Ludvík Streinz

Comparison of methods employing gas chromatography retention data to determine vapour pressures at 298 K

Validity of five models suggested for expressing the relationship between vapour pressures and GC retention times measured on a non-polar capillary column were tested on a common set of compounds [five homologous series of the type H-(CH2)n-Y, where Y denotes Cl, Br, CHO, OCOCH3 and COOCH3, and n varies from 6 to 14]. Standard methods of statistical analysis, as well as vapour pressure values obtained independently from direct vapour pressure measurements were used as validity criteria. For the 40-compound data set examined, the methods provided vapour pressures agreeing within 9.2-24.7% (average absolute percent error) with direct experimental data.

In Vitro Transfection Mediated by Dendrigraft Poly(L-lysines): The Effect of Structure and Molecule Size

Dendritic poly(L-lysines) (DGL) constitute promising nanomaterials applicable as a nonviral gene-delivery vector. In this study, we evaluate the transfection abilities of four DGL generations with special emphasis on the systematic description of the relationship of how generation (i.e., molecule size) affects the transfection efficacy. Using Hep2 cells, we demonstrated that the capability of unmodified DGL to deliver plasmid is of a magnitude lower than that of jetPEI. On the other hand, employing the Hep2 cell line stably transduced with eGFP, we observed that DGL G5 delivers the siRNA oligonucleotide with the same efficiency as Lipofectamine 2000. In further experiments, it was shown that DGL affords excellent ability to bind DNA, protect it against DNase I attack, and internalize it into cells.

Chiral precursors of optically active juvenoids

Abstract For preparation of all four enantiomers of 2-(4-hydroxybenzyl)-1-cyclohexanol ( 1a–4a ) by biotransformation reactions, Saccharomyces cerevisiae (SC) and pig pancreatic lipase (PPL) were used in aqueous media. The THP-protected substrates ( 5b, 6b and 7b ) gave products with a good enantiomeric excess comparable with that of the CH 3 -protected substrates ( 5c, 6c and 7c ), whereas the deprotection was much easier in case of the THP-protected compounds.

Profiling and characterization of volatile secretions from the European stink bug Graphosoma lineatum (Heteroptera: Pentatomidae) by two-dimensional gas chromatography/time-of-flight mass spectrometry.

An efficient method combining the headspace solid-phase microextraction (HS-SPME) sampling procedure and comprehensive two-dimensional gas-chromatography/time-of-flight mass spectrometry (GC×GC/TOF-MS) was established to study the volatile secretion components of stink bugs (Heteroptera: Pentatomidae). The combined power of this approach is illustrated by the identification of fifty-seven compounds in the secretion of a European stink-bug representative, Graphosoma lineatum. (E)-4-oxohex-2-enal and (E)-dec-2-enal were found to be the major components in the adult bug secretions followed by lower amounts of n-alkenal (C₅-C₁₂), n-alkenyl acetate (C₅-C₁₁), n-alkane (C₁₁-C₁₇) homologs, dienals and other compounds. More than thirty known compounds have been identified that had not been described before in G. lineatum adults. Of these compounds, (E)-4-oxohex-2-enal is of particular interest, since its isolation and identification, while calling some previous reports into question, clearly demonstrates a potential ability of our approach to yield artifact-free secretion profiles.

Reduction of 2-Substituted Cyclohexanones by Saccharomyces Cerevisiae

An enzymatic reduction of 2-substituted cyclohexanones mediated by Saccharomyces cerevisiae was studied with respect to the stereochemical course and optical purity of the products. Reduction of ketones 1b-1f resulted in separable diastereoisomeric mixtures of cis- and trans-stereoisomers of 2-substituted cyclohexanols (2b-2f and 3b-3f) having the (S) absolute configuration at the chiral center bearing the hydroxyl functionality with high enantiomeric purity. Reduction of ketone 1a yielded mixture of cis-(1S, 2R)- and trans-(1R, 2R)-stereoisomers (2a and 3a) with lower enantiomeric purity. Changes in the nature of the C(2)-substituent affect the stereochemical course of the biotransformation. However, they significantly influenced the enantiomeric purity of the products. The diastereoselectivity of the process was studied as well; high diastereoselectivity was observed with the substrates 1a, 1e and 1f.

