Antimicrobial compounds isolated from Tropaeolum tuberosum.

Activity-guided fractionations of black tubers of Tropaeolum tuberosum led to the isolation of 3-[3-(3-pyridinyl)-1,2,4-oxadiazol-5-yl] benzonitrile (1) and [3,5-Bis (1,1-dimethylethyl)-4-hydroxyphenyl] ethenylidene] bis-phosphonic acid tetraethyl ester (2). Compounds 1 and 2 showed an antibacterial effect against almost all the strains assayed, especially compound 2, showing the same inhibition potential for Enterococcus faecalis and Salmonella enteritidis as the ampicillin (MIC = 1.5 μM) and a better potential than chloramphenicol which has a MIC of 3.5 μM. In addition, compounds 1 and 2 showed a relevant antifungal inhibition against Candida tropicalis with MICs of 100 μM and 50 μM, and against Saccharomyces kudriavzevii with MICs of 25 μM and 1.5 μM. This is in comparison to fluconazole which had MICs of 150 μM (against Candida tropicalis) and 3.5 μM (against Saccharomyces kudriavzevii). This is the first time that compounds 1 and 2 are reported as showing antimicrobial activities.