Dipeptide, chemical structure

In the course of investigations of aspartyl dipeptide esters, we had to draw their chemical structures in a unified formula. In an attempt to find a convenient method for predicting the sweettasting property of new peptides and, in particular, to elucidate more definite structure-taste relationships for aspartyl dipeptide esters, we previously applied the Fischer projection technique in drawing sweet molecules in a unified formula 04). 

The structure-taste relationships will be discussed in detail. Dipeptide esters are closely related to amino acids in chemical structure and properties. Hence, we selected amino acids as the standard to which sweet peptides were related. The structural features of sweet-tasting amino acids have been best explained by Kaneko (12) as shown in Figure 2, in which an amino acid will taste sweet when R2 is H, CH3 or C2H5, whereas the size of Ri is not restricted if the amino acid is soluble in water. 

Figure 2 Small-molecule inhibitors of caspases. (a) Schematic of a typical caspase inhibitor (b) caspases substrate specificities preferred amino acids in PI -P4 positions (c) chemical structure of PAC-1, procaspase-3 activator (EC50 of 0.22 uM) (d) low-nanomolar inhibitors of caspases-3 and -7 (compound 1) and caspases-3, -7 and -9 (compound 2) (e) caspase-1 peptidomimetic inhibitor VX-740 or pralnacasan from Vertex Pharmaceutical (Cambridge, MA) (f) peptidomimetic irreversible oxamyl dipeptide pan-caspase inhibitor IDN-6556 from IDUN Pharmaceuticals and (g) caspase-3 inhibitor.

Fig. 12. Chemical structures of the (A) N-acetyrnurarnyl-dipeptide-cysteamine/ and (B) lipo-N-aceytlmuramyl-tripeptide-cysteamine/IMax15 -gastrin-[2-17 adduct...

FI GU RE 9.1 Proposed chemical structure of dipeptide from Brazil nut protein extraction. 

Figure 5 Reaction scheme for the preparation of tyrosine-derived polyiminocarbonates. The basic monomeric repeat unit is tyrosyl-tyrosine dipeptidc. To optimize the polymer properties, the chemical structures of the N- and C-terminal protecting groups (Rj and R2) have to be designed carefully. In the first reaction step, protected tyrosyl-tyrosine dipeptide is cyanylated with cyanogen bromide (CNBr). In the next step, polymerization occurs when equimolar quantities of the dipeptide and tlie cyanylated dipeptide are mixed in the presence of a base catalyst.

The chemical structure and composition of thin films of the two dipeptides on Ti02 were experimentally investigated by XPS at both O and N K-edges. Theoretical ab initio calculations (ASCF) were also performed to simulate the spectra, allowing for a direct comparison between experiment and theory (see Fig. 4.37). 

The primary structure of a polypeptide is its sequence of amino acids. It is customary to write primary structures of polypeptides using the three-letter abbreviation for each amino acid. By convention, the structure is written so that the amino acid on the left bears the terminal amino group of the polypeptide and the amino acid on the right bears the terminal carboxyl group. Figure 13-35 shows the two dipeptides that can be made from glycine and serine. Although they contain the same amino acids, they are different molecules whose chemical and physical properties differ. Example shows how to draw the primary stmcture of a peptide. 

So far, we have investigated higher-order structure of polypeptides by solid-state high-resolution NMR not only using experimental but also theoretical methods[2-4]. The chem cal shifts can be characterized by variations in the electronic states of the local conformation as defined by the dihedral angles(4>,W). Ando et al. have calculated contour map for the Cp carbons of an alanine dipeptide by using the FPT INDO method within the semi-empirical MO framework. The calculated map reasonably predicts the experimental version. This shows that the chemical shift behavior of the L-alanine residue Cp-carbonyl carbons in the... 

The dependence of the principal components of the nuclear magnetic resonance (NMR) chemical shift tensor of non-hydrogen nuclei in model dipeptides is investigated. It is observed that the principal axis system of the chemical shift tensors of the carbonyl carbon and the amide nitrogen are intimately linked to the amide plane. On the other hand, there is no clear relationship between the alpha carbon chemical shift tensor and the molecular framework. However, the projection of this tensor on the C-H vector reveals interesting trends that one may use in peptide secondary structure determination. Effects of hydrogen bonding on the chemical shift tensor will also be discussed. The dependence of the chemical shift on ionic distance has also been studied in Rb halides and mixed halides. Lastly, the presence of motion can have dramatic effects on the observed NMR chemical shift tensor as illustrated by a nitrosyl meso-tetraphenyl porphinato cobalt (III) complex. 

A number of x-ray structures of monoperoxoheteroligand complexes of vanadate have been reported. The heteroligands have included picolinate, dipicolinate, dipeptides, and a number of a-hydroxycarboxylate. Solution NMR studies have been carried out for several of these systems, and various solution products described. Table 6.4 gives the 51V NMR chemical shifts for a number of products that have been studied. This table covers a variety of types of complexes, and the chemical shifts range over about 100 ppm, from about -580 to -680 ppm. 

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