Tri-, Tetra-, and Penta-peptides

Some of the cyclic tripeptides investigated so far have been described in earlier parts of this article. In addition, Deber et d. 77) invest ted Cyclo-(Pi03), Cyclo-(Pro-Pro-Hyp), Cyclo-(Pro-Pro-Hyp), and Cyclo-(Pro Jho-Ifyp). According to their investi- 

The X-ray diffraction study of crystalline Cyclo-(Pro3) and Cydo-(Pro-Pro-Ifyp) has been reported by Kartha et d. 109). 

Some of the cyclic tetrapeptides investigated so far have been described in earlier parts of this article. In addition, Deber etd, 110) investigated C yclo-(Pro-Gly)2. Accordii to their investigation it was made clear that the peptide bonds of Cydo-(Pro-Gly)2 has a ds-trans-cis-trans sequence, and that one of the Pro-C —C = O bonds is cis p = —60°) and the other is tmns ip = 120°). and H NMR spectroscopies of Cyclo-(Pro-Gly)2 in D2O-CH3CN (9 1) or DMSO-d6-CD2Cl2 (2 5) mixed solvents showed that on heatup the solution the X-Pio bond remained cis but a slow cis —tram interconversion (AF 13—15 kcal/mol) of fto-C —C = O bond took (dace. This (dienomenon mi t be characteristic of relatively crowded cyclic tetrapeptides such as C ydo-(Pro-Gly)2. However, the slow cis —tram interconversion has not been observed with Cyclo-(D-Pro-Gly) and Cyclo-(Pro-Sar)2, which leaves the complete understanding of the problem for the future. Such a slow cis -tram interconversion would not be the case for larger cyclic peptides and linear peptides. 

Gupta and Singh (111) investigated the vibrational ctra of Cyclo-(Ala4). 

Metaldi ef o . 112) nthesized a cyclic pentapeptide, Cyclo Qly-Ala-Gly-Gly Pro), and invest ted the 220-MHz NMR spectra in DMSO-d. Each proton gave two sets of resonance signals, so that the existence of two different conformations was considered, a nu r conformation being represented by M and a minor conformation by m. Hie chemical shift and the temperature dependence of the resonance signal, and die oinqparison with model peptides suggested the structures shown in Fig. 19 

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Studies on the tri-, tetra- and penta-peptides of a-methylalanine (65T3209, 73ACS1509) have shown that cyclization to the imidazo[l,2-a]pyrazine ring system occurs and a sequence for its formation from the tripeptide suggested (467) -> (468) -> (469). Another tripeptide cyclizes to a piperazine and then to the bicyclic system (78TL1009). 

Serotonin transporter gene (5-HTTLPR) BRCA gene BRCA1 and 2 genes Viral DNA DMD gene Tetanus toxin C fragment Uracil Uracil ATP ATP Guanine Des-Tyr-Leu-enkephalin Des-Tyr-Leu-enkephalin Tri-, tetra-, penta-, octa-peptides... 

It is less well known that tri-, tetra-, penta-, and even hex-asulfanes also occur in organisms or materials produced from them, including peptides. In this section, a brief overview will be presented of chainlike and cyclic organic polysulfanes, which have so far been isolated from or detected in biological materials. For sulfur-rich peptides, see refs. An extensive review on organic sulfur compounds from marine organisms is available. ... 

Microwave heating can be nsed to facilitate peptide synthesis using other non-traditional coupling methodologies. Eor example, A/-Fmoc-protected(a-aminoacyl) benzotriazoles have been nsed in the preparation of tri-, tetra-, penta-, hexa-, and heptapeptides on solid-snpport with an average crnde yield of 71% (Scheme 9.2). ° Acylbenzotriazoles are easily prepared, chirally stable analogs of acid halides that are relatively water stable. Coupling reactions of A/-protected(a-aminoacyl)... 

The aldol reaction between functionalized ketones, such as hydroxyacetone (8a, 29.2 equiv.) with high electrophilic aldehydes, was possible using different A -terminal proline peptide derivatives (10-20 mol%) in mixtures of THF water at 0°C. Among ten screened different di-, tri-, tetra-, penta- and hexapeptides, catalysts 120a, b (Fig. 4.20) with lipophilic phenylalanine residues gave the best performance, providing mainly regioisomers /xo-10 (Scheme 4.3, R =H) in 82 and 76% yield, and 82 and 87% ee, respectively [207]. 

Copper oxide-covered electrodes in alkaline media have been anployed for detection of peptides in both HPLC [112,114] and CE [116]. Peptides that have been determined include small peptides such as Gly-Gly-amide [112,116], Gly-Gly [112,116], tri-, tetra-, penta-, and hexaglycine [114,116], aspartame [116] cyclic Leu-Trp-Asp-Pro-Val [116], cycfic Leu-Tyr-Asp-Pro-Val [116], and des-Tyr-leucine enkephalin [114]. Detection limits (withont on-column preconcentration) are poor, typically in the 5-100 pM range [114,116]. 

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