Synthesis of modified peptides

SARAH L. MELLOR, DONALD A. WELLINGS, JEAN-ALAIN FEHRENTZ, MARIELLE PARIS, JEAN MARTINEZ, NICHOLAS J. EDE, ANDREW M. BRAY, DAVID J. EVANS and G. B. BLOOMBERG 

Several important hormones such as oxytocin, secretin, and LHRH are known to be peptidyl amides (1-3). In addition to these, other peptidyl amides such as indolicidin and the protegrins have been shown to exhibit potent antimicrobial activity (4, 5). The in vivo production of such compounds is via endogenous enzymatic cleavage of propeptides (6), making their synthesis by genetic engineering notoriously difficult. Furthermore, to facilitate the survival of synthetic peptidyl amides in vivo, an obvious defence against the action of carboxypeptidases is the N-alkylation of the carboxylic amide terminus. Such secondary amides would be expected to exhibit vastly different solubility and transport properties to primary amides, thus their chemical synthesis is of immense importance. 

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If not noted elsewhere, all data correspond to the preparation of a 10 x 12 cm cellulose membrane (96-well plate size). For larger membranes preparation of related amounts of reagents is required. If we write about the use of amino acids, it should always include the use of other organic building blocks (e.g., PNA monomers, peptoidic elements, heterocycles) (22,23), which can be used under spot synthesis conditions. Here we describe only the basic procedures for spot synthesis of linear peptides. For the synthesis of modified peptides, such as cyclization or side-chain modifications, see ref. (24). 

The application of this photoalkylation reaction to peptides may lead to a new route to the synthesis of modified peptides. 

The wide use of peptides for biological applications has led to the SPS of many relevant sequences. The well-known drawbacks of natural peptides, such as their poor penetration through biological membranes and their poor stability in biological fluids, has stimulated the synthesis of modified peptides to overcome these limitations. There have been corresponding advances in SPS to accommodate altered structures, and some generic examples of peptide analogs prepared on SP are shown in Fig. 2.3. 

Coutrot, P., Grison, C., and Charbonnier-Gerardin, C., Synthesis of modified peptides incorporating a phosphorane moiety in a terminal nitrogen or carbon, Tetrahedron, 48, 9841, 1992. 

Synthesis of modified peptides containing a-amino aldehydes on the C-end 00MI17. 

Studies of PTM have been benefited from the recent advancements in mass spectrometry, the introduction of new software and Internet-based MS data search facilities, computer-assisted topology prediction for a variety of PTMs (visit http // ca.expasy.org/), chemical synthesis of modified peptides and proteins, development of modified peptide specific antibody, in vitro modification techniques, exploitation of other eukaryotic cells such as insect cells for protein expression [4, 5, 16, 32], and progress in affinity purification of modified proteins. 

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