Amino proline

B L-4-trans-amino proline +2 (towards C-terminus) +2 (towards iV-terminus) n.d. [112]... 

The easy N-amination of Pro by the oxaziridine reagent 72 82 allows for a step-by-step synthesis of 89 where N-amination is performed on the growing peptide and Np-coupling of the A-amino proline residue is carried out classically with the activated ester procedure (Scheme 27). 109 ... 

In 2004, the tra s-4-amino-L-proline derived di-, tri- and tetrapeptides 13a-c were studied in the group of Tsogoeva for asymmetric 1,4-conjugate addition reactions. The addition of different nitroalkanes to cyclic a,p-unsaturated ketones in the presence of achiral tra s-2,5-dimethylpiperazine (14) of Hanessian as a stoichiometric additive and peptides 13a-c at only 2 mol% loading were investigated. Two 4-trans-amino-proline residues (catalyst 13a) were shown to be sufficient to eatalyse the conjugate addition reactions with up to 88% enantiomeric excess and up to 100% yield (Scheme 13.11). 

Unclassified amino Proline > methio- Only methionine Serine > cystine > Only methionine at- Proline not attacked... 

The positions of the three amino-acids are shown clearly by the colour of their zones or spots, the proline being yellow and the glycine and phenylalanine being blue. Note the Rp value for each amino-acid ... 

The principle of this method depends on the formation of a reversible diastereomeric complex between amino acid enantiomers and chiral addends, by coordination to metal, hydrogen bonding, or ion—ion mutual action, in the presence of metal ion if necessary. L-Proline (60), T.-phenylalanine (61),... 

Thin-Layer Chromatography (tic). Tic (126) is used widely for quahtative analysis and micro-quantity separation of amino acid mixtures. The amino acids detected are developed by ninhydrin coloring, except for proline and hydroxyproline. Isatia has been recommended for specific coloring of pToline (127). 

Fig. 1. The side chain R of the 20 standard amino acids +H3N—CHR—COO at pH 7. For proline, the complete stmcture is shown. Amino acid side chains can be categorized as aUphatic (Gly, Ala, Val, Leu, and He), hydrophilic (Ser, Thr, Asp, Glu, Asn, Gin, Lys, and Arg), sulfur-containing (Cys and...

Fig. 10. Sequences (see Table 1) of betabeUins. In each case, only one-half of the P-sandwich is shown. The dimer is formed from identical monomeric sets of four P-strands. In the pattern sequence, e is for end, p is for polar residue, n is for nonpolar residue, and t and r are for turn residues. Lower case f is iodophenyialanine lower case a, d, k, and p are the D-amino acid forms of alanine, aspartic acid, lysine, and proline, respectively B is P-alanine (2,53,60,61).

Alkyldithio carbamates are prepared from the acid chloride (Et N, EtOAc, 0°) and amino acid, either free or as the O-silyl derivatives (70-88% yield). The N- i-propyldithio) carbamate has been used in the protection of proline during peptide synthesis. Alkyldithio carbamates can be cleaved with thiols, NaOH, Ph P/TsOH. They are stable to acid. Cleavage rates are a function of the size of the alkyl group as illustrated in the table below. 

Reduce the size of the alphabet from 20 amino acids to a smaller alphabet of, say, six (aliphatic, aromatic, charged, polar, glycine, proline). 

Fhe amino acid side chains project out from the a helix (see Figure 2.2e) and do not interfere with it, except for proline. The last atom of the proline side... 

Figure 14.1 Each polypeptide chain in the collagen molecule folds into an extended polyproline type II helix with a rise per turn along the helix of 9.6 A comprising 3.3 residues. In the collagen molecule three such chains are supercoiled about a common axis to form a 3000-A-long rod-like molecule. The amino acid sequence contains repeats of -Gly-X-Y- where X is often proline and Y is often hydroxyproline. (a) Ball and stick model of two turns of one polypeptide chain.

Glycine residues have more conformational freedom than any other amino acid, as discussed in Chapter 1. A glycine residue at a specific position in a protein has usually only one conformation in a folded structure but can have many different conformations in different unfolded structures of the same protein and thereby contribute to the diversity of unfolded conformations. Proline residues, on the other hand, have less conformational freedom in unfolded structures than any other residue since the proline side chain is fixed by an extra covalent bond to the main chain. Another way to decrease the number of possible unfolded structures of a protein, and hence stabilize the native structure, is, therefore, to mutate glycine residues to any other residue and to increase the number of proline residues. Such mutations can only be made at positions that neither change the conformation of the main chain in the folded structure nor introduce unfavorable, or cause the loss of favorable, contacts with neighboring side chains. 

Amino-4,6-dimethyl-3-oxo-3//-phenoxazine-l,9-dicarboxylic acid also named actinocin is the chromophor of the red antineoplastic chromopeptide aetinomyein D (formula A). Two cyclopenta-peptide lactone rings (amino acids L-threonine, D-valine, L-proline, sarcosine, and 7V-methyl-L-valine) are attached to the carboxy carbons of actinocin by two amide bonds involving the amino groups of threonine. 

Over 30 amino acids have been identified in the hydrolysis product of casein of which glutamic acid, hydroxyglutamic acid, proline, valine, leucine and lysine comprise about 60%. The residues of the aminoacid arginine also appear to be of importance in the cross-linking of casein with formaldehyde. 

The most successful of the Lewis acid catalysts are oxazaborolidines prepared from chiral amino alcohols and boranes. These compounds lead to enantioselective reduction of acetophenone by an external reductant, usually diborane. The chiral environment established in the complex leads to facial selectivity. The most widely known example of these reagents is derived from the amino acid proline. Several other examples of this type of reagent have been developed, and these will be discussed more completely in Section 5.2 of part B. 

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