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Isocaloteysmannic acid (<b>1</b>), a new chromanone, was isolated from the leaf extract of the medicinal species <i>Calophyllum tacamahaca</i> Willd. along with 13 known metabolites belonging to the families of biflavonoids (<b>2</b>), xanthones (<b>3</b>–<b>5</b>, <b>10</b>), coumarins (<b>6</b>–<b>8</b>) and triterpenes (<b>9</b>, <b>11</b>–<b>14</b>). The structure of the new compound was characterized based on nuclear magnetic resonance (NMR), high-resolution electrospray mass spectrometry (HRESIMS), ultraviolet (UV) and infrared (IR) data. Its absolute configuration was assigned through electronic circular dichroism (ECD) measurements. Compound (<b>1</b>) showed a moderate cytotoxicity against HepG2 and HT29 cell lines, with IC₅₀ values of 19.65 and 25.68 µg/mL, respectively, according to the Red Dye method. Compounds <b>7</b>, <b>8</b> and <b>10</b>–<b>13</b> exhibited a potent cytotoxic activity, with IC₅₀ values ranging from 2.44 to 15.38 µg/mL, against one or both cell lines. A feature-based molecular networking (FBMN) approach led to the detection of a large amount of xanthones in the leaves extract, and particularly analogues of the cytotoxic isolated xanthone pyranojacareubin (<b>10</b>).