1100 capillary hplc system

The synthesized compounds were analyzed using a Finnigan TSQ Quantum Discovery instrument (Thermo Electron, San Jose, CA) coupled to an Agilent 1100 Capillary HPLC system. The MS was operated in the negative ion ESI mode. A 250 × 10 mm, 5 μm, C18 Luna column and a Krudkatcher disposable precolumn filter (Phenomenex, Torrance, CA) were used. The column was eluted at 10 μL/min with a linear gradient of CH₃CN in 15 mM NH₄OAc. CH₃CN was brought from 15% to 75% in 30 min, then the organic solvent was held at 75% for 5 min followed by a 14 min reequilibration at 15% CH₃CN. The ESI source was set in the negative ion mode as follows: voltage 5 kV; current 50 μA; heated ion transfer tube 330 °C. The metabolites were measured by MS/MS using selected reaction monitoring (SRM) mode. The collision energy for all transitions was 15 eV, and the Ar collision gas pressure was 1.0 mTorr. The MS settings of the ion source were optimized using standard solutions of compounds 6 and 9, 7 and 10, and 8 and 11 to produce maximum MS/MS signals at m/z 356 → m/z 209, m/z 338 → 209 and m/z 354 → 225, respectively.