Turning the Other Cheek: Influence of the cis-Tetrafluorocyclohexyl Motif on Physicochemical and Metabolic Properties

The targeted introduction of substituents in order to tailor a molecule’s pharmacologic, physicochemical, and metabolic properties has long been of interest to medicinal chemists. The all-cis tetrafluorocyclohexyl motif—dubbed Janus face, due to its electrostatically polarized cyclohexyl ring—represents one such example where chemists might incorporate a metabolically stable, polar, lipocompatible motif. To better understand its potential utility, we have synthesized three series of matched molecular pairs (MMPs) where each MMP differs only in the cyclohexane unit, i.e., with a tetrafluorocyclohexyl or a standard cyclohexyl motif. With the introduction of the facially polarized all-cis tetrafluorocyclohexyl ring, the resulting compounds have significantly modified physicochemical properties (e.g., kinetic solubility, lipophilicity and permeability) and metabolic stabilities. These results further speak to the promise of this substituent as a tactic to improve the drug-like properties of molecules.

Janus All-Cis 2,3,4,5,6-Pentafluorocyclohexyl Building Blocks Applied to Medicinal Chemistry and Bioactives Discovery Chemistry

Monoalkylated derivatives of the unusually polar all-cis 2,3,4,5,6- pentafluorocyclohexyl (Janus face) motif are prepared starting from an aryl hydrogenation of 2,3,4,5,6- pentafluorophenylacetate methyl ester 15. The method used Zeng's Rh(CAAC) carbene catalyst 4 in the hydrogenation following the protocol developed by Glorius. The resultant Janus pentafluorocyclohexylacetate methyl ester 16 was converted to the corresponding alcohol 18, aldehyde 13, bromide 29 and azide 14 through functional group manipulations, and some of these building blocks were used in Ugi-multicomponent and Cu-catalysed click reactions. NBoc protected pentafluoroarylphenylalanine methyl ester 35 was also subject to an aryl hydrogenation, and then deprotection to generate the Janus face β-pentafluorocyclohexyl-alanine amino acid 15, which was incorporated into representative members of an emerging class of candidate antiviral compounds. Log P measurements demonstrate that the all-cis 2,3,4,5,6-pentafluorocyclohexyl ring system is more polar than a phenyl ring. In overview the paper introduces new building blocks containing this Janus ring and demonstrates their progression to molecules typically used in bioactives discovery programmes.

From Carbohydrates to Complex Organofluorines: Synthesis, Conformation, and Lipophilicity of Multivicinal-Fluorine-Containing Hexitol Analogues

There is growing interest in the preparation of fluorine-containing organic molecules. Multivicinal-fluorine analogues are among the most intriguing and promising compounds, but their physical and biological investigations are held back by challenging syntheses. Herein, we report on the synthesis of a large set of novel polyfluorohexitols. The dominant solution-state conformation of all trifluorohexitols was determined, and the solid-state conformations of some analogues were compared. Finally, the lipophilicity of a large set of polyfluorinated hexopyranose and hexitol analogues was attributed by using a log P determination method based on ¹⁹ F NMR spectroscopy.

Polar Organofluorine Substituents: Multivicinal Fluorines on Alkyl Chains and Alicyclic Rings

This Review outlines the progression, primarily of our own work, but with important contributions from other labs, on the synthesis and properties of multiple vicinally fluorinated alkyl chains and rings. Chain conformations of individual diastereoisomers with -CHF- at adjacent carbons are influenced by stereoelectronic factors associated with the polar C-F bond and the polarised geminal hydrogens. Generally, the chain will prefer a conformation which acts to minimise overall molecular polarity, and where the C-F bonds orient away from each other. However, when vicinal fluorine atoms are positioned on a ring then conformations are more constrained. The ring will adopt optimal conformations such as a chair in cyclohexane and then C-F bonds can be introduced with a stereochemistry that forces parallel (axial) orientations. In the case of cyclohexane, 1,3-diaxial arrangements of C-F bonds impart considerable polarity to the ring, resulting in an electronegative 'fluorine face' and an electropositive 'hydrogen face'. For all-syn 1,2,3,4,5,6-hexafluorocyclohexane, this arrangement generates an unusually polar aliphatic ring system. Most recently the concept has been extended to the preparation of all-syn 1,2,3-trifluorocyclopropanes, a rigid ring system with fluorine atoms on one face and hydrogens on the other. Lipophilicity Log P values of such compounds indicate that they are significantly more polar than their parent alicyclic hydrocarbons and give some positive indication for a future role of such substituents in medicinal chemistry. Expanding to such a role will require access to improved synthesis methods to these motifs and consequently access to a broader a range of building blocks, however some exciting new methods have emerged recently and these are briefly reviewed.