- Functional consequences of homocysteinylation of the elastic fiber proteins fibrillin-1 and tropoelastin
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Homocystinuria caused by cystathionine-β-synthase deficiency represents a severe form of homocysteinemias, which generally result in various degrees of elevated plasma homocysteine levels. Marfan syndrome is caused by mutations in fibrillin-1, which is one of the major constituents of connective tissue microfibrils. Despite the fundamentally different origins, both diseases share common clinical symptoms in the connective tissue such as long bone overgrowth, scoliosis, and ectopia lentis, whereas they differ in others. Fibrillin-1 contains ～13% cysteine residues and can be modified by homocysteine. We report here that homocysteinylation affects functional properties of fibrillin-1 and tropoelastin. We used recombinant fragments spanning the entire fibrillin-1 molecule to demonstrate that homocysteinylation, but not cysteinylation leads to abnormal self-interaction, which was attributed to a reduced amount of multimerization of the fibrillin-1 C terminus. The deposition of the fibrillin-1 network by human dermal fibroblasts was greatly reduced by homocysteine, but not by cysteine. Furthermore, homocysteinylation, but not cysteinylation of elastin-like polypeptides resulted in modified coacervation properties. In summary, the results provide new insights into pathogenetic mechanisms potentially involved in cystathionine-β-synthase-deficient homocystinuria.
- Hubmacher, Dirk,Cirulis, Judith T.,Miao, Ming,Keeley, Fred W.,Reinhardt, Dieter P.
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Read Online
- Exploration of the six tryptophan residues of Escherichia coli cystathionine β-lyase as probes of enzyme conformational change
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Cystathionine β-lyase (CBL) catalyzes the hydrolysis of l-cystathionine (l-Cth), producing l-homocysteine (l-Hcys), pyruvate and ammonia, in the second step of the transsulfuration pathway of bacteria and plants. A series of 17 site-directed variants of Escherichia coli CBL (eCBL) was constructed to probe the contributions of the six tryptophan residues (W131, W188, W230, W276, W300 and W340) to the fluorescence spectrum of eCBL and to assess their mutability and utility as conformational probes. The effects of these Trp → Phe substitutions on kcat and Km l-Cth are less than 2-fold, with the exception of the 8-fold increase in Kml-Cth observed for eCBL-W340F. The midpoint of thermal denaturation, as monitored by circular dichroism spectroscopy, is reduced 4.7 C by the W188F substitution while the targeted replacement of the other five tryptophans alter Tm by less than 1.7 C. The fluorescence spectrum of eCBL is dominated by W230 and the contribution of W340, situated in the active site, is minor. The observed 5-fold increase in the 336 nm fluorescence emission of W188 between 0 and 2 M urea, suggests a conformational change at the domain interface. Residues W188 and W340, conserved in proteobacterial CBL enzymes, are situated at the core of the domain interface that forms the active-site cleft. The results of this study suggest that W188 is a useful probe of subtle conformational changes at the domain interface and active site.
- Jaworski, Allison F.,Aitken, Susan M.
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Read Online
- Identification of O-acetylhomoserine sulfhydrylase, a putative enzyme responsible for methionine biosynthesis in Clostridioides difficile: Gene cloning and biochemical characterizations
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O-acetylhomoserine sulfhydrylase (OAHS) is a pyridoxal 5′-phosphate-dependent enzyme involved in microbial methionine biosynthesis. In this study, we report gene cloning, protein purification, and some biochemical characteristics of OAHS from Clostridioides difficile. The enzyme is a tetramer with molecular weight of 185 kDa. It possesses a high activity in the reaction of L-homocysteine synthesis, comparable to reported activities of OAHSes from other sources. OAHS activity is inhibited by metabolic end product L-methionine. L-Propargylglycine was found to be a suicide inhibitor of the enzyme. Substrate analogue Nγ-acetyl-L-2,4-diaminobutyric acid is a competitive inhibitor of OAHS with Ki = 0.04 mM. Analysis of C. difficile genome allows to suggest that the bacterium uses the way of direct sulfhydrylation for the synthesis of L-methionine. The data obtained may provide the basis for further study of the role of OAHS in the pathogenic bacterium and the development of potential inhibitors.
- Kulikova, Vitalia V.,Revtovich, Svetlana V.,Bazhulina, Natalia P.,Anufrieva, Natalya V.,Kotlov, Mikhail I.,Koval, Vasiliy S.,Morozova, Elena A.,Hayashi, Hideyuki,Belyi, Yury F.,Demidkina, Tatyana V.
