Pyralomicins, Novel Antibiotics From Microtetraspora Spiralis .4. Absolute Configuration

The absolute configurations of pyralomicin 1a and pyralomicin 2a were determined by X-ray crystallographic analyses of crystalline 7'-O-p-bromobenzoylpyralomicin 1a and 2'-O-p-bromobenzoylpyralomicin 2a derived from pyralomicin 1a and pyralomicin 2a using anomalous scattering of the bromine atom. The absolute configurations of pyralomicins 1b-1d and 2b-2c were suggested to be the same as pyralomicin 1a and pyralomicin 2a, respectively, by comparing the circular dichroism spectra.