Bacteriopurpurinimides: highly stable and potent photosensitizers for photodynamic therapy.

The in situ conversion of the unstable bacteriochlorophyll a present in Rhodobacter sphaeroides produced highly stable bacteriopurpurin-18 which in a sequence of reactions was converted into a series of alkyl ether analogues of bacteriopurpurin-18-N-alkylimides with long wavelength absorption near 800 nm. The effective photosensitizers were found to localize in mitochondria but did not show any specific displacement of (3)H-PK11195, suggesting that the mitochondrial peripheral benzodiazepine receptor is not the cellular binding site for this class of compounds.