Absorption Spectra of N-Acetyl-bis(1-pyrenylalanine)methylester in the Excited and Ionic States

Abstract

ABSTRACT:Absorption spectra of the excited and ionic states of threo-and erythro-Nacetyl(l-pyrenylalanine)methylester were measured by ps and ns laser photolysis methods. Interchromophoric interaction affecting the absorption spectrum was observed only in the excited singlet state, while neither triplet excimer nor dimer cation was detected. The present results are quite different from those of other bichromophoric systems, which were ascribed to rather distant structures of relevant chromophores in dipeptides. recently that meso-and rac-2,4-diarylpentanes are more appropriate model compounds. Excellent examples are 2,4-diphenylpentane for polystyrene and 2,4-di(N-carbazolyl)-pentane for poly(N-vinylcarbazole) and their photophysical aspects have been studied in detail. 3 The influence of the conformational distribution on the dynamics of their excited singlet states has been elucidated by single photon counting measurement. On the other hand, the triplet, cationic, and anionic states can be studied with a laser photolysis method, previously demonstrated in the systematic study on di(N-carbazolyl) compounds. 4 Bipyrenyl and binaphthyl compounds are being studied in detail as the next target systems, 5 -7 since pyrene and naphthalene are molecules showing typically distinct intermolecular interactions in the excited singlet and cationic states. Excimer formation and decay dynamics of bis [l-(1-pyrenyl)ethyl]ethers as well as 2,4-di(l-pyrenyl)pentane, and N-acetylbis(l-pyrenylalanine )methylester are closely related to the conformational and configurational aspects of vinyl polymers and polypeptides. Recently, we succeeded in measuring for the first time absorption spectra of the triplet excimer of pyrene, examining bis[l-(1-pyrenyl)ethyl]ethers. 8 Intramolecular association of two pyrenyl chromophores in the

Enzymes in organic synthesis. 48. Pig liver esterase and porcine pancreatic lipase catalyzed hydrolyses of 3,4-(isopropylidenedioxy)-2,5-tetrahydrofuranyl diesters

“…To our knowledge, this represents the first time such a high degree of stereoselection has been observed in such reductions. Attempted determination of the relative stereochemistry of the diester 3 by NMR gave ambiguous results. The structure was therefore confirmed by X-ray crystallographic analysis.14 Chiral synthons such as 6,7, and 9 are useful precursors for the sugar moieties of C-nucleosides,15 but the ee levels of the enzymically derived products are presently too low to be of asymmetric synthetic value.…”