Department of Pharmaceutical Sciences, School of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Av. do Café, s/n, Ribeirão Prêto, SP, 14040-903, Brazil.
Organic Chemistry Department, Chemistry Institute, Federal University of Bahia, Rua Barão de Jeremoabo, s/n, Salvador, BA, 40110-060, Brazil.
Bioprocess Biosyst Eng. 2020 Jun;43(6):1051-1059. doi: 10.1007/s00449-020-02303-x. Epub 2020 Feb 4.
Labdane diterpenes and their derivatives have shown remarkable biological activities and are useful as chiral building blocks for the synthesis of a variety of bioactive compounds. There is great interest in developing biocatalyst technology to achieve regio- and stereoselective hydroxylation of unactivated C-H bonds in complex natural products, since the functionalization of unactivated C-H bonds generally requires hard reaction conditions and highly reactive oxidizing agents, which are limited regarding the control of regio- and stereoselectivity. Filamentous fungi are efficient biocatalysts capable of catalyzing a wide variety of hydroxylation reactions, and the use of whole cell biocatalysts provides advantages regarding cofactor regeneration and is much less expensive. Therefore, the goal of this study was to select biocatalysts to develop biotransformation processes that can be scalable under mild reaction conditions for hydroxylation of a labdane diterpene, 3β-acetoxy-copalic acid, which contains the trans-decalin moiety and a side chain dienic system appropriate for the preparation of a variety of compounds. Biotransformation processes were carried out and five filamentous fungi were selected as capable of producing hydroxylated diterpenes at positions C-3, C-6, C-7 and C-18 of the trans-decalin moiety and C-13 of the side chain dienic system. Hydroxylation reactions occurred with regio- and stereoselectivity by using some fungi that produced only the 6α, 7α and 13α-hydroxyl derivatives. The chemical structures of the hydroxylated diterpenes were determined from spectrometric and spectroscopic data, and the relative stereochemistry of stereogenic centers was established from coupling constants, by NOE-diff experiments and/or by computational calculations.
拉伯烷二萜及其衍生物具有显著的生物活性，可用作合成各种生物活性化合物的手性构建块。人们对开发生物催化剂技术以实现复杂天然产物中未活化 C-H 键的区域和立体选择性羟化非常感兴趣，因为未活化 C-H 键的功能化通常需要苛刻的反应条件和高反应性氧化剂，这在区域和立体选择性控制方面受到限制。丝状真菌是有效的生物催化剂，能够催化广泛的羟化反应，而使用全细胞生物催化剂在辅酶再生方面具有优势，并且成本要低得多。因此，本研究的目的是选择生物催化剂来开发生物转化工艺，这些工艺可以在温和的反应条件下进行规模放大，用于羟化拉伯烷二萜 3β-乙酰氧基-贝壳杉酸，该化合物含有反式十氢化萘部分和侧链二烯系统，适合制备各种化合物。进行了生物转化过程，选择了五种丝状真菌能够在反式十氢化萘部分的 C-3、C-6、C-7 和 C-18 以及侧链二烯系统的 C-13 位置产生羟基化的二萜。一些产生仅 6α、7α 和 13α-羟基衍生物的真菌通过区域和立体选择性发生羟化反应。通过光谱和光谱数据确定了羟基化二萜的化学结构，并通过偶合常数、NOE-diff 实验和/或计算计算确定了立体中心的相对立体化学。
