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ABSTRACT: A general three-component triple cascade reaction through an iminium-enamine-iminium sequential activation initiated by a hetero-Michael addition to alpha,beta-unsaturated aldehyde affords [3.2.0]heterobicycles in high diastereoselectivity. The rate and diastereoselectivity of the reaction depended on the (E)-4-heterocrotonate and size of the secondary amine. The enantiomers of the major diastereoisomer of oxa- and azabicyclo[3.2.0]heptane derivatives were separated by enzymatic kinetic resolution with immobilized Candida Antarctica Lipase B (CALB), with E values up to 153. The absolute configuration of the nonacylated enantiomer of oxabicyclo[3.2.0]heptane was determined by single crystal X-ray analysis.
The Journal of Organic Chemistry 10/2012; · 4.45 Impact Factor
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ABSTRACT: A new methodology was developed for the synthesis of enantiomerically enriched 3,3-disubstituted 3-chlorooxindoles 3 via a Michael addition of 3-chloroxindoles to nitroolefins 2, catalyzed by chiral squaramide 10. Products with adjacent quaternary-tertiary centers were isolated in excellent yields (up to 99%), high diastereoselectivities (up to 11:1), and enantiomeric purities (up to 92%). This is the first example where 3-chloroxoindoles 1 have been used as nucleophiles in a highly stereoselective organocatalytic reaction.
Organic Letters 09/2012; 14(18):4922-5. · 5.86 Impact Factor
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ABSTRACT: The organocatalytic Michael addition of malonates to symmetric unsaturated 1,4-diketones catalyzed by thiourea and squaramide derivatives with Cinchona alkaloids afforded the formation of a new C-C bond in high yields (up to 98%) and enantiomeric purities (up to 93%). The absolute configuration of the product was suggested from comparison of the experimental and calculated VCD spectra of the reaction product 3a.
Beilstein Journal of Organic Chemistry 01/2012; 8:1452-7. · 2.52 Impact Factor
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ABSTRACT: A new enantiomerically pure carbacyclic nucleoside analogue with bimorpholine as a nonaromatic nucleobase was synthesized. The nucleoside analogue and bimorpholine were tested for cytotoxicity using an MTT assay and the xCELLigence System. Both assays revealed that compound 3 was highly cytotoxic at a 50 μM concentration while the cytotoxic effect of compound 1 was much less prominent. No antiretroviral activity was detected for this compound. In contrast, it acted as a potent inhibitor of hepatitis C virus (HCV) replication. Most likely this effect originates largely from the cytotoxicity of the compound; however, it is possible that a specific mechanism of HCV inhibition also exists.
Nucleosides Nucleotides & Nucleic Acids 11/2011; 30(11):897-907. · 0.90 Impact Factor
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ABSTRACT: A new general methodology was developed to access highly enantiomerically enriched 1,4-dihydropyridines (DHPs) 3 via an organocatalytic asymmetric aza-ene-type cascade reaction, cocatalyzed by (S)-diarylprolinol-TMS ether V and benzoic acid (BA). Both aliphatic and aryl enals 1 reacted smoothly with enaminones and β-enamino esters 2, affording highly functionalized 1,4-DHPs 3 in high enantioselectivities and good yields.
The Journal of Organic Chemistry 02/2011; 76(6):1538-45. · 4.45 Impact Factor
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ABSTRACT: Spin-spin coupling constants between nuclei in NMR spectroscopy reflect their spatial arrangement. A number of calculation methods, applying different levels of theory, have been developed to support the stereochemical assignment of novel compounds. Nevertheless, revisions of the assignment of structures in the literature are not rare. In the present work, the reliability of the calculation methods amenable for a theoretical prediction of spin-spin coupling constants of vicinal protons to support correct stereochemical assignment of substitution at five-membered rings of 3-alkoxy-6,7-epoxy-2-oxabicyclo[3.3.0]octanes was studied. Experimental (3)J(H,H) coupling constants were compared with the coupling constants calculated for all possible diastereomers. The fully quantum chemical approach provided theoretical (3)J(H,H) coupling constants with an absolute deviation of no more than 1.1 Hz for 91% of the experimentally studied coupled spins, whereas the methods without quantum chemical geometry optimization resulted in completely unreliable predictions. Consequently, for a reliable stereochemical assignment of small and medium size molecules, the protocol for calculating the coupling constants based on the results of the quantum chemical geometry optimization is recommended.
