ABSTRACT
All chemical reagents were purchased from Aldrich (Saint Quentin Fallavier, France) or Acros (Noisy-Le-Grand, France). The cyclic peptide (3) was prepared following the procedure described in reference 9a, using protected amino acids, Fmoc-Gly-Sasrin resin, and PyBOP from Advanced ChemTech Europe (Brussels, Belgium), Bachem Biochimie SARL (Voisins-Les-Bretonneux, France), and France Biochem S.A. (Meudon, France). The reaction progress was monitored by reverse-phase HPLC on Waters equipment at 1.3 mL/min (Macherey-Nagel (Hoerdt, France) Nucleosil 300 Å 5µm C18 particles, 125 × 3 mm) with ultraviolet (UV) monitoring at 214 nm and 250 nm using a linear A-B gradient (solvent A: water containing 0.09% triuoroactic acid (TFA); solvent B: acetonitrile containing 0.09% TFA and 9.91% H2O). Preparative separation was operated at 22 mL/min (Delta-PakTM 100 Å 15 µm C18 particles, 200 × 25 mm) with UV monitoring at 214 nm and 250 nm using a linear A-B gradient. Rt indicates the peak retention time. Mass spectra were acquired using electrospray ionization in positive mode on an Esquire 3000+ Bruker Daltonics. 1H and 13C NMR (nuclear magnetic resonance) spectra were recorded in D2O at 400 MHz with a Bruker Avance 400. Chemical shifts (δ) were reported in parts per million (ppm). Spectra were referenced to the residual proton solvent peaks relative to the signal of D2O (δ 4.79 ppm for 1H NMR). Proton assignment was done using gradient COrrelation SpectroscopY (gCOSY) experiment.
