Structure Prediction and Synthesis of a New Class of Macrocyclic Peptide Natural Products

Abstract

<p>Owing to advances in genomic sequencing and bioinformatics, the breadth of natural product biosynthetic gene clusters (BGCs) has meteorically risen. This remains true for ribosomally synthesized and post-translationally modified peptides (RiPPs), where the rate of bioinformatically identifying clusters vastly outpaces characterization efforts. Uniting bioinformatics and enzymological knowledge to predict the chemical product(s) of a RiPP BGC with total chemical synthesis to obtain the natural compound is an effective platform for investigating cryptic gene clusters. Herein, we report the bioinformatic identification of a biosynthetically divergent class of RiPP bearing a subset of enzymes involved in thiopeptide biosynthesis. These natural products were predicted based on BGC architecture to undergo a formal, enzymatic [4+2]-cycloaddition with subsequent elimination of the leader peptide and water to produce a tri-substituted pyridine-based macrocycle. Bearing a pyridine similar to thiopeptides but lacking the ubiquitous thiazole heterocycles, these new RiPPs were termed pyritides. One of the predicted natural products was chemically synthesized using an 11-step synthesis. This structure was verified to be chemically identical by an orthogonal chemoenzymatic synthesis utilizing the precursor peptide and the cognate [4+2]-cycloaddition enzyme. The chemoenzymatic platform was used to synthesize a second in-cluster pyritide product as well as analogs from other bioinformatically identified pyritide BGCs. This work exemplifies complementary bioinformatic, enzymological, and synthetic techniques to characterize a structurally distinct class of RiPP natural product.</p>