Next, we assessed the aqueous solubility, chemical stability, and in vitro metabolic stability of 5b. The thermodynamic solubility of 5b was determined in phosphate-buffered saline (PBS, 25 °C, pH 7.4) after 4 and 24 h incubation time (Supplementary Note 2). Ondansetron was used as a reference compound with high solubility of 95 µM. The thermodynamic solubility of 5b was low, ranging from 4 µM after 4 h to 8 µM after 24 h (n = 2).