TY  - JOUR
A1  - Yaouba, Souaibou
A1  - Koch, Andreas
A1  - Guantai, Eric M.
A1  - Derese, Solomon
A1  - Irungu, Beatrice
A1  - Heydenreich, Matthias
A1  - Yenesew, Abiy
T1  - Alkenyl cyclohexanone derivatives from Lannea rivae and Lannea schweinfurthii
JF  - Phytochemistry letters / Phytochemical Society of Europe
N2  - Phytochemical investigation of the CH2Cl2/MeOH (1:1) extract of the roots of Lannea rivae (Chiov) Sacleux (Anacardiaceae) led to the isolation of a new alkenyl cyclohexenone derivative: (4R,6S)-4,6-dihydroxy-6-((Z)-nonadec-14′-en-1-yl)cyclohex-2-en-1-one (1), and a new alkenyl cyclohexanol derivative: (2S*,4R*,5S*)-2,4,5-trihydroxy-2-((Z)-nonadec-14′-en-1-yl)cyclohexanone (2) along with four known compounds, namely epicatechin gallate, taraxerol, taraxerone and β-sitosterol; while the stem bark afforded two known compounds, daucosterol and lupeol. Similar investigation of the roots of Lannea schweinfurthii (Engl.) Engl. led to the isolation of four known compounds: 3-((E)-nonadec-16′-enyl)phenol, 1-((E)-heptadec-14′-enyl)cyclohex-4-ene-1,3-diol, catechin, and 1-((E)-pentadec-12′-enyl)cyclohex-4-ene-1,3-diol. The structures of the isolated compounds were determined by NMR spectroscopy and mass spectrometry. The absolute configuration of compound 1 was established by quantum chemical ECD calculations. In an antibacterial activity assay using the microbroth kinetic method, compound 1 showed moderate activity against Escherichia coli while compound 2 exhibited moderate activity against Staphylococcus aureus. Compound 1 also showed moderate activity against E. coli using the disc diffusion method. The roots extract of L. rivae was notably cytotoxic against both the DU-145 prostate cancer cell line and the Vero mammalian cell line (CC50 = 5.24 and 5.20 μg/mL, respectively). Compound 1 was also strongly cytotoxic against the DU-145 cell line (CC50 = 0.55 μg/mL) but showed no observable cytotoxicity (CC50 > 100 μg/mL) against the Vero cell line. The roots extract of L. rivae and L. schweinfurthii, epicatechin gallate as well as compound 1 exhibited inhibition of carageenan-induced inflammation.
KW  - Lannea rivae
KW  - Lannea schweinfurthii
KW  - Alkenyl cyclohexenone
KW  - Alkenyl cyclohexanone
KW  - Anti-inflammatory
KW  - Cytotoxicity
KW  - Antimicrobial
Y1  - 2017
U6  - https://doi.org/10.1016/j.phytol.2017.12.001
SN  - 1874-3900
SN  - 1876-7486
VL  - 23
SP  - 141
EP  - 148
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Tahtinen, Petri
A1  - Bagno, Alessandro
A1  - Koch, Andreas
A1  - Pihlaja, Kalevi
T1  - Conformational analysis of saturated trans-fused 1,3,2-benzoxazaphosphinine 2-oxides - DFT calculation of NMR J(PH) coupling constants
N2  - The (3)J(P,H) and (4)J(P,H) spin-spin coupling constants of a selected test set of organophosphorus compounds, calculated by density functional theory (DFT) methods, were found to correlate well with the experimentally measured coupling constants. The contribution of the spin-dipole (SD) term to the coupling constants was found to be negligible, and the diamagnetic and paramagnetic spin-orbit (DSO and PSO) terms cancelled each other, as in the case of J(H,H). Calculation solely of the Fermi contact (FC) term was found to be sufficient to provide good estimates of the coupling constants. In the second part of the work, the conformational equilibria and coupling constants in 2-bis(2- chloroethyl)amino-trans-octahydro-2H-1,3,2-benzoxazaphosphinine 2-oxide and its 3-methyl derivative were studied. DFT methods failed in predicting the relative stabilities of the conformations but yielded good geometries and coupling constants. Optimization of the conformations at the Moller-Plesset second-order perturbation theory (MP2) level resulted in energy differences compatible with previous experimental observations. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Y1  - 2004
SN  - 1434-193X
ER  - 
TY  - JOUR
A1  - Yenesew, Abiy
A1  - Mushibe, E. K.
A1  - Induli, M.
A1  - Derese, Solomon
A1  - Midiwo, Jacob O.
A1  - Kabaru, Jacques M.
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Peter, Martin G.
