In the course of our studies on the function and distribution of vasoconstrictive polyhydroxy compounds zooxanthellatoxins (ZTs), we found structurally related compounds to ZTs, named zooxanthellamide A (1) and its derivatives 2, 3 from one species of the genus Symbiodinium (strain HA3-5) isolated in the free-living state from an Hawaiian tide pool. The structural determination of these compounds was performed by spectroscopic methods mainly by 2D NMR techniques. 2 and 3 were determined to be δ-lactone and macrocyclic lactone derivatives of 1, respectively. These compounds 1-3 possess a molecular weight of 2715 or 2697, which are a little smaller than those of ZTs. Although 1 is a large polyhydroxy molecule like ZTs, 1 differs from ZTs in the following points. Thus, 1 does not possess a diepoxide and an exomethylene that are present in ZTs. Amide and sulfate groups exist singly in ZTs, whereas there are a pair of both of these groups in 1. In an evaluation of vasoconstrictive activity, 3 showed a higher activity than that of a positive control ZT-A, whereas 1 and 2 did not show the activity. The presence of a macrolide structure in 3 might be important for the vasoconstrictive activity. Further studies on structural analysis of macrolide 3 are in progress.
