Zsuzsanna Tegyey

Conformational recognition by central benzodiazepine receptors

Abstract In order to distinguish conformational recognition by the receptor from steric effects brought about by substituents attached to C3 of 1,4-benzodiazepines, two series of closely related compounds were tested for binding potency. Increasing size of the 3-substituent up to isopropyl decreases both the binding and its enantioselectivity. Synthesis and X-ray determination of the molecular structure of 3,3-dimethyl derivatives possessing quasi-axial methyl substituents were followed by a mathematical separation of conformational and substituent effects for quartets with successive 3-methylation [(H)2, (S)-Me, (R)-Me, (Me)2 at C3]. Results indicate a very high preference for conformation M of the ligand by the receptor (the primary reason of stereoselectivity) and a large steric hindrance resulting from the axial methyl substituent. A lower but still unexpectedly substantial steric effect is exerted by the equatorial methyl group.

PNA-DNA chimeras containing 5-alkynyl-pyrimidine PNA units. Synthesis, binding properties, and enzymatic stability.

Abstract Three chimeric dimer synthons (oeg_tNHT, oeg_upNHT and oeg_uhNHT) containing thymine (t), 5-(l-propynyl)-uracil (up) and 5-(1-hexyn-1-yl)-uracil (uh) PNA units with N-(2-hydroxyethyl)glycine (oeg) backbone were synthesized in solution and incorporated into T20 oligonucleotide analogues, using standard P-amidite chemistry. Insertion of dimer blocks led to destabilization of duplexes with dA20 target. The smallest T m drops were found for chimeras containing oeg_upNHT dimers. Incorporation of the chimeric synthons into the 3′-end of T20 brought about growing resistance to 3′-exonucleolytic (SV PDE) cleavage in the order of oeg_tNHT < oeg_upNHT < oeg_uhNHT. Due to different endonuclease activities of 3′- and 5′-exonucleases applied, placing of five consecutive dimers at the 5′-terminus resulted in a relatively smaller, but also side-chain dependent, stabilization towards the hydrolysis by 5′-exonuclease (BS PDE). Neither exonucleases (SV and BS PDE) nor an endonuclease (Nuclease P1) could hydrolyse the unnatural phosphodiester bond linking the 3′-OH of thymidine to the terminal OH of N-(2-hydroxyethyl)glycine PNA backbone.

Structural parameters in the microsomal hydrolysis of 3-acyloxy-l, 4-benzodiazepines and the multiplicity of the esterases involved

SummaryThe biotransformation of several prodrug-type esters of centrally acting 1, 4-benzodiazepines was studied. Their rates of hydrolysis catalyzed by the hepatic microsomal fraction of mice were measured by pH-stat. The heterogeneity of the microsomal esterases was investigated with induction by phenobarbital and with inhibition by DFP. The resulting changes in esterase activity indicated that the phenyl-substituted esters separate from the homogenous sets of oxazepam and lorazepam esters. Regression analysis of the relative hydrolysis rates of the homogenous ester sets revealed a similar dependence on the steric ES′ the polar σ* and hydrophobic ΔRM terms of the acyl moiety. The role of the polar term shows that a nucleophilic attack of the acyl moiety determines the hydrolysis rate. The role of hydrophobicity can be attributed to its interrelation with the steric parameter. The common equations for the aliphatic esters of oxazepam and larazepam suggest the similar nature of the esterases in question and the same catalytic mechanism. Different 3-acetoxy-l, 4-benzodiazepines were also synthetised and their maximal hydrolysis rates were quite different. This excludes the possibility that the deacylation step of the enzymes is rate-determining. Instead, our data suggest that acylation of the microsomal esterases is rate-limiting for the hydrolysis of the aliphatic esters of 3-OH-benzodiazepines.

Synthesis, biophysical, and biochemical properties of PNA-DNA chimeras.

Abstract Three PNA-DNA chimeric dimer synthons (tT, upT and uhT, see Sch. 1) have been synthesized in solution and used to make T20-analogue chimeras applying standard solid-phase DNA synthesis protocol. Duplex forming ability of chimeras with dA20 and their hydrolyses by 3′- and 5′-exonucleases (snake venom and bovine spleen phosphodiesterase, respectively) have been investigated.

SYNTHESIS AND ENZYMATIC CHARACTERIZATION OF P1-THIO-P2-OXO TRIDEOXYNUCLEOSIDE DIPHOSPHATES HAVING AZT, FdU, OR dT AT THE 3′-POSITION

ABSTRACT Model compounds for oligonucleotide-prodrugs, P1-thio-P2-oxo-trideoxyribonucleoside diphosphates: d[GsCoX] and d[TsAoX] (X=AZT, FdU or dT) have been prepared, and their hydrolyses by snake venom phosphodiesterase and nuclease S1 are described.

Kinetic isotope effect in the metabolic demethylation of temazepam

The kinetics of the metabolic demethylation of temazepam were examined. Oxidative cleavage of the 1-methyl C–H bonds is rate-determining in the 13 000 g supernatant of mouse liver homogenate, as shown by the primary deuterium isotope effect (3.6) for demethylation of 1-CD3-labelled temazepam. With a reduced supply of NADPH, reduction of the cytochrome P-450–substrate complex becomes rate-limiting. Decomposition of the 1-N-hydroxymethyl intermediate is fast enough not to influence the rate of demethylation.

Stereoselective labelling of racemic oxazepam acetate and its use in studying stereoselective binding to human serum albumin

Stereoselective binding of a racemate to a chiral adsorbent allows highly stereoselective labelling of racemic mixtures by an ultrafiltration method; the method can be used to study binding equilibria.