Cross-linked aggregates of (R)-oxynitrilase: a stable, recyclable biocatalyst for enantioselective hydrocyanation

[Reaction: see text] The (R)-oxynitrilase from almonds was immobilized as a cross-linked enzyme aggregate (CLEA) via precipitation with 1,2-dimethoxyethane and subsequent cross-linking using glutaraldehyde. The resulting preparation was a highly effective hydrocyanation catalyst under microaqueous conditions, which suppress the nonenzymatic background reaction. The beneficial effect of these latter conditions on the hydrocyanation of slow-reacting aldehydes is demonstrated. The oxynitrilase CLEA was recycled 10 times without loss of activity.     

Synthesis of (R)-cyanohydrins by crude (R)-oxynitrilase-catalyzed reactions in micro-aqueous medium

In diisopropyl ether or ethyl acetate under micro-aqueous conditions, the enantioselective synthesis of (R)-cyanohydrins from aldehydes and methyl ketones was studied using crude (R)-oxynitrilase prepared from almonds. This reaction system performed well over the temperature range of 4°C to 30°C.     

A theoretical study of imine hydrocyanation catalyzed by halogen‐bonding

A detailed theoretical study of the mechanism and energetics of an organocatalysis based on C?N activation by halogen‐bonding is presented for the hydrocyanation of N‐benzylidenemethylamine. The calculations at the level of scalar‐relativistic gradient‐corrected density functional theory give an insight in this catalytic concept and provide information on the characteristics of four different monodentate catalyst candidates acting as halogen‐bond donors during the reaction. © 2015 Wiley Periodicals, Inc.     

Nickel(0)-catalyzed asymmetric hydrocyanation of 1,3-dienes

1,2-Bis-diarylphosphinites are excellent ligands for the Ni(0)-catalyzed hydrocyanation of certain types of 1,3-dienes. 1-Phenyl-1,3-butadiene, 1-vinyl-3,4-dihydronaphthalene, and 1-vinylindene undergo highly regioselective hydrocyanation under ambient conditions to give exclusively the 1,2-adducts in good to excellent yields. Using bis-1,2-diarylphosphinites derived from d-glucose, the highest enantioselectivities to-date for asymmetric hydrocyanation of 1,3-dienes (70-83% ee's) have been obtained.     

反-Prelog还原体系、微水相羟氰化酶工作体系的发现 及光学活性化合物的合成

我们从土壤中筛选出一株有自主知识产权的霉菌(白地霉G.38),并发现它有独特的还原性能和优越的反应活性。与啤酒酵母作用相比,催化还原羰基,产物的立体化学上是按anti-Prelog的构型模式进行的。同时我们还开展了羟氰化酶合成光学活性的氰醇化合物的研究,发现和建立了一种适合粗酶作用的微水相工作体系,在工业上有实用前景。并筛选到3个高活性的(R)-氰醇酶源。     

Asymmetric hydrocyanation of hydrazones catalyzed by lanthanide--PYBOX complexes

[reaction: see text] The asymmetric addition of HCN to hydrazones is catalyzed in high yield and good-to-excellent enantioselectivity by the easily prepared (PhPYBOX)ErCl3 complex. This constitutes the first example of asymmetric catalytic hydrocyanation of hydrazones.     

Catalytic asymmetric epoxidation of chalcones under poly(ethylene glycol)-supported Cinchona ammonium salt catalyzed conditions

Dimeric cinchonine, cinchonidine, and quinine have been anchored (via nitrogen) to long linear PEG chains to afford soluble polymer-supported chiral ammonium salts, which were employed as phase-transfer catalysts in the asymmetric epoxidation of chalcones. The highest enantiomeric excess obtained was 86%.     

A novel strategy for the asymmetric synthesis of chiral cyclopropane carboxaldehydes

A new way of combining chiral auxiliaries and substrate-directable reactions for asymmetric synthesis is described that employs a three-step sequence of aldol-cyclopropanation-retro-aldol reactions for the stereoselective synthesis of enantiopure cyclopropane carboxaldehydes.     

