Susana Zacchino

In Vitro Antifungal Evaluation and Structure-Activity Relationships of a New Series of Chalcone Derivatives and Synthetic Analogues, with Inhibitory Properties Against Polymers of the Fungal Cell Wall

Here we report the synthesis, in vitro antifungal evaluation and SAR study of 41 chalcones and analogues. In addition, all active structures were tested for their capacity of inhibiting Saccharomyces cerevisiae beta(1,3)-glucan synthase and chitin synthase, enzymes that catalyze the synthesis of the major polymers of the fungal cell wall.

In vitro antifungal activity of new series of homoallylamines and related compounds with inhibitory properties of the synthesis of fungal cell wall polymers

The synthesis, in vitro antifungal evaluation and SAR studies of 101 compounds of the 4-aryl-, 4-alkyl-, 4-pyridyl or -quinolinyl-4-N-arylamino-1-butenes series and related compounds, are reported here. Active structures showed to inhibit (1,3)-beta-D-glucan and mainly chitin synthases, enzymes that catalyze the synthesis of the major fungal cell wall polymers.

Inhibitors of the fungal cell wall. Synthesis of 4-aryl-4-N-arylamine-1-butenes and related compounds with inhibitory activities on β(1-3) glucan and chitin synthases

As part of our project devoted to the search for antifungal agents, which act via a selective mode of action, we synthesized a series of new 4-aryl- or 4-alkyl-N-arylamine-1-butenes and transformed some of them into 2-substituted 4-methyl-tetrahydroquinolines and quinolines by using a novel three-step synthesis. Results obtained in agar dilution assays have shown that 4-aryl homoallylamines not possessing halogen in their structures, tetrahydroquinolines and quinolines, display a range of antifungal properties in particular against Epidermophyton floccosum and Microsporum canis. Regarding the mode of action, all active compounds showed in vitro inhibitory activities against beta(1-3) glucan-synthase and mainly against chitin-synthase. These enzymes catalyze the synthesis of beta(1-3) glucan and chitin, respectively, major polymers of the fungal cell wall. Since fungal but not mammalian cells are encased in a cell wall, its inhibition may represent a useful mode of action for these antifungal compounds.

Value of the ethnomedical information for the discovery of plants with antifungal properties. A survey among seven Latin American countries.

ETHNOPHARMACOLOGICAL RELEVANCE This study reports the antifungal evaluation of 327 plant species (92 families and 251 genera) from seven Latin American countries which were selected on the basis of their reported ethnomedical uses and compared them with plants selected at random. AIM OF THE STUDY (a) The main aim of this study was to investigate whether the probability of detecting antifungal plants is higher when plants have reports of ethnopharmacological uses related to fungal infections (PAU group) than when they are selected at random (PNAU group). (b) The second objective was to determine, within the PAU group, whether the probability of obtaining a positive result will be higher when the plants are tested against dermatophytes, than against yeasts or Aspergillus spp. (c) The third goal was to investigate, within all MICs<or=1000 microg/mL, if the MICs displayed by the PAU group are comparatively lower than MIC values of the PNAU group; that is to say, if they can be expected more potent antifungal plants within the group of plants that have a history of traditional use related to fungal infections than when they do not have one. MATERIALS AND METHODS A five-stage process of documentation, evaluation and analysis of results was conducted: (1) selection of words that could describe the ethnopharmacological use related to fungal infections; (2) a survey of specialized literature in each country; (3) collection and preparation of an extract of each plant; (4) antifungal evaluation of the selected plants and (5) statistical analysis of the results. For the antifungal evaluation, the microbroth dilution assay recommended by the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) was used against a panel of eleven human opportunistic and pathogenic fungi. For the statistical analysis the Pearsons Chi Square test and the Scores test were used. RESULTS (a) A significantly higher probability of detecting plants with antifungal activity against at least one fungus was found within the PAU (40.3%) than the PNAU group (21.3%) (p<0.01). (b) A similar higher probability than in (a) (39.6% vs. 20.8%) was found when plants were tested against dermatophytes (p<0.01) but not against yeasts or Aspergillus spp. (p>0.05). (c) Within the detected antifungal plants from both groups, plants of the PAU group displayed higher activities (lower MICs) than those of PNAU group against dermatophytes (p<0.05) but not against yeasts or Aspergillus spp. CONCLUSIONS Considering that dermatophytes are the cause of superficial fungal infections, which can be easily detected and followed by traditional healers, our findings suggest that the ethnopharmacological approach is useful in guiding the detection of antifungal plants in Latin America mainly for infections in which the pathological expression is obvious and, therefore, the cure can be clearly observed.

Evidence for the Mechanism of Action of the Antifungal Phytolaccoside B Isolated from Phytolacca tetramera Hauman

Phytolaccoside B (1), an antifungal monodesmoside triterpenoid glycoside isolated from berries of Phytolacca tetramera Hauman (Phytolaccaceae), alters the morphology of yeasts and molds. The malformations were similar to those produced by enfumafungin, a known inhibitor of (1-->3)-beta-D-glucan synthase, an enzyme that catalyzes the synthesis of (1-->3)-beta-D-glucan, one of the major polymers of the fungal cell wall. However, enzymatic assays revealed that 1 did not inhibit (1-->3)-beta-D-glucan synthase, but it did produce a notable enhancement of the chitin synthase 1 activity and, concomitantly, a rise in chitin, another important polymer of the fungal cell walls. This finding was corroborated by fluorescence microscopy and also by quantification of the chitin. In addition, a 2-fold increase in the thickness of the fungal cell wall was observed with transmission electronic microscopy. On the other hand, 1 neither bound to ergosterol nor caused hemolysis of red blood cells, although some fungal membrane damage was observed at the MIC of 1.

