• Cystobactamid 507: Concise Synthesis, Mode of Action and Optimization toward More Potent Antibiotics.

      Elgaher, Walid A M; Hamed, Mostafa M; Baumann, Sascha; Herrmann, Jennifer; Siebenbürger, Lorenz; Krull, Jana; Cirnski, Katarina; Kirschning, Andreas; Brönstrup, Mark; Müller, Rolf; et al. (Wiley-VCH, 2020-01-26)
      Lack of new antibiotics and increasing antimicrobial resistance are the main concerns of healthcare community nowadays, which necessitate the search for novel antibacterial agents. Recently, we discovered the cystobactamids - a novel natural class of antibiotics with broad-spectrum antibacterial activity. In this work, we describe a concise total synthesis of cystobactamid 507, the identification of the bioactive conformation using non-covalently bonded rigid analogs, the first structure–activity relationship (SAR) study for cystobactamid 507 leading to new analogs with high metabolic stability, superior topoisomerase IIA inhibition, antibacterial activity and, importantly, stability toward the resistant factor AlbD. Deeper insight into the mode of action revealed that the cystobactamids employ DNA minor groove binding as part of the drug–target interaction without showing significant intercalation. By designing a new analog of cystobactamid 919-2 we finally demonstrated that these findings could be further exploited to obtain more potent hexapeptides against Gram-negative bacteria.
    • Discovery of Novel Latency-Associated Nuclear Antigen Inhibitors as Antiviral Agents Against Kaposi's Sarcoma-Associated Herpesvirus.

      Kirsch, Philine; Jakob, Valentin; Elgaher, Walid A M; Walt, Christine; Oberhausen, Kevin; Schulz, Thomas F; Empting, Martin; HIPS, Helmholtz-Institut für Pharmazeutische Forschung Saarland, Universitätscampus E8.1 66123 Saarbrücken, Germany.;HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (American Chemical Society (ACS), 2020-01-24)
      With the aim to develop novel antiviral agents against Kaposi's Sarcoma Herpesvirus (KSHV), we are targeting the latency-associated nuclear antigen (LANA). This protein plays an important role in viral genome maintenance during latent infection. LANA has the ability to tether the viral genome to the host nucleosomes and, thus, ensures latent persistence of the viral genome in the host cells. By inhibition of the LANA-DNA interaction, we seek to eliminate or reduce the load of the viral DNA in the host. To achieve this goal, we screened our in-house library using a dedicated fluorescence polarization (FP)-based competition assay, which allows for the quantification of LANA-DNA-interaction inhibition by small organic molecules. We successfully identified three different compound classes capable of disrupting this protein-nucleic acid interaction. We characterized these compounds by IC50 dose-response evaluation and confirmed the compound-LANA interaction using surface plasmon resonance (SPR) spectroscopy. Furthermore, two of the three hit scaffolds showed only marginal cytotoxicity in two human cell lines. Finally, we conducted STD-NMR competition experiments with our new hit compounds and a previously described fragment-sized inhibitor. Based on these results, future compound linking approaches could serve as a promising strategy for further optimization studies in order to generate highly potent KSHV inhibitors.
    • Semisynthesis and biological evaluation of amidochelocardin derivatives as broad-spectrum antibiotics.

      Grandclaudon, Charlotte; Birudukota, N V Suryanarayana; Elgaher, Walid A M; Jumde, Ravindra P; Yahiaoui, Samir; Arisetti, Nanaji; Hennessen, Fabienne; Hüttel, Stephan; Stadler, Marc; Herrmann, Jennifer; et al. (Elsevier, 2019-12-20)
      To address the global challenge of emerging antimicrobial resistance, the hitherto most successful strategy to new antibiotics has been the optimization of validated natural products; most of these efforts rely on semisynthesis. Herein, we report the semisynthetic modification of amidochelocardin, an atypical tetracycline obtained via genetic engineering of the chelocardin producer strain. We report modifications at C4, C7, C10 and C11 by the application of methylation, acylation, electrophilic substitution, and oxidative C-C coupling reactions. The antibacterial activity of the reaction products was tested against a panel of Gram-positive and Gram-negative pathogens. The emerging structure-activity relationships (SARs) revealed that positions C7 and C10 are favorable anchor points for the semisynthesis of optimized derivatives. The observed SAR was different from that known for tetracyclines, which underlines the pronounced differences between the two compound classes.