Antiproliferative Constituents of the Roots of Ethiopian <i>Podocarpus falcatus</i> and Structure Revision of 2α-Hydroxynagilactone F and Nagilactone I

Bioassay-guided fractionation using the human colorectal adenocarcinoma (HT-29) cell line of the methanol extract of dried roots of Podocarpus falcatus led to the isolation of two new type C nagilactones, 16-hydroxynagilactone F (1) and 2β,16-dihydroxynagilactone F (2), and the new totarane-type bisditerpenoid 7β-hydroxymacrophyllic acid (4), along with the seven known compounds 2β-hydroxynagilactone F (3), macrophyllic acid (5), nagilactone D (6), 15-hydroxynagilactone D (7), nagilactone I (8), inumakiol D (9), and ponasterone A (10). The structures of the new compounds were determined by 1D and 2D NMR, HRESIMS, UV, and IR and by comparison with the reported spectroscopic data of their congeners. The orientation of the C-2 hydroxy group of 3 and 8 was revised to be β based on evidence from detailed analysis of 1D and 2D NMR data and single-crystal X-ray diffraction studies. Among the isolated compounds, the nagilactones, including the new dilactones 16-hydroxynagilactone F (1) and 2β,16-dihydroxynagilactone F (2), were the most active (IC50 0.3–5.1 μM range) against the HT-29 cell line, whereas the bisditerpenoids (4 and 5) and the other known compounds 9 and 10 were inactive. The presence of the bioactive nagilactones in P. falcatus supports its traditional use.采用人结直肠腺癌细胞（HT-29）株作为生物活性导向分离模型，对镰状罗汉松（Podocarpus falcatus）干燥根的甲醇提取物进行生物活性导向分级分离，经分离得到两个新型C型竹柏内酯：16-羟基竹柏内酯F（1）与2β,16-二羟基竹柏内酯F（2），以及一个新型罗汉松烷（totarane）型双二萜类化合物7β-羟基大叶松酸（4），同时获得7个已知化合物：2β-羟基竹柏内酯F（3）、大叶松酸（5）、竹柏内酯D（6）、15-羟基竹柏内酯D（7）、竹柏内酯I（8）、罗汉松醇D（9）与杯苋甾酮A（10）。新化合物的结构通过一维（1D）、二维（2D）核磁共振波谱（NMR）、高分辨电喷雾电离质谱（HRESIMS）、紫外光谱（UV）及红外光谱（IR）进行解析，并与同类化合物已发表的波谱数据比对后确定。基于对1D和2D NMR数据的详细分析以及单晶X射线衍射实验结果，化合物3与8的C-2位羟基的构型被修正为β构型。在所分离得到的全部化合物中，竹柏内酯类成分（包括新型双内酯16-羟基竹柏内酯F（1）与2β,16-二羟基竹柏内酯F（2））对HT-29细胞株表现出最强的细胞毒活性，其半数抑制浓度（IC50）范围为0.3~5.1 μM；而双二萜类化合物（4、5）以及其余已知化合物9和10则无细胞毒活性。镰状罗汉松（P. falcatus）中含有具有生物活性的竹柏内酯类成分，这为其传统药用应用提供了科学依据。