The bidentate phosphine ligand 1,2-bis(di-tert-butylphosphinomethyl)-benzene (1,2-DTBPMB) has been reported over the years as being one of, if not the, best ligands for achieving the alkoxycarbonylation of various unsaturated compounds. Bonded to palladium, the ligand provides the basis for the first step in the commercial (Alpha) production of methyl methacrylate as well as very high selectivity to linear esters and acids from terminal or internal double bonds. The present review is an overview covering the literature dealing with the 1,2-DTBPMB ligand: from its first reference, its catalysis, including the alkoxycarbonylation reaction and its mechanism, its isomerization abilities including the highly selective Isomerizing methoxycarbonylation, other reactions such as cross-coupling, recycling approaches, and the development of improved, modified ligands, in which some tert-butyl ligands are replaced by 2-pyridyl moieties and which show exceptional rates for carbonylation reactions at low temperatures.

Bioproduction of polymethyl methacrylate is a fast growing global industry that is limited by cellular toxicity of monomeric methacrylate intermediates to the producer strains. Maintaining high methacrylate concentrations during biofermentation, required by economically viable technologies, challenges bacterial membrane stability and cellular viability. Studying the stability of model lipid membranes in the presence of methacrylates offers unique molecular insights into the mechanisms of methacrylate toxicity, as well as into the fundamental structural bases of membrane assembly. We investigate the structure and stability of model membranes in the presence of high levels of methacrylate esters using solid-state nuclear magnetic resonance (NMR) and small angle X-ray scattering (SAXS). Wideline 31P NMR spectroscopy shows that butyl methacrylate (BMA) can be incorporated into the lipid bilayer at concentrations as high as 75 mol% without significantly disrupting membrane integrity and that lipid acyl chain composition can influence membrane tolerance and ability to accommodate BMA. Using high resolution 13C magic angle spinning (MAS) NMR we show that the presence of 75 mol% BMA lowers the lipid main transition temperature by over 12 degrees, which suggests BMA intercalates between the lipid chains causing uncoupling of collective lipid motions that are typically dominated by chain trans-gauche isomerisation. Potential uncoupling of the bilayer leaflets to accommodate a separate BMA sub-phase was not supported by the SAXS experiments, which showed that membrane thickness remained unchanged even at 80% BMA. Reduced X-ray scattering contrast at the polar/apolar interface suggests BMA localisation in that region between the lipid molecules.

Productivity of bacterial cell factories is frequently compromised by stresses imposed by recombinant protein synthesis and carbon-to-product conversion, but little is known about these bioprocesses at a systems level. Production of the unnatural metabolite citramalate in Escherichia coli requires the expression of a single gene coding for citramalate synthase. Multiomic analyses of a fermentation producing 25 g liter(-1) citramalate were undertaken to uncover the reasons for its productivity. Metabolite, transcript, protein, and lipid profiles of high-cell-density, fed-batch fermentations of E. coli expressing either citramalate synthase or an inactivated enzyme were similar. Both fermentations showed downregulation of flagellar genes and upregulation of chaperones IbpA and IbpB, indicating that these responses were due to recombinant protein synthesis and not citramalate production. Citramalate production did not perturb metabolite pools, except for an increased intracellular pyruvate pool. Gene expression changes in response to citramalate were limited; none of the general stress response regulons were activated. Modeling of transcription factor activities suggested that citramalate invoked a GadW-mediated acid response, and changes in GadY and RprA regulatory small RNA (sRNA) expression supported this. Although changes in membrane lipid composition were observed, none were unique to citramalate production. This systems analysis of the citramalate fermentation shows that E. coli has capacity to readily adjust to the redirection of resources toward recombinant protein and citramalate production, suggesting that it is an excellent chassis choice for manufacturing organic acids. IMPORTANCE Citramalate is an attractive biotechnology target because it is a precursor of methylmethacrylate, which is used to manufacture Perspex and other high-value products. Engineered E. coli strains are able to produce high titers of citramalate, despite having to express a foreign enzyme and tolerate the presence of a nonnative biochemical. A systems analysis of the citramalate fermentation was undertaken to uncover the reasons underpinning its productivity. This showed that E. coli readily adjusts to the redirection of metabolic resources toward recombinant protein and citramalate production and suggests that E. coli is an excellent chassis for manufacturing similar small, polar, foreign molecules.

In the reaction of [RuHClP3] (P = PPh3) with NaOMe in methanol, the product is [RuH2(CO)P3]. Short reaction times show that the final product is formed through [RuH4P3] as the major intermediate. Using NaOCD3 in CD3OD, the first formed product is [RuH4P'3] (P' is PPh3 partially deuterated in the ortho positions of the aromatic rings). Further reaction leads to a mixture of [RuHnD2-n(CO)P3] (n = 0, 22%; n = 1, 2 isomers each 28%; n = 2, 22%). Mechanistic aspects of both steps of the reaction are explored and, together with previously published calculations, they provide definitive mechanisms for both dehydrogenation and decarbonylation in these interesting systems.

