Oligopeptide catalysts

Zamarev, K. I., Romannikov, V. N., Salganik, R. I., Wlassoff, W. A., and Khramtsov, V. V. (1997). Modelling of theprebiotic synthesis of oligopeptides silicate catalysts help to overcome the critical stage. Orig. Life Evol Biosph., 27, 325-37. 

Biocatalysts do not operate by different scientific principles from organic catalysts. The existence of a multitude of enzyme models including oligopeptidic or polypeptidic catalysts proves that all enzyme action can be explained by rational chemical and physical principles. However, enzymes can create unusual and superior reaction conditions such as extremely low pfCa values or a high positive potential for a redox metal ion. Enzymes increasingly have been found to catalyze almost any reaction of organic chemistry. 

All peptide-catalyzed enone epoxidations described so far were performed using insoluble, statistically polymerized materials (neat or on solid supports). One can, on the other hand, envisage (i) generation of solubilized poly-amino acids by attachment to polyethylene glycols (PEG) and (ii) selective construction of amino acid oligomers by standard peptide synthesis-linked to a solid support, to a soluble PEG, or neat as a well-defined oligopeptide. Both approaches have been used. The former affords synthetically useful and soluble catalysts with the interesting feature that the materials can be kept in membrane reactors for continuously oper-... 

In addition to phosphines and pyridines, N-alkylated imidazoles are also known to act as a nucleophilic catalysts in acylation reactions [1], In the approach by Miller et al. short oligopeptides incorporating N-alkylhistidine derivatives were used as enantioselective acylation catalysts [27]. The design of, e.g., the tripeptide... 

Fig. 5.5 A model of conformational autocatalysis for the oligopeptide of Fig.5.4. The lowest-energy a-helical form (two-helix bundle, left-hand side) interacts with the frozen metastable (3 form (four-member (3 barrel, center). After a long Monte Carlo run (symbolized by an arrow), which consists of a million of intermediate conformations of various type, both molecules form a strong complex of two (3 type metastable forms right). During this run the a conformation unfolds and then refolds to the (3 conformation. Thus, the (3 metastable form plays a role of a catalyst in the transformation of the a native structure into the (3 form (autocatalysis)...

Acylation Reactions with Oligopeptide-Based Catalysts... 

Poly(amino acids) are attractive enzyme models because of their structural similarity. In fact, characteristic pH dependences of the cataljrtic rate were found and this was considered to reflect the conformational peculiarity of poly(amino acids). Unfortur nately, rate enhancements are only moderate and characterization of the catal3rtic site is difficult. Interesting results were obtained in the catalysis of oligopeptides, which supposedly mimic the active site of some hydrolytic enzymes. The stereoselectivity seems to be realized with oligopeptides more easily than with vinyl polymer catalysts. 

The enantioselective discrimination of one of the hydroxyl groups of meso-diols can give chiral monoprotected diols, which serve as versatile intermediates for asymmetric organic synthesis. In addition to the enzymatic methods, a number of chemical approaches have been reported using chiral 1,2-diamine catalysts, chiral phospholane-based catalysts, planar chiral DMAP derivatives, and oligopeptide-based catalysts [2,28], Surprisingly, however, relatively a few publications are devoted to this reaction with cinchona-based organocatalysts. 

Isocyanide polymerization has also been used to polymerize peptide-based monomers. Cornelissen et al. [31,32] prepared oligopeptides based on alanine and functionalized the N-terminus with an isocyanide moiety. These monomers were subsequently polymerized using a Ni catalyst into /3-helical poly isocyanopeptides with the dipeptides in the side chain. It was found that these polymers formed rigid rods, which were revealed by AFM to have extremely long persistence lengths. This rigidity was caused by the formation of /5-sheets between the alanines in the side chain. The same group... 

C. Oligopeptide-Cleaving Catalysts Selective for Angiotensins or Melanin-Concentratiiig... 

Catalysts for oxidative decarboxylation of the Wterminal aspartate residue contained in an oligopeptide are unprecedented in both biological and chemical systems. In biological systems, malic enzyme catalyzes conversion of aspartate to pyruvate (145). The substrate of malic enzyme is the free amino acid, whereas those of the angiotensin-cleaving catalysts discovered in this study are oligopeptides containing Wterminal aspartate residue. 

Results of this study indicate that the concept of the peptide-cleaving catalysts can be expanded to include oligopeptides as the targets and nonhy-drolytic reactions as the means for cleavage. 

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