Neochrysosporazines: Precursor-Directed Biosynthesis Defines a Marine-Derived Fungal Natural Product P-Glycoprotein Inhibitory Pharmacophore.

Upregulation of ATP binding cassette (ABC) transporter efflux pumps (i.e. P-glycoprotein, P-gp) can impart multidrug resistance, rendering many chemotherapeutics ineffective and seriously limiting treatment regimes. While ABC transporters remain an attractive target for therapeutic intervention, the development of clinically useful small-molecule inhibitors has proved challenging. In this report, we describe the structure-activity relationship (SAR) analysis of a newly discovered P-gp inhibitory pharmacophore, phenylpropanoid piperazine chrysosporazines, produced by co-isolated marine-derived fungi. In the absence of any total syntheses, we apply an innovative precursor-directed biosynthesis strategy that successfully repurposed fungal biosynthetic output, allowing us to isolate, characterize, and identify the structurally diverse neochrysosporazines A-Q. SAR analysis utilizing all known (and new) neochrysosporazines, chrysosporazines, and azachrysosporazines, plus semi-synthetic analogues, established the key structure requirements for the P-gp inhibitory pharmacophore, and, in addition, identified non-essential sites that allow for the design of affinity and other conjugated probes.