Dedicated to Professor Dieter Seebach on the occasion of his 65th birthdayIn an attempt to synthesize a homologous series of peptide peresters, we investigated the reaction of the oxazol-5(4H)-ones of Pht-(Aib) n -OH (n 2 ± 8) and tert-butyl hydroperoxide in the presence of 4-(dimethylamino)pyridine. Unexpectedly, the major product isolated in each case proved to be the peptide dialkyl peroxide. This novel class of peptide derivatives was characterized by FT-IR, 1 H-NMR, MS, cyclic voltammetry, and X-ray diffraction. On the basis of the experimental data, a plausible mechanism is proposed for this reaction.Introduction. ± In the last few years, the study of intramolecular electron-transfer (ET) reactions in donor-spacer-acceptor (D-spacer-A) molecules has provided relevant information on how electrons are transferred through bonds and through space (solvent). We have recently investigated intramolecular ET reactions in systems in which A undergoes reductive cleavage of a s-bond (dissociative electron transfer, DET). More specifically, as illustrated in Scheme 1, the phthalimido (Pht) moiety of Aib (a-aminoisobutyric acid), which is easily reduced to its radical anion, was selected as the donor D. In this system, the acceptor A is the Aib-O-O t Bu perester function, a well-characterized dissociative-type acceptor [1]. Interestingly, we found in our electrochemical study that the DET rate of Pht-Aib-O-O t Bu is several orders of magnitude lower than the adiabatic limit.

A homologous series of stable N(alpha)-phthaloyl peptide peroxyesters based on alpha-aminoisobutyric acid residues was prepared. In each of the six oligomers synthesized, the chain of alpha-amino acids is separated from the peroxyester function by a beta-amino acid. [structure: see text]

Understanding the distance dependence of electron transfer (ET) through peptides is a topic of continuous interest. We studied a series of donor‐bridge‐acceptor (D‐B‐A) systems. The peptide bridges (B) were oligomers of the strongly helicogenic α‐aminoisobutyric acid, and were prepared in different lengths to form 0, 1, 2, 3, 4, or 5 intramolecular H‐bonds. D was a phthalimide group and A was a perester. The study was carried out in DMF, acetonitrile, and dichloromethane. Cyclic voltammetry (CV) and convolution analysis of the model donors and acceptor yielded the relevant thermodynamic information, whereas homogenous redox catalysis provided information on the competitive intermolecular ET. CV analysis of the D‐B‐A systems showed that, independently of the solvent used, the intramolecular ET occurs by a superexchange mechanism strongly affected by intramolecular H‐bonds and the extent of conjugation of the peptide bridge with D and A.

Synthesis and Characterization of a Series of Homooligopeptide Peroxyesters.Pages 2755 and 2756. All instances of "(RS)", originally meant to indicate a racemate, should be replaced by the clearer prefix "rac" because, in this work, the racemic "trans-1,2-Chx" residue was used. However, in the case of "cis-1,4-Chx", "(RS)" should be simply removed, as this amino acid is achiral. Supporting Information. Corrected Supporting Information has also been posted.