Peptide side chain

S Guttmann, RA Boissonnas. Synthesis of benzyl V-acetyl-L-seryl-L-tyrosyl-L-seryl-L-methionyl-y-glutamate and related peptides, (side-chain alkylation) Helv ChimActa 41, 1852, 1958. 

The Q -heUcal turn of residues Met P5-Ala P8 exposes the last four peptide side chains for specific interactions, most of which differ from those in the pentasaccharide complex. The only structurally mimetic hydrogen bond here is from the side chain of His P6 to Tyr L32 OH, which is similar to the hydrogen bond from Rha B 4-OH in the pentasaccharide complex. An additional interaction of the peptide is another hydrogen bond of the His P6 side chain... 

This sequence was found to enhance the staltility of the superoxidized state of 4Fe-cluster probably by its hydrophobic peptide side chains. Thus, the CV results indicated a quasi-reversible redox couple at +0.12 V (SCE) in DMF (see Table III). Thus the complex may be regarded as a model of HiPIP. Simple model complexes, [Fe4S4(S-r-Bu)4]2- (27), [Fe4S4(2,4,6-trimethylbenzenethiolato)4]2- (28), and [Fe4S4(2,4,6-triisopropylbenzenethiolato)4]2 (16), have been synthesized, and the latter has been crystalligraphically characterized (29). 

The enzymic processes appear exactly equivalent, except that protons are removed and supplied through the involvement of peptide side-chains. It is unlikely that a distinct enolate anion is formed instead, we should consider the process as concerted with a smooth flow of electrons. Thus, as a basic group removes a proton from one part of the molecule, an acidic group supplies a proton at another. 

The first antitumor antibiotic was actinomycin A which was isolated from a Streptomyces species. The actinomycins are chromopeptides containing a planar chromophore, responsible for the bright color of the compounds, with peptide side chains. The most important representative of this group which is in clinical use is actinomycin D, or dactinomycin. 

To get a directed coupling of a peptide via its N-terminal NH2-group, the introduction of a monochloroacetylglycyl residue during peptide synthesis is recommended. Of course, coupling via NH2-, SH-, or carboxyl groups of peptide side chains is also possible. 

O-Acylated Hmb is stable to acidolysis by TFA giving a useful additional feature to Hmb-containing peptides. Side-chain protection and the V -protection, if it is first replaced with Boc before Hmb O-acetylation, can be removed and backbone protection retained. After deacetylation of Hmb with aqueous hydrazine the peptide can be further purified before removal of the Hmb groups, useful when the product is poorly soluble. This feature is also useful for the purification of large polypeptides as the presence of backbone protection on the side-chain deprotected peptide prevents the formation of relatively stable folded structures that can complicate HPLC purification.1 11... 

The synthesis of type I bicyclic peptides is the most simple as the two side-chain-to-side-chain cyclizations can be performed successively on the assembled peptide or more appropriately by condensation of the two monocyclic segments preferably in solution. As shown in Scheme 23 (path A), for the synthesis of suitably protected monocyclic peptides, side-chain attachment of Asp or Glu residues to the oxime resin is proposed,[436,43T which leads to the desired cyclization and release of the protected segments as Pac or preferably as A1 es-tersJ396 These are C-terminally deprotected, when required, and then assembled in solution into bi- or polycyclic peptides of type I. 

Figure 11. (a) The chemical structure of a 24-membered macrocyclic molecule composed of alternating D- and L-amino acids, cyclo(Gln-(D-Leu-Trp)4-D-Leu 7. (b)A self-assembled tubular structure spanned across the bilayer lipid membrane. Flat ring-shaped units in the antiparallel configuration stack to form a tubular structure through extensive inter subunit hydrogen bonding and peptide side chain-lipid interactions. ... 

The antihypertensive agent 278 has been 14C-labelled by carbonation of the 2-lithiated indole, 279 (R = Li), with 14CC>2 and subsequent combination with a preformed peptide side chain. In 279 (R = H) the indole nitrogen has been converted into its benzenesulphonyl derivative to direct properly the lithiation while the 2-hydroxy-3-isopropylaminopropoxy side chain has been protected as oxazolidin-2-one290. 

Fig. 3. Schematic presentation of the design of the second-generation (4)M2e-Sl-S2 construct. The numbers indicate the number of amino acid residues in each peptide side chain.

Fig. B.15.1. Most protease inhibitors are substrate analogs. Binding to the substrate binding sites (S) of the enzyme is established by interactions with the peptide side-chains (P) and the substrate...

Parker KC, Bednarek MA, Coligan JE (1994) Scheme for ranking potential HLA-A2 binding peptides based on independent binding of individual peptide side-chains. J Immunol 152 163-175... 

The muramyl peptides (MP) of the bacterial cell walls are polymeric chain molecules composed of N-acetylglucosamine and N-acetylmuramic acid, each carrying a peptide side chain and crosslinked with one another (Fig. 8). The N-terminal D-Ala residues of the side chains are bound covalently to the peptide side chains of neighboring polysaccharide chains via pentaglycine units. 

In the case of a simple redox enzyme such as cytochrome c where both sites of the heme iron are ligated by peptide side chains, two pathways have been suggested by which an electron can travel to or from the... 

Such chemical changes may lead to compounds that are not hydrolyzable by intestinal enzymes or to modifications of the peptide side chains that render certain amino acids unavailable. Mild heat treatments in the presence of water can significantly improve the protein s nutritional value in some cases. Sulfur-containing amino acids may become more available and certain antinutritional factors such as the trypsin inhibitors of soybeans may be deactivated. Excessive heat in the absence of water can be detrimental to protein quality for example, in fish proteins, tryptophan, arginine, methionine, and lysine may be damaged. A number of chemical reactions may take place during heat treatment including decomposition, dehydration of serine and threonine, loss of sulfur from cysteine, oxidation of cysteine and methio-... 

Figure 12. Combinatorial Library Scaffold compared to pepstatin. (a) Pepstatin (b) scaffold for combinatorial library (c) portion ofpepstatin used to test methodology. The P1-P3 peptide side-chains are indicated...

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