Peptides aspartyl

Some peptides have special tastes. L-Aspartyl phenylalanine methyl ester is very sweet and is used as an artificial sweetener (see Sweeteners). In contrast, some oligopeptides (such as L-ornithinyltaurine HQ. and L-oriuthinyl-jB-alariine HQ), and glycine methyl or ethyl ester HQ have been found to have a very salty taste (27). 

Aspartame (L-aspartyl-L-phenylalanine methyl ester [22839-47-0]) is about 200 times sweeter than sucrose. The Acceptable Daily Intake (ADI) has been estabUshed by JECFA as 40 mg/kg/day. Stmcture-taste relationship of peptides has been reviewed (223). Demand for L-phenylalanine and L-aspartic acid as the raw materials for the synthesis of aspartame has been increasing, d-Alanine is one component of a sweetener "Ahtame" (224). 

Under basic coupling conditions an aspartyl peptide that has a /3-phenacyl ester i converted to a succinimide. The use of PhSeH prevents the a,/3-rearrangement c the aspartyl residue during deprotection. 

Cycloalkyl esters have.been used to protect the /3-CO2H group in aspartyl peptides to minimize aspartimide formation during acidic or basic reactions. Aspartimide foimation is limited to 2-3% in TFA (20 h, 25°), 5-7% with HF at 0°, and 1.5-4% TfOH (thioanisole in TFA). Cycloalkyl esters are also stable to Et3N, whereas use of the benzyl ester leads to 25 % aspartimide formation during Et3N treatment. Cycloalkyl esters are stable to CF3COOH, but are readily cleaved with HF or TfOH. - ... 

The HIV-1 protease, like other retroviral proteases, is a homodimeric aspartyl protease (see Fig. 1). The active site is formed at the dimer interface, with the two aspartic acids located at the base of the active site. The enzymatic mechanism is thought to be a classic acid-base catalysis involving a water molecule and what is called a push-pull mechanism. The water molecule is thought to transfer a proton to the dyad of the carboxyl groups of the aspartic acids, and then a proton from the dyad is transferred to the peptide bond that is being cleaved. In this mechanism, a tetrahedral intermediate transiently exists, which is nonconvalent and which is mimicked in most of the currently used FDA approved inhibitors. 

Cathepsin D. The design of inhibitors of the aspartyl protease cathepsin D started from a virtual library of peptide analogs that contained the typical hydroxyethylamine isoster for the cleavable peptide bond. As the availability of starting materials would have generated a library of about 1 billion compounds, virtual screening was applied to reduce this multitude of candidate structures to a reasonable number. The backbone of a peptide... 

Haque TS, Skillman AG, Lee CE, Habashita H, Gluzman lY, Ewing TJA, Goldberg DE, Kuntz ID, Ellman JA. Potent, low-molecnlar-weight non-peptide inhibitors of malarial aspartyl protease plasmepsin II. J Med Chem 1999 42 1428-40. 

T. Geiger and S. Clarke, Deamidation, isomerization and racemization at asparaginyl and aspartyl residues in peptides, J. Biol. Chem, 262, 785 (1987). 

JP Tam, TW Wong, MW Reimen, FS Tjoeng, RB Merrifield. Cyclohexyl ester as a new protecting group for aspartyl peptides to minimize aspartimide formation in acidic and basic treatments. Tetrahedron Lett 4033, 1979. 

FIGURE 6.15 Imide formation from a dipeptide sequence containing an aspartyl residue with side-chain functional group in various states followed by generation of two peptide chains resulting from cleavage at the bonds indicated by the dashed arrows. The reaction is catalyzed by base52 or acid. [Merrifield, 1967]. The table shows the effect of the nature of the substituent on the extent of this side reaction. Dmpn = 2,4-dimethylpent-3-yl. 

A Battersby, JC Robinson. Studies on the specific fission of peptide links. Part 1. The rearrangement of aspartyl and glutamyl peptides. J Chem Soc 259, 1955. 

CC Yang, RB Merrifield. The P-phenacyl ester as a temporary protecting group to minimize cyclic amide formation during subsequent treatment of aspartyl peptides with HF. J Org Chem 41, 1032, 1976. 

M Bodanszky, JZ Kwei. Side reactions in peptide synthesis. VI1. Sequence dependence in the formation of aminosuccinyl derivatives from P-benzyl-aspartyl peptides. 

M Bodanszky, J Martinez. Side reactions in peptide synthesis. 8. On the phenacyl group in the protection of the p-carboxyl function of aspartyl peptides. J Org Chem 43, 3071, 1978. 

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