Substrate fragment condensation

Celovsky, V. and Bordusa, F. (2000). Protease-catalyzed fragment condensation via substrate mimetic strategy a useful combination of solid-phase peptide synthesis with enzymatic methods. /. Pept. Res., 55, 325-9. 

Recently, two moderately active (V-hydroxyamide) analogues of the HIV protease substrate have been prepared in two different ways, with O-benzyl protection of the TV-hydroxy-a-amino acid residue.150 Boc-Phet >[CO-N(OH)]Gly-Ile-Phe-OMe is constructed by the mixed anhydride procedure in a step-by-step elongation of the peptide backbone. In contrast, Boc-Phei i[CO-N(OH)]Phe-Ile-Phe-OMe 49 is prepared by fragment condensation (Scheme 15). 

The syntheses of only a very few (A-aminoamide) peptides, with no examples of solid-phase synthesis, have been reported in the literature. The low yield in -coupling calls for the fragment condensation methodology, which has been applied to the synthesis of the HIV protease substrate analogues 79 and 80 (Scheme 23)J50]... 

Synthesis of Boc-Leu-Asn-Lys-De-Val-Arg-Ala-Ala-Ala-Gly-OH by Chymotrpysin-Catalyzed (5+5) Fragment Condensation Using the Combined Solid-Phase Peptide Synthesis Substrate Mimetic Approach... 

Scheme 14 General Course of the Combined Solid-Phase Peptide Synthesis Substrate Mimetic Fragment Condensation Approach Generation of the Protected Peptide Fragment by Aminolysis Using an Amino Acid Substrate Mimetic, and Irreversible Protease-Catalyzed Fragment Condensation ...

Furthermore, phenyl ester are also suitable substrate mimetics for chymotrypsin-catalyzed peptide synthesis, as was established by Bordusa s group and will demonstrated by sophisticated fragment condensations in Sect. 12.5.3.7. 

In reaction mixtures where two or more templates compete for common substrates, the observed selectivity in template-directed fragment condensation reactions can be rationalized based on the relative stability differences between the competing intermediates and product ensembles (Figure 5). Using these, it might be possible to determine in advance the network pathways, by estimating the differences in the stability of all reasonable template-product ensembles. 

The j8-oxidation-condensation mechanism depicted above is an oversimplification of the actual process since (1) endogenous 2-carbon fragments may interact with those from the substrate fatty acid, and (2) not all 2-carbon fragments necessarily condense to form acetoacetate but may proceed along other pathways (see Fig. 2). We shall also see, in a later section, that, in general, complete randomization of 2-carbon fragments does not occur. Furthermore, any randomization that does occur takes place before the 2-carbon fragments condense to form acetoacetate. ... 

The rapid spontaneous mutarotation of glucose-6-phosphate has been shown to result from an intramolecular catalysis of the reaction by the phosphate group at carbon 6 (81). The cleavage of glucose into three carbon fragments, which is essentially a reversal of the aldol condensation reaction, requires the ketohexose as substrate. The necessary isomerization reaction to form the ketohexose then uses the open-chain form intermediate of the mutarotation reaction. Salas et al. (80) have speculated that the enhanced mutarotation of glucose-6-phosphate may thus have been the key requirement which led to the evolution of the phosphorolytic pathway for glucose metabolism. 

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