A compound of unusual structure was isolated from red beetroot (Beta vulgaris) peel extract and i... more A compound of unusual structure was isolated from red beetroot (Beta vulgaris) peel extract and identified as 5,5′ ,6,6′-tetrahydroxy-3,3′-biindolyl based on the combination of NMR and MS studies.
Changes in morphology and chemistry of leaf surface in response to herbivore damage may increase ... more Changes in morphology and chemistry of leaf surface in response to herbivore damage may increase plant resistance to subsequent herbivore attack; however, there is lack of studies on induced responses of glandular trichomes and their exudates in woody plants and on effects of these changes on herbivores. We studied delayed induced responses in leaf surface traits of five clones of silver birch (Betula pendula Roth) subjected to various types of mechanical defoliation and simulated winter browsing. Glandular trichome density and concentrations of the majority of surface lipophilic compounds increased in trees defoliated during the previous summer. This induced response was systemic, since control branches in branch defoliated trees responded to the treatments similarly to defoliated branches, but differently from control trees. In contrast to defoliation treatments, simulated winter browsing reduced glandular trichome density on the following summer and had fewer effects on individual surface lipophilic compounds. Moreover, constitutive density of glandular trichomes was negatively correlated with induced total amount of lipophilic compounds per trichome, indicating a trade-off between constitutive and induced resistance in silver birch. Induced changes in leaf surface traits had no significant effect on leaf damage by chewers, miners and gall mites, but increased susceptibility of birch trees to aphids. However, leaf damage by chewers, miners and gall mites in defoliated (but not in control) trees was correlated with concentrations of some fatty acids and triterpenoids, although the direction of relationships varied among herbivore species. This indicates that induction of surface lipophilic compounds may influence birch resistance to herbivores. Our study thus demonstrated both specificity of elicitation of induced responses of birch leaf surface traits by different types of damage and specificity of the effects of these responses on different types of herbivores.
The energies of the preferred conformations of four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3... more The energies of the preferred conformations of four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were investigated by DFT methods. Following geometry optimization at the B3LYP/6-31G(d,p) level, both the proton chemical shifts and the vicinal coupling constants between H-4a and the H-4 and H-5 protons were calculated at the B3LYP/cc-pVTZ level and compared to the previously experimentally measured values. The agreement between the calculated and the experimental chemical shifts was found to be good. Similarly, the agreement between the calculated and the experimental vicinal coupling constants was also found to be good, thus providing a methodology for determining the conformational equilibria of such systems that is comparable in many respects to experimental approaches such as variable-temperature NMR or to the use of model coupling constant values, when available, from analogous compounds.
A simply connected compact Kaehler manifold X is an irreducible symplectic manifold if there is a... more A simply connected compact Kaehler manifold X is an irreducible symplectic manifold if there is an everywhere non-degenerate holomorphic 2-form Ω on X with . By definition, X has even complex dimension. There is a canonical symmetric form q X on H 2 (X, Z), which is called the Beauville-Bogomolov form (cf. [Be]). On the other hand, since X is Kaehler, H 2 (X, Z) has a natural Hodge structure of weight 2. If two irreducible symplectic manifolds X and Y are bimeromorphically equivalent, then there is a natural Hodge isometry between (H 2 (X, Z), q X ) and Debarre [De] has constructed bimeromorphically equivalent irreducible symplectic manifolds X and Y such that X and Y are not isomorphic. This is a counter-example to the following problem. Biregular Torelli Problem: Let X and Y be irreducible symplectic manifolds of the same dimension such that there is a Hodge isometry φ : (H 2 (X, Z), q X ) → (H 2 (Y, Z), q Y ). Is X isomorphic to Y ? In this paper we shall give a counter-example to the following problems. Bimeromorphic Torelli Problem (cf. (5.10)], [Huy, (10.1)]): Let X and Y be irreducible symplectic manifolds of the same dimension such that there is a Hodge isometry φ : (H 2 (X, Z), q X ) → (H 2 (Y, Z), q Y ). Are X and Y bimeromorphically equivalent ? Polarized Torelli Problem: Let (X, L) and (Y, M ) be polarized irreducible symplectic manifolds of the same dimension such that there is a Hodge isometry In the paragraphs 1, ..., 4 we construct a counter-example to Bimeromorphic Torelli Problem, and in 5 we discuss Polarized Torelli Problem.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
The following major phenolics with non-flavonoid structure were identified from leaves of Betula ... more The following major phenolics with non-flavonoid structure were identified from leaves of Betula pubescens (white birch) and Betula pendula (silver birch): 1-O-galloyl-/3-d-(2-O-acetyl)-glucopyranose, 1-(4"-hydroxyphenyl)-3'-oxopropyl-/3-d-glucopyranose, gallic, chlorogenic, neo-chlorogenic, c/s-and trans-forms of 3-and 5-pcoumaroylquinic acids. Chromatographic (analytical and preparative HPLC), chemical (hydrolysis) and spectroscopic (UV, ~H and 13C NMR, MS) techniques were applied for separation, isolation, purification and identification of these phenolics. Moreover, 33 low-molecular-mass phenolics were detected and quantitated and their occurrence was compared in leaves of white and silver birches.
