Conformation of cyclosporin A in polar solvents.

A major conformation of cyclosporin A in methanol and in aqueous methanol was revealed by some simple NMR experiments. Thus, a stepwise transition of cyclosporin A conformation from 100% CDCl3 to 100% CD3OD was followed by 1H NMR, which showed that the chloroform conformation of cyclosporin A was still the major one in methanol. Employing the same technique, it was also shown that the chloroform conformation of cyclosporin A was one of the major conformations in 50% aqueous methanol. This may be the first experimental determination of a major conformation of cyclosporin A in polar solvents.