作者:Vida Esparan、Ulrich Krings、Marlene Struch、Ralf Berger
DOI:10.3390/molecules20046640
日期:——
The symmetrical structure of curcumin includes two 4-hydroxy-3-methoxyphenyl substructures. Laccase catalyzed formation of a phenol radical, radical migration and oxygen insertion at the benzylic positions can result in the formation of vanillin. As vanillin itself is a preferred phenolic substrate of laccases, the formation of vanillin oligomers and polymers is inevitable, once vanillin becomes liberated. To decelerate the oligomerization, one of the phenolic hydroxyl groups was protected via acetylation. Monoacetyl curcumin with an approximate molar yield of 49% was the major acetylation product, when a lipase from Candida antarctica (CAL) was used. In the second step, monoacetyl curcumin was incubated with purified laccases of various basidiomycete fungi in a biphasic system (diethyl ether/aqueous buffer). A laccase from Funalia trogii (LccFtr) resulted in a high conversion (46% molar yield of curcumin monoacetate) to vanillin acetate. The non-protected vanillin moiety reacted to a mixture of higher molecular products. In the third step, the protecting group was removed from vanillin acetate using a feruloyl esterase from Pleurotus eryngii (PeFaeA) (68% molar yield). Alignment of the amino acid sequences indicated that high potential laccases performed better in this mediator and cofactor-free reaction.
姜黄素的对称结构包括两个 4-羟基-3-甲氧基苯基亚结构。漆酶催化苯酚自由基的形成、自由基迁移和苄基位置的氧插入可导致香兰素的形成。由于香兰素本身是漆酶首选的酚类底物,一旦香兰素被释放出来,就不可避免地会形成香兰素低聚物和聚合物。为了减缓低聚物的形成,其中一个酚羟基通过乙酰化得到了保护。当使用来自南极念珠菌(CAL)的脂肪酶时,主要的乙酰化产物是单乙酰姜黄素,摩尔产率约为 49%。第二步,在双相体系(二乙醚/水缓冲液)中将单乙酰姜黄素与各种玄拟真菌的纯化漆酶进行孵育。来自 Funalia trogii 的一种漆酶(LccFtr)可将姜黄素单乙酸酯高度转化为乙酸香兰素(姜黄素单乙酸酯的摩尔产率为 46%)。未受保护的香兰素分子反应生成高分子产物的混合物。在第三步中,使用红豆杉中的阿魏酰酯酶(PeFaeA)从醋酸香兰素中去除保护基(摩尔收率为 68%)。氨基酸序列的比对表明,在这种不含介质和辅助因子的反应中,高潜能的漆酶表现更好。