The title compound △14,15-anhydro-24-thiocarbonylbufalin （1） was prepared by the reaction of natural product bufalin with Lawesson reagent. The crystal structure of 1, C24H3002S＇C24H3002S, was determined by single-crystal X-ray diffraction analysis. It belongs to monoclinic, space group C2, with a = 30.9845（2）, b = 6.8036（3）, c = 22.5791（15）/k, V= 4241.7（4） A3, Mr = 384.21, Z = 4, Dc= 1.204 g/cm3,μ = 1.463 mm4, F（000） = 1664, S = 1.064, R = 0.0487 and wR = 0.0645 for 4683 unique reflections, of which 3757 were observed （I 〉 2σ（/））. The asymmetric unit contains two independent molecules （ⅠandⅡ）, which are closely similar to each other except for the orientation of the lactone ring. Both conformations of I and II are in good agreement with the solution structure in methanol as indicated by 1H-NMR analysis. Due to the presence of heavy atom sulfur in the molecules, the final refinement resulted in a small Flack parameter 0.02（3）, permitting the assignments of the absolute configuration. In the solid state, intermolecular hydrogen bonds involving thiocarbonyl group in the lactone moiety and the hydroxyl groups in the steroid moiety ester linked adjacent molecules into a three-dimensional network. Compound 1 showed weak inhibition on Na＋/K＋-ATPase in contrast to the strong inhibitory activity of the parent compound bufalin, suggesting that the carbonyl group in lactone moiety and the hydroxyl group atC-14 play important roles for the inhibition of Na＋/K＊-ATPase.
The title compound cinobufagin 3-hemisuberate methyl ester（1） was isolated from the venom of Bufo bufo gargarizans CANTOR. The crystal structure of 1, C35H48O9, was determined by single-crystal X-ray diffraction analysis. It belongs to orthorhombic, space group P212121 with a = 8.9338（3）, b = 16.2970（4）, c = 22.4019（6） , V = 3261.59（16） 3, Mr = 612.73, Z = 4, Dc = 1.248 g/cm3, μ = 0.725 mm-1, F（000） = 1320, S = 1.040, the final R = 0.0374 and wR = 0.0412 for 4458 unique reflections, of which 4088 were observed（I 〉 2σ（I））. In the solid state, short intermolecular C-H...O interactions involving a methine and the ester carbonyl group in cinobufagin moiety and a methyl in the suberate moiety linked adjacent molecules into a three-dimensional network. Detailed analysis of the 1H-NMR data showed that X-ray structure of 1 would be expected to closely resemble the solution conformation in chloroform. Compound 1 was inactive for the inhibition of PC3 and HepG2 cancer cells, but the parent compound cinobufagin showed potent inhibition with IC50 values of 0.145 and 5.48 μM, respectively, indicating that esterification at C（3） decreased the cytotoxic effect of 1.
Three new C-3 dehydrated bufadienolides were isolated from the venom of Bufo bufo gargarizans. Their structures were elucidated as 5β,12β-12,14-dihydroxy-11-oxobufa-3,20,22-trienolide （1）, 5β,12β- 12,14-dihydroxy-11 -oxobufa-2,20,22-trienolide （2）, and 5β,12β-12,14-dihydroxy-11 -oxobufa-2,20,22- trienolide （3） on the basis of extensive spectroscopic analysis, especially 1D NMR and 2D NMR data. In addition, all three compounds were tested for their cytotoxic activities against A549 and HepG2 cancer cell lines. Compounds 2 and 3 showed significant cytotoxicities with IC50 values less than 10 μmol/L on both cancer cells.
Hai-Yan TianPeng-Wei ZhangJun-Shan LiuDong-Mei ZhangXiao-Qi ZhangRen-Wang JiangWen-Cai Ye
