636-93-1Relevant articles and documents
Engineering Orthogonal Methyltransferases to Create Alternative Bioalkylation Pathways
Bennett, Matthew R.,Cronin, Victoria A.,Herbert, Abigail J.,Micklefield, Jason,Shepherd, Sarah A.,Sung, Rehana
supporting information, p. 14950 - 14956 (2020/07/04)
S-adenosyl-l-methionine (SAM)-dependent methyltransferases (MTs) catalyse the methylation of a vast array of small metabolites and biomacromolecules. Recently, rare carboxymethylation pathways have been discovered, including carboxymethyltransferase enzymes that utilise a carboxy-SAM (cxSAM) cofactor generated from SAM by a cxSAM synthase (CmoA). We show how MT enzymes can utilise cxSAM to catalyse carboxymethylation of tetrahydroisoquinoline (THIQ) and catechol substrates. Site-directed mutagenesis was used to create orthogonal MTs possessing improved catalytic activity and selectivity for cxSAM, with subsequent coupling to CmoA resulting in more efficient and selective carboxymethylation. An enzymatic approach was also developed to generate a previously undescribed co-factor, carboxy-S-adenosyl-l-ethionine (cxSAE), thereby enabling the stereoselective transfer of a chiral 1-carboxyethyl group to the substrate.
Temperature-dependent regioselectivity of nucleophilic aromatic photosubstitution. Evidence that activation energy controls reactivity
Wubbels, Gene G.,Tamura, Ryo,Gannon, Emmett J.
, p. 4834 - 4839 (2013/07/11)
Irradiation (λ > 330 nm) of 2-chloro-4-nitroanisole (1) at 25 C in aqueous NaOH forms three substitution photoproducts: 2-methoxy-5-nitrophenol (2), 2-chloro-4-nitrophenol (3), and 3-chloro-4-methoxyphenol (4), in chemical yields of 69.2%, 14.3%, and 16.5%. The activation energies for the elementary steps from the triplet state at 25 °C were determined to be 1.8, 2.4, and 2.7 kcal/mol, respectively. The chemical yields of each of the three products were determined for exhaustive irradiations at 0, 35, and 70 °C. The variation with temperature of the experimental yields is reproduced almost exactly by the yields calculated with the Arrhenius equation. This indicates that activation energy is the fundamental property related to regioselectivity in nucleophilic aromatic photosubstitution of the SN2 Ar* type. The many methods proposed for predicting regioselectivity in reactions of this type have had limited success and have not been related to activation energy.
The element effect and nucleophilicity in nucleophilic aromatic photosubstitution (SNAR*). Local atom effects as mechanistic probes of very fast reactions
Wubbels, Gene G.,Brown, Toby R.,Babcock, Travis A.,Johnson, Kandra M.
, p. 1925 - 1934 (2008/09/19)
(Chemical Equation Presented) Photoreactions of 4-nitroanisole and the 2-halo-4-nitroanisoles (halogen = F, Cl, Br, and I) with the nucleophiles hydroxide ion and pyridine have been investigated quantitatively to extend the findings recently communicated for cyanide ion. The halonitroanisoles on excitation form triplet π,π* states, which undergo substitution of the halogen by nucleophiles. Chemical yields of photoproducts, Stern-Volmer kinetic plots, triplet lifetimes, and triplet yields are reported for the five compounds with the three nucleophiles. Following a standard kinetic treatment, 73 rate constants are determined for elementary reactions of the triplets including quenching and various nucleophilic addition processes. The photoadditions are roughly 14 orders of magnitude faster than thermal counterparts. Rate constants for attack at the fluorine-bearing carbon of triplet 2-fluoro-4-nitroanisole are 2.9 × 109, 1.3 × 109, and 6.3 × 108 M-1 s-1 for cyanide ion, hydroxide ion, and pyridine, respectively. The relative rates for attack at the halogen-bearing carbons for F/Cl/Br/I are 27:1.9:1.9:1 (cyanide ion), 29:2.6:2.4:1 (hydroxide ion), and 39:3.9: 3.5:1 (pyridine), respectively. The relative nucleophilicities vary somewhat with the attack site; they are about 5:2:1 for cyanide ion, hydroxide ion, and pyridine for attack at the halogen-bearing carbons. The trend of the element effect opposes that of aliphatic substitution and elimination but is similar in size and parallel to that of thermal nucleophilic aromatic substitution. Relative nucleophilicities in the photoreactions are also similar to those of comparable but vastly slower thermal reactions. The findings imply that the efficiency-determining step of the halogen photosubstitution is simple formation of a σ-complex through electron-paired bonding within the triplet manifold.
