Tripeptides aspartyl

FIGURE 10.10 The reaction of tridated sodium borohydride with the aspartyl phosphate at the active site of Na, K -ATPase. Acid hydrolysis of the enzyme following phosphorylation and sodium borohydride treatment yields a tripeptide containing serine, homoserine (derived from the aspartyl-phosphate), and lysine as shown. The site of phosphorylation is Asp" in the large cytoplasmic domain of the ATPase. 

A medicinal example is provided by klerval (Fig. 6.18). The aspartic acid residue in this tripeptide analogue is also a site of chemical instability. At pH 1, cleavage of the Asp-Xaa bond (Fig. 6.18, Reaction b) was second in importance after C-terminal deamidation (see Sect. 6.3.2.1), and cleavage of the Xaa-Asp bond (Fig. 6.18, Reaction c) was third. At pH 4, cleavage of the Asp-Xaa bond was the major reaction and was accompanied by the formation of the succinimide and the iso-aspartyl peptide cleavage of the Xaa-Asp bond was minor. At pH 7, the major products were the L-iso-Asp and D-iso-Asp peptides, together with minor amounts of the D-Asp peptide. 

De Boni, S., NeusiiB, C., Pelzing, M., and Scriba, G. K. E. (2003). Identification of degradation products of aspartyl tripeptides by capillary electrophoresis-tandem mass spectrometry. Electrophoresis 24, 874-882. 

After the finding of a sweet taste in L-Asp-L-Phe-OMe (aspartame) by Mazur et at. (6), a number of aspartyl dipeptide esters were synthesized by several groups in order to deduce structure-taste relationships, and to obtain potent sweet peptides. In the case of the peptides, the configuration and the conformation of the molecule are important in connection with the space-filling properties. The preferred conformations of amino acids can be shown by application of the extended Hiickel theory calculation. However, projection of reasonable conformations for di- and tripeptide molecules is not easily accomplished. 

Further examinations of the molecular features and of the model of receptor have suggested that several aspartyl tripeptide esters may also taste sweet. In confirmation of the idea, several tripeptide esters have been synthesized. In the first place, L-Asp-Gly-Gly-OMe (38) was synthesized as an arbitrarily-selected standard of tripeptides, because it was considered that this peptide ester had the simplest structure, and correlation of other peptides to (38) was easy. The tripeptide ester was predicted that it would be slightly sweet or tasteless because its projection formula was similar in size and shape to that of L-Asp-Gly-0Bum which is 13 times sweeter than sucrose (16) and because it is more hydrophilic than the dipeptide. The tripeptide (38) was devoid of sweetness and almost tasteless. 

Finally, L-Asp-D-Val-Gly-OMe (41) was synthesized in order to see whether it remained sweet. The peptide was devoid of sweetness and almost tasteless, though D-valine-containing aspartyl dipeptide esters such as L-Asp-D-Val-0Pr (17) and L-Asp-D-Val-OPrt (8, 17), which are similar to the tripeptide ester in size and shape and have potent sweet taste. 

The organic phase is dried over sodium sulfate, and solvent is removed by rotary evaporation to leave 1132 mg (97%) of the crude pale-yellow tripeptide. For further purification the crude product is dissolved in ethyl acetate, treated with some activated carbon and filtered through Celite. Removal of the solvent and crystallization from ethyl acetate/ether/petroleum ether (ca. 2 1 1) yields 993 mg (85%) of colorless crystals of benzyloxy-carbonyl-L-aspartyl-(tert-butyl ester)-L-phenylalanyl-L-valine methyl ester mp 119-120°C (Note 5). 

This modification seems to mimic the presumed tetrahedral intermediate involved in the aspartyl protease-catalyzed hydrolysis of the peptide bond. A HIV-1 protease inhibitor containing a hydroxyethylene bond isostere has been prepared on solid phase [143]. A Boc-N-protected bromomethyl ketone was coupled to the resin-bound N-free Pro-Ile-Val tripeptide, and the keto function was reduced to an OH group with NaBH4.The peptide analogue was then elongated on the resin.This procedure allows rapid access to a variety of hydroxyethylamino peptide bond isosteres, and in good yield. 

S Sabah, GKE Scriba. Resolution of aspartyl dipeptide and tripeptide stereoisomers by capillary electrophoresis. J Microcol Sep 10 255-258, 1998. 

Epoxidation. For asymmetric epoxidation of alkenes capable of H-bonding by aqueous H2O2 and AT,iV -diisopropylcarbodiimide the proline-based tripeptide 12 plays a catalytic role by transforming the aspartyl residue into a chiral peracid. ... 

HCl or 0.25 M acetic acid are sufficient to effect hydrolysis of the peptide bonds on both sides of aspartyl residues. For instance the hexapeptide Val-Leu-Gly-Asp-Phe-Pro yields the tripeptide Val-Leu-Gly, the dipeptide Phe-Pro and free aspartic acid. Release of aspartic acid is usually complete after a day of hydrolysis at 100 °C in 0.25 M AcOH while hydrolytic fission of other peptide bonds is negligible. Asparagine creates a notable exception because the carboxamide group in its side chain is fairly sensitive to acid catalyzed hydrolysis and the free carboxyl group of the gradually formed aspartyl residue provides the neighboring group effect which leads to the excision of aspartic acid from the chain. 

Figure 4 Simultaneous chiral separation of the isomeric tripeptides Gly-a-Asp-PheNH2 and Gly- -Asp-PheNHa. Experimental conditions 40/47cm polyacrylamide-coated capillary, 50 im, 50 mmol I sodium phosphate buffer, pH 5.25, 60mgmr car-boxymethyl- -cyclodextrin, -20 kV, UV detection at 215 nm. (Reprinted with permission from Sabah S and Scriba GKE (1998) Electrophoretic stereoisomer separation of aspartyl dipeptides and tripeptides in untreated fused-siiica and polyacrylamide-coated capillaries using charged cyclodextrins. Journal of Chromatography A 822 137-145 Elsevier.)...

Sabah S, Scriba G (1998) Electrophoretic stereoisomer separation of aspartyl dipeptides and tripeptides in untreated fused-silica and polyacrylamide-coated capillaries using charged cyclodextrins. J Chromatogr A 822 137-145... 

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