Absolute configuration assignment to anticancer Amaryllidaceae alkaloid jonquailine

Jonquailine, a new alkaloid recently isolated from Narcissus jonquilla quail, an Amaryllidaceae species cultivated for its flowers fragrance in Europe and USA, shows very significant anti-proliferative activity against several malignant cancer cell types. Although it was reported that this activity is related to the functionalities and to its stereochemistry at C-8 of B ring, the absolute configuration at this stereocenter was not known. Density functional theory (DFT) calculations of chiroptical properties, namely electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and optical rotatory dispersion (ORD) are employed here to complete assignment of absolute configuration of jonquailine, and then, by extension, to its analogues pretazettine and 8-O-methylpretazettine. While ECD is not discriminating and ORD is of limited use, VCD reveals decisive in the task of absolute configuration assignment.