- Toward Cleavable Metabolic/pH Sensing “Double Agents” Hyperpolarized by NMR Signal Amplification by Reversible Exchange
-
We show the simultaneous generation of hyperpolarized 13C-labeled acetate and 15N-labeled imidazole following spin-relay of hyperpolarization and hydrolysis of the acetyl moiety on 1–13C-15N2-acetylimidazole. Using SABRE-SHEATH (Signal Amplification by Reversible Exchange in SHield Enables Alignment Transfer to Heteronuclei), transfer of spin order occurs from parahydrogen to acetylimidazole 15N atoms and the acetyl 13C site (≈263-fold enhancement), giving rise to relatively long hyperpolarization lifetimes at 0.3 T (T1≈52 s and ≈149 s for 13C and 15N, respectively). Immediately following polarization transfer, the 13C-labeled acetyl group is hydrolytically cleaved to produce hyperpolarized 13C-acetate/acetic acid (≈140-fold enhancement) and 15N-imidazole (≈180-fold enhancement), the former with a 13C T1 of ≈14 s at 0.3 T. Straightforward synthetic routes, efficient spin-relay of SABRE hyperpolarization, and facile bond cleavage open a door to the cheap and rapid generation of long-lived hyperpolarized states within a wide range of molecular targets, including biologically relevant carboxylic acid derivatives, for metabolic and pH imaging.
- Kidd, Bryce E.,Mashni, Jamil A.,Limbach, Miranda N.,Shi, Fan,Chekmenev, Eduard Y.,Hou, Yuqing,Goodson, Boyd M.
-
-
Read Online
- Hydrogen exchange study on the hydroxyl groups of serine and threonine residues in proteins and structure refinement using NOE restraints with polar side-chain groups
-
We recently developed new NMR methods for monitoring the hydrogen exchange rates of tyrosine hydroxyl (Tyr-OH) and cysteine sulfhydryl (Cys-SH) groups in proteins. These methods facilitate the identification of slowly exchanging polar side-chain protons in proteins, which serve as sources of NOE restraints for protein structure refinement. Here, we have extended the methods for monitoring the hydrogen exchange rates of the OH groups of serine (Ser) and threonine (Thr) residues in an 18.2 kDa protein, EPPIb, and thus demonstrated the usefulness of NOE restraints with slowly exchanging OH protons for refining the protein structure. The slowly exchanging Ser/Thr-OH groups were readily identified by monitoring the 13Cβ-NMR signals in an H 2O/D2O (1:1) mixture, for the protein containing Ser/Thr residues with 13C, 2H-double labels at their β carbons. Under these circumstances, the OH groups exist in equilibrium between the protonated and deuterated isotopomers, and the 13C β peaks of the two species are resolved when their exchange rate is slower than the time scale of the isotope shift effect. In the case of EPPIb dissolved in 50 mM sodium phosphate buffer (pH 7.5) at 40 °C, one Ser and four Thr residues were found to have slowly exchanging hydroxyl groups (k ex -1). With the information for the slowly exchanging Ser/Thr-OH groups in hand, we could collect additional NOE restraints for EPPIb, thereby making a unique and important contribution toward defining the spatial positions of the OH protons, and thus the hydrogen-bonding acceptor atoms.
