Actinoidins A and A2: structure determination using 2D NMR methods.

Abstract

The structural analysis of the intact glycopeptide antibiotics, actinoidins A (1a) and A2 (1b), by two-dimensional 1H NMR is described. The location of the single chlorine at the A3 position and the sites of attachment of the four carbohydrate substituents in actinoidin A are elucidated based on correlation spectroscopy (COSY), double quantum coherence experiments (DQCE), homonuclear Hartmann-Hahn experiments (HOHAHA) and nuclear Overhauser spectroscopy (NOESY). Similar 2D correlation and NOE NMR experiments are then performed on the novel analog, actinoidin A2, to determine its structure. The structural difference between actinoidins A and A2 is shown to reside in the presence of L-rhamnose in actinoidin A2 in place of L-acosamine in actinoidin A. All questions concerning the stereo-chemistry of the chiral centers in both the heptapeptide core and the carbohydrate moieties in each of these antibiotics could be successfully addressed with the exception of Gl', the alpha-carbon on the N-terminal amino acid which is known to have the R-configuration from previous studies.