Tritoniopsins A–D, Cladiellane-Based Diterpenes from the South China Sea Nudibranch Tritoniopsis elegans and Its Prey Cladiella krempfi

Four diterpenes, tritoniopsins A–D (1–4), have been isolated from the South China Sea nudibranch Tritoniopsis elegans and its prey, the soft coral Cladiella krempfi. They display an unprecedented pyran ring in the cladiellane framework, thus representing a novel cladiellane-based diterpene family. Their structures have been mainly characterized by NMR and mass spectrometric techniques, whereas the relative configuration of compound 1 was secured by X-ray analysis. Antiproliferative assays on tumor and nontumor cell lines have been carried out for the main metabolite, tritoniopsin B (2).