Solvent-free asymmetric olefin hydroformylation catalyzed by highly cross-linked polystyrene-supported (R,S)-BINAPHOS-Rh(I) complex

Using an (R,S)-BINAPHOS-Rh(I) catalyst that is covalently anchored to a highly cross-linked polystyrene support, asymmetric hydroformylation of olefins was performed in the absence of organic solvents. The reaction of cis-2-butene, a gaseous substrate, provided (S)-2-methylbutanal with 100% regioselectivity and 82% ee upon treatment with H(2) (12 atm) and CO (12 atm) in a batchwise reactor equipped with a fixed bed. The polymer-supported catalyst was applicable to a continuous vapor-flow column reactor, and thus, 3,3,3-trifluoropropene was converted into (S)-2-trifluoromethylpropanal with an iso/normal ratio of 95/5 and 90% ee. Less volatile olefins, such as styrene, vinyl acetate, 1-alkenes, and fluorinated alkenes, were successfully converted into the corresponding isoaldehydes with high ee values, when they were injected through a supercritical CO(2)-flow column reactor. Successive injection of a series of olefins realized the conversion of an olefin library into an optically active aldehyde library.     

Highly efficient oxidation of alcohols using Oxone(R) as oxidant catalyzed by ruthenium complex under mild reaction conditions

Aromatic and alkyl alcohols were oxidized to the corresponding aldehydes or ketones at room temperature with high conversion and selectivity using Oxone (2KHSO5·KHSO4·K2SO4) as oxidant catalyzed by ruthenium complex Quin-Ru-Quin (where Quin = 8-hydroxyquinoline). The reaction time is very short and the preparation of complex is simple. 2008 Zi Qiang Lei. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

Facile synthesis of 3,3-di(heteroaryl)indolin-2-one derivatives catalyzed by ceric ammonium nitrate (CAN) under ultrasound irradiation

Ceric ammonium nitrate efficiently catalyzes the reaction of isatin with indoles under sonic waves to afford symmetrical 3,3-di(indolyl)indolin-2-ones in excellent yields, as well as the reaction of 3-hydroxy-3-indolylindolin-2-ones with indoles, pyrrole to afford the corresponding adducts in excellent yields, which provides an efficient route to the synthesis of symmetrical and unsymmetrical 3,3-di(indolyl)indolin-2-one derivatives, respectively.     

Reverse-docking study of the organocatalyzed asymmetric Strecker hydrocyanation of aldimines and ketimines

A methodology for reverse-docking flexible organocatalysts to rigid transition state models of catalyst-free asymmetric reactions has been developed. The investigation of Jacobsen's chiral thiourea-based organocatalyst for the hydrocyanation of aldimines and ketimines (Strecker reaction) via reverse-docking is described. Results from reverse-docking Jacobsen's organocatalyst to both enantiomers of six Strecker TS-models (i.e., rigid transition state models of the catalyst-free asymmetric reaction) indicate a clear energetic preference for binding the organocatalyst to the R-enantiomer TS-model, which is in agreement with experimental results. The most favorable docking poses reveal structural features consistent with principles of molecular recognition, catalysis, and NMR data. These poses may represent simplified geometric models of the transition state for the catalyzed reaction.     

Lewis acid-catalyzed, copper(II)-mediated synthesis of heteroaryl thioethers under base-free conditions

A Lewis acid (Ag(I), Ni(II), or Fe(II)) catalyzed, Cu(II)-mediated thiolation reaction between heteroarenes and thiols was achieved with good yield under base-free conditions. DMSO could serve as an effective methylthiolation reagent for the synthesis of heterocyclic methyl thioethers.     

One-pot synthesis of dihydropyrimidiones catalyzed by strontium(II) triflate under solvent-free conditions

A simple, efficient and practical procedure for the Biginelli reaction using strontium(II) triflate [Sr(OTf)₂] as a novel catalyst is described under solvent-free conditions in high yields. The catalyst exhibited remarkable reactivity and it is reusable. Some of dihydropyrimidiones showed strong pesticidal activity.     

