Activity of isoflavans of Dalea aurea (Fabaceae) against the opportunistic ameba Naegleria fowleri

Abstract One new and one known isoflavan, 3S(+)-7-methoxymanuifolin K (1) and manuifolin K (2), respectively, were isolated from methanolic extracts of DALEA AUREA (Fabaceae). Isoflavans 1 and 2 exhibited significant IN VITRO activity against the ameba NAEGLERIA FOWLERI, an organism responsible for an infrequent but rapidly fatal form of primary amebic meningoencephalitis (PAM). At concentrations of 30 μM, both 1 and 2 caused growth inhibition of N. FOWLERI at a level comparable to amphotericin B (at 0.1 μM), the currently preferred treatment for this disease. Over a seven-day growth period, 1 and 2 (30 μM) exhibited superior growth inhibition of N. FOWLERI than amphotericin B after day 4. Isoflavan 2 was evaluated in a mouse model of PAM at a dose of 25 mg/kg/day for five days. While amphotericin B (2.5 mg/kg/day) offered 12.5 % protection of the mice, compound 2 did not protect the mice from PAM infection compared to controls.