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Abstract
Two new ent-clerodane diterpenoids have been isolated from Scutellaria barbata, and their structures were established by detailed spectroscopic analyses as (13R)-6α,7β-dihydroxy-8β,13-epoxy-11β-nicotinyloxy-ent-clerodan-3-en-15,16-olide (scutelinquanine D, 1) and (11E)-6α-acetoxy-7β,8β-dihydroxy-ent-clerodan-3,11,13-trien-15,16-olide (6-acetoxybarbatin C, 2). In vitro, the isolated two new compounds showed significant cytotoxic activities against three human cancer cell lines (HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells), and gave IC50 values in the range of 2.5–6.6 μM.
Acknowledgements
This study was financially supported by the National Natural Science Foundation of China (No. 20772104). The authors are grateful to Mr Ji-Yong Chen and Ms Hong Yu (School of Pharmaceutical Science, Yantai University) for the measurement of FAB-MS, HR-FAB-MS, UV, IR, and NMR spectra, respectively. The authors also gratefully acknowledge Mr Zhen Li (School of Pharmaceutical Science, Yantai University) for the bioactivity screenings.