(S)-stereoisomer of telomestatin as a potent G-quadruplex binder and telomerase inhibitor

Total synthesis of the (S)-stereoisomer of telomestatin (1) was accomplished. (S)-Telomestatin exhibited potency four times that of the natural product, (R)-telomestatin, which was the most potent telomerase inhibitor previously reported. In the circular dichroism spectral analysis of the complexes possessing randomly structured single-stranded d[TTAGGG](4) oligonucleotide, (S)-telomestatin, like (R)-telomestatin, induced an antiparallel G-quadruplex structure. The melting temperature (T(m)) value of the (S)-isomer complex was greater than that of the (R)-telomestatin complex. Therefore, it is concluded that the stereochemistry of the thiazoline of telomestatin is important to the binding ability of a G-quadruplex binder, and (S)-telomestatin as a G-quadruplex binder is more potent than the natural product.     

Determination of parabens in cosmetic products by solid-phase microextraction of poly(ethylene glycol) diacrylate thin film on fibers and ultra high-speed liquid chromatography with diode array detector

The fabrication of a solid-phase microextraction (SPME) fiber through UV-induced polymerization of poly(ethylene glycol) diacrylate (PEG-DA) for determination of parabens in cosmetic products is presented in this work. The PEG-DA polymer coating was covalently attached to the fiber by introducing a surface modification with 3-(trichlorosilyl)propyl methacrylate (TPM). The PEG-DA polymer thin film coated on the fiber was homogeneous and wrinkled, which led to an increase of the surface area and high extraction efficiency. The extraction performances of the prepared SPME fibers were assessed by preconcentration of parabens including methylparaben, ethylparaben, propylparaben and benzylparaben from cosmetic products. The analysis was performed on an ultra high-speed liquid chromatography with diode array detector. The prepared SPME fibers exhibited good repeatability (for one fiber) and reproducibility (fiber-to-fiber) with RSDs of 5.4 and 6.9%, respectively. The optimized SPME method supported a wide linear range of 0.50-160 μg/mL and the detection limits for parabens were in the range of 0.12-0.15 μg/mL (S/N=3). The developed method was successfully applied for determination of parabens in cosmetic products with different natures.     

Hypervalent phenyl-λ3-iodane-mediated para-selective aromatic fluorination of 3-phenylpropyl ethers

Exposure of 3-phenylpropyl ethers to an activated iodosylbenzene monomer·18-crown-6 complex [PhI(OH)BF(4)·18C6] in the presence of BF(3)-Et(2)O and water results in the para-selective monofluorination of benzene ring via neighboring alkoxy group participation and directly affords 3-(4-fluorophenyl)propyl ethers regioselectively in good yields.     

Reaction of alkynyltrimethylsilanes with a hypervalent organoiodine compound: A new general synthesis of alkynyliodonium salts

New general methods for the synthesis of alkynyl(phenyl)iodonium tetrafluoroborate 2 from alkynyltrimethylsilanes 1 utilizing the combination of iodosylbenzene and triethyloxonium tetrafluoroborate or boron trifluoride etherate were developed. The medium effect observed in the reaction was also discussed.     

Synthesis and characterization of beta-haloalkenyl-lambda3-bromanes: stereoselective Markovnikov addition of difluoro(aryl)-lambda3-bromane to terminal acetylenes

Reported here for the first time are the synthesis, isolation, and characterization of hypervalent beta-haloalkenyl-lambda3-bromanes. Exposure of terminal alkynes to p-trifluoromethylphenyl(difluoro)-lambda3-bromane activated by BF3-i-Pr2O resulted in fluoro-lambda3-bromanation of the triple bonds in a Markovnikov fashion, yielding (E)-beta-fluoroalkenyl-lambda3-bromanes stereoselectively in good yields. 5-Chloro-1-pentynes undergo domino lambda3-bromanation-chlorine shift-fluorination or lambda3-bromanation-chlorine shift-alkyl shift-fluorination reaction, depending on the substituents and afford (E)-beta-chloroalkenyl-lambda3-bromanes stereoselectively in high yields. The beta-chloroalkenyl-lambda3-bromanes contain three kinds of halogen atoms, F, Cl, and Br, in the molecule.     

Iodobenzene-catalyzed alpha-acetoxylation of ketones. in situ generation of hypervalent (diacyloxyiodo)benzenes using m-chloroperbenzoic acid

Reported here for the first time is the iodobenzene-catalyzed alpha-oxidation of ketones, in which diacyloxy(phenyl)-lambda3-iodanes generated in situ act as real oxidants of ketones and m-chloroperbenzoic acid serves as a terminal oxidant. Oxidation of a ketone with m-chloroperbenzoic acid in acetic acid in the presence of a catalytic amount of iodobenzene, BF3.Et2O, and water at room temperature under argon affords an alpha-acetoxy ketone in good yield. p-Methyl- and p-chloroiodobenzene also serve as efficient catalysts in this direct oxidation. We found that when the reaction was carried out in the absence of a catalytic amount of iodobenzene, Baeyer-Villiger oxidation of a ketone took place. It is noted that use of water and BF3.Et2O is crucial to the success of this alpha-acetoxylation.     

Domino Michael addition-carbene rearrangement-cyclization reaction of 1-alkynyl(aryl)-lambda3-bromanes with 2-mercapto-1,3-benzazoles

Exposure of 1-alkynyl[p-(trifluoromethyl)phenyl](tetrafluoroborato)-lambda3-bromanes to 2-mercaptobenzimidazole or benzothiazole in dichloromethane at 0 degrees C under argon resulted in a domino Michael addition-carbene rearrangement-cyclization reaction to produce directly tricyclic heterocycles in high yields, whereas the reaction with 2-mercaptobenzoxazole afforded 1-alkynyl sulfides.