Monomeric and Dimeric Abyssomicins from the Endophytic Actinomycete Streptomyces sp. ns5-4 as Neuroprotective Agents

Five new abyssomicin monomers (1−5), three new abyssomicin dimers (6−8), as well as the known abyssomicin analogues (9−13), were obtained from the endophytic Streptomyces sp. ns5-4 isolated from the medicinal herb Polygonatum sibiricum. The chemical structures of these compounds were identified by the analysis of the NMR, MS, and ECD spectra. The neuroprotective activities of the isolates were evaluated by the MTT assay. Abyssomicin 7 (3) and 9-O-methylabyssomicin 7 (4) showed significant neuroprotective activities against glutamate-induced excitotoxicity in HT22 cells, with EC50 values of 2.98 and 0.49 μM, respectively. Furthermore, compounds 3 and 4 exhibited negligible cytotoxicities toward normal HT22 cells at a concentration of 200 μM.