Tonis Pehk

National Institute of Chemical Physics and Biophysics | KBFI

Scalable protocols of straightforward synthesis of enantiomeric γ‐(acyloxy)carboxylic acids and γ‐lactones are presented. The key step is lipase‐catalyzed stereoselective acylation of γ‐hydroxycarboxylic acid sodium salt in organic solvent followed by acidification of the product, extraction and acidic relactonization of the unreacted enantiomer. T...

Incorporating rigid cyclic acetal and ketal units into polymer structures is an important strategy toward recyclable high-performance materials from renewable resources. In the present work, citric acid, a widely used platform chemical derived from biomass, has been efficiently converted into di- and tricyclic diketones. Ketalization with glycerol...

A method for the synthesis of 9,11-secosteroids starting from the natural corticosteroid cortisol is described. There are two key steps in this approach, combining chemistry and synthetic biology. Stereo- and regioselective hydroxylation at C9 (steroid numbering) is carried out using whole-cell biocatalysis, followed by the chemical cleavage of the...

Introducing biobased polymers from renewable sources for use as high-performance thermoplastics with high demands on mechanical rigidity, transparency, thermal stability, as well as good processability, is a significant challenge. In the present work we have designed and prepared a rigid biobased bis-spirocylic diol by di-cycloketalization of a bic...

We demonstrate that Ullman fragment-coupling can be used to synthesise an oxacalix[4]arene monocarboxylic acid, which provides easy access to its water-soluble carboxylato derivatives. Crystallographic and computational data suggest that the new carboxyl-substituted oxacalix[4]arene adopts a 1,3-alternate conformation both in the solid-state and in...

Isosorbide is a stiff bicyclic diol derived from glycose-based polysaccharides, and is thus an attractive building block for novel rigid bioplastics. In the present work a highly regioselective biocatalytic approach for the synthesis of isosorbide 5-methacrylate was developed. The Lipozyme RM IM (Rhizomucor miehei lipase) catalyzed process is strai...

We present single crystal structures of unsubstituted oxacalix[4]arene and oxacalix[8]arene macrocycles and investigate the weak supramolecular interactions that govern their packing in the solid state. We further show that the unsubstituted oxacalix[4]arene shows weak complexation with two aromatic guest species, benzoic acid and ferrocene, in CDC...

Supporting Information for Shortfall of B3LYP in Reproducing NMR JCH Couplings in Some Isomeric Epoxy Structures with Strong Stereoelectronic Effects: A Benchmark Study on DFT Functionals

Unprecedented scatter plots of calculated versus measured NMR 2,3JCH coupling constants in six densely oxygen functionalized epoxides are found with some B3LYP protocols, an effect attributed to stereoelectronic effects. Hence, 26 other exchange-correlation density functionals (xc DFs) are benchmarked in this work. Very good results are achieved wi...

An enantio- and regioselective organocatalytic cascade starting from isatin has been disclosed to construct tetrahydrofuranyl spirooxindoles in high yields and stereoselectivities. Also, a triple cascade leading to the pentacyclic compound with two quaternary and a tertiary stereocenter is described. The reactions were catalyzed by cinchonine-based...

This expansive and practical textbook contains organic chemistry experiments for teaching in the laboratory at the undergraduate level covering a range of functional group transformations and key organic reactions.The editorial team have collected contributions from around the world and standardized them for publication. Each experiment will explor...

No abstract is available for this article.

The first time application of hydroformylation on olefinic derivatives of isosorbide and isomannide is shown by which a new carbon-carbon bond is formed. Depending on the ligand and reaction conditions used, the C6 regioisomer a can be obtained in 4:1 ratio and excellent yield, whereas C5 isomer b is achieved in almost complete regioselectivity (46...

When investigating the Sharpless epoxidation of enol-protected 4-hydroxy-1,2-cyclopentanediones, the ability of the asymmetric Ti(O_i_Pr)4/tartaric ester complex to discriminate between enantiomeric epoxides formed in situ was discovered, leading to the epoxide opening reaction of only one enantiomer. This observation was used in the kinetic resolu...

An organocatalytic cascade Michael addition-cyclization reaction of cyclopentane-1,2-dione with substituted (E)-2-oxobut-3-enoates, creating two stereocenters and giving bicyclic hemiacetals 3 in excellent yield (up to 93%) and enantioselectivity (up to 96% ee) was developed. From 2-chlorophenyl-substituted (E)-2-oxobut-3-enoate, the adduct reveale...

