Triterpenes and phenolic compounds isolated from the aerial parts of Herissantia tiubae and evaluation of 5,4′,-dihydroxy-3,6,7,8,3′-pentamethoxyflavone as a modulator of bacterial drug resistance

In our continuous study of the Malvaceae family, we describe here the isolation of four triterpenes (frideline, lupeol, cycloartenol, and cycloeucalenol), a steroid (β-sitosterol), and four phenolic compounds from the aerial parts of Herissantia tiubae (K. Schum.) Brizicky (i.e., a benzoic acid derivative, a coumarin and two flavonoids, kaempferol 7-O-α-l-rhamnopyranoside and 4′,5-dihydroxy-3,6,7,8,3′-pentamethoxyflavone). The structural identification of the compounds was made by comparison with literature data and spectral analysis, including two-dimensional NMR techniques. These compounds are reported here for the first time in genus Herissantia. The pentamethoxyflavone was assayed against strains of Staphylococcus aureus possessing efflux mechanisms of resistance to norfloxacin, tetracycline, and erythromycin. Although the compound did not display relevant antibacterial activity (MIC ≥ 512 μg/mL), it modulated the activity of antibiotics, i.e., in combination with antibiotics (at 128 μg/mL), a two-fol...