@article{ModarresiAlamInalooKleinpeter2012, author = {Modarresi-Alam, Ali Reza and Inaloo, Iman Dindarloo and Kleinpeter, Erich}, title = {Synthesis of primary thiocarbamates by silica sulfuric acid as effective reagent under solid-state and solution conditions}, series = {Journal of molecular structure}, volume = {1024}, journal = {Journal of molecular structure}, number = {9}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2012.05.033}, pages = {156 -- 162}, year = {2012}, abstract = {A simple and efficient method for the conversion of alcohols and phenols to primary O-thiocarbamates and S-thiocarbamates in the absence of solvent (solvent-free condition) using silica sulfuric acid (equivalent to SiO2-OSO3H) as a solid acid is described. The products are easily distinguished by IR, NMR and X-ray data. X-ray data of the compounds reveal a planar trigonal orientation of the NH2 nitrogen atom with the partial C,N double-bond character and the C=S or C=O groups in synperiplanar position with C-aryl-O and C-alkyl-S moieties, respectively. Moreover, the -O-CS-NH2 group which is perpendicular to the plane of the benzene ring in 1c and the central thiocarbamate -S-CO-NH2 group in 2b are essentially planar.}, language = {en} } @article{KirpichenkoShainyanKleinpeter2012, author = {Kirpichenko, Svetlana V. and Shainyan, Bagrat A. and Kleinpeter, Erich}, title = {Unusual conformational preferences of 1,3-dimethyl-3-isopropoxy-3-silapiperidine}, series = {Journal of physical organic chemistry}, volume = {25}, journal = {Journal of physical organic chemistry}, number = {12}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0894-3230}, doi = {10.1002/poc.3028}, pages = {1321 -- 1327}, year = {2012}, abstract = {The conformational analysis of the first representative of the Si-alkoxy substituted six-membered Si,N-heterocycles, 1,3-dimethyl-3-isopropoxy-3-silapiperidine, was performed by low-temperature 1H and 13C NMR spectroscopy and DFT theoretical calculations. In contrast to the expectations from the conformational energies of methyl and alkoxy substituents, the Meaxi-PrOeq conformer was found to predominate in the conformational equilibrium in the ratio Meaxi-PrOeq : Meeqi-PrOax of ca. 2 : 1 as from the 1H and 13C NMR study. The thermodynamic parameters obtained by the complete line shape analysis showed that the main contribution to the barrier to ring inversion originates from the entropy term of the free energy of activation.}, language = {en} } @article{BaranacStojanovicKochKleinpeter2012, author = {Baranac-Stojanovic, Marija and Koch, Andreas and Kleinpeter, Erich}, title = {Density Functional Calculations of the Anisotropic Effects of Borazine and 1,3,2,4-Diazadiboretidine}, series = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, volume = {13}, journal = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, number = {17}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1439-4235}, doi = {10.1002/cphc.201200732}, pages = {3803 -- 3811}, year = {2012}, abstract = {On the basis of the nucleus-independent chemical shift (NICS) concept, the anisotropic effects of two inorganic rings, namely, borazine and planar 1,3,2,4-diazadiboretidine, are quantitatively calculated and visualized as isochemical shielding surfaces (ICSSs). Dissection of magnetic shielding values along the three Cartesian axes into contributions from s and p bonds by the natural chemical shieldingnatural bond orbital (NCSNBO) method revealed that their appearance is not a simple reflection of the extent of (anti)aromaticity.}, language = {en} } @article{KleinpeterKoch2013, author = {Kleinpeter, Erich and Koch, Andreas}, title = {(Anti)aromaticity of dehydroannulenes of various ring size proved by the ring current effect in H-1 NMR spectra}, series = {Tetrahedron}, volume = {69}, journal = {Tetrahedron}, number = {5}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2012.12.019}, pages = {1481 -- 1488}, year = {2013}, abstract = {The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of already synthesized dehydro[n]annulenes of various ring size (from C-12 to C-20) have been computed, visualized as Isochemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to present (anti)aromaticity. For this purpose the thus quantified ring current effect of the macro cycles on proximate protons in proton NMR spectra was employed.