3-Amino-Substituted Analogues of Fusidic Acid as Membrane-Active Antibacterial Compounds

Abstract

Fusidic acid (FA) is an antibiotic with high activity against Staphylococcus aureus; it has been used in clinical practice since the 1960s. However, the narrow antimicrobial spectrum of FA limits its application in the treatment of bacterial infections. In this regard, this work aims both at the study of the antimicrobial effect of a number of FA amines and at the identification of their potential biological targets. In this way, FA analogues containing aliphatic and aromatic amino groups and biogenic polyamine, spermine and spermidine, moieties at the C-3 atom, were synthesized (20 examples). Pyrazinecarboxamide-substituted analogues exhibit a high antibacterial activity against S. aureus (MRSA) with MIC ≤ 0.25 μg/mL. Spermine and spermidine derivatives, along with activity against S. aureus, also inhibit the growth and reproduction of Gram-negative bacteria Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa, and have a high fungicidal effect against Candida albicans and Cryptococcus neoformans. The study of the membrane activity demonstrated that the spermidine- and spermine-containing compounds are able to immerse into membranes and disorder the lipidsleading to a detergent effect. Moreover, spermine-based compounds are also able to form ion-permeable pores in the lipid bilayers mimicking the bacterial membranes. Using molecular docking, inhibition of the protein synthesis elongation factor EF-G was proposed, and polyamine substituents were shown to make the greatest contribution to the stability of the complexes of fusidic acid derivatives with biological targets. This suggests that the antibacterial effect of the obtained compounds may be associated with both membrane activity and inhibition of the elongation factor EF-G.

Effect of Fusidic Acid and Some Nitrogen-Containing Derivatives on Liposomal and Mitochondrial Membranes

“…Moreover, spermine-based derivatives formed pores in lipid bilayers, mimicking bacterial membranes. This also contributed to the antibacterial effect of the obtained analogues [8]. Fusidane triterpenoid oximes were shown to effectively inhibit the bacteria growth and proliferation of cancer cells [18].…”

“…It is known that FA, and especially its derivatives, are able to integrate into lipid membranes and disrupt the dynamics of phospholipids [4,8]. In this work, we evaluated the effect of FA and its derivatives on the phase behavior and properties of lipid membranes, using a laurdan fluorescent probe.…”

“…The action of FA is due to the inhibition of the elongation of the bacterial protein polypeptide chain by selectively binding to the ribosome elongation factor G (EF-G)-GDP complex and preventing its dissociation [6]. It should be noted that eukaryotes also contain several other elongation factors (EF-2), which, however, are not inhibited by FA [7,8].…”

“…properties [14]. Synthesis of FA N-substituted analogues was shown to be a promising strategy to obtain active molecules with antimicrobial properties, which not only possess high affinity to EF-G, but also impart additional properties [8,[15][16][17]. In particular, it has recently been shown that spermidine and spermine-conjugated FA derivatives are able to be immersed in lipid membranes and exhibit a detergent action.…”

“…In this work, we evaluated the membranotropic properties of FA and its two nitrogencontaining derivatives, dioxime (1) and amine (2), which we synthesized previously [18,24] (Figure 1), using a model of dipalmitoylphosphatidylcholine (DPPC) and lecithin liposomes that was similar in composition to eukaryotic lipid membranes. Dioxime (compound 1) showed antibacterial activity towards Gram-positive S. aureus (MRSA) with MIC 4.0 µg/mL and cytotoxicity levels similar to those of FA [18], whereas compound 2 showed neither antimicrobial nor antitumor activity [8,25]. Considering the important role of mitochondria in the biological effects of terpenoids, we also evaluated the effects of the tested compounds on major functional parameters of these organelles: (1) the effect of the compounds on the state of the inner mitochondrial membrane and its permeability; (2) membrane potential;…”