Magnetic Resonance in Chemistry 02/2011; 49(2):76-82. · 1.44 Impact Factor
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ABSTRACT: Spin-spin coupling constants between nuclei in NMR spectroscopy reflect their spatial arrangement. A number of calculation methods, applying different levels of theory, have been developed to support the stereochemical assignment of novel compounds. Nevertheless, revisions of the assignment of structures in the literature are not rare. In the present work, the reliability of the calculation methods amenable for a theoretical prediction of spin-spin coupling constants of vicinal protons to support correct stereochemical assignment of substitution at five-membered rings of 3-alkoxy-6,7-epoxy-2-oxabicyclo[3.3.0]octanes was studied. Experimental (3)J(H,H) coupling constants were compared with the coupling constants calculated for all possible diastereomers. The fully quantum chemical approach provided theoretical (3)J(H,H) coupling constants with an absolute deviation of no more than 1.1 Hz for 91% of the experimentally studied coupled spins, whereas the methods without quantum chemical geometry optimization resulted in completely unreliable predictions. Consequently, for a reliable stereochemical assignment of small and medium size molecules, the protocol for calculating the coupling constants based on the results of the quantum chemical geometry optimization is recommended. Copyright © 2011 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry 01/2011; · 1.44 Impact Factor
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ABSTRACT: A novel multicomponent cascade reaction led to the formation of a strained 3-azabicyclo[3.2.0]heptane derivative 4. The unstable ester 4 was reduced in a one-pot procedure to a stable alcohol 6. The formation of the bicyclic product is highly diastereoselective, predominantly affording one diastereoisomer. The obtained azabicycloheptanes are important pharmacophores.
Organic Letters 04/2010; 12(10):2230-3. · 5.86 Impact Factor
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ABSTRACT: A complex derived from the enantiomeric bipiperidine and copper(II) acetate hydrate is an efficient catalyst for the enantioselective Henry reaction. The easy availability of both catalyst components, mild reaction conditions, high yield, and good to excellent enantioselectivity make the catalyst useful for everyday practice.
The Journal of Organic Chemistry 02/2010; 75(4):1313-6. · 4.45 Impact Factor
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ABSTRACT: A complex derived from the enantiomeric bipiperidine and copper(II) acetate hydrate is an efficient catalyst for the enantioselective Henry reaction. The easy availability of both catalyst components, mild reaction conditions, high yield, and good to excellent enantioselectivity make the catalyst useful for everyday practice.
01/2010;
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ABSTRACT: The chiral title compound, C(15)H(22)O(5), is an inter-mediate in the total synthesis of biologically active 9,11-secosterols. In the crystal, the cyclo-hexane rings are trans-fused and both adopt chair conformations. In the crystal, mol-ecules are loosely held together in a layer parallel to (100) by weak inter-molcular C-H⋯O hydrogen bonds accepted by carbonyl O atoms of the acetyl groups.
Acta Crystallographica Section E Structure Reports Online 01/2010; 66(Pt 10):o2584. · 0.35 Impact Factor
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ABSTRACT: A general method for the synthesis of 5,5′-disubstituted bimorpholines is proposed. According to the method, methyl-substituted and benzyl-substituted compounds were synthesized, starting from tartaric ester acetal. Target compounds were obtained in good yield and high enantiomeric purity.
