Opisthobranchs are marine gastropod molluscs, the shell of which is either reduced or completely absent in the adults. Being loss of physical protection, the survival of opisthobranchs mainly relies on a series of chemical strategies. Most of the animals protect themselves from predators by selecting appropriate diet, and consequently transforming and bioaccumulating some useful dietary metabolites into selected body parts as defensive substances. A few of animals are capable of biosynthesizing the necessary substances to establish their chemical defensive systems. Obviously, chemical studies on constituents of molluscs and their preys can reveal the dietary relationship between them, and suggest the ecology role of the metabolite as a consequence.

Dr. Margherita Gavagnin’s group in Istituto di Chimica Biomolecolare (ICB), Italy, and Dr. Yuewei Guo’s group in Shanghai Institute of Materia Medica (SIMM), China, have collaboration work on marine natural products of opisthobranch molluscs.
Chemical studies on two opisthobranch molluscs, Actinocyclus papillatus and Phidiana militaris, have resulted in the isolation of (-)-actisonitrile, a unique lipid possessing a 1,3-propanediol ether skeleton, and phidianidines A, B, two indole alkaloids exhibiting an uncommon 1,2,4-oxadiazole ring linked to the indole system, respectively.
The absolute configuration of natural (-)-actisonitrile was determined by comparing its optical properties with those of (±)-synthetic enantiomers. In bioassay, (±)-actisonitriles exhibited a parallel concentration-dependent toxic profile, displaying IC50 values within the micromolar range. While phidianidines are strongly active against both tumor (C6 and HeLa) and nontumor (fibroblasts) cells, showing IC50 values within within the nanomolar range. These interesting bioactive secondary metabolities were only found in the mantles of the mollucs, suggesting a possible involvement of these molecules in the defensive mechanisms of the opisthobranch and a potent function in ecology.
These study results were published on Organic Letters (2011, 13, 1897-1899; 2011, 13, 2516-2519). These research works were supported by grants from Chinese Minister of Science and Technology, Natural Science Foundation of China, and Science and Technology Commission of Shanghai municipality.