Multi-Modal Design, Synthesis, and Biological Evaluation of Novel Fusidic Acid Derivatives

Fusidic acid (FA), a tetracyclic triterpenoid, has been approved to treat methicillin-resistant Staphylococcus aureus (MRSA) infections. However, there are few reports about FA derivatives with high efficacy superior to FA, manifesting the difficulty of discovering the derivatives based on experience-based drug design. In this study, we employed a stepwise method to discover novel FA derivatives. First, molecular dynamics (MD) simulations were performed to identify the molecular mechanism of FA against elongation factor G (EF-G) and drug resistance. Then, we utilized a scaffold decorator to design novel FA derivatives at the 3- and 21-positions of FA. The ligand-based and structure-based screening models, including Chemprop and RTMScore, were employed to identify promising hits from the generated set. Ten generated FA derivatives with high efficacy in the Chemprop and RTMScore models were synthesized for in vitro testing. Compounds 4 and 10 demonstrated a 2-fold increase in potency against MRSA strains compared to FA. This study highlights the significant impact of AI-based methods on the design of novel FA derivatives with drug efficacy, which provides a new approach for drug discovery.

Synthesis of fusidane triterpenoid Mannich bases as potential antibacterial and antitumor agents

Mannich bases (8 examples) were synthesized via aminomethylation of fusidane propargyl esters. In vitro antimicrobial screening against key ESKAPE pathogens showed that the fusidic acid based Mannich products exhibit a high antimicrobial effect against Gram-positive bacteria Staphylococcus aureus and the fungus Cryptococcus neoformans. Moreover, the cytotoxic effect of fusidic acid and its analogs, which showed high antibacterial activity, was determined by MTT assay on cancer HepG2, HCT-116, SH-SY5Y, MCF-7, A549 and conditionally normal cells HEK293. A remarkable cytotoxic activity of fusidic acid propargyl ester and its aminomethylene derivatives against cancer and nontumoral HEK293 cells with IC50 values within 4.2-25 µM was found.

Synthesis and Biological Evaluation of Novel Fusidic Acid Derivatives as Two-in-One Agent with Potent Antibacterial and Anti-Inflammatory Activity

Fusidic acid (FA), a narrow-spectrum antibiotics, is highly sensitive to various Gram-positive cocci associated with skin infections. It has outstanding antibacterial effects against certain Gram-positive bacteria whilst no cross-resistance with other antibiotics. Two series of FA derivatives were synthesized and their antibacterial activities were tested. A new aromatic side-chain analog, FA-15 exhibited good antibacterial activity with MIC values in the range of 0.781–1.563 µM against three strains of Staphylococcus spp. Furthermore, through the assessment by the kinetic assay, similar characteristics of bacteriostasis by FA and its aromatic derivatives were observed. In addition, anti-inflammatory activities of FA and its aromatic derivatives were evaluated by using a 12-O-tetradecanoylphorbol-13-acetate (TPA) induced mouse ear edema model. The results also indicated that FA and its aromatic derivatives effectively reduced TPA-induced ear edema in a dose-dependent manner. Following, multiform computerized simulation, including homology modeling, molecular docking, molecular dynamic simulation and QSAR was conducted to clarify the mechanism and regularity of activities. Overall, the present work gave vital clues about structural modifications and has profound significance in deeply scouting for bioactive potentials of FA and its derivatives.

Bioactivities and Structure-Activity Relationships of Fusidic Acid Derivatives: A Review

Fusidic acid (FA) is a natural tetracyclic triterpene isolated from fungi, which is clinically used for systemic and local staphylococcal infections, including methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci infections. FA and its derivatives have been shown to possess a wide range of pharmacological activities, including antibacterial, antimalarial, antituberculosis, anticancer, tumor multidrug resistance reversal, anti-inflammation, antifungal, and antiviral activity in vivo and in vitro. The semisynthesis, structural modification and biological activities of FA derivatives have been extensively studied in recent years. This review summarized the biological activities and structure-activity relationship (SAR) of FA in the last two decades. This summary can prove useful information for drug exploration of FA derivatives.

Rv0684/fusA1, an Essential Gene, Is the Target of Fusidic Acid and Its Derivatives in Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis, is a major global health concern given the increase in multiple forms of drug-resistant TB. This underscores the importance of a continuous pipeline of new anti-TB agents. Drug repurposing has shown promise in expanding the therapeutic options for TB chemotherapy. Fusidic acid (FA), a natural product-derived antibiotic, is one such candidate for repurposing. The present study aimed to understand the mechanism of action of FA and its selected analogs in M. tuberculosis. By using chemical biology and genetics, we identified elongation factor G as the target of FA in M. tuberculosis. We showed essentiality of its encoding gene fusA1 in M. tuberculosis by demonstrating that the transcriptional silencing of fusA1 is bactericidal in vitro and in macrophages. Thus, this work validated a novel drug target FusA1 in M. tuberculosis.