Photochemical nucleophile mapping: Identification of Tyr311 within the catalytic domain of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase
Hatanaka, Yasumaru,Kaneda, Masaki,Tomohiro, Takenori
, p. 213 - 217 (2008/02/01)
Photochemical mapping of nucleophiles in close proximity to the active site Cys149 of rabbit glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was demonstrated based on the nucleophilic aromatic photosubstitution reaction using two regioisomers of alkoxy-fluoro-nitro-substituted benzenes. Two photophores were covalently attached to the active site SH group of GAPDH and the protein was subjected to photolysis then to the cyanogen bromide cleavage reaction. The advantage of this method is the capability to chase labeled products by monitoring absorption at 380 nm because of the chromogenic property of photophore. HPLC separation identified a large labeled peptide fragment that was further digested by V8 protease for Edman sequence analysis. From the recent X-ray crystallography of rabbit GAPDH, Tyr311, His176, Ser238 and Lys183 are closely located to catalytic Cys149. Among these nucleophiles, Tyr311 was preferentially labeled with 2-fluoro-4-nitrophenoxy photophore and no label was identified with the isomeric 4-fluoro-2-nitrophenoxy photophore. The result clearly reflects the distance between Cys149 and nucleophiles to distinguish the nearest Tyr311. As photophores show great reactivity even with water under neutral conditions, the distance between nucleophiles and photophores is important for photo-induced nucleophilic aromatic substitution. The method will provide a useful technique to survey nucleophiles within the catalytic domain.
Rates of reductive elimination of substituted nitrophenols from the (indol-3-yl)methyl position of indolequinones
Swann,Moody,Stratford,Patel,Naylor,Vojnovic,Wardman,Everett
, p. 1340 - 1345 (2007/10/03)
A series of indolequinones bearing substituted nitrophenols on the (indol-3-yl)methyl position was synthesised. The nitrophenol leaving groups were appropriately substituted to give a wide range (4 units) in phenolic pKa value. The rate of redu
Etherification of phenols catalysed by solid-liquid phase transfer catalyst PEG400 without solvent
Cao, Yu-Qing,Pei, Ben-Gao
, p. 1759 - 1766 (2007/10/03)
Aromatic ethers were synthesised in excellent yields(above 86 %) and purity by the etherification of phenols with dimethyl sulfate or alkyl halides, catalysed by phase transfer catalyst PEG400 under solvent-free conditions, and the effects of some key reaction conditions were also studied.
Photosubstitution-photoreduction mechanistic duality in the SET photoreactions of nitrophenyl ethers with amines. The role of the steps that follow the ET
Mir, Miquel,Marquet, Jordi,Massot, Oriol
, p. 12603 - 12614 (2007/10/03)
Nitrophenyl ethers are photoreduced by primary amines in water through a mechanism initiated by single electron transfer that is in direct competition with the single electron transfer photosubstitution mechanism (S(N)Ar*-SET). Our results indicate that the preferred pathway does not depend on the electron donor or proton donor ability of the amine. The key factor that determines the progress of the photoreaction is the structure of the carbon skeleton of the amine, particularly the type of hydrogens on the carbon α to the amino group. A mechanistic rationale that includes hydrogen atom transfer as a key step is discussed.
Effects of superoxide anion generated from aromatic radical anions produced in nucleophilic aromatic photosubstitution reactions
Cervera, Maria,Marquet, Jordi
, p. 966 - 969 (2007/10/03)
Superoxide anion is generated from aromatic radical anions produced in nucleophilic aromatic photosubstitutions when the reactions are carried out in non-deoxygenated solutions of polar aprotic solvents. Superoxide anion thus generated displaces cyanide anion from acetonitrile and benzyl cyanide, ethoxide anion from ethyl acetate, and methanesulfenate anion from dimethyl sulfoxide. Hence, non-deoxygenated polar aprotic solvents should be avoided in nucleophilic aromatic photosubstitution reactions.
Topologically Controlled Coulombic Interactions, a New Tool in the Developing of Novel Reactivity. Photochemical and Electrochemical Cleavage of Phenyl Alkyl Ethers
Marquet, Jorge,Cayon, Eduard,Martin, Xavier,Casado, Francisco,Gallardo, Iluminada,et al.
, p. 3814 - 3825 (2007/10/02)
The hypothesis that a specific placement of a positive charge would dramatically alter the behavior of a charged intermediate has been tested.Phenyl ethers substituted by electron-attracting groups do not undergo reductive fragmentation.However, related α-piperidino-ω-(4-substituted-phenoxy)alkanes give alkyl ether photocleavage when the linker between the redox centers is short, or the usual substitution-reduction photochemistry when it is long.Mechanistic experiments suggest that the photofragmentation process operates through space intramolecular electron transfer to the triplet aromatic chromophore and that a coplanar relative orientation of the alkyl ether bond and the phenyl ring is compulsory for the photofragmentation to be observed.Configuration interaction AM1 calculations justify the described facts, indicating that the fragmentation process is only operative when a Coulombic stabilization of a ?* intramolecular electron transfer excited state is produced.Electrochemical studies carried out with the corresponding quaternary salts (intermolecular generation of the phenyl ether radical anion) confirm the conclusions derived from the photochemical experiments.
Phosphomonoesters and phosphodiesters derived from the photohydrolysis of 2-methoxy-5-nitrophenyl substituted phosphotriesters
Graciani, Nilsa R.,Swanson, Daniel S.,Kelly, Jeffery W.
, p. 1077 - 1086 (2007/10/02)
Phosphotriesters composed of one or two 2-methoxy-5-nitrophenyl group(s) can be quantatively photohydrolyzed in aqueous acetonitrile to yield the desired phosphodiester or phosphomonoester, respectively. Photohydrolysis occurs by attack of hydroxide at both the phosphoryl phosphorus and at the ipso-carbon in the triplet exited state of the 2-methoxy-5-nitrophenyl substituted phosphoesters. The photophysical studies described within imply that this type of reaction may be synthetically useful.
