Thiol Probes To Detect Electrophilic Natural Products Based on Their Mechanism of Action

Abstract

New methods are urgently needed to find novel natural products as structural leads for the development of new drugs against emerging diseases such as cancer and multiresistant bacterial infections. Here we introduce a reactivity-guided drug discovery approach for electrophilic natural products, a therapeutically relevant class of natural products that covalently modify their cellular targets, in crude extracts. Using carefully designed halogenated aromatic reagents, the process furnishes derivatives that are UV-active and highly conspicuous via mass spectrometry by virtue of an isotopically unique bromine or chlorine tag. In addition to the identification of high-value metabolites, the process facilitates the difficult task of structure elucidation by providing derivatives that are primed for X-ray crystallographic analysis. We show that a cysteine probe efficiently and chemoselectively labels enone-, β-lactam-, and β-lactone-based electrophilic natural products (parthenolide, andrographolide, wortmannin, penicillin G, salinosporamide), while a thiophenol probe preferentially labels epoxide-based electrophilic natural products (triptolide, epoxomicin, eponemycin, cyclomarin, salinamide). Using the optimized method, we were able to detect and isolate the epoxide-bearing natural product tirandalydigin from Salinispora and thereby link an orphan gene cluster to its gene product.

The Photochemical Degradation of Bacterial Cell Wall Using Penicillin-Based Carbon Dots: Weapons Against Multi-Drug Resistant (MDR) Strains

“…Reduction of MDR bacterial growth was also confirmed by CFU analysis (Figure S5 A, S5B). As the mechanism of action of penicillin is reported to break down the cell wall of gram +ve bacteria, by binding with PPB protein, however to support the antibacterial mechanism of action of penicillin‐based dots against gram –ve bacteria, we employed SEM analysis of treated and non‐treated cells. Nontreated cells possessed smooth and clear cell wall while treated cells had damaged and wrinkled cell wall.…”

“…Reduction of MDR bacterial growth was also confirmed by CFU analysis (Figure S5 A, S5B). As the mechanism of action of penicillin is reported to break down the cell wall of gram + ve bacteria, by binding with PPB protein, [24] however to support the antibacterial mechanism of action of penicillin-based dots against gram -ve bacteria, we employed SEM analysis of treated and non -1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 treated cells. Nontreated cells possessed smooth and clear cell wall while treated cells had damaged and wrinkled cell wall.…”

Targeting Reactive Carbonyls for Identifying Natural Products and Their Biosynthetic Origins

“…Recent examples of this approach have utilized thiol-based probes to successfully target electron-deficient alkenes, β-lactams, β-lactones, and epoxides by nucleophilic addition, resulting in the discovery of several novel natural products. 14,15,16 Here we expand the scope of RBS to target additional functional groups as well as introduce a method for the straightforward identification of labeled compounds based on a unique isotopic signature (Figure 1). …”

Targeting pharmacophore with probe‐reactivity‐guided fractionation to precisely identify electrophilic sesquiterpenes and its activity of anti‐TNBC

“…Scholars have employed GSH as a nucleophilic probe, in company with LC‐MS, to rapidly discover active compounds such as Michael receptors in natural products . Halogenated aromatic reagents such as 4‐chlorothiophenol, 4‐bromonitrosobenzene have also been utilised as probes in discovering electrophilic and polyketide natural products from bacterial extracts . Given the advantages of GSH and halogenated aromatic reagents used as probes in discovery of specific structural types of natural products, GSH and BTP were selected.…”

“…The targeted compounds are irreversibly modified, and, the resulting conjugates often have enhanced visibility using liquid chromatography/UVD/mass spectrometry (LC/UV/MS) instruments. Recently, examples of this approach have been utilised to successfully target chemical functionalities such as β ‐lactams, alkenes, β ‐lactones, and epoxides, resulting in the discovery of several novel natural products . Nevertheless, few reports have been presented on the basis of pharmacophore identification, and, subsequent employment of probe‐reactivity‐guided strategy for the discovery of bioactive natural products.…”