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Read Online
- Hyperhomocysteinemia leads to exacerbation of ischemic brain damage: Role of GluN2A NMDA receptors
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Hyperhomocysteinemia has been implicated in several neurodegenerative disorders including ischemic stroke. However, the pathological consequences of ischemic insult in individuals predisposed to hyperhomocysteinemia and the associated etiology are unknown. In this study, we evaluated the outcome of transient ischemic stroke in a rodent model of hyperhomocysteinemia, developed by subcutaneous implantation of osmotic pumps containing L-homocysteine into male Wistar rats. Our findings show a 42.3% mortality rate in hyperhomocysteinemic rats as compared to 7.7% in control rats. Magnetic resonance imaging of the brain in the surviving rats shows that mild hyperhomocysteinemia leads to exacerbation of ischemic injury within 24 h, which remains elevated over time. Behavioral studies further demonstrate significant deficit in sensorimotor functions in hyperhomocysteinemic rats compared to control rats. Using pharmacological inhibitors targeting the NMDAR subtypes, the study further demonstrates that inhibition of GluN2A-containing NMDARs significantly reduces ischemic brain damage in hyperhomocysteinemic rats but not in control rats, indicating that hyperhomocysteinemia-mediated exacerbation of ischemic brain injury involves GluN2A-NMDAR signaling. Complementary studies in GluN2A-knockout mice show that in the absence of GluN2A-NMDARs, hyperhomocysteinemia-associated exacerbation of ischemic brain injury is blocked, confirming that GluN2A-NMDAR activation is a critical determinant of the severity of ischemic damage under hyperhomocysteinemic conditions. Furthermore, at the molecular level we observe GluN2A-NMDAR dependent sustained increase in ERK MAPK phosphorylation under hyperhomocysteinemic condition that has been shown to be involved in homocysteine-induced neurotoxicity. Taken together, the findings show that hyperhomocysteinemia triggers a unique signaling pathway that in conjunction with ischemia-induced pathways enhance the pathology of stroke under hyperhomocysteinemic conditions.
- Jindal, Ankur,Rajagopal, Sathyanarayanan,Winter, Lucas,Paul, Surojit,Poddar, Ranjana,Brigman, Jonathan,Allan, Andrea M.,Miller, Joshua W.,Jacobsen, Donald W.
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Read Online
- COMPOSITONS AND METHODS FOR TREATING BRAIN INJURY
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A method for treating a hyperhomocysteinemic subject having cerebral ischemic stroke generally includes administering to the hyperhomocysteinemic subject, following cerebral stroke, a composition that includes an inhibitor or an antagonist of a GluN2A-containing N-methyl-D-aspartate receptor (NMDAR) in an amount effective to ameliorate at least one symptom or clinical sign of cerebral stroke.
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Page/Page column 42
(2020/02/06)
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- Preparation method of N-fluorenylmethoxycarbonyl-S-(4-methoxytribenzyl)-L-homocysteine
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The invention relates to a preparation method of N-fluorenylmethoxycarbonyl-S-(4-methoxytribenzyl)-L-homocysteine, and solves the technical problem that there is no effective synthesis method in the prior art. The preparation method comprises following steps: (1) dissolving L-methionine into a solvent, and under the action of a strong reducing agent, removing one methyl group to prepare a crude product of L-homocysteine; (2) dissolving the crude product of L-homocysteine and 4-methoxytriphenyl chloromethane into a solvent, slowly adding a strong acid, TLC monitoring the reactions for 12 to 24 hours, carrying out suction filtration, adjusting the pH to 7 by an alkaline solution, carrying out suction filtration, and washing the obtained solid by a solvent to obtain S-(4-methoxytribenzyl)-L-homocysteine; and (3) dissolving S-(4-methoxytribenzyl)-L-homocysteine into a solvent, adding a fluorenylmethoxycarbonyl protective group onto S-(4-methoxytribenzyl)-L-homocysteine, TLC monitoring the reactions for 6 to 10 hours, washing to remove impurities, and carrying out extraction, drying, and crystallization t obtain a solid namely N-fluorenylmethoxycarbonyl-S-(4-methoxytribenzyl)-L-homocysteine.
