Chemical profile and antifungal potential of Avicennia schaueriana Stapf & Leech. from two places of occurrence, and identification of active compounds

Abstract

In our search for antifungal extracts from Brazilian plants, stems of Avicennia schaueriana (Acanthaceae), a mangrove plant without records on phytochemical studies, was pursued. The aim of this work was to compare the chemical profile of A. schaueriana collected in two mangroves in the state of São Paulo, regarding the identification of compounds responsible for the antifungal activity. Stems of A. schaueriana collected at Ilha do Cardoso (IC) and Itanhaém (ITA) were extracted with ethanol, and partitioned with petroleum ether (PE) and chloroform (CHCl3). The antifungal activity was evaluated by bioautography with Cladosporium sphaerospermum, C. cladosporioides and Colletotrichum lagenarium and by agar dilution method with Colletotrichum gloeosporioides. The minimum inhibitory concentration (MIC) was determined with C. gloeosporioides and C. sphaerospermum. The fractions were purified by preparative TLC and their compounds identified by GC-MS analysis. Extracts of A. schaueriana IC were more active compared with extracts of A. schaueriana ITA, with 85.5% and 30.7% inhibition of C. gloeosporioides, respectively. Fractions of IC in PE and CHCl3, both showed inhibition of 62% and MIC of 1 mg/ml, while fractions of ITA in PE and CHCl3 showed 12% and 33.3% of inhibition and MIC of 6 mg/ml and 1.5 mg/ml respectively. Twenty four compounds were identified in the purified fractions, among them methyl ester of palmitic acid, present in all samples (0.52% to 9.18%), lapachol and avicequinone-B in PE-IC fractions (2.22%; 7.13%), naphtho[2,3-b]furan-4,9-dione, 2-isopropyl (28.57% PE-IC; 81.21% CHCl3-IC; 27.01% CHCl3-ITA), 2-isopropenylnaphtho[2,3-b]furan-4,9-quinone (7.32% PE-IC; 8.03% CHCl3-IC), avicenol-C (20.61% PE-IC; 7.56% CHCl3-IC; 56.47% CHCl3-ITA), and lupeol (61.06% PE-IC; 23.97% PE-ITA). The greatest antifungal potential of IC can probably be related to their higher proportion of naphthoquinones compared to ITA.