Dipeptides, structure

Using the general synthetic concepts described in Sec. II, we employed tyrosine dipeptides as the monomeric starting material. After protection of the N and C termini, the reactivity of a fully protected tyrosine dipeptide (structure 2) could be expected to resemble the... 

An early example of this type of transformation was described in 1964 by Drehfahl and Horhold (310). These authors prepared racemic 4-hydroxyproline, albeit with low diastereoselectivity for the isoxazoline reduction step [Scheme 6.75, (1)] (310). Much higher selectivity was achieved using 5-halomethylisoxazolines bearing a 3-(l-oxyalkyl) side chain, which was introduced from the nitrile oxide portion. The examples presented in Scheme 6.75 outline the synthesis of 4-hydroxy-pyrrolidines, which contain a dioxyethyl or trioxypropyl side chain. Both of these substrates were converted into the corresponding imino acids of 4-hydroxyproline (23,225,234) and 4, 1 -dihydroxyhomoproline, respectively (23,207,225) (Eq. 2, 3). The latter compound is part of an N-Val dipeptide structure, that was mistakenly proposed for the antibiotic Tii 1718B (311,312). 

As in the case of dipeptide esters in solution, the rate of piperazine-2,5-dione formation in SPPS strongly depends on steric and chiral features of the original dipeptide structure.11501 The rate of the cyclization increases upon catalysis by weak carboxylic acids.11761 However, it was also reported that piperazine-2,5-diones are formed under basic conditions, e.g. removal of the Fmoc protecting group. Formation of piperazine-2,5-diones is generally overcome by... 

A range of functionalized and unfunctionalized self-assembling fibrous structures have been tested for their biocompatibility and ability to provide cells with a favorable micro- and nanoenvironments for soft tissue engineering. In this section, studies that focus on amyloid fibrils, on peptide amphi-philes, on ionic complementary peptides, and on dipeptide structures are reviewed. Hard tissue engineering, composites, and coating are also explored followed by macroscopic structures and networks that can be created from fibrous protein structures. 

Reaction of (A-benzyl-amino) propionic acid 337a and its 3-methyl derivative 337b with phenylphosphonic dichloride in the presence of excess of NEt3 gave the diazocinediones 9a,b, which have a cyclo-/3-dipeptide structure (Equation 13). The reaction was performed under different reaction conditions, that is, changing solvents, temperature, reaction time, and reactant concentration. The best results (54-68% yields) were obtained in benzene at 80°C for 20h. The diazocinediones 9a,b were formed in similar yields at high and low concentrations of the reactant <2001T1883>. 

Aspartate protease (pol gene encoded) is a viral enzyme that cleaves precursor polypeptides in HIV buds to form the proteins of the mature virus core. The enzyme contains a dipeptide structure not seen in mammalian proteins. Pis bind to this dipeptide, inhibiting the enzyme. 

HIV aspartate protease has a unique dipeptide structure that has been used as a target for protease j inhibitory drugs. 

A conjugate of probable dipeptide structure, dimethyldithiocarbamoyl-(N-y-glutamil)alanine (53), has also been detected. 

The enzyme contains a dipeptide structure not seen in mammalian proteins. Pis bind to this dipeptide, inhibiting the enzyme. 

Write the dipeptide structures that can be made by linking alanine and glycine with a peptide bond. 

Bacilysin is a hydrophilic substance formed by certain aerobic sporeforming bacteria which causes lysis in cultures of growing staphylococci. Abraham and his collaborators have described its production by aerated cultures of a strain of Bacillus subtilis, and they showed that on hydrolysis (6m HCl) it gave L-alanine and L-tyrosine, although it did not contain a tyrosine residue. On the basis of physiochemical measurements the unusual dipeptide structure (96) was assigned to bacilysin. In later work a further substance (A A 1), identical with the C-terminal amino acid of bacilysin, was isolated from the culture fluid of Bacillus subtilis strains and the same amino acid has been obtained from stirred cultures of Streptomyces griseoplanus by Neuss and his collaborators and named anticapsin. Detailed analysis of the products of acid hydrolysis of anticapsin or A A 1 showed them to contain both L-tyrosine and m-L-tyrosine in a ratio of 9 2. 

Fig. 1 Top dipeptide structure (I) and bottom peptide structure (II) and a combination of the two shown with TEM and with inset to better show local fibril structure. The scale bar is 200 nm. a I alone, b II alone, c combination of I and II [80]...

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