Access to “Friedel–Crafts-Restricted” <i>tert</i>-Alkyl Aromatics by Activation/Methylation of Tertiary Benzylic Alcohols

Herein we describe a two-step protocol to prepare <i>m</i>-<i>tert</i>-alkylbenzenes. The appropriate tertiary benzylic alcohols are activated with SOCl₂ or concentrated HCl and then treated with trimethylaluminum, affording the desired products in 68–97% yields (22 examples). This reaction sequence is successful in the presence of a variety of functional groups, including acid-sensitive and Lewis-basic groups. In addition to <i>t</i>-Bu groups, 1,1-dimethylpropyl and 1-ethyl-1-methylpropyl groups can also be installed using this method

Structure–Activity Relationship and Pharmacokinetic Studies of 1,5-Diheteroarylpenta-1,4-dien-3-ones: A Class of Promising Curcumin-Based Anticancer Agents

Forty-three 1,5-diheteroaryl-1,4-pentadien-3-ones were designed as potential curcumin mimics, structurally featuring a central five-carbon dienone linker and two identical nitrogen-containing aromatic rings. They were synthesized using a Horner–Wadsworth–Emmons reaction as the critical step and evaluated for their cytotoxicity and antiproliferative activities toward both androgen-insensitive and androgen-sensitive prostate cancer cell lines and an aggressive cervical cancer cell line. Most of the synthesized compounds showed distinctly better in vitro potency than curcumin in the four cancer cell lines. The structure–activity data acquired from the study validated (1<i>E</i>,4<i>E</i>)-1,5-dihereroaryl-1,4-pentadien-3-ones as an excellent scaffold for in-depth development for clinical treatment of prostate and cervical cancers. 1-Alkyl-1<i>H</i>-imidazol-2-yl, ortho pyridyl, 1-alkyl-1<i>H</i>-benzo­[<i>d</i>]­imidazole-2-yl, 4-bromo-1-methyl-1<i>H</i>-pyrazol-3-yl, thiazol-2-yl, and 2-methyl-4-(trifluoromethyl)­thiazol-5-yl were identified as optimal heteroaromatic rings for the promising in vitro potency. (1<i>E</i>,4<i>E</i>)-1,5-Bis­(2-methyl-4-(trifluoromethyl)­thiazol-5-yl)­penta-1,4-dien-3-one, featuring thiazole rings and trifluoromethyl groups, was established as the optimal lead compound because of its good in vitro potency and attractive in vivo pharmacokinetic profiles

Select Small Core Structure Carbamates Exhibit High Contact Toxicity to “Carbamate-Resistant” Strain Malaria Mosquitoes, <em>Anopheles gambiae</em> (Akron)

<div><p>Acetylcholinesterase (AChE) is a proven target for control of the malaria mosquito (<em>Anopheles gambiae</em>). Unfortunately, a single amino acid mutation (G119S) in <em>An. gambiae</em> AChE-1 (<em>Ag</em>AChE) confers resistance to the AChE inhibitors currently approved by the World Health Organization for indoor residual spraying. In this report, we describe several carbamate inhibitors that potently inhibit G119S <em>Ag</em>AChE and that are contact-toxic to carbamate-resistant <em>An. gambiae</em>. PCR-RFLP analysis was used to confirm that carbamate-susceptible G3 and carbamate-resistant Akron strains of <em>An. gambiae</em> carry wild-type (WT) and G119S AChE, respectively. G119S <em>Ag</em>AChE was expressed and purified for the first time, and was shown to have only 3% of the turnover number (<em>k</em>_cat) of the WT enzyme. Twelve carbamates were then assayed for inhibition of these enzymes. High resistance ratios (>2,500-fold) were observed for carbamates bearing a benzene ring core, consistent with the carbamate-resistant phenotype of the G119S enzyme. Interestingly, resistance ratios for two oxime methylcarbamates, and for five pyrazol-4-yl methylcarbamates were found to be much lower (4- to 65-fold). The toxicities of these carbamates to live G3 and Akron strain <em>An. gambiae</em> were determined. As expected from the enzyme resistance ratios, carbamates bearing a benzene ring core showed low toxicity to Akron strain <em>An. gambiae</em> (LC₅₀>5,000 μg/mL). However, one oxime methylcarbamate (aldicarb) and five pyrazol-4-yl methylcarbamates (<b>4a</b>–<b>e</b>) showed good to excellent toxicity to the Akron strain (LC₅₀ = 32–650 μg/mL). These results suggest that appropriately functionalized “small-core” carbamates could function as a resistance-breaking anticholinesterase insecticides against the malaria mosquito.</p> </div

Electrophoretic analysis (SDS-PAGE) of the purified r<i>Ag</i>AChE (WT and G119S).

