Dopamine-Derived Guanidine Alkaloids from a Didemnidae Tunicate: Isolation, Synthesis, and Biological Activities.

Mellpaladines A-C () and dopargimine () are dopamine-derived guanidine alkaloids isolated from a specimen of Palauan Didemnidae tunicate as possible modulators of neuronal receptors. In this study, we isolated the dopargimine derivative 1-carboxydopargimine (), three additional mellpaladines D-F (), and serotodopalgimine (), along with a dimer of serotonin, 5,5'-dihydroxy-4,4'-bistryptamine (). The structures of these compounds were determined based on spectrometric and spectroscopic analyses.