Waters delta prep system

All chemicals involved in synthesis or analysis were obtained from Aldrich (Milwaukee, WI, USA) or Novabiochem (San Diego, CA, USA) unless otherwise indicated. All reactions were performed at room temperature unless indicated otherwise. Analytical HPLC was performed on a HP1100 series instrument (Agilent, Santa Clara, CA, USA) with 220 and 280 nm detection using a Vydac C18 column (5 μm, 4.6 × 150 mm; Grace, Columbia, MD, USA) at a flow rate of 1 mL/min. Preparative and semipreparative HPLC were performed on a Waters Delta Prep system (Waters Co., Milford, MA, USA) fitted with a Waters 2487 UV-visible detector using either a Vydac C18 column (15–20 μm, 50 × 250 mm) or a Vydac C18 (15–20 μm, 10 × 250 mm) at a flow rate of 50 or 5 mL/min, respectively. All runs used linear gradients of 0.1% aqueous trifluoroacetic acid (TFA) (solvent A) vs. 0.1% TFA, 90% acetonitrile in H₂O (solvent B). Ultraviolet-visible (UV-vis) spectroscopy was carried out on an Agilent 8453 diode array spectrophotometer (Agilent). Electrospray mass spectrometry (ES-MS) analysis was routinely applied to all compounds and components of reaction mixtures. ES-MS was performed on an Applied Biosystems API 3000 triple quadrupole electrospray mass spectrometer (Applied Biosystems, Foster City, CA, USA) using Analyst 1.4.2. Calculated masses were obtained using Analyst 1.4.2.