Chemical investigation of the roots of Croton crassifolius led to the isolation of five pyran-2-one derivatives, including two brand new compounds (1–2), one new natural product (3) and two known compounds (4–5). Their structures and absolute configurations were established by spectroscopic analyses as well as comparison between the calculated optical rotation (OR) values with the experimental data. Interestingly, the new compound 1 showed an unusual negative chemical shift at H-11. It is well known that negative chemical shift values of ¹H NMR spectrum are extremely rare in natural products. Such a negative chemical shift of ¹H NMR spectrum was reproduced by density functional theory (DFT) calculations and explained by the shielding effect from the pyran-2-one ring over the hydrogen atom in the 3D conformations. Then, MTT assay was applied to evaluate the cytotoxicity of the isolated compounds (1–5) against two liver cancer cell lines (HepG2 and MHCC97H). The results suggested that compound 1 displayed the highest cytotoxicity with an IC₅₀ value of 9.8 μM against HepG2 cells. Moreover, there was no obvious cytotoxicity of compounds 1–5 on normal liver cell line LO2. Furthermore, the mechanism of apoptosis induction in compound 1-treated HepG2 cells was investigated. The results showed that compound 1 could induce apoptosis via p53-mediated Ras/Raf/ERK suppression in HepG2 cells.

的根的化学调查巴豆crassifolius导致5吡喃-2-酮衍生物的分离，其中包括两个品牌的新化合物（1 - 2），一个新的天然产物（3）和两个已知的化合物（4 - 5）。通过光谱分析以及将计算的旋光度（OR）值与实验数据进行比较，确定了它们的结构和绝对构型。有趣的是，新化合物1在H-11处显示出异常的负化学位移。众所周知，¹ H NMR光谱的负化学位移值在天然产物中极为罕见。如此负的化学位移¹ H NMR光谱是通过密度泛函理论（DFT）计算得出的，并通过吡喃-2-酮环对3D构象中氢原子的屏蔽作用进行了解释。然后，MTT测定法评估分离的化合物（的细胞毒性1 - 5）针对两种肝癌细胞系（HepG2和MHCC97H）。结果表明，化合物1对HepG2细胞显示出最高的细胞毒性，IC ₅₀值为9.8μM。此外，没有化合物的无明显细胞毒性1 - 5对正常肝细胞系LO2。此外，化合物1诱导细胞凋亡的机制研究了经处理的HepG2细胞。结果表明，化合物1可通过p53介导的Ras / Raf / ERK抑制作用诱导HepG2细胞凋亡。