Synthesis and anti-tumour, immunomodulating activity of diosgenin and tigogenin conjugates.

A series of novel diosgenin (DSG) and tigogenin (TGG) derivatives with diosgenin or tigogenin steroid aglycons linked to levulinic and 3,4-dihydroxycinnamic acids, dipeptides and various amino acids by an ester bond at the C3-oxygen atom of the steroid skeleton has been synthesized. Diosgenyl esters have been prepared by an esterification reaction (DCC/DMAP) of diosgenin with the corresponding acids. All analogues have been evaluated in vitro for their antiproliferative profile against cancer cell lines (MCF-7, MDA-MB-231, PC-3) and human umbilical vein endothelial cells (HUVEC). Analogue2c (l-serine derivative of TGG), the best representative of the series showed IC50 of 1.5 µM (MCF-7), and induced apoptosis in MCF-7 by activating caspase-3/7. The immunomodulatory properties of six synthesized analogues have been determined by examining their effects on the expression of cytokine genes essential for the functioning of the human immune system (IL-1, IL-4, IL-10, IL-12 and TNF-α). Biological evaluation has revealed that new compounds 4c and 16a do not induce the expression of pro-inflammatory cytokines in THP-1 cells after the lipopolysaccharide (LPS) stimulation. They also stimulate the expression of anti-inflammatory IL-10 that acts stronger than diosgenin itself. An in silico ADME properties(absorption, distribution, metabolism, excretion) study was also performed to predict the pharmacokinetic profile of the synthesized compounds. To shed light on the molecular interactions between the synthesized compounds and the glucocorticoid receptor and the estrogen receptor, 2c, 4c and 16a compounds were docked into the active binding sites of these receptors. The in silico and in vitro data suggested that this new group of compounds might be considered as a promising scaffold for further modification of more potent and selective anticancer and immunomodulatory agents.

Hoveyda-Grubbs catalyst analogues bearing the derivatives of N-phenylpyrrol in the carbene ligand - structure, stability, activity and unique ruthenium-phenyl interactions.

We have synthesized a series of N-phenylpyrrole and N-phenylindole carbenes and used them as ruthenium-ligating moieties in the synthesis of Hoveyda-Grubbs catalyst derivatives. We show that most of these complexes are difficult to synthesize and unstable apart from the N-phenylpyrrole-2,6-diisopropylphenyl ruthenium complex and its perbrominated derivative. These two systems are almost completely inactive in ring-closing metathesis at room temperature and become active only at 80 °C. DFT, SAPT0 and DLPNO-CCSD(T) calculations suggest that the rarely occurring phenyl-ruthenium interactions are responsible for the very slow initiation of these precatalysts at low temperatures.

Development of selective agents targeting serotonin 5HT1A receptors with subnanomolar activities based on a coumarin core.

A series of 18 new 5-[3-(4-aryl-1-piperazinyl)propoxy]coumarin derivatives from the corresponding bromoalkyl derivatives have been designed and synthesized by us using a microwave-assisted protocol. Radioligand binding assays of this series of compounds as well as a previously synthesized series of 17 structurally-similar compounds showed that six systems have very high affinities to the 5-HT1A receptor (0.3-1.0 nM) and good selectivity against the 5-HT2A receptor. Molecular docking, structural studies and structure-activity relationship studies were used to gain more insight into the atomistic details of ligand binding and rationalize the obtained results.

Nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in olefin metathesis: a computational study.

We used the density functional theory to evaluate the suitability of nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in ruthenium-based metathesis catalysts. We demonstrate that these analogues induce only minor structural changes in Hoveyda-Grubbs-like precatalysts, but have major impact on precatalyst initiation. Nitrenium ion-modified precatalysts are characterized by a weak Ru-N bond resulting in a relatively strong Ru-O bond and large free energy barriers for initiation, making them good candidates for efficient latent Ru-based catalysts. On the other hand the trivalent boron ligand, bearing a formal -1 charge, binds strongly to the ruthenium ion, weakening the Ru-O bond and facilitating its dissociation, to promote fast reaction initiation. We show that the calculated bond dissociation energy of the Ru-C/N/B bond may serve as an accurate indicator of the Ru-O bond strength and the rate of metathesis initiation.

Automatic removal of sonomotor waves from auditory brainstem responses.

We have developed a computerized technique for automatic detection and removal of sonomotor waves (SMWs) from auditory brainstem responses (ABRs). Our approach is based on adaptive decomposition using a redundant set of Gaussian and 1-cycle-limited Gabor functions. In order to find optimal parameters and evaluate the efficiency of the methods, simulated data were first used before applying it to clinical data. Results were good and confirmed by an expert with years of clinical experience in ABR evaluation.

Action of molecular switches in GPCRs--theoretical and experimental studies.

G protein coupled receptors (GPCRs), also called 7TM receptors, form a huge superfamily of membrane proteins that, upon activation by extracellular agonists, pass the signal to the cell interior. Ligands can bind either to extracellular N-terminus and loops (e.g. glutamate receptors) or to the binding site within transmembrane helices (Rhodopsin-like family). They are all activated by agonists although a spontaneous auto-activation of an empty receptor can also be observed. Biochemical and crystallographic methods together with molecular dynamics simulations and other theoretical techniques provided models of the receptor activation based on the action of so-called "molecular switches" buried in the receptor structure. They are changed by agonists but also by inverse agonists evoking an ensemble of activation states leading toward different activation pathways. Switches discovered so far include the ionic lock switch, the 3-7 lock switch, the tyrosine toggle switch linked with the nPxxy motif in TM7, and the transmission switch. The latter one was proposed instead of the tryptophan rotamer toggle switch because no change of the rotamer was observed in structures of activated receptors. The global toggle switch suggested earlier consisting of a vertical rigid motion of TM6, seems also to be implausible based on the recent crystal structures of GPCRs with agonists. Theoretical and experimental methods (crystallography, NMR, specific spectroscopic methods like FRET/BRET but also single-molecule-force-spectroscopy) are currently used to study the effect of ligands on the receptor structure, location of stable structural segments/domains of GPCRs, and to answer the still open question on how ligands are binding: either via ensemble of conformational receptor states or rather via induced fit mechanisms. On the other hand the structural investigations of homoand heterodimers and higher oligomers revealed the mechanism of allosteric signal transmission and receptor activation that could lead to design highly effective and selective allosteric or ago-allosteric drugs.

Multivariate autoregressive model for a study of phylogenetic diversity.

We present a computationally effective model to parameterize DNA sequences in a way describing comprehensively its auto and cross-correlation structure. The approach is based on four-channel Multivariate Autoregressive Model (MVAR). The model was applied to a study of genes from the globin family for 6 vertebrate species. First, the sequences were coded as four signals (corresponding to the nucleotides), which were fitted to a four-channel MVAR. From the correlation matrices the vectors of model coefficients were calculated as functions of the nucleotide distance. The between-chromosomes and inter-species differences were best distinguished in the cross-coefficients binding different nucleotide sequences. For clustering purposes different metrics were tested and then two clustering procedures (Nearest Neighbor and UPGMA) were applied. The clustering trees and consensus trees were constructed for exons, introns and whole genes. The results were in agreement with the known dependencies between the chromosomes of the globin family. The orthological genes for different species were grouped together. Inside these groups the phylogenetically close organisms were localized in proximity.