The NanoComBac project, carried out at Ruhr‑Universität Bochum from 1 April 2019 to 31 March 2023, aimed to create new antibacterial agents that can penetrate the formidable outer membrane of Gram‑negative bacteria and thereby address the urgent need for drugs that can overcome resistance. The research focused on two natural products, actinonin and moiramide, which act on bacterial protein maturation and fatty‑acid synthesis, respectively, and on a novel delivery platform based on gold nanoparticles that themselves possess antibacterial activity. By combining these natural compounds with gold nanocarriers, the project sought to develop a dual‑mode strategy that would both inhibit essential bacterial enzymes and facilitate their entry into the cell.

Actinonin is a peptide that inhibits the bacterial metalloprotease peptide‑deformylase (PDF), blocking the removal of the formyl group from nascent proteins. Although actinonin and its analogues had entered early clinical stages, toxicity due to insufficient selectivity for bacterial versus human PDF halted development. In NanoComBac, a thiol‑modified actinonin derivative was synthesized that retained comparable potency against bacterial PDF while allowing covalent attachment to gold nanoparticles of 2–4 nm diameter. Nuclear magnetic resonance (NMR) spectroscopy confirmed that the gold‑actinonin conjugate binds to Escherichia coli PDF (EcPDF) and that the thiol linkage can be cleaved under mildly reducing, physiological conditions (e.g., with dithiothreitol), thereby releasing the active inhibitor inside the bacterial cell. The gold nanoparticles themselves exhibited intrinsic antibacterial activity, and the conjugate demonstrated enhanced efficacy against resistant Gram‑negative strains in preliminary assays. This work established a proof of concept for a dual‑mode antibacterial approach that combines enzyme inhibition with nanocarrier‑mediated delivery.

Moiramide, a natural inhibitor of the biotin‑dependent acetyl‑CoA carboxylase (ACC) essential for fatty‑acid synthesis in Mycobacterium tuberculosis, was investigated to clarify the role of its sorbic acid tail. Molecular‑modeling studies using the Schrödinger suite revealed a previously unreported binding pocket that explains the importance of the sorbic acid moiety for ACC inhibition. Guided by this model, new moiramide derivatives were designed and synthesized, and their antibacterial activity was evaluated. The results, published in ChemMedChem (DOI 10.1002/cmdc.202200631), confirmed that the sorbic acid tail is critical for both ACC binding and antibacterial potency, providing a rational basis for further optimization of this scaffold.

The project was organized into five work packages (WPs). WP 2, led by Ag Metzler‑Nolte, focused on the synthesis and functionalization of gold nanoparticles. WP 3, headed by AG Stoll, performed the biomolecular NMR studies that validated the interaction between the conjugates and bacterial targets. WPs 4 and 5 carried out the biological evaluation of the compounds against a panel of Gram‑negative pathogens, including resistant strains. The collaboration involved close integration of computational modeling, synthetic chemistry, and microbiological testing, with data sharing and joint manuscript preparation across the WPs. The project was funded under the German funding code 16GW0224, and the results were disseminated through peer‑reviewed publications and conference presentations.

In summary, NanoComBac delivered a novel dual‑mode antibacterial platform that couples a PDF inhibitor or ACC inhibitor with an antibacterial gold nanocarrier, overcoming membrane penetration barriers and reducing the likelihood of early resistance. The work provides a foundation for the development of next‑generation antibiotics that target mechanisms not exploited by current commercial drugs, and it demonstrates the feasibility of integrating nanotechnology with natural product chemistry to address the global challenge of antimicrobial resistance.