A Six‐Oxidase Cascade for Tandem C−H Bond Activation Revealed by Reconstitution of Bicyclomycin Biosynthesis

• Published in: Angewandte Chemie International Edition Vol. 57; no. 3; pp. 719 - 723
• Main Authors: Meng, Song, Han, Wei, Zhao, Juan, Jian, Xiao‐Hong, Pan, Hai‐Xue, Tang, Gong‐Li
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 15.01.2018
• Edition: International ed. in English
• Subjects: Alkaloids; Antibiotics; Bicozamycin; bicyclomycin; Biosynthesis; Cytochrome; Cytochrome P450; Cytochrome P450 monooxygenase; cytochromes; C−H bond activation; dioxygenases; Enzymatic synthesis; Iron; Isoleucine; Ketoglutaric acid; Leucine; Methylene; Transcription termination; Transcription termination factor RHO; tRNA; C−H bond activation; bicyclomycin; dioxygenases; biosynthesis; cytochromes
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201710529

As a commercial antibiotic, bicyclomycin (BCM) is currently the only known natural product targeting the transcription termination factor rho. It belongs to a family of highly functionalized diketopiperazine (DKP) alkaloids and bears a unique O‐bridged bicyclo[4.2.2]piperazinedione ring system, a C1 triol, and terminal exo‐methylene groups. We have identified and characterized the BCM biosynthetic pathway by heterologous biotransformations, in vitro biochemical assays, and one‐pot enzymatic synthesis. A tRNA‐dependent cyclodipeptide synthase guides the heterodimerization of leucine and isoleucine to afford the DKP precursor; subsequently, six redox enzymes, including five α‐ketoglutarate/Fe2+‐dependent dioxygenases and one cytochrome P450 monooxygenase, regio‐ and stereoselectively install four hydroxy groups (primary, secondary, and two tertiary), an exo‐methylene moiety, and a medium‐sized bridged ring through the functionalization of eight unactivated C−H bonds. Enzymatic characterization of the biosynthesis of the antibiotic bicyclomycin revealed a tRNA‐dependent cyclodipeptide synthase for the heterodimerization of Leu and Ile to afford the diketopiperazine precursor. Subsequently, six redox enzymes activate eight unactivated C−H bonds through regio‐ and stereoselective hydroxylation, alkenylation, heterocyclization, and desaturation/epoxidation.