<p>A: Protein standard (Da); B: r<i>Ag</i>AChE-WT (“n”); C: r<i>Ag</i>AChE-G119S mutant (“m”).</p

Enzyme resistance ratios and <i>Ag</i>AChE vs <i>h</i>AChE selectivity of selected carbamates.

a<p>Recombinant sources of <i>Ag</i>AChE are r<i>Ag</i>AChE-WT and r<i>Ag</i>AChE-G119S; homogenates are G3 (WT) and Akron (G119S). ^bResistance ratio is calculated as <i>k</i>_i(WT)/<i>k</i>_i(G119S); values are taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046712#pone-0046712-t002" target="_blank">Table 2</a>. Standard error in the ratio is calculated according to a standard propagation of error formula <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046712#pone.0046712-Andraos1" target="_blank">[61]</a>. ^cSelectivity for inhibiting <i>Ag</i>AChE (WT) vs <i>h</i>AChE, calculated as <i>k</i>_i(<i>Ag</i>AChE)/<i>k</i>_i(<i>h</i>AChE), with standard error in the ratio calculated according to a standard propagation of error formula <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046712#pone.0046712-Andraos1" target="_blank">[61]</a>.</p

Tarsal contact toxicity (24 h) to G3 and Akron strain <i>An. gambiae</i>, and toxicity resistance ratios.

a<p>No mortality at this concentration. ^bLess than 10% mortality at this concentration. ^cDefined by LC₅₀ (Akron)/LC₅₀ (G3).</p

Nucleotide and deduced amino acid sequences of the <i>ace</i>-<i>1</i> amplicons of susceptible (G3) and resistant (Akron) <i>An. gambiae</i>.

<p>The alignment of DNA sequences illustrates the presence of the AG|CT <i>Alu</i>I restriction site in the Akron <i>ace</i>-<i>1</i> amplicon (194 bp) spanning the 119 (G/S) and 120 (F) codons of the <i>Ag</i>AChE-1 amino acid sequence; the 119 codon is marked with a rectangle. The arrows indicate the position of the degenerate primers (Moustdir1 and Moustrev1) used for the PCR amplification and sequencing of genomic DNA. Nucleotide numbers in the amplicon are provided above the G3 sequence.</p

Carbamate inactivation rate constants <i>k</i>_i for r<i>Ag</i>AChE (WT & G119S), <i>An. gambiae</i> homogenates (G3 & Akron), and r<i>h</i>AChE.^a

a<p>Measured at 23±1°C, pH 7.7, 0.1% (v/v) DMSO. ^bG3 strain <i>An. gambiae</i> carry WT <i>Ag</i>AChE and possess a carbamate-susceptible phenotype. ^cAkron strain <i>An. gambiae</i> carry G119S mutant <i>Ag</i>AChE and possess a carbamate-resistant phenotype.</p

Computational modeling of tetrahedral intermediates formed by addition of the <i>Ag</i>AChE catalytic serine (S199) Oγ to carbamates.

<p>A) terbam with WT enzyme; location of catalytic serine oxygen Oγ is highlighted with the green arrow. B) terbam with G119S mutant enzyme; steric clash of the hydroxyl group of S119 with aromatic ring of terbam is noted with a blue arrow. C) Aldicarb with G119S mutant enzyme; note the absence of a steric clash with the hydroxyl group of S119. D) Pyrazol-4-yl methylcarbamate <b>4c</b> ((<i>S</i>)-enantiomer) with the G119S mutant enzyme; note the absence of a steric clash with the hydroxyl group of S119. Nonbonded contact distances in B and D are given in Å.</p

Kinetic parameters (23±1°C, pH 7.7) of r<i>Ag</i>AChE (WT & G119S) and r<i>h</i>AChE, and <i>K</i>_m values for the ATCh-hydrolyzing enzyme in <i>An. gambiae</i> homogenate (G3 and Akron).

a<p>Enzyme velocity at saturating ATCh concentrations; 1 unit (U)  = 1 μmol ATCh substrate processed per minute (μmol min⁻¹). Protein concentrations were determined using the Thermo Scientific Micro BCA Protein Assay Kit 23235 (see Materials and Methods). ^bTurnover numbers (<i>k</i>_cat) were determined based on <i>V</i>_max and the calculated molecular mass of the enzyme catalytic subunits (see Materials and Methods). ^cSpecific activity determined at [ATCh]  = 0.50 mM, according to convention.</p