The Quinoline Alkaloids

The quinoline alkaloids from higher plants are best classified according to their biogenetic derivation from either anthranilic acid or tryptophan. A number of simple quinolines, including the parent structure have been isolated from rutaceous plants. Most of these alkaloids are substituted at position 2 of the heterocycle. In addition to the quinolines, angostura bark also contains 1-methyl-2-quinolone. The co-occurrence of 2- and 4-quinolones is a common feature in many plants of the Rutaceae; fortunately spectroscopy allows an easy distinction to be made between these two types of alkaloids. Some thirty alkaloids derived from 9-acridone have been isolated from rutaceous plants; the main structural diversity stems from the substitution of O-methyl, methylenedioxy or O-prenyl functions at the 1-, 2-, 3- or 4-positions. The seeds of several Echinops species (Compositae) contain the alkaloid echinorine. The cinchona alkaloids occur in the bark of Cinchona and Remijia species (Family Rubiaceae), which are indigenous to the eastern tropical slopes of the Andes. Until quite recent times cinchona preparations have been the sole treatment for malaria, for example, Quinine. Pumiliotoxin-C1 is one of the toxic principals of the skin of the highly colored Panamanian frog Dendrobates pumilio.