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Paragraph 0010; 0021; 0025; 0029; 0033
(2019/10/04)
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- Poly(S-ethylsulfonyl- l -homocysteine): An α-Helical Polypeptide for Chemoselective Disulfide Formation
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Homocysteine and cysteine are the only natural occurring amino acids that are capable of disulfide bond formations in peptides and proteins. The chemoselective formation of asymmetric disulfide bonds, however, is chemically challenging and requires an activating group combining stability against hard nucleophiles, e.g., amines, with reactivity toward thiols and soft nucleophiles. In light of these considerations, we introduced the S-alkylsulfonyl cysteines in our previous work. Here, we present the synthesis and ring-opening polymerization of S-ethylsulfonyl-l-homocysteine N-carboxyanhydrides. We demonstrate that the polymerization leads to narrowly distributed polypeptides (D= 1.1-1.3) with no detectable side reactions in a chain length regime from 11 to 165. In contrast to the already reported cysteine derivatives, poly(S-ethylsulfonyl-l-homocysteine)s do not form β-sheets, which reduce solubility and limit the degree of polymerization of poly(S-ethylsulfonyl-l-cysteine)s to 50. Instead, these polymers form α-helices as confirmed by circular dicroism (CD) experiments and infrared spectroscopy (FT-IR). In comparison to the cysteine derivatives, the α-helix formation leads to slightly faster polymerization kinetics (rate constants from 1.44 × 10-5 to 5.29 × 10-5 s-1). In addition, the ability for the chemoselective formation of asymmetric disulfides is preserved as monitored via 1H NMR experiments. Consequently, this new polypeptide overcomes the chain length limitations of poly(S-ethylsulfonyl-l-cysteine)s and thus provides convenient access to reactive poly(S-ethylsulfonyl-l-homocysteine)s for chemoselective disulfide formation.
- Muhl, Christian,Sch?fer, Olga,Bauer, Tobias,R?der, Hans-Joachim,Barz, Matthias
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p. 8188 - 8196
(2018/10/31)
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- A green and expedient synthesis of enantiopure diketopiperazines via enzymatic resolution of unnatural amino acids
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Dipeptides comprising a d-phenylglycyl moiety coupled to the l-enantiomer of 2-amino butyric acid, norvaline, norleucine, and homocysteine were successfully synthesized from d-phenylglycine amide and the racemate of the corresponding unnatural amino acid.
- Pereira, Pedro C.,Arends, Isabel W.C.E.,Sheldon, Roger A.
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supporting information
p. 4991 - 4993
(2015/01/09)
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- A role for glutamate-333 of Saccharomyces cerevisiae cystathionine γ-lyase as a determinant of specificity
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Cystathionine γ-lyase (CGL) catalyzes the hydrolysis of l-cystathionine (l-Cth), producing l-cysteine (l-Cys), α-ketobutyrate and ammonia, in the second step of the reverse transsulfuration pathway, which converts l-homocysteine (l-Hcys) to l-Cys. Site-directed variants substituting residues E48 and E333 with alanine, aspartate and glutamine were characterized to probe the roles of these acidic residues, conserved in fungal and mammalian CGL sequences, in the active-site of CGL from Saccharomyces cerevisiae (yCGL). The pH optimum of variants containing the alanine or glutamine substitutions of E333 is increased by 0.4-1.2 pH units, likely due to repositioning of the cofactor and modification of the pKa of the pyridinium nitrogen. The pH profile of yCGL-E48A/E333A resembles that of Escherichia coli cystathionine β-lyase. The effect of substituting E48, E333 or both residues is the 1.3-3, 26-58 and 124-568-fold reduction, respectively, of the catalytic efficiency of l-Cth hydrolysis. The Kml-Cth of E333 substitution variants is increased ~ 17-fold, while Km l-OAS is within 2.5-fold of the wild-type enzyme, indicating that residue E333 interacts with the distal amine moiety of l-Cth, which is not present in the alternative substrate O-acetyl-l-serine. The catalytic efficiency of yCGL for α,γ-elimination of O-succinyl-l-homoserine (k cat/Kml-OSHS = 7 ± 2), which possesses a distal carboxylate, but lacks an amino group, is 300-fold lower than that of the physiological l-Cth substrate (kcat/Kml-Cth = 2100 ± 100) and 260-fold higher than that of l-Hcys (k cat/Kml-Hcys = 0.027 ± 0.005), which lacks both distal polar moieties. The results of this study suggest that the glutamate residue at position 333 is a determinant of specificity.
