Gentiocrucine was first isolated from Gentiana cruciata by Popov and Marekov, who proposed structure (I) for the compound. The authors isolated the same compound from Enicostemma hyssopifolium (Willd.) Verd. and reinvestigated its structure. Through UV, IR, MS, 100 MHz Fourier transform PMR, 25.2 MHz 13C Fourier transform NMR spectral analyses and chemical studies (e.g., formation of two dinitrophenylhydrazones, reduction with 98% formic acid to a β-amino ketone), it was revealed that gentiocrucine exists as cis-trans isomers (II and III) which are stable aliphatic primary enamino ketones. Such compounds have not been encountered before in nature or prepared synthetically.