Synthetic approaches to long-wavelength photosensitizers for photodynamic therapy and their preliminary biological activity

The chlorophyll-a degradation product, purpurin-18 methyl ester (4), was converted into a series of new bacteriochlorins (18)-(20). These stable bacteriochlorins have strong long- wavelength absorptions > 800 nm, and were tested for in vivo photosensitizing activity using the standard screening system of DBA/2 mice bearing transplanted SMT/F tumors. In preliminary screening, among the photosensitizers tested so far, bacteriochlorins (19) and (20) have shown promising anti-tumor activity. Preliminary attempts are described, using photo- Fenton chemistry, to synthesize photosensitizers which display both Type-I and Type-II photochemical behavior.