Synthesis and Reaction of Fluorescent, Photolabile (1-pyrenyl) methyl Esters of Carboxylic and phosphoric Acids

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1.1-(alpha-Diazobenzyl) pyrene (DBP), which is stable at room temperature for several months, reacts with carboxylic acids to give fluorescent, photolable (1-pyrenyl) methyl esters in high yields. DBP was used for fluorescent, photolabile protection of carboxyl group of amino acids and peptides. However, DBP did not give good result for the protection of phosphoric acids. (1-pyrenyl) methyl bromide was found to react in the presence of silver oxide either with carboxylic acids or with phosphoric acids resultong in the formation of the corresponding esters in high yield. Esters are easily obtained by filtrating silver bromide formed. Esterification of uronic acids and c-AMP by this procedure is now under way.2. Mechanistic studies on photosolvolysis of (1-pyrenyl) methyl carboxylates and determination of quantum yields of the reaction were carried out. It was found that introduction of an electron withdrawing group on (1-pyrenyl) methyl group causes unusual ester O-CO cleavage in addition to CH-OCO cleavage.3. Intramolecular electron transfer in the excited states of omega-(l-pyrenyl) alkyl p-substituted benzoate was studied. Energy of exciplex formation and activation, rates constants were determined for 2-(l-pyrenyl) ethyl p-cyanobenzoates (P2CN). From the results of single-photon-counting measurement and ^1NMR NOE, it is concluded that the folded conformer of the p-cyanobenzoate is responsible to the exciplex formation. This is the first example of correlation of exciplex formation with ground state conformations.