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,C23H29NO)6,was determined by single-crystal X-ray diffraction analysis.The crystal belongs to orthorhombic system,space group P212121 with a=8.5698(6),b=14.0460(11),c=17.8815(17)?,V=2152.4(3)?3,Z=4,Mr=415.47,Dc=1.282 g/cm3,λ=0.71079?,μ=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>2σ(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 mM,respectively.It is noteworthy that the natural maistemonine(1)is different from the synthetic compound which was a racemic with the triclinic space group P1.The lactone rings E from the natural and synthetic 1 are almost perpendicular to each other when overlapping the remaining parts of the molecules.