Dipeptides table

A number of 3/(N-H) coupling constants have been experimentally determined (95) for some dipeptides (Table XXXV, N-Ha couplings), but since the absolute values are rather small, experimental errors tend to obscure the geometrical effects. 

N-H) coupling constants across two saturated carbon atoms have been determined (95) for a number of dipeptides (Table XXXV, N-Hp couplings) and their significance in estimating molecular geometry discussed. It was deduced that the absolute values of 3J(N-H)/ra j a°d 3 /(N-H)faucA(, are 4-8 0 -1 and 1-8 0-1 Hz, respectively. 

Though the preparation of polypeptides directly from free amino acids is very difficult because of their tendency to give cyclic dimers (dioxopiperazines) by ordinary methods22, we have succeeded in obtaining linear polypeptides with relatively high molecular weights by the direct polycondensation of a-amino acids through the use of diphenyl and triaryl phosphites in pyridine. We have also obtained polypeptides with ordered sequences by the indirect polycondensation of activated derivatives of peptides, such as their active esters by ordinary methods, directly from unactivated dipeptides (Table 13)23. ... 

Furthermore, the peptide-imprinted polymer bound its target selectively over other tri-peptides, in addition, the polymer also showed selectivity for the TV-terminal dipeptide subunit over other similar dipeptides (Table 1). 

The sidechain of the second amino acid residue of the Tm(III) dipeptide complexes studied appeared in different parts of space depending upon the nature of the carboxyl residue, e.g. whether it was alanine or glycine, while the — aC proton(s) was in a fixed position for the different ligands. The fixed conformation may be seen from the agreement of the shift ratios for the carboxylate residue of different dipeptides (Table IV). This difference in spatial orientation of the second residue is exemplified by a comparison of the computed conformations of the Tm(III) complexes of phenylalanyl glycine and phenylalanyl alanine (Figure 7). In the case of the aminoacyl glycine the... 

There are several levels of pepfide sfrucfure The primary structure is the ammo acid sequence plus any disulfide links With the 20 ammo acids of Table 27 1 as building blocks 20 dipeptides 20 tripeptides 20" tetrapeptides and so on are possible Given a peptide of unknown structure how do we determine its ammo acid sequence" ... 

The first two entries in Table 9 illustrate the above principle. Both tripeptide Boc—Cys(SBzl)—D-vai-OBzi and dipeptide Z—Tyr—D-Arg-OMe are... 

Each SynChropak column is tested chromatographically to assure that it has been packed according to specifications. For SynChropak GPC columns, a mixture of a high molecular weight DNA and glycyltyrosine, a dipeptide, is used to evaluate internal volume and efficiency. The mobile phase used for the test is 0.1 M potassium phosphate, pH 7, and the flow rate is 0.5 ml/min for 4.6-mm i.d. columns. Minimum plate count values and operational flow rates are listed in Table 10.4 for 4.6-mm i.d. columns of all supports and the various diameters of the SynChropak GPC 100 columns. 

First, they compared CSPs 1 and 3 prepared by the two-step solid-phase methodology with their commercially available counterparts (CSPs 2 and 4) obtained by direct reaction of the preformed selector with a silica support. Although no exact data characterizing the surface coverage density for these phases were reported, all of the CSPs separated all four racemates tested equally. These results shown in Table 3-3 subsequently led to the preparation of a series of dipeptide and tripeptide CSPs 5-10 using a similar synthetic approach. Although the majority of these phases exhibited selectivities lower or similar to those of selectors built around a single amino acid (Table 3-3), this study demonstrated that the solid-phase synthesis was a... 

The addition of titanated allyl carbamates to jV-protectcd (S )-amino aldehydes allows rapid access to intermediates for various dipeptide isosteres98-10°, offering a versatile brick-box system (Table 5). If an acidic amino group is present, two equivalents of reagent are required. 

Table 20 Synthesis of dipeptides from aminocarbenes and a-aminoesters...

Perhaps most encouraging in these discoveries was the observation that NDA/CN worked equally well for derivatization of dipeptides and higher homologues of the primary amino acid series. Again, a stable, fluorescent, isolatable derivative was obtained. One of the most important initial findings was the high fluorescence efficiency of the CBI adduct (12). Tables 1 and 2 list the efficiencies for a representative group of mono-, di-, and tripeptides and a limited comparison of the CBI efficiencies with the more traditional OPA (8) and dansyl (9) derivatives, respectively. 

Our initial attempts with this design using the NDA/CN" system were encouraging far beyond our expectations. Our enthusiasm was sustained when we found that dipeptide-CBI derivatives could be detected at the femtomole level (Tables IV and V) and that such limits of detection with our purified derivatives under less-than-... 

Table 4 In Vitro Opioid Activities of Dipeptide 6-Opioid Agonists... 

More advanced peptides have also been prepared in a similar automated flow sequence through sequential activation of the carboxylic motif in a linear fashion (Baxendale et al. 2006d). Initially a series of the protected dipeptides were generated (Table 2), but this process has now been extended to the formation of tripeptides (Scheme 6) and could easily be further modified to allow additional couplings. 

Table VI lists a number of dipeptide ester complexes prepared via aminolysis in Me2SO and isolated using ion-exchange chromatography many others have been obtained from similar syntheses. Crystal structures are available for A-[Co(en)2((S)-Ala-CR)-Phe)]Br3 H20 (26), obtained from reaction of A-[Co(en)2((S)-AlaOMe]3+ with (i )-PheOMe and acid hydrolysis (Fig. 1), and for A-[Co(en)2((S)-Leu-(S)-Leu OMe)]Cl3 4H20 (24), A-[Co(en)2((S,fl)-Ala-(S)-ValOMe)](C104)3 (24), and /3-[Co(trien)(Gly-GlyOEt)](C104)3 H20 (10). These show considerable variation in chelate 0-Ci-C2-N dihedral angles (0-35°) (10) and it remains to be seen whether this property is important to epimerization (at C2) in these species.

By quenching the aminolysis reaction at various times and examining the diastereomer ratios in the unreacted Co(III)-ester and Co(III)-dipeptide products it has been possible to build up complete concentration-stereochemistry-time profiles for several couplings. One such example is given in Fig. 7, and kinetic analysis of these data allows the rate constants for epimerization (ku k2) and aminolysis (k3, ki) to be found. Some results obtained in this way are listed in Table X. 

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. 

Table 1 Some naturally occurring simple cyclic dipeptides in the protist and plant kingdoms Diketopiperazine (all amino acids are in the L-configuration) Species...

A bigger effect for H2O than OH is very unusual and is a behavior certainly not shown by the uncoordinated amide. The effect is ascribed to a benefit from cyclization and concerted loss of protonated amide, without formation of the tetrahedral intermediate. Although the coordinated OH is some 10 times less effective than coordinated HjO (Table 6.4), it is still about 10 times faster with 15 than via external attack by OH at pH 7 on the chelated amide 13. Early studies showed that complexes of the type CoN4(H20)OH can promote the hydrolysis of esters, amides and dipeptides and that this probably arises via formation of ester, amide or peptide chelates. These then hydrolyze in the manner above. 

Glutamine Glutamine is the most frequently discussed nutraceutical in the cUnical literature as it is an essential fuel for immune and other proliferating cells and the plasma concentration decreases in a number of clinical conditions (Table 18.5). Provision of glutamine (or a dipeptide that contains glutamine), either enterally or parenteraUy, has... 

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