The chiroptical properties of the strychnine alkaloids: strychnine, β-colubrine, brucine, and their dihydro derivatives

Ultraviolet absorption and circular dichroism spectra of the strychnine alkaloids strychnine, β-colubrine, brucine, dihydrostrychnine, dihydro-β-colubrine, and dihydrobrucine have been investigated under various experimental conditions. It appears that at least five electronic transitions are required to account for the spectroscopic properties of these molecules in the ultraviolet region above 190 nm. Transitions, which are tentatively assigned as the 1Lb, 1La, 1Bb, and 1Ba in the notation due to Platt, and an n → π* transition apparently make significant contributions to the spectra of ail of the molecules studied.