The chlorophyll-a (1) was converted into the chlorins 2b～4b by air-oxidation in acid or basic condition. The methyl pheophorbide-a (5) was obtained from chlorophyll-a by transesterification and demetallation. The addition to double bond at 3-position of 5 with hydrochloric acid yielded alcohol chlorin 6 which was oxidized purpure-18 derivative (7) by air-oxidation in basic condition. The methyl pheophorbide-a (5) was oxidized with osmium oxide and sodium periodate to give chlorin 8 which was converted into aldehyde purpure-18 (9) and purpure-7 trimethyl ester (10) by air-oxidation in butanol in the presence of sodium. The purpure-18 ester (3), prepared also from the pheophorbide-a (4) in the same reaction condition like the chlorophyll-a (1), reacted with 2-methylbutylamine to give N-(2-methylbutyl)-purpure-18 imide (11a) and 12-formyl-purpure-18 imide (11b). The structures of all chlorophyll derivatives were characterized by UV, IR, 1H NMR spectra and elemental analysis. The possible mechanisms in accordance with the corresponding chemical reaction and reaction condition were tentatively proposed.

Key words: chlorophyll-a, rearrangement, photodynamic therapy (PDT), mechanism, air-oxidation