Total Synthesis, Assignment of the Relative and Absolute Stereochemistry, and Structural Reassignment of Phostriecin (aka Sultriecin)

A total synthesis of phostriecin (2), previously known as sultriecin (1), its structural reassignment as a phosphate versus sulfate monoester, and the assignment of its relative and absolute stereochemistry are disclosed herein. Key elements of the work, which provided first the originally assigned sulfate monoester 1 and then the reassigned and renamed phosphate monoester 2, relied on diagnostic 1H NMR spectroscopic properties of the natural product for the assignment of relative and absolute stereochemistry as well as the subsequent structural reassignment, and a convergent asymmetric total synthesis to provide the unequivocal authentic materials. Key steps of the synthetic approach include a Brown allylation for diastereoselective introduction of the C9 stereochemistry, an asymmetric CBS reduction to establish the lactone C5-stereochemistry, diastereoselective oxidative ring expansion of an α-hydroxyfuran to access the pyran lactone precursor, and single-step installation of the sensitive Z,Z,E-triene unit through a chelation-controlled cuprate addition with installation of the C11 stereochemistry. The approach allows ready access to analogues that can now be used to probe important structural features required for protein phosphatase 2A inhibition, the mechanism of action defined herein.