Negishi cross-coupling of the silyl-protected 3-bromoenol of 1,2-cyclopentanedione with primary and secondary alkylzinc reagents using Pd-catalysts affords 3-alkyl substituted 1,2-cyclopentanediones in good yield. The method was applied to obtain 3-methylalkoxycarbonyl- and 3(2-Boc-aminoethyl)-alkoxycarbonyl-1,2-cyclopentanediones - homocitric and...

Organocatalytic Michael additions of cyclopentane-1,2-dione to different nitroolefins have been investigated. Cyclopentane-1,2-dione undergoes an organocatalytic reaction with substituted nitroolefins giving 3-substituted products in good to high yields (48-97%) and good stereoselectivity (up to 76% ee).

A new general method for the synthesis of enols of cyclic 3-alkynyl-substituted 1,2-diketones is developed. Sonogashira cross-coupling of silyl enolates of cyclic 3-bromo-cyclopentane- and 3-bromo-cyclohexane-1,2-diones with variety of substituted acetylenes afforded enols of cyclic 3-alkynyl-1,2-diones with good yields (up to 93%) in a short react...

Treatment of 1-Boc-1-tosyl-hydrazine with 1,1,3,3-tetramethylguanidine (TMG) gave rise to two products, one containing and the other not containing TMG. The latter was identified as 1-Boc-2-tosyl-hydrazine. This rearrangement provided useful insight into the nature of the first product that had previously been isolated and assigned an incorrect ten...

Organocatalytic Michael additions of cyclopentane-1,2-dione to different nitroolefins have been investigated. Cyclopentane-1,2-dione undergoes an organocatalytic reaction with substituted nitroolefins giving 3-substituted products in good to high yields (48-97%) and good stereoselectivity (up to 76% ee).

Michael addition of the isatin imine (I) to aliphatic 1,4-ketoesters requires a much longer reaction time than the one to aromatic 1,4-ketoesters.

1H and 13C NMR spectra of Ti(OiPr)4 complexes with 3-methyl-1,2-cyclopentanedione in deuterochloroform solution reveal formation of different compounds, depending on the molar ratio of diketone and Ti-isopropoxide. The obtained results were compared with the DFT calculations of these complexes. Both NMR study and theoretical calculations show that...

A lipase may catalyze either one or more of the three reactions of 11-acetyl-prostaglandin E2 in methanol-containing reaction medium: esterification, deacetylation, and/or elimination. The catalytic performance depends on the lipase and on the methanol content. An increase in the methanol concentration in benzene from 5 % to 95 % leads to the exclu...

Critical assessment of performance of alternative molecular modeling methods depending on a specific object and goal of the investigation is a question of continuous interest. This prompted us to demonstrate the origin of the guidelines we have used for a rational choice and use of a proper low level calculation method (LLM) for an initial geometry...

3-Substituted 1,2-cyclopentanediones 1 were transformed to 2-substituted 5-oxotetrahydrofuran-2-carboxylic acids 2 using a catalytic process with 0.2-0.3 equivalent of Ti(OiPr)(4)/tartaric ester/tBuO0H complex in up to 72% isolated yield and up to 94% ee. Different functional groups in the 3-alkyl substituent of 1 like, hydroxy, ether, Boc-amino an...

The concept of the remote activation of reactivity was first applied in asymmetric organocatalysis. An isatin 3-phenylimine derivative acts as a donor in the thiourea catalyzed asymmetric addition to unsaturated 1,4-ketoesters, affording aza-Michael adducts in high enantiomeric purity and yield.

3-Substituted 1,2-cyclopentanediones 1 were transformed to 2-substituted 5-oxotetrahydrofuran-2-carboxylic acids 2 using a catalytic process with 0.2-0.3 equivalent of Ti(OiPr)4/tartaric ester/tBuOOH complex in up to 72% isolated yield and up to 94% ee. Different functional groups in the 3-alkyl substituent of 1 like, hydroxy, ether, Boc-amino and...

