Synthesis and Anticancer Activity of All Known (−)-Agelastatin Alkaloids

The full details of our enantioselective total syntheses of (−)-agelastatins A–F (1–6), the evolution of a new methodology for synthesis of substituted azaheterocycles, and the first side-by-side evaluation of all known (−)-agelastatin alkaloids against nine human cancer cell lines are described. Our concise synthesis of these alkaloids exploits the intrinsic chemistry of plausible biosynthetic precursors and capitalizes on a late-stage synthesis of the C-ring. The critical copper-mediated cross-coupling reaction was expanded to include guanidine-based systems, offering a versatile preparation of substituted imidazoles. The direct comparison of the anticancer activity of all naturally occurring (−)-agelastatins in addition to eight advanced synthetic intermediates enabled a systematic analysis of the structure–activity relationship within the natural series. Significantly, (−)-agelastatin A (1) is highly potent against six blood cancer cell lines (20–190 nM) without affecting normal red blood cells (>333 μM). (−)-Agelastatin A (1) and (−)-agelastatin D (4), the two most potent members of this family, induce dose-dependent apoptosis and arrest cells in the G2/M-phase of the cell cycle; however, using confocal microscopy, we have determined that neither alkaloid affects tubulin dynamics within cells.