Pyrenylamino Acids: Synthesis, Photophysical and Electrochemical Studies

Several beta-pyrenyldehydroamino acids and a pyrenylalanine derivative have been synthesized in good-to-high yields from dehydroamino acids by several types of reactions. A beta-[(pyren-1-yl)methylamino]alanine was prepared by treating the methyl ester of N,N-(di-tert-butoxycarbonyl)dehydroalanine with (pyren-1-yl)methylamine hydrochloride in the presence of an excess of potassium carbonate. The E isomer of the methyl esters of N-(tert-butoxycarbonyl)-beta-(1,2,4-triazol-1-yl)dehydroalanine and dehydroaminobutyric acid were treated with (pyren-1-yl)methylamine hydrochloride in the presence of triethylamine to give the E isomers of the beta-aminomethylpyrene dehydroalanine and dehydroarninobutyric acid derivatives. beta-(Pyren-1-yl)dehydrophenylalanine and dehydroaminobutyric acid derivatives were obtained from the pure stereoisomer of the corresponding beta-bromodehydroamino acids and (pyren-1-yl)boronic acid by Suzuki cross-coupling. This reaction was also applied successfully to beta-bromodehydrodipeptides. The electrochemical behaviour of some of the compounds prepared was studied by cyclic voltammetry. The peak potentials for the oxidation and reduction of pyrenylalanines were similar to those reported for pyrene. However, it was found that when the pyrene ring was conjugated with the dehydroamino acid moiety, the compounds had higher oxidation and reduction peak potentials than pyrene. The fluorescence properties of four of the pyrenylamino acids synthesized were evaluated in cyclohexane and alcohols. The methyl ester of N,N-bis(tert-butoxycarbonyl)-beta-[(pyren-1-yl)methylamino]alanine presented high fluorescence quantum yields in cyclohexane and ethanol (Phi(F) = 0.45 and 0.35, respectively). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)