Regio- and Stereoselective Oxidative Phenol Coupling in Aspergillus niger
Regio- and Stereoselective Oxidative Phenol Coupling in Aspergillus niger
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DOI：
10.1002/anie.201203603
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Mueller, Michael
中科院分区：
文献类型：
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作者：
Girol, Christian Gil;Fisch, Katja M.;Mueller, Michael
自1925年Pummerer及其同事首次提到氧化苯酚偶联反应以来，[1]控制生物体中分子间苯酚偶联的区域和立体选择性的机制仍然不清楚。细胞色素P450酶参与苄基异喹啉生物碱salutaridine和berbamunine的生物合成的第一个证据。[2]Davin等人表明，连翘属物种中（E）-松柏醇二聚成（+）-松柏醇的过程受一种发散蛋白的控制，尽管弗罗伊登贝格曾假设木质素与聚合木质素偶然偶联。[3，4]该反应是由漆酶或任何其他自由基形成氧化剂催化的，而dirigent蛋白质决定了偶联的选择性。在转化与对映体互补的dirigent蛋白从拟南芥，漆酶催化氧化偶联得到（α）-pinobenzinol。[5]然而，分歧蛋白的同源物仅限于种子植物。因此，在其他生物体中哪些蛋白质介导区域和立体选择性分子间苯酚偶联的问题仍然没有解决。[6]子囊菌曲霉属和裸孢菌属通过单体香豆素铁黄素（1）或其去甲基衍生物2和3的二聚化产生多种双香豆素。[7]到目前为止，已经从不同的子囊菌中分离出12种bicoumarins，4-15，代表6种可能的区域异构体二聚体中的5种（方案1）。在此，我们报道了在A.尼日尔FGSC A1180。通过同源建模和底物对接，区域和立体选择性苯酚偶联反应的基本原理。以前，我们证明了在A。单体香豆素2区域和立体选择性地仅偶联到8，8 ′-双香豆素P-（+）-6上，随后O-甲基化形成P-（+）-kotanin [P-（+）-4]（结构见方案2）。[15]我们用α-d-[13 C6]葡萄糖进行的喂养实验证明了4及其前体的聚酮来源（参见支持信息）。真菌聚酮化合物通常由迭代作用的I型聚酮化合物酶（PKS）产生，所述I型聚酮化合物酶可根据其结构域组织和同源性进一步细分为高度还原性、部分还原性和非还原性PKS。[16]4的两个测序生产者A.尼日尔ATCC 1015和CBS 513.88具有约35个PKS基因（参见支持方案1）。由铁黄素（1）或其衍生物2和3偶联形成的双香豆素。Kotanin（4），7-demethylkotanin（5），[8] orceptide（6），[9] desertorin A-C（7-9），[10] isokotanin A-C（10-12），[11] 7-O-去甲基-3，8 '-bisiderin（13），[12] aflavarin（14）[13]和bicoumanigrin（15）。[14个]
Since the first mention of the oxidative phenol coupling reaction by Pummerer and colleagues in 1925,[1] the mechanism which governs the regio-and stereoselectivity of the intermolecular phenol coupling in organisms has remained unclear. The first evidence for the involvement of cytochrome P450 enzymes was found for the biosynthesis of the benzylisoquinoline alkaloids salutaridine and berbamunine.[2] Davin et al. showed that the dimerization of (E)-coniferyl alcohol into (+)-pinoresinol in Forsythia sp. is controlled by a dirigent protein, although Freudenberg had postulated a fortuitous coupling of lignols to polymeric lignin.[3, 4] The reaction is catalyzed by laccase or any other radical-forming oxidant, whereas the dirigent protein determines the selectivity of the coupling. In transformations with an enantiocomplementary dirigent protein from Arabidopsis thaliana, the laccasecatalyzed oxidative coupling gave (À)-pinoresinol.[5] However, homologues of the dirigent proteins are limited to spermatophytes. Thus, the question of which proteins mediate the regio-and stereoselective intermolecular phenol coupling in other organisms remains unsolved.[6] The ascomycetes Aspergillus and Emericella produce a variety of bicoumarins putatively by dimerization of the monomeric coumarin siderin (1) or its demethyl derivatives 2 and 3.[7] Twelve bicoumarins, 4–15, representing five of the six possible regioisomeric dimers, have been isolated from diverse ascomycetes species so far (Scheme 1). Herein, we report the identification and analysis of the biosynthetic cluster responsible for kotanin (4) production in A. niger FGSC A1180. Through homology modeling and substrate docking, a rationale for the regio-and stereoselective phenol coupling reaction was derived. Previously, we demonstrated that in A. niger the monomeric coumarin 2 is coupled regio-and stereoselectively exclusively to the 8, 8’-bicoumarin P-(+)-6, and subsequent O-methylation forms P-(+)-kotanin [P-(+)-4](see Scheme 2 for structures).[15] Our feeding experiments with α-d-[13C6] glucose proved the polyketidic origin of 4 and its precursors (see the Supporting Information). Fungal polyketides are usually produced by iteratively acting typeI polyketide synthases (PKSs) which can be further subdivided by their domain organization and phylogeny into highly reducing, partially reducing, and nonreducing PKSs.[16] The two sequenced producers of 4, A. niger ATCC 1015 and CBS 513.88, harbor about 35 PKS genes (see the SupportingScheme 1. Bicoumarins formed by the coupling of siderin (1) or its derivatives 2 and 3. Kotanin (4), 7-demethylkotanin (5),[8] orlandin (6),[9] desertorin A–C (7-9),[10] isokotanin A–C (10–12),[11] 7-O-demethyl-3, 8’-bisiderin (13),[12] aflavarin (14)[13] and bicoumanigrin (15).[14]