Discovery of Tetrahydropyrazolo­pyridine as Sphingosine 1‑Phosphate Receptor 3 (S1P₃)‑Sparing S1P₁ Agonists Active at Low Oral Doses

FTY720 is the first oral small molecule approved for the treatment of people suffering from relapsing–remitting multiple sclerosis. It is a potent agonist of the S1P1 receptor, but its lack of selectivity against the S1P3 receptor has been linked to most of the cardiovascular side effects observed in the clinic. These findings have triggered intensive efforts toward the identification of a second generation of S1P3-sparing S1P1 agonists. We have recently disclosed a series of orally active tetrahydroisoquinoline (THIQ) compounds matching these criteria. In this paper we describe how we defined and implemented a strategy aiming at the discovery of selective structurally distinct follow-up agonists. This effort culminated with the identification of a series of orally active tetrahydropyrazolo­pyridines.