Small circular RNAs occur in many cells. Theoretical considerations designed to mimick primordial RNAs designed 25 theoretical, minimal 22-nucleotide long circular RNAs (RNA rings) forming stem-loop hairpins, including one codon per amino acid, a start and a stop codon. These RNA rings resemble consensus tRNAs, whose predicted anticodons assign to each RNA ring a potential cognate amino acid. Assuming dual translator and messenger roles, three consecutive translation rounds produce 21-residue-long peptides, seven codons at each round. In these conditions, steric hindrances between tRNA(-like) translators competing for partially overlapping nucleotide triplets can be reduced if none of the seven codons produces by circular permutation (position 1 → 3, or position 3 → 1) any of the six others. This non-permutability of codon sets is one of the conditions that define potential circular codes regulating translational frame. A near-universal maximal self-complementary circular code exists in reading frames of natural genes, and permutations of this circular code define maximal circular codes in each +1, +2 gene frames. Chronologically scaling RNA rings according to the genetic code inclusion order of their cognate amino acid, codon numbers belonging to the natural frame +1 circular code X1 decrease with cognate amino acid inclusion order, those belonging to the natural frame 0 circular code X0 increase. RNA rings with early cognates apparently reflect pre-(tRNA-like)-adaptor translation by direct codon-amino acid affinity with partially overlapping consecutive codons where X1 regulated translation. Translation of non-overlapping consecutive codons evolved in parallel with RNA rings' cognate inclusion in the genetic code and with X0. Hence the complex “multi-frame” natural circular codes potentially evolved spontaneously from small coding circular RNAs mimicked by theoretical minimal RNA rings. Modern reading frames evolved from earlier reading frames corresponding to modern +1 frames.

Citramalic acid is a central intermediate in a combined biocatalytic and chemocatalytic route to produce bio-based methylmethacrylate, the monomer used to manufacture Perspex and other high performance materials. We developed an engineered E. coli strain and a fed-batch bioprocess to produce citramalate at concentrations in excess of 80 g l −1 in only 65 h. This exceptional efficiency was achieved by designing the production strain and the fermentation system to operate synergistically. Thus, a single gene encoding a mesophilic variant of citramalate synthase from Methanococcus jannaschii, CimA3.7, was expressed in E. coli to convert acetyl-CoA and pyruvate to citramalate, and the ldhA and pflB genes were deleted. By using a bioprocess with a continuous, growth-limiting feed of glucose, these simple interventions diverted substrate flux directly from central metabolism towards formation of citramalate, without problematic accumulation of acetate. Furthermore, the nutritional requirements of the production strain could be satisfied through the use of a mineral salts medium supplemented only with glucose (172 g l −1 in total) and 1.4 g l −1 yeast extract. Using this system, citramalate accumulated to 82±1.5 g l −1 , with a productivity of 1.85 g l −1 h −1 and a conversion efficiency of 0.48 g citramalate g −1 glucose . The new bioprocess forms a practical first step for integrated bio- and chemocatalytic production of methylmethacrylate.

Bio-production of fuels and chemicals from lignocellulosic C5 sugars usually requires the use of the pentose phosphate pathway (PPP) to produce pyruvate. Unfortunately, the oxidation of pyruvate to acetyl-coenzyme A results in the loss of 33 % of the carbon as CO2, to the detriment of sustainability and process economics. To improve atom efficiency, we engineered Escherichia coli to utilize d-xylose constitutively using the Weimberg pathway, to allow direct production of 2-oxoglutarate without CO2 loss. After confirming enzyme expression in vitro, the pathway expression was optimized in vivo using a combinatorial approach, by screening a range of constitutive promoters whilst systematically varying the gene order. A PPP-deficient (ΔxylAB), 2-oxoglutarate auxotroph (Δicd) was used as the host strain, so that growth on d-xylose depended on the expression of the Weimberg pathway, and variants expressing Caulobacter crescentus xylXAB could be selected on minimal agar plates. The strains were isolated and high-throughput measurement of the growth rates on d-xylose was used to identify the fastest growing variant. This strain contained the pL promoter, with C. crescentus xylA at the first position in the synthetic operon, and grew at 42 % of the rate on d-xylose compared to wild-type E. coli using the PPP. Remarkably, the biomass yield was improved by 53.5 % compared with the wild-type upon restoration of icd activity. Therefore, the strain grows efficiently and constitutively on d-xylose, and offers great potential for use as a new host strain to engineer carbon-efficient production of fuels and chemicals via the Weimberg pathway.

