Total Synthesis and Biological Evaluation of Leptosphaerone B and Derivatives of Microketide A

ABSTRACT: Microketide A and B are fungal polyketides reported to display potent activity against Gram-negative pathogens, yet the complex and low yielding isolation from fungal cultures and a lack of synthetic access have prevented detailed investigation of their mode of action and structure-activity relationship. Here, we report the first total synthesis of two close analogues of microketide A, dihydro-MikA, and 11-deoxy-MikA as well as of racemic leptosphaerone B, another member of this cyclohexenone-based natural product family. Our route features a modular assembly of highly functionalized fragments and enables divergent access to analogs through selective dihydroxylation and late-stage fragment fusion. Despite extensive exploration of multiple C–C bond-forming strategies, unfavorable sterics and competing eliminations prevented successful connection of the fully elaborated fragments required for microketide A. The synthesized compounds leptosphaerone B, dihydro-MikA, and 11-deoxy-MikA were evaluated for antibacterial activity and human cytotoxicity but showed no effects up to 200 μM. Competitive residue-specific chemoproteomics and in vitro nucleophile-trapping experiments further revealed no covalent protein engagement, indicating that these scaffolds are intrinsically weak electrophiles and unlikely to act through Michael addition. Together, our findings suggest that microketide A possesses a restrictive structure–activity relationship, in which even subtle modifications abolish biological function. The synthetic strategy described herein provides a robust platform for exploiting alternative modifications for in-depth structure activity relationship studies assessing the biological potential of this natural product.

INSTRUMENT(S):

ORGANISM(S): Staphylococcus Aureus Subsp. Aureus Nctc 8325 Escherichia Coli (strain K12)

TISSUE(S): Cell Culture

SUBMITTER: Martin Frederik Köllen  

LAB HEAD: Stephan Axel Sieber

PROVIDER: PXD071945 | Pride | 2026-02-28

REPOSITORIES: Pride