Evolution of a Strategy for the Total Synthesis of Psymberin

Psymberin (also known as irciniastatin A) is a marine-derived polyketide that displays potent and selective cytotoxicity against melanoma, breast, and colon cancer cell lines, with LC₅₀ values below 2.5 nM. Its complex molecular architecture, notable biological activity, and scarcity in nature have made psymberin a compelling target for synthetic chemists since its discovery. This account outlines our efforts toward the total synthesis of psymberin, highlighting two distinct generations of synthetic strategies. The first-generation approach featured several innovative transformations, including a transannular Michael addition followed by lactone reduction to establish the 2,6-trans-tetrahydropyran core, a diastereoselective iodocarbonate cyclization induced by iodine bromide (IBr), and a Diels-Alder/aromatization sequence to construct the highly substituted aromatic ring system. The second-generation synthesis adopted a more efficient and convergent strategy. Key advances included a Heck coupling to join a sterically hindered aryl fragment with a terminal alkene, followed by a palladium-catalyzed cyclization to form the isocoumarin scaffold. This revised route reduced the longest linear sequence by seven steps compared to the original synthesis, representing a significant improvement in overall efficiency. Together, these strategic developments─both designed and serendipitous─highlight the synthetic challenges and opportunities presented by psymberin's complex structure. The approaches described herein provide valuable insights for the synthesis of structurally related natural products and other architecturally sophisticated molecules.