- Hopwood, Emily M.S.,Ahmed, Duale,Aitken, Susan M.
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p. 465 - 472
(2014/01/17)
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- BINARY AND TERTIARY GALVANIC PARTICULATES AND METHODS OF MANUFACTURING AND USE THEREOF
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The present invention relates to galvanic particulates, their methods of manufacture and uses in treatments are described. The galvanic particulates may be binary or tertiary galvanic particulates, for example, containing multiple layers or phases of conductive materials.
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- Structure of Candida albicans methionine synthase determined by employing surface residue mutagenesis
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Fungal methionine synthase, Met6p, transfers a methyl group from 5-methyl-tetrahydrofolate to homocysteine to generate methionine. The enzyme is essential to fungal growth and is a potential anti-fungal drug design target. We have characterized the enzyme from the pathogen Candida albicans but were unable to crystallize it in native form. We converted Lys103, Lys104, and Glu107 all to Tyr (Met6pY), Thr (Met6pT) and Ala (Met6pA). All variants showed wild-type kinetic activity and formed useful crystals, each with unique crystal packing. In each case the mutated residues participated in beneficial crystal contacts. We have solved the three structures at 2.0-2.8 resolution and analyzed crystal packing, active-site residues, and similarity to other known methionine synthase structures. C. albicans Met6p has a two domain structure with each of the domains having a (βα)8-barrel fold. The barrels are arranged face-to-face and the active site is located in a cleft between the two domains. Met6p utilizes a zinc ion for catalysis that is bound in the C-terminal domain and ligated by four conserved residues: His657, Cys659, Glu679 and Cys739.
- Ubhi, Devinder,Kavanagh, Kathryn L.,Monzingo, Arthur F.,Robertus, Jon D.
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experimental part
p. 19 - 26
(2012/03/27)
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- Protein thiocarboxylate-dependent methionine biosynthesis in Wolinella succinogenes
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Thiocarboxylated proteins are important intermediates in a variety of biochemical sulfide transfer reactions. Here we identify a protein thiocarboxylate-dependent methionine biosynthetic pathway in Wolinella succinogenes. In this pathway, the carboxy terminal alanine of a novel sulfur transfer protein, HcyS-Ala, is removed in a reaction catalyzed by a metalloprotease, HcyD. HcyF, an ATP-utilizing enzyme, catalyzes the adenylation of HcyS. HcyS acyl-adenylate then undergoes nucleophilic substitution by bisulfide produced by Sir to give the HcyS thiocarboxylate. This adds to O-acetylhomoserine to give HcyS-homocysteine in a PLP-dependent reaction catalyzed by MetY. HcyD-mediated hydrolysis liberates homocysteine. A final methylation completes the biosynthesis. The biosynthetic gene cluster also encodes the enzymes involved in the conversion of sulfate to sulfide suggesting that sulfate is the sulfur source for protein thiocarboxylate formation in this system.
- Krishnamoorthy, Kalyanaraman,Begley, Tadhg P.
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supporting information; experimental part
p. 379 - 386
(2011/03/16)
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- Residue N84 of Yeast Cystathionine β-Synthase is a Determinant of Reaction Specificity
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Cystathionine β-synthase (CBS) catalyzes the pyridoxal 5'-phosphate (PLP)-dependent condensation of l-serine and l-homocysteine to form l-cystathionine in the first step of the reverse transsulfuration pathway. Residue N84 of yeast CBS (yCBS), predicted to form a hydrogen bond with the hydroxyl moiety of the PLP cofactor, was mutated to alanine, aspartate and histidine. The truncated form of yCBS (ytCBS, residues 1-353) was employed in this study to eliminate any effects of the C-terminal, regulatory domain. The kcat/Kml-Ser of the N84A, N84D and N84H mutants for the β-replacement reaction is reduced by a factor of 230, 11000 and 640, respectively. Fluorescence resonance energy transfer between tryptophan residue(s) of the enzyme and the PLP cofactor, observed in the wild-type enzyme and N84A mutant, is altered in N84H and absent in N84D. PLP saturation values of 73%, 30% and 67% were observed for the alanine, aspartate and histidine mutants, respectively, compared to 98% for the wild-type enzyme. A marginal β-elimination activity was detected for N84D (kcat/Kml-Ser = 0.23 ± 0.02 M-1 s-1) and N84H (kcat/Kml-Ser = 0.34 ± 0.06 M-1 s-1), in contrast with wild-type ytCBS and the N84A mutant, which do not catalyze this reaction. The ytCBS-N84D enzyme is also inactivated upon incubation with l-serine, via an aminoacrylate-mediated mechanism. These results demonstrate that residue N84 is essential in maintaining the orientation of the pyridine ring of the PLP cofactor and the equilibrium between the open and closed conformations of the active site.
