Quinoline, Indole, and Isogranatanine Alkaloids from Malayan Leuconotis eugeniifolia .

Nine new alkaloids, eugeniinalines A-H ( 1 - 8 ) and (+)-eburnamenine N -oxide ( 9 ), comprising one quinoline, six indole, and two isogranatanine alkaloids, were isolated from the stem-bark extract of the Malayan Leuconotis eugeniifolia . The structures and absolute configurations of these alkaloids were established based on the analysis of the spectroscopic data, GIAO NMR calculations, DP4+ probability analysis, TDDFT-ECD method, and X-ray diffraction analysis. Eugeniinaline A ( 1 ) represents a new pentacyclic quinoline alkaloid with a 6/6/5/6/7 ring system. Eugeniinaline G ( 7 ) and its seco -derivative, eugeniinaline H ( 8 ), were the first isogranatanine alkaloids isolated as natural products. The known alkaloids leucolusine ( 10 ) and melokhanine A ( 11 ) were found to be the same compound, based on comparison of the spectroscopic data of both compounds, with the absolute configuration of (7 R , 20 R , 21 S ). Eugeniinalines A and G ( 1 and 7 ) showed cytotoxic activity against the HT-29 cancer cell line with IC 50 values of 7.1 and 7.2 μM, respectively.