Asymmetric Sulfoxidation Reaction Research Articles

Construction and functional analysis of a whole-cell biocatalyst based on CYP108N7.

Cytochrome P450 enzymes are versatile biocatalysts with great potential in biotechnology. A new bacterial P450 was identified from the genome of Rhodococcus wratislaviensis NBRC 100605 and annotated as CYP108N7. The enzyme accepted the ferredoxin and ferredoxin reductase from spinach as surrogate redox partners for improved electron transfer efficiency. It was heterologous expressed in Escherichia coli together with the redox partners and a glucose dehydrogenase which supplied the reduced cofactor NADPH. The resulting whole-cell biocatalyst catalyzed a variety of reactions including sulfoxidation, epoxidation, hydroxylation, demethylation and dehalogenation. Remarkable stereoselectivity was observed in asymmetric sulfoxidation reaction, which could deliver chiral sulfoxides with >99% ee from thioanisole and derivatives.

An efficient silica supported Chitosan@vanadium catalyst for asymmetric sulfoxidation and its application in the synthesis of esomeprazole

A new type of silica supported Chitosan@vanadium complex was used as a highly active heterogeneous catalyst for asymmetric oxidation of aryl alkyl sulfides. With the economic aqueous H2O2 (30%) as the oxidant, the oxidation products were obtained in high yields (up to 95%) with good enantioselectivities (up to 68% ee). It is noted that the marketed drug Nexium (first proton-pump inhibitor, esomeprazole) could be synthesized easily by the newly developed asymmetric sulfoxidation reaction. In addition, the highly active catalyst can be reused five times without losing its catalytic activity.

Axially Chiral Imidodiphosphoric Acid Catalyst for Asymmetric Sulfoxidation Reaction: Insights on Asymmetric Induction

Insights into chiral induction for an asymmetric sulfoxidation reaction involving a single oxygen atom transfer are gained through analyzing the stereocontrolling transition states. The fitting of the substrate into the chiral cavity of a new class of imidodiphosphoric Brønsted acids, as well as weak CH⋅⋅⋅π and CH⋅⋅⋅O noncovalent interactions, are identified as responsible for the observed chiral induction.

Axially Chiral Imidodiphosphoric Acid Catalyst for Asymmetric Sulfoxidation Reaction: Insights on Asymmetric Induction

AbstractInsights into chiral induction for an asymmetric sulfoxidation reaction involving a single oxygen atom transfer are gained through analyzing the stereocontrolling transition states. The fitting of the substrate into the chiral cavity of a new class of imidodiphosphoric Brønsted acids, as well as weak CH⋅⋅⋅π and CH⋅⋅⋅O noncovalent interactions, are identified as responsible for the observed chiral induction.

In situ-generated chiral iron complex as efficient catalyst for enantioselective sulfoxidation using aqueous H2O2as oxidant

This study represents the rare combination of non-toxic Fe based catalyst/H2O2as an efficient catalytic protocol for asymmetric sulfoxidation reaction.

Simultaneous synthesis of modified Binol-periodic mesoporous organosilica SBA-15 type material. Application as catalysts in asymmetric sulfoxidation reactions

The synthesis of a chiral periodic mesoporous organosilica (chiral PMO) SBA-15 type, using a bis-silylated Binol precursor, has been studied through two different heterogenization routes. On the one hand, the immobilization of a (R)-(+)-1,1′-bi-2-naphthol (Binol) derivative was accomplished by following a standard multistep synthesis methodology. On the other hand, a new route consisting of an easy one-step synthesis was developed achieving a simultaneous formation of mesoporous structure and Binol chiral ligand immobilization in the walls. The addition of KCl “salting out” electrolytes favored the micellization, obtaining the well-ordered chiral PMO materials. The thioanisole asymmetric oxidation reaction was used to validate the enantio-catalysts activity. The materials synthesized by the multistep method reached yield and enantiomeric excess of 41 and 15 %, respectively, while the synthesized one-pot chiral PMO materials achieved up to 58 and 42 %, respectively. This difference could be attributed to a more homogenous distribution of the chiral moiety as well as the simultaneous micellization and formation of the siliceous mesostructure, in the one-pot procedure. This promotes higher reagents accessibility to the active center, and therefore an enhancement of the chiral induction. Thereby, materials with Binol ligand incorporated into the three-dimensional silica framework were successfully accomplished.

