Circular Dichroism of Some Alkaloid Enaminoketones and v-Pyridones

Multiflorine (1) and seco(11,12)-12-dehydromultiflorine (2) were isolated from Lupinus albus seeds (cultivar BAC).l The stereochemistry of multiflorine (1) was studied and the negative n-'It* Cotton effect, displayed in the ORD curve of 1, was used to support the assignment of the absolute configuration of 1.2 The structure of 2, originally formulated as N-methylalbine,1 has recently been established on the basis of the NMR spectra." Both alkaloids contain Z-s-trans enaminoketone chromophore, the spectral properties of which differ from those of simple enones, due to conjugation with the nitrogen p-orbital. Optically active compounds of this type are scarce, hence 1 and 2 provide unique opportunity to study the enaminoketone chromophore by circular dichroism, including solvent and protonation effects.