Chlorins with six-membered imide ring as prospective sensitizers for cancer PDT

A series of promising PDT sensitizers having intensive absorbtion maximum at 710-750 nm has been synthesised from the readily available purpurin 18. Modification of an anhydride ring in purpurin 18 afforded two series of cyclic imides. The first group comprises the N-substituted derivatives containing residues of aliphatic alcohols (C-2-C-4) and carboxylic acids (C-1, C-5). The second series is represented by the cyclic N-hydroxyimides containing the -N-OR group, where R is either alkyl or acyl residue. Cyclic imides possess increased resistance to alkali treatment, which enhances their water solubility, They absorb in the region of 706-718 nm. Further development of the spectral characteristics was achieved by the oxidation of a 3-vinyl group into the formyl one. The obtained compounds have the absorbtion maximum in the region of 750 nm, which makes them comparable to those of bacteriochlorophyll derivatives. The presence of a spacer group in the molecule of compounds synthesised affords their attachment to the carriers for the directed transport of a sensitizer into tumor.