Fungal Indole Alkaloid Biogenesis Through Evolution of a Bifunctional Reductase/Diels-Alderase

26 December 2018, Version 1

Abstract

Prenylated indole alkaloids isolated from various fungi possess great structural diversity and pharmaceutical utility. Among them are the calmodulin inhibitory malbrancheamides and paraherquamides, used as anthelmintics in animal health. Herein, we report complete elucidation of the malbrancheamide biosynthetic pathway accomplished through complementary approaches. These include a biomimetic total synthesis to access the natural alkaloid and biosynthetic intermediates in racemic form, and in vitro enzymatic reconstitution that provides access to the natural antipode (+)-malbrancheamide. Reductive cleavage of a L-Pro-L-Trp dipeptide from the MalG nonribosomal peptide synthetase (NRPS) followed by reverse prenylation and a cascade of post-NRPS reactions culminates in an intramolecular [4+2] hetero-Diels-Alder (IMDA) cyclization to furnish the bicyclo[2.2.2]diazaoctane scaffold. Enzymatic assembly of optically pure (+)-premalbrancheamide involves an unexpected zwitterionic intermediate where MalC catalyzes enantioselective cycloaddition as a bifunctional NADPH-dependent reductase/Diels-Alderase. Crystal structures of substrate and product complexes together with site-directed mutagenesis and molecular dynamics simulations demonstrated how MalC and PhqE, its homolog from the paraherquamide pathway, catalyze diastereo- and enantioselective cyclization in the construction of this important class of secondary metabolites.

Keywords

Natural Products Chemistry
diels-alderase
indole alkaloids
biomimetic synthesis strategy

Supplementary materials

Title
Description
Actions
Title
MalManuscript SI V3
Description
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.