Structure of the antibiotic OA-7653

The structure of the glycopeptide antibiotic OA-7653 is assigned. Elucidation of the structure is based primarily on two-dimensional NMR experiments, analogies with other glycopeptide antibiotics of the vancomycin series, and selective degradation studies. Antibiotic OA-7653 contains a heptapeptide aglycon core in which the amino acids N,N-dimethylalanine and glutamine are encountered as the G and F components of this unit. Mild acid hydrolysis of the antibiotic effects the conversion of the gamma -carboxamide of the glutamine residue to yield the carboxylic acid 3 in a reaction that is shown to proceed without rearrangement. This latter conversion to 3 proceeds without effecting cleavage of the beta -glycosidic link between the aglycon and glucose. The super(1)H spectra of OA-7653 and its derivatives in DMSO at pH 4.0 are shown to represent major and minor conformers that are exchanging at rates comparable to the NMR time scale.