with essential components of the nervous system, acting on presynaptic and postsynaptic receptors, enzymes involved in inactivation of neurotransmitters or in the postsynaptic signal transduction pathway, as well as on specific ion channels. Some alkaloids cause detrimental effects by influencing the function of the cytoskeleton or by interacting unspecifically with DNA or proteins (Table 9.1).