Tripeptide mixture

Figure 3.1 On-flow 600 MHz 1 H NMR spectral detection of the HPLC separation of a tripeptide mixture [24]. The horizontal axis corresponds to the 1 H NMR spectrum and the vertical axis represents time, with the total acquisition period being 50 min. The asterisks denote non-peptide impurity peaks, and the labels at the right-hand side denote the classes of tripeptide, e.g. A2M refers to the three compounds, A-A-M-NH2, A-M-A-NH2 and M-A-A-NH2...

Figure 77. OH /NICI mass spectrum of tripeptide mixture [222].

The synthesis of aldehydes and ketoamides was performed on solid phase as well as in solution (Scheme 2.2). A semicarbazone linker (6) was employed for the assembly of the aldehydes on solid phase whereas the corresponding aminoalcohol was coupled in solution to the tripeptide and oxidized to the aldehyde, which produced epimeric mixtures [137]. For the synthesis of the ketoamides, hydroxyester THP resins were used as solid support ((7), Scheme 2.2) [138]. In solution the peptide bond was formed using an aminohydroxycarboxylic acid building block [138, 147]. Oxidation of the free hydroxyl group yielded the final inhibitors ((8), Scheme 2.2). 

Buryak and Severin have described the use of dynamic libraries of Cu(II) and Ni(II) complexes as sensors for tripeptides [61]. A notable aspect of this work is that as isolation of the metal complexes is not necessary (sensing is accomplished by observing changes in the UV-vis spectrum), potential concerns over the lability of coordination complexes do not apply. Specifically, three common dyes [Arsenazo I (41), Methyl Calcein Blue (42), and Glycine Cresol Red (43), Fig. 1.18] were mixed with varying ratios and total concentrations of Cu(II) and Ni(II) salts in a 4X5 array. Previous work had demonstrated that these conditions produced equilibrating mixtures of 1 1 and 2 1 homo- and heteroleptic complexes [62], These arrays were able to clearly and unambiguously differentiate tripeptides based on the differential pattern of response. The Severin laboratory has... 

Severin and Buryak have utilized mixtures of commercial dyes and simple metals [Cu(II) and Ni(II)] to generate DCLs capable of distinguishing closely related di- and tripeptides [11]. The DCL was generated by the combination of metal and dye, which created a complex mixture of uniquely UV-Vis-absorbing coordination compounds. Addition of the analyte (usually a di- or tripeptide) shifted the library speciation that then created a new UV-Vis spectrum (Fig. 5.10). Combining this principle with linear discriminant analysis of the spectrum (in conjunction with learning datasets)... 

Re-formation of the Taste of BMP. According to the above results, the taste of BMP might produced by the combination of the basic amino acid (Lys) at N-terminal and acidic amino acids at the middle part. To confrnn this idea, we prepared a mixed solution of the N-terminal dipeptide (Lys-Gly), the acidic tripeptide at the middle part (Asp-Glu-Glu) and C-terminal tripeptide (Ser-Leu-Ala) and examined the taste. We also studied tastes of a mixture in which a basic dipeptide fragment was replaced by Orn-p-Ala, a salty dipeptide, and a mixture in which Glu-Glu replaced an acidic tripeptide fragment. The result are shown in Table XIV. All of the combinations produced the same character of the taste as BMP. It means that the taste of BMP is mainly produced by the combined effect of the N-terminus basic dipeptide and the acidic tripeptide of the middle part. However, taste strength of the mixture became... 

Large peptides are partially hydrolyzed with enzymes (trypsin and chymotropsin) or acid to mixtures of di- and tripeptides. From the composition of these small units we establish the sequence of amino acids in the large polypeptide. 

In 1986, Drey and co-workersp6l synthesized the first example of a cyclic oligo-p-peptide. They made use of an anhydride method based on o-phenylenephosphochloridite (OPPC) and found that cyclization of a sample of ( )-(P3-HAla)3-OH (53) led to the formation of the cyclic tripeptide 54 in 40% yield (Scheme 17). However, cyclization of the analogous enantiomerically pure peptide under identical conditions failed to produce any cyclic product. Their work showed that the conditions needed to be altered (by using an excess of diethyl phosphite) in order to ensure the starting material dissolved in the reaction mixture. More problems with solubility were encountered when dealing with the cyclic product. In this context, they noted that the enantiomerically pure c [-(5)-p3-HAla-]3 was insoluble in a variety of apolar and more polar solvents. 

Then the tripeptide will consist of a mixture of four diastereomers, only 64% of which will be the desired l,l,l diastereomer (Equation 25-7) ... 

Separation of diastereoisomeric peptides by HPLC is more common. Since each diastereo-isomer has different physicochemical and biological properties, this is of great interest. Separations of diastereoiosomeric di- and tripeptides have usually been performed on reversed-phase columns. Cahill et al. (119) separated diastereoisomeric amino acids and derivatized dipeptides using esters of the /V-hydroxysuccinamide of f-butyl carbonyl-L-amino acid on Cl8 and C8 columns. Linder et al. (120) separated amino acid and peptide derivatives on an RP-C8 column, adding a metal chelate. Mixtures of DL and LD-dipeptides can be separated by RP-HPLC into two peaks, one containing LL- and DD-isomers, the other containing LD and DL-isomers. Sep-... 

Cyclic amide 100 was iV-Boc deprotected and coupled with the tripeptide 102 (Scheme 20) t47l subsequent diaryl ether formation led to an 8 1 mixture of (P)- and (M)-104 with the natural D-O-E isomer predominating. This stands in contrast to the Nicolaou process (Section 16.7.2), in which the unnatural isomer predominated at this step. Removal of protecting groups led to vancomycin aglycon (105). 

A soln of tripeptide 96 (350 mg, 0.385 mmol)[471 in DMF (80 mL) was treated with K2C03 (267 mg, 1.93 mmol), CaC03 (193 mg, 1.93 mmol), and 4-A molecular sieves (700 mg), and the mixture was stirred for 14 h at 45 °C. This was filtered through Celite (EtOAc wash) and the solvent was removed. Flash chromatographic purification (silica gel, EtOAc/hexane 67 33, then acetone/hexane 44 56) gave nitro compound 97 [yield 95mg (27%)] and recovered tripeptide 96 (53mg, 15%). 

A protected serine hydrazide was condensed by the azide method to an S-protected tripeptide H-Asn-Cys-Tyr-NHNH-Cbz to form a protected tetrapeptide Boc-Ser-Asn-Cys-Tyr-NHNH-Cbz 1.02 g of N-rerr-butoxycarbonylserine hydrazide (Boc-Ser-NH-NHj) >n DMF containing HCI in dioxane was mixed at -20 °C with reri-butyl nitrite. This mixture containing the azide Boc-Ser-Nj was neutralized with triethylamine, and a solution of 3.4 g asparaginyl-S-(ethylcarbamoyl)cysteinyl-tyrosinyl 2-(benzyloxy-carbonyl)hydrazide trifluoroacetate was added. After 72 hours at 4 °C a simple work-up procedure and precipitation from methanol-petroleum ether yielded 3 g of impure protected retrapeptide hydrazide. It... 

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