Development of a Scalable Synthesis of a Pyridinyl-3-azabicyclononene, a Novel Nicotinic Partial Agonist

The process research and development of two syntheses of a novel nicotinic partial agonist, TC-8817 ((+)-5), are described. The original Medicinal Chemistry route had multiple flaws, making it unsuitable for further development. A second approach was explored which was more amenable to optimization. The key steps were an intramolecular Lewis acid-promoted cyclization, a dibromination/elimination sequence to provide a vinyl bromide, and subsequent Suzuki coupling with 3-pyridineboronic acid. The overall yield of ∼3–16% over nine steps was offset by the low cost of goods and ease of synthesis. A major drawback was the need for simulated moving bed chiral separation on the penultimate intermediate to afford the subsequently desired single enantiomer version. A third-generation, asymmetric variation afforded a key intermediate in good yield and enantiomeric purity, providing proof of concept for a more efficient production of the desired (+)-enantiomer.