Chemical modification of chlorophyll a: Synthesis of new regiochemically pure benzoporphyrin and dibenzoporphyrin derivatives

Starting from pheophorbide a methyl ester (5), a degradation product of chlorophyll a, routes for the preparation of 3-vinylporphyrins 6 and 9 and of an [A,C]-divinylporphyrin 16 are described. These porphyrins were obtained as a result of chemical modification of 5 on ring D and the exocyclic ring E. Diels-Alder reactions of these (di)vinylporphyrins with dimethyl acetylenedicarboxylate, to afford new regiochemically pure benzoporphyrin derivatives 29 and 30 and dibenzoporphyrin derivative 33 for potential use as sensitizers in photodynamic therapy of tumors, were also investigated.