T1  - 7a-O-methyldeguelol, a modified rotenoid with an open ring-C, from the roots of Derris trifoloata
N2  - From the acetone extract of the roots of Derris trifoliata an isollavonoid derivative, named 7a-O- methyldeguelol, a modified rotenoid with an open ring-C, representing a new sub-class of isollavonoids (the sub-class is here named as rotenoloid), was isolated and characterised. In addition, the known rotenoids, rotenone, deguelin and alpha-toxicarol, were identified. The structures were determined on the basis of spectroscopic evidence. Rotenone and deguelin were identified as the larvicidal principles of the acetone extract of the roots of Derris trifoliata. (c) 2005 Elsevier Ltd. All rights reserved
Y1  - 2005
SN  - 0031-9422
ER  - 
TY  - JOUR
A1  - Marco, Makungu
A1  - Deyou, Tsegaye
A1  - Gruhonjic, Amra
A1  - Holleran, John
A1  - Duffy, Sandra
A1  - Heydenreich, Matthias
A1  - Firtzpatrick, Paul A.
A1  - Landberg, Goran
A1  - Koch, Andreas
A1  - Derese, Solomon
A1  - Pelletier, Jerry
A1  - Avery, Vicky M.
A1  - Erdelyi, Mate
A1  - Yenesew, Abiy
T1  - Pterocarpans and isoflavones from the root bark of Millettia micans and of Millettia dura
JF  - Phytochemistry letters
KW  - Millettia micans
KW  - Millettia dura
KW  - Pterocarpan
KW  - Isoflavone
KW  - Cytotoxicity
KW  - Plasmodium falciparum
Y1  - 2017
U6  - https://doi.org/10.1016/j.phytol.2017.07.012
SN  - 1874-3900
SN  - 1876-7486
VL  - 21
SP  - 216
EP  - 220
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Koch, Andreas
A1  - Stamboliyska, Bistra
A1  - Mikhova, Bozhana
A1  - Breznica-Selmani, Pranvera
A1  - Mladenovska, Kristina
A1  - Popovski, Emil
T1  - Calculations of C-13 NMR chemical shifts and F-C coupling constants of ciprofloxacin
JF  - Magnetic resonance in chemistry
N2  - Ciprofloxacin is a widely used fluoroquinolone antibiotic. In this work, a comprehensive evaluation of MP2 and DFT with different functionals and basis sets was carried out to select the most suitable level of theory for the study of the NMR properties of ciprofloxacin. Their relative predictive capabilities were evaluated comparing the theoretically predicted and experimental spectral data. Our computational results indicated that in contrast to the solid state, the molecule of ciprofloxacin does not exist as a zwitterion in gaseous state. The results of the calculations of the chemical shifts most close to the experimental were obtained with B3LYP/aug-cc-pVDZ. The F-C coupling constants were calculated systematically with different DFT methods and several basis sets. In general, the calculations of the coupling constants with the BHandH computational method including the applied in this work 6-311++G**, EPRII, and EPRIII basis sets showed a good reproducibility of the experimental values of the coupling constants.
KW  - C-13 chemical shifts
KW  - ciprofloxacin
KW  - DFT calculations
KW  - F-C coupling constants
KW  - NMR
Y1  - 2019
U6  - https://doi.org/10.1002/mrc.4827
SN  - 0749-1581
SN  - 1097-458X
VL  - 57
IS  - 4
SP  - 75
EP  - 84
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Starke, Ines
A1  - Koch, Andreas
A1  - Kammer, Stefan
A1  - Holdt, Hans-Jürgen
A1  - Möller, Heiko Michael
T1  - Electrospray mass spectrometry and molecular modeling study of formation and stability of silver complexes with diazaperylene and bisisoquinoline
JF  - Journal of mass spectrometry
N2  - The complex formation of the following diazaperylene ligands (L) 1,12-diazaperylene 1, 1,1-bisisoquinoline 2, 2,11-disubstituted 1,12-diazaperylenes (alkyl=methyl, ethyl, isopropyl, 3, 5, 7), 3,3-disubstituted 1,1-bisisoquinoline (alkyl=methyl, ethyl, isopropyl, 4, 6, 8 and with R=phenyl, 11 and with pyridine 12), and the 5,8-dimethoxy-substituted diazaperylene 9, 6,6-dimethoxy-substituted bisisoquinoline 10 with AgBF4 was investigated. Collision-induced dissociation measurements were used to evaluate the relative stabilities of the ligands themselves and for the [1:1](+) complexes as well as for the homoleptic and heteroleptic silver [1:2](+) complexes in the gas phase. This method is very useful in rapid screening of the stabilities of new complexes in the gas phase. The influence of the spatial arrangement of the ligands and the type of substituents employed for the complexation were examined. The effect of the preorganization of the diazaperylene on the threshold activation voltages and thus of the relative binding energies of the different complexes are discussed. Density functional theory calculations were used to calculate the optimized structures of the silver complexes and compared with the stabilities of the complexes in the gas phase for the first time.
