Four new meridamycin congeners from Streptomyces sp. SR107

Meridamycin and its naturally occurring analog normeridamycin are non-immunosuppressive macrocyclic polyketides with potent neuroprotective activity in dopaminergic neurons. Although the biosynthetic gene cluster of meridamycin has been cloned and therefore generated the analogue, C36-keto-meridamycin, the diversity of this type of unique macrolide is still undiscovered. In this paper, four meridamycin congeners, namely meridamycin A (2), meridamycin B (3), meridamycin C (4) and meridamycin D (5), together with meridamycin (1), were isolated from the agar fermentation of the strain Streptomyces sp. SR107. The structures of these compounds were elucidated on the basis of 1D-, 2D-NMR, and HRESIMS data analysis. The antibacterial activities of compounds 1–5 were also evaluated.