Constituents of the Argentinian medicinal plant Baccharis grisebachii and their antimicrobial activity.

The resinous exudate of Baccharis grisebachii which is used to treat ulcers, burns, and skin sores in Argentina showed activity towards dermatophytes and bacteria. Two diterpenes, eight p-coumaric acid derivatives, and two flavones were isolated from the exudate and the structures elucidated by spectroscopic methods. 3-Prenyl-p-coumaric acid and 3,5-diprenyl-p-coumaric acid were active towards Epidermophyton floccosum and Trichophyton rubrum with MICs of 50 and 100-125 microg/ml, respectively. The diterpene labda-7,13E-dien-2beta,15-diol was active towards Epidermophyton floccosum and Trichophyton rubrum with MICs of 12.5 microg/ml while the MIC against Microsporum canis and Trichophyton mentagrophytes was 25 microg/ml. The diterpene was also active towards Microsporum gypseum with a MIC of 50 microg/ml, and showed inhibition in both Staphylococcus aureus (methicilline resistant and sensible strains) with MICs of 125 microg/ml. The results support the use of Baccharis grisebachii in Argentinian traditional medicine.

Composition and biological activity of the essential oil from leaves of Plinia cerrocampanensis, a new source of α-bisabolol.

The essential oil from fresh leaves of Plinia cerrocampanensis Barrie (Myrtaceae), obtained by hydrodistillation, was analysed by GC-FID and GC-MS. Forty components, representing more than 91% of the oil, were identified. Oxygenated sesquiterpenes represented the main fraction with alpha-bisabolol (42.8%) as the major constituent, making this plant a new and good source of this substance. Biological activity of the essential oil was evaluated against several bacterial and fungal strains as well as larvae from Aedes aegypti. The highest activity was found against Staphylococcus aureus, Pseudomonas aeruginosa, Microsporum gypseum, Trichophyton mentagrophytes and Trichophyton rubrum with MIC values from 32 to 125 microg/ml. The essential oil also showed potent inhibitory and bactericidal activities against three H. pylori strains, with MIC and MBC values of 62.5 microg/ml, and caused 100% mortality of A. aegypti larvae at a concentration of 500 microg/ml.

Antimicrobial activity of plants used in traditional medicine of San Juan province, Argentine

Eighteen extracts from Acaena magellanica, Baccharis grisebachii, Ephedra breana, Oxalis erythrorhiza, Pachylaena atriplicifolia and Satureja parvifolia were assessed for antimicrobial activity against bacteria and fungi with the agar dilution method. The hexane (H) and dichloromethane (DCM) extracts of B. grisebachii and O. erythrorhiza showed the broadest spectrum of action against fungi, inhibiting all of the tested dermatophytes with MICs ranging from < or =25 to < or =1000 microg/ml. Trichophyton rubrum was the most susceptible species and Cryptococcus neoformans was inhibited only by the DCM extract of B. grisebachii with MIC of 600 microg/ml. Regarding the antibacterial activity, H and DCM extracts of B. grisebachii as well as the DCM of O. erythrorhiza, were active on methicillin-resistant and methicillin-sensitive Staphylococcus aureus with MIC from < or =125 to < or =500 microg/ml. The DCM extract of B. grisebacchii was more active against methicillin-resistant than methicillin-sensitive strains.

In vitro antifungal activity of polyfunctionalized 2-(hetero)arylquinolines prepared through imino Diels-Alder reactions.

Diverse polyfunctionalized quinolines, easily prepared using Lewis acid-catalyzed imino Diels-Alder reactions between corresponding aldimines, were tested for antifungal properties against standardized as well as clinical isolates of clinically important fungi. Among them, 4-pyridyl derivatives displayed the best activities mainly against dermatophytes. The activity appears not to be related neither to the lipophilicity nor to the basicity of compounds.

Chemically engineered extracts as an alternative source of bioactive natural product-like compounds

The access to libraries of molecules with interesting biomolecular properties is a limiting step in the drug discovery process. By virtue of a long molecular evolution process, natural products are recognized as biologically validated starting points in structural space for library development. We introduce here a strategy to generate natural product-like libraries. A semisynthetic mixture of compounds was produced by diversification of a natural product extract through the chemical transformation of common chemical functionalities in natural products into chemical functionalities rarely found in nature. The resulting mixture showed antifungal activity against Candida albicans, whereas the starting extract did not show such activity. Bioguided fractionation led to the isolation of a previously undescribed active semisynthetic pyrazole. The result illustrates how biological activity can be generated by designed chemical diversification of a natural product mixture, and represents the proof of principle of an alternative strategy for producing natural product-like libraries from natural products libraries.