Ellagitannin Oligomers from Eucalyptus camaldulensis Leaves and Their Role in the Detoxification of Aluminum

<i>Eucalyptus camaldulensis</i> of the Myrtaceae family shows high resistance to aluminum (Al) ions and contains various compounds such as steroids, terpenoids, saponins, flavonoids, glycosides, alkaloids, and tannins. Although the ellagitannin oenothein B (<b>12</b>) isolated from <i>E. camaldulensis</i> exhibits remarkable properties for Al detoxification, likely contributing to its Al resistance, other ellagitannin oligomers present in <i>E. camaldulensis</i> have not been investigated in detail. In this study, novel dimeric and trimeric ellagitannin oligomers eucarpanin D₂ (<b>1</b>) and eucamalin A (<b>2</b>), together with known gallotannins (<b>7</b>, <b>8</b>, and <b>10</b>), monomeric ellagitannins (<b>4</b>-<b>6</b>, and <b>11</b>), and dimeric ellagitannins (<b>3</b>, <b>9</b>, and <b>12</b>-<b>14</b>), were isolated from <i>E. camaldulensis</i> leaves. The structures of these novel compounds were elucidated based on their chemical and physicochemical properties, including the orientations of tergalloyl groups in compounds <b>1</b> and <b>2</b>. Similar to compound <b>12</b>, previously isolated from the roots of <i>E. camaldulensis</i>, the ellagitannins demonstrated good Al detoxification properties. Hence, these tannins may play a critical role in the high Al resistance of <i>E. camaldulensis</i> in acidic soils. This paper reports for the first time the isolation of ellagitannin oligomers from the leaves of <i>E. camaldulensis</i>.