Single mutations of ketoreductase ChKRED20 enhance the bioreductive production of (1S)-2-chloro-1-(3, 4-difluorophenyl) ethanol.

(1S)-2-chloro-1-(3, 4-difluorophenyl) ethanol ((S)-CFPL) is an intermediate for the drug ticagrelor, and is manufactured via chemical approaches. To develop a biocatalytic solution to (S)-CFPL, an inventory of ketoreductases from Chryseobacterium sp. CA49 were rescreened, and ChKRED20 was found to catalyze the reduction of the ketone precursor with excellent stereoselectivity (>99 % ee). After screening an error-prone PCR library of the wild-type ChKRED20, two mutants, each bearing a single amino acid substitution of H145L or L205M, were identified with significantly increased activity. Then, the two critical positions were each randomized by constructing saturation mutagenesis libraries, which delivered several mutants with further enhanced activity. Among them, the mutant L205A was the best performer with a specific activity of 178 µmol/min/mg, ten times of that of the wild-type. Its k cat/K m increased by 15 times and half-life at 50 °C increased by 70 %. The mutant catalyzed the complete conversion of 150 and 200 g/l substrate within 6 and 20 h, respectively, to yield enantiopure (S)-CFPL with an isolated yield of 95 %.

Crystal structure and iterative saturation mutagenesis of ChKRED20 for expanded catalytic scope.

ChKRED20 is an efficient and robust anti-Prelog ketoreductase that can catalyze the reduction of ketones to chiral alcohols as pharmaceutical intermediates with great industrial potential. To overcome its limitation on the bioreduction of ortho-substituted acetophenone derivatives, the X-ray crystal structure of the apo-enzyme of ChKRED20 was determined at a resolution of 1.85 Å and applied to the molecular modeling and reshaping of the catalytic cavity via three rounds of iterative saturation mutagenesis together with alanine scanning and recombination. The mutant Mut3B was achieved with expanded catalytic scope that covered all the nine substrates tested as compared with two substrates for the wild type. It exhibited 13-20-fold elevated k cat/K m values relative to the wild type or to the first gain-of-activity mutant, while retaining excellent stereoselectivity toward seven of the substrates (98-> 99% ee). Another mutant 29G10 displayed complementary selectivity for eight of the ortho-substituted acetophenone derivatives, with six of them delivering excellent stereoselectivity (90-99% ee). Its k cat/K m value toward 1-(2-fluorophenyl)ethanone was 5.6-fold of the wild type. The application of Mut3B in elevated substrate concentrations of 50-100 g/l was demonstrated in 50-ml reactions, achieving 75-> 99% conversion and > 99% ee.

Rapid asymmetric reduction of ethyl 4-chloro-3-oxobutanoate using a thermostabilized mutant of ketoreductase ChKRED20.

Ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE) is an important chiral intermediate for the synthesis of "blockbuster" drug statins. The carbonyl reductase ChKRED20 from Chryseobacterium sp. CA49 was found to catalyze the bio-reductive production of (S)-CHBE with excellent stereoselectivity (>99.5 % ee). Perceiving a capacity for improvement, we sought to increase the thermostability of ChKRED20 to allow a higher reaction temperature. After one round of error-prone PCR (epPCR) library screening followed by the combination of beneficial mutations, a triple-mutant MC135 was successfully achieved with substantially enhanced thermostablity. The activity of MC135 at 50 °C was similar to the wild type. However, at its temperature optima of 65 °C, the mutant displayed 63 % increase of activity compared to the wild type and remained >95 % activity after being incubated for 15 days, while the wild type had a half-life of 11.9 min at 65 °C. At a substrate/catalyst ratio of 100 (w/w), the mutant catalyzed the complete conversion of 300 g/l substrate within 1 h to yield enantiopure (S)-CHBE with an isolated yield of 95 %, corresponding to a space-time yield of 1824 mM/h.

Effect of the Hydrogen Bond on Photochemical Synthesis of Silver Nanoparticles.

The effect of a hydrogen bond on the photochemical synthesis of silver nanoparticles has been investigated via experimental and theoretical methods. In a benzophenone system, the photochemical synthesis process includes two steps, which are that hydrogen abstraction reaction and the following reduction reaction. We found that for the first step, an intermolecular hydrogen bond enhances the proton transfer. The efficiency of hydrogen abstraction increases with the hydrogen bond strength. For the second step, the hydrogen-bonded ketyl radical complex shows higher reducibility than the ketyl radical. The inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurement exhibits a 2.49 times higher yield of silver nanoparticles in the hydrogen bond ketyl radical complex system than that for the ketyl radical system. Theoretical calculations show that the hydrogen bond accelerates electron transfer from the ketyl radical to the silver ion by raising the SOMO energy of the ketyl radical; thus, the SOMO-LUMO interaction is more favorable.

Improving near-infrared luminescence in Er3+ doped CsPbBr3 quantum dots glasses through a certain energy transfer process.