- Takeda, Mitsuhiro,Jee, Jungoo,Ono, Akira M.,Terauchi, Tsutomu,Kainosho, Masatsune
-
-
Read Online
- Preparation and mechanism of solvolysis of N-hydroxy-α- oxobenzeneethanimidoyl chloride, a 2-(hydroxyimino)-1-phenylethan-1-one derivative: Molecular structure of α-oxo-oximes (=α-(hydroxyimino) ketones)
-
Acid-catalyzed methanolysis of N-hydroxy-α-oxobenzeneethanimidoyl chloride (1), a 2-(hydroxyimino)-1-phenylethan-1-one derivative obtained in one step from acetophenone, leads to a constant ratio of methyl α- oxobenzeneacetate (2) and methyl α-(hydroxyimino)benzeneacetate (3). 13C(α) Labelled [13C]-1 affords 13C(α) labelled [13C]-3, thus discarding the hypothesis of its formation via 1,2-arene migration. The reported sequence opens a novel approach to phenylglyoxylic and mandelic acid esters (=α-oxobenzeneacetic and α-hydroxybenzeneacetic acid esters), from acetophenone. The molecular structures of 1 and 3 were determined by X-ray structure analysis and compared with previously reported crystallographic data of α-oxo-oximes (=α-(hydroxyimino) ketones) 4 and 6-8. The unique stereoelectronic characteristics of the α-oxo-oxime moiety are discussed. All α-oxo-oximes share the following structural characteristics: (E)- configuration of the oxime C=N-OH bond (i.e. OH and C=O trans), the s-trans conformation of the oxo and imino moieties about the C(α)-C(=NOH) single bond, and intermolecular H-bonding. They differ from the isostructural α- diketone enols by the absence of resonance-assisted intramolecular H-bonding.
- Hamersak, Zdenko,Peric, Berislav,Kojic-Prodic, Biserka,Cotarca, Livius,Delogu, Pietro,Sunjic, Vitomir
-
p. 1289 - 1301
(2007/10/03)
-
- Electrophilic amination of catecholboronate esters formed in the asymmetric hydroboration of vinylarenes
-
(S)-(4-Methoxyphenyl)-ethyl-1,3,2-benzodioxaborole, (S)-1-(4-chlorophenyl)ethyl-1,3,2-benzodioxaborole and (S)-1-indanyl-1,3,2-benzodioxaborole, intermediates in the catalytic asymmetric hydroboration of 4-chloro- and 4-methoxystyrene, were isolated as pure oils in 75%, 84% and 49% yield respectively. For the first example, amination with N-chloromagnesio-N-methyl-O-trimethylsilylhydroxylamine gave a mixture of (S)-1-(4-methoxyphenyl)-N- methylethylamine in 33% yield, 88% e.e. and (S)-1-(4-methoxyphenyl) ethanol in 31% yield, 86% e.e.. Related results were obtained in the other cases, and the steps of catalytic hydroboration and amination could be combined in a single sequence without isolation of the intermediate Numerous variants were carried out in the amination procedure with only marginal improvements in chemoselectivity. An investigation of the mechanism was carried out using low temperature heteronuclear NMR on 13C-1-(S)-1-(4-chlorophenyl)ethyl-1,3,2-benzodioxaborole. The dual pathway is a result of an irreversible and unselective initial step.
- Knight, Frances I.,Brown, John M.,Lazzari, Dario,Ricci, Alfredo,Blacker, A. John
-
p. 11411 - 11424
(2007/10/03)
-
- A Dynamic Equilibrium of Oxaphosphetanes
-
The course of the Wittig reaction was investigated by rapid injection NMR spectroscopy.Rate constants for the formation of oxaphosphetanes were determined.A new dynamic equilibrium of oxaphosphetanes was observed for the first time.The solvent and substituent dependence of the new effect was investigated.By labeling various oxaphosphetanes with 13C and 17O the lithium salt dependence of the new equilibrium was shown.A lithium adduct of oxaphosphetanes under these conditions is proposed. - Key Words: Wittig reaction / Rapid injection NMR / Dynamic NMR / Oxaphosphetanes
- Geletneky, Christian,Foersterling, Frank-Holger,Bock, Willi,Berger, Stefan
-
p. 2397 - 2402
(2007/10/02)
-
- Synthesis and spectroscopic study of 13C-labelled citric acids
-
The synthesis of (1'-13C)-, (3-13C)- and (2,4-13C2)citric acid from simple starting compounds is described.Using the same procedure, any mono- or multiply-labelled citric acid can be prepared.The 13C-labelled citric acids have been characterized by 1H NMR, 13C NMR and mass spectroscopy.
- Winkel, C.,Buitenhuis, E. G.,Lugtenburg, J.