}, language = {en} } @article{KleinpeterWernerKoch2013, author = {Kleinpeter, Erich and Werner, Peter and Koch, Andreas}, title = {Push-pull allenes-conjugation, (anti)aromaticity and quantification of the push-pull character}, series = {Tetrahedron}, volume = {69}, journal = {Tetrahedron}, number = {11}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2013.01.027}, pages = {2436 -- 2445}, year = {2013}, abstract = {Structures, H-1/C-13 chemical shifts, and pi electron distribution/conjugation of an experimentally available and theoretically completed set of push-pull allenes Acc(2)C=C=CDon(2) (Acc=F, CHO, CF3, C N; Don=t-Bu, OMe, OEt, SMe, SEt, NCH2R) have been computed at the OFT level of theory. Both orthogonal linear and orthogonal bent structures have been obtained. In the latter case the push-pull character could be quantified by the quotient method. The C-13 chemical shift of the central allene carbon atom C-2 and chemical shift differences Delta delta(C-1, C-2) and Delta delta(C-2, C-3) of allene carbon atoms proved to be a quantitative alternative. TSNMRS of ring-closed push-pull allenes have been computed in addition and were employed to identify polar, carbene-like and carbone-like canonical structures of these molecules.}, language = {en} } @article{ShainyanKirpichenkoKleinpeteretal.2013, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Kleinpeter, Erich and Shlykov, Sergey A. and Osadchiy, Dmitriy Yu and Chipanina, Nina N. and Oznobikhina, Larisa P.}, title = {1,3-Dimethy1-3-silapiperidine - synthesis, molecular structure, and conformational analysis by gas-phase electron diffraction, low temperature NMR, IR and Raman Spectroscopy, and quantum chemical calculations}, series = {The journal of organic chemistry}, volume = {78}, journal = {The journal of organic chemistry}, number = {8}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/jo400289g}, pages = {3939 -- 3947}, year = {2013}, abstract = {The first Si-H-containing azasilaheterocycle, 1,3-dimethyl-3-silapiperidine 1, was synthesized, and its molecular structure and conformational properties were studied by gas-phase electron diffraction (GED), low temperature NMR, IR and Raman spectroscopy and quantum chemical calculations. The compound exists as a mixture of two conformers possessing the chair conformation with the equatorial NMe group and differing by axial or equatorial position of the SiMe group. In the gas phase, the SiMeax conformer predominates (GED: ax/eq = 65(7):35(7)\%,Delta G = 0.36(18) kcal/mol; IR: ax/eq = 62(5):38(5)\%,Delta G = 0.16(7) kcal/mol). In solution, at 143 k the SiMeeq conformer predominates' in the frozen equilibrium (NMR: ax/eq = 31.5(1.5):68.5(1.5)\%, Delta G = -0.22(2) kcal/mol). Thermodynamic parameters of the ring inversion are determined (Delta G(double dagger) = 8.9-9.0 kcal/mol, Delta H-double dagger = 9.6 kcal/mol, Delta S-double dagger = 2.1 eu). High-level quantum chemical calculations :(MP2, G2, CCSD(T)) nicely reproduce the experimental geometry and the predominance of the axial conformer in the gas phase.}, language = {en} } @article{NitschkeWangSchmiederetal.2013, author = {Nitschke, Felix and Wang, Peixiang and Schmieder, Peter and Girard, Jean-Marie and Awrey, Donald E. and Wang, Tony and Israelian, Johan and Zhao, XiaoChu and Turnbull, Julie and Heydenreich, Matthias and Kleinpeter, Erich and Steup, Martin and Minassian, Berge A.}, title = {Hyperphosphorylation of glucosyl C6 carbons and altered structure of glycogen in the neurodegenerative epilepsy lafora disease}, series = {Cell metabolism}, volume = {17}, journal = {Cell metabolism}, number = {5}, publisher = {Cell Press}, address = {Cambridge}, issn = {1550-4131}, doi = {10.1016/j.cmet.2013.04.006}, pages = {756 -- 767}, year = {2013}, abstract = {Laforin or malin deficiency causes Lafora disease, characterized by altered glycogen metabolism and teenage-onset neurodegeneration with intractable and invariably fatal epilepsy. Plant starches possess small amounts of metabolically essential monophosphate esters. Glycogen contains similar phosphate amounts, which are thought to originate from a glycogen synthase error side reaction and therefore lack any specific function. Glycogen is also believed to lack monophosphates at glucosyl carbon C6, an essential phosphorylation site in plant starch metabolism. We now show that glycogen phosphorylation is not due to a glycogen synthase side reaction, that C6 is a major glycogen phosphorylation site, and that C6 monophosphates predominate near centers of glycogen molecules and positively correlate with glycogen chain lengths. Laforin or malin deficiency causes C6 hyperphosphorylation, which results in malformed long-chained glycogen that accumulates in many tissues, causing neurodegeneration in brain. Our work advances the understanding of Lafora disease pathogenesis and suggests that glycogen phosphorylation has important metabolic function.