Chapter 1 The Structure and Synthesis of C19-Diterpenoid Alkaloids

Publisher Summary Since the early 1800s, the alkaloids (nitrogenous organic bases) isolated from plants of the Delphinium and Aconitum genera (Ranunculaceae) and more recently the Garrya genus (Garryaceae) and Inula royleana (Compositae) have been of interest because of their pharmacological properties, complex structures, and interesting chemistry. Biogenetically, these diterpenoid alkaloids are possibly formed in nature from tetracyclic or pentacyclic diterpenes in which the nitrogen atom of β -aminoethanol, methylamine, or ethylamine is linked to C-19 and C-20 in the C 20 -diterpenoid skeleton and C-17 and C-19 in the C 19 -diterpenoid skeleton to form a substituted piperidine ring. These diterpenoid alkaloids may be divided into two broad groups: those based on a hexacyclic C 19 -skeleton, and those based on a C 20 -skeleton. The C 19 -alkaloids are commonly called aconitines, and all possess the aconitine, the lycoctonine, or the heteratisine skeleton. Usually in the literature, the C 19 -diterpenoid alkaloids are referred to as either aconitinetype or lycoctonine-type alkaloids without structural differentiation. This practice sometimes creates confusion, therefore, this chapter has divided the C 19 -diterpenoid alkaloids into three categories, defined as follows: (1) Aconifine-type ; (2) Lycoctonine –type ; and (3) Heterutisine-type. These alkaloids possess the skeleton of heteratisine, in which a lactone moiety is always present.