Identification of an unexpected shunt pathway product provides new insights into tirandamycin biosynthesis.

Tirandamycin K ( 7 ), the first linear 7,13;9,13-diseco-tirandamycin derivative, was isolated from the tamI (encoding the TamI P450 monooxygenase) disruption mutant strain ( ΔtamI ) of marine Streptomyces sp. 307-9. Its chemical structure with relative and absolute configurations was elucidated by a combination of extensive spectroscopic analyses and biosynthetic inferences. Structural elucidation of this unusual compound provides new insights into tirandamycin biosynthesis. Moreover, examination of the biological activity of 7 confirms the essential function of the bicyclic ketal ring for antibiotic activities of tirandamycins.