Tunichlorin: a nickel chlorin isolated from the Caribbean tunicate Trididemnum solidum

Tunichlorin, a blue-green pigment isolated from the Caribbean tunicate Trididemnum solidum, has been identified as nickel(II) 2-devinyl-2-hydroxymethylpyropheophorbide a by chemical and spectroscopic methods, with confirmation by partial synthesis of dimethyl tunichlorin from chlorophyll a. Nickel chlorins have been reported from geological sources but not from living organisms. Its occurrence in a living system suggests a metabolic role for tunichlorin and may clarify the selective accumulation of nickel by marine tunicates. Because Trididemnum tunicates are associated with algal symbionts, tunichlorin may arise directly from the tunicate, from symbiotic algae, or from tunicate modification of an algal chlorin.