Chavicol formation in sweet basil (Ocimum basilicum): cleavage of an esterified C9 hydroxyl group with NAD(P)H-dependent reduction
作者:Daniel G. Vassão、David R. Gang、Takao Koeduka、Brenda Jackson、Eran Pichersky、Laurence B. Davin、Norman G. Lewis
DOI:10.1039/b605407b
日期:——
Propenyl- and allyl-phenols, such as methylchavicol, p-anol and eugenol, have gained importance as flavoring agents and also as putative precursors in the biosynthesis of 9,9′-deoxygenated lignans, many of which have potential medicinal applications. In spite of several decades of investigation, however, the complete biosynthetic pathway to a propenyl/allylphenol had not yet been reported. We have subjected a Thai basil variety accumulating relatively large amounts of the simplest volatile allylphenol, methylchavicol, to in vivo administration of radiolabeled precursors and assays of protein preparations in vitro. Through these experiments, the biosynthesis of chavicol was shown to occur via the phenylpropanoid pathway to p-coumaryl alcohol. Various possibilities leading to deoxygenation of the latter were examined, including reduction of the side-chain double bond to form p-dihydrocoumaryl alcohol, followed by dehydration to afford chavicol, as well as formation of p-methoxycinnamyl alcohol, with further side-chain modification to afford methylchavicol. A third possibility studied was activation of the side-chain alcohol of p-coumaryl alcohol, e.g.via esterification, to form a more facile leaving group via reductive elimination. The latter was shown to be the case using p-coumaryl esters as potential substrates for a NAD(P)H-dependent reductase to afford chavicol, which is then O-methylated to afford methylchavicol.
丙烯基和烯丙基苯酚(如甲基茶维醇、对乙醇和丁香酚)作为调味剂和 9,9′-脱氧木酚素生物合成的假定前体(其中许多具有潜在的药用价值),其重要性日益凸显。然而,尽管经过了几十年的研究,丙烯基/烯丙基酚的完整生物合成途径仍未见报道。我们对一种积累了相对大量最简单挥发性烯丙基酚(甲基芹维醇)的泰国罗勒品种进行了体内放射性标记前体给药和体外蛋白质制备试验。通过这些实验,证明了俏皮醇的生物合成是通过苯丙醇途径转化为对迷迭香醇的。研究了导致后者脱氧的各种可能性,包括还原侧链双键形成对二氢香豆醇,然后脱水生成茶维醇,以及形成对甲氧基肉桂醇,进一步修饰侧链生成甲基茶维醇。研究的第三种可能性是通过酯化等方式活化对羟基肉桂醇的侧链醇,从而通过还原消除形成更容易离开的基团。研究表明,将对香豆素酯作为 NAD(P)H 依赖性还原酶的潜在底物,可以生成茶维醇,然后将茶维醇 O-甲基化,生成甲基茶维醇。