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 pirlimycin is presented. The degradant was discovered during thermal stress stability testing of pirlimycin. The structure was determined using high resolution mass spectrometry, ms/ms fragmentation, and extensive nmr studies including 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 sugar portion of the molecule forming a tetrahydrofurano[3,2-b]perhydropyran ring structure. The X-ray crystal structure is reported for pirlimycin. Using this structure molecular modelling studies are performed which demonstrate the feasibility of the formation of the new structure.