@article{peres_nagem_1997,  title={Naturally occurring pentaoxygenated, hexaoxygenated and dimeric xanthones: a literature survey},  volume={20},  ISSN={0100-4042},  url={https://doi.org/10.1590/S0100-40421997000400009},  DOI={10.1590/S0100-40421997000400009},  number={4},  journal={Química Nova},  publisher={Sociedade Brasileira de Química},  author={Peres, V. and Nagem, T. J.},  year={1997},  month={Jul},  pages={388–397} }