Rhodospermals A–G: an Extension to the Chemical Diversity of Compounds Possessing a Unique Spiroketal with a Fused α,β-Unsaturated δ-Lactone Isolated from the Leaves of <i>Cryptocarya rhodosperma</i> (Lauraceae)

Phytochemical investigation of the Australian rainforest plant <i>Cryptocarya rhodosperma</i> B. Hyland (Lauraceae) led to the isolation and structural elucidation of seven new unique spiroketals fused with an α,β-unsaturated δ-lactone, namely, rhodospermals A-G (<b>1</b> - <b>7</b>), and a new alkylbenzodioxole α,β-<i>unsaturated</i>-δ-lactone rhodopyrone A (<b>8</b>) along with the known compounds EBC-23 (<b>9</b>) and EBC-73 (<b>10</b>). The chemical structures of these compounds were established by NMR spectroscopic data analysis, relative stereochemistry confirmed by distinct <i>J</i> coupling, NOESY correlations, and a close comparison of the NMR data and optical rotation of the previously reported compounds (<b>9</b>, <b>10</b>). X-ray crystallography analysis and Mosher ester analysis of <b>1</b> confirmed the absolute stereochemistry of the fused spiroketal with an α,β-unsaturated δ-lactone. A plausible identical stereochemistry of the common fused spiroketal with an α,β-unsaturated δ-lactone observed in the remaining analogues (<b>2</b>-<b>7</b>) was proposed. The absolute stereochemistry of <b>8</b> was determined by performing a Mosher ester analysis and distinct <i>J</i> coupling. Compounds <b>1-10</b> exhibited cytotoxic activity in several cancer cell lines, highlighting their potential use in the treatment of human tumors.