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Peptides peptide ester complexes

Reaction of Co111 amine complexes with glycine esters gives products which are dependent on the solvent used (Scheme 7). In non-aqueous solvents peptide bond formation is observed.78"80 It is concluded that the reaction proceeds via the initial formation of a bidentate glycine ester complex in which the coordinated carbonyl group is activated (by the metal ion) towards nucleophilic attack by a further molecule of the glycine ester. Similar reactions have been observed with other Co111 complexes. [Pg.758]

The palladium(II)-promoted hydrolysis of methyl glycylglycinate and isopropyl glycylglycinate has been investigated over a temperature range.80 Complexes of type (22) are formed in which the amino, deprotonated amide and alkoxycarbonyl groups act as donors. Hydrolysis by both H20 and OH ion is observed. Base hydrolysis of the coordinated peptide esters is ca. 105-fold faster than the unprotonated peptide esters. [Pg.424]

Peptide bond formation using non-labile cobalt(III) complexes has now been developed to a useful synthetic level (Section 61.4.2.2.4), but few attempts have been made to use other metal centres. The formation of glycine peptide esters in the presence of copper(II) has been noted.133 Treatment of glycine esters with copper(II) (other metal ions can also be used) in a non-aqueous solvent at room temperature gave di-, tri- and tetra-glycine peptide esters. After carbobenzyloxyla-tion, the peptide esters were separated by column chromatography, and no evidence was obtained... [Pg.426]

The use of kinetically inert cobalt(III) complexes has led to important developments in our understanding of the metal ion-promoted hydrolysis of esters, amides and peptides. These complexes have been particularly useful in helping to define the mechanistic pathways available in reactions of this type. Work in this area has been the subject of a number of reviews.21-24 Although most of the initial work was connected with cobalt(III), investigations are now being extended to other kinetically inert metal centres such as Rhin, lrni and Ru111. [Pg.427]

The structure of the complex cw-[Co(trien)(GlyGlyOEt)](C104)3 H20 has been determined by X-ray diffraction.206 The peptide ester is coordinated via the terminal amino group and the carbonyl oxygen of the same amino acid residue. [Pg.436]

If we treat alkoxycarbcne complexes not with phosphines but with primary or secondary amines, we observe a new kind of reaction, reminiscent of the reactions of esters. This observation led us into peptide chemistry along a path that proved to be quite surprising to a coordination chemist. We could show that the alkoxy group of alkoxy(organo) carbene complexes can be substituted not only by mono- or dialkylamino residues but also by free amino groups of amino acid and peptide esters (63, 64). The principle of this reaction is shown in Scheme 2. [Pg.11]

Job A, Janeck CF, Bettray W, Peters R, Enders D (2002) Tetrahedron 58 2253 Josephsohn NS, Kuntz KW, Snapper ML, Hoveyda AH (2001) Mechanism of enantioselective Ti-catalyzed Strecker reaction peptide-based metal complexes as bifunctional catalysts. J Am Chem Soc 123 11594—11599 Juhl K, Gathergood N, Jprgensen KA (2001) Catalytic asymmetric direct Man-nich reactions of carbonyl compounds with alpha-imino esters. Angew Chem Int Ed Engl 40 2995-2997... [Pg.248]

Stopped-flow fluorescence studies of ES complexes provided a direct comparison of the peptide binding aflBnities of the zinc and cadmium enzymes and, simultaneously, an explanation for the different roles of metals in peptide and ester hydrolysis (48). Cadmium carboxypeptidase binds the peptide Dns-(Gly)3-L-Phe as readily as does [(CPD)Zn] but catalyzes its hydrolysis at a rate that is reduced considerably (Figure 8). Initial rate studies of oligopeptides are in agreement with this observation. For all peptides examined, the catalytic rate constants of the cadmium enzyme are decreased markedly, but the association constants (1) (Km values) of the cadmium enzyme are identical to those of the zinc enzyme (48,51,57). However, in marked contrast, for all esters examined the catalytic rate constants of the cadmium enzyme are nearly the same as those of the zinc enzyme, but the association constants are decreased greatly. [Pg.126]

Recent studies of Co (III) carboxypeptidases are also consistent with these proposals (60). The Co (III) enzyme is inactive toward both peptides and esters, but examination of ES complexes by stopped-fiow fluorescence demonstrates that the peptide still binds to the modified enzyme while the ester does not. Since Co (III) complexes are "exchange inert, these results suggest that an innersphere complex is formed between the ester and the metal atom during binding but not for the peptide. [Pg.128]


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See also in sourсe #XX -- [ Pg.324 , Pg.325 , Pg.326 , Pg.327 , Pg.328 , Pg.329 ]




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