X-ray wavefunction refinement and comprehensive structural studies on bromo-substituted analogues of 2-deoxy-d-glucose in solid state and solution

The structural studies on two bromo-substituted derivatives of 2-deoxy-d-glucose (2-DG), namely 2-deoxy-2-bromo-d-glucose (2-BG) and 2-deoxy-2-bromo-d-mannose (2-BM) are described. 2-DG itself is an inhibitor of hexokinase, the first enzyme in the glycolysis process, playing a vital role in both cancer cell metabolism and viral replication in host cells. Because of that, 2-DG derivatives are considered as potential anti-cancer and anti-viral drugs. An X-ray quantum crystallography approach allowed us to obtain more accurate positions of hydrogen atoms by applying Hirshfeld atom refinement, providing a better description of hydrogen bonding even in the case of data from routine X-ray experiments. Obtained structures showed that the introduction of bromine at the C2 position in the pyranose ring has a minor influence on its conformation but still, it has a noticeable effect on the crystal structure. Bromine imposes the formation of a layered supramolecular landscape containing hydrogen bonds, which involves the bromine atom. Periodic DFT calculations of cohesive and interaction energies (at the B3LYP level of theory) have supported these findings and highlighted energetic changes upon bromine substitution. Based on molecular wavefunction from the refinement, we calculated the electrostatic potential, Laplacian, and ELI-D, and applied them to charge-density studies, which confirmed the geometry of hydrogen bonding and involvement of the bromine atom with these intermolecular interactions. NMR studies in the solution show that both compounds do not display significant differences in their anomeric equilibria compared to 2-DG, and the pyranose ring puckering is similar in both aqueous and solid state.

Photoredox-catalyzed redox-neutral difluoroalkylation to construct perfluoroketones with difluoroenoxysilanes

A mild and facile approach to construct various perfluoroketones via photo-catalyzed difluoroalkylation of difluoroenoxysilanes is developed. The reaction includes a strategy of combination of two fluorine-containing functional groups, which confers the reaction with characteristics like high efficiency, mild conditions, and broad scope. A variety of fluoroalkyl halides including perfluoroalkyl iodides, bromo difluoro esters and amides can be employed as radical precursors. Control experiments indicate that a single-electron transfer pathway may be involved in the reaction.

Fluorinated carbohydrates as chemical probes for molecular recognition studies. Current status and perspectives

This review provides an extensive summary of the effects of carbohydrate fluorination with regard to changes in physical, chemical and biological properties with respect to regular saccharides. The specific structural, conformational, stability, reactivity and interaction features of fluorinated sugars are described, as well as their applications as probes and in chemical biology.

Synthetic strategies for fluorination of carbohydrates

Different synthetic strategies for accomplishing regio- and stereoselective fluorinations of carbohydrate scaffolds are discussed in light of the biological implications arising from such substitutions.

Stereochemically Defined Various Multisubstituted Alkenes Bearing a Tetrafluoroethylene (-CF2CF2-) Fragment

Highly regio- and stereoselective transformation of commercially available 4-bromo-3,3,4,4-tetrafluoro-1-butene into multisubstituted alkenes having a tetrafluoroethylene fragment through Heck reactions and/or Suzuki-Miyaura cross-coupling reactions was established. Thus, the obtained alkenes underwent a smooth reductive coupling reaction with aldehydes under the influence of MeLi/LiBr-free, affording structurally unprecedented fluorinated materials.

Nucleophilic Tetrafluoroethylation Employing in Situ Formed Organomagnesium Reagents

Tetrafluoroalkyl bromides are metalated with equimolar iPrMgCl·LiCl (Turbo Grignard) to form organomagnesium compounds which are stable at low temperatures and react with various electrophiles (aldehydes, ketones, CO₂, cyclic sulfate and sulfamidate, N-sulfonylimines, nitrone, chlorophosphate, nonaflyl azide) to afford novel functionalized tetrafluoroethylene-containing products. Ease of operation, excellent selectivity, high nucleophilicity, and enhanced stability of the reactive species together with a broad substrate scope comprise a highly attractive nucleophilic tetrafluoroethylation protocol affording unique synthetic building blocks.

