Aldecalmycin, a new antimicrobial antibiotic from Streptomyces. II. Structure elucidation by NMR studies

A new antibiotic, aldecalmycin (1) was isolated from the culture broth of Streptomyces sp. MJ147-72F6. The 1H and 13C NMR spectra of 1 were complicated due to the presence of a beta-ketoaldehyde moiety. Therefore, 1 was converted into an ethylene ketal derivative (2) and into a dihydroaldecalmycin (3). These derivatives gave assignable NMR spectra. The planar structure was elucidated by using 1H-1H COSY, 2D-HOHAHA, 1H-13C COSY and HMBC spectra of 2. The conformation of the decalin ring was elucidated by using ID-HOHAHA, NOE difference and NOESY spectra of 3. The geometry of double bond in the side chain was determined by NOE difference and NOESY spectra of 3.