Synthesis and Structure−Activity Relationship Study of Potent Cytotoxic Analogues of the Marine Alkaloid Lamellarin D

The marine alkaloid, Lamellarin D (Lam-D), has shown potent cytotoxicity in numerous cancer cell lines and was recently identified as a potent topoisomerase I inhibitor. A library of open lactone analogues of Lam-D was prepared from a methyl 5,6-dihydropyrrolo[2,1-a]isoquinoline-3-carboxylate scaffold (1) by introducing various aryl groups through sequential and regioselective bromination, followed by Pd(0)-catalyzed Suzuki cross-coupling chemistry. The compounds were obtained in a 24-44% overall yield, and tested in a panel of three human tumor cell lines, MDA-MB-231 (breast), A-549 (lung), and HT-29 (colon), to evaluate their cytotoxic potential. From these data, the SAR study concluded that more than 75% of the open-chain Lam-D analogues tested showed cytotoxicity in a low micromolar GI50 range.