A highly effective synthetic method via ruthenium catalyzed asymmetric hydrogenation was developed for (S)-methyl-2-(6-hydroxy-2,3-dihydrobenzofuran-3-yl)acetate, a key intermediate in the synthesis of the active pharmaceutical ingredient for GPR40/FFAR1 agonist, fasiglifam (TAK-875). In the 1st generation asymmetric hydrogenation, the cost ratio of a chiral amine ((S)-ADPP) to upgrade for enantiomer excess and the chiral ruthenium catalyst was high in overall manufacturing cost of fasiglifam. We tried to change to an inexpensive chiral amine ((R)-PEA) and reduce the chiral ruthenium catalyst amount. It was important to control the dissolved oxygen in solvent and to purify the substrate as a (R)-PEA salt. As a result, we successfully reduced the asymmetric catalyst amount to s/c 20,000 by application of the ruthenium catalyst and the changing substrate form under the tightly controlled conditions (2nd generation asymmetric hydrogenation). Finally, this manufacturing process was successfully performed at commercial scale.