- Lodha, Pratik H.,Hopwood, Emily M.S.,Manders, Adrienne L.,Aitken, Susan M.
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experimental part
p. 1424 - 1431
(2011/11/13)
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- Characterization of site-directed mutants of residues R58, R59, D116, W340 and R372 in the active site of E. coli cystathionine β-lyase
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Cystathionine β-lyase (CBL) catalyzes the hydrolysis of L-cystathionine (L-Cth) to produce L-homocysteine, pyruvate, and ammonia. A series of active-site mutants of Escherichia coli CBL (eCBL) was constructed to investigate the roles of residues R58, R59, D116, W340, and R372 in catalysis and inhibition by aminoethoxyvinylglycine (AVG). The effects of these mutations on the kcat/KmL-Cth for the β-elimination reaction range from a reduction of only 3-fold for D116A and D116N to 6 orders of magnitude for the R372L and R372A mutants. The order of importance of these residues for the hydrolysis of L-Cth is: R372?R58 > W340 ≈ R59 > D116. Comparison of the kinetic parameters for L-Cth hydrolysis with those for inhibition of eCBL by AVG demonstrates that residue R58 tethers the distal carboxylate group of the substrate and confirms that residues W340 and R372 interact with the α-carboxylate moiety. The increase in the pKa of the acidic limb and decrease in the pKa of the basic limb of the kcat/KmL-Cth versus pH profiles of the R58K and R58A mutants, respectively, support a role for this residue in modulating the pKa of an active-site residue. Published by Wiley-Blackwell.
- Lodha, Pratik H.,Jaworski, Allison F.,Aitken, Susan M.
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experimental part
p. 383 - 391
(2011/01/04)
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- S-NITROSOMERCAPTO COMPOUNDS AND RELATED DERIVATIVES
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The present invention is directed to mercapto-based and S- nitrosomercapto-based SNO compounds and their derivatives, and their use in treating a lack of normal breathing control, including the treatment of apnea and hypoventilation associated with sleep, obesity, certain medicines and other medical conditions.
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Page/Page column 102
(2010/01/07)
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- Searching for DDAH inhibitors: S-nitroso-L-homocysteine is a chemical lead
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The cysteine-hydrolase dimethylargininase-1 (DDAH-1) is an important regulator of NO production in mammalian tissue for which the availability of an inhibitor for clinics and research would be most appreciated. While studying the effect of the endogenously occurring S-nitroso-l-homocysteine on DDAH-1, an unusual N-thiosulfoximide modification was identified in the active site of the enzyme. Thus, S-nitroso-l-homocysteine in combination with the mechanism proposed herein offers a basis for the rational design of DDAH inhibitors. Copyright
- Knipp, Markus,Braun, Oliver,Vasak, Milan
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p. 2372 - 2373
(2007/10/03)
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- 5-(2-Aminoethyl)dithio-2-nitrobenzoate as a more base-stable alternative to ellman's reagent
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(Chemical Equation Presented) 5-(2-Aminoethyl)dithio-2-nitrobenzoate (ADNB) reacts with free thiols with kinetics similar to those of Ellman's reagent but has dramatically improved stability under alkaline conditions, making it an excellent alternative to Ellman's reagent for the quantitation of thiol contents and enzymatic assays under basic pH conditions.
