Biosynthesis of Defensive Allomones in Leaf Beetle Larvae: Stereochemistry of Salicylalcohol Oxidation in Phratora vitellinae and Comparison of Enzyme Substrate and Stereospecificity with Alcohol Oxidases from Several Iridoid Producing Leaf Beetles
作者:Martin Veith、Neil J. Oldham、Konrad Dettner、Jacques M. Pasteels、Wilhelm Boland
DOI:10.1023/b:joec.0000006369.26490.c6
日期:1997.2
(7S)-[H-2(5)]-Salicylalcohol (3) and (7R)-[H-2(1)]-salicylalcohol (5) have been synthesized in order to examine the stereospecificity of salicylalcohol oxidase from the defensive secretion of the salicylaldehyde-producing leaf beetle Phratora vitellinae. Oxidation was found to proceed by selective removal of the C(7)-H-R hydrogen atom (Re-specificity) to yield salicylaldehyde. (7S)-[H-2(6)]-Benzylalcohol (9) was also oxidized Re-specifically to benzaldehyde, but in much lower yield, indicating the importance of the orthohydroxy group of salicylalcohol in substrate enzyme binding. The stereospecificities of terpenoid oxidases from six species of iridoid-producing leaf beetle were examined using (1R,8R)-[H-2(2)]-8-hydroxygeraniol (10), and were all found to oxidize the substrate Re-specifically. Cross-activity of oxidation was found in a number of species, with P. vitellinae able to oxidize terpenoid (10) and two of the iridoid-producing species able to oxidize salicylalcohol analogue (3), again with Re-specificity. However, when the two substrate analogs were presented together, in equal concentrations, preferential oxidation of the natural analog was observed in each case. The kinetics of oxidation for a number of terpenoid and aromatic alcohols by the defensive secretion of the iridoid-producing leaf beetle Phaedon armoraciae have been studied, revealing a large difference between the rate of(primary, allylic) terpenoid alcohol oxidation and the rate of salicylalcohol oxidation, thus accounting for the observed selectivity.
为了研究来自分泌水杨醛的叶甲Phratora vitellinae防御分泌物的水杨醛醇氧化酶的立体特异性,合成了(7S)-[H-2(5)]-水杨醛醇(3)和(7R)-[H-2(1)]-水杨醛醇(5)。发现氧化反应通过选择性地去除C(7)-H-R氢原子(Re特异性)来生成水杨醛。另外,(7S)-[H-2(6)]-苯甲醇(9)也被Re特异性地氧化为苯甲醛,但产率较低,这表明水杨醛醇中的邻羟基在底物与酶的结合中非常重要。
使用(1R,8R)-[H-2(2)]-8-羟基香叶醇(10),研究了来自六种产生吲哚苷的叶甲的萜类氧化酶的立体特异性,发现所有酶都对底物进行Re特异性的氧化。在多个物种中发现了氧化反应的交叉活性,Phratora vitellinae能够氧化萜类(10),而两种产生吲哚苷的物种能够氧化水杨醛醇类似物(3),同样具有Re特异性。然而,当两种底物类似物以相等浓度同时存在时,每种情况下都观察到对天然底物类似物的选择性氧化。
还研究了由产生吲哚苷的叶甲Phaedon armoraciae防御分泌物对多种萜类和芳族醇的氧化动力学,揭示了(主要,烯丙位)萜类醇氧化速率与水杨醛醇氧化速率之间存在显著差异,从而解释了观察到的选择性。