The substrate tolerance of alcohol oxidases

Alcohols are a rich source of compounds from renewable sources, but they have to be activated in order to allow the modification of their carbon backbone. The latter can be achieved via oxidation to the corresponding aldehydes or ketones. As an alternative to (thermodynamically disfavoured) nicotinamide-dependent alcohol dehydrogenases, alcohol oxidases make use of molecular oxygen but their application is under-represented in synthetic biotransformations. In this review, the mechanism of copper-containing and flavoprotein alcohol oxidases is discussed in view of their ability to accept electronically activated or non-activated alcohols and their propensity towards over-oxidation of aldehydes yielding carboxylic acids. In order to facilitate the selection of the optimal enzyme for a given biocatalytic application, the substrate tolerance of alcohol oxidases is compiled and discussed: Substrates are classified into groups (non-activated prim- and sec-alcohols; activated allylic, cinnamic and benzylic alcohols; hydroxy acids; sugar alcohols; nucleotide alcohols; sterols) together with suitable alcohol oxidases, their microbial source, relative activities and (stereo)selectivities.

Structural basis of ligand binding to UDP-galactopyranose mutase from Mycobacterium tuberculosis using substrate and tetrafluorinated substrate analogues

UDP-Galactopyranose mutase (UGM) is a flavin-containing enzyme that catalyzes the reversible conversion of UDP-galactopyranose (UDP-Galp) to UDP-galactofuranose (UDP-Galf) and plays a key role in the biosynthesis of the mycobacterial cell wall galactofuran. A soluble, active form of UGM from Mycobacterium tuberculosis (MtUGM) was obtained from a dual His6-MBP-tagged MtUGM construct. We present the first complex structures of MtUGM with bound substrate UDP-Galp (both oxidized flavin and reduced flavin). In addition, we have determined the complex structures of MtUGM with inhibitors (UDP and the dideoxy-tetrafluorinated analogues of both UDP-Galp (UDP-F4-Galp) and UDP-Galf (UDP-F4-Galf)), which represent the first complex structures of UGM with an analogue in the furanose form, as well as the first structures of dideoxy-tetrafluorinated sugar analogues bound to a protein. These structures provide detailed insight into ligand recognition by MtUGM and show an overall binding mode similar to those reported for other prokaryotic UGMs. The binding of the ligand induces conformational changes in the enzyme, allowing ligand binding and active-site closure. In addition, the complex structure of MtUGM with UDP-F4-Galf reveals the first detailed insight into how the furanose moiety binds to UGM. In particular, this study confirmed that the furanoside adopts a high-energy conformation ((4)E) within the catalytic pocket. Moreover, these investigations provide structural insights into the enhanced binding of the dideoxy-tetrafluorinated sugars compared to unmodified analogues. These results will help in the design of carbohydrate mimetics and drug development, and show the enormous possibilities for the use of polyfluorination in the design of carbohydrate mimetics.

Tetrafluorination of sugars as strategy for enhancing protein-carbohydrate affinity: application to UDP-Galp mutase inhibition

Tetrafluorinated analogues of both UDP-galactopyranose and UDP-galactofuranose have been synthesized and assayed against UDP-galactopyranose mutase, a key enzyme for Mycobacterium tuberculosis cell wall biosynthesis. Competition assays and STD-NMR spectroscopy techniques have evidenced not only the first unambiguous case of affinity enhancement through local sugar polyfluorination, but also showed that tetrafluorination can still have a beneficial effect on binding when monofluorination at the same position does not.

Stereoselectively fluorinated N-heterocycles: a brief survey

The stereoselective incorporation of fluorine atoms into N-heterocycles can lead to dramatic changes in the molecules’ physical and chemical properties. These changes can be rationally exploited for the benefit of diverse fields such as medicinal chemistry and organocatalysis. This brief review will examine some of the effects that fluorine substitution can have in N-heterocycles, including changes to the molecules’ stability, their conformational behaviour, their hydrogen bonding ability, and their basicity. Finally, some methods for the synthesis of stereoselectively fluorinated N-heterocycles will also be reviewed.

Fluorine-directed β-galactosylation: chemical glycosylation development by molecular editing

Validation of the 2-fluoro substituent as an inert steering group to control chemical glycosylation is presented. A molecular editing study has revealed that the exceptional levels of diastereocontrol in glycosylation processes by using 2-fluoro-3,4,6-tri-O-benzyl glucopyranosyl trichloroacetimidate (TCA) scaffolds are a consequence of the 2R,3S,4S stereotriad. This study has also revealed that epimerization at C4, results in a substantial enhancement in β-selectivity (up to β/α 300:1).