*2.5. Chromatographic Conditions*

SYP-9625 was analyzed using Ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS) (AQUITY TQD, Waters, Milford, MA, USA) with a C18 column (2.1 mm × 100 mm, 1.7 μm, Waters, UPLC ® BEH). The mobile phase was acetonitrile (A) and 0.1% formic acid-water (B). The linear mobile phase gradient started at 40% A (0 to 0.5 min), increasing to 80% A (0.5 to 3.5 min), after which the column was equilibrated at 40% A (3.5 to 5.0 min). Tandem mass spectrometry was operated in positive electrospray ionization (ESI) and multiple reaction monitoring (MRM) mode. The optimized values of the MS parameters were as follows: source temperature 150 ◦C, desolvation temperature 350 ◦C, cone gas (N2) flow of 50 <sup>L</sup>·h−1, desolvation gas (N2) flow of 650 L·h−1. The analytical instrument control, data acquisition, and processing were performed by MassLynx V4.1 software (Waters). The mass spectrometric parameters for UPLC-MS determination of SYP-9625 concentrations were listed in Table S1. The UPLC-MS chromatogram for SYP-9625 were in Figure S2.
