The scalable total synthesis of portimine A (1) and B (2) presented herein benefits from a strategy that is distinct from both biosynthesis and prior approaches. Driven by a desire to avoid an abundance of functional group manipulations, non-strategic redox fluctuations, and PGs, a plan was forged to forego the installation of oxygenation until a late stage. By analogy to two-phase terpenoid synthesis, this required the construction of a minimally decorated carbon skeleton followed by sequential oxidations. In this way, the innate reactivity of a macrocycle could be leveraged to install both the correct oxygenation pattern as well as the stereochemistry. Certain intermediates served to "self-protect" key functional groups and enable the final sequence by strategically timed ring-chain tautomerization events. Finally, an unusually stable vinyl triflate was carried through the majority of the synthesis allowing for flexible diversification of this biologically promising lead compound, enabling the construction of photoaffinity probes for target identification studies. With sizable quantities of PA (1) in hand, we have shown that PA (1) potently induces G1 cell cycle arrest and apoptosis in multiple human cancer cell lines, but not in human PBMCs. Further, chemical proteomic studies revealed NMD3 to be the primary target of PA , and to our knowledge, is the first reported small molecule ligand of NMD3. Engagement of NMD3 by PA results in a buildup of 80S ribosome and blockade of polysome formation. Further, the observation that decreasing NMD3 expression reduces PA potency is suggestive of a gain-of-function or neo-function mechanism, however, the molecular details of how binding of PA (1) to NMD3 induces this cascade are not yet clear and will be subject of future studies. Overall, this study demonstrates the utility of totally synthetic routes designed with ideality criterion combined with powerful chemical proteomic methods to reveal new potential therapeutic targets .