Syntheses and cellular investigations of di-aspartate and aspartate-lysine chlorin e6 conjugates

Abstract

Chlorin e₆ is a tricarboxylic acid degradation product of chlorophyll a. Four chlorin e₆ bis(amino acid) conjugates were regioselectively synthesized bearing two aspartate conjugates in the 13¹,17³- and 15²,17³-positions, or at the 13¹,15²via an ethylene diamine linker. One additional conjugate bearing two different amino acids, lysine at 13¹via an ethylene diamine linker and an aspartate at 15²via a β-alanine linker was also synthesized. The cytotoxicity and uptake of four di(amino acid) chlorin e₆ conjugates were investigated in human HEp2 cells, and compared with chlorin e₆. The most cytotoxic and most taken up conjugates were the zwitterionic 13¹,15²-disubstituted conjugates 28 and 33; these also localized in multiple organelles. In contrast, the anionic 13¹,17³- and 15²,17³-di-aspartyl chlorin e₆ conjugates 12 and 13 showed low dark cytoxicity and lower phototoxicity compared with chlorin e₆.