The work on developing a scalable lipase-catalytic method for the kinetic resolution of long-chain 1,2-alkanediols, complemented by crystallization of the pure enantiomers from the reaction mixtures, offered the possibility of a more detailed study of the aggregation of such diols. MD modeling, mass spectrometry, (1)H NMR, and DOSY studies provided...

A stereochemically safe high-yielding procedure for linking unprotected as well as protected hydroxycarboxylic acids to chiral secondary alcohols via glycolic acid linker is proposed. L-menthol has been linked with both enantiomers of mandelic, malic, and methoxyphenylacetic acid using bromo- or iodoacetyl group as a precursor of the glycolic acid...

3-Chlorooxoindoles have emerged as versatile precursors in the synthesis of spirocyclopropyl oxindoles. High enantio- and diastereoselectivity was attained under conditions of both iminium/enamine and H-bonding catalysis.

A method for the synthesis of 1-methylcarbapentofuranose derivatives was developed, where 1,2-cis- and 1,2-trans-4-hydroxymethyl-1-methylcyclopentanediols were obtained from intramolecular opening of a 4-epoxy-4-methyl-γ-lactone. An intramolecular aldol reaction of 4-methyl-4-(2-oxoethyl)-γ-lactone derivatives yielded 1,3-cis- and 1,3-trans-4-hydro...

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 secon...

Rye sourdough breads go stale more slowly than wheat breads. To understand the peculiarities of bread staling, rye sourdough bread, wheat bread, and a number of starches were studied using wide-angle X-ray diffraction, nuclear magnetic resonance ((13)C CP MAS NMR, (1)H NMR, (31)P NMR), polarized light microscopy, rheological methods, microcalorimet...

Novel carbanucleoside (VII) displays high cytotoxicity, whilst the parent bimorpholine (VI) is only moderately cytotoxic.

A new bifunctional thiourea II catalyzed methodology was developed for the synthesis of chiral trisubstituted pyrrolidines using 4-aminocrotonate 1a/1b and nitroolefins 2a–g as starting materials. Two different N-protected 4-aminocrotonates 1a and 1b were tested for the reaction with 1a giving the desired product 3a with a high diastereomeric ratio...

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...

The asymmetric oxidation of 3-alkyl-cyclopentane-1,2-diones with the Ti(OiPr)4/tartaric ester/t-BuOOH complex, which gives, in a cascade process, highly enantiomerically enriched γ-lactone acids, was studied by 18O isotopic labeling in the substrate and in the oxidant. The path of the labeled atoms was followed by 13C NMR spectroscopy. It was found...

The invention of electrospinning has solved the problem of producing micro- and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO2, TiO2, ZrO2, HfO2 and CeO...

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 prese...

An extension of the scope of the chemoenzymatic strategy for the synthesis of stereochemically pure pyranose deoxy sugar esters of different carboxylic acids has been achieved. The objective of the work was to extend the strategy to the synthesis of furanose deoxy sugar derivatives and additionally, to N-Boc-protected amino acid esters. With all us...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A series of novel acyclic thymine nucleoside analogues were prepared by the Mitsunobu reaction from appropriately protected chiral triols. The enantiomeric triols were obtained from substituted gamma-lactone acids, prepared by asymmetric oxidation of 3-substituted-1,2-cyclopentanediones. The cytotoxic activity of new analogues was evaluated on MCF-...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The reactions of brexadiene I with bromine, iodine, deuterotrifluoroacetic and Tetradeuteroacetic acid are described. These reactions proceed mainly as electrophilic exo-attack followed by Wagner-Meerwein rearrangement.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

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 import...

Thermal behaviour of industrial UF resins modified by low level of melamine was followed by TG-DTA technique on the labsys TM instrument Setaram together with the 13C NMR analysis of resin structure and testing boards in current production at Estonian particleboard factory Pärnu Plaaditehas AS. DTA curve of UF resin which has been cocondensed durin...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

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.

Prepolymer resol resins with different phenol/formaldehyde/NaOH molar ratios were synthesized and characterized by technical analysis as well as by C-13 NMR spectra for samples in CD3OD solution. Larger amounts of NaOH promoted the binding of formaldehyde and para substitution including the formation of benzoquinone rings with two o,p'-methylene gr...

