Structural identification of a novel degradant of the antibiotic pirlimycin formed under thermal stress conditions

The structure of a novel, thermally-induced degradant of the antibiotic pir limycin is presented. The degradant was discovered during thermal stress st ability testing of pirlimycin. The structure was determined using high reso lution mass spectrometry, ms/ms fragmentation, and extensive nmr studies in cluding a combination of homonuclear TOCSY and gradient, inverse-detected 2 -D nmr experiments which included GHSQC and GHMBC. All nmr, high resolution ms and ms/ms fragmentation data are consistent with loss of a molecule of HCl during a ring closure involving one of the hydroxyl moieties from the s ugar portion of the molecule forming a tetrahydrofurano[3,2-b]perhydropyran ring structure. The X-ray crystal structure is reported for pirlimycin. Us ing this structure molecular modelling studies are performed which demonstr ate the feasibility of the formation of the new structure.