Porphyrins and related macrocycles are widely studied and show considerable promise as photosensitizers in photodynamic therapy (PDT). Dihydroporphyrins or chlorins have some advantages over porphyrins because they exhibit absorptions at wavelengths near 650 nm that can more easily penetrate bodily tissues. For instance, vertporfin (1) has been used in PDT treatments of age related macular degeneration. This drug is obtained from the Diels-Alder cycloaddition of a divinylporphyrin (protoporphyrin IX), followed by further modification. In our laboratory, porphyrin analogues with carbon atoms in place of one of the internal nitrogens (carbaporphyrins) are under investigations. In this project, the synthesis of a divinylcarbaporphyrin 2 has been developed, and it is anticipated that this system will also undergo cycloaddition reactions. Condensation of a chloroethylpyrrole 3 with 3,4-diethylpyrrole gave a tripyrrane 4a and subsequent deprotection of the terminal benzyl esters with hydrogen over Pd/C afforded the related dicarboxylic acid 4b. Acid-catalyzed condensation with an indene dialdehyde then produced a bis(2-chloroethyl)carbaporphyrin 5. It is anticipated that dehydrohalogenation will give the required divinyl compound and Diels-Alder cyclizations to product adducts such as 6 will then be investigated.

Synthesis of a divinylic carbaporphyrin for investigations into Diels-Alder cycloaddition reactions

255th National Meeting (2018)

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