Lipase-mediated hydrolysis and esterification

Abstract Catalytic properties of commercially available lipases from Candida cylindracea, Rhizopus arrhizus, Aspergillus niger, Penicillium roqueforti, Geotrichum candidum , and porcine pancreas, and those of a crude lipase isolated from G. candidum were studied. Esterification of the racemic cis - and trans -isomers of 2-(4-methoxymethoxybenzyl)-1-cyclohexanol in organic solvents and hydrolysis of the racemic cis - and trans -isomers of 2-(4-methoxymethoxybenzyl)-1-cyclohexyl acetates were investigated, and all existing enantiomers of 2-(4-methoxymethoxy-benzyl)-1-cyclohexanol were prepared, isolated, and characterized by their physicochemical properties. Alcohols 2a and 2b and acetates 4a and 4b were found to be the principle products of enzymemediated reactions. The optimum reaction conditions for the enzyme-mediated hydrolysis of 1a and 1b and for the enzyme-mediated esterification of 3a or 3b were found, when G. candidum was used. We also compare the advantages and disadvantages of employing the appropriate enzymes.

New mimics of the acetate function in pheromone-based attraction

Several analogues of (Z)-8-dodecenyl acetate (1a), the major pheromone component of the Oriental fruit moth, Cydia molesta, with chloroformate and lactone functional groups in place of the acetate moiety, were synthesized and investigated for their biological activity at four evaluation levels, i.e. by electroantennography (EAG), electrosensillography (ESG), short-range sexual stimulation and activation in the flight-tunnel. We found very strict requirements on the shape as well as on the electron distribution of the acetate group for a productive interaction with the receptor. The behavioral results showed that, among the analogues investigated, the chloroformate 1b, alken-4-olide 2a and also dodecyl acetate (1c) possess significant (60-85%) inhibitory activities. Based on electrophysiological evidence demonstrating that (i) only 1b is competing with the major pheromone component 1a for the same receptor sites on the male antennal sensilla, (ii) 1c elicits moderate EAG but no ESG responses and (iii) 2a does not produce any electrophysiological response at all, three possible inhibitory mechanisms by which these analogues are acting could be distinguished.

Biotransformation of 2-(4-methoxybenzyl)-l-cyclohexanone by cell cultures ofSolatium aviculare

During the search for compounds with insect juvenile hormone activity, the biotransformation of 2-(4-methoxybenzyl)-l-cyclohexanone, of 2-(4-methoxybenzyl)-l-cyclohexanone ethylene acetal and of both isomers of 2-(4-methoxybenzyl)-l-cyclohexanol by plant cells was examined. The compounds were metabolized by cell suspension culture of Solatium aviculare Forst. The reaction conditions were optimized and the metabolic products isolated and identified. A scheme of biotransformation pathway has been proposed.

A new access to β-methyl substituted secondary alcohols. Application to the synthesis of 4-methylheptan-3-ol

Abstract All four stereoisomers of 4-methylheptan-3-ol were synthesized by a five-step route starting from 4-thianones. Key steps in the synthesis include: (a) reduction of 3-propyl-4-thianone to yield an easily separable isomeric mixture of cis - and trans -3-propyl-4-thianols; and (b) a highly efficient resolution of the particular cis / trans -isomers through a chromatographic separation of their respective esters with ( S )-chlorofluoroacetic acid. Subsequent hydrolysis and desulfurization gave the required compounds in 18% overall yield. All the stereoisomers are obtained with purities better than 90%.

Enzyme mediated hydrolysis of acetates

SummaryThe investigation of enzyme mediated hydrolysis of the respective cis- and trans-2-(4-methoxybenzyl)-1-cyclohexyl acetates has been provided using several lipases. A comparison of results obtained has been summarized in this paper.