Specimens of the red alga Bostrychia tenella J. Agardh (Rhodomelaceae, Ceramiales) were collected from the São Paulo coast and submitted to room temperature solvent extraction. The resulting extract was fractionated by partitioning with organic solvent. The n-hexane (BT-H) and dichloromethane (BT-D) fractions showed antiprotozoal potential in biological tests with Trypanosoma cruzi and Leishmania amazonensis and presented high activity in an antifungal assay with the phytopathogenic fungi Cladosporium cladosporioides and Cladosporium sphaerospermum. Chromatography methods were used to generate subfractions from BT-H (H01 to H11) and from BT-D (D01 to D19). The subfractions were analyzed by gas chromatography-mass spectrometry (GC/MS), and the substances were identified by retention index (Kovats) and by comparison to databases of commercial mass spectra. The volatile compounds found in marine algae were identified as fatty acids, low molecular mass hydrocarbons, esters and steroids; some of these have been previously described in the literature based on other biological activities. Moreover, uncommon substances, such as neophytadiene were also identified. In a trypanocidal assay, fractions BT-H and BT-D showed IC(50) values of 16.8 and 19.1 microg/mL, respectively, and were more active than the gentian violet standard (31 microg/mL); subfractions H02, H03, D01 and D02 were active against L. amasonensis, exhibiting IC(50) values of 1.5, 2.7, 4.4, and 4.3 microg/mL, respectively (standard amphotericin B: IC(50)=13 microg/mL). All fractions showed antifungal potential. This work reports the biological activity and identification of compounds by GC/MS for the marine red alga B. tenella for the first time.
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