Rhodium complexes peptides

Since catalytic asymmetric hydrogenation can generate either or R configuration at the position of the dehydroamino acid residue, this method could be potentially useful for the specific labeling of certain amino acid residues in a polypeptide. The regiospecific and stereoselective labeling of an amino acid residue is difficult to achieve with the conventional stepwise peptide synthesis. We carried out the dideuteration of Ac-APhe-( )Ala-OMe with the use of the cationic rhodium complexes with (-)BPPM and (+)BPPM (Scheme 1), which gave Ac- (R,R)Phe (d ) - (S)Ala-OMe [(R,Rf )/... 

In addition to dendrimers, hyperbranched polymers have been used by several groups as soluble supports for catalysts [7, 17]. These supports are polydisperse and randomly branched, and, since they are prepared in a single reaction step, are generally much cheaper materials. Nevertheless, it has been shown that catalysts immobilized on hyperbranched polymers may possess similar properties as dendritic systems [18]. Therefore, dendritic catalysts serve as ideal model systems for catalysts attached to hyperbranched polymers. We functionalized several hyperbranched polyethyleneimines (PEIs) employing the peptide coupling protocol in reactions with the pyrphos linker system. The pyrphos-rhodium complexes bound to the hyperbranched polymers were also found to be active catalysts for the hydrogenation ofZ-methyl-a-acetamidocinnamate [16]. As observed for the... 

A library of 63 peptides, each containing one of the two phosphine-substituted amino acids 8 or 9, was prepared by Gilbertson and coworkers in a parallel synthesis on polymer beads [13]. After complexation of all peptides with rhodium, the obtained polymer-bound complexes were employed in the asymmetric hydrogenation of 10 (Fig. 5). 

Severin etal recently pnblished another successful array for differentiating peptides by employing three commercially available metal complexes (27-29). One complex contained rhodium, one ruthenium, and one palladium. In the presence of six selected fluorophores, these constituents formed a collection of differential sensors. The receptors were able to differentiate 10 dipeptides at a 50 pM concentration (the closed symbols in Figure 9) and 2 dipeptides at 20 pM concentration (the open symbols in Figure 9). The authors found that peptides containing histidine and methionine residues were best discriminated, most likely because these residues displaced a larger fraction of... 

The bioconjugation of iridium complexes remains currently under intense exploration. For example, two new, cyclometalated iridium(III) and rhodium(III) bis(pyridylbenzaldehyde) complexes were designed by Lo et al. in 2010 both with and without biotin tags, with their uptake followed in HeLa cells.Furthermore, cell-penetrating peptides conjugated to Ir(III)... 

One of the standard methods for preparing enantiomerically pure compounds is the enantioselective hydrogenation of olefins, a,/3-unsaturated amino acids (esters, amides), a,/3-unsaturated carboxylic acid esters, enol esters, enamides, /3- and y-keto esters etc. catalyzed by chiral cationic rhodium, ruthenium and iridium complexes ". In isotope chemistry, it has only been exploited for the synthesis of e.p. natural and nonnatural H-, C-, C-, and F-labeled a-amino acids and small peptides from TV-protected a-(acylamino)acrylates or cinnamates and unsaturated peptides, respectively (Figure 11.9). This methodology has seen only hmited use, perhaps because of perceived radiation safety issues with the use of hydrogenation procedures on radioactive substrates. Also, versatile alternatives are available, including enantioselective metal hydride/tritide reductions, chiral auxiliary-controlled and biochemical procedures (see this chapter. Sections 11.2.2 and 11.3 and Chapter 12). 

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