Pyralomicins, novel antibiotics from Microtetraspora spiralis. IV. Absolute configuration

The absolute configurations of pyralomicin la 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 approximately 1d and 2b approximately 2e were suggested to be the same as pyralomicin 1a and pyralomicin 2a, respectively, by comparing the circular dichroism spectra.