Chapter one Carbon-13 and proton NMR shift assignments and physical constants of diterpenoid alkaloids

Abstract

Publisher Summary This chapter describes various types of diterpenoid alkaloids and presents proton and/or carbon-13 NMR chemical shift assignments and physical constants for many of the naturally occurring diterpenoid alkaloids and their derivatives. Diterpenoid alkaloids have been isolated from the genera of the families Ranunculaceae (Aconitum, Consolida, Delphinium, Thalictrum), Garryaceae (Garraya), Rosaceae (Spiraea), and Compositae (Inula). These alkaloids can be divided into two broad categories: norditerpenoid alkaloids (based on a C19-skeleton) and the diterpenoid alkaloids (based on a C20-skeleton). The structures of more than 240 naturally occurring diterpenoid alkaloids have been determined in the past twenty five years by using 13C nuclear magnetic resonance (NMR) studies. The diterpenoid alkaloids are derived from tetra- or pentacyclic diterpenes in which C(19) and C(20) are linked with the nitrogen of β-aminoethanol, methyl, or ethylamine to form a heterocyclic ring. These alkaloids can be divided in two broad types namely, atisanes and the kauranes. The atisane skeleton contains the [2,2,2]-bicyclic ring system with the C(15)–C(16) bridge attached at C(12). The kaurane skeleton possesses a [3,2,l]-bicyclic ring system with C(15)- C(16) bridge connected to C(13), forming the five-member ring D.