1H NMR analysis of isocyclosporin A prepared in organic solvent and in aqueous solution

Isocyclosporins are isomers of cyclosporins deriving from an N,O-acyl transfer occurring under acidic conditions. For the identification by 1H NMR of isocyclosporins prepared in organic solvents the signal at 2.3 ppm assigned to three hydrogens of the NHCH3 group is considered. Results reported here show that the 1H NMR spectrum of isocyclosporin A prepared in aqueous acidic conditions lacks of the above signal and profoundly differs from that of isocyclosporin A prepared in organic solvents, despite the identity of the primary structures determined on the basis of mass spectrometric analysis.