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Norikazu Nishino - One of the best experts on this subject based on the ideXlab platform.

  • epoxy amino acids produced from allylglycines intramolecularly cyclised to yield four stereoisomers of 4 hydroxyproline derivatives
    RSC Advances, 2014
    Co-Authors: Suvratha Krishnamurthy, Kanae Nakanishi, Toru Arai, Norikazu Nishino

    Derivatives of 2-amino-4-pentenoic acid (allylglycine) were efficiently resolved using Subtilisin or acylase. The side-chain unsaturated bond of the enantiomerically pure amino acid with tert-butoxycarbonyl (Boc) protection was smoothly epoxidized with m-chloroperbenzoic acid. When the Boc protection of the amino group was removed, the amino group intramolecularly attacked the side-chain epoxide, generating compounds with five-membered rings: the 4-Hydroxyproline derivatives. Two diastereomeric products were formed through the cyclisation reaction, for example, (2S,4S)-4-Hydroxyproline benzyl ester (cis-8) and (2S,4R)-4-Hydroxyproline benzyl ester (trans-8) were formed from (2S)-amino acid with a side-chain epoxide. Compound (2S,4S)-4-Hydroxyproline benzyl ester (cis-8) was transformed to a lactone (cis-hydroxyproline lactone, 10) with the removal of benzyl alcohol. The cis-conformation was essential for the intramolecular ester exchange reaction; in fact, no lactone formation was observed for the trans isomer (trans-8). The separation of cis-hydroxyproline lactone and the trans-isomeric hydroxyproline benzyl ester was facile and clear, in contrast to the difficult separation of cis- and trans-hydroxyproline derivatives. Thus, two diastereomers of hydroxyproline derivatives for L-hydroxyproline and also for D-hydroxyproline were obtained, i.e., four diastereomers of hydroxyproline derivatives.

Daniel Seidel - One of the best experts on this subject based on the ideXlab platform.

Gerald Gübitz - One of the best experts on this subject based on the ideXlab platform.

  • Enantiorecognition of triiodothyronine and thyroxine enantiomers using different chiral selectors by HPLC and micro-HPLC.
    Journal of Biochemical and Biophysical Methods, 2008
    Co-Authors: Julia Koidl, Martin G. Schmid, Heike Hödl, Bianca Neubauer, Marlene Konrad, Sabine Petschauer, Gerald Gübitz

    Abstract This paper deals with the chiral separation of triiodothyronine (T 3 ) and thyroxine (T 4 ) by HPLC and micro-HPLC. The separation of T 3 and T 4 is of great pharmaceutical and clinical interest, since the enantiomers exhibit different pharmacological activities. The HPLC measurements were performed on a chiral stationary ligand-exchange phase using l -4-Hydroxyproline bonded via 3-glycidoxypropyltrimethoxysilane to silica gel as a selector. Also a chiral teicoplanin (Chirobiotic ™®) phase was used. In micro-HPLC the chiral separation behaviour of l -4-Hydroxyproline, and of the macrocyclic antibiotics teicoplanin and teicoplanin aglycone was investigated for the enantioseparation of T 3 and T 4 . l -4-Hydroxyproline was bonded to 3 μm and the glycopeptide antibiotics were bonded to 3.5 μm silica gel and separations were accomplished by microbore HPLC columns (10 cm × 1 mm I.D.). With both techniques and all chiral selectors investigated T 3 and T 4 were baseline resolved. micro-HPLC was found to be superior to analytical HPLC with respect to low consumption of packing material, mobile phase and analyte.

  • Fast chiral separation by ligand-exchange HPLC using a dynamically coated monolithic column.
    Journal of Separation Science, 2006
    Co-Authors: Martin G. Schmid, Karin Schreiner, Daniela Reisinger, Gerald Gübitz

    The preparation and application of dynamically coated ligand-exchange chromatography phases for enantioseparation is described. The phases were prepared by pumping a solution of N-decyl-L-4-Hydroxyproline, N-hexadecyl-L-4-Hydroxyproline, or N-2-hydroxydodecyl-L-4-Hydroxyproline through a commercially available monolithic RP-18 column. These coatings are stable against desorption for months at ambient temperature when aqueous mobile phases are used. The columns were applied to the chiral separation of amino acids, glycyl dipeptides and diastereomeric dipeptides, and tripeptides. The chiral selector can be removed or changed easily by washing the column with ACN or methanol. Ultrafast separations in the range of seconds were achieved using high flow rates.

  • Chiral separation of β-methyl-amino acids by ligand exchange using capillary electrophoresis and HPLC
    Journal of Pharmaceutical and Biomedical Analysis, 2001
    Co-Authors: Nina Grobuschek, Martin G. Schmid, Claudia Tuscher, M Ivanova, Gerald Gübitz

    This paper deals with the chiral separation of optical isomers of β-methyl-amino acids by CE and HPLC using the principle of ligand-exchange. Capillary zone electrophoresis was carried out using Cu(II) complexes of l-4-Hydroxyproline (l-4-Hypro), N-(2-hydroxypropyl)-l-4-Hydroxyproline (HP-l-4-Hypro) and N-(2-hydroxyoctyl)-l-4-Hydroxyproline (HO-l-4-Hypro) as chiral selectors, added to the electrolyte. The HPLC separations were performed on a chiral stationary ligand-exchange chromatography phase containing l-4-Hypro chemically bonded to silica gel. With both techniques nearly all compounds investigated are baseline resolved using different background electrolytes and mobile phases, respectively.

