Carbon-13 Magnetic Resonance: Diterpenoid Alkaloids From the Delphinium Species

Abstract

The carbon-13 magnetic resonance spectra of the diterpenoid alkaloids lycoctonine (1), deoxylycoctonine (2), deoxymethylenelycoctonine (3), browniine (4), isolatizidine (5), delphonine (6), lycoctonal (7),and their corresponding hydrochloride or perchlorate salts have been determined at 22.63 MHz in the Fourier mode. With the aid of proton decoupling techniques, additivity relationships and the effects induced by specific structural changes, self-consistent assignments of nearly all the resonances have been made. Substituent effects are often of the same order but differ in magnitude from those for simpler systems reported in the literature. The effects of protonation do not unambiguously follow the additive trends indicated in simpler systems but do exhibit a reasonably constant pattern. The data have been applied in the structural elucidation of two previously unknown bases isolated from Delphinium bicolor Nutt.