Highly Oxygenated Triterpenoids and Rare Tetraterpenoids from <i>Abies chensiensis</i> and Their Antibacterial Activity

Nine new cycloartane triterpenoids (1, 2, 4, 7, 8, 12, 15, 17, and 18) and two new rare tetraterpenoids (24 and 25) formed via a [4 + 2] Diels–Alder cycloaddition between a lanostane triterpenoid and a monoterpenoid, along with 14 previously known triterpenoids, were isolated from the bark of the branches of Abies chensiensis. The structures and absolute configurations of new compounds were elucidated based on spectroscopic data, X-ray diffraction analysis, and electronic circular dichroism. Some of the isolates were evaluated for their antibacterial activity by determining their minimum inhibitory concentrations and growth inhibition curves and examining for morphological alterations. Among the compounds tested, the new cycloartane triterpenoid 8 was the most active against Bacillus subtilis. Thus, morphological alterations of B. subtilis on treatment with 8 were observed by scanning electron microscopy, showing that the cells were irregular, wrinkled, and disrupted.本研究从秦岭冷杉（Abies chensiensis）的枝条树皮中，分离得到9种新的环阿尔廷烷三萜类化合物（cycloartane triterpenoids，编号1、2、4、7、8、12、15、17、18）、2种经由羊毛甾烷三萜类化合物（lanostane triterpenoid）与单萜类化合物（monoterpenoid）经[4+2]狄尔斯–阿尔德环加成反应生成的罕见新型四萜类化合物（tetraterpenoids，编号24、25），以及14种已报道的三萜类化合物。新化合物的结构与绝对构型通过光谱数据、X射线衍射分析以及电子圆二色谱（electronic circular dichroism）得以解析。部分分离得到的化合物被开展抗菌活性评价，通过测定其最低抑菌浓度、绘制生长抑制曲线，并观察其诱导的菌体形态改变。在受试化合物中，新型环阿尔廷烷三萜类化合物8对枯草芽孢杆菌（Bacillus subtilis）表现出最强的抑菌活性。进一步采用扫描电子显微镜（scanning electron microscopy）观察经化合物8处理后的枯草芽孢杆菌，可见菌体呈现不规则形态、表面皱缩且发生破裂。