Anti-leishmania activity of isochromenes from an unidentified endophytic fungus isolated from Spermacoce verticillata L.

Endophytes could be defined as microorganisms (fungi or bacteria) that can be detected at a given moment within the tissues of an apparently healthy host plant. The metabolic interactions of an endophyte with its host may also favour the biosynthesis of different bioactive natural products that includes polyketides, shikimate derivatives, terpenes, as well as steroids, alkaloids, and peptides. In fact, a huge number of bioactive compounds has been isolated from endophytes [1,2]. The aim of the present work was to isolate and identify bioactive secondary metabolites from an endophytic fungus strain isolated from the medicinal plant Spermacoce verticillata L. (Rubiaceae), native to South America. The fungus was grown in solid medium for 30 days at 30 °C. The ethanol crude extract of the culture was submitted to different chromatographic methods to afford austidiol (1) and a novel natural product, austidiol dimer (2). The structures of the compounds were elucidated by NMR spectroscopy (¹H, ¹³C, HMQC, HMBC and COSY) and HRMS data. Also austidiol diacetate (3) was obtained by austidiol acetylation [Fig.1]. These compounds were tested for anti-leishmania activity in vitro against Leishmania major to determine the lethal dose (LD₅₀). Compounds 1-3 displayed promising LD₅₀ results: 0.52, 0.13 and 0.28µM, respectively, in comparison with the positive control geneticin (G418) (LD₅₀ 3.43µM). Therefore, it is suggested that the isochromenes isolated could be used as lead compounds for the development of new anti-leishmania agents.

Fig.1

Acknowledgements: Capes, CNPq and FAPESP, INCT-INBEQUIMeDI.

References: 1. Gunatilaka, A.A.L. (2006). J. Nat. Prod. 69, 509–526.

2. Borges, W.S., Borges, K.B., Bonato, P.S., Said, S., Pupo, M.T. (2009) Curr. Org. Chem. 13, 1137–1163.