A series of novel purpurin-18 imide derivatives which had long wavelength absorption, were synthesized by modification of methyl pheophorbide-a. The 3-(2,2-dimethoxyethyl)-3-devinyl methyl pheophorbide-a was prepared by oxidation of methyl pheophorbide-a (MPa) with Tl(NO₃)₃ and transformed to 3-(2-oxo-ethyl)-3-devinyl methyl pheophor-bide-a with formic acid. The Grignard reaction of the formyl group at 3-position was carried out to give efficiently the corresponding 3-(2-hydroxylalkyl)-3-devinyl methyl pheophorbide-a. In basic conditions E-ring was converted into the six-membered cyclic anhydride to form purpurin-18 derivatives by the air-oxidation. The experimental results showed that 13²-methyloxy- carbonyl group of methyl pheophorbide-a was not destroyed in the process of Grignard reaction. The spectral data of ¹H NMR of the compounds showed that there were two methoxy groups in the molecule after Grignard reaction. It was possible to modify 3-vinyl by Grignard reaction and then transform E-ring as long as controlling reaction conditions. The title compounds were synthesized by transforming E-ring to im-ide-ring and then modifing 3-vinyl by Grignard reaction. They demonstrated a considerable bathochromic shift of the major absorption band in the red region of the optical spectrum. The effect on their visible spec-trum by variation of chemical construction was discussed. The structures of all new compounds were char-acterized by elemental analysis, UV, IR and ¹H NMR spectra.

Key words: purpurin-18 imide, methyl pheophorbide-a, photosensitizer, photodynamic ther-apy