DIMETHYLALLYLTRYPTOPHAN SYNTHASE - AN ENZYME-CATALYZED ELECTROPHILIC AROMATIC-SUBSTITUTION
DIMETHYLALLYLTRYPTOPHAN SYNTHASE - AN ENZYME-CATALYZED ELECTROPHILIC AROMATIC-SUBSTITUTION
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DOI：
10.1021/ja00045a004
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发表时间：
1992-09-09
影响因子：
15
通讯作者：
POULTER, CD
中科院分区：
文献类型：
--
作者：
GEBLER, JC;WOODSIDE, AB;POULTER, CD
在麦角生物碱生物合成的第一个途径特异性步骤中，二甲基烯丙基色氨酸 (DMAT) 合酶催化二甲基烯丙基二磷酸 (DMAPP) 在 C(4) 处对 L-色氨酸进行烷基化。用两种底物的类似物研究了反应机理。合成了 N-乙酰色氨酸的五种 7-取代衍生物（2，Z = OCH3、CH3、F、CF3 和 NO2）。游离氨基酸的L对映体是通过使用来自曲霉属的氨酰化酶选择性水解外消旋体而获得的。此外，还制备了 DMAPP 的 E 和 Z 氟甲基和二氟甲基类似物（1，Y = CH3、CH2F、CHF2）。测量二甲基烯丙基衍生物与L-色氨酸的酶催化反应速率以及L-色氨酸衍生物与DMAPP的酶催化反应速率。此外，还测定了 DMAPP 类似物的甲磺酸酯衍生物在丙酮水溶液中的溶剂分解的相对反应性。色氨酸类似物的哈米特图给出了与 rho = -2.0 良好的线性相关性。此外，溶剂分解和酶催化烷基化的相对速率的哈米特图给出了正线性相关。这些结果表明，DMAT合酶催化的异戊二烯基转移反应是亲电芳香取代，并且在机制上与法呢基二磷酸合酶催化的亲电烷基化相似。
Dimethylallyltryptophan (DMAT) synthase catalyzes the alkylation of L-tryptophan at C(4) by dimethylallyl diphosphate (DMAPP) in the first pathway-specific step in the biosynthesis of ergot alkaloids. The mechanism of the reaction was studied with analogs of both substrates. Five 7-substituted derivatives of N-acetyltryptophan (2, Z = OCH3, CH3, F, CF3, and NO2) were synthesized. The L enantiomers of the free amino acids were obtained by selective hydrolysis of the racemate using aminoacylase from Aspergillus. In addition, the E and Z fluoromethyl and difluoromethyl analogs of DMAPP (1, Y = CH3, CH2F, CHF2) were prepared. Rates of the enzyme-catalyzed reactions were measured for the dimethylallyl derivatives with L-tryptophan and for the L-tryptophan derivatives with DMAPP. In addition, the relative reactivities of the methanesulfonate derivatives of the DMAPP analogs were determined for solvolysis in aqueous acetone. A Hammett plot for the tryptophan analogs gave a good linear correlation with rho = -2.0. In addition, a Hammett plot of the logarithms of the relative rates of solvolysis and enzyme-catalyzed alkylation gave a positive linear correlation. These results indicate that the prenyl-transfer reaction catalyzed by DMAT synthase is an electrophilic aromatic substitution and is mechanistically similar to the electrophilic alkylation catalyzed by farnesyl diphosphate synthase.