The distribution of total phenolics and main betacyanins in red beetroot (Beta vulgaris) root was... more The distribution of total phenolics and main betacyanins in red beetroot (Beta vulgaris) root was determined. Also, the subsequent effects of cold storage on the content of total phenolics, main betacyanins (betanin and isobetanin), and the main known ferulic acid ester (β-D-fructofuranosyl-R-D-(6-O-(E)-feruloylglucopyranoside) were determined in the peel, which is the root part containing the largest amount of total phenolics. The content of total phenolics in the red beetroot water extracts was determined according to a modification of the Folin-Ciocalteu method and expressed as gallic acid equivalents (GAE). The compounds of interest were identified by HPLC-ESI-MS and NMR techniques, and the contents of compounds were determined by HLPC analyses. The total phenolic contents in various root parts were found to decrease in the order peel, crown, flesh. Significant differences in the contents of total phenolics and individual compounds were found when the effect of cold storage (5 °C, 0-196 days) on the constituents of the peel from intact roots was examined. In addition to the betacyanins of red beetroot peel found in our earlier study, tentative identifications of betanidin and feruloylamaranthin were made.
Four cultivars of red beetroot (Beta vulgaris) were evaluated with respect to their betalain and ... more Four cultivars of red beetroot (Beta vulgaris) were evaluated with respect to their betalain and phenolic contents. The compounds were analysed using HPLC and identified by HPLC-DAD, HPLC-ESI-MS and NMR techniques. Betalains (vulgaxanthins I and II, betanin and isobetanin) and phenolics [5,5',6,6'-tetrahydroxy-3,3'-biindolyl, feruloylglucose and were determined in different parts of the root; betalains were analysed separately in the water extract and phenolics in the fractionated 80% aqueous methanol extract (betalain-free water fraction). In each cultivar, both betanin and isobetanin were found in greater amounts in the peel than in the flesh. A similar trend was not observed in the distribution of vulgaxanthins. The three studied phenolics appeared in all root parts of the beetroot cultivars with the flesh generally containing the least content. Additionally, two phenolic amides (N-trans-feruloyltyramine and N-trans-feruloylhomovanillylamine) and four flavonoids (betagarin, betavulgarin, cochliophilin A and dihydroisorhamnetin) were detected in the fractionated 80% aqueous methanol peel extracts (acetonitrile fraction) of beetroot.
Collection of Czechoslovak Chemical Communications, 2004
The structure, fluorescence, biological properties and S(N)-methylation reactions of ten 1,1-alky... more The structure, fluorescence, biological properties and S(N)-methylation reactions of ten 1,1-alkyl/aryl-disubstituted 3-(acridin-9-yl)thioureas 4 have been studied. Various reaction conditions allowed to obtain corresponding S-methyl 5 and S,N-dimethyl derivatives 6 in good yields. Structure and stereochemistry of the synthesized products are demonstrated by ab initio quantum chemical calculations and NMR techniques including PDQF-COSY, selective INEPT and NOE-difference experiments. Remarkable upfield 13C shifts of resonance signals of carbons C-4a, C-10a adjacent to acridine N-10 are characteristic of hydroiodides in contrast to free bases. Z configuration in isothioureas 7 with secondary amino rest in relation to E configuration of isothioureas with primary amino rest is discussed. Of the obtained products, some isothiourea salts 6 exhibit more than 2 orders of magnitude higher intensity of fluorescence, using 9-isothiocyanatoacridine as a standard. The obtained isothiourea hydro...
