Syntheses and photosensitizing activity of porphyrins joined with ester linkages

In order to investigate the structure of hematoporphyrin derivative and its purified version, Photofrin-II, porphyrin dimers with ester linkage were synthesized. 2,4-Diacetyldeuteroporphyrin dimethyl ester and protoporphyrin IX dimethyl ester were used as starting materials. The methyl esters were replaced by trimethylsilylethyl esters to protect the carboxylic groups. Deprotection using tetra-n-butylammonium fluoride in tetrahydrofuran regenerated the carboxylic functions. Reversed phase high performance liquid chromatography was used to compare the synthetic dimers with components of Photofrin-II. Our data indicate that these dimers are not components of Photofrin-II. During the synthesis of a ¹³ C-labeled dimer with an ester linkage, a small amount of trimer was also isolated. The structures of these compounds were confirmed by nuclear magnetic resonance and mass spectroscopy. Using a standard screening system with DBA/2 mice bearing transplanted SMT-F tumors, these dimers were found not to be as active as Photofrin-II.