Bioisosteric modification on benzylidene-carbonyl compounds improved the drug-likeness and maintained the antifungal activity against Sporothrix brasiliensis.

Considering the emergence of antifungal resistance on Sporothrix brasiliensis, we aimed to assess new benzylidene-carbonyl compounds against feline-borne S. brasiliensis isolates. The compounds were designed as bioisosteres from previously reported benzylidene-ketones generating the p-coumaric (1), cinnamic (2), p-methoxycinnamic (3) and caffeic acid (4) analogues. The corresponding compounds were tested against feline isolates of S. brasiliensis with sensitivity (n = 4) and resistance (n = 5) to itraconazole (ITZ), following the M38-A2 protocol (CLSI, Reference method for broth dilution antifungal susceptibility testing of filamentous fungi M38-A2 Guideline, 2008). Eleven analogues showed activity against all fungal strains with minimum inhibitory concentrations (MIC) ≤1 mg/ml (1a-d, 2e, 3b, 3e, 4, 4a and 5e) and fungicidal concentrations (MFC) ≤1 mg/ml (1b, 1d, 3e and 4a), whereas 3 was the less active with both MIC and MFC values above 1 mg/ml. Compound 3e (4-methoxy-N-butylcinnamamide) was the most potent (MIC 0.08-0.16 mg/ml; MFC 0.32-0.64 mg/ml) from the set, suggesting a different role of the substituents in ester and amide derivatives. The designed compounds proved to be important prototypes with improved drug-likeness to achieve compounds with higher activity against ITZ-resistant S. brasiliensis.