A study of asymmetric hydrocyanation of heteroaryl carboxaldehydes catalyzed by (R)-oxynitrilase under micro-aqueous conditions

A number of new optically active heteroaryl cyanohydrins have been prepared by hydrocyanation under micro-aqueous conditions catalyzed by almond meal (containing (R)-oxynitrilase). Substituent effects on the reaction are discussed. This micro-aqueous method provides an efficient, convenient and economical approach to optically active cyanohydrins.     

(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.     

An efficient enantioselective synthesis of (R,R)-formoterol,a potent bronchodilator,using lipases

The potent β₂-adrenergic receptor agonist formoterol (R,R)-1 has been obtained in enantiomerically pure form by a convenient chemoenzymatic approach by coupling of epoxide (R)-6 with the unprotected primary amine (R)-9. Both chiral precursors have been prepared by enantiodifferentiation processes involving Pseudomonas cepacia (lipase PS) and Candida antarctica lipase (CALB), respectively. For the resolution of amine 9, we have found that utilization of triethylamine as non-reactive base enhances the reaction rate and the enantioselectivity of the process. The key coupling reaction of (R)-6 and (R)-9 has been conducted through derivatization of the amine with the labile trimethylsilyl group, which liberates the amino group of the resulting amino alcohol (R,R)-11 upon column chromatography purification. In this way, the overall approach is shorter than others previously described.     

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。     

Catalytic enantioselective Diels-Alder reaction in ionic liquid via a recyclable chiral In(III) complex

[Structure: see text] A recyclable, air- and moisture-stable chiral indium complex in [hmim][PF6-] ionic liquid has been developed. The cycloaddition of a variety of cyclic and open-chained dienes to 2-methacrolein and 2-bromoacrolein resulted in good yields and excellent enantioselectivities (up to 98% ee). Moreover, the chiral In(III) complex can be reused for seven successive cycles with comparable enantioselectivities and yields without loss of catalytic activity.     

Highly enantioselective aldol reactions catalyzed by a recyclable fluorous (S) pyrrolidine sulfonamide on water

Fluorous (S) pyrrolidine sulfonamide serves as an efficient promoter for highly enantioselective aldol reactions of ketones and aldehydes with aromatic aldehydes on water. A notable feature of the organocatalyst is that it can be recovered from the reaction mixtures by simple fluorous solid-phase extraction and subsequently reused (up to seven cycles) without a significant loss of catalytic activity and stereoselectivity.     

Polystyrene copolymer supported by substituted (1R,2R)-1,2-diphenylethane-1,2-diamine-copper(II) complexes: a recyclable catalyst for asymmetric Henry reactions

Herein described the preparation of swelling pearl-like copolymer styrene—4-vinylbenzyl chloride cross-linked by means of tetra(ethylene glycol)-bis(4-vinylbenzyl)ether (200–800 μm). The pearl-like polymer was used to anchor (1R,2R)-1-amino-2-(2,3-dihydro-1H-isoindole-2-yl)-1,2-diphenylethane by a covalent bond; the product was subsequently transformed into the corresponding complex with Cu(II) acetate. The synthesized catalyst was used for the catalysis of the Henry reaction of functionalized aldehydes with nitromethane in ethanol. The reactions proceeded in a polymeric matrix of the swelling catalyst at a rate comparable with the rates of reactions in a homogeneous medium. The corresponding functionalized 2-nitroethanols were formed in quantitative yields (20 °C, 24 h) with enantiomeric excess values of up to 96%. The catalyst was recycled five times without losing its effectiveness with regard to the yield and enantioselectivity; only a partial mechanical degradation of the polymeric matrix occurred due to stirring.     

Cross-linked enzyme aggregates: a simple and effective method for the immobilization of penicillin acylase

[reaction--see text] Penicillin G acylase (penicillin amidohydrolase, E.C. 3.5.1.11) was immobilized in a simple and effective way by physical aggregation of the enzyme, using a precipitant, followed by chemical cross-linking to form insoluble cross-linked enzyme aggregates (CLEAs). These had the same activity in the synthesis of ampicillin as cross-linked crystals of the same enzyme, but the accompanying hydrolysis of the side-chain donor was much less. Penicillin G acylase CLEAs also catalyzed the synthesis of ampicillin in a broad range of organic solvents.     

An enantioselective synthesis of (R)-4-piperidinylglycine

An efficient process for the synthesis of (R)-N-t-Boc-4-piperidinylglycine 8a, an unnatural amino acid, via enantioselective rhodium-catalyzed hydrogenation of the Cbz-enamide 5a is described. Subsequent deprotection of 8a affords unprotected (R)-4-piperidinylglycine 9 in good yield.     

An enantioselective synthesis of (S)- and (R)-curcuphenol

The enantioselective synthesis of the phenolic sesquiterenses (S)- and (R)-curcuphenol is reported. The key step in this synthesis is the asymmetric conjugate addition using a readily available enantiomerically pure sulfoxide as the chiral auxiliary.     

