Cis-3-Hydroxyproline

Similar method has been applied for the simultaneous determination of proline enantiomers, trans-4-hydroxyproline and cis-4-hydroxyproline, in serum and collagen-rich skin tissue of mammals. As the first dimension, a monolithic ODS column of 0.53 mm diameter was used whereas DIPPCQN column was employed in the second dimension. Such a system gave the separation factor in the range... 

The obvious extension of the above concept was made by Wessig etal. [23] to obtain optically active cis-3-hydroxyproline derivatives 66 in moderate to good yields by irradiating chiral N-(2-benzoylethyl)-N-tosy] glycinamide (65) in cyclohexane/ benzene (4 1) mixture. The diastereomeric excess (de) of the photocyclization was... 

On hydrolysis with acids phalloidin yields L-alanine, 4-cis-L-hydroxyproline, D-threonine, L-y, -dihydroxyleucine, L-cysteine and j8-oxindolalanine ( oxytryptophan ). The tryptophan derivative is not a genuine building component of the cyclic peptides it is formed by hydrolysis of a thioether crosslink between position 2 of tryptophan and the side chain of cysteine (tryptathionine). The structure of the bicyclic heptapeptide is shown in Fig. 21. 

This stereoelectronic approach can be used for the rational design of conformations and stability of proteins where these units are incorporated. For example, the sequence ProHypGly (Gly=glydne, fto=proline and Hyp=4(/ )-hydroxyproline) occurs approximately 300 times in collagen s triple helix. The trans configuration is required for triple helix formation, thus stabilization relative to cis should increase the folded proteins stability. The stability of the helices can be increased by incorporation of Hp (4(/ )-fluoroproline), which enforces the trans conformation. 

Free hydroxyproline (4-hydroxy-L-proline) interferes not only with the incorporation of C-proline into protein, but also with the subsequent conversion of proline into protein-bound hydroxyproline, as in collagen formation. The hydroxylation mechanism was ascertained by the use of two isomeric fluoroprolines, -cis- and /roiu-4-fluoroprolines. Although both amino acids were incorporated into protein from homogenates of guinea-pig granuloma, the sole trans- isomer behaved as an efficient precursor for hydroxyproline. Therefore the hydroxylation mechanism involves a direct oxidative attack upon, and displacement of, the trans-H atom at the 4-position. 

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