Antileishmanial Acetylene Fatty Acid and Acetogenins from Seeds of Porcelia macrocarpa

In the present work five acetylene derivatives (1-5), including three unknowns (1, 3 and 4), were isolated from seeds of Porcelia macrocarpa (Annonaceae). The structures of isolated compounds were determined as docos-13-yn-21-enoic acid (1), 3-hydroxy-4-methylene-2-(eicos-11’-yn-19’-enyl)but-2-enolide (2), 3-hydroxy-4-methylene-2-(octadec-9’-yn-17’-enyl)but-2-enolide (3), 3-hydroxy-4-methylene-2-(hexadec-7’-yn-15’-enyl)but-2-enolide (4), and (2S,3R,4R)-3-hydroxy-4-methyl-2-(eicos-11’-yn-19’-enyl)butanolide (5) by analysis of nuclear magnetic resonance (NMR) and electrospray ionization high-resolution mass spectrometry (ESI-HRMS) data. Moreover, all isolated compounds demonstrated selectivity towards intracellular amastigotes of Leishmania (L.) infantum, especially 2-4 with 50% inhibitory concentration (IC50) values of 9.2, 10.4 and 11.0 µM, respectively, indicating superior activity of that determined to positive control miltefosine (IC50 of 17.8 µM). Furthermore, these compounds showed higher selectivity index (SI) in comparison with miltefosine. Since related acetylene fatty acid 1 displayed reduced antiparasitic potential (IC50 of 48.5 µM), the obtained results suggested that the γ-lactone plays an important role in the antileishmanial activity. However, 2-4 exhibited cytotoxicity to mammalian NCTC cells (CC50 ca. 80 µM), which could be a result of the presence of a conjugated carbonyl system in the lactone ring, since 5, the only acetogenin that presents the saturated ring, lacked mammalian cytotoxicity (CC50 > 200 µM).本研究从番荔枝科（Annonaceae）大果瓷木（Porcelia macrocarpa）的种子中分离得到5种乙炔衍生物（1~5），其中包含3种未见报道的新化合物（1、3和4）。通过核磁共振波谱（nuclear magnetic resonance, NMR）与电喷雾电离高分辨质谱（electrospray ionization high-resolution mass spectrometry, ESI-HRMS）数据分析，确定了各分离化合物的结构：分别为二十二碳-13-炔-21-烯酸（1）、3-羟基-4-亚甲基-2-(二十碳-11’-炔-19’-烯基)丁-2-烯内酯（2）、3-羟基-4-亚甲基-2-(十八碳-9’-炔-17’-烯基)丁-2-烯内酯（3）、3-羟基-4-亚甲基-2-(十六碳-7’-炔-15’-烯基)丁-2-烯内酯（4）以及(2S,3R,4R)-3-羟基-4-甲基-2-(二十碳-11’-炔-19’-烯基)丁内酯（5）。此外，所有分离得到的化合物均对婴儿利什曼原虫（Leishmania (L.) infantum）的细胞内无鞭毛体表现出选择性抑制活性，其中化合物2~4的半数抑制浓度（50% inhibitory concentration, IC50）分别为9.2、10.4和11.0 µM，其活性优于阳性对照米替福新（miltefosine，IC50=17.8 µM）。进一步研究显示，相较于米替福新，这些化合物拥有更高的选择性指数（selectivity index, SI）。由于相关乙炔脂肪酸1仅表现出较弱的抗寄生虫活性（IC50=48.5 µM），本研究结果表明γ-内酯在抗利什曼原虫活性中发挥关键作用。不过，化合物2~4对哺乳动物NCTC细胞系表现出细胞毒性（半数细胞毒性浓度CC50约为80 µM），这一现象可能源于其内酯环中存在共轭羰基体系；而唯一带有饱和内酯环的聚乙炔内酯（acetogenin）5则未表现出哺乳动物细胞毒性（CC50 > 200 µM）。