Synthesis, Structure and Reactivity of a Mononuclear N,N,O-Bound Fe(II) α-Keto-Acid Complex

A bulky, tridentate phenolate ligand (ImPh2 NNOtBu ) was used to synthesise the first example of a mononuclear, facial, N,N,O-bound iron(II) benzoylformate complex, [Fe(ImPh2 NNOtBu )(BF)] (2). The X-ray crystal structure of 2 reveals that the iron centre is pentacoordinate (τ=0.5), with a vacant site located cis to the bidentate BF ligand. The Mössbauer parameters of 2 are consistent with high-spin iron(II), and are very close to those reported for α-ketoglutarate-bound non-heme iron enzyme active sites. According to NMR and UV-vis spectroscopies, the structural integrity of 2 is retained in both coordinating and non-coordinating solvents. Cyclic voltammetry studies show that the iron centre has a very low oxidation potential and is more prone to electrochemical oxidation than the redox-active phenolate ligand. Complex 2 reacts with NO to form a S=3 /2 {FeNO}7 adduct in which NO binds directly to the iron centre, according to EPR, UV-vis, IR spectroscopies and DFT analysis. Upon O2 exposure, 2 undergoes oxidative decarboxylation to form a diiron(III) benzoate complex, [Fe2 (ImPh2 NNOtBu )2 (μ2 -OBz)(μ2 -OH)2 ]+ (3). A small amount of hydroxylated ligand was also observed by ESI-MS, hinting at the formation of a high-valent iron(IV)-oxo intermediate. Initial reactivity studies show that 2 is capable of oxygen atom transfer reactivity with O2 , converting methyl(p-tolyl)sulfide to sulfoxide.

Biosynthesis of β-lactam nuclei in yeast

We have engineered brewer's yeast as a general platform for de novo synthesis of diverse β-lactam nuclei starting from simple sugars, thereby enabling ready access to a number of structurally different antibiotics of significant pharmaceutical importance. The biosynthesis of β-lactam nuclei has received much attention in recent years, while rational engineering of non-native antibiotics-producing microbes to produce β-lactam nuclei remains challenging. Benefited by the integration of heterologous biosynthetic pathways and rationally designed enzymes that catalyze hydrolysis and ring expansion reactions, we succeeded in constructing synthetic yeast cell factories which produce antibiotic cephalosporin C (CPC, 170.1 ± 4.9 μg/g DCW) and the downstream β-lactam nuclei, including 6-amino penicillanic acid (6-APA, 5.3 ± 0.2 mg/g DCW), 7-amino cephalosporanic acid (7-ACA, 6.2 ± 1.1 μg/g DCW) as well as 7-amino desacetoxy cephalosporanic acid (7-ADCA, 1.7 ± 0.1 mg/g DCW). This work established a Saccharomyces cerevisiae platform capable of synthesizing multiple β-lactam nuclei by combining natural and artificial enzymes, which serves as a metabolic tool to produce valuable β-lactam intermediates and new antibiotics.

Multipoint TvDAAO Mutants for Cephalosporin C Bioconversion

d-amino acid oxidase (DAAO, EC 1.4.3.3) is used in many biotechnological processes. The main industrial application of DAAO is biocatalytic production of 7-aminocephalosporanic acid from cephalosporin C with a two enzymes system. DAAO from the yeast Trigonopsis variabilis (TvDAAO) shows the best catalytic parameters with cephalosporin C among all known DAAOs. We prepared and characterized multipoint TvDAAO mutants to improve their activity towards cephalosporin C and increase stability. All TvDAAO mutants showed better properties in comparison with the wild-type enzyme. The best mutant was TvDAAO with amino acid changes E32R/F33D/F54S/C108F/M156L/C298N. Compared to wild-type TvDAAO, the mutant enzyme exhibits a 4 times higher catalytic constant for cephalosporin C oxidation and 8- and 20-fold better stability against hydrogen peroxide inactivation and thermal denaturation, respectively. This makes this mutant promising for use in biotechnology. The paper also presents the comparison of TvDAAO catalytic properties with cephalosporin C reported by others.