Borrelidins C-E: New Antibacterial Macrolides from a Saltern-Derived Halophilic Nocardiopsis sp

Chemical investigation of a halophilic actinomycete strain belonging to the genus inhabiting a hypersaline saltern led to the discovery of new 18-membered macrolides with nitrile functionality, borrelidins C-E ( - ), along with a previously reported borrelidin ( ). The planar structures of borrelidins C-E, which are new members of the rare borrelidin class of antibiotics, were elucidated by NMR, mass, IR, and UV spectroscopic analyses. The configurations of borrelidines C-E were determined by the interpretation of ROESY NMR spectra, J-based configuration analysis, a modified Mosher's method, and CD spectroscopic analysis. Borrelidins C and D displayed inhibitory activity, particularly against the Gram-negative pathogen , and moderate cytotoxicity against the SNU638 and K562 carcinoma cell lines.