Introduction: Chromoblastomycosis is a subcutaneous mycosis whose main etiologic agent is the dematiaceous fungus Fonsecaea pedrosoi. Drug treatment includes antifungals such as itraconazole, fluconazole and amphotericin B, either applied systemically or topically, combined or not. Some cases are refractory to treatment with these antifungals, and this has encouraged the search for new drugs with fungistatic and/or fungicidal properties. Objective: The aim of the present paper was to investigate the development of a protocol for the assessment of the quantitative relationship between antifungal structure and activity of phenol and salicylic acid derivatives against Fonsecaea pedrosoi ATCC 46428. Material and Methods: Derivatives of 4-substituted (F-X) phenols and 5-substituted (A-X) salicylic acids with X = H, NO2, NH2, NHAc and OH were obtained through organic synthesis, or commercially acquired. The antifungal activity was determined by microdilution in Sabouraud broth with 1% of yeast extract (SBD-DOX) using a sample of Fonsecaea pedrosoi ATCC 46428. Tubes containing SBD-DOX broth (4.5mL) received 0.05mL of 3.2x10-1 solutions of drugs in dimethyl sulfoxide at 1.25x10-3M (serial dilution at half) and 0.45mL of fungal cell suspension standardized with an absorbance of 0.1 at 550nm. The tubes were incubated at 30¨¬C for 72 hours, and optical density was read before and after centrifugation at 550nm. The curves for biological activity were compared with the following physical and chemical parameters: hydrophobic (log P, Rmw, and ¥•), electronic (¥ëmsx(ultraviolet/visible), ¥í-OH (infrared) and ¥òp), and steric (STERIMOL-B5 and MR). A multivariate exploratory analysis was performed with Pirouette 2.7 software. Results: All of the 10 drugs showed antifungal activity. The curves revealed fluctuations with higher discriminatory power for drugs at concentrations 2.0x10-2 and 1.25x10-3M. Phenols showed a different antifungal activity from that of homologous salicylic acids. The chromatographic parameters Rmw, log P, and ¥• did not show covariance. Electronic parameters ¥òp and UV absorbances showed covariance, whereas infrared absorbances yielded combined results. We were able to determine the power of the drugs in terms of electronic and hydrophobic parameters based upon their class and substituent; in phenols the derivative with nitro substituent was more powerful, while the derivative with X=NH2 was more powerful in the case of salicylic acids. Conclusion: The power of the analyzed homologous series may be explained by considering the association between electronic, steric and hydrophobic factors between substituents and the OH group common to all drugs, which alters the acidity of this group and interferes with fungal growth. Our conclusion is that the position used for structural variation is significant in such a way that it influences biological activity and has to be maintained for the increase of structural complexity.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)