4)] with 2,6-trans-disubstitution has been prepared via the Grignard reaction of the correspondin... more 4)] with 2,6-trans-disubstitution has been prepared via the Grignard reaction of the corresponding axial 2-methoxy-1,3-dioxanes. Inspection of their 13 C NMR chemical shifts in respect of different substituent effects showed that 1 and 3 attain exclusively the 1,4-twist form whereas 2 and 4 still favor clearly the chair form due to the very strong steric interaction caused by the pseudo axial methyl groups at position 5. We also manage to equilibrate 1 and its cisepimer (5) although less than 1% of 4 was present at equilibrium. Thus only -G o = 12.9±0.5 kJ mol -1 could be given and it compares well with some literature values. Since the conformational energy of 4-axial methyl group in 5 is 12.2 kJ mol -1 the H(1,4-CT) is equal to 25 kJ mol -1 again in good agreement with an earlier estimate.
Aquatic humic (HA) and fulvic acids (FA) from two different origins were fractionated by the tand... more Aquatic humic (HA) and fulvic acids (FA) from two different origins were fractionated by the tandem size-exclusion chromatography and polyacrylamide gel electrophoresis (tandem SEC-PAGE). Three HA and two FA fractions exhibited different molecular sizes, electrophoretic mobilities and structural compositions based on elemental analyses and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) after tetramethyl-ammonium hydroxide (TMAH) treatment. Based on comparison of the size-separates and unfractionated bulk samples, the highest molecular size fractions of aquatic humic substances (HS) appear to be enriched in fatty acids (mainly C 16 and C 18), which are strictly linked to the humic core. This and the presence of low chain fatty acids and unsaturated and di-tri acids may suggest a microbial rather than a vascular plant origin. Even if the majority of lignin derived components in aquatic HS represent relatively high state of biodegradation (oxidation), a certain variation between different sizefractions also exists, supporting a high heterogeneity and composite nature of aquatic HS. Although SEC-PAGE fractionation appears to produce fairly homogeneous HS fractions, the absorption of some urea into of the separates cannot be completely avoided in this method, which limits its suitability for evaluating, especially the presence of N-containing constituents.
Reaction of diketene with N-substituted hydrazones of aldehydes and sterically crowded ketones le... more Reaction of diketene with N-substituted hydrazones of aldehydes and sterically crowded ketones leads to the corresponding N-acetoacetylhydrazones. With hydrazones of other ketones, this reaction yields cyclic isomers of N-acetoacetylhydrazones, namely, 2,5,5trisubstituted 4-acetylpyrazolidin-3-ones. The products where characterized by 1 H and 13 C NMR and electron ionization (EI) mass spectrometry. The EI mass spectra of the latter compounds and those of linear N-acetoacetylhydrazones show that in the gas phase their molecular ions attain predominantly similar forms as the respective neutral compounds in solutions. The mass-spectrometric fragmentation of both forms is characterized by retrosynthetic cleavages with the loss of neutral acetylketene. The imines produced from 2,5,5trisubstituted 4-acetyl-3-pyrazoli-dinones and primary amines predominantly exist in solutions in the enamine form. The EI mass spectra of these condensation products show that in the gas phase their molecular ions exist as pyrazolidinones. Characteristic fragmentation paths under the EI conditions include the pyrazolidine ring cleavages at the N1-C5 and C3-C4 bonds, with the positive charge mainly localized in the enamine moiety. There is no evidence for ring-chain isomerism of the compounds studied.
