Heterogeneous Chemoenzymatic Catalyst Combinations for One-Pot Dynamic Kinetic Resolution Applications

Strategies to Design Chemocatalytic Racemization of Tertiary Alcohols: State of the Art & Utilization for Dynamic Kinetic Resolution

The synthesis of enantiomerically pure tertiary alcohols is an important issue in organic synthesis of a range of pharmaceuticals including molecules such as the anti-HIV drug Efavirenz. A conceptually elegant approach to such enantiomers is the dynamic kinetic resolution of racemic tertiary alcohols, which, however, requires efficient racemization strategies. The racemization of tertiary alcohols is particularly challenging due to various side reactions that can occur because of their high tendency for elimination reactions. In the last few years, several complementary catalytic concepts for racemization of tertiary alcohols have been developed, characterized by efficient racemization and suppression of unwanted side-reactions. Besides resins bearing sulfonic acid moieties and a combination of boronic acid and oxalic acid as heterogeneous and homogeneous Brønsted-acids, respectively, immobilized oxovanadium and piperidine turned out to be useful catalysts. The latter two catalysts, which have already been applied to different types of substrates, also have proven good compatibility with lipase, thus leading to the first two examples of chemoenzymatic dynamic kinetic resolution of tertiary alcohols. In this review, the difficulties in racemizing tertiary alcohols are specifically described, and the recently developed complementary concepts to overcome these hurdles are summarized.

Biocatalysis: landmark discoveries and applications in chemical synthesis

Biocatalysis has become an important tool in chemical synthesis, allowing access to complex molecules with high levels of activity and selectivity and with low environmental impact. Key discoveries in protein engineering, bioinformatics, recombinant technology and DNA sequencing have contributed towards the rapid acceleration of the field. This tutorial review explores enzyme engineering strategies and high-throughput screening approaches that have been applied for the discovery and development of enzymes for synthetic application. Landmark developments in the field are discussed and have been carefully selected to highlight the diverse synthetic applications of enzymes within the pharmaceutical, agricultural, food and chemical industries. The design and development of artificial biocatalytic cascades is also examined. This tutorial review will give readers an insight into the landmark discoveries and milestones that have helped shape and grow this branch of catalysis since the discovery of the first enzyme.

Expanding the Synthetic Toolbox through Metal-Enzyme Cascade Reactions

The combination of metal-, photo-, enzyme-, and/or organocatalysis provides multiple synthetic solutions, especially when the creation of chiral centers is involved. Historically, enzymes and transition metal species have been exploited simultaneously through dynamic kinetic resolutions of racemates. However, more recently, linear cascades have appeared as elegant solutions for the preparation of valuable organic molecules combining multiple bioprocesses and metal-catalyzed transformations. Many advantages are derived from this symbiosis, although there are still bottlenecks to be addressed including the successful coexistence of both catalyst types, the need for compatible reaction media and mild conditions, or the minimization of cross-reactivities. Therefore, solutions are here also provided by means of catalyst coimmobilization, compartmentalization strategies, flow chemistry, etc. A comprehensive review is presented focusing on the period 2015 to early 2022, which has been divided into two main sections that comprise first the use of metals and enzymes as independent catalysts but working in an orchestral or sequential manner, and later their application as bionanohybrid materials through their coimmobilization in adequate supports. Each part has been classified into different subheadings, the first part based on the reaction catalyzed by the metal catalyst, while the development of nonasymmetric or stereoselective processes was considered for the bionanohybrid section.

Current Progress in the Chemoenzymatic Synthesis of Natural Products

Natural products, with their array of structural complexity, diversity, and biological activity, have inspired generations of chemists and driven the advancement of techniques in their total syntheses. The field of natural product synthesis continuously evolves through the development of methodologies to improve stereoselectivity, yield, scalability, substrate scope, late-stage functionalization, and/or enable novel reactions. One of the more interesting and unique techniques to emerge in the last thirty years is the use of chemoenzymatic reactions in the synthesis of natural products. This review highlights some of the recent examples and progress in the chemoenzymatic synthesis of natural products from 2019–2022.