Synthetic Communications 01/2010; 40(2):266-281. · 1.06 Impact Factor
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ABSTRACT: The utility of C(2)-symmetric bipiperidine and bimorpholine derivatives as organocatalysts in the Michael addition of enamine intermediates formed from aldehydes to nitroolefins has been demonstrated. The best results were obtained when the reaction was run in the presence of (2R,2'R)-N-iPr-bipiperidine. The products were formed via an enamine intermediate with high diastereo- and enantioselectivity with relatively short reaction times.
The Journal of Organic Chemistry 05/2009; 74(10):3772-5. · 4.45 Impact Factor
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ABSTRACT: Monosalts of N-substituted bimorpholine derivatives are efficient organocatalysts in intramolecular and intermolecular aldol reactions. The properties of the catalysts can be tuned either by the selection of an appropriate acid for the salt formation or by the change of a substituent at the nitrogen atom. In aldol condensation, i-Pr-substituted bimorpholine is the most stereoselective catalyst affording products in high yield with enantioselectivities up to 95% ee.
The Journal of Organic Chemistry 08/2007; 72(14):5168-73. · 4.45 Impact Factor
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ABSTRACT: Synthesis of regioisomeric cyclopentanones 3-alkyloxy-2-oxabicyclo[3.3.0]octan-6-one (overall yield up to 34%) and 3-alkyloxy-2-oxabicyclo[3.3.0]octan-7-one (overall yield up to 18%) in four steps, starting from enantiomerically pure (–)-(1S,5R)-2-oxabicyclo[3.3.0]oct-6-en-3-one is described.
Proceedings of the Estonian Academy of Sciences 01/2007; 56(1):3-13. · 0.49 Impact Factor
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ABSTRACT: An efficient synthesis of bis-nor Wieland-Miescher ketone and its derivatives starting from commercially available 2-allyl-2-methylcyclopenta-1,3-dione is described.
Synthesis 01/2005; 18:3147 - 3151. · 2.47 Impact Factor
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ABSTRACT: Electrophoretically mediated microanalysis (EMMA) was used to monitor the on-column complexation of Pb2+ and fulvic acid (FA). Electropherograms revealed several characteristic regions, the areas of which correlate with the metal concentration. The analysis of the electropherograms suggests that at least two different complexes are formed. Therefore, the EMMA is a prospective technique for structural investigation of humic substances (HS).
Journal of Chromatography 12/2004; 1057(1-2):253-6. · 4.53 Impact Factor
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ABSTRACT: Capillary electrophoresis (CE) has been used to characterize humic acid (HA) aggregation. It was found that when pumping HA solution through the capillary at a constant flow rate with no electric field, the number of spikes could be reduced by filtration of the solution. Applying high voltage (30 kV), the amount of spikes increased again. This is associated with the formation of new aggregates caused by electric field. Aggregation is influenced by the concentration of HA, applied voltage and presence of imidazole in the solution. It is supposed that this phenomenon is characteristic of all solutions that can form colloidal particles: in beta-cyclodextrin solution, similar spikes appear in a high-voltage electric field.
Journal of Chromatography 09/2004; 1045(1-2):253-8. · 4.53 Impact Factor
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ABSTRACT: Scope and GoalHumic substances (HSs) are the product of microbial degradation, chemical polymerisation and oxidation of organic matter. Scope and GoalHumic substances (HSs) are the product of microbial degradation, chemical polymerisation and oxidation of organic matter.
HSs can be divided into different fractions: humic acid (HA), hymatomelanic acid (HMA), fulvic acid (FA) and humin. HSs play HSs can be divided into different fractions: humic acid (HA), hymatomelanic acid (HMA), fulvic acid (FA) and humin. HSs play
a fundamental role in accumulation and exchange processes of chemical compounds (metals and organic pollutants) in the environment. a fundamental role in accumulation and exchange processes of chemical compounds (metals and organic pollutants) in the environment.
