Geosmin biosynthesis. Mechanism of the fragmentation-rearrangement in the conversion of germacradienol to geosmin
Geosmin biosynthesis. Mechanism of the fragmentation-rearrangement in the conversion of germacradienol to geosmin
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DOI：
10.1021/ja077792i
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发表时间：
2008-01-16
影响因子：
15
通讯作者：
Cane, David E.
中科院分区：
文献类型：
--
作者：
Jiang, Jiaoyang;Cane, David E.
土臭素（1）是湿帆特有气味的来源。将法呢基二磷酸（2，FPP）与重组天蓝色链霉菌germacradienol/geosmin一起孵育，合成geosmin（1）、germacradienol（3）、germacrene D（4）、octtin 5和丙酮，丙酮通过与半胱胺反应被捕获为2，2-二甲基噻唑烷（9）。通过与[13.13，13-H-2（3）]FPP（2a）孵育，证明丙酮是通过大根香叶烯醇的2-羟丙基部分片段化得到的。得到相应的D（3）-丙酮衍生物9a。GC-MS分析由germacradienol/土臭素合酶与[2-H-2]FPP（2 B）孵育产生的[6-H-2]土臭素（1 B）的标记模式显示，FPP上的H-2质子导致预测的土臭素的1.2-氢化物移位至环B。这两组实验结果与所提出的土臭素形成机制一致，该机制涉及大根香叶烯醇的质子化环化，通过逆Prins断裂以丙酮形式损失2-羟丙基部分，得到奥他林中间体5，然后进行5，1，2-氢化物移位的质子化。和水的捕获。
Geosmin (1) is responsible for the characteristic odor of moist sail. Incubation of famesyl diphosphate (2, FPP) with recombinant Streptomyces coelicolor germacradienol/geosmin synthese generetes geosmin (1), germacradienol (3), germacrene D (4), octatin 5, and acetone, which was trapped as 2,2-dimethylthiamzolidine (9) by reaction with cysteamine. The acetone was shown to be derived by fragmentation of the 2-hydroxypropyl moiety of germacradienol by incubation with [13.13,13-H-2(3)]FPP (2a). giving rising to the corresponding derivative of d(3)-acetone, 9a. GC-MS analysis of the labeling pattern of [6-H-2]geosmin (1b) resulting from the incubation of germacradienol/geosmin synthase with [2-H-2]FPP (2b) revealed that the H-2 proton on FPP underyoes the predicted 1.2-hydride shift to ring B of geosmin. Both sets of experimental results are consistent with a proposed mechanism of geosmin fomation involving protonation-cyclization of germacradienol with loss of the 2-hydroxypropyl moiety as acetone by a retro-Prins fragmentation to give octalin intermediate 5, followed by protonation of 5, 1,2-hydride shift. and capture of water.