PHOTOMODULATION OF CONFORMATIONAL STATES OF P-PHENYLAZOBENZYLOXYCARBONYL-L-PROLINE AND RELATED PEPTIDES

In linear flexible peptides the isomeric equilibria of aminoacyl-L-pro line peptide bonds are known to be shifted in favor of the trans confi guration, whereas in N-urethanyl-L-proline compounds the cis configura tion is preferred with stabilization of a C-7 conformation, i.e. of an inverse gamma-type rum. To analyze the effects of a photoswitchable c onfiguration in the urethane moiety on this small ordered structure el ement the photochrome azobenzene was incorporated as a urethane group into proline and the proline peptides Pro-Phe and Pro-Phe-Gly. The p-p henylazobenzyloxycarbonyl compounds retain the preferred cis configura tion of the C-N urethane bond and undergo a reversible photomodulated trans to cis isomerization of the azobenzene moiety with more or less pronounced effects on the distribution of the four possible isomers as detected by FTIR and NMR spectroscopy. Correspondingly, detectable ch anges in the population of the C-7 conformation were observed upon irr adiation making this system highly promising for monitoring dynamics b y time-resolved spectroscopy. (C) 1997 Elsevier Science S.A.