Evaluation of guanabana (Annona muricata) seed meal as a source of (S)-oxynitrilase

Guanabana seed meal is a source of (S)-oxynitrilase which biocatalyzes the enantioselective addition of HCN to aromatic, heteroaromatic and α,β-unsaturated aldehydes to produce cyanohydrins.     

Effective and recyclable dendritic ligands for the enantioselective epoxidation of enones

An operationally simple and mild protocol for the catalytic enantioselective epoxidation of enones has been established using a series of chiral pyrrolidinylmethanol-based dendritic catalysts and tert-butyl hydroperoxide (TBHP) as an oxidant. The epoxides have been obtained in good yields and ee up to 78%.     

A new and short enantioselective synthesis of (R)-pantolactone

Dihydro-4,4-dimethyl-2(3H)-furanone 6, the key intermediate to (R)-pantolactone 2, has been synthesized in two steps via the radical cyclization of bromoether 5. Silyl enol ether 7, prepared from 6, on Sharpless asymmetric dihydroxylation gave (R)-pantolactone 2 in moderate yield and excellent enantioselectivity.     

Ag@AgCl embedded on cellulose film: a stable,highly efficient and easily recyclable photocatalyst

In this work, cellulose–Ag@AgCl composite films have been fabricated directly through a one-step coagulation of a cellulose/1-butyl-3-methylimidazolium chloride (BmimCl) solution with AgNO₃ and PVP. The AgCl was formed upon the addition of AgNO₃ to a cellulose/BmimCl solution, and underwent further reaction with excess Cl^?, leading to the complete dissolution of AgCl. The AgCl crystals were regenerated on the cellulose matrix during the coagulation process. The AgCl was partial decomposed to Ag⁰ and formed Ag@AgCl under visible light irradiation. The morphology of Ag@AgCl in the cellulose matrix was controlled by varying the concentration of PVP. The addition of PVP enabled the formation of stable cellulose films embedded with Ag@AgCl. The composite film demonstrated efficient photodegradation of methyl orange, which was retained upon recycling. This work thus provides a simple pathway for the preparation of Ag@AgCl embedded on a polymer support via one-step coagulation.     

Chiral ligand derived from (1S,2R)-norephedrine as a catalyst for enantioselective prochiral ketone reduction

Chiral oxazaborolidines derived from (1S,2R)-(+)-norephedrine and substituted salicylaldehydes were employed in the asymmetric reduction of prochiral ketones using borane dimethyl sulfide as a reducing agent. The secondary alcohols were formed in excellent yields (45–99.8%) with enantioselectivities up to 99.8%. The effect of the substitution in the aromatic ring of the ligand was discussed with the enantioselectivity of the product.     

Cross-linked poly (4-vinylpyridine) supported azide ion as a versatile and recyclable polymeric reagent for synthesis of 1-substituted-1H-1,2,3,4-tetrazoles

Cross-linked poly (4-vinylpyridine) supported azide ion, [P₄-VP]N₃, is easily prepared and used as an efficient polymeric reagent for synthesis of 1-substituted-1H-1,2,3,4-tetrazoles via condensation reaction of azide ion, primary aromatic amines, and triethyl orthoformate in glacial acetic acid. After optimization of the reaction conditions, a wide variety of primary aromatic amines were also subjected to preparation of the corresponding 1-aryl-1 H-1,2,3,4- tetrazoles using [P₄-VP]N₃ under heterogeneous conditions. In this method, the reaction times were very short and the isolated yields were excellent (90–98 %). 1-Aryl-1H-1,2,3,4- tetrazole products were characterized by Fourier transform infrared (FT-IR) and some of them were also characterized by proton nuclear magnetic resonance (¹H NMR) spectroscopy, and physical properties were compared with the literature values of known compounds. The spent polymeric reagent were regenerated quantitatively and reused for several cycles without significant loss of their activity.     

Organocatalytic enantioselective (3+2) cycloaddition using stable azomethine ylides

We have developed a highly efficient procedure for carrying out the catalytic enantioselective (3+2) cycloaddition between enals and stable azomethine ylides such as isoquinolinium and phthalizinium methylides. Under the optimized reaction conditions highly substituted chiral pyrroloisoquinolines and pyrrolophthalazines have been obtained in high yields and excellent diastereo- and enantioselectivities.     

First enantioselective total synthesis of (8S,12R,15S)-prostaglandin J(2)

Enantioselective synthesis of natural PGJ(2) has been accomplished for the first time starting from the commercially available enantiopure aldehyde 7 in 10% overall yield. The key reaction was a novel prostaglandin class interconversion, i.e., an allylic 1,3-transposition across alcohol 9 derived from compound 14 in 73% overall yield. In principle, the unnatural enantiomer of PGJ(2) could be obtained starting from the commercially available enantiopure monobenzoate 7a following our strategy.