Mechanism of the lethal effect of Riparin E against bacterial and yeast strains

Two-Step Flow Amidation of Natural Phenolic Acids as Antiradical and Antimicrobial Agents

Natural hydroxycinnamic acid amides (HCAAs) and riparins offer significant health benefits. However, their extraction from natural sources is difficult, and traditional synthetic methods remain wasteful, raising the need for more efficient alternatives. In this work, a two-step chemo-enzymatic flow method for the efficient esterification and amidation of phenolic acids was developed and successfully applied to the synthesis of riparin derivatives and HCAAs. The flow Fischer esterification was optimized using vanillic acid as a model starting material and SiliaBond Tosic Acid (SCX-3) as an immobilized acid catalyst, achieving a quantitative yield in a short residence time. The following amidation step, catalyzed by immobilized Candida antarctica lipase B, was optimized in toluene, leading to the desired amides. The synthesized compounds were evaluated for their radical scavenging, antibacterial, and antileishmanial properties. Overall, this work disclosed a novel approach for the efficient synthesis of riparin derivatives and HCAAs with interesting biological properties.

Inhibition of the morphological transition of Candida spp. by riparins I-IV

Candida spp. is an opportunistic pathogen capable of causing superficial to invasive infections. Morphological transition is one of the main virulence factors of this genus and, therefore, is an important variable to be considered in pharmacological interventions. Riparins I, II, III, and IV are alkamide-type alkaloids extracted from the unripe fruit of Aniba riparia, whose remarkable pharmacological properties were previously demonstrated. This work aimed to evaluate in silico and in vitro the inhibitory effects of Riparins on the morphological transition of Candida albicans, Candida tropicalis, and Candida krusei. Molecular docking was applied to analyze the inhibitory effects of riparins against proteins such as N-acetylglucosamine, CYP-51, and protein kinase A (PKA) using the Ramachandran plot. The ligands were prepared by MarvinSketch and Spartan software version 14.0, and MolDock Score and Rerank Score were used to analyze the affinity of the compounds. In vitro analyses were performed by culturing the strains in humid chambers in the presence of riparins or fluconazole (FCZ). The morphology was observed through optical microscopy, and the size of the hyphae was determined using the ToupView software. In silico analysis demonstrated that all riparins are likely to interact with the molecular targets: GlcNAc (>50%), PKA (>60%), and CYP-51 (>70%). Accordingly, in vitro analysis showed that these compounds significantly inhibited the morphological transition of all Candida strains. In conclusion, this study demonstrated that riparins inhibit Candida morphological transition and, therefore, can be used to overcome the pathogenicity of this genus.

Discovery and Optimization of Novel SaFabI Inhibitors as Specific Therapeutic Agents for MRSA Infection

As the rate-limiting enzyme in fatty acid biosynthesis, Staphylococcus aureus enoyl-acyl carrier protein reductase (SaFabI) emerges as a compelling target for combating methicillin-resistant S. aureus (MRSA) infections. Herein, compound 1, featuring a 4-(1H-benzo[d]imidazol-2-yl)pyrrolidin-2-one scaffold, was identified as a potent SaFabI inhibitor (IC50 = 976.8 nM) from an in-house library. Subsequent optimization yielded compound n31, with improved inhibitory efficacy on enzymatic activity (IC50 = 174.2 nM) and selective potency against S. aureus (MIC = 1-2 μg/mL). Mechanistically, n31 directly inhibited SaFabI in cellular contexts. Moreover, n31 exhibited favorable safety and pharmacokinetic profiles, and dose-dependently treated MRSA-induced skin infections, outperforming the approved drug, linezolid. The chiral separation of n31 resulted in (S)-n31, with superior activities (IC50 = 94.0 nM, MIC = 0.25-1 μg/mL) and in vivo therapeutic efficacy. In brief, our research proposes (S)-n31 as a promising candidate for SaFabI-targeted therapy, offering specific anti-S. aureus efficacy and potential for further development.