TriO -galloyl-2,4-chebuloyl-β-D-glucopyranoside (chebulinic acid, 1) and its novel thricehydrolyz... more TriO -galloyl-2,4-chebuloyl-β-D-glucopyranoside (chebulinic acid, 1) and its novel thricehydrolyzed derivative, 2,4-chebuloyl-β-D-glucopyranoside (galloyl-free chebulinic acid, 2), together with ellagic (3) and gallic acids (4), ethyl gallate (5), and luteolin (6), were isolated from the dried fruit of Terminalia chebula by bioactivity-guided fractionation of the extract. The compounds were variously identified on the basis of UV, MS, and NMR data. The latter proved that the glucose unit in 1 adopts a well defined 1 C 4 chair conformation with all substituents in axial positions. However, the absolute configurations of the three stereocenters in the chebuloyl group have been reassigned. For 2, a solvent-dependent mixture of both open-chain and cyclic pyranose forms was observed, the latter with a β configuration for the anomeric C-1 sugar carbon being heavily preferred in aqueous solution. In contrast to 1, a dynamic equilibrium consisting of several possible skew conformers (5 S 1 , 1 S 5 , 1 S 3 , and 2 S O) was designated for the sugar ring of 2. Antioxidant activities of the isolated compounds were assessed by measuring their ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and to inhibit the autoxidation of methyl linoleate in vitro. Of the isolated compounds, 1 showed the highest radical scavenging activity in the DPPH assay. For the methyl linoleate assay, 2 and 4−6 all exhibited strong antioxidant activities whereas the activities of 1 and 3 were only moderate. The fruit extract itself was highly effective in both tests.
The total reaction of 4-chloro-2-butanol 1 with NaOH(aq) is dominated (74%) by intramolecular sub... more The total reaction of 4-chloro-2-butanol 1 with NaOH(aq) is dominated (74%) by intramolecular substitution (SNi), besides which bimolecular substitution (SN2, 12%) and 1,4-elimination (i.e. fragmentation, contrary to earlier arguments) exhibit a significant contribution (11%). The total reaction of 3-chloro-1-butanol 2 instead is dominated by 1,4-(72%) and 1,2-elimination (25%), the substitution reactions being just observable (SNi 2% and SN2 1%). In 1 both the +I-effect and the conformational factors in the intermediate chloroalkoxy anion favour the SNi-reaction, whereas in 2 the situation is opposite and the location of Cl on a secondary carbon also makes the SNi-reaction less favourable. The relative proportions of 1,4-and 1,2-eliminations for 2 can be explained by thermodynamic basis since the consequent products are more stable than the corresponding products from 1. 1-chloro-2-propanol 3 and 2-chloro-1-propanol 4 both react with isopropyl amine giving the same product, namely 1-isopropylamino-2-propanol, which indicates that the reaction proceeds through the propylene oxide intermediate. Compound 1 also reacted with isopropyl amine predominantly via SNi-reaction, giving first 2-methyloxetane which then further gave 4isopropylamino-2-butanol, whereas 2 gave 3-isopropylamino-1-butanol through a direct SN2reaction.
Enthalpies of combustion of 2,2-trans-4,6- (1) and 4,4,6,6-tetramethyl- (2) and 2,4,4,6,6- (3) an... more Enthalpies of combustion of 2,2-trans-4,6- (1) and 4,4,6,6-tetramethyl- (2) and 2,4,4,6,6- (3) and 2,2,4,4,6-pentamethyl-1,3-dioxanes (4) were determined to estimate their enthalpies of formation in the gas phase. By comparing the latter with the corresponding enthalpies estimated based on the various bond–bond interactions allowed to determine the chair–2,5-twist energy difference (ΔHCT = 29.8 kJ mol–1) for 1 since C-13 shift correlations indicate that it escapes to the 2,5-twist form where the 2-methyl groups are isoclinal and 4- and 6-methyl groups pseudoequatorial to avoid syn-axial interactions. Compounds 2 and 3 in turn give the values 21.0 and 21.6 kJ mol–1 for the 4,6-diaxial Me,Me-interaction. Finally compound 4, which retains the chair conformation to avoid pseudoaxial interactions in the twist forms gives the value 19.5 kJ mol–1 for the 2,4-diaxial Me,Me-interaction indicating that its chair form appears to be somewhat deformed.
