Molecular mass was determined at high resolution by electrospray ionization (ESI) mass spectrometry with an LCT instrument from Waters (Milford, MA).
1H and 13C NMR spectra were acquired with an Avance III 400 spectrometer or Avance III 500I spectrometer equipped with a cryogenic probe from Bruker (Billerica, MA). Chemical shifts are reported in units of δ (ppm) relative to tetramethylsilane as the internal standard. In the spectrum of each compound herein, multiple conformers are apparent due to cis–trans isomerism around amide and/or carbamide bonds.
Peptide purity was assessed by reverse-phase chromatography with a Discovery BIO Wide Pore C5-5 column from Supelco (Bellefonte, PA). The column was eluted with 5–95% v/v B over 10 min, 95% v/v B for 2 min, 95–5% over 2 min, and 5% v/v B for 5 min (A: H2O containing 0.1% v/v formic acid; B: acetonitrile containing 0.1% v/v formic acid). Absorbance at 254 nm and molecular mass were monitored with an LCMS-2020 instrument from Shimadzu (Kyoto, Japan).
1H and 13C NMR spectra were acquired with an Avance III 400 spectrometer or Avance III 500I spectrometer equipped with a cryogenic probe from Bruker (Billerica, MA). Chemical shifts are reported in units of δ (ppm) relative to tetramethylsilane as the internal standard. In the spectrum of each compound herein, multiple conformers are apparent due to cis–trans isomerism around amide and/or carbamide bonds.
Peptide purity was assessed by reverse-phase chromatography with a Discovery BIO Wide Pore C5-5 column from Supelco (Bellefonte, PA). The column was eluted with 5–95% v/v B over 10 min, 95% v/v B for 2 min, 95–5% over 2 min, and 5% v/v B for 5 min (A: H2O containing 0.1% v/v formic acid; B: acetonitrile containing 0.1% v/v formic acid). Absorbance at 254 nm and molecular mass were monitored with an LCMS-2020 instrument from Shimadzu (Kyoto, Japan).