Subject tripeptides

In order to check the role of proline at the C-terminus, linear tripeptides with other imino acids at that position have been subjected to cyclization. Both (74) and (76), the former having L-azetidine-2-carboxylic acid, and the latter sarcosine, gave the respective cyclols (75) and (77). The difference is that (75) can be dissolved in alkali and regenerated by acidification, whereas (77) is isomerized to the N-acylpiperazinedione and hydrolyzed under these conditions (78TL1009). 

Piperazine-2,5-dione formation can occur not only in the case of dipeptides esters or amides containing a free amino group, but also during the activation of N-blocked or protected IV-alkyl amino acids containing dipeptides or even tripeptides. Thus, the activated dipeptide Z-Gly-Pro-ONp (76) afforded the Z-protected piperazine-2,5-dione 77 when subjected to buffered dioxane solution at pH 8 (Scheme 29)J159 ... 

The Finnish fermented milk drink Evolus is fermented with a L. helveticus strain and contains the same tripeptides as Calpis . The Evolus drink has been demonstrated to exert a significant reduction in blood pressure of mildly hypertensive human subjects upon daily intake of 150 ml during a 21-week intervention period (Seppo et al., 2003). A fermented low-fat hard cheese Festivo was developed in Finland (Ryhanen et al., 2001) with probiotic lactic acid bacteria and was found to produce during maturation, high amounts of ACE-inhibitory peptides derived from asi-casein. The peptides emerged at the age of three months and their level remained rather stable at least for six months. 

In practice it is not feasible to determine the sequence of all the residues in a long peptide chain by the stepwise removal of terminal residues. Instead, the chain is subjected to partial hydrolysis (acidic or enzymatic), and the fragments formed— dipeptides, tripeptides, and so on—are identified, with the aid of terminal residue analysis. When enough of these smaller fragments have been identified, it is possible to work out the sequence of residues in the entire chain. 

Thus, Elhnan and coworkers adopted the TTN-mediated oxidative cyclization strategy to synthesize the macrocychc diaryl ether as a key compound , because of the simple procedures and the ready availability of the amino acid starting materials as compared with other synthetic strategies . The easily available tripeptide 839 was subjected to TTN-mediated oxidation, followed by zinc reduction under similar conditions as reported by Yamamura and coworkers to give a 45-60% overall yield of the desired diaryl ether 840, from which a number of receptors such as 841 were synthesized (Scheme 168). The oligopeptide 841 exhibited binding to tripeptide N-Ac2-L-Lys-D-Ala-D-Ala that is... 

The synthesis of a 400 member library of aryl substituted 2-iminohydantoin tripeptide compounds has been accomplished by subjecting resin bound thioureas (36) with 10 equivalents of 1 in the presence of excess triethylamine in DMF for 18 hours.16... 

Lactic bacteria (De Roissart and Luquet, 1994) are known to have membrane amino peptidases which enable them to assimilate small peptides, especially tripeptides. These substances have organoleptic properties that are likely to affect wine flavor, but no specific studies have been carried out on this subject. 

Intramolecular enantiosituselectivity is exemplified by the biosynthetic formation of the mustard oil glucoside sinigrin (60) in horseradish, " the deprotonation of N-Boc-pyrrolidine (62) with sec-butyllithium (s-BuLi)/(-)-sparteine, followed by methylation, "" and, the oxidation of enol 64. Intermolecular enantiosituselective transformations are exemplified by the hydrolysis of racemic N-dodecanoylphenylalanine p-nitrophenyl esters (( )-67) in the presence of tripeptide catalyst (Z)-L-Phe-L-His-L-Leu (68) in each of the latter two cases, only one (externally) enantiotopic carbonyl reacts preferentially. It should be pointed out parenthetically, that as a result of the enantiosituselectivity in these transformations, one has, in effect, kinetic resolution of ( )-67. The electron-impact induced elimination in acetate 71, and the oxidation of 73 exemplify intramolecular diastereosituselective transformations. The epoxidation of the mixture 76/77 is an example of an intermolecular diastereosituselective process at the same time that each substrate is subject to enantiositunonselectivity of the carbonyl sub-sites. 

We then subject the pentapeptide to partial acid hydrolysis and obtain the following dipeptides. (We also get individual amino adds and larger pieces, i.e., tripeptides and tetrapepddes.)... 

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