A compound of unusual structure was isolated from red beetroot (Beta vulgaris) peel extract and i... more A compound of unusual structure was isolated from red beetroot (Beta vulgaris) peel extract and identified as 5,5′ ,6,6′-tetrahydroxy-3,3′-biindolyl based on the combination of NMR and MS studies.
Changes in morphology and chemistry of leaf surface in response to herbivore damage may increase ... more Changes in morphology and chemistry of leaf surface in response to herbivore damage may increase plant resistance to subsequent herbivore attack; however, there is lack of studies on induced responses of glandular trichomes and their exudates in woody plants and on effects of these changes on herbivores. We studied delayed induced responses in leaf surface traits of five clones of silver birch (Betula pendula Roth) subjected to various types of mechanical defoliation and simulated winter browsing. Glandular trichome density and concentrations of the majority of surface lipophilic compounds increased in trees defoliated during the previous summer. This induced response was systemic, since control branches in branch defoliated trees responded to the treatments similarly to defoliated branches, but differently from control trees. In contrast to defoliation treatments, simulated winter browsing reduced glandular trichome density on the following summer and had fewer effects on individual surface lipophilic compounds. Moreover, constitutive density of glandular trichomes was negatively correlated with induced total amount of lipophilic compounds per trichome, indicating a trade-off between constitutive and induced resistance in silver birch. Induced changes in leaf surface traits had no significant effect on leaf damage by chewers, miners and gall mites, but increased susceptibility of birch trees to aphids. However, leaf damage by chewers, miners and gall mites in defoliated (but not in control) trees was correlated with concentrations of some fatty acids and triterpenoids, although the direction of relationships varied among herbivore species. This indicates that induction of surface lipophilic compounds may influence birch resistance to herbivores. Our study thus demonstrated both specificity of elicitation of induced responses of birch leaf surface traits by different types of damage and specificity of the effects of these responses on different types of herbivores.
The energies of the preferred conformations of four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3... more The energies of the preferred conformations of four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were investigated by DFT methods. Following geometry optimization at the B3LYP/6-31G(d,p) level, both the proton chemical shifts and the vicinal coupling constants between H-4a and the H-4 and H-5 protons were calculated at the B3LYP/cc-pVTZ level and compared to the previously experimentally measured values. The agreement between the calculated and the experimental chemical shifts was found to be good. Similarly, the agreement between the calculated and the experimental vicinal coupling constants was also found to be good, thus providing a methodology for determining the conformational equilibria of such systems that is comparable in many respects to experimental approaches such as variable-temperature NMR or to the use of model coupling constant values, when available, from analogous compounds.
A simply connected compact Kaehler manifold X is an irreducible symplectic manifold if there is a... more A simply connected compact Kaehler manifold X is an irreducible symplectic manifold if there is an everywhere non-degenerate holomorphic 2-form Ω on X with . By definition, X has even complex dimension. There is a canonical symmetric form q X on H 2 (X, Z), which is called the Beauville-Bogomolov form (cf. [Be]). On the other hand, since X is Kaehler, H 2 (X, Z) has a natural Hodge structure of weight 2. If two irreducible symplectic manifolds X and Y are bimeromorphically equivalent, then there is a natural Hodge isometry between (H 2 (X, Z), q X ) and Debarre [De] has constructed bimeromorphically equivalent irreducible symplectic manifolds X and Y such that X and Y are not isomorphic. This is a counter-example to the following problem. Biregular Torelli Problem: Let X and Y be irreducible symplectic manifolds of the same dimension such that there is a Hodge isometry φ : (H 2 (X, Z), q X ) → (H 2 (Y, Z), q Y ). Is X isomorphic to Y ? In this paper we shall give a counter-example to the following problems. Bimeromorphic Torelli Problem (cf. (5.10)], [Huy, (10.1)]): Let X and Y be irreducible symplectic manifolds of the same dimension such that there is a Hodge isometry φ : (H 2 (X, Z), q X ) → (H 2 (Y, Z), q Y ). Are X and Y bimeromorphically equivalent ? Polarized Torelli Problem: Let (X, L) and (Y, M ) be polarized irreducible symplectic manifolds of the same dimension such that there is a Hodge isometry In the paragraphs 1, ..., 4 we construct a counter-example to Bimeromorphic Torelli Problem, and in 5 we discuss Polarized Torelli Problem.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
The following major phenolics with non-flavonoid structure were identified from leaves of Betula ... more The following major phenolics with non-flavonoid structure were identified from leaves of Betula pubescens (white birch) and Betula pendula (silver birch): 1-O-galloyl-/3-d-(2-O-acetyl)-glucopyranose, 1-(4"-hydroxyphenyl)-3'-oxopropyl-/3-d-glucopyranose, gallic, chlorogenic, neo-chlorogenic, c/s-and trans-forms of 3-and 5-pcoumaroylquinic acids. Chromatographic (analytical and preparative HPLC), chemical (hydrolysis) and spectroscopic (UV, ~H and 13C NMR, MS) techniques were applied for separation, isolation, purification and identification of these phenolics. Moreover, 33 low-molecular-mass phenolics were detected and quantitated and their occurrence was compared in leaves of white and silver birches.