- Zhu, Jinge,Dhimitruka, Ilirian,Pei, Dehua
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p. 3809 - 3812
(2007/10/03)
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- Catalytic Mechanism of S-Ribosylhomocysteinase (LuxS): Direct Observation of Ketone Intermediates by 13C NMR Spectroscopy
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S-Ribosylhomocysteinase (LuxS) catalyzes the cleavage of the thioether linkage of S-ribosylhomocysteine (SRH) to produce l-homocysteine and 4,5-dihydroxy-2,3-pentanedione (DHPD). This is a key step in the biosynthetic pathway of the type II autoinducer (AI-2) in both Gram-positive and Gram-negative bacteria. Previous studies demonstrated that LuxS contains a catalytically essential Fe2+ ion. The catalytic mechanism of LuxS was investigated using 2- and 3-13C-labeled SRH as substrate and 13C NMR spectroscopy. These studies revealed the presence of 2- and 3-keto intermediates in the catalytic pathway. The 2-keto intermediate was chemically synthesized, and its chemical and kinetic competence was demonstrated. The results support a catalytic mechanism in which the metal ion catalyzes an internal redox reaction, shifting the carbonyl group from the C-1 position to the C-3 position. Subsequent β-elimination at the C-4 and C-5 positions releases homocysteine as a free thiol. The results also suggest that Cys-84 and Glu-57 are the possible general acids/bases for proton transfer during catalysis and that the keto intermediates are released from the enzyme active site before rebinding and completion of the reaction. Copyright
- Zhu, Jinge,Hu, Xubo,Dizin, Eric,Pei, Dehua
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p. 13379 - 13381
(2007/10/03)
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- Immonological detection of the homocystamide adduct and a thiolactone immunoassay for endogeneous homocysteine
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An antibody specific for homocystamide adducts is disclosed. In a preferred embodiment of the present invention, the antibody is used to evaluate the level of homocysteine in a biological sample.
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- Synthesis of optically active homocysteine from methionine and its use in preparing four stereoisomers of cystathionine
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In order to synthesize four stereoisomers of cystathionine (CYT), D- and L-homocysteines (D- and L-Hcy) were synthesized from methionine (Met) by a facile procedure. L-Met was reacted with dichloroacetic acid in concentrated hydrochloric acid under reflux to give (4S)-1,3-thiazane-2,4-dicarboxylic acid hydrochloride [(4S)-TDC? HCl]. L-Hcy was obtained by treatment of (4S)-TDC? HCl with hydroxylamine. D-Hcy was also synthesized from D-Met via (4R)-TDC? HCl intermediate. The obtained D- and L-Hcy were condensed with (R)- and (S)-2-amino-3-chloropropanoic acid hydrochlorides under alkaline conditions to give four stereoisomers of CYT.
- Shiraiwa, Tadashi,Nakagawa, Kazuo,Kanemoto, Norito,Kinda, Tomohiro,Yamamoto, Hiroki
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p. 1081 - 1085
(2007/10/03)
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- Inhibition of inducible nitric oxide synthase by acetamidine derivatives of hetero-substituted lysine and homolysine
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The synthesis and in vitro evaluation of the acetamidine derivatives of hetero-substituted lysine and homolysine analogues have identified potent inhibitors of human nitric oxide synthase enzymes, including examples with marked selectivity for the inducible isoform. (C) 2000 Elsevier Science Ltd. All rights reserved.
- Young, Robert J.,Beams, Richard M.,Carter, Keith,Clark, Helen A.R.,Coe, Diane M.,Chambers, C. Lynn,Davies, P. Ifeyinwa,Dawson, John,Drysdale, Martin J.,Franzman, Karl W.,French, Colin,Hodgson, Simon T.,Hodson, Harold F.,Kleanthous, Savvas,Rider, Peter,Sanders, Daniela,Sawyer, David A.,Scott, Keith J.,Shearer, Barry G.,Stocker, Richard,Smith, Steven,Tackley, Miriam C.,Knowles, Richard G.
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p. 597 - 600
(2007/10/03)
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- Method for purifying homocystine
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Disclosed is a method for purifying homocystine comprising treating crude homocystine with a base, a method for purifying homocystine comprising recovering homocystine by neutralizing an alkaline aqueous solution of crude homocystine with an acid, and a homocystine powder containing 1,000 ppm or less of a polysulfide.
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- Facile synthesis of optically active homocysteine from methionine
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L-Methionine (L-Met) reacted with dichloroacetic acid in concentrated hydrochloric acid under refluxing to give (45)-1,3-thiazane-2,4-dicarboxylic acid hydrochloride [(4S)-TDC· HCl]. L-Homocysteine (L-Hcy) was obtained in an optically pure form by treatme
- Shiraiwa, Tadashi,Nakagawa, Kazuo,Kanemoto, Norito
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p. 468 - 469
(2007/10/03)
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- Synthesis of highly enantio-enriched α-amino acids by carboxylation of N-(α-lithioalkyl)oxazolidinones
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N-(α-Stannylalkyl)oxazolidinones can be obtained as a mixture of diastereomers in three steps from aldehydes with yields dependent on the R group of R-CHO. They can be transformed by a tin-lithium exchange to N-(α- lithioalkyl)oxazolidinones which equilibrate rapidly to one diastereomer. These compounds give rise, after carboxylation, to the diastereopure N-(α- carboxyalkyl)oxazolidinones. Transformation of the oxazolidinone moiety to a free amino group is accomplished by a Birch-type reduction. Using this method, L-methionine, L-alanine, L-leucine and L-homocysteine were obtained in good yields and ee = 92% to 95%. The short time required for the whole sequence makes this method ideal for synthesising 1-[11C]amino acids.
