Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The incorporation of [2‐<jats:sup>14</jats:sup>C]acetate, [2‐<jats:sup>14</jats:sup>C]mevalonate, and [<jats:sup>3</jats:sup>H]squalene proved the squalenoid nature of the iridals, novel triterpenoids from rhizomes of swordlilies. Methionine is readily incorporated into cycloiridalls of <jats:italic>Iris pallida dalmatica</jats:italic>, thus indicating that the methylation of iridals <jats:italic>via S</jats:italic>‐adenosyl‐L‐methionine leads to the formation of the irone moiety of the bicyclic compounds. The <jats:sup>3</jats:sup>H/<jats:sup>14</jats:sup>C ratio of the transferred labelled methyl group remained unchanged. Therefore, the methylation/cyclization of the terpenoid side chain of iridals must proceed by a concerted mechanism without formation of a cyclopropanoid intermediate.</jats:p>