Progress on the Stereoselective Synthesis of Chiral Molecules Based on Metal-Catalyzed Dynamic Kinetic Resolution of Alcohols with Lipases

Metal/lipase-combo catalyzed dynamic kinetic resolution (DKR) of racemic chiral alcohols is a general and practical process to obtain the corresponding enantiopure esters R with quantitative conversion. The use of known Ru-catalysts as well as newly developed homogeneous and heterogeneous metal catalysts (Fe, V) contributed to make the DKR process more sustainable and to expand the substrate scope of the reaction. In addition to classical substrates, challenging allylic alcohols, tertiary alcohols, C1-and C2-symmetric biaryl diols turned out to be competent substrates. Synthetic utility further emerged from the integration of this methodology into cascade reactions leading to linear/cyclic chiral molecules with high ee through the formation of multiple bonds, in a one-pot procedure.

The various levels of integration of chemo- and bio-catalysis towards hybrid catalysis

Hybrid catalysis is an emerging concept that combines chemo- and biocatalysts in a wide variety of approaches. Combining the specifications and advantages of multiple disciplines, it is a very promising way to diversify tomorrow's catalysis.

Synthesis of enantiomerically pure alcohols and amines via biocatalytic deracemisation methods

Deracemisation via chemo-enzymatic or multi-enzymatic approaches is the optimum substitute for kinetic resolution, which suffers from the limitation of a theoretical maximum 50% yield albeit high enantiomeric excess is attainable. This review covers the recent progress in various deracemisation approaches applied to the synthesis of enantiomerically pure alcohols and amines, such as (1) dynamic kinetic resolution, (2) cyclic deracemisation, (3) linear deracemisation (including stereoinversion) and (4) enantioconvergent methods.

Mild dynamic kinetic resolution of amines by coupled visible-light photoredox and enzyme catalysis

Herein, we described photoenzymatic dynamic kinetic resolution (DKR) of amines under mild conditions. The racemization of amines via a photoredox-mediated hydrogen atom transfer (HAT) protocol in conjunction with an enzyme catalyst to achieve the DKR of amines allows a variety of primary amines to be converted into a single enantiomer in high yield and with excellent enantioselectivity. Notably, this protocol can also be extended to 1,4-diamine derivatives with high levels of diastereo- and enantioselectivity.

Asymmetric one-pot reactions using heterogeneous chemical catalysis: recent steps towards sustainable processes

Asymmetric one-pot reactions applying heterogeneous chemical catalysts and unifying the benefits of these catalytic materials with the advantages of one-pot methods, are surveyed.

From sequential chemoenzymatic synthesis to integrated hybrid catalysis: taking the best of both worlds to open up the scope of possibilities for a sustainable future

Here an overview of all pathways that integrate chemical and biological catalysis is presented. We emphasize the factors to be considered in order to understand catalytic synergy.

Asymmetric Chemoenzymatic Reductive Acylation of Ketones by a Combined Iron-Catalyzed Hydrogenation-Racemization and Enzymatic Resolution Cascade

A general and practical process for the conversion of prochiral ketones into the corresponding chiral acetates has been realized. An iron carbonyl complex is reported to catalyze the hydrogenation-dehydrogenation-hydrogenation of prochiral ketones. By merging the iron-catalyzed redox reactions with enantioselective enzymatic acylations a wide range of benzylic, aliphatic and (hetero)aromatic ketones, as well as diketones, were reductively acylated. The corresponding products were isolated with high yields and enantioselectivities. The use of an iron catalyst together with molecular hydrogen as the hydrogen donor and readily available ethyl acetate as acyl donor make this cascade process highly interesting in terms of both economic value and environmental credentials.

Dynamic kinetic resolution of aromatic sec-alcohols by using a heterogeneous palladium racemization catalyst and lipase

A novel recyclable chemoenzymatic catalyst combination has been designed, which successfully converted sec-alcohols to chiral acetates under microwave irradiation.

4-Dimethylaminopyridine-catalyzed dynamic kinetic resolution in asymmetric synthesis of P-chirogenic 1,3,2-oxazaphospholidine-2-oxides

Excellent diastereoselectivity was achieved in DMAP-catalyzed P–N bonding in the synthesis of P-chirogenic organophosphines through dynamic kinetic resolution.

Spatial effects of oxovanadium-immobilized mesoporous silica on racemization of alcohols and application in lipase-catalyzed dynamic kinetic resolution

The nano-scale pores of mesoporous silica and their polar environment accelerate the racemization to make the lipase/oxovanadium combo-catalysed DKR applicable to a wider range of alcohols.