}, language = {en} } @article{NeuvonenNeuvonenKochetal.2013, author = {Neuvonen, Kari and Neuvonen, Helmi and Koch, Andreas and Kleinpeter, Erich}, title = {Nature of the steric Omega(S), E-R and E-S ' substituent constants - comparison with the aid of NBO and STERIC analysis}, series = {Computational and theoretical chemistry}, volume = {1015}, journal = {Computational and theoretical chemistry}, number = {4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2210-271X}, doi = {10.1016/j.comptc.2013.03.025}, pages = {34 -- 43}, year = {2013}, abstract = {The nature of the major steric substituent constant scales for alkyl substituents, i.e. Omega(S), E-R and E-S' scales, was studied with the aid of the NBO and the natural steric (STERIC) analyses. Cyclohexyl esters R-3-CCOOC6H11 (R = alkyl or H) were used as the model compounds. Special emphasis was laid on the potential contribution of the polar component in these steric substituent parameters. In the light of our model the Omega(S) scale seems to be dominantly a steric substituent constant scale as is seen on the strengths of the good correlation between the Omega(S) constants of the CR3 group and the total steric exchange energy values E-TSEE for the model compounds. However, the Omega(S) values also seem to include a minor electronic component due to the varying electrostatic effect via the C alpha atom. On the other hand, E-R and E-S' parameters largely hinge on the size dependent polar effect of the CR3 alkyl group. By way of our model this repulsive interaction can be quantified by descriptor Delta q(OCO), the natural charge difference q(C)(C=O) - Sigma qO for the O-C(=O) functional group. Delta q(OCO) depends on the E-TSEE values, on qC alpha and on the polarization coefficients of the oxygen hybrid in the NBO of the pi(C=O) bond. The size sensitivity of the kinetic E-S' constants can be connected to variation of the Burgi-Dunitz angle in the transition state for the standard reaction used. A comparison is made for the q(C)(C=O) or Delta q(OCO) values computed on the one hand with the NBO formalism and on the other hand with the Hirshfeld formalism. A practical novel substituent constant q(C)(C=O) for the size of the alkyl groups is introduced.}, language = {en} } @article{ShainyanKleinpeter2013, author = {Shainyan, Bagrat A. and Kleinpeter, Erich}, title = {Silacyclohexanes and silaheterocyclohexanes-why are they so different from other heterocyclohexanes?}, series = {Tetrahedron}, volume = {69}, journal = {Tetrahedron}, number = {29}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2013.04.126}, pages = {5927 -- 5936}, year = {2013}, abstract = {Stereochemical studies on silaheterocyclohexanes is a 'hot topic' as evidenced by the growing number of publications. During last 10 years a substantial number of substituted silacyclohexanes and heterocyclohexanes containing sulfur, oxygen or nitrogen as the second (or third) heteroatom have been synthesized and studied by variable temperature dynamic NMR spectroscopy, gas-phase electron diffraction, variable temperature IR, Raman, microwave spectroscopy with respect to thermodynamic (frozen conformational equilibria) and kinetic (barrier to ring inversion) information. As the stereochemistry of cyclohexane and its N-, O-, P-, S-hetero analogues is one of keystones of modern theoretical and synthetic organic and heterocyclic chemistry, the stereochemistry of silacyclohexane and its hetero analogs is an important element of theoretical and synthetic organosilicon chemistry. The various classes of saturated six-membered rings were critically compared and studied in detail with respect to differences in their stereochemistry and dynamic behavior.}, language = {en} } @article{DzambaskiMarkovicKleinpeteretal.2013, author = {Dzambaski, Zdravko and Markovic, Rade and Kleinpeter, Erich and Baranac-Stojanovic, Marija}, title = {2-Alkylidene-4-oxothiazolidine S-oxides - synthesis and stereochemistry}, series = {Tetrahedron}, volume = {69}, journal = {Tetrahedron}, number = {31}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2013.05.087}, pages = {6436 -- 6447}, year = {2013}, abstract = {A series of 5-unsubstituted and 5-substituted 2-alkylidene-4-oxothiazolidine-S-oxides were synthesized by the sulfur-oxidation with m-CPBA. The stereochemistry of 5-substituted sulfoxides was determined by means of NMR spectroscopy and DFT theoretical calculations. It was found that the thermodynamically less stable anti-isomer was initially formed in the course of the oxidation, but it underwent epimerization to the mixture enriched in the more stable syn-isomer, during the work-up process. The higher stability of syn-isomers is ascribed to the stronger hyperconjugative sigma(C-H)->sigma*(S-O) interaction versus the weaker sigma(C-C)->sigma*(S-O) delocalization in their anti-counterparts and to the existence of intramolecular 1,5-CH center dot center dot center dot C hydrogen bonds.}, language = {en} }