HSs can form soluble complexes that migrate long distances or precipitate, carrying bound cations with them. The migration/precipitation HSs can form soluble complexes that migrate long distances or precipitate, carrying bound cations with them. The migration/precipitation
abilities depend on the metal ion, the ion charge, the degree of ionisation of the organic molecule, the ionic strength of abilities depend on the metal ion, the ion charge, the degree of ionisation of the organic molecule, the ionic strength of
the media, and the location of the metal ion. the media, and the location of the metal ion.
ObjectiveEstonia is rich in the Baltic Sea and lake sediments. Historically, mud has been used in human treatment as a curative mud. ObjectiveEstonia is rich in the Baltic Sea and lake sediments. Historically, mud has been used in human treatment as a curative mud.
High-molecular HSs are an important part of curative mud and they have a strong effect on its properties. The curative mud High-molecular HSs are an important part of curative mud and they have a strong effect on its properties. The curative mud
which is used in human therapy may not be polluted with different organic and inorganic contaminants. The aim of this work which is used in human therapy may not be polluted with different organic and inorganic contaminants. The aim of this work
is to characterise and compare HSs isolated from the Baltic Sea mud (Haapsalu Bay) and from the sediments of Lake Ermistu is to characterise and compare HSs isolated from the Baltic Sea mud (Haapsalu Bay) and from the sediments of Lake Ermistu
(Estonia). (Estonia).
Results and ConclusionsWe determined the yield of basic extraction of different HSs components from mud in the course of separation. We found that Results and ConclusionsWe determined the yield of basic extraction of different HSs components from mud in the course of separation. We found that
acid pre-treatment of mud increased the amount of extracted HSs more in the sea mud than in the lake mud. These results show acid pre-treatment of mud increased the amount of extracted HSs more in the sea mud than in the lake mud. These results show
that HSs are bound to the inorganic/organic structure of mud and are released during prolonged treatment with an acid. that HSs are bound to the inorganic/organic structure of mud and are released during prolonged treatment with an acid.
We performed elemental analysis of the different fractions of HS extracts. HMA fractions had the highest carbon content and We performed elemental analysis of the different fractions of HS extracts. HMA fractions had the highest carbon content and
the lowest nitrogen content. HMA contains more polysaccharides than amino acid residues. These subunits may cause a better the lowest nitrogen content. HMA contains more polysaccharides than amino acid residues. These subunits may cause a better
solubility of HMA in water as compared to HA. Acid pre-treatment of the natural sea and the lake mud diminished the content solubility of HMA in water as compared to HA. Acid pre-treatment of the natural sea and the lake mud diminished the content
of carbon in most of the HS fractions. The content of nitrogen in the sea and in lake FA diminished by about two times. of carbon in most of the HS fractions. The content of nitrogen in the sea and in lake FA diminished by about two times.
We determined the metal content in the mud and its HS fractions. We found that the concentration of heavy metals Pb and Cr We determined the metal content in the mud and its HS fractions. We found that the concentration of heavy metals Pb and Cr
is lower than <0.08 mg/kg. As expected, the total metal concentration is considerably lower in the lake than in the sea mud. is lower than <0.08 mg/kg. As expected, the total metal concentration is considerably lower in the lake than in the sea mud.
