4-Methoxy cinnamic acid → 5-[(R)-2-(2-{4-[4-(2-amino-2-methyl-propoxy)-phenylamino]-phenyl}-ethylamino)-1-hydroxy-ethyl]-8-hydroxy-1H-quinolin-2-one 4-methoxy cinnamate

5-[(R)-2-(2-{4-[4-(2-amino-2-methyl-propoxy)-phenylamino]-phenyl}-ethylamino)-1-hydroxy-ethyl]-8-hydroxy-1H-quinolin-2-one (0.101 g) was slurried in aqueous tetrahydrofuran (1:1 THF:H2O vol/vol, 1.2 mL). 4-Methoxycinnamic acid (0.036 g, predominantly trans) was added to the mixture. A solution formed before crystallisation spontaneously occurred. The resultant slurry was stirred overnight at room temperature and then filtered. The filtered solid was washed with aqueous tetrahydrofuran (1:1 THF:H2O vol/vol, 3×0.2 mL) and dried at 45° C. in vacuo overnight to give the title compound.