Synthesis of Fusidic Acid Derivatives Yields a Potent Antibiotic with an Improved Resistance Profile

Fusidic acid (FA) is a potent steroidal antibiotic that has been used in Europe for more than 60 years to treat a variety of infections caused by Gram-positive pathogens. Despite its clinical success, FA requires significantly elevated dosing (3 g on the first day, 1.2 g on subsequent days) to minimize resistance, as FA displays a high resistance frequency, and a large shift in minimum inhibitory concentration is observed for resistant bacteria. Despite efforts to improve on these aspects, all previously constructed derivatives of FA have worse antibacterial activity against Gram-positive bacteria than the parent natural product. Here, we report the creation of a novel FA analogue that has equivalent potency against clinical isolates of Staphylococcus aureus (S. aureus) and Enterococcus faecium (E. faecium) as well as an improved resistance profile in vitro when compared to FA. Importantly, this new compound displays efficacy against an FA-resistant strain of S. aureus in a soft-tissue murine infection model. This work delineates the structural features of FA necessary for potent antibiotic activity and demonstrates that the resistance profile can be improved for this scaffold and target.

Structure-activity relationship analyses of fusidic acid derivatives highlight crucial role of the C-21 carboxylic acid moiety to its anti-mycobacterial activity

Fusidic acid (FA) is a potent congener of the fusidane triterpenoid class of antibiotics. Structure-activity relationship (SAR) studies suggest the chemical structure of FA is optimal for its antibacterial activity. SAR studies from our group within the context of a drug repositioning approach in tuberculosis (TB) suggest that, as with its antibacterial activity, the C-21 carboxylic acid group is indispensable for its anti-mycobacterial activity. Further studies have led to the identification of 16-deacetoxy-16β-ethoxyfusidic acid (58), an analog which exhibited comparable activity to FA with an in vitro MIC₉₉ value of 0.8 µM. Preliminary SAR studies around the FA scaffold suggested that the hydrophobic side chain at C-20, like the C-11 OH group, was required for activity. The C-3 OH group, however, can be functionalized to obtain more potent compounds.

An epigrammatic status of the 'azole'-based antimalarial drugs

The development of multidrug resistance in the malarial parasite has sabotaged majority of the eradication efforts by restraining the inhibition profile of first line as well as second line antimalarial drugs, thus necessitating the development of novel pharmaceutics constructed on appropriate scaffolds with superior potency against the drug-resistant and drug-susceptible Plasmodium parasite. Over the past decades, the infectious malarial parasite has developed resistance against most of the contemporary therapeutics, thus necessitating the rational development of novel approaches principally focused on MDR malaria. This review presents an epigrammatic collation of the epidemiology and the contemporary antimalarial therapeutics based on the 'azole' motif.

Substituted 1,3-dioxoisoindoline-4-aminoquinolines coupled via amide linkers: Synthesis, antiplasmodial and cytotoxic evaluation

Synthesis of C-5-substituted 1,3-dioxoisoindoline-4-aminoquinolines having amide group as a spacer was developed with an intent to evaluate their antiplasmodial activities. The synthesized dioxoisoindoline-aminoquinolines tethered with β-alanine as a spacer and secondary amine as substituent displayed good anti-plasmodial activities. Compound 7j, with an optimum combination of β-alanine and an ethyl chain length as linker along with diethylamine as the secondary amine counterpart at dioxoisoindoline proved to be most potent and non-cytotoxic with IC₅₀ of 0.097 µM against W2 strain of P. falciparum and a selective index of >2000.

Identification of steroid-like natural products as antiplasmodial agents by 2D and 3D similarity-based virtual screening

The emergence of drug resistance in Plasmodium falciparum to available antimalarial drugs has challenged current antimalarial treatments. New antimalarials, particularly those with novel mechanisms of action and no cross resistance to current drugs, are therefore urgently needed. To identify new growth inhibitors of Plasmodium falciparum, 2D and 3D similarity-based virtual screening methods were employed in parallel with an in-house database of steroid-type natural products using fusidic acid as a search query. The resulting hit compounds were further filtered based on the predicted partition coefficient, log P. The virtual screening strategy resulted in the identification of nine new compounds that inhibited parasite growth with IC₅₀ values of <20 μM. Four compounds exhibited IC₅₀ values in the range of 1.39-3.45 μM and three of which showed a promising selectivity index. Further, the predicted ADME properties of the four most active compounds were found to be comparable to fusidic acid. These compounds can be further explored using structural modifications in the identification and development of more potent parasite growth inhibitors with improved selectivity.