Oligopeptides, acidic

The following short descriptions of the steps involved in the synthesis of a tripeptide will demonstrate the complexity of the problem amino acid units. In the later parts of this section we shall describe actual syntheses of well defined oligopeptides by linear elongation reactions and of less well defined polypeptides by fragment condensation. 

First the protected oligopeptide is coupled with polymer-bound nitrophenol by DCC. N"-Deblocking leads then to simultaneous cycliiation and detachment of the product from the polymer (M. Fridkin, 1965). Recent work indicates that high dilution in liquid-phase cycli-zation is only necessary, if the cyclization reaction is sterically hindered. Working at low temperatures and moderate dilution with moderately activated acid derivatives is the method of choice for the formation of macrocyclic lactams (R.F. Nutt, 1980). 

Short chains of amino acid residues are known as di-, tri-, tetrapeptide, and so on, but as the number of residues increases the general names oligopeptide and polypeptide are used. When the number of chains grow to hundreds, the name protein is used. There is no definite point at which the name polypeptide is dropped for protein. Twenty common amino acids appear regularly in peptides and proteins of all species. Each has a distinctive side chain (R in Figure 45.3) varying in size, charge, and chemical reactivity. 

Fig. 1. Schematic drawing of precursors for selected brain oligopeptides. Shaded areas represent the location of sequences of active peptide products which are normally cleaved by trypsin-like enzymes acting on double-basic amino acid residues. Precursors are not necessarily drawn to scale, (a) CRF precursor (b) proopiomelanocortin (POMC) (c) P-protachykinin (d) proenkephalin A (e) CGRP precursor (f) preprodynorphin, ie, preproenkephalin B. Terms are...

The elemental and vitamin compositions of some representative yeasts are Hsted in Table 1. The principal carbon and energy sources for yeasts are carbohydrates (usually sugars), alcohols, and organic acids, as weU as a few other specific hydrocarbons. Nitrogen is usually suppHed as ammonia, urea, amino acids or oligopeptides. The main essential mineral elements are phosphoms (suppHed as phosphoric acid), and potassium, with smaller amounts of magnesium and trace amounts of copper, zinc, and iron. These requirements are characteristic of all yeasts. The vitamin requirements, however, differ among species. Eor laboratory and many industrial cultures, a commercial yeast extract contains all the required nutrients (see also Mineral nutrients). 

Fmoc-OSu (Su = succinimidyl), H2O, CH3CN. The advantage of Fmoc-OSu is that little or no oligopeptides are formed when amino acid derivatives are prepared. 

Cl3CCH20C0-0-succinimidyl, 1 N NaOH or 1 N Na2C03, dioxane, 77-96% yield/ This method does not result in oligopeptide formation when used to prepare amino acid derivatives. 

Teoc-O-succinimidyl, NaHC03 or TEA, dioxane, H2O, rt, overnight, 43-96% yield.The use of Teoc-OSu for the protection of amino acids proceeds without oligopeptide formation. Teoc-O-benzotriazolyl was also examined, but was inferior to the succinimide derivative. Teoc-OC6H4-4-N02, NaOH, r-BuOH, 66-89% yield. - ... 

Peptide is the name assigned to short polymers of amino acids. Peptides are classified by the number of amino acid units in the chain. Each unit is called an amino acid residue, the word residue denoting what is left after the release of HgO when an amino acid forms a peptide link upon joining the peptide chain. Dipeptides have two amino acid residues, tripeptides have three, tetrapeptides four, and so on. After about 12 residues, this terminology becomes cumbersome, so peptide chains of more than 12 and less than about 20 amino acid residues are usually referred to as oligopeptides, and, when the chain exceeds several dozen amino acids in length, the term polypeptide is used. The distinctions in this terminology are not precise. 

Amino acid analysis of an oligopeptide seven residues long gave... 

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

The Ugi reaction has been successfully applied to the synthesis of oligopeptide derivatives, c.g.. in the construction of a pure tetra-L-valine derivative69. The 2-methylpropanaldimine 2 of (/7)-l-ferroccnyl-2-rnethylpropylarnine with /V-formyl-L-2-amino-3-methylbulanoic acid (3) as the carboxylic acid component and methyl A/-[(.S)-2-isocyano-3-mcthyl-l -nxo-buLyl -L-2-aiuino-3-inethylbutanoate (4) furnishes the diastereomeric valyl-valyl-valyl-valine derivatives in a ratio (S,S[R],S,S)i(S,R[R],S,S) of 91 9. The stereoselectivity of the process can be enhanced to 98.5 1.5 when two equivalents of tetraethylammonium A -formylvalinate are added. 

The —CO—NH - link shown in the red box is called a peptide bond, and each monomer used to form a peptide is called a residue. A typical protein is a polypeptide chain of more than a hundred residues joined through peptide bonds and arranged in a strict order. When only a few amino acid residues are present, we call the molecule an oligopeptide. The artificial sweetening agent aspartame is a type of oligopeptide called a dipeptide because it has two residues. 

The initial discoveries of the extension of the aromatic ring of the ortho-phthalaldehyde (OPA) to a naphthalene-2,3-dicarboxaldehyde (NBA) and the substitution of cyanide (CN ) for 2-ME as the nucleophile have provided the Center with a much more versatile reagent system (5,11), which maintains the sensitivity for primary aliphatic amines and amino acids, and now is known to form fluorescent products with oligopeptides, proteins, and other related analytes that possess a primary amine function (Equation 1). 

The end product of the action of endopeptidases and exopeptidases is a mixmre of free amino acids, di- and tripeptides, and oligopeptides, all of which are absorbed. Free amino acids are absorbed across the intestinal mucosa by sodium-dependent active transport. There are... 

In this work we will focus on the use of the cubic phase as a delivery system for oligopeptides - Desmopressin, Lysine Vasopressin, Somatostatin and the Renin inhibitor H214/03. The amino acid sequences of these peptides are given in Table I. The work focuses on the cubic phase as a subcutaneous or intramuscular depot for extended release of peptide drugs, and as a vehicle for peptide uptake in the Gl-tract. Several examples of how the peptide drugs interact with this lipid-water system will be given in terms of phase behaviour, peptide self-diffusion, in vitro and in vivo release kinetics, and the ability of the cubic phase to protect peptides from enzymatic degradation in vitro. Part of this work has been described elsewhere (4-6). 

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