Oncibauerins A and B, new flavanones from Oncidium baueri (Orchidaceae)

- Two new and thirteen known compounds were obtained from Oncidium baueri.
- The new structures were determined by 1D and 2D NMR spectroscopy and HRMS.
- Compounds 11, 13 and 14 exhibited moderate cytotoxicity against seven cancer cell lines.

The phytochemical study of Oncidium baueri (Orchidaceae) afforded two new compounds (1 and 2), along with thirteen known structures (3-15). The chemical structures were established on the basis of spectral evidence and the new compounds, obtained as a mixture of two glycosylated flavanones were assigned by comprehensive spectroscopic analysis by 1D and 2D NMR spectroscopy and HRMS. Moreover, the cytotoxic activity of the crude extract (EBOB), semi-purified fractions (HEOB, CLOB, ACOB, BUOB and HMOB) and some isolated metabolites against ten human cancer cell lines (U251, UACC-62, MCF-7, NCI-ADR/RES, 786-0, NCI-H460, PC-3, OVCAR-3, HT29, K562) and the antiprotozoal activity against Trypanosoma cruzi and Leishmania amazonensis were evaluated. The CLOB fraction showed the best antitrypanosomal and antileishmanial activities, as well as considerable cytotoxicity against cancer cell lines UACC-62 (melanoma) and K562 (leukemia) with GI50 values of 6.83 μg/mL and 0.5 μg/mL, respectively. Furthermore, BUOB and HMOB fractions showed selectivity for UACC-62 (melanoma) with GI50 < 0.01 μg/mL and the compounds 11, 13 and 14 had inhibited cell growth of almost cancer cell lines tested with GI50 values close to 30 μg/mL.

This work is the first phytochemical study conducted with Amazonian orchid Oncidium baueri focused on contributing to a better knowledge of Brazilian biodiversity applied to the discovery of new bioactive compounds against cancer, Chagas disease and leishmaniasis.