Pyrazine arotinoids with inverse agonist activities on the retinoid and rexinoid receptors.

RAR and RXR agonists: A collection of pyrazine-based RAR/RXR ligands were prepared by a series of palladium catalyzed cross-coupling reactions and characterized. Structure-activity relationships were elucidated. Retinoic acid receptor (RAR) alpha/beta-subtype-selective and retinoid X receptor (RXR) inverse agonist activities are described for pyrazine acrylic acid arotinoid, 14 d. Heterocyclic arotinoids derived from central-region dihalogenated pyrazine scaffolds have been synthesized by consecutive halogen and/or position-selective palladium-catalyzed cross-coupling reactions. Pyrazines were further functionalized as alkyl ethers or methylamines prior to the last Pd-catalyzed reactions. Transient transactivation studies with the retinoic acid receptor (RAR) alpha, beta, and gamma subtypes and with retinoid X receptor (RXR) alpha revealed distinct agonist, antagonist, and inverse agonist activities for these compounds. Of interest are the RARalpha,beta-selective inverse agonists with pyrazine acrylic acid structures, in particular 14 c, which is RARbeta-selective, and 14 d, a pan-RAR/RXR inverse agonist with more affinity for the RAR subtypes that enhance the interaction of RAR with cognate corepressors.

Highly potent naphthofuran-based retinoic acid receptor agonists.

A collection of arotinoids with a central benzofuran or naphthofuran ring structure was efficiently synthesized by a three-step process that comprises a Sonogashira coupling, an iodine-induced 5-endo-dig cyclization of the o-methoxyphenyl- or naphthyl-ethynyl benzoates, and finally a Suzuki/Sonogashira coupling of the corresponding 3-iodobenzo- or naphthofurans. Most of these 3-substituted naphthofuran arotinoids (but not the 5,7-di-tert-butylbenzofurans with the same substitution pattern at the C2 and C3 positions) are potent agonists of the retinoic acid receptor (RAR) subtypes, with activities in the nanomolar range.

Activation of alpha- and beta-estrogen receptors by persistent pesticides in reporter cell lines.

Many persistent pesticides have been implicated in reproductive and developmental adverse effects, in man and wildlife. It has been hypothesized that these so-called xeno-hormones could upset the endocrine system function by binding to human estrogen receptor alpha and beta (ERalpha, beta) and thus be responsible for the higher incidence of breast and cervical cancer, infertility and endometriosis. In this report, forty-nine pesticides were tested for ERalpha and beta activation or inhibition in stable reporter cell lines, HELN ERalpha and ERbeta. Stable transfection of the ERalpha and ERbeta constructs together with an estrogen reporter luciferase vector into the HeLa cell line resulted in two estradiol-sensitive cell lines. In our model, fifteen of the tested pesticides were found to agonize the ERalpha-mediated transcription in a dose-dependent manner and DDT, trans-nonachlor, chlordane, fenvalerate and toxaphene were also capable to activate ERbeta. Antagonistic activities toward hERalpha and hERbeta were shown in three (carbaryl, pentachlorophenol and 2,4,5-trichlorophenoxyacetic acid) and seven (chlordecone, methoxychlor, carbaryl, endosulfan, endrin, dieldrin, aldrin) pesticides, respectively. Remarkably chlordecone and methoxychlor which were the most effective antagonist compounds for hERbeta, were agonists for hERalpha. Although the ERalpha activation potential of the pesticides was lower than that of estradiol, the overall body scale response might be amplified by the ability of pesticides to act via several mechanisms and by frequent and prolonged exposure to different pesticides, even at low concentrations.

Design and synthesis of bridged gamma-lactams as analogues of beta-lactam antibiotics.

Anti-Bredt bridged bicyclo[3.2.1] gamma-lactams were designed as inhibitors of penicillin binding proteins (PBPs). The compounds were prepared by a carbenoid insertion into a lactam N-H bond. Their weak antibacterial activity could either be explained by a poor chemical stability or by unfavorable steric interactions of the methylene bridge of the gamma-lactam with the targeted enzymes.

Effect of organochlorine pesticides on human androgen receptor activation in vitro.

Many persistent organochlorine pesticides (OCs) have been implicated in adverse effects, that is, reproductive and developmental effects, in man and in wildlife alike. It has been hypothesized that these so-called xeno-hormones could be responsible for the increased incidence in various male sexual differentiation disorders such as hypospadias, cryptorchidism, low sperm counts and quality. In this report, OCs, called endocrine disrupters, were tested for their interaction with the androgen receptor. The stable prostatic cell line PALM, which contains a human androgen receptor (hAR) expression vector and the reporter MMTV-luciferase, was used to characterize the response of hAR to OC and was compared with synthetic androgen compound R1881. We found that all the OC pesticides tested were able to shift the agonist [(3)H]-R1881 from its binding site to the AR in competitive binding assays. In addition, these compounds antagonize-in a dose-dependent manner-the AR-mediated transcription by synthetic AR ligand R1881. None of the pesticides reacted as agonists. These results demonstrate that OC endocrine activities in vivo probably result from direct and specific binding to the AR ligand-binding domain. Although the antagonistic potential of OC pesticides is lower than that of hydroxyflutamide, they are capable of disrupting the male hormone signaling pathway. Because these chemicals are extremely persistent and tend to bioaccumulate, these results support the hypothesis that the recent increase in the incidence of male sexual disorders could be due to long exposure to ubiquitous OC pesticides found in the environment.

Antibiotic resistance peptides: interaction of peptides conferring macrolide and ketolide resistance with Staphylococcus aureus ribosomes: conformation of bound peptides as determined by transferred NOE experiments.

Two antibiotic resistance peptides, the E-peptide (MRLFV) and the K-peptide (MRFFV) conferring macrolide and ketolide resistance, respectively, were studied in the complex state with bacterial Staphylococcus aureus ribosomes. Interactions of antibiotic resistance peptides with ribosomes were investigated using two-dimensional transferred nuclear Overhauser effect spectroscopy (TRNOESY), suggesting that the peptide-ribosome interaction was associated with the low-affinity binding level. K-Peptide displayed a significantly better response in TRNOEs NMR experiments, in agreement with a better overall antibiotic activity of ketolides. This difference highlights a mimetic effect displayed by the E- and K-peptides. This study shows that conformation plays an essential role for the affinity binding site and, thus, for the resistance mechanism. Specific conformations were preferred in the bound state; their superimposition exhibited a similar cyclic peptidyl chain, while the side chain region varies. The F4 phenyl moiety in E-peptide has moved out of the turn region compared to its folding in the ketolide resistance peptide. In the K-peptide binding surface, the F4 aromatic chain is maintained by stacking with the guanidyl group of the R2 residue providing a particular hydrophobic and globular fragment, which may be important for the ketolide resistance peptide mode of action. Additionally, T(2) (CPMG) measurements were used to characterize equilibrium binding of antibiotic resistance peptides to bacterial ribosomes. The results bring to the fore E- and K-peptide competition with antibiotics for binding to the ribosomes. Their specific interaction and their competitive effects reveal a novel aspect of interaction of resistance peptides with ribosomes and suggest new insights about their mode of action. The resistance mechanism may imply two steps, a competitive effect of the resistance peptide for the macrolide (or ketolide) binding site followed by a "bottle brush" effect in which the drug and the peptide are driven out their binding site on the ribosome.