The dTDP-glucose 4,6-dehydratase catalyzed conversion of dTDP-glucose to dTDP-4-keto-6-deoxyglucose occurs in three sequential chemical steps: dehydrogenation, dehydration, and rereduction. The enzyme contains the tightly bound coenzyme NAD(+), which mediates the dehydrogenation and rereduction steps of the reaction mechanism. In this study, we have determined that Asp135 and Glu136 are the acid and base catalysts, respectively, of the dehydration step. Identification of the acid catalyst was performed using an alternative substrate, dTDP-6-fluoro-6-deoxyglucose (dTDP-6FGlc), which undergoes fluoride ion elimination instead of dehydration, and thus does not require protonation of the leaving group. The steady-state rate of conversion of dTDP-6FGlc to dTDP-4-keto-6-deoxyglucose by each Asp135 variant was identical to that of wt, in contrast to turnover using dTDP-glucose where differences in rates of up to 2 orders of magnitude were observed. These results demonstrate Asp135's role in protonating the glucosyl-C6(OH) during dehydration. The base catalyst was identified using a previously uncharacterized, enzyme-catalyzed glucosyl-C5 hydrogen-solvent exchange reaction of product, dTDP-4-keto-6-deoxyglucose. Base catalysis of this exchange reaction is analogous to that occurring at C5 during the dehydration step of net catalysis. Thus, the decrease in the rate of catalysis ( approximately 2 orders of magnitude) of the exchange reaction observed with Glu136 variants demonstrates this residue's importance in base catalysis of dehydration.
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http://dx.doi.org/10.1021/bi011138c | DOI Listing |
J Org Chem
January 2025
Department of Chemistry and Chemical Engineering, Shandong Provincial Key Laboratory of Chemical Energy Storage and Novel Cell Technology, Liaocheng University, Liaocheng 252059, China.
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January 2025
Department of Materials Science and Engineering, and Center for Functional Photonics (CFP), City University of Hong Kong, Hong Kong SAR, 999077, P. R. China.
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Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, Valladolid, Spain.
This article reports a theoretical study on the halogen exchange reactions YX + CHO → Y + XCHO (with Y = F, Cl, Br; X = Cl, Br, I) carried out at a high level of accuracy using coupled-cluster based methodologies including CCSD(T)-F12, CCSD(T)/CBS and CCSDT(Q). Most of the reactions are exothermic at room temperature, with the exception of the reactions FI + CHO → F + ICHO and ClI + CHO → Cl + ICHO. Exothermicity follows two concurrent trends established by the strength of the bonds being cleaved and formed: Y = F < Cl < Br (X-Y bond strength) and X = Cl > Br > I (C-X bond strength).
View Article and Find Full Text PDFOrg Lett
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Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, Wisconsin 53706, United States.
Although alkyl alcohols and aryl chlorides are the two most abundant substrate pools for cross-electrophile coupling, methods to couple them remain limited. Herein we demonstrate a simple procedure for the in situ deoxychlorination of alcohols followed by XEC with aryl chlorides. A broad substrate scope can be achieved by tuning the rate of the reaction via halide exchange.
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January 2025
Yunnan Key Laboratory of Modern Separation Analysis and Substance Transformation, College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650500, China.
We successfully synthesize monodisperse sulfhydryl-modified mesoporous organosilica nanospheres (MONs-SH) via one-step hydrolytic condensation, where cetyltrimethylammonium chloride and dodecyl sulfobetaine are employed as dual-template agents with (3-mercaptopropyl)triethoxysilane and 1,2-bis(triethoxysilyl)ethane as the precursors and concentrated ammonia as the alkaline catalyst. The prepared MONs-SHs deliver a large specific surface area (729.15 m g), excellent monodispersity, and homogeneous particle size.
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