Methyl and p-Bromobenzyl Esters of Hydrogenated Kaurenoic Acid for Controlling Anthracnose in Common Bean Plants

Kaurenoic acid derivatives were prepared and submitted to in vitro assays with the fungus Colletotrichum lindemuthianum, which causes anthracnose disease in the common bean. The most active substances were found to be methyl and p-bromobenzylesters, 7 and 9, respectively, of the hydrogenated kaurenoic acid, which presented a minimum inhibitory concentration (MIC) of 0.097 and 0.131 mM, respectively, while the commercial fungicide methyl thiophanate (MT) presented a MIC of 0.143 mM. Substances 7 (1.401 mM) and 9 (1.886 mM) reduced the severity of anthracnose in common bean to values statistically comparable to MT (2.044 mM). According to an in silico study, both compounds 7 and 9 are inhibitors of the ketosteroid isomerase (KSI) enzyme produced by other organisms, the amino acid sequence of which could be detected in fungal genomes. These substances appeared to act against C. lindemuthianum by inhibiting its KSI. Therefore, substances 7 and 9 are promising for the development of new fungicides.

Action mechanism for 3β-hydroxykaurenoic acid and 4,4-dimethylanthracene-1,9,10(4H)-trione on Botrytis cinerea

The mechanism of action of the diterpenoid 3β-hydroxykaurenoic acid and the anthraquinone 4,4-dimethylanthracene-1,9,10(4H)-trione on the phytopathogenic fungus Botrytis cinerea was studied. The effect of both compounds on the respiratory process and on the membrane integrity of B. cinerea was evaluated. The results showed that 3β-hydroxykaurenoic acid inhibited the growth of this fungus by disrupting the plasmatic membrane. This compound also partially affected oxygen consumption of B. cinerea germinating conidia. Conversely, 4,4-dimethylanthracene-1,9,10(4H)-trione did not produce membrane disruption of B. cinerea. The effect of this compound on mycelial growth was notably increased by the presence of an inhibitor of the cyanide-resistant respiration pathway. It also was shown that the anthraquinone inhibited oxygen consumption by about 80%; therefore this compound would act as a potent inhibitor of the cytochrome pathway of the respiratory chain to exert its antifungal effect.