Colocynthenins A-D, Ring-A seco-Cucurbitane Triterpenoids from the Fruits of Citrullus colocynthis

Four ring-A seco-cucurbitane triterpenoids, colocynthenins A-D (1-4), together with seven known cucurbitane triterpenoids (5-11), were isolated from the fruits of Citrullus colocynthis. Their structures and absolute configurations were elucidated based on spectroscopic analysis and quantum chemical ECD calculations. Compound 1 possesses an unprecedented 2,11-lactone moiety, while compound 2 is the first reported cucurbitane triterpenoid with an unusual cyano group. Compounds 1 and 3 showed acetylcholinesterase inhibitory activities in a standard in vitro assay, with IC50 values of 2.6 and 3.1 mu M, respectively.

从药西瓜（Citrullus colocynthis）果实中分离出四种四环二葫芦烷型三萜类化合物，药西瓜素A - D（1 - 4），以及七种已知的葫芦烷型三萜类化合物（5 - 11）。通过光谱分析和量子化学电子圆二色谱（ECD）计算阐明了它们的结构和绝对构型。化合物1具有一种前所未有的2,11 - 内酯结构单元，而化合物2是首个报道的具有不寻常氰基的葫芦烷型三萜类化合物。在标准的体外实验中，化合物1和3显示出乙酰胆碱酯酶抑制活性，其半数抑制浓度（IC₅₀）值分别为2.6和3.1 μM。