The distribution of total phenolics and main betacyanins in red beetroot (Beta vulgaris) root was... more The distribution of total phenolics and main betacyanins in red beetroot (Beta vulgaris) root was determined. Also, the subsequent effects of cold storage on the content of total phenolics, main betacyanins (betanin and isobetanin), and the main known ferulic acid ester (β-D-fructofuranosyl-R-D-(6-O-(E)-feruloylglucopyranoside) were determined in the peel, which is the root part containing the largest amount of total phenolics. The content of total phenolics in the red beetroot water extracts was determined according to a modification of the Folin-Ciocalteu method and expressed as gallic acid equivalents (GAE). The compounds of interest were identified by HPLC-ESI-MS and NMR techniques, and the contents of compounds were determined by HLPC analyses. The total phenolic contents in various root parts were found to decrease in the order peel, crown, flesh. Significant differences in the contents of total phenolics and individual compounds were found when the effect of cold storage (5 °C, 0-196 days) on the constituents of the peel from intact roots was examined. In addition to the betacyanins of red beetroot peel found in our earlier study, tentative identifications of betanidin and feruloylamaranthin were made.
Four cultivars of red beetroot (Beta vulgaris) were evaluated with respect to their betalain and ... more Four cultivars of red beetroot (Beta vulgaris) were evaluated with respect to their betalain and phenolic contents. The compounds were analysed using HPLC and identified by HPLC-DAD, HPLC-ESI-MS and NMR techniques. Betalains (vulgaxanthins I and II, betanin and isobetanin) and phenolics [5,5',6,6'-tetrahydroxy-3,3'-biindolyl, feruloylglucose and were determined in different parts of the root; betalains were analysed separately in the water extract and phenolics in the fractionated 80% aqueous methanol extract (betalain-free water fraction). In each cultivar, both betanin and isobetanin were found in greater amounts in the peel than in the flesh. A similar trend was not observed in the distribution of vulgaxanthins. The three studied phenolics appeared in all root parts of the beetroot cultivars with the flesh generally containing the least content. Additionally, two phenolic amides (N-trans-feruloyltyramine and N-trans-feruloylhomovanillylamine) and four flavonoids (betagarin, betavulgarin, cochliophilin A and dihydroisorhamnetin) were detected in the fractionated 80% aqueous methanol peel extracts (acetonitrile fraction) of beetroot.
Collection of Czechoslovak Chemical Communications, 2004
The structure, fluorescence, biological properties and S(N)-methylation reactions of ten 1,1-alky... more The structure, fluorescence, biological properties and S(N)-methylation reactions of ten 1,1-alkyl/aryl-disubstituted 3-(acridin-9-yl)thioureas 4 have been studied. Various reaction conditions allowed to obtain corresponding S-methyl 5 and S,N-dimethyl derivatives 6 in good yields. Structure and stereochemistry of the synthesized products are demonstrated by ab initio quantum chemical calculations and NMR techniques including PDQF-COSY, selective INEPT and NOE-difference experiments. Remarkable upfield 13C shifts of resonance signals of carbons C-4a, C-10a adjacent to acridine N-10 are characteristic of hydroiodides in contrast to free bases. Z configuration in isothioureas 7 with secondary amino rest in relation to E configuration of isothioureas with primary amino rest is discussed. Of the obtained products, some isothiourea salts 6 exhibit more than 2 orders of magnitude higher intensity of fluorescence, using 9-isothiocyanatoacridine as a standard. The obtained isothiourea hydro...