A simple and short synthetic pathway to novel chiral enantioenriched 2,2-disubstituted tetrahydrofuran derivatives, starting from enantiomeric lactone acids in 2 steps was developed in 36-54% overall yield. The method enables also to obtain enantioenriched 2,3’-spiro ditetrahydrofuran (1,7-dioxaspiro[4.4]nonane) starting from the spirodilactone (R-...

Urea–formaldehyde (UF) and phenol–formaldehyde (PF) resins are the most widely used wood adhesives. The first stage in resin manufacturing is the formation of methylol derivatives which polycondensation leads to building the tridimensional network. Understanding the behaviour of methylol compounds in curing provides useful information for developin...

A series of 4′-aryl-2′,3′-dideoxynucleoside analogues were synthesized from optically pure 5-oxo-2-aryl-tetrahydrofuran-2-carboxylic acids up to 62% overall yield. 5-Oxo-2-aryl-tetrahydrofuran-2-carboxylic acids were obtained from 2-hydroxy-3-arylcyclopent-2-en-1-ones by asymmetric oxidation in up to 38–57% yield.Graphical abstract

The composition, structure, and thermal stability of carrageenans from unattached Coccotylus truncatus (the Baltic Sea, Estonia) were investigated. The complex polysaccharide was characterized by (13)C NMR and FTIR spectroscopy, ICP-OES and gel permeation chromatography methods. The main components of C. truncatus galactan are 3,6-anhydro-alpha-D-g...

The structure and composition of galactan from Furcellaria lumbricalis (furcellaran) were investigated in connection with rheological specificities, gel structure, and extraction conditions. The polysaccharide was characterized by 13C nuclear magnetic resonance (13C-NMR) and Fourier transform infrared spectroscopy, inductively coupled plasma-optica...

Prepolymer resol resins with the molar ratio of phenol/formaldehyde 1/2.4 and different amounts of NaOH were synthesized and characterized using 13C NMR spectra for samples in CD3OD solution. Nearly the full substitution in ortho and para aromatic positions occurred, and quite constant ratios of hydroxymethyl/methylene or o, p'/p, p'-methylene grou...

A simple and short synthetic pathway to novel chiral enantioenriched 2,2-disubstituted tetrahydrofuran derivatives, starting from enantiomeric lactone acids in 2 steps was developed in 36-54% overall yield. The method enables also to obtain enantioenriched 2,3'-spiro ditetrahydrofuran (1,7-dioxaspiro[4.4]nonane) starting from the spirodilactone (R-...

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 of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The thermal behaviour of MUF resins from different suppliers with different content of melamine was studied, along with the 13C NMR spectroscopic analysis of resin structure and the testing of particleboards in current production at Estonian PB factory Pärnu Plaaditehas AS. The chemical structure of resins from DMSO-d6 solutions was analysed by 13C...

Asymmetric aldol reactions were studied in the presence of heterocyclic bimorpholine- and bipiperidine-type organocatalysts. Bimorpholine derivatives were found to be more reactive and more selective in intramolecular, as well as intermolecular, reactions.

Both enantiomers of the key intermediate, 2-benzyl-5-oxo-tetrahydro-furan-2-carboxylic acid were obtained by asymmetric oxidation of 3-benzyl-2-hydroxy-2-cyclopenten-1-one with an ee⩾96%, using the tartaric ester/Ti(OiPr)4/t-BuOOH complex, and transformed to the corresponding 4′-substituted nucleoside analogues with up to 61% overall yield.

Thermal behaviour of cure-accelerated phenol-formaldehyde (PF) resins was studied using the addition of commercial mixture of water soluble oil shale alkylresorcinols (AR) to PF resin, 5-MR being as model compound. The acceleration effect of AR is based on the promotion of condensation of resin methylol groups and subsequent reaction of released fo...

A total conformational analysis of diastereomeric esters was performed and the conformational shielding models (CSM) of the esters necessary for the NMR spectroscopic stereochemical assignment of carboxylic acids or alcohols were calculated. The esters of (R)-2-butanol and both enantiomers of O-methylphenylacetic acid (MPA), 2-phenoxypropanoic, 2-(...

A new method for the aerobic oxidation of cyclopentane-1,2-diols to corresponding 1,2-diones using heterogeneous Pt/C catalyst in the presence of LiOH is described. Different functional groups tolerate the oxidation conditions. Yields of 1,2-diones up to 76% were achieved.