Acid pre-treatment of mud shows that the sea HA forms more stable Fe and Mg complexes, while the sea HMA contains more stable Acid pre-treatment of mud shows that the sea HA forms more stable Fe and Mg complexes, while the sea HMA contains more stable
Zn and Cu complexes. The lake HSs result in more stable Mg complexes with HA and HMA fractions. Sea FA binds Cu and Mg better, Zn and Cu complexes. The lake HSs result in more stable Mg complexes with HA and HMA fractions. Sea FA binds Cu and Mg better,
but lake FA is more effective in binding Zn. To compare the amount of metals extracted from HA, HMA, FA (with that, remains but lake FA is more effective in binding Zn. To compare the amount of metals extracted from HA, HMA, FA (with that, remains
in HS fractions), the metal concentration in the alkaline full extract of the sea mud was determined. Alkaline treatment removed in HS fractions), the metal concentration in the alkaline full extract of the sea mud was determined. Alkaline treatment removed
0.8% Mg, 7.9% Cu, 5.2% Zn and 3.8% Fe together with HSs from the sea mud, the rest remained in humin and in the mineral part 0.8% Mg, 7.9% Cu, 5.2% Zn and 3.8% Fe together with HSs from the sea mud, the rest remained in humin and in the mineral part
of the mud. The following work-up was additionally carried out for most of the metals. So, we found that there was only 1.7% of the mud. The following work-up was additionally carried out for most of the metals. So, we found that there was only 1.7%
of Fe, 2.1 % of Mg, 23.2% of Zn and 45.2% of Cu left in HA, HMA and the FA fraction (as a sum) from the total amount of those of Fe, 2.1 % of Mg, 23.2% of Zn and 45.2% of Cu left in HA, HMA and the FA fraction (as a sum) from the total amount of those
metals in HSs. This means that Cu is the metal most strongly bound to HSs. On the bases of HS separation data we found that metals in HSs. This means that Cu is the metal most strongly bound to HSs. On the bases of HS separation data we found that
the order of stability of the metal-humate complexes is Cu>Zn>Mg>Fe. the order of stability of the metal-humate complexes is Cu>Zn>Mg>Fe.
The ultraviolet spectra of HA, HMA and FA revealed that HMA had the biggest molar absorption and calculated aromaticity. Recommendations The ultraviolet spectra of HA, HMA and FA revealed that HMA had the biggest molar absorption and calculated aromaticity. Recommendations
and Outlook. The characteristics of HSs, isolated from the Baltic Sea and Lake Ermistu mud reveal the difference of HSs from and Outlook. The characteristics of HSs, isolated from the Baltic Sea and Lake Ermistu mud reveal the difference of HSs from
the sea and the lake mud. Also, different properties of HS fractions are observed. Metals are concentrated variously in different the sea and the lake mud. Also, different properties of HS fractions are observed. Metals are concentrated variously in different
HS fractions. In all cases the content of Pb and Cr was low, meaning that the mud preparations are nontoxic in respect to HS fractions. In all cases the content of Pb and Cr was low, meaning that the mud preparations are nontoxic in respect to
these metals. The order of stability of metal-humate complexes is Cu>Zn>Mg>Fe. The order of affinity of metals to HS fractions these metals. The order of stability of metal-humate complexes is Cu>Zn>Mg>Fe. The order of affinity of metals to HS fractions
obtained have to be extended to other metals of environmental interest. The ability of HSs to bind metals may make them a obtained have to be extended to other metals of environmental interest. The ability of HSs to bind metals may make them a
candidate for natural, environmentally safe substances to concentrate hazardous metals and to remove them from natural water candidate for natural, environmentally safe substances to concentrate hazardous metals and to remove them from natural water
reservoirs. reservoirs.
Journal of Soils and Sediments 02/2004; 4(1):24-29. · 1.86 Impact Factor
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ABSTRACT: The results of the oxidation of 6-methyl-7-tert-butyldimethylsilyloxybicyclo[4.4.0]dec-1-en-3-one and its derivative 6-methyl-7-tert-butyldimethylsilyloxybicyclo[4.4.0]dec-10-en-3-one by O 2 , H 2 O 2 , and t-BuOOH under basic conditions in the presence of K 2 CO 3 , Et 3 N, and t-BuOK are reported. The relevant γ-hydroxyenones, 1,4-diketoenone, and 1,2-diketoenone were isolated. The oxidation was found to proceed through the dienolate formation. A possible mechanism for α-and γ-oxidation is discussed.
Proceedings of the Estonian Academy of Sciences 01/2001; 50(3):138-146. · 0.49 Impact Factor
