Enantiomerically Pure and Highly Substituted Alicyclic α,α-Difluoro Ketones: Potential Inhibitors for Malarial Aspartic Proteases, the Plasmepsins

Synthesis of 2,2-difluoro-1,3-diketone and 2,2-difluoro-1,3-ketoester derivatives using fluorine gas

Solutions of 1,3-diketones and 1,3-ketoester derivatives react with fluorine to give the corresponding 2,2-difluoro-1,3-dicarbonyl derivatives in the presence of quinuclidine. Quinuclidine reacts with fluorine in situ to generate a fluoride ion that facilitates limiting enolization processes, and an electrophilic N-F fluorinating agent that is reactive towards neutral enol species.

Species-specific lipophilicities of fluorinated diketones in complex equilibria systems and their potential as multifaceted reversible covalent warheads

Combined molecular, physicochemical and chemical properties of electrophilic warheads can be applied to create covalent drugs with diverse facets. Here we study these properties in fluorinated diketones (FDKs) and their multicomponent equilibrium systems in the presence of protic nucleophiles, revealing the potential of the CF2(CO)2 group to act as a multifaceted warhead for reversible covalent drugs. The equilibria compositions of various FDKs in water/octanol contain up to nine species. A simultaneous direct species-specific 19F-NMR-based log P determination of these complex equilibria systems was achieved and revealed in some cases lipophilic to hydrophilic shifts, indicating possible adaptation to different environments. This was also demonstrated in 19F-MAS-NMR-based water-membrane partitioning measurements. An interpretation of the results is suggested by the aid of a DFT study and 19F-DOSY-NMR spectroscopy. In dilute solutions, a model FDK reacted with protected cysteine to form two hemi-thioketal regioisomers, indicating possible flexible regio-reactivity of CF2(CO)2 warheads toward cysteine residues.

Synthesis of Difluoromethylated Carbinols via a HFIP-Promoted Hydroxydifluoromethylation of Aniline, Indole, and Pyrrole Derivatives with Difluoroacetaldehyde Ethyl Hemiacetal

A hexafluoroisopropanol (HFIP)-promoted hydroxydifluoromethylation of aniline, indole, and pyrrole derivatives with difluoroacetaldehyde ethyl hemiacetal has been developed. This protocol provides a facile and straightforward approach to access diverse difluoromethylated carbinols in good to excellent yields under mild conditions. Furthermore, gram-scale and synthetic derivatization experiments have also been demonstrated.

Metal-free electrochemical fluorodecarboxylation of aryloxyacetic acids to fluoromethyl aryl ethers

Electrochemical decarboxylation of aryloxyacetic acids followed by fluorination provides easy access to fluoromethyl aryl ethers. This electrochemical fluorodecarboxylation offers a sustainable approach with electric current as traceless oxidant. Using Et3N·5HF as fluoride source and as supporting electrolyte, this simple electrosynthesis affords various fluoromethoxyarenes in yields up to 85%.

Highly Carbon-Selective Monofluoromethylation of β-Ketoesters with Fluoromethyl Iodide

A highly carbon-selective monofluoromethylation of a broad range of β-ketoesters with fluoromethyl iodide under mild conditions is described. The uses of lithium tert-butoxide as the base and diglyme as the solvent made great contributions to the high C/O regioselectivity.

Molecular recognition in chemical and biological systems

Structure-based ligand design in medicinal chemistry and crop protection relies on the identification and quantification of weak noncovalent interactions and understanding the role of water. Small-molecule and protein structural database searches are important tools to retrieve existing knowledge. Thermodynamic profiling, combined with X-ray structural and computational studies, is the key to elucidate the energetics of the replacement of water by ligands. Biological receptor sites vary greatly in shape, conformational dynamics, and polarity, and require different ligand-design strategies, as shown for various case studies. Interactions between dipoles have become a central theme of molecular recognition. Orthogonal interactions, halogen bonding, and amide⋅⋅⋅π stacking provide new tools for innovative lead optimization. The combination of synthetic models and biological complexation studies is required to gather reliable information on weak noncovalent interactions and the role of water.

Stereoselective nucleophilic fluoromethylation of aryl ketones: dynamic kinetic resolution of chiral α-fluoro carbanions

Although many methods are available for the synthesis of optically enriched monofluoromethyl secondary alcohols, synthesizing optically enriched monofluoromethyl tertiary alcohols remains a challenge. An efficient and easy-to-handle nucleophilic fluoromethylation protocol was developed. The current monofluoromethylation showed much higher facial selectivity than the corresponding difluoromethylation and proceeded via a different type of transition state. Excellent stereoselective control at the fluorinated carbon chiral center was found, an effect believed to be facilitated by the dynamic kinetic resolution of the chiral α-fluoro carbanions.

Synthesis of α-halo-α,α-difluoromethyl ketones by a trifluoroacetate release/halogenation protocol

Three series of α-halo-α,α-difluoromethyl ketones are prepared from highly α-fluorinated gem-diols by exploiting the facile release of trifluoroacetate, followed by immediate trapping of the liberated α,α-difluoroenolate with an electrophilic chlorine, bromine, or iodine source. The products are typically isolated in good yields, even in the case of sensitive, α-iodo-α,α-difluoromethyl ketones. Also, we demonstrate that an α-iodo-α,α-difluoromethyl ketone will participate in a copper-promoted reaction to forge a new carbon-carbon bond.