Chiral VIVO-Sal-Indanol complex over modified SBA-15: An efficient, reusable enantioselective catalyst for asymmetric sulfoxidation reaction

A reusable, mesoporous, heterogeneous vanadium complex, VIVO-Sal-Ind-SBA-15 has been synthesized first time from (1R,2S)-(+)-Cis-1-amino-2-indanol for enantioselective sulfoxidation reaction. The physico-chemical properties of the functionalized catalyst were analyzed by a series of characterization techniques like XRD, N2 sorption measurement isotherm, TEM, FT-IR, XPS, EPR, DRS UV–Visible, ICP-OES and solid & liquid state 13C, 29Si and 51V NMR spectroscopy. Powder X-ray diffraction patterns, TEM and N2 physisorption analysis confirmed the retention of mesoporous structure after various modifications. Solid-state NMR (13C CP-MAS NMR, 29Si MAS NMR) and FT-IR analysis certified the integrity of organocatalyst residing inside the pore channels of the mesoporous support. Further, XPS, EPR, 51V NMR and DRS UV–Visible analyses help to find out the oxidation state and coordination environment of vanadium in VIVO-Sal-Ind-SBA-15. Catalytic evaluation in asymmetric sulfoxidation reaction of sulfides indicated that VOIV-Sal-Ind-SBA-15 exhibited higher catalytic activity, stability, reusability and comparable enantioselectivity than SBA-15, PrNH2-SBA-15, neat VIVO-Sal-Indanol complex and without catalyst. The effect of different catalysts, temperature, solvents and substrates on sulfoxidation reaction were examined in order to optimize the conversion and enantioselectivity of thioanisoles to sulfoxides.

Mechanism of the Asymmetric Sulfoxidation in the Esomeprazole Process: Effects of the Imidazole Backbone for the Enantioselection

Abstractmagnified imageThe asymmetric sulfoxidation reaction of imidazole‐based prochiral sulfides was studied to explore the mechanistic details of the highly efficient esomeprazole process, which is one of the few industrial scale catalytic asymmetric procedures. The synthetic studies revealed that the smallest subunit governing the selectivity in the esomeprazole process is an imidazole ring. Thus, by using the esomeprazole procedure methyl imidazole sulfide could be oxidized as efficiently as its several functionalized derivatives, including pyrmetazol. However, alkylation of the imidazole nitrogen led to a major drop of the enantioselectivity. Our atmospheric pressure chemical ionization‐mass spectrometry (APCI/MS) studies indicate that addition of small amounts of water to the reaction mixture facilitates the formation of mononuclear titanium species, which are the active catalytic intermediates of the selective oxidation reaction. One of the most important features of the esomeprazole procedure is that amine additives increase the enantioselectivity of the oxidation process. The NMR studies of the presumed reaction intermediates show that under catalytic conditions the amines are able to coordinate to titanium and dissociate the coordinated imidazole substrate. The density functional theory (DFT) modelling studies provided new insights in the mechanism of the asymmetric induction. It was found that the oxidation requires a lower activation energy if the imidazole sulfide precursor does not coordinate to titanium. Two possible reaction paths were explored for this out of sphere oxidation mechanism. The most important interaction governing the enantioselection is hydrogen bonding between the NH of the imidazole ring and the chiral tartrate ligand on titanium. Furthermore, the oxidation reaction imposes an important structural constraint to the TS structure involving a linear arrangement of the peroxide oxygens and the sulfur atom. This constraint and the N coordination of imidazole leads to a very strained structure for the inner sphere mechanism of the oxidation, which leads to a much higher activation barrier than the corresponding out of sphere process, and therefore it is unlikely.

An enantiopure pseudo-C3-symmetric titanium triflate with propeller-like chirality as a catalyst for asymmetric sulfoxidation reactions

A chiral pseudo-C(3)-symmetric titanium triflate that employs the point chirality of a single stereogenic centre to control the propeller chirality of its aryl rings has been used to catalyse an asymmetric sulfoxidation reaction.

Iron‐Catalyzed Oxidation of Thioethers by Iodosylarenes: Stereoselectivity and Reaction Mechanism

Catalytic properties of a series of iron(III)-salen (salen=N,N'-bis(salicylidene)ethylenediamine dianion) and related complexes in asymmetric sulfoxidation reactions, with iodosylarenes as terminal oxidants, have been explored. These catalysts have been found to efficiently catalyze oxidation of alkyl aryl sulfides to sulfoxides with high chemoselectivity (up to 100 %) and moderate-to-high enantioselectivity (up to 84 % with isopropylthiobenzene and iodosylmesitylene), the TON (TON=turnover number) approaching 500. The influence of the ligand (electronic and steric effects of the substituents), oxidant, and substrate structures on the oxidation stereoselectivity has been investigated systematically. The structure of the reactive intermediates (complexes of the type [Fe(III)(ArIO)(salen)] and the reaction mechanism have been revealed by both mechanistic studies with different iodosylarenes and direct in situ (1)H NMR observation of the formation of the reactive species and its reaction with the substrate.

A convenient approach to renewable hydroperoxides

2-(1-Hydroperoxyalkyl)-furans and 6-hydroperoxy-2 H-pyran-3(6 H)-ones are alternatively accessible by acid-catalyzed oxidation of 2-furyl alcohols with hydrogen peroxide under appropriate conditions. Representative compounds of both classes of hydroperoxides have been used, as easily renewable oxygen donors, in asymmetric sulfoxidation reactions.