Isolation, Crystal Structure and Cytotoxic Activity of Natural Maistemonine and Comparison with the Synthetic Compound

The title compound maistemonine (1) was isolated from the total alkaloid fraction of the 95% ethanol extract of the roots of Stemona japonica, followed by preparative HPLC and recrystallization from a mixture of n-hexane and ethyl acetate. The crystal structure of 1, C23H29NO6, was determined by single-crystal X-ray diffraction analysis. The crystal belongs to orthorhombic system, space group P2(1)2(1)2(1) with a = 8.5698(6), b = 14.0460(11), c = 17.8815(17) angstrom, V = 2152.4(3) angstrom(3), Z = 4, M-r = 415.47, D-c = 1.282 g/cm(3), lambda = 0.71079 angstrom, mu = 0.092 cm(-1), F(000) = 888, S = 0.995, R = 0.0535 and wR = 0.1067. A total of 5136 unique reflections were collected, of which 3523 were observed (I > 2 sigma(I)). The absolute configuration of 1 could be assigned by referring to the conserved configuration of the methyl groups at C(2). Compound 1 shows mild cytotoxic activity against the prostate cancer cells LNCaP and PC3 with the IC50 values of 29.4 +/- 2.3 and 46.6 +/- 3.1 mu M, respectively. It is noteworthy that the natural maistemonine (1) is different from the synthetic compound which was a racemic with the triclinic space group P (1) over bar. The lactone rings E from the natural and synthetic 1 are almost perpendicular to each other when overlapping the remaining parts of the molecules.