3,3-Diisopentenyl-N-Methyl-2,4-Quinoldione from Esenbeckia Almawillia: The Antitumor Activity of this Alkaloid and its Derivatives

n-Hexane, chloroform and ethyl acetate fractions obtained from methanol extracts of the wood and roots of Esenbeckia almawillia (Rutaceae) were tested against five tumor cells lines (HL-60, CEM, B-16, HCT-8 and MCF-7). The most active fractions were the less polar ones (IC50 from 1.7 to 5.3 μg/mL) and these were subjected to column chromatography, allowing the isolation of the alkaloid 3,3-diisopentenyl-N-methyl-2, 4-quinoldione (1) in high yields. Alkaloid 1 was bioassayed and gave an IC50 value in the range 9.2 to >25 μg/mL. Derivatives 2–12, obtained by chemical modifications of 1, were tested and lower IC50 values were found for compounds 4 (IC50 from 2.8 to 17.0 μg/mL), 10 (IC50 from 5.9 to 15.8 μg/mL) and 11 (IC50 from 6.7 to 14.8 μg/mL).