SYNTHESIS OF NEW PYROPHEOPHYTIN-NAPHTHOQUINONE DYADS FOR INVESTIGATIONS OF PHOTOINDUCED ELECTRON-TRANSFER

Two new, covalently-linked pyropheophytin-naphthoquinone dyads 1 and 2 have been synthesized for use as model compounds in studies of photoi nduced electron transfer. The starting material for the synthesis was chlorophyll a (3). This was first pyrolyzed to 13(2)-demethoxycarbonyl chlorophyll a (4), which was then oxidized regioselectively to 13(2)-d emethoxycarbonyl-P4(R/S) -hydroxypheophytin a (5). Compound 5 was este rified with naphthoquinone carboxylic acid 17 by the carbodiimide meth od to afford rboxyethyl)-3-methyl-1,4-naphthoquinone]pheophytin a (1) and (2). The observation that fluorescence emission is effectively que nched in dyads 1 and 2, relative to compound 5 which does not bear an electron-acceptor, indicates that intramolecular electron transfer fro m the excited donor part to the ground state acceptor part of the mole cule occurs readily.