There is a growing interest in organic compounds containing the difluoromethyl group, as it is considered a lipophilic hydrogen bond donor that may act as a bioisostere of hydroxyl, thiol, or amine groups. A series of difluoromethyl anisoles and thioanisoles was prepared and their druglike properties, hydrogen bonding, and lipophilicity were studied. The hydrogen bond acidity parameters A (0.085-0.126) were determined using Abraham's solute H NMR analysis. It was found that the difluoromethyl group acts as a hydrogen bond donor on a scale similar to that of thiophenol, aniline, and amine groups but not as that of hydroxyl. Although difluoromethyl is considered a lipophilicity enhancing group, the range of the experimental Δlog P(water-octanol) values (log P(XCFH) - log P(XCH)) spanned from -0.1 to +0.4. For both parameters, a linear correlation was found between the measured values and Hammett σ constants. These results may aid in the rational design of drugs containing the difluoromethyl moiety.

The effects of the CF2H moiety on H-bond (HB) acidity and lipophilicity of various compounds, when attached directly to an aromatic ring or to other functions like alkyls, ethers/thioethers, or electron-withdrawing groups, are discussed. It was found that the CF2H group acts as a HB donor with a strong dependence on the attached functional group (A = 0.035–0.165). Regarding lipophilicity, the CF2H group may act as a more lipophilic bioisostere of OH but as a similar or less lipophilic bioisostere of SH and CH3, respectively, when attached to Ar or alkyl. In addition, the lipophilicity of ethers, sulfoxides, and sulfones is dramatically increased upon CH3/CF2H exchange at the α position. Interestingly, this exchange significantly affects not only the polarity and the volume of the solutes but also their HB-accepting ability, the main factors influencing log P oct. Accordingly, this study may be helpful in the rational design of drugs containing this moiety.

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The origins of human acetylcholinesterase (HuAChE) reactivity toward the lethal chemical warfare agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) and its stereoselectivity toward the P(S)-VX enantiomer (VX(S)) were investigated by examining the reactivity of HuAChE and its mutant derivatives toward purified enantiomers of VX and its noncharged isostere O-ethyl S-(3-isopropyl-4-methylpentyl) methylphosphonothioate (nc-VX) as well as echothiophate and its noncharged analogue. Reactivity of wild-type HuAChE toward VX(S) was 115-fold higher than that toward VX(R), with bimolecular rate constants of 1.4 x 10(8) and 1.2 x 10(6) min(-1) M(-1). HuAChE was also 12500-fold more reactive toward VX(S) than toward nc-VX(S). Substitution of the cation binding subsite residue Trp86 with alanine resulted in a 3 order of magnitude decrease in HuAChE reactivity toward both VX enantiomers, while this replacement had an only marginal effect on the reactivity toward the enantiomers of nc-VX and the noncharged echothiophate. These results attest to the critical role played by Trp86 in accommodating the charged moieties of both VX enantiomers. A marked decrease in stereoselectivity toward VX(S) was observed following replacements of Phe295 at the acyl pocket (F295A and F295A/F297A). Replacement of the peripheral anionic site (PAS) residue Asp74 with asparagine (D74N) practically abolished stereoselectivity toward VX(S) (130-fold decrease), while a substitution which retains the negative charge at position 74 (D74E) had no effect. The results from kinetic studies and molecular simulations suggest that the differential reactivity toward the VX enantiomers is mainly a result of a different interaction of the charged leaving group with Asp74.

Organophosphorus (OP) insecticides and nerve agents that contain P-S bond are relatively more resistant to enzymatic hydrolysis. Purified phenol oxidase (laccase) from the white rot fungus Pleurotus ostreatus (Po) together with the mediator 2,2P-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) displayed complete and rapid oxidative degradation of the nerve agents VX and Russian VX (RVX) and the insecticide analog diisopropyl-Amiton with specific activity: k sp = 2200, 667 and 1833 nmol min 3I mg 3I , respectively (pH 7.4, 37³C). A molar ratio of 1:20 for OP/ABTS and 0.05 M phosphate at pH 7.4 provided the highest degradation rate of VX and RVX. The thermostable laccase purified from the fungus Chaetomium thermophilium (Ct) in the presence of ABTS caused a 52-fold slower degradation of VX with k sp = 42 nmol min 3I mg 3I . The enzymatic biodegradation products were identified by QI P-NMR and GC/MS analysis.z 1998 Federation of European Biochemical Societies.