Biosynthesis of the unusual sesquiterpenes, (+)-kelsoene and (−)-prespatane, that accumulate in the cultured cells of the liverwort Ptychanthus striatus was investigated. A mixture of (+)- and (−)-alloaromadendrene was isolated from a variety of unidentified sesquiterpenes from cultured cells. However, the (−)-isomer, which is thought to be an immediate precursor to kelsoene, was present only as a minor component [a ratio of (−)-isomer to (+)-isomer of 1∶25]. When the cells were incubated with a higher dosage (1.0 mmol) of mevalonate (MVA, 3,5-dihydroxy-3-methylvalerate) under heterotrophic conditions or with a normal dosage (0.5 mmol) under photoautotrophic conditions, the 2H- and 13C-labels from 2H- and 13C-MVA were incorporated into the sesquiterpenes at an extremely high level (30 to 40 and 46 atom% excess, respectively). Labelling patterns of the biosynthetically 2H- or 13C-labelled kelsoene and prespatane were determined by GLC-MS and 2H- and 13C-NMR analyses. The labelling pattern of the kelsoene demonstrates the randomization of the 2H- and 13C-labels between the isopropenylmethyl and the methylene groups, with loss of one H-1 proton of farnesyl diphosphate (FPP, farnesyl = 3,7,11-trimethyldodeca-2,6,10-trienyl), suggesting that kelsoene is biosynthesized from a germacradienyl cation with 7R configuration by means of a (−)-alloaromadendranyl cation. Randomization of the labels between the isopropenylmethyl and the methylene and loss of one H-1 proton of FPP were also observed in 2H- and 13C-labelled prespatane. Thus, prespatane is postulated to be biosynthesized from a (7S)-germacradienyl cation by means of a guaianyl cation. During the third cyclization of the guaianyl cation, one proton at the C-1 position of FPP was lost.
研究了肝草(Ptychanthus striatus)培养细胞中积累的不常见
倍半萜烯--(+)-kelsoene 和 (-)-respatane--的
生物合成。从培养细胞中的多种不明
倍半萜中分离出了(+)-和(-)-alloaromadendrene的混合物。然而,被认为是棣棠烯直接前体的(-)-异构体仅作为次要成分存在[(-)-异构体与(+)-异构体之比为 1∶25]。在异养条件下用较高剂量(1.0 毫摩尔)的甲羟
戊酸(MVA,
3,5-二羟基-3-甲基戊酸)或在光自养条件下用正常剂量(0.5 毫摩尔)培养细胞时,来自 2H- 和 13C-MVA 的 2H- 和 13C- 标记以极高的
水平(分别为 30 至 40 和 46 原子过量)结合到
倍半萜中。通过 GLC-MS 以及 2H 和 13C-NMR 分析,确定了
生物合成的 2H 或 13C 标记的葵烯和前帕坦的标记模式。异亚甲基异
丙烯基和亚甲基之间的 2H 和 13C 标记模式表明,随着二
磷酸法呢基一个 H-1 质子(FPP、法呢基 = 3,7,11-三甲基十二-2,6,10-
三烯基),这表明葵烯是由具有 7R 构型的胚芽鞘烯阳离子通过 (-)- 阿洛芳基
腺苷阳离子
生物合成的。在 2H 和 13C 标记的前帕坦中,还观察到异
丙烯甲基和亚甲基之间标记的随机化以及 FPP 一个 H-1 质子的损失。因此,推测前帕他烷是由 (7S)-germacradienyl 阳离子通过 guaianyl 阳离子
生物合成的。在
愈创木酰基阳离子的第三次环化过程中,FPP 的 C-1 位失去了一个质子。