Synthesis of α,α-Difluoro-ß-amino Ketones from N-Boc-α-Amidosulfones and Pentafluoro-gem-diols.

To circumvent the synthesis and isolation of imines, a method was devised to construct α,α-difluoro-ß-amino ketones from N-Boc-α-amidosulfones. The reactive nucleophiles, difluoroenolates, are generated in situ from the pentafluoro-gem-diols using cesium fluoride in pyridine. NMR studies confirm the role of the α-amidosulfones in this process. Incubation of the α,α-difluoro-ß-amino ketones in rat serum demonstrates the relative stability of this structure as well as its value as a chemical probe or lead.

Comparison of Conformational Analyses of Naturally Occurring Flavonoid-O-Glycosides with Unnatural Flavonoid-CF2-Glycosides Using Molecular Modeling.

Many glycosylated natural products display biological activity and are deglycosylated by the metabolic processes of the body. Although unnatural CF2-glycosides have been proposed as nonhydrolyzable analogues, CF2-derivatives of natural products are exceedingly challenging to synthesize and few examples exist. These difluorinated molecules may have unique conformational behavior as a consequence of changing the glycosidic linkage. In this study, we performed conformational searches using MacroModel followed by molecular dynamics simulations to investigate the conformational behavior of the glycosidic bonds in flavonoid-O-glycosides and in corresponding CF2-glycosylated derivatives. Compared to their O-glycosylated analogues, flavonoid-3-CF2-glycosides and flavonoid-5-CF2-glycosides showed conformational bias, whereas flavonoid-7-CF2-glycosides showed more flexibility. Flavonoid-5-CF2-glycosides were the least flexible compared to all others. Our results show that the site of the glycosylation and the substitution pattern on the flavonoid determine the conformational properties of these molecules. These two factors influence the steric destabilization and/or stereoelectronic stabilization which govern the conformational behavior of the flavonoid glycosides. Moreover, a docking study of quercitrin and its CF2-analogue into murine ribosomal kinase RSK2 demonstrated the potential for flavonoid-CF2-glycosides to retain a similar binding pose as the parent O-glycoside. These findings will assist in designing stable flavonoid-CF2-glycosides for carbohydrate research.

Transient Formation of Hemiketals from Pentafluoro-gem-diols in the Presence of Alcohols.

Pentafluoro-gem-diols have emerged as a source of reactive intermediates for synthesizing fluorinated molecules. When pentafluoro-gem-diols were exposed to alcohols as solvents, the formation of transient hemiketals was detected by 19F NMR. The conversion rates to hemiketals were found to be higher with primary alcohols than with secondary or fluorinated alcohols. These findings provide valuable insight for developing novel techniques to construct intricate fluorinated structures using pentafluoro-gem-diols.

Synthesis, biological evaluation, and NMR studies of 3-fluorinated derivatives of 3',4',5'-trihydroxyflavone and 3',4',5'-trimethoxyflavone.

Flavones are valuable scaffolds in medicinal chemistry, especially as they display activity as antioxidants and neuroprotective agents. The need to incorporate a fluorine atom on flavones has driven much of the recent synthetic work in this area. We now report a route for the production of 3-fluorinated derivatives of 3',4',5'-trihydroxyflavone and 3',4',5'-trimethoxyflavone. Biological evaluation of these agents, along with their non-fluorinated counterparts, demonstrate that antioxidant activity may be enhanced whereas neuroprotective activity is conserved. Also, the 3-fluoro-3',4',5'-trihydroxyflavone can act as an NMR probe to detect structural changes during its action as a radical scavenger.

Controlling the Cleavage of Carbon-Carbon Bonds To Generate α,α-Difluorobenzyl Carbanions for the Construction of Difluoromethylbenzenes.

Controlling the cleavage of carbon-carbon bonds during a chemical reaction is a substantial challenge; however, synthetic methods that accomplish this objective produce valuable and often unexplored reactivity. We have designed a mild process to generate α,α-difluorobenzyl carbanions in the presence of potassium carbonate by exploiting the cleavage of C-C bonds during the release of trifluoroacetate. The initiating reagent is potassium carbonate, which represents an improvement over existing protocols that require a strong base. Fragmentation studies across substituted arenes and heteroarenes were conducted along with computational analyses to elucidate reactivity trends. Furthermore, the mildly generated α,α-difluorobenzyl carbanions from electron-deficient aromatics and heteroaromatic rings can react with aldehydes to create derivatives of difluoromethylbenzenes, which are valuable synthetic targets.

Magnesium-Promoted Additions of Difluoroenolates to Unactivated Imines.

