Chan Pui-Kwong
Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA.
Biochem Pharmacol. 2007 Feb 1;73(3):341-50. doi: 10.1016/j.bcp.2006.10.007. Epub 2006 Nov 7.
Saponins are natural surfactants, found in many plants. Certain saponins are bioactive compounds with anticancer, antivirus and hemolytic activities. The mechanism is unknown. A saponin with antitumor activity was identified in Xanthoceras sorbifolia Bunge (Sapindaceae) and purified. This saponin is a triterpenoid saponin with a trisaccharide chain attached at C3 of the aglycone and two angeloyl groups acylated at C21 and C22. It inhibits the growth of tumor cells with IC50=2 microg/ml in OVCAR3 cells. To study the structure-activity relationship, the diangeloyl group or the carbohydrates of Xanifolia-Y were removed and tested for activity. It was found that removal of both angeloyl groups in C21 and C22 positions completely abolished its activity (IC50>120 microg/ml). However, when carbohydrates were remove, its activity was reduced but was not abolished (IC50=10 microg/ml). These results suggest that a presence of diangeloyl group in the triterpene structure play an essential role for activity. By comparison, compounds with a similar structure as Xanifolia-Y but have only one angeloyl group at C22: Xanifolia-X (IC50=6 microg/ml) or at C21: beta-escin (IC50=10 microg/ml), have less activity. Results suggest that diangeloyl group in both C21 and C22 positions are important contributing activity. Similar results were observed in hemolytic activity. It is concluded that acylation with angeloyl group at C21 and C22 positions of triterpenoid saponin is essential for its activity.
皂苷是天然表面活性剂，存在于许多植物中。某些皂苷是具有抗癌、抗病毒和溶血活性的生物活性化合物。其作用机制尚不清楚。从文冠果（无患子科）中鉴定并纯化出一种具有抗肿瘤活性的皂苷。这种皂苷是一种三萜皂苷，在苷元的C3位连接有一个三糖链，在C21和C22位有两个当归酰基酰化。它在OVCAR3细胞中抑制肿瘤细胞生长，IC50 = 2微克/毫升。为了研究构效关系，去除了文冠果皂苷-Y的双当归酰基或碳水化合物并测试其活性。发现去除C21和C22位的两个当归酰基后其活性完全丧失（IC50>120微克/毫升）。然而，当去除碳水化合物时，其活性降低但并未丧失（IC50 = 10微克/毫升）。这些结果表明，三萜结构中双当归酰基的存在对活性起着至关重要的作用。相比之下，与文冠果皂苷-Y结构相似但仅在C22位有一个当归酰基的化合物：文冠果皂苷-X（IC50 = 6微克/毫升）或在C21位的化合物：β-七叶皂苷（IC50 = 10微克/毫升），活性较低。结果表明，C21和C22位的双当归酰基对活性有重要贡献。在溶血活性方面也观察到了类似的结果。得出的结论是，三萜皂苷在C21和C22位用当归酰基进行酰化对其活性至关重要。
