Synthesis and evaluation of aromatic methoxime derivatives against five postharvest phytopathogenic fungi of fruits. Main structure-activity relationships.

The antifungal activity of a library of twenty-four aromatic methoximes was examined against five representative postharvest phytopathogenic fungi. The panel included Penicillium digitatum, Penicillium italicum, Rhizopus stolonifer, Botrytis cinerea and Monilinia fructicola, all of which cause relevant economic losses worldwide as a result of affecting harvested fruits. The minimum inhibitory concentrations and minimum fungicidal concentrations of each compound were defined and the main structure-activity relationships were determined. Although other congeners were more potent, drug likeliness considerations pointed to the methoxime derived from 2,4-dihydroxypropiophenone as the compound with the most suitable profile. The morphology of the colonies of the fungal strains treated with the methoxime was examined microscopically and the compound was also tested in freshly harvested peaches and oranges, exhibiting promising control profiles in both fruits, similar to those of the commercial agents Imazalil and Carbendazim.

Zanthosimuline and Related Pyranoquinolines as Antifungal Agents for Postharvest Fruit Disease Control.

The natural product zanthosimuline and its 18 analogues were easily prepared from simple starting materials and evaluated in vitro against postharvest fruit fungal pathogens. The panel included Penicillium digitatum, Botrytis cinerea, Monilinia fructicola, and Rhizopus stolonifer; all of them causing relevant economic losses worldwide. The minimum inhibitory concentrations and minimum fungicidal concentrations of each compound were determined, and the main structure-activity relationships were established. The biological activity observed was strongly increased by maintaining the prenyl side chain of zanthosimuline in an N-demethylated derivative. In addition, the compound that is the most active in the in vitro evaluation was tested in freshly harvested peaches exhibiting a promising brown rot control profile, comparable to the commercial agent carbendazim but demonstrating less toxicity against human liver cell lines.

Activity of the pterophyllins 2 and 4 against postharvest fruit pathogenic fungi. Comparison with a synthetic analog and related intermediates.

The antifungal activity of pterophyllin 2, pterophyllin 4, a 5-desmethyl analog of the latter and some of their synthetic intermediates, against three postharvest phytopathogenic fungi, was evaluated. The target fungi were Rhizopus stolonifer, Botrytis cinerea and Monilinia fructicola, which affect fruits worldwide, causing important economic losses. The tests were carried out with imazalil and carbendazim as positive controls. Minimum inhibitory concentrations and minimum fungicidal concentrations were determined, and the morphology of the colonies was examined microscopically. In liquid medium, it was found that pterophyllin 4 exhibited selective fungicidal activity toward M. fructicola, whereas its congener pterophyllin 2 proved to be less potent and not selective and the 5-desmethyl analog of pterophyllin 4 displayed a different activity profile. Morphological changes were observed in the colonies exposed to pterophyllin 4. The results highlighted the importance of small structural features for the antifungal behavior and also suggested that, in Nature, the pterophyllins may act as plant defenses against pathogens.

Efficient production of the flavoring agent zingerone and of both (R)- and (S)-zingerols via green fungal biocatalysis. Comparative antifungal activities between enantiomers.

Zingerone (1) and both chiral forms of zingerol (2) were obtained from dehydrozingerone (3) by biotransformation with filamentous fungi. The bioconversion of 3 with A. fumigatus, G. candidum or R. oryzae allowed the production of 1 as the sole product at 8 h and in 81%-90% at 72 h. In turn, A. flavus, A. niger, C. echinulata, M. circinelloides and P. citrinum produced 1 at 8 h, but at 72 h alcohol 2 was obtained as the major product (74%-99%). Among them, A. niger and M. circinelloides led to the anti-Prelog zingerol (R)-2 in only one step with high conversion rates and ee. Instead, C. echinulata and P. citrinum allowed to obtain (S)-2 in only one step, with high conversion rates and ee. Both chiral forms of 2 were tested for antifungal properties against a panel of clinically important fungi, showing that (R)-, but not (S)-2 possessed antifungal activity.

Antifungal activity of eugenol analogues. Influence of different substituents and studies on mechanism of action.

Twenty one phenylpropanoids (including eugenol and safrole) and synthetic analogues, thirteen of them new compounds, were evaluated for antifungal properties, first with non-targeted assays against a panel of human opportunistic pathogenic fungi. Some structure-activity relationships could be observed, mainly related to the influence of an allyl substituent at C-4, an OH group at C-1 and an OCH(3) at C-2 or the presence of one or two NO(2) groups in different positions of the benzene ring. All active compounds were tested in a second panel of clinical isolates of C. albicans and non-albicans Candida spp., Cryptococcus neoformans and dermatophytes. The eugenol derivative 4-allyl-2-methoxy-5-nitrophenol (2) was the most active structure against all strains tested, and therefore it was submitted to targeted assays. These studies showed that the antifungal activity of 2 was not reversed in the presence of an osmotic support such as sorbitol, suggesting that it does not act by inhibiting the fungal cell wall synthesis or assembly. On the other hand, the Ergosterol Assay showed that 2 did not bind to the main sterol of the fungal membrane up to 250 µg mL-1. In contrast, a 22% of fungal membrane damage was observed at concentrations = 1 × MIC and 71% at 4× MIC, when 2 was tested in the Cellular Leakage assay. The comparison of log P and MICs for all compounds revealed that the antifungal activity of the eugenol analogues would not to be related to lipophilicity.

Antifungal activity of saponin-rich extracts of Phytolacca dioica and of the sapogenins obtained through hydrolysis.

A saponin-rich extract of Phytolacca dioica L. berries, its acid hydrolysate, and its major aglycone, phytolaccagenin, were assayed for antifungal activity against ATCC standard cultures of Candida albicans and Cryptococcus neoformans, and against clinical isolates of these fungi. The activity of the extract was either low or negligible, but the hydrolysate, containing the sapogenins, including phytolaccagenin, and also pure phytolaccagenin, showed promising antifungal potency. Hydrolysis of a natural product extract is shown to be a useful modification leading to improved bioactivity.