- Jeanjean, Fabien,Fournet, Guy,Bars, Didier Le,Gore, Jacques
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p. 1297 - 1305
(2007/10/03)
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- The first asymmetric syntheses of L-homocysteine and L-homocystine
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Asymmetric syntheses of L-homocysteine 1 and L-homocystine 2 are described. Alkylation of the carbanion derived from Schollkopf reagent 3 and ensuing hydrolyses gave S-triphenylmethyl-L-homocysteine 6. Removal of the triphenylmethyl group gave L-homocysteine 1 and subsequent oxidation provided L-homocystine 2.
- Adamczyk, Maciej,Fishpaugh, Jeffrey R.,Thiruvazhi, Mohan
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p. 4151 - 4156
(2007/10/03)
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- Method for producing homocystine
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Homocystine is produced by heating methionine in the presence of sulfuric acid and a hydrogen halide.
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- The synthesis of tritium-labeled methyl iodide and L-methionine
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A procedure for the preparation of methyl iodide-3H3 of high specific activity starting with tritium gas, its use for the synthesis of tritium-labeled L-methionine-[methyl-3H3] are described. The tritiated L-methionine can be used as a building block for the preparation of tritium labeled peptide containing terminal L-methionine.
- Liu, Yu-Ying,Chen, Lu
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- Preparations of Optically Active Homocysteine and Homocystine by Asymmetric Transformation of (RS)-1,3-Thiazane-4-carboxylic Acid
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DL-Homocysteine from (RS)-homocysteine thiolactone hydrochloride was subjected to reaction with formaldehyde in acetic acid to give (RS)-1,3-thiazane-4-carboxylic acid monohydrate .An asymmetric transformation of (RS)-THA*H2O was achieved via salt formation with optically active tartaric acid in the presence of salicylaldehyde in acetic acid.The (R)- and (S)-THA obtained, respectively, from the salt of (R)-THA with (2R,3R)-tartaric acid and its enantiomeric salt were treated with hydroxylamine hydrochloride to give D- and L-Hcy of 100percent optical purity, respectively, in 50percent yield from (RS)-HTL*HCl.Oxidation of D- and L-Hcy with hydrogen peroxide gave D- and L-homocystine, respectively, in 47percent yield.
- Miyazaki, Hideya,Ohta, Atsushi,Kawakatsu, Nobuyuki,Waki, Yukitaka,Gogun, Yasuhiro,et al.
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p. 536 - 540
(2007/10/02)
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- Kinetics and Equilibria of Thiol/Disulfide Interchange Reactions of Selected Biological Thiols and Related Molecules with Oxidized Glutathione
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Rate constants for reaction of coenzyme A and cysteine with oxidized glutathione (GSSG) and equilibrium constants for the reaction of coenzyme A, cysteine, homocysteine, cysteamine, and related thiols with GSSG by thiol/disulfide interchange were determined over a range of pD values by NMR spectroscopy.The rate constants for reaction of the thiolate anion forms of coenzyme A and cysteine with GSSG suggest that reduction of GSSG by coenzyme A and cysteine is a mechanistically uncomplicated SN2 reaction.Equilibrium constants for the thiol/disulfide interchange reactions show a strong dependence on the Bronsted basicity of the thiolate anion.In a similar way, ΔE0', the difference between the half-cell potentials for the RSSR/RSH and GSSG/GSH redox couples, is linearly dependent on the difference between the pKA values of RSH and glutathione: ΔE0' = 64ΔpKA - 7.7 where ΔE0' is in units of mV.The reducing strength at a given pH is also determined by the fraction of the thiol present in the reactive thiolate form.At pD 7, the half-cell potentials for coenzyme A, cysteine, homocysteine, and cysteamine are close to that of glutathione, the major intracellular thiol redox system, which suggests that small changes in the intracellular redox potential can cause significant changes in the intracellular distribution of these biological thiols between their reduced and oxidized forms.