4)] with 2,6-trans-disubstitution has been prepared via the Grignard reaction of the correspondin... more 4)] with 2,6-trans-disubstitution has been prepared via the Grignard reaction of the corresponding axial 2-methoxy-1,3-dioxanes. Inspection of their 13 C NMR chemical shifts in respect of different substituent effects showed that 1 and 3 attain exclusively the 1,4-twist form whereas 2 and 4 still favor clearly the chair form due to the very strong steric interaction caused by the pseudo axial methyl groups at position 5. We also manage to equilibrate 1 and its cisepimer (5) although less than 1% of 4 was present at equilibrium. Thus only -G o = 12.9±0.5 kJ mol -1 could be given and it compares well with some literature values. Since the conformational energy of 4-axial methyl group in 5 is 12.2 kJ mol -1 the H(1,4-CT) is equal to 25 kJ mol -1 again in good agreement with an earlier estimate.
Aquatic humic (HA) and fulvic acids (FA) from two different origins were fractionated by the tand... more Aquatic humic (HA) and fulvic acids (FA) from two different origins were fractionated by the tandem size-exclusion chromatography and polyacrylamide gel electrophoresis (tandem SEC-PAGE). Three HA and two FA fractions exhibited different molecular sizes, electrophoretic mobilities and structural compositions based on elemental analyses and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) after tetramethyl-ammonium hydroxide (TMAH) treatment. Based on comparison of the size-separates and unfractionated bulk samples, the highest molecular size fractions of aquatic humic substances (HS) appear to be enriched in fatty acids (mainly C 16 and C 18), which are strictly linked to the humic core. This and the presence of low chain fatty acids and unsaturated and di-tri acids may suggest a microbial rather than a vascular plant origin. Even if the majority of lignin derived components in aquatic HS represent relatively high state of biodegradation (oxidation), a certain variation between different sizefractions also exists, supporting a high heterogeneity and composite nature of aquatic HS. Although SEC-PAGE fractionation appears to produce fairly homogeneous HS fractions, the absorption of some urea into of the separates cannot be completely avoided in this method, which limits its suitability for evaluating, especially the presence of N-containing constituents.
Reaction of diketene with N-substituted hydrazones of aldehydes and sterically crowded ketones le... more Reaction of diketene with N-substituted hydrazones of aldehydes and sterically crowded ketones leads to the corresponding N-acetoacetylhydrazones. With hydrazones of other ketones, this reaction yields cyclic isomers of N-acetoacetylhydrazones, namely, 2,5,5trisubstituted 4-acetylpyrazolidin-3-ones. The products where characterized by 1 H and 13 C NMR and electron ionization (EI) mass spectrometry. The EI mass spectra of the latter compounds and those of linear N-acetoacetylhydrazones show that in the gas phase their molecular ions attain predominantly similar forms as the respective neutral compounds in solutions. The mass-spectrometric fragmentation of both forms is characterized by retrosynthetic cleavages with the loss of neutral acetylketene. The imines produced from 2,5,5trisubstituted 4-acetyl-3-pyrazoli-dinones and primary amines predominantly exist in solutions in the enamine form. The EI mass spectra of these condensation products show that in the gas phase their molecular ions exist as pyrazolidinones. Characteristic fragmentation paths under the EI conditions include the pyrazolidine ring cleavages at the N1-C5 and C3-C4 bonds, with the positive charge mainly localized in the enamine moiety. There is no evidence for ring-chain isomerism of the compounds studied.
