Themed collection Collection Honouring Roger Sheldon

Editorial on resource efficiency and waste minimisation – concepts at the heart of green chemistry.

Roger Sheldon ‘father’ of the concept of E-factors—for assessing the environmental footprint of chemical processes—explains why ‘green chemistry’ and sustainability of resources is essential for our future.

The solution to plastic pollution is not less chemistry but more, greener chemistry in a circular bio-based economy.

Enzymes are excellent catalysts that are increasingly being used in industry and academia. This Perspective provides a general and practical guide to enzymes and their synthetic potential, primarily aimed at synthetic organic chemists.

The global impact of green chemistry and sustainability and the pivotal role of the E factor concept, over the last twenty five years, is reviewed.

This perspective reviews the effect that the E Factor concept has had over the last fifteen years on developments in the (fine) chemical industry and pharmaceutical industry with regard to waste minimisation and to assess its current status in the broader context of green chemistry and sustainability.

This review summarises the use of engineered ketoreductases (KREDS), both as whole microbial cells and isolated enzymes, in the highly enantiospecific reduction of prochiral ketones.

Biocatalysts have been supercharged through genetic and chemical modifications, expanding their capabilities.

The role of catalysis (homogeneous, heterogeneous, organocatalysis and biocatalysis), alternative reaction media and renewable raw materials in the development of green and sustainable processes and products is reviewed.

This review focuses on recent advances in the use of elegant bio-orthogonal chemistry in conjunction with rec-DNA to affect highly precise, cost-effective immobilisation of enzymes directly from cell lysate.

This tutorial review focuses on recent advances in technologies for enzyme immobilisation, enabling their cost-effective use in the bio-based economy and continuous processing in general.

In this tutorial review we describe a holistic approach to the invention, development and optimisation of biotransformations utilising isolated enzymes.

This tutorial review explains why enzyme immobilisation is important from a practical viewpoint, what it is and how it is achieved.

The fundamental principles underlying the concepts of green chemistry and sustainability are elucidated and illustrated with examples of chemo- and biocatalytic processes for the oxidation of alcohols and the enantioselective reduction of ketones.

Recent advances and strategies for the green and sustainable valorization of waste biomass to commodity chemicals are critically reviewed.

The use of alternative reaction media—water, fluorous solvents, supercritical carbon dioxide and ionic liquids—which circumvent problems associated with conventional organic solvents, and facilitate the recovery of catalysts, is critically reviewed.

Effective acylation of 1-phenyl ethanol catalysed by Candida antarctica lipase B in protic ionic liquids (PILs).

Rhodium-MonoPhos was successfully immobilised by ionic interactions on aluminosilicate AlTUD-1. The resulting new heterogeneous catalyst can be used in water and showed excellent enantioselectivity and activity in the asymmetric hydrogenation of methyl-2-acetamidoacrylate.

[CuBr₂(2,2′-bipyridine)] catalyses the selective and mild aerobic oxidation of primary alcohols to aldehydes in acetonitrile : water (2 : 1) in the presence of 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) and potassium tert-butoxide as cocatalysts.

Selective oxidation of (cyclic) ethers using as little as 0.25% ruthenium catalyst together with the theoretical amount of NaOCl (2 equiv.) was achieved through careful pH control during the reaction.

Linear orderly combi-crosslinked enzymes (O-CLEs) were designed and constructed for green cascade catalysis using bio-orthogonal chemistry.

Green and sustainable drug manufacturing goes hand in hand with forward-looking visions seeking to balance the long-term sustainability of business, society, and the environment.

Environmentally acceptable ester solvents, notably isopropyl acetate and methyl acetate, gave results comparable to or better than dichloromethane in the N-oxy radical catalysed bleach oxidation of alcohols.

Lipase-dissolving, hydrogen-bond-donating ionic liquids show promise as process solvents for epoxidations and Baeyer–Villiger oxidations. Their coordinating character promotes the electrophilic oxygen transfer by peracids.

A novel and green three-enzyme process for the highly enantioselective synthesis of a key intermediate for the cholesterol lowering agent, atorvastatin, is reported. The overall process has an E factor of 5.8 or 18 if water is included.

The first successful attempt to immobilize cell-free nitrile hydratase is described. Nitrile hydratase cross-linked enzyme aggregates (CLEAs^®) are easy to separate and recover from the reaction medium and have a higher operational and storage stability than cell-free and whole cell nitrile hydratase.

A green, fully enzymatic kinetic resolution of chiral amines has been demonstrated. The methodology obviates the common, waste-generating deacylation under strongly alkaline conditions.

In this research, we have combined reaction in an ionic liquid phase with simultaneous separation of the product from the immobilized catalyst + ionic liquid phase, without loss of catalyst reactivity. The role of CO₂ as potential reaction enhancer was also studied.

Aggregation of Candida antarctica Lipase B (CALB) in water, DMSO and three ionic liquids, [C₂mim]X ([C₂mim] = 1-ethyl-3-methylimidazolium; X = [N(CN)₂]⁻, [NO₃]⁻ or [EtOSO₃]⁻) was studied by dynamic light scattering and small angle neutron scattering: CALB formed micellar aggregates in DMSO and all three ionic liquids, correlated with loss of enzymatic activity.

Metal-catalysed hydrogenation combined with enzymatic resolution (Candida antarctica lipase B in the form of Novozym 435 and CLEA) in supercritical carbon dioxide is reported. Reactions are performed in series in a continuous flow reactor with potential economic advantage since re-pressurization of solvent is avoided.

Pure products can be recovered either by extraction with carbon dioxide as a co-solvent, or by precipitation using carbon dioxide as an anti-solvent.

Candida antarctica lipase B maintained transesterification activity upon dissolution in the ionic liquid [Et₃MeN][MeSO₄], but not in other ionic liquids that dissolved CaLB, such as [BMIm][[dca]. Cross-linked enzyme aggregates of CaLB, in contrast, remained active in this latter ionic liquid.

The use of carbohydrates as renewable feedstocks is greatly hampered by their low solubility in any solvent but water. Ionic liquids that contain the dicyanamide ion (dca) dissolve approx. 200 g L⁻¹ of glucose, sucrose and cyclodextrin. Candida antarctica lipase B mediated the esterification of sucrose with dodecanoic acid in [BMIm][dca].

Candida antarctica lipase B maintained transesterification activity upon dissolution in the ionic liquid [Et₃MeN][MeSO₄]. Native structural elements were maintained, representing the first step towards the use of dissolved, rather than dispersed, enzymes in ionic liquid medium.

Analogous to galactose oxidase and mimics thereof, the oxidation of alcohols mediated by CuCl and TEMPO involves copper(II) mediated dehydrogenation.

This review describes the recent developments of enzymatic catalysis in ionic liquids, reporting the use of different biocatalysts in organic synthesis. Several ionic liquids appear as an alternative to conventional organic solvents, providing comparable or higher rates and, in some cases, improved enantioselectivity.

Improved selenium catalysed epoxidation with aqueous hydrogen peroxide.