Er3+ has received extensive attention due to its excellent optical properties, especially its emission at 1535 nm in atmospheric propagation window. Enhancement and regulation of 1535 nm emission of Er3+ is of great significance to optical communication. In this work, growing of CsPbBr3 QDs has been controlled through adjusting annealing time which would precisely regulate conduction band of CsPbBr3 QDs to match energy levels of Er3+ enabling energy transfer between Er3+ and CsPbBr3 QDs. By steady-state and transient PL emission and excitation spectroscopy, we reveal multiple energy transfer processes between Er3+ and CsPbBr3 QDs under different excitation wavelengths in Er3+ doped CsPbBr3 QDs glass: under higher energy excitation (∼378 nm), energy transfer from Er3+ to CsPbBr3 QDs and this extra energy within CsPbBr3 QDs decay via a non-radiative pathway; under lower energy excitation (∼524 nm), energy transfer from conduction band of CsPbBr3 QDs to 4S3/2 energy level of Er3+ which significantly enhances PL emission of Er3+ in near infrared region (∼1535 nm, 4I13/2 â†’ 4I15/2). These results provide a facile approach to enhance and regulate PL emission of Er3+ in near infrared region.

High-resolution laser induced excitation spectroscopy and decay dynamics of YNbO4:Er3.

The rare earth materials have attracted intensive attention due to their strong luminescent characteristic. However, the split fine Stark levels are difficult to be determined. Here we report a room-temperature detection for Stark levels of YNbO4: Er3+ using established laser-induced spectroscopy system with dye laser of superhigh resolution of wavelength at 0.005 nm. From excitation spectra, six split Stark levels of 4G11/2 (Er3+) were directly detected. Moreover, nonradiative relaxations of 4G9/2→4G11/2 and 4G11/2→2H11/2/ 4S3/2 have been observed with weighed lifetimes of 0.70 µs and 6.15 µs, and characteristic green emission of Er3+ (@555 nm) yields lifetime of 31.78 µs.

Current Progress and Future Perspectives of Immune Checkpoint Inhibitors in Biliary Tract Cancer.

Biliary tract cancer (BTC) is an uncommon and aggressive neoplasm, with most patients presenting in an advanced stage. Systemic chemotherapy is the limited treatment available but is unsatisfactory, while targeted therapy is still awaiting validation from clinical trials. Given the potential effect of immune checkpoint inhibitors (ICIs) in the treatment of BTC, this review aims to summarize the evidence-based benefits and predictive biomarkers for using inhibitors of cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) ligand, or programmed cell death protein-1 and its ligand (PD-1 and PD-L1) as monotherapy or combined with other anti-tumor therapies, while also pointing out certain pitfalls with the use of ICIs which need to be addressed.

Study on efficacy and safety of Huangqi Guizhi Wuwu decoction treatment for oxaliplatin induced peripheral neurotoxicity: A protocol for a randomized, controlled, double-blind, multicenter trial.

BACKGROUND: Oxaliplatin can cause severe peripheral neurotoxicity, which is an important reason for clinical oxaliplatin reduction and cessation of treatment. Oxaliplatin induced peripheral neurotoxicity (OIPN) can cause paresthesia and dysesthesia, even affect the quality life of patients. So far, there are no recognized and effective measures to prevent OIPN. Huangqi Guizhi Wuwu decoction is a classical prescription of ancient Chinese medicine recorded in "the synopsis of the Golden Chamber," which can be used in the treatment of various neurotoxicity. However, there is a lack of large-scale and high-quality clinical studies on the prevention of OIPN by Huangqi Guizhi Wuwu decoction. The purpose of this study is to evaluate the efficacy and safety of Huangqi Guizhi Wuwu decoction on preventing OIPN. METHODS/DESIGN: This study is a randomized, controlled, double-blind, and multicenter clinical trial. Three hundred sixty patients will be randomly assigned into Huangqi Guizhi Wuwu decoction group and Huangqi Guizhi Wuwu decoction mimetic agent group. Patients will receive chemotherapy with FOLFOX of 8 cycles of 3 weeks with Traditional Chinese Medicine (TCM) for 6 months and 1-year follow-up. The primary outcome measure is the differences in the incidence of chronic neurotoxicity of grade 2 and above during and after treatment. The secondary outcome measure is the improvement in other symptoms associated with chemotherapy. Four methods will be used to evaluate the efficacy of neurotoxicity, including oxaliplatin specific toxicity grading standard (Levi classification); CTCAE4.02 version; EORTC QLQ-CIPN20 scale, EORTC QLQ C30 scale, and EORTC QLQ-CR29 scale are used at the same time; Electromyography. DISCUSSION: This study will provide objective evidences to evaluate the efficacy and safety of Huangqi Guizhi Wuwu Decoction on preventing OIPN. TRIAL REGISTRATION: Clinical Trials.gov (Identifier: NCT04261920).

Structure-guided engineering of ChKRED20 from Chryseobacterium sp. CA49 for asymmetric reduction of aryl ketoesters.

ChKRED20 is a robust NADH-dependent ketoreductase identified from the genome of Chryseobacterium sp. CA49 that can use 2-propanol as the ultimate reducing agent. The wild-type can reduce over 100 g/l ketones for some pharmaceutical relevant substrates, exhibiting a remarkable potential for industrial application. In this work, to overcome the limitation of ChKRED20 to aryl ketoesters, we first refined the X-ray crystal structure of ChKRED20/NAD+ complex at a resolution of 1.6 Å, and then performed three rounds of iterative saturation mutagenesis at critical amino acid sites to reshape the active cavity of the enzyme. For methyl 2-oxo-2-phenylacetate and ethyl 3-oxo-3-phenylpropanoate, several gain-of-activity mutants were achieved, and for ethyl 2-oxo-4-phenylbutanoate, improved mutants were achieved with kcat/Km increasing to 196-fold of the wild-type. All three substrates were completely reduced at 100 g/l loading catalyzed with selected ChKRED20 mutants, and deliver the corresponding chiral alcohols with >90% isolated yield and 97 - >99%ee.