Although there are many synthetic methods to produce fluorinated and trifluoromethylated organic structures, the construction of difluoromethylated compounds remains a synthetic challenge. We have discovered that unactivated imines will react with difluoroenolates under exceedingly mild conditions when using magnesium salts and organic bases. We have applied this approach to the iminoaldol reaction to produce difluoromethylene groups as α,α-difluoro-ß-amino-carbonyl groups. This method provides synthetically useful quantities of difficult to access α,α-difluoro-ß-aminoketones without the need of protecting groups or the use of activated imines. Moreover, we have applied this strategy to create analogues of the dual orexin receptor antagonist, almorexant, in only two synthetic steps.

Agonists of the γ-aminobutyric acid type B (GABAB) receptor derived from ß-hydroxy and ß-amino difluoromethyl ketones.

ß-Hydroxy difluoromethyl ketones represent the newest class of agonists of the GABA-B receptor, and they are structurally distinct from all other known agonists at this receptor because they do not display the carboxylic acid or amino group of γ-aminobutyric acid (GABA). In this report, the design, synthesis, and biological evaluation of additional analogues of ß-hydroxy difluoromethyl ketones characterized the critical nature of the substituted aromatic group on the lead compound. The importance of these new data is interpreted by docking studies using the X-ray structure of the GABA-B receptor. Moreover, we also report that the synthesis and biological evaluation of ß-amino difluoromethyl ketones provided the most potent compound across these two series.

Generation of Magnesium Pentafluoropropen-2-olate from Hexafluoroisopropanol and Synthesis of 2,2,4,4,4-Pentafluoro-3,3-dihydroxyketones.

2,2,4,4,4-Pentafluoro-3,3-dihydroxyketones are valuable precursors to difluoroenolates following fragmentation during the release of trifluoroacetate; however, there are few synthetic strategies to prepare this unique class of compound. We addressed this issue and report a mild, two-step synthesis of 2,2,4,4,4-pentafluoro-3,3-dihydroxyketones from aldehydes. Specifically, aldehydes are treated with pentafluoropropen-2-olate, generated from a new fragmentation of hexafluoroisopropanol with a mixed Mg/Li amide, to give pentafluoroalcohols. A subsequent oxidation with Dess-Martin periodinane provides the targets in good isolated yields.

Conversion of Methyl Ketones and Methyl Sulfones into α-Deutero-α,α-Difluoromethyl Ketones and α-Deutero-α,α-Difluoromethyl Sulfones in Three Synthetic Steps.

Deuterodifluoromethyl ketones and sulfones were assembled in three synthetic steps from methyl ketones and sulfones, respectively. The key synthetic transformation is the deuteration of the difluorocarbanion generated by the release of trifluoroacetate from highly α-fluorinated gem-diols. High levels of deuterium on the "CF2D" group were routinely observed. This strategy is mild and versatile and it can be applied to both ketones and sulfones without additional concerns of over- or under-fluorination. Additional examples address issues of over-deuteration when compounds with other acidic protons are subjected to the reaction conditions. This process not only demonstrates a new method to install a "CF2D" group but also extends the scope of trifluoroacetate release to sulfones.

A small molecule screen identifies a novel compound that induces a homeotic transformation in Hydra.

Developmental processes such as morphogenesis, patterning and differentiation are continuously active in the adult Hydra polyp. We carried out a small molecule screen to identify compounds that affect patterning in Hydra. We identified a novel molecule, DAC-2-25, that causes a homeotic transformation of body column into tentacle zone. This transformation occurs in a progressive and polar fashion, beginning at the oral end of the animal. We have identified several strains that respond to DAC-2-25 and one that does not, and we used chimeras from these strains to identify the ectoderm as the target tissue for DAC-2-25. Using transgenic Hydra that express green fluorescent protein under the control of relevant promoters, we examined how DAC-2-25 affects tentacle patterning. Genes whose expression is associated with the tentacle zone are ectopically expressed upon exposure to DAC-2-25, whereas those associated with body column tissue are turned off as the tentacle zone expands. The expression patterns of the organizer-associated gene HyWnt3 and the hypostome-specific gene HyBra2 are unchanged. Structure-activity relationship studies have identified features of DAC-2-25 that are required for activity and potency. This study shows that small molecule screens in Hydra can be used to dissect patterning processes.

Optimized Synthesis of a Pentafluoro-gem-diol and Conversion to a CF2Br-Glucopyranose through Trifluoroacetate-Release and Halogenation.

Pentafluoro-gem-diols are substrates that enable the synthesis of valuable difluoromethylene-containing organic molecules through the release of trifluoroacetate. Currently, only one synthetic strategy is available to assemble these important precursors. Herein, two new synthetic strategies to a complex pentafluoro-gem-diol are compared to the existing route, and an improved synthetic route has completed. Moreover, the first synthesis of a CF2Br-glucopyranose was finished by a tandem trifluoroacetate-release halogenation/cyclization protocol.

