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Three new ent-kaurane diterpenoids laxiflorin E (1), laxiflorin H (6) and laxiflorin I (8) were isolated from the leaves of Isodon eriocalyx var. laxiflora, along with nine known diterpenoids, eriocalyxin A (2), laxiflorin C (3), laxiflorin D (4), laxiflorin A (5), maoecrystal S (7), maoecrystal Q (9), eriocalyxin B (10), maoecrystal C (11) and enmelol (12). The structures of the new compounds were determined by spectroscopic methods. Compounds 1-5 are 6,7-seco-ent-kaurane-7,20-olide diterpenoids, and 6-12 belong to 7,20-epoxy-ent-kauranoids. The spectral data of enmelol (12) are reported here for the first time. Ten of these compounds were tested for their cytotoxicity toward K562 and T24 human tumor cells. Compounds 1, 3 and 10 showed significant inhibitory effects on K562 cells with IC50 values 0.077, 0.569 and 0.373 microg/mL, and compounds 1 and 10 also demonstrated significant inhibitory activities toward T24 cells with IC50 values 0.709 and 0.087 microg/mL. Compounds 8 and 11 also displayed inhibitory effect on both two kinds of cells with IC 50 value less than 6.5 microg/mL.

Eight new abietane diterpenoids, coleon U 11-acetate (1), 16-acetoxycoleon U 11-acetate (2), and xanthanthusins F-K (3-8), together with five known analogues, coleon U (9), 16-O-acetylcoleon C (10), coleon U-quinone (11), 8alpha,9alpha-epoxycoleon U-quinone (12), and xanthanthusin E (13), were isolated from the aerial parts of Coleus xanthanthus. The structures of 1-8 were elucidated on the basis of spectral methods. Compounds 1, 5, and 11-13 were evaluated for their cytotoxicity against K562 human leukemia cells.

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Four new ent-kaurane diterpenoids, laxiflorins J-M (1-4), along with maoecrystal A (5) and maoecrystal P (6), were isolated from the leaves of Isodon eriocalyx var. laxiflora. Their structures were determined by spectroscopic analyses. All the compounds were assayed for their cytotoxic effects on human tumor K562, A549, and T24 cell lines. Compounds 1 and 6 showed significant inhibitory effects on human tumor K562 and T24 cells, with IC(50) values less than 0.5 microg/mL. Compound 3 also demonstrated cytotoxic activities against all three types of human tumor cells, with IC(50) values in the range of 1-25 microg/mL.