| Summary: | The hydroalcoholic extract of the steam bark of <em>B. fagaroides</em> var. <em>fagaroides</em> displayed potent cytotoxic activity against four cancer cell lines, namely KB (ED<sub>50</sub> = 9.6 × 10<sup>−2</sup> μg/mL), PC-3 (ED<sub>50</sub> = 2.5 × 10<sup>−1</sup> μg/mL), MCF-7 (ED<sub>50</sub> = 6.6 μg/mL), and HF-6 (ED<sub>50</sub> = 7.1 × 10<sup>−3</sup> μg/mL). This extract also showed anti-tumour activity when assayed on mice inoculated with L5178Y lymphoma cells. Bioactivity-directed isolation of this extract, afforded seven podophyllotoxin-type lignans identified as podophyllotoxin (<strong>1</strong>), β-peltatin-A-methylether (<strong>2</strong>), 5′-desmethoxy-β-peltatin-A-methylether (<strong>3</strong>), desmethoxy-yatein (<strong>4</strong>), desoxypodophyllotoxin (<strong>5</strong>), burseranin (<strong>6</strong>), and acetyl podophyllotoxin (<strong>7</strong>) by 1D and 2DNMR and FAB-MS analyses, and comparison with reported values. All the isolated compounds showed potent cytotoxic activity in the cell lines tested, especially compound <strong>3</strong>, which exhibited greater activity than camptothecin and podophyllotoxin against PC-3 (ED<sub>50</sub> = 1.0 × 10<sup>−5</sup> μg/mL), and KB (ED<sub>50</sub> = 1.0 × 10<sup>−5</sup> μg/mL). This is the first report of the isolation of podophyllotoxin and its acetate in a <em>Bursera</em> species.
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