TriO -galloyl-2,4-chebuloyl-β-D-glucopyranoside (chebulinic acid, 1) and its novel thricehydrolyz... more TriO -galloyl-2,4-chebuloyl-β-D-glucopyranoside (chebulinic acid, 1) and its novel thricehydrolyzed derivative, 2,4-chebuloyl-β-D-glucopyranoside (galloyl-free chebulinic acid, 2), together with ellagic (3) and gallic acids (4), ethyl gallate (5), and luteolin (6), were isolated from the dried fruit of Terminalia chebula by bioactivity-guided fractionation of the extract. The compounds were variously identified on the basis of UV, MS, and NMR data. The latter proved that the glucose unit in 1 adopts a well defined 1 C 4 chair conformation with all substituents in axial positions. However, the absolute configurations of the three stereocenters in the chebuloyl group have been reassigned. For 2, a solvent-dependent mixture of both open-chain and cyclic pyranose forms was observed, the latter with a β configuration for the anomeric C-1 sugar carbon being heavily preferred in aqueous solution. In contrast to 1, a dynamic equilibrium consisting of several possible skew conformers (5 S 1 , 1 S 5 , 1 S 3 , and 2 S O) was designated for the sugar ring of 2. Antioxidant activities of the isolated compounds were assessed by measuring their ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and to inhibit the autoxidation of methyl linoleate in vitro. Of the isolated compounds, 1 showed the highest radical scavenging activity in the DPPH assay. For the methyl linoleate assay, 2 and 4−6 all exhibited strong antioxidant activities whereas the activities of 1 and 3 were only moderate. The fruit extract itself was highly effective in both tests.
The total reaction of 4-chloro-2-butanol 1 with NaOH(aq) is dominated (74%) by intramolecular sub... more The total reaction of 4-chloro-2-butanol 1 with NaOH(aq) is dominated (74%) by intramolecular substitution (SNi), besides which bimolecular substitution (SN2, 12%) and 1,4-elimination (i.e. fragmentation, contrary to earlier arguments) exhibit a significant contribution (11%). The total reaction of 3-chloro-1-butanol 2 instead is dominated by 1,4-(72%) and 1,2-elimination (25%), the substitution reactions being just observable (SNi 2% and SN2 1%). In 1 both the +I-effect and the conformational factors in the intermediate chloroalkoxy anion favour the SNi-reaction, whereas in 2 the situation is opposite and the location of Cl on a secondary carbon also makes the SNi-reaction less favourable. The relative proportions of 1,4-and 1,2-eliminations for 2 can be explained by thermodynamic basis since the consequent products are more stable than the corresponding products from 1. 1-chloro-2-propanol 3 and 2-chloro-1-propanol 4 both react with isopropyl amine giving the same product, namely 1-isopropylamino-2-propanol, which indicates that the reaction proceeds through the propylene oxide intermediate. Compound 1 also reacted with isopropyl amine predominantly via SNi-reaction, giving first 2-methyloxetane which then further gave 4isopropylamino-2-butanol, whereas 2 gave 3-isopropylamino-1-butanol through a direct SN2reaction.
Enthalpies of combustion of 2,2-trans-4,6- (1) and 4,4,6,6-tetramethyl- (2) and 2,4,4,6,6- (3) an... more Enthalpies of combustion of 2,2-trans-4,6- (1) and 4,4,6,6-tetramethyl- (2) and 2,4,4,6,6- (3) and 2,2,4,4,6-pentamethyl-1,3-dioxanes (4) were determined to estimate their enthalpies of formation in the gas phase. By comparing the latter with the corresponding enthalpies estimated based on the various bond–bond interactions allowed to determine the chair–2,5-twist energy difference (ΔHCT = 29.8 kJ mol–1) for 1 since C-13 shift correlations indicate that it escapes to the 2,5-twist form where the 2-methyl groups are isoclinal and 4- and 6-methyl groups pseudoequatorial to avoid syn-axial interactions. Compounds 2 and 3 in turn give the values 21.0 and 21.6 kJ mol–1 for the 4,6-diaxial Me,Me-interaction. Finally compound 4, which retains the chair conformation to avoid pseudoaxial interactions in the twist forms gives the value 19.5 kJ mol–1 for the 2,4-diaxial Me,Me-interaction indicating that its chair form appears to be somewhat deformed.
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