NMR studies of aureobasidins A and E.

The 1H and 13C NMR spectra of aureobasidins A and E were analyzed by a variety of 2D NMR techniques. Two isomers of aureobasidin A existed as an equilibrium mixture in deuteriochloroform. The isomerism was associated with cis-trans rotation of the amide bond between N-methylphenylalanine and proline. Almost all of the aureobasidin E was found in deuteriochloroform as one conformer; the amide bond between beta-hydroxy-N-methylphenylalanine and proline was in the cis-conformation. Experiments with the NOE made identification of the conformation of the amide bonds of aureobasidins A and E possible.