  • Enantioseparation of α-amino acids and dipeptides by ligand-exchange capillary electrophoresis of various l-4-Hydroxyproline derivatives
    Journal of Chromatography A, 1999
    Co-Authors: Martin G. Schmid, R Rinaldi, D Dreveny, Gerald Gübitz

    Abstract The principle of ligand exchange has been applied to the enantioseparation of underivatized aromatic and aliphatic amino acids as well as dipeptides. Two non commercially available N-alkyl- l -4-Hydroxyproline derivatives were compared to underivatized l -4-Hydroxyproline for their ability to resolve α-amino acids and dipeptides. N-(2-hydroxyoctyl)- l -4-Hydroxyproline and N-(2-hydroxypropyl)- l -4-Hydroxyproline were used as their copper(II) complexes as chiral selectors. With these selectors, several aliphatic amino acids and dipeptides, in addition to aromatic amino acids, were resolved. The pH optimum was found to be 4.3 for amino acids and 6.0 for dipeptides.

Ronald T Raines - One of the best experts on this subject based on the ideXlab platform.

  • the aberrance of the 4s diastereomer of 4 hydroxyproline
    Journal of the American Chemical Society, 2010
    Co-Authors: Matthew D Shoulders, Frank W Kotch, Amit Choudhary, Ilia A Guzei, Ronald T Raines

    Prolyl 4-hydroxylases install a hydroxyl group in the 4R configuration on the γ-carbon atom of certain (2S)-proline (Pro) residues in tropocollagen, elastin, and other proteins to form (2S,4R)-4-Hydroxyproline (Hyp). The gauche effect arising from this prevalent post-translational modification enforces a Cγ-exo ring pucker and stabilizes the collagen triple helix. The Hyp diastereomer (2S,4S)-4-Hydroxyproline (hyp) has not been observed in a protein, despite the ability of electronegative 4S substituents to enforce the more common Cγ-endo ring pucker of Pro. Here, we use density functional theory, spectroscopy, crystallography, and calorimetry to explore the consequences of hyp incorporation on protein stability using a collagen model system. We find that the 4S-hydroxylation of Pro to form hyp does indeed enforce a Cγ-endo ring pucker but a transannular hydrogen bond between the hydroxyl moiety and the carbonyl of hyp distorts the main-chain torsion angles that typically accompany a Cγ-endo ring pucker. ...

David R Eyre - One of the best experts on this subject based on the ideXlab platform.

  • evolutionary origins of c terminal gpp n 3 hydroxyproline formation in vertebrate tendon collagen
    PLOS ONE, 2014
    Co-Authors: David M Hudson, Maryann Weis, Jiannjiu Wu, Rachel Werther, David R Eyre

    Approximately half the proline residues in fibrillar collagen are hydroxylated. The predominant form is 4-Hydroxyproline, which helps fold and stabilize the triple helix. A minor form, 3-hydroxyproline, still has no clear function. Using peptide mass spectrometry, we recently revealed several previously unknown molecular sites of 3-hydroxyproline in fibrillar collagen chains. In fibril-forming A-clade collagen chains, four new partially occupied 3-hydroxyproline sites were found (A2, A3, A4 and (GPP)n) in addition to the fully occupied A1 site at Pro986. The C-terminal (GPP)n motif has five consecutive GPP triplets in α1(I), four in α2(I) and three in α1(II), all subject to 3-hydroxylation. The evolutionary origins of this substrate sequence were investigated by surveying the pattern of its 3-hydroxyproline occupancy from early chordates through amphibians, birds and mammals. Different tissue sources of type I collagen (tendon, bone and skin) and type II collagen (cartilage and notochord) were examined by mass spectrometry. The (GPP)n domain was found to be a major substrate for 3-hydroxylation only in vertebrate fibrillar collagens. In higher vertebrates (mouse, bovine and human), up to five 3-hydroxyproline residues per (GPP)n motif were found in α1(I) and four in α2(I), with an average of two residues per chain. In vertebrate type I collagen the modification exhibited clear tissue specificity, with 3-hydroxyproline prominent only in tendon. The occupancy also showed developmental changes in Achilles tendon, with increasing 3-hydroxyproline levels with age. The biological significance is unclear but the level of 3-hydroxylation at the (GPP)n site appears to have increased as tendons evolved and shows both tendon type and developmental variations within a species.

  • a novel 3 hydroxyproline 3hyp rich motif marks the triple helical c terminus of tendon type i collagen
    Journal of Biological Chemistry, 2011
    Co-Authors: David R Eyre, Maryann Weis, David M Hudson, Jiannjiu Wu

    Because of its unique physical and chemical properties, rat tail tendon collagen has long been favored for crystallographic and biochemical studies of fibril structure. In studies of the distribution of 3-hydroxyproline in type I collagen of rat bone, skin, and tail tendon by mass spectrometry, the repeating sequences of Gly-Pro-Pro (GPP) triplets at the C terminus of α1(I) and α2(I) chains were shown to be heavily 3-hydroxylated in tendon but not in skin and bone. By isolating the tryptic peptides and subjecting them to Edman sequence analysis, the presence of repeating 3-hydroxyprolines in consecutive GPP triplets adjacent to 4-Hydroxyproline was confirmed as a unique feature of the tendon collagen. A 1960s study by Piez et al. (Piez, K. A., Eigner, E. A., and Lewis, M. S. (1963) Biochemistry 2, 58–66) in which they compared the amino acid compositions of rat skin and tail tendon type I collagen chains indeed showed 3–4 residues of 3Hyp in tendon α1(I) and α2(I) chains but only one 3Hyp residue in skin α1(I) and none in α2(I). The present work therefore confirms this difference and localizes the additional 3Hyp to the GPP repeat at the C terminus of the triple-helix. We speculate on the significance in terms of a potential function in contributing to the unique assembly mechanism and molecular packing in tendon collagen fibrils and on mechanisms that could regulate 3-hydroxylation at this novel substrate site in a tissue-specific manner.