A process for the carbonylation of an ethylenically unsatur ated compound comprising the step of reacting said com pound with carbon monoxide in the presence of a co-5 reac tant having a mobile hydrogen atom and a catalyst system is described. The catalyst system is obtainable by combining: (a) a metal of Group 8.9 or 10 or a suitable compound thereof; (b) a ligand of general formula (I): and c) optionally, a source of anions. The invention is characterised in that the catalyst system includes an enhancer compound comprising an aro matic ring or ring system substituted by at least one hydroxyl group wherein the hydroxyl group pKa at 25°C. is greater than 3.0 and less than 9.1, the said enhancer compound excluding 3-quinolinol. Catalyst systems for use with the enhancer compound are described as are a method of increas ing the efficacy of a catalyst system for the carbonylation of ethylenically unsaturated compounds and a method of increasing the rate of carbonylation of an ethylenically unsat urated compound comprising the step of adding Such a com pound to the reaction.

A one-pot system for the conversion of methyl propanoate (MeP) to methyl methacrylate (MMA) has been investigated. In particular, this study is focused on the possibility of performing catalytic dehydrogenation of methanol for the in situ production of anhydrous formaldehyde, which is then consumed in a one-pot base-catalysed condensation with MeP to afford methyl 3-hydroxy-2methylpropanoate, which spontaneously dehydrogenates to MMA, some of which is subsequently hydrogenated to methyl 2methypropanoate (MiBu).

A one‐pot system for the conversion of methyl propanoate (MeP) to methyl methacrylate (MMA) has been investigated. In particular, this study is focused on the possibility of performing catalytic dehydrogenation of methanol for the in situ production of anhydrous formaldehyde, which is then consumed in a one‐pot base‐catalysed condensation with MeP to afford methyl 3‐hydroxy‐2‐methylpropanoate, which spontaneously dehydrogenates to MMA, some of which is subsequently hydrogenated to methyl 2‐methypropanoate (MiBu).

ABSTRACT Mevalonate diphosphate decarboxylase (MVD) is an ATP-dependent enzyme that catalyzes the phosphorylation/decarboxylation of ( R )-mevalonate-5-diphosphate to isopentenyl pyrophosphate in the mevalonate (MVA) pathway. MVD is a key enzyme in engineered metabolic pathways for bioproduction of isobutene, since it catalyzes the conversion of 3-hydroxyisovalerate (3-HIV) to isobutene, an important platform chemical. The putative homologue from Picrophilus torridus has been identified as a highly efficient variant in a number of patents, but its detailed characterization has not been reported. In this study, we have successfully purified and characterized the putative MVD from P. torridus. We discovered that it is not a decarboxylase per se but an ATP-dependent enzyme, mevalonate-3-kinase (M3K), which catalyzes the phosphorylation of MVA to mevalonate-3-phosphate. The enzyme's potential in isobutene formation is due to the conversion of 3-HIV to an unstable 3-phosphate intermediate that undergoes consequent spontaneous decarboxylation to form isobutene. Isobutene production rates were as high as 507 pmol min −1 g cells −1 using Escherichia coli cells expressing the enzyme and 2,880 pmol min −1 mg protein −1 with the purified histidine-tagged enzyme, significantly higher than reported previously. M3K is a key enzyme of the novel MVA pathway discovered very recently in Thermoplasma acidophilum . We suggest that P. torridus metabolizes MVA by the same pathway.

Methyl propanoate is an important precursor for polymethyl methacrylates. The use of a Baeyer-Villiger monooxygenase (BVMO) to produce this compound was investigated. Several BVMOs were identified that produce the chemically non-preferred product methyl propanoate in addition to the normal product ethyl acetate.

Methyl 10-undecenoate from castor oil is aminocarbonylated to α,ω-amidoesters for possible use in polyamide or polyester amide monomer production.

The utilisation of the PNP iridium pincer complex [Ir(PNP)(COE)][BF4] [PNP = 2,6-bis{(di-tert-butylphosphino)methyl}pyridine; COE = cyclooctene] in the sp(3) C-H activation of methyl propanoate and other related esters was explored. In particular, this study provides further insight into the factors that govern the regioselectivity of such reactions. These included factors such as the steric demands of the substrate, the formation of favourable ring systems as well as the electronic effects that may influence the pKa values of protons. In particular, the effects of water on the outcome of these reactions were of great interest, since earlier literature reports have shown the presence of water to promote selective C-H activation in the α-position of ketones.

The coordination chemistry and solution behaviour of Rh(i) and Ru(ii) complexes derived from mixed anhydride ligands of carboxylic acids and phosphorus acids were explored. Similar to the free ligand systems, mixed anhydride complexes rearranged in solution via a number of pathways, with the pathway of choice dependent on the mixed anhydride employed, the auxiliary ligands present as well as the nature of the metal centre. Plausible mechanisms for some of the routes of rearrangement and by-product formation are proposed. Where stability allowed, new complexes were fully characterised, including solid state structures for four of the unrearranged mixed anhydride complexes and two of the interesting rearrangement products.