Asymmetric chemoenzymatic synthesis of ramatroban using lipases and oxidoreductases

Diiodine–Triethylsilane System: Formation of N-Alkylsulfonamides from Aldehydes or Ketones and Sulfonamides

Reductive amination has not been commonly used in the preparation of N-alkylsulfonamides because of the low nucleophilicity of sulfonamides. In this work, a protocol for the synthesis of N-alkylsulfonamides from aldehydes or ketones and sulfonamides was developed. Molecular iodine, triethylsilane, and ethyl acetate were used as the initiator, reductant, and solvent, respectively. The key role of triethyl(iodo)silane in the reaction was confirmed through control experiments.

Water Modulated Diastereoselective Synthesis of cis/trans-Spiro[indoline-3,6'-naphtho[2,3-c]carbazoles]

p-TsOH catalyzed Diels-Alder reaction of 2-(1-alkylindol-3-yl)naphthalene-1,4-diones and 3-phenacylideneoxindoles showed fascinating diastereoselectivity. The reaction with the hydrated p-TsOH afforded trans-isomers of dihydrospiro[indoline-3,6'-naphtho[2,3-c]carbazoles] as major products. Alternatively, the reaction with anhydrous p-TsOH under a Dean and Stark apparatus predominately gave cis-isomer of dihydrospiro[indoline-3,6'-naphtho[2,3-c]carbazoles]. On the other hand, the similar p-TsOH catalyzed reaction of 2-(indol-3-yl)naphthalene-1,4-diones with 3-arylideneindolin-2-ones afforded cis/trans-isomers of dihydrospiro[indoline-3,6'-naphtho[2,3-c]carbazoles]. Additionally, the p-TsOH catalyzed reaction of 2-(indol-3-yl)naphthalene-1,4-diones with 2-arylidene-1,3-indanediones gave the expected spiro[indene-2,6'-naphtho[2,3-c]carbazoles] in satisfactory yields.

Rhodococcus as A Versatile Biocatalyst in Organic Synthesis

The application of purified enzymes as well as whole-cell biocatalysts in synthetic organic chemistry is becoming more and more popular, and both academia and industry are keen on finding and developing novel enzymes capable of performing otherwise impossible or challenging reactions. The diverse genus Rhodococcus offers a multitude of promising enzymes, which therefore makes it one of the key bacterial hosts in many areas of research. This review focused on the broad utilization potential of the genus Rhodococcus in organic chemistry, thereby particularly highlighting the specific enzyme classes exploited and the reactions they catalyze. Additionally, close attention was paid to the substrate scope that each enzyme class covers. Overall, a comprehensive overview of the applicability of the genus Rhodococcus is provided, which puts this versatile microorganism in the spotlight of further research.

Catalytic asymmetric synthesis of tetrahydrocarbazoles

This feature article summarises recent advances in catalytic asymmetric synthesis of THCs, with emphases on reaction type and reaction mechanism.

Organocatalytic asymmetric synthesis of tetrahydrocarbazoles via an inverse-electron-demand Diels–Alder reaction of 2,3-indole-dienes with enals

A novel 2,3-indole-diene synthon was designed and first applied to an inverse-electron-demand Diels–Alder reaction to construct tetrahydrocarbazoles with excellent stereoselectivities.

Application of ω-Transaminases in the Pharmaceutical Industry

Chiral amines are valuable building blocks for the pharmaceutical industry. ω-TAms have emerged as an exciting option for their synthesis, offering a potential "green alternative" to overcome the drawbacks associated with conventional chemical methods. In this review, we explore the application of ω-TAms for pharmaceutical production. We discuss the diverse array of reactions available involving ω-TAms and process considerations of their use in both kinetic resolution and asymmetric synthesis. With the aid of specific drug intermediates and APIs, we chart the development of ω-TAms using protein engineering and their contribution to elegant one-pot cascades with other enzymes, including carbonyl reductases (CREDs), hydrolases and monoamine oxidases (MAOs), providing a comprehensive overview of their uses, beginning with initial applications through to the present day.