-
-
- Development of methodology for the rapid incorporation of carbon-13 into 1,2,4-triazolo systems from carbon dioxide
-
An in situ production of C-13 acetyl chloride and subsequent reaction with amidrazones affords anxiolytic 1,2,4-triazolobenzodiazepines in reaction times suitable for labelling with carbon-11 (t( 1/2 ) = 20.4 min).
- Banks,Digenis
-
p. 6473 - 6476
(2007/10/02)
-
- Manipulation of Vinyl Groups in Protoporphyrin IX: Introduction of Deuterium and Carbon-13 Labels for Spectroscopic Studies
-
Using commercially available hemin (5) as the starting material, routes for preparation of monovinyl deuterated (27), monovinyl carbon-13 enriched (41,42), and divinyl carbon-13 enriched (43,44) derivatives of protoporphyrin IX dimethyl ester (1) are described.The monovinyl carbon-13 enriched porphyrins 41 and 42 were obtained by way of a previously reported Wittig reaction on Spirographis and iso-Spirographis porphyrin dimethyl esters 28 and 39, respectively.A new efficient partial synthesis of Spirographis porphyrin dimethyl ester (28) from deuteroporphyrin IX dimethyl ester (7) is reported, and in this the key formyl group at the 2 position is inserted by way of a Vilsmeier reaction employing a hindered amide.
- Smith, Kevin M.,Fujinari, Eugene M.,Langry, Kevin C.,Parish, Daniel W.,Tabba, Hani D.
-
p. 6638 - 6646
(2007/10/02)
-
- Biosynthesis of Porphyrins and Related Macrocycles. Part 16. Proof that the Single Intramolecular Rearrangement leading to Natural Porphyrins (Type-III) occurs at the Tetrapyrrole Level
-
The unrearranged aminomethylbilane (2) is synthesised by a rational route and is proved to be converted by the enzymes deaminase and cosynthetase, working co-operatively, into uro'gen-III (3).The single rearrangement step established earlier is thus proved to take place at the tetrapyrrole level.Synthesis of singly 13C-labelled bilane (2) followed by its enzymic conversion into uro'gen-III serves to register each of the pyrrole rings of the product relative to the initial bilane.Finally, methods for synthesis of the bilane are developed in two different doubly 13C-labelled forms to allow the following key points to be established largely by 13C n.m.r. spectroscopy: (a) as the bilane system is converted into uro'gen-III, intramolecular rearrangement of the terminal ring D occurs, and (b) the linear tetrapyrrole is converted intact into uro'gen-III.Syntheses of -, and -uroporphyrin octamethyl ester are described together with improved h.p.l.c. conditions for the separation of isomeric coproporphyrin tetramethyl esters.
- Battersby, Alan R.,Fookes, Christopher J. R.,Meegan, Mary J.,McDonald, Edward,Wurziger, Hanns K. W.
-
p. 2786 - 2799
(2007/10/02)
-
- Mechanism of Reductive Elimination of Acetophenone from N(CH3)4+-
-
Decomposition of N(CH3)4+- (1) in the presence og P(C6H5)3 gives N(CH3)4+Mn(CO)4- and provides evidence for a Mn(CO)4- intermediate.Decomposition of 90percent 13C-acetyl labeled N(CH3)4+- (1A) gave 42.7percent 13C-labeled acetophenone.Decomposition of 90percent 13C-benzoyl labeled N(CH3)4+- (1b) gave 6.0percent 13C-labeled acetophenone.These results are interpreted in terms of a mechanism involving loss of CO from 1 and formation of a five-coordinate intermediate Mn(CO)3(COCH3)(COC6H5)- (2), which is in rapid equilibrium with benzoylmethyl intermediate Mn(CO)4(CH3)(COC6H5)- (3).Conversion of 3 to the acetylphenyl intermediate Mn(CO)4(C6H5)(COCH3)- (4) is followed by reductive elimination to give acetophenone.
- Casey, Charles P.,Scheck, Daniel M.
-
p. 2728 - 2731
(2007/10/02)
-
