NMR study of peplomycin in aqueous solution. Assignment of resonances by means of two-dimensional spectroscopy

1H-NMR spectra of peplomycin (PEP) recorded at 400 and, for the first time, 900 MHz at 2 °C were examined. All the spin systems in the PEP molecule were identified through 2D NMR spectroscopy. The use of NMR spectroscopy allowed the unambiguous assignment of 62 protons, generating 47 non-exchangeable and 15 exchangeable signals. The analysis of the signals observed in 2D-NOE spectra indicates that PEP exhibits an extended conformation at 2 °C. A comparison between the solution conformation of apo-PEP and the solution structure of HOO-Co(III)-PEP indicates that the overall structure of apo-PEP is extended in solution, but exhibiting a conformation of the bithiazole (B)-sulfonium (S) unit similar to that of HOO-Co(III)-PEP. The present investigation represents the initial stage of an NMR study of the solution conformation and dynamics of PEP, its derivatives, its metal complexes and the interactions of metallo-PEPs with their target DNA.