Many definitions of alkaloids can be found, but generally all include the statement that alkaloids are naturally occurring, organic, N-containing bases, most often produced by plants. Many alkaloids have important medical uses, whereas others are very toxic to humans. Morphine, quinine, atropine, and vincristine are examples of plant-derived alkaloids with applications in medical therapies. Some alkaloids such as cocaine, heroin, caffeine, and nicotine are addictive. Others, such as strychnine and coniine are very toxic in small amounts; ergotamine, although also toxic, has some medical uses. In early investigations, alkaloids were often given names associated with the plant from which they were first isolated, for example, nicotine from Nicotiana spp. and vinblastine and vincristine from Vinca rosea L. [=Catharanthus roseus (L.) G. Don]. As more became known about the biosynthetic origins of alkaloids, classifications were based on metabolic pathway rather than origin.
Alkaloids of tall fescue are most often identified by common name, which will be used here. The first alkaloids reported in tall fescue were those produced by the plant, with perloline being the principal alkaloid of this group. Neil (1941) reported the occurrence of the endophytic fungus N. coenophialum in tall fescue (see Chapters 1 and Chapter 14). The host-endophyte symbiotic association has three other types of alkaloids occurring in infected herbage: peramine, ergot and loline. These groups all appear to be bioactive, for they can inhibit functions in bacteria, insects, mammals and plants. This chapter will describe the chemistry and incidence of alkaloids, whereas other chapters detail the biological activity and practical impact of these compounds (see Chapters 11, Chapter 12, Chapter 16, and Chapter 17).
A common suite of signs in herbivorous animals that have consumed E+ tall fescue is fescue toxicosis. There is strong evidence that this manifestation is caused by the ergot alkaloid group, but no definitive experiment has been reported to demonstrate this. In the following sections, plant-derived alkaloids and those from the grass-endophyte symbiotum-peramine, ergot, and loline alkaloids, are discussed.