Syntheses of porphyrins isolated from the Coral Sea demosponge Corallistessp.

Methyl esters 2, 3, and 5 of corallistins B, C, and E, respectively, isolated from the Coral Sea demosponge Corallistes sp., were successfully synthesized by the MacDonald method (for corallistin B ester) and via a,c-biladiene cyclization (for corallistins C and E esters). In order to compare with the ¹H-NMR data reported in the literature, zinc(II) complexes of these corallistins were prepared, and their ¹H-NMR spectra were measured. Most chemical shifts were found to be within 0.1 ppm of the reported values, except in the case of corallistin B ester, where signal broadening due to porphyrin aggregation made the comparison with literature values difficult. Overall, the NMR data provided support for the structures proposed for the natural corallistins. Postulates on the biosynthetic origins of the corralistins are also presented.