Proposed actions for the US Food and Drug Administration to implement to minimize adverse effects associated with energy drink consumption.

Energy drink sales are expected to reach $52 billion by 2016. These products, often sold as dietary supplements, typically contain stimulants. The Dietary Supplement Protection Act claims an exemplary public health safety record. However, in 2011 the number of emergency department visits related to consumption of energy drinks exceeded 20,000. Nearly half of these visits involved adverse effects occurring from product misuse. Political, social, economic, practical, and legal factors shape the landscape surrounding this issue. In this policy analysis, we examine 3 options: capping energy drink caffeine levels, creating a public education campaign, and increasing regulatory scrutiny regarding the manufacture and labeling of energy drinks. Increased regulatory scrutiny may be in order, especially in light of wrongful death lawsuits related to caffeine toxicity resulting from energy drink consumption.

Synthesis of 15-methylene-eburnamonine from (+)-vincamine, evaluation of anticancer activity, and investigation of mechanism of action by quantitative NMR.

The biological role of installing a critical exocyclic enone into the structure of the alkaloid, (-)-eburnamonine, and characterization of the new chemical reactivity by quantitative NMR without using deuterated solvents are described. This selective modification to a natural product imparts potent anticancer activity as well as bestows chemical reactivity toward nucleophilic thiols, which was measured by quantitative NMR. The synthetic strategy provides an overall conversion of 40%. In the key synthetic step, a modified Peterson olefination was accomplished through the facile release of trifluoroacetate to create the requisite enone in the presence of substantial steric hindrance.

Generation of formaldehyde and formaldehyde-d2 for hydroxymethylations and hydroxydeuteromethylations of difluoroenolates and difluorobenzyl carbanions.

A method for the in situ production of formaldehyde from dimethylsulfoxide, bromine, and cesium carbonate is reported for reactions with difluoroenolates and difluorobenzyl carbanions. This process also generates formaldehyde-d2 for the production of 2,2-difluoro-1,1-deuteroethanols. Mechanistic and computational studies further characterize the production of hydroxymethylated and hydroxydeuteromethylated difluorinated organic molecules.

Cleavage of carbon-carbon bonds through the mild release of trifluoroacetate: generation of α,α-difluoroenolates for aldol reactions.

The selective cleavage of carbon-carbon bonds is a significant challenge in synthetic chemistry, yet this strategy can be a powerful way to generate reactive intermediates. We have discovered that, through the facile release of trifluoroacetate which occurs by C-C bond scission, difluoroenolates can be generated under very mild reaction conditions. Unlike existing reactions, this method is not limited to a small group of fluorinated building blocks. We have applied this process to the aldol reaction to install difluoromethylene groups.

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.

Exploiting the facile release of trifluoroacetate for the α-methylenation of the sterically hindered carbonyl groups on (+)-sclareolide and (-)-eburnamonine.

An efficient method for the α-methylenation of carbonyl groups is reported, and this transformation is accomplished by a facile elimination of trifluoroacetate during the formation of the olefin. This method represents an improvement beyond existing protocol in cases of steric hindrance, and we have demonstrated the utility of the process across a series of ketones, lactams, and lactones. Additionally, we have applied this method to produce semisynthetic derivatives of the natural products (+)-sclareolide and (-)-eburnamonine, in which the carbonyl group is proximal to bulky functional groups. Mechanistic insight is also provided from a time course of (19)F NMR. Biological evaluation of the natural-product-derived enones led to the identification of a derivative of (-)-eburnamonine with significant cytotoxicity (LC(50) = 14.12 µM) in drug-resistant MDA-MB-231 breast cancer cells.

Synthesis of Difluorinated Halohydrins by the Chemoselective Addition of Difluoroenolates to α-Haloketones.

α-Haloketones are valuable intermediates in the synthesis of pharmaceuticals and natural products because they display two electrophiles. Although chemoselective additions to each of these functional groups are known, the use of fluorinated nucleophiles has not been characterized, except for the dimerization of fluorohalomethyl ketones. Our studies demonstrate the use of difluoroenolates to create difluorinated bromohydrins and chlorohydrins from α-haloketones without any cyclization or rearrangement due to the mild conditions.

A practical deuterium-free NMR method for the rapid determination of 1-octanol/water partition coefficients of pharmaceutical agents.

A simple and rapid NMR method is described to determine the logP of pharmaceutical agents. This method is highly versatile and efficient, because it does not require the use of deuterated solvents or the addition of any internal/external standards to the sample. We demonstrate that logP can be accurately measured using NMR for pharmaceutical agents with known logP values. Our proposed method is made possible by the combination of state-of-the-art NMR techniques including the solvent concentration reference and robust solvent suppressions.