Scapairrins A–Q, Labdane-Type Diterpenoids from the Chinese Liverwort Scapania irrigua and Their Cytotoxic Activity

Seventeen new labdane-type diterpenoids, scapairrins A–Q (1–17), including six pairs of diastereoisomers, and three known analogues (18–20) were isolated from the Chinese liverwort Scapania irrigua. The structures of 1–17 were determined based on a combination of the analysis of their MS and NMR spectroscopic data, single-crystal X-ray diffraction, and electronic circular dichroism calculations. Cytotoxicity testing showed that compounds 7–10 exhibited inhibitory activities against a small panel of human cancer cell lines.