Solvent-free asymmetric aldol reaction organocatalyzed by (S)-proline-containing thiodipeptides under ball-milling conditions

An efficient, solvent-free ball-milling protocol for the asymmetric aldol reaction between cyclohexanone and cyclopentanone with various aromatic aldehydes using a novel series of (S)-proline-containing dipeptides and thiodipeptides 1a–f as organocatalysts is reported. In general, (S)-proline-containing thiodipeptides proved to be better organocatalysts relative to their analogous amides. In particular, thiodipeptide (S,S)-1d catalyzed the stereoselective formation of the expected aldol products with excellent diastereo- and enantioselectivity (up to 98:2 anti/syn dr and up to 96% ee). This observation may be ascribed to the increased N–H acidity of the thioamide segment that leads to stronger H-bonding interaction with the aldehyde carbonyl at the transition state and thus higher stereoinduction. Furthermore, thiodipeptide 1f proved to be an efficient organocatalyst for the aldol reaction of acetone with isatin and isatin derivatives (ee 56–86%).     

DFT study of the asymmetric nitroaldol (Henry) reaction catalyzed by a dinuclear Zn complex

We report the mechanism of asymmetric nitroaldol (Henry) reaction catalyzed by a dinuclear Zn complex using density functional theory. The experimentally proposed catalytic cycle is validated, in which the first step is the deprotonation of nitromethane by the ethyl anion of the catalyst, subsequently a C? C bond formation step, and then the protonation of the resulting alkoxide. Three mechanistic scenarios (differing in binding modes) have been considered for the C? C bond formation step. The origin of the enantioselectivity is discussed. Our calculations supported that the S configurations are the major products, which is in agreement with the experimental observations. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Homocoupling of arylboronic acids catalyzed by dinuclear copper(I) complexes under mild conditions

An efficient protocol for C–C coupling has been developed using three iodo-bridged copper(I) complexes as catalysts. Complexes [CuI(bpy)]₂ (1), [CuI(phen)]₂·DMF (2), and [CuI(Mephen)]₂ (3) were successfully synthesized via solvothermal method (bpy = 2,2′-dipyridyl, phen = 1,10-phenanthroline, and Mephen = 2,9-dimethylphenanthroline). The self-coupling reaction of phenylboronic acid was selected as a model reaction to evaluate the catalytic property of the complexes. Moreover, this method tolerates various substituents on the arylboronic acids such as halogens, carbonyls, and nitro groups. It shows that the iodo-bridged Cu(I) center serves as the active site to activate molecular oxygen during the catalytic process. The result illustrates that these complexes were found to be excellent catalysts for self-coupling of arylboronic acids under mild conditions.

     

(R)-(+)-N-methylbenzoguanidine ((R)-NMBG) catalyzed kinetic resolution of racemic secondary benzylic alcohols with free carboxylic acids by asymmetric esterification

(R)-(+)-N-Methylbenzoguanidine ((R)-NMBG) was found to function as an efficient acyl-transfer catalyst for the kinetic resolution of racemic secondary benzylic alcohols in the presence of achiral carboxylic acids and pivalic anhydride. The use of a tertiary amine in this reaction is not necessary to attain good chemical yields of the products. It was determined that diphenylacetic acid could be employed as the most suitable acyl donor for achieving a high enantioselectivity for the kinetic resolution of the racemic secondary benzylic alcohols having normal aliphatic alkyl chains at the C-1 positions. On the other hand, a less-hindered carboxylic acid, such as 3-phenylpropanoic acid, functioned as a better acyl donor for the kinetic resolution of racemic secondary benzylic alcohols having branched aliphatic alkyl chains at the C-1 positions.     

Heterogeneous asymmetric addition of diethylzinc to aromatic aldehydes catalyzed by Ti(IV)/imine bridged poly(R)-binaphthol

Heterogeneous asymmetric addition of diethylzinc to aldehydes catalyzed by chiral polymer catalysts has been achieved. The conjugated polymers based on a BINOL skeleton were synthesized in five steps and applied to this reaction with yield and e.e. up to 95 and 84.5%, respectively. These chiral polymers can be easily quantitatively recovered and reused without decreasing of e.e. or catalytic activity.     

(R)-Oxynitrilase-catalyzed hydrocyanation: the first synthesis of optically active fluorinated mandelonitriles

The first enantioselective synthesis of (R)-fluorinated mandelonitriles, by hydrocyanation under micro-aqueous conditions with almond meal as catalyst is reported.