Walton Nicholas J, Mayer Melinda J, Narbad Arjan
Food Safety Science Division, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Phytochemistry. 2003 Jul;63(5):505-15. doi: 10.1016/s0031-9422(03)00149-3.
Vanillin (4-hydroxy-3-methoxybenzaldehyde) is an important flavour and aroma molecule, but is also of interest because of its biogenetic relationship to the phenylpropanoid pathway and to other molecules of physiological significance, notably salicylate. Recent progress towards characterisation of the biosynthesis of vanillin is reviewed. In Vanilla, there is some evidence that the route to vanillin-beta-D-glucoside may proceed from 4-coumaric acid via 4-hydroxybenzaldehyde, with glucoside formation occurring not necessarily as the final step, and possibly with the involvement of 4-hydroxybenzyl alcohol beta-D-glucoside tartrate bis-esters as "shunt" metabolites. This appears to be given tentative support by the recent partial characterisation of a 4-hydroxybenzaldehyde synthase from Vanilla. On the other hand, a well-characterised, CoA-dependent, non-oxidative chain-shortening mechanism to produce vanillin from ferulic acid, occurring as part of a pathway of hydroxycinnamate degradation in Pseudomonas, may not be representative of hydroxycinnamate chain-shortening mechanism(s) occurring in Vanilla and other plants. Nevertheless, by expression of the Pseudomonas enzyme 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL), attempts have been made to introduce a direct capacity for vanillin formation into model plants by diversion of the phenylpropanoid pathway. The results obtained have emphasised the obstacles to achieving the desired oxidation level (aldehyde) and ring substitution (4-hydroxy-3-methoxyphenyl), even when a substantial metabolic diversion is successfully achieved. Finally, the significance of the latest biosynthetic and biotechnological developments is reviewed briefly in relation to authentication of vanillin.
香草醛（4-羟基-3-甲氧基苯甲醛）是一种重要的风味和香气分子，同时因其与苯丙烷类途径以及其他具有生理意义的分子（尤其是水杨酸酯）的生源关系而备受关注。本文综述了香草醛生物合成表征方面的最新进展。在香草属植物中，有证据表明香草醛-β-D-葡萄糖苷的合成途径可能从4-香豆酸经4-羟基苯甲醛开始，葡萄糖苷的形成不一定是最后一步，并且可能涉及4-羟基苄醇β-D-葡萄糖苷酒石酸双酯作为“分流”代谢产物。香草属植物中一种4-羟基苯甲醛合酶的近期部分表征似乎为此提供了初步支持。另一方面，在假单胞菌中，由阿魏酸产生香草醛的一种特征明确的、依赖辅酶A的非氧化链缩短机制，作为羟基肉桂酸降解途径的一部分，可能并不代表香草属植物和其他植物中发生的羟基肉桂酸链缩短机制。尽管如此，通过表达假单胞菌的酶4-羟基肉桂酰辅酶A水合酶/裂解酶（HCHL），人们试图通过改变苯丙烷类途径将香草醛形成的直接能力引入模式植物中。所获得的结果强调了即使成功实现了大量的代谢改变，达到所需的氧化水平（醛基）和环取代（4-羟基-3-甲氧基苯基）仍存在障碍。最后，简要综述了最新生物合成和生物技术进展对于香草醛鉴定的意义。