Selective construction of polycyclic spirooxindoles via a Cu(OTf)2/HOTf-catalyzed domino reaction of o-arylalkynylacetophenones and 3-phenacylideneoxindoles

Under the combined catalysis of Cu(OTf)₂/HOTf, the domino annulation reaction ofo-arylalkynyl acetophenones with 3-phenacylideneoxindoles in refluxing acetonitrile selectively afforded functionalized spiro[indoline-3,7′-tetrapheno[7,6-bc]furans].

Lipase-Catalyzed Kinetic Resolution of Novel Antifungal N-Substituted Benzimidazole Derivatives

A series of new N-substituted benzimidazole derivatives was synthesized and their antifungal activity against Candida albicans was evaluated. The chemical step included synthesis of appropriate ketones containing benzimidazole ring, reduction of ketones to the racemic alcohols, and acetylation of alcohols to the esters. All benzimidazole derivatives were obtained with satisfactory yields and in relatively short times. All synthesized compounds exhibit significant antifungal activity against Candida albicans 900028 ATCC (% cell inhibition at 0.25 μg concentration > 98%). Additionally, racemic mixtures of alcohols were separated by lipase-catalyzed kinetic resolution. In the enzymatic step a transesterification reaction was applied and the influence of a lipase type and solvent on the enantioselectivity of the reaction was studied. The most selective enzymes were Novozyme SP 435 and lipase Amano AK from Pseudomonas fluorescens (E > 100).

Silver(i)-catalysed domino alkyne-annulation/Diels–Alder reaction: a mild synthetic approach to tetrahydrospiro[carbazole-4,3′-indoline] scaffolds

A mild and efficient AgOTf catalyzed alkyne-annulation/Diels–Alder cascade for the construction of tetrahydrospiro[carbazole-4,3′-indoline] derivatives has been established.

The Industrial Age of Biocatalytic Transamination

During the last decade the use of ω-transaminases has been identified as a very powerful method for the preparation of optically pure amines from the corresponding ketones. Their immense potential for the preparation of chiral amines, together with their ease of use in combination with existing biocatalytic methods, have made these biocatalysts a competitor to any chemical methodology for (asymmetric) amination. An increasing number of examples, especially from industry, shows that this biocatalytic technology outmaneuvers existing chemical processes by its simple and flexible nature. In the last few years numerous publications and patents on synthetic routes, mainly to pharmaceuticals, involving ω-transaminases have been published. The review gives an overview of the application of ω-transaminases in organic synthesis with a focus on active pharmaceutical ingredients (APIs) and the developments during the last few years.

Total synthesis of a thromboxane receptor antagonist, terutroban

Synthesis of terutroban (2) is achieved following a non-Diels–Alder approach using cost-effective chemicals.

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

Enantioenriched promethazine and ethopropazine were synthesized through a simple and straightforward four-step chemoenzymatic route. The central chiral building block, 1-(10H-phenothiazin-10-yl)propan-2-ol, was obtained via a lipase-mediated kinetic resolution protocol, which furnished both enantiomeric forms, with superb enantioselectivity (up to E = 844), from the racemate. Novozym 435 and Lipozyme TL IM have been found as ideal biocatalysts for preparation of highly enantioenriched phenothiazolic alcohols (up to >99% ee), which absolute configurations were assigned by Mosher's methodology and unambiguously confirmed by XRD analysis. Thus obtained key-intermediates were further transformed into bromide derivatives by means of PBr3, and subsequently reacted with appropriate amine providing desired pharmacologically valuable (R)- and (S)-stereoisomers of title drugs in an ee range of 84-98%, respectively. The modular amination procedure is based on a solvent-dependent stereodivergent transformation of the bromo derivative, which conducted in toluene gives mainly the product of single inversion, whereas carried out in methanol it provides exclusively the product of net retention. Enantiomeric excess of optically active promethazine and ethopropazine were established by HPLC measurements with chiral columns.

Stereoselective direct reductive amination of ketones with electron-deficient amines using Re2O7/NaPF6 catalyst

The first example of direct reductive amination (DRA) of ketones with electron-deficient amines (EDA) such as Cbz-, Boc-, EtOCO-, Fmoc-, Bz-, ArSO2-, etc. protected amines have been achieved using catalytic Re2O7/NaPF6. Excellent chemoselectivities as well as diastereoselectivity (for 2-alkyl cyclohexanones) were obtained.