H-1 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 H-1 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 H-1 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. (C) 1997 Academic Press.