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Zoltán Tuba

Publications and source records attributed to Zoltán Tuba.

8 recordsLinked to original sources
PubMed2004

Steroid epimers studied by different mass spectrometric methods.

The combined use of different mass spectrometric ionization methods and MS/MS techniques provide the possibility to differentiate between stereoisomers or epimers. In this paper the mass spectral decomposition of 11alpha- and 11beta-substituted estrans was studied. Distinctive stereochemical effects have been observed in their fast atom bombardment product ion spectra. In the electron ionisation (EI) mode, the 5alpha- and 5beta-hydroxylated compounds showed significant differences in the abundance of water elimination. Mass spectrometry has proved to be an effective tool when stereoisomer steroids are compared.

Estranes↗
PubMed2003

Hydrolytic behavior of 5alpha-hydroxy-11beta- and 5beta-hydroxy-11alpha-substituted 19-norsteroids.

Teutsch G. and Bélanger A. treated 5alpha,10alpha epoxides with Grignard-reagents catalyzed by copper(I) ions. The reaction with steroidal epoxides proceeded with complete regio- and stereospecificity, leading exclusively to the 11beta-substituted compounds. According to our synthetic strategy, the 5,10 epoxide isomers were not separated; instead, the pure 11beta, and in some cases, 11alpha-substituted molecules were isolated after the conjugate addition of the Grignard-reagents, followed by deketalization and dehydration. Surprisingly, appearance of a third compound was generally observed beside the expected deprotected products, and this compound turned out to have a 3-keto-5(10),9(11) structural unit. Starting from pure 3-ethylenedioxy-5alpha,10alpha-epoxy-estr-9(11)-ene-17-one and 3-ethylenedioxy-5beta,10beta-epoxy-estr-9(11)-ene-17-one, four model compounds were synthesized (11alpha- and 11beta-[4-[1,1-(ethylenedioxy)-ethyl]phenyl]-estra-, as well as 11alpha- and 11beta-cyclohexyl-estra-derivatives) to study the process of deprotection and dehydration. 3-keto-5(10),9(11)-derivatives were found to form after deketalization and dehydration only from 11alpha-substituted derivatives, while 11beta-derivatives resulted in only the expected 3-keto-5,9-diene structure. After observing this remarkable difference between the behavior of 11alpha-, 11beta-substituted isomers we decided to take a closer look at the processes of deketalization and dehydration. In order to carry out the hydrolysis under mild conditions, pyridinium paratoluenesulfonate, a weakly acidic salt, was applied. All the intermediate products observed by TLC were isolated. The outcome of the deprotection and elimination reactions can be rationalized by two factors: conjugation of olefins (with the 3-oxo-group or the 11-phenyl group) and orientation of groups to be eliminated.

Catalysis↗
PubMed2003

Seasonal changes in the levels of compatible osmolytes in three halophytic species of inland saline vegetation in Hungary.

Seasonal changes in the leaf concentration of compatible osmolytes were investigated in three halophytic species (Lepidium crassifolium, Camphorosma annua and Limonium gmelini subsp. hungaricum) native to a salty-sodic grassland. The investigated species were shown to accumulate both carbohydrate- and amino acid-derived osmolytes. The leaf tissues of C. annua (Chenopodiaceae) preferentially stored glycine betaine and pinitol, while in L. gmelini (Plumbaginaceae) beta-alanine betaine, choline-O-sulphate, and pinitol were accumulated. In the leaves of L. crassifolium (Brassicaceae) a very high amount of proline, associated with a high level of soluble carbohydrates was found. Not only the biochemical nature of the osmolyte, but also the seasonal pattern of osmolyte accumulation showed significant species-specific fluctuations. In addition, the cellular levels of the observed osmolytes changed with the growth period and according to the environmental parameters. The highest concentrations of osmolytes were found in March, when low temperatures, hypoxic conditions and high salt concentrations were the main constraints to plant growth. The high structural diversity of osmolytes combined with their multifunctionality and the seasonal flexibility of the metabolism in plants facing multiple stresses is discussed.

Amaranthaceae↗
PubMed2002

Synthesis of steroidal diacyl hydrazines and their 1,3,4-oxadiazole derivatives.

Homogeneous catalytic hydrazinocarbonylation of some steroid derivatives possessing iodo-alkenyl moiety (17-iodo-androst-16-ene 1, 17-iodo-3-methoxy-estra-1,3,5(10),16-tetraene 2, 17-iodo-4-aza-4-methyl-androst-16-en-3-one 3 and 17-iodo-6beta-hydroxy-3alpha,5alpha-cycloandrost-16-ene 4) were carried out in the presence of a palladium catalyst, a base and acetic or benzoic hydrazide as the nucleophilic reagent. The corresponding N-acetamido-carbamoyl 1a-4a or N-benzamido-carbamoyl derivatives 1b-4b were obtained in high yields. Some of these derivatives served as starting materials for the synthesis of new steroidal 1,3,4-oxadiazole compounds.

Acetylation↗
PubMed2002

Microwave-assisted Stille-coupling of steroidal substrates.

Steroidal dienes were synthesised by Stille-coupling of the corresponding alkenyl iodides with vinyltributyltin under microwave irradiation in a domestic microwave oven in drastically reduced reaction times. Rate acceleration was observed also in the one-pot Stille-coupling-Diels-Alder reaction of 17-iodo-5alpha-androst-16-ene. Stereoselectivity of cycloaddition was slightly improved with diethyl maleate as the dienophile, compared to that achieved with thermal heating.

Alkenes↗
PubMed2002

Facile synthesis of 17-formyl steroids via palladium-catalyzed homogeneous carbonylation reaction.

17-formyl-androst-16-ene and its analogues were synthesized from the corresponding 17-iodo-16-ene derivatives in palladium-catalyzed formylation reaction using tributyltin hydride as hydrogen source under mild reaction conditions. The formation of androst-16-ene and its isomerization products, as well as that of analogous steroidal olefins as side-products, was found to be dependent on the reaction conditions. The formylation reaction tolerates various functional groups on the A and B rings of the steroids.

Catalysis↗
PubMed2002

Investigations on ecological effects of heavy metal pollution in Hungary by moss-dwelling water bears (Tardigrada), as bioindicators.

The authors demonstrate a possible relationship between the concentrations of metals (Cd, Cr, Cu, Fe, Ni, Pb, V, Zn) measured in mosses and the composition of Tardigrade species detected in the same samples. Cushions of Hypnum cupressiforme were collected at 18 sites distributed in the whole of Hungary to estimate the background air pollution, then analyzed by ICP-AES to determine the concentrations of heavy metals. Data reflect the expected correlation; elevated heavy metal contents decrease the number of water bear species and of specimens, and abundance of Tardigrada depends strongly on air pollution. Higher concentrations of cadmium and chromium seem to have particularly damaging and toxic influence on community structure. As the biologically relevant effects of pollution can only be evaluated by carrying out measurements on the organisms themselves, our method applied species of Bryophyte and of Tardigrade, as bioindicators were appeared to be an adequate method to show the effect of air pollution on abundance of water bears.

Air Pollutants↗