Mechanistic analysis of carbon–carbon bond formation by deoxypodophyllotoxin synthase

Haoyu Tang, Min Hao Wu, Hsiao Yu Lin, Meng Ru Han, Yueh Hua Tu, Zhi Jie Yang, Tun Cheng Chien*, Nei Li Chan*, Wei Chen Chang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

Deoxypodophyllotoxin contains a core of four fused rings (A to D) with three consecutive chiral centers, the last being created by the attachment of a peripheral trimethoxyphenyl ring (E) to ring C. Previous studies have suggested that the iron(II)- and 2-oxoglutarate–dependent (Fe/2OG) oxygenase, deoxypodophyllotoxin synthase (DPS), catalyzes the oxidative coupling of ring B and ring E to form ring C and complete the tetracyclic core. Despite recent efforts to deploy DPS in the preparation of deoxypodophyllotoxin analogs, the mechanism underlying the regio- and stereoselectivity of this cyclization event has not been elucidated. Herein, we report 1) two structures of DPS in complex with 2OG and (±)-yatein, 2) in vitro analysis of enzymatic reactivity with substrate analogs, and 3) model reactions addressing DPS’s catalytic mechanism. The results disfavor a prior proposal of on-pathway benzylic hydroxylation. Rather, the DPS-catalyzed cyclization likely proceeds by hydrogen atom abstraction from C7', oxidation of the benzylic radical to a carbocation, Friedel–Crafts-like ring closure, and rearomatization of ring B by C6 deprotonation. This mechanism adds to the known pathways for transformation of the carbon-centered radical in Fe/2OG enzymes and suggests what types of substrate modification are likely tolerable in DPS-catalyzed production of deoxypodophyllotoxin analogs.

Original languageEnglish
Article numbere2113770119
JournalProceedings of the National Academy of Sciences of the United States of America
Volume119
Issue number1
DOIs
Publication statusPublished - 2022 Jan 4

Keywords

  • CC coupling
  • Cyclization
  • Natural product
  • Oxygenase
  • Reaction mechanism

ASJC Scopus subject areas

  • General

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