Peptides general structure

Important products derived from amino acids include heme, purines, pyrimidines, hormones, neurotransmitters, and biologically active peptides. In addition, many proteins contain amino acids that have been modified for a specific function such as binding calcium or as intermediates that serve to stabilize proteins—generally structural proteins—by subsequent covalent cross-hnk-ing. The amino acid residues in those proteins serve as precursors for these modified residues. Small peptides or peptide-like molecules not synthesized on ribosomes fulfill specific functions in cells. Histamine plays a central role in many allergic reactions. Neurotransmitters derived from amino acids include y-aminobutyrate, 5-hydroxytryptamine (serotonin), dopamine, norepinephrine, and epinephrine. Many drugs used to treat neurologic and psychiatric conditions affect the metabolism of these neurotransmitters. 

The neuropeptide Y (NPY) belongs to a family of peptides that includes peptide YY and pancreatic polypeptide, and it is associated with several diseases such as asthma, immune system disorders, inflammatory diseases, anxiety, depression and diabetes mellitus. NPY is found in the central and peripheral nervous system, and its biological functions are mediated by interactions with five receptor sub-types, i.e. Yl, Y2, Y4, Y5 and Y6. Several studies indicate that the feeding behavior is influenced by interactions between NPY and Yl and Y5. Deswal and Roy used Cerius descriptors and genetic function approximation QSAR to investigate the structural determinants for the inhibition potency of 24 compounds with the general structure 4 for the NPY Y5 receptor [31]. The best QSAR (H = 0.720,... 

Small peptides generally do not form significant secondary structure in water (there are some that do). For small peptides that do not form stable secondary structure, there are often other favorable interactions within the peptide that stabilize the formation of the helix or sheet structure. 

Electron-Transfer in Simple Binuclear Complexes. In trying to understand the electron transfer mediation effects of peptide bonds and amino acid side chains on rates of electron transfer in simple systems that are amenable to detailed investigation, we have designed and synthesized a series of complexes which contain within a single molecule two different oxidizing agents —both of which are inert to substitution. The series of complexes we have synthesized is represented schematically by the general structure 1. 

The two-step activation of oxazolidinones is depicted in Fig. 8.26. Hydrolysis yields an A-(l -hydroxy alkyl) derivative, which breaks down to liberate the peptide or A-acylamino acid (Fig. 8.26, Reactions a and b). Since oxazolidinones are prepared by the condensation of a peptide and an aldehyde (Fig. 8.26, Reaction c), the reverse reaction (i. e., one-step activation) cannot be excluded. Examples of this type of prodrug are provided by a series of oxazolidinones of the general structure 8.190 (R = PhCH20 R = H, Me, i-Pr, or PhCH2 R" = H, Me, or Ph Fig. 8.26) [248]. In phosphate buf-... 

Figure 7 CD Spectra (Methanol) of Five Peptides with the General Structure of Dnp-Gly-Pro-Xaa -Gly-...

Merck and Co., Inc., have patented imidazo[4,5-3]pyridines of the general structure 194, which have been found to be antagonists of calcitonin gene-related peptide (CGRP) receptors, which are useful for the treatment of the symptoms for headache, migraine, and cluster headaches <2005W0013894>. Merck have also patented the... 

Peptides containing the general structure 84 (Scheme 39) underwent between 50-100% cleavage in 95%TFA/H20 at room temperature in 60 minutes, that is, under routine conditions for the removal of a peptide from the resin after SPPS. The hydrolysis yielded the N-acyl-A-methyl peptide fragment 88.12041 The same peptides were also cleaved in solution but at a much slower rate (13-18 h). The hydrolysis occurs only when a carbonyl group is present at the N-terminal side of the N-methylated residue. The hydrolysis was accompanied by racemization of the N-methylated residue. The suggested mechanism involves the formation of the oxazolonium tetrahedral intermediate 87. This hydrolysis was circumvented by cleavage of the peptide (that did not contain functional side chains) from the resin with 0.1% NaOH in 50% aq MeOH (rt, 60 min). 

A more versatile route to synthesize peptide thioesters is by the preparation of a peptide thioacid via the solid-phase method and then reaction with a halo derivative to form the thioester. This route can be achieved via the preparation of thioester linkers that can be applied in stepwise solid-phase peptide synthesis. The general structure of the N-protected amino thioacid attached to the linker is shown in Scheme 14. t65-80 ... 

Amino acids and the structure of the polypeptide chain. Polypeptides are composed of L-amino acids covalently linked together in a sequential manner to form linear chains, (a) The generalized structure of the amino acid. The zwitterion form, in which the amino group and the carboxyl group are ionized, is strongly favored. (b) Structures of some of the R groups found for different amino acids, (c) Two amino acids become covalently linked by a peptide bond, and water is lost, (d) Repeated peptide bond formation generates a polypeptide chain, which is the major component of all proteins. 

Methylene-bridged resorcin[4]arenes or cavitands, of the general structure shown in Scheme 8, are suitable as templates for the organization of peptide structure because of their rigidity, enforced cavities and synthetic availability.132 59 ... 

As illustrated by the synthesis of 13, which can be viewed as a Gly-Hse (Hse = homoserine) mimic (Scheme 1.2.4), aminals of the general structure 11 serve as versatile educts for the preparation of pipecolyl-dipeptide analogs with fixed anti-peptide geometry. The stereochemistry of compound 13 was determined unambiguously by 2D NOESY NMR spectroscopy and is in accordance with a re-... 

A short introduction to peptide synthesis will be given before the synthesis of glycopeptides is discussed. Proteins are assembled by a nucleic acid templated reaction from a menu comprising 19 L-oc-amino acids of general structure 1 and the amino acid L-proline (2) (Figure 5.1). Nature synthesises proteins by a stepwise assembly of amino acid building blocks. Since these compounds are readily available in... 

Figure 5.1 Amino acid and peptide structures. 1 = general structure 2 — L-proline.

---