@article{gering_li_tang_swartz_chang_makris_2023, title={A Ferric-Superoxide Intermediate Initiates P450-Catalyzed Cyclic Dipeptide Dimerization}, volume={8}, ISSN={["1520-5126"]}, url={https://doi.org/10.1021/jacs.3c04542}, DOI={10.1021/jacs.3c04542}, abstractNote={The cytochrome P450 (CYP) AspB is involved in the biosynthesis of the diketopiperazine (DKP) aspergilazine A. Tryptophan-linked dimeric DKP alkaloids are a large family of natural products that are found in numerous species and exhibit broad and often potent bioactivity. The proposed mechanisms for C-N bond formation by AspB, and similar C-C bond formations by related CYPs, have invoked the use of a ferryl-intermediate as an oxidant to promote substrate dimerization. Here, the parallel application of steady-state and transient kinetic approaches reveals a very different mechanism that involves a ferric-superoxide species as a primary oxidant to initiate DKP-assembly. Single turnover kinetic isotope effects and a substrate analog suggest the probable nature and site for abstraction. The direct observation of CYP-superoxide reactivity rationalizes the atypical outcome of AspB and reveals a new reaction manifold in heme enzymes.}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Gering, Hannah E. and Li, Xiaojun and Tang, Haoyu and Swartz, Paul D. and Chang, Wei-Chen and Makris, Thomas M.}, year={2023}, month={Aug} }
 @article{manley_tang_xue_guo_chang_makris_2021, title={BesC Initiates C-C Cleavage through a Substrate-Triggered and Reactive Diferric-Peroxo Intermediate}, volume={12}, ISSN={["1520-5126"]}, url={https://doi.org/10.1021/jacs.1c11109}, DOI={10.1021/jacs.1c11109}, abstractNote={BesC catalyzes the iron- and O2-dependent cleavage of 4-chloro-l-lysine to form 4-chloro-l-allylglycine, formaldehyde, and ammonia. This process is a critical step for a biosynthetic pathway that generates a terminal alkyne amino acid which can be leveraged as a useful bio-orthogonal handle for protein labeling. As a member of an emerging family of diiron enzymes that are typified by their heme oxygenase-like fold and a very similar set of coordinating ligands, recently termed HDOs, BesC performs an unusual type of carbon-carbon cleavage reaction that is a significant departure from reactions catalyzed by canonical dinuclear-iron enzymes. Here, we show that BesC activates O2 in a substrate-gated manner to generate a diferric-peroxo intermediate. Examination of the reactivity of the peroxo intermediate with a series of lysine derivatives demonstrates that BesC initiates this unique reaction trajectory via cleavage of the C4-H bond; this process represents the rate-limiting step in a single turnover reaction. The observed reactivity of BesC represents the first example of a dinuclear-iron enzyme that utilizes a diferric-peroxo intermediate to capably cleave a C-H bond as part of its native function, thus circumventing the formation of a high-valent intermediate more commonly associated with substrate monooxygenations.}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, publisher={American Chemical Society (ACS)}, author={Manley, Olivia M. and Tang, Haoyu and Xue, Shan and Guo, Yisong and Chang, Wei-chen and Makris, Thomas M.}, year={2021}, month={Dec} }
 @article{tang_tang_kurnikov_liao_chan_kurnikova_guo_chang_2021, title={Harnessing the Substrate Promiscuity of Dioxygenase AsqJ and Developing Efficient Chemoenzymatic Synthesis for Quinolones}, volume={11}, ISSN={["2155-5435"]}, DOI={10.1021/acscatal.1c01150}, abstractNote={Nature has developed complexity-generating reactions within natural product biosynthetic pathways. However, direct utilization of these pathways to prepare compound libraries remains challenging due to limited substrate scopes, involvement of multiple-step reactions, and moderate robustness of these sophisticated enzymatic transformations. Synthetic chemistry, on the other hand, offers an alternative approach to prepare natural product analogs. However, owing to complex and diverse functional groups appended on the targeted molecules, dedicated design and development of synthetic strategies are typically required. Herein, by leveraging the power of chemo-enzymatic synthesis, we report an approach to bridge the gap between biological and synthetic strategies in the preparation of quinolone alkaloid analogs. Leading by in silico analysis, the predicted substrate analogs were chemically synthesized. The AsqJ-catalyzed asymmetric epoxidation of these substrate analogues was followed by an Lewis Acid-triggered ring contraction to complete the viridicatin formation. We evaluated the robustness of this method in gram-scale reactions. Lastly, through chemoenzymatic cascades, a library of quinolone alkaloids is effectively prepared.}, number={12}, journal={ACS CATALYSIS}, author={Tang, Haoyu and Tang, Yijie and Kurnikov, Igor V and Liao, Hsuan-Jen and Chan, Nei-Li and Kurnikova, Maria G. and Guo, Yisong and Chang, Wei-chen}, year={2021}, month={Jun}, pages={7186–7192} }
 @article{tang_wu_lin_han_tu_yang_chien_chan_chang_2022, title={Mechanistic analysis of carbon-carbon bond formation by deoxypodophyllotoxin synthase}, volume={119}, ISSN={["1091-6490"]}, DOI={10.1073/pnas.2113770119}, abstractNote={Significance
          The completion of the tetracyclic core of etoposide, classified by the World Health Organization as an essential medicine, by the Fe/2OG oxygenase deoxypodophyllotoxin synthase follows a hybrid radical-polar pathway not previously seen in other members of this enzyme class. The implication of a substrate-based benzylic carbocation in this mechanism will inform ongoing efforts to create analogs of this important drug with improved or emergent properties and represents a new route for resolution of the initial substrate radical that is common to members of the class. This study adds to our understanding on a growing number of biochemical transformations in which carbocation intermediates are likely to be crucial.}, number={1}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Tang, Haoyu and Wu, Min-Hao and Lin, Hsiao-Yu and Han, Meng-Ru and Tu, Yueh-Hua and Yang, Zhi-Jie and Chien, Tun-Cheng and Chan, Nei-Li and Chang, Wei-chen}, year={2022}, month={Jan} }