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Molecular Basis for Spirocycle Formation in the Paraherquamide Biosynthetic Pathway

submitted on 20.08.2019, 22:52 and posted on 21.08.2019, 18:34 by Amy E. Fraley, Kersti Caddell Haatveit, Ying Ye, Samantha P. Kelly, Sean A. Newmister, Fengan Yu, Robert M. Williams, Janet L. Smith, K. N. Houk, David H. Sherman

The paraherquamides are potent anthelmintic natural products with complex heptacyclic scaffolds. One key feature of these molecules is the spiro-oxindole moiety that lends a strained three-dimensional architecture to these structures. The flavin monooxygenase PhqK was found to catalyze spirocycle formation through two parallel pathways in the biosynthesis of paraherquamides A and G. Two new paraherquamides (K and L) were isolated from a ΔphqK strain of Penicillium simplicissimum, and subsequent enzymatic reactions with these compounds generated two additional metabolites paraherquamides M and N. Crystal structures of PhqK in complex with various substrates provided a foundation for mechanistic analyses and computational studies. While it is evident that PhqK can react with various substrates, reaction kinetics and molecular dynamics simulations indicated that the dioxepin-containing paraherquamide L was the favored substrate. Through this effort, we have elucidated a key step in the biosynthesis of the paraherquamides, and provided a rationale for the selective spirocyclization of these powerful anthelmintic agents.


NIH R01 CA070375 to R.M.W. and D.H.S.

NIH R35 GM118101 to D.H.S.

Hans Vahlteich Professorship to D.H.S.

R01 GM124480 to K.N.H.

Margaret J. Hunter Professorship to J.L.S.

Rackham Predoctoral Fellowship to A.E.F.

NIH Predoctoral Training Grant GM067555 to K.C.H.


Email Address of Submitting Author


University of Michigan


United States

ORCID For Submitting Author


Declaration of Conflict of Interest

The authors declare no competing financial interest.


Read the published paper

in Journal of the American Chemical Society