- Keire, David A.,Strauss, Erin,Guo, Wei,Noszal, Bela,Rabenstein, Dallas L.
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p. 123 - 127
(2007/10/02)
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- Syntheses of S-Substituted L-Homocysteine Derivatives by Cystathionine γ-Lyase of Streptomyces phaeochromogenes
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Cystationine γ-lyase from Streptomyces phaeochromogenes catalyzes not only the α,γ-elimination rection of L-cystathionine, but also the γ-replacement reaction of L-homoserine in the presence of thiol compounds.Substrates for the enzyme in the γ-replacement reaction were examined.It was found that D-cysteine, L- and D-homocysteine, and 3- and 2-mercaptopropionate served as preferable substrates in the γ-replacement reaction.D-Allocystathionine, L- and mesohomolanthionine, S-carboxyethyl-L-homocysteine and S-methylcarboxymethyl-L-homocysteine were enzymatically synthesized from L-homoserine and the corresponding thiol compounds.The thus synthesized S-substituted L-homocysteine derivatives were isolated from large scale reaction mixtures and identified physicochemically.
- Kanzaki, Hiroshi,Kobayashi, Michihiko,Nagasawa, Toru,Yamada, Hideaki
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p. 391 - 398
(2007/10/02)
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- AN IMPROVED SYNTHESIS OF S-ADENOSYL-L-HOMOCYSTEINE AND RELATED COMPOUNDS
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5'-Chloro-5'-deoxy-2',3'-O-isopropylideneadenosine reacts with disodium salts of L-homocysteine, L-cysteine or 3-mercaptopropanoic acid in liquid ammonia to afford 2',3'-O-isopropylidene derivatives which are easily desalted by chromatography on octadecyl-silica column.On acid treatment, the high purity preparations of S-adenosyl-L-homocysteine, S-adenosyl-L-cysteine, and 5'-carboxyethylthio-5'-deoxyadenosine are obtained in respectable yield.
- Holy, Antonin,Rosenberg, Ivan
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p. 1514 - 1518
(2007/10/02)
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- Process for obtaining D,L-homocystine (I)
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D,L-Homocystine is obtained by treating an aqueous solution of the disodium salt of D,L-homocysteine having a concentration between 0.4 and 1.6 moles/l and an initial pH between 7.0 and 8.0 under vigorous stirring with at least the equivalent amount of an aqueous solution of hydrogen peroxide and after the end of the oxidation adjusting the pH to about 5.3. The hydrogen peroxide solution can be employed with a concentration between 20 and 60 weight percent.
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- Process for obtaining D,L-homocystine (II)
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D,L-Homocystine is obtained by introducing molecular oxygen into an aqueous solution of the disodium salt of D,L-homocysteine having a concentration between 0.8 and 1.2 moles/l and an initial pH between 7.0 and 8.0 in the presence of a catalytic amount of iron(III) ions until there is no longer an increase in pH and subsequently adjusting the pH to about 5.3 with stirring.
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- Diastereospecific, Enzymically Catalysed Transmethylation from S-Methyl-L-methionine to L-Homocysteine, a Naturally Occuring Process
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A known catabolic pathway of S-methyl-L-methionine in higher plants: donation of a methyl group to L-homocysteine resulting in the production of two molecules of L-methionine, is subjected to stereochemical studies.The two, diastereoisomeric (2-2H, methyl-13C)-S-methyl-L-methionines are synthesized and utilised in transmethylation reactions with L-homocysteine as the acceptor and an enzyme preparation from jack beans as a catalyst.The resulting, variously labelled methionine species are converted into butyl esters of the N-trifluoroacetylated derivatives and, as such, subjected to g.l.c. combined with mass spectrometry in two ionisation modes.Experimentally determined parameters such as mass peack intensities, isotopic enrichment factors, diastereoisomeric purities, and protein-derived methionine, are utilised for calculating the stereoselectivity in the enzyme transfer of the diastereoisotopic methyl groups from S-methyl-L-methionine to L-homocysteine.Together, the independent results from the two series of diastereoisomers reveal an enzymatic preference of the pro-(R)-methyl group to the extent of 94percent or more.
- Grue-Soerensen, Gunnar,Kelstrup, Ebbe,Kjaer, Anders,Madsen, Joergen Oegaard
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p. 1091 - 1097
(2007/10/02)
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