Net per client costs to the health service were modest. Quantitative evidence of improved antenatal outcomes was limited, but qualitative evaluation suggested the service was strongly valued. The outcomes examined in this study were broader than those used in conventional forms of economic evaluation and this enabled identification and analysis of more diverse sources of value from this programme.

Although chemical and enzymatic catalysts have been combined, reactions in which an organometallic catalyst and a metalloenzyme work cooperatively to create products, which cannot be generated with either catalyst alone or in comparable yields by sequential reactions of the two catalysts, have not been reported. Such reactions are challenging to achieve, in part because the milieu in which these catalysts operate are typically different. Herein, two classes of catalysts are demonstrated to react cooperatively in the same system. Combination of a metathesis catalyst and a P450 enzyme lead to a dynamic equilibration of alkenes and a selective epoxidation of the cross-metathesis products. These results show the potential of combining the two classes of catalysts for synthetic transformations.

ConspectusThe development of catalytic enantioselective transformations has been the focus of many research groups over the past half century and is of paramount importance to the pharmaceutical and agrochemical industries. Since the award of the Nobel Prize in 2001, the field of enantioselective transition metal catalysis has soared to new heights, with the development of more efficient catalysts and new catalytic transformations at increasing frequency. Furthermore, catalytic reactions that allow higher levels of redox- and step-economy are being developed. Thus, alternatives to asymmetric alkene dihydroxylation and the enantioselective reduction of α,β-unsaturated ketones can invoke more strategic C–C bond forming reactions, such as asymmetric aldol reactions of an aldehyde with α-hydroxyketone donors or enantioselective alkynylation of an aldehyde, respectively. To facilitate catalytic enantioselective addition reactions, including the aforementioned aldol and alkynylation reactions, our lab has developed the ProPhenol ligand.In this Account, we describe the development and application of the ProPhenol ligand for asymmetric additions of both carbon- and heteroatom-based nucleophiles to various electrophiles. The ProPhenol ligand spontaneously forms chiral dinuclear metal complexes when treated with an alkyl metal reagent, such as Et2Zn or Bu2Mg. The resulting complex contains both a Lewis acidic site to activate an electrophile and a Brønsted basic site to deprotonate a pronucleophile. Initially, our research focused on the use of Zn-ProPhenol complexes to facilitate the direct aldol reaction. Fine tuning of the reaction through ligand modification and the use of additives enabled the direct aldol reaction to proceed in high yields and stereoselectivities with a broad range of donor substrates, including acetophenones, methyl ynones, methyl vinyl ketone, acetone, α-hydroxy carbonyl compounds, and glycine Schiff bases. Additionally, an analogous magnesium ProPhenol complex was used to facilitate enantioselective diazoacetate aldol reactions with aryl, α,β-unsaturated, and aliphatic aldehydes.The utility of bimetallic ProPhenol catalysts was extended to asymmetric additions with a wide range of substrate combinations. Effective pronucleophiles include oxazolones, 2-furanone, nitroalkanes, pyrroles, 3-hydroxyoxindoles, alkynes, meso-1,3-diols, and dialkyl phosphine oxides. These substrates were found to be effective with a number of electrophiles, including aldehydes, imines, nitroalkenes, acyl silanes, vinyl benzoates, and α,β-unsaturated carbonyls. A truly diverse range of enantioenriched compounds have been prepared using the ProPhenol ligand, and the commercial availability of both ligand enantiomers makes it ideally suited for the synthesis of complex molecules. To date, enantioselective ProPhenol-catalyzed reactions have been used in the synthesis of more than 20 natural products.

We report the development of a tandem chemoenzymatic transformation that combines alkene metathesis with enzymatic epoxidation to provide aryl epoxides. The development of this one-pot reaction required substantial protein and reaction engineering to improve both selectivity and catalytic activity. Ultimately, this reaction converts a mixture of alkenes into a single epoxide product in high enantioselectivity and moderate yields and illustrates both the challenges and benefits of tandem catalysis combining organometallic and enzymatic systems.

We report the development of a modular, one-pot, sequential chemoenzymatic system for the formal enantioselective construction of the C–C bond in 2-aryl 1,4-dicarbonyl compounds. This sequence comprises a rhodium-catalyzed diazocoupling that provides >9:1 selectivity for heterocoupling of two diazoesters and a reduction mediated by an ene-reductase (ER), which occurs in up to 99% enantiomeric excess (ee). The high yield and enantioselectivity of this system result from the preferential generation of an (E)-alkene from the diazo coupling reaction and selective reduction of the (E)-alkene in a mixture of (E) and (Z) isomers by the ER. Screening of a panel of ERs revealed that OPR1 from Lycopersicum esculentum catalyzes the reduction of bulky tert-butyl or benzyl esters to afford chiral diesters that are poised for orthogonal reactions at the two distinct ester units of the product. Overall, this work demonstrates the benefit of combining organometallic and enzymatic catalysis to create unusual overall transformations that do not require the isolation and purification of intermediates.