The synthesis, preliminary in vivo biological activity, singlet oxygen and fluorescence yields of a series of alkyl ether derivatives of chlorophyll-alpha analogs are described. For short-chain carbon ethers (1-7 carbon units), it was observed that the biological activity increased by increasing the length of the carbon chain, being maximum in compounds with n-hexyl and n-heptyl chains. Related sensitizers prepared by reacting 2-(1-bromoethyl)-2-devinylpyropheophorbide-alpha with (sec)alcohols were found to be less effective. Under similar treatment conditions, photosensitizers containing cis- and trans- 3-hexenyl side chains were ineffective. Thus, both stereochemical and steric factors caused differences in sensitizing activity. In general, pyropheophorbide-alpha analogs were found to be more active than related chlorin e6 derivatives, in which the isocyclic ring (ring "E") was cleaved. Related photosensitizers in the 9-deoxy- series were found to be as effective as the corresponding pyropheophorbide-alpha analogs. The photosensitizers prepared from pyropheophorbide-alpha methyl ester and chlorin e6 trimethyl ester have long wavelength absorption at 660 nm (epsilon 45 000 to 50 000). Reduction of the carbonyl group in the pyropheophorbide-alpha to methylene (ring E) resulted in a blue shift to 648 nm (epsilon 38 000).

The synthesis, photophysical characteristics, in vivo photosensitizing efficacy, human serum albumin (HSA) binding properties, and skin phototoxicity of some stable bacteriochlorins were investigated. The novel bacteriochlorins, obtained from chlorophyll-a, have long-wavelength absorptions in the range lambda max = 734-758 nm. Preferential migration of ethyl over methyl substituents among ketobacteriochlorins obtained in the pinacol-pinacolone rearrangements of vic-dihydroxybacteriochlorins was confirmed by NOE studies. The bacteriochlorins show relatively low fluorescence quantum yields. Among all the bacteriochlorins the triplet states were quenched by ground state molecular oxygen in a relatively similar manner, yielding comparable singlet oxygen quantum yields. In preliminary in vivo studies (DBA/2 mice, transplanted with SMT/F tumors), ketobacteriochlorins were found to be more photodynamically active than the related vic-dihydroxy analogues. Replacement of the methyl ester functionalities with di-tert-butylaspartic acids enhanced the in vivo efficacy. Site specific human serum albumin (HSA) binding studies indicated a direct correlation between the ability of the compound to bind to the diazepam binding site (albumin site II) and the in vivo photosensitizing efficacy.

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