KW  - electrospray ionization mass spectrometry and modeling
KW  - silver(1) complexes
KW  - stability
Y1  - 2018
U6  - https://doi.org/10.1002/jms.4071
SN  - 1076-5174
SN  - 1096-9888
VL  - 53
IS  - 5
SP  - 408
EP  - 418
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Awad, Duha Jawad
A1  - Conrad, Franziska
A1  - Koch, Andreas
A1  - Friedrich, Alwin
A1  - Poeppl, Andreas
A1  - Strauch, Peter
T1  - 2,2'-Bipyridin-1,2-dithiolat Gemischtligand-Komplexe : Systhese, Charakterisierung und EPR-Spektroskopie
N2  - A series of new 2 2'-bipyridine/1 2-dithiolate transition metal complexes has been synthesised and characterised As 1,2-dithiolate ligands 1,2 dithiooxalate (dto) and 1 2-dithiosquarate (dtsq) were used It follows from the IR spectra that the multidentate dithiolate ligands coordinate exclusively via their sulfur atoms forming an MN2S2 coordination sphere The central metal ions (M) are Cu2+ Ni2+ Pd2+ Pt2+, and Zn2+ The complex [Cu-II(bpy)(dto)] could be studied by EPR spectroscopy and was measured as powder diamagnetically diluted in the isostructural [Ni-II(bpy)(dto)] host structure The spin density contribution calculated from the experimental parameters is compared with the electronic situation in the frontier orbitals namely in the semi occupied SOMO of the copper complex derived from quantum chemical calculations on different levels (EHT and DFT)
Y1  - 2010
UR  - http://www.znaturforsch.com/b.htm
SN  - 0932-0776
ER  - 
TY  - JOUR
A1  - Awad, Duha Jawad
A1  - Conrad, Franziska
A1  - Koch, Andreas
A1  - Schilde, Uwe
A1  - Poeppl, Andreas
A1  - Strauch, Peter
T1  - 1,10-phenanthroline-dithiolate mixed ligand transition metal complexes : synthesis, characterization and EPR spectroscopy
N2  - A series of new N2S2 mixed ligand transition metal complexes, where N-2 is phenanthroline and S-2 is 1,2- dithiooxalate (dto) or 1,2-dithiosquarate (dtsq), has been synthesized and characterized. IR spectra reveal that the 1,2- dithiolate ligands are coordinated via the sulfur atoms forming a N2S2 coordination sphere. The copper(II) complex [Cu(phen)(dto)] was studied by EPR spectroscopy as a diamagnetically diluted powder. The diamagnetic dilution resulted from doping of the copper complex into the isostructural host lattice of the nickel complex [Ni(phen)(dto)]. The electronic situation in the frontier orbitals of the copper complex calculated from the experimental data is compared to the results of EHT and DFT calculations. Furthermore, one side product, chlorobis(1,10-phenanthroline)copper(I) ethanol solvate hydrate [(phen)(2)CuCl]center dot C2H5OH center dot H2O, was formed by a reduction process and characterized by X-ray diffraction. In the crystal packing one-dimensional columns of dimers are formed, stabilized by significant pi-pi interactions.
Y1  - 2010
UR  - http://www.sciencedirect.com/science/journal/00201693
U6  - https://doi.org/10.1016/j.ica.2010.01.021
SN  - 0020-1693
ER  - 
TY  - JOUR
A1  - Awad, Duha Jawad
A1  - Koch, Andreas
A1  - Mickler, Wulfhard
A1  - Schilde, Uwe
A1  - Strauch, Peter
T1  - EPR spectroscopy of 4, 4 '-Bis(tert-butyl)-2, 2 '-bipyridine-1, 2-dithiolatocuprates(II) in host lattices with different coordination geometries
JF  - Zeitschrift für anorganische und allgemeine Chemie
N2  - A series of new heteroleptic MN2S2 transition metal complexes with M = Cu2+ for EPR measurements and as diamagnetic hosts Ni2+, Zn2+, and Pd2+ were synthesized and characterized. The ligands are N2 = 4, 4'-bis(tert-butyl)-2, 2'-bipyridine (tBu2bpy) and S2 =1, 2-dithiooxalate, (dto), 1, 2-dithiosquarate, (dtsq), maleonitrile-1, 2-dithiolate, or 1, 2-dicyanoethene-1, 2-dithiolate, (mnt). The CuII complexes were studied by EPR in solution and as powders, diamagnetically diluted in the isostructural planar [NiII(tBu2bpy)(S2)] or[PdII(tBu2bpy)(S2)] as well as in tetrahedrally coordinated[ZnII(tBu2bpy)(S2)] host structures to put steric stress on the coordination geometry of the central CuN2S2 unit. The spin density contributions for different geometries calculated from experimental parameters are compared with the electronic situation in the frontier orbital, namely in the semi-occupied molecular orbital (SOMO) of the copper complex, derived from quantum chemical calculations on different levels (EHT and DFT). One of the hosts, [NiII(tBu2bpy)(mnt)], is characterized by X-ray structure analysis to prove the coordination geometry. The complex crystallizes in a square-planar coordination mode in the monoclinic space group P21/a with Z = 4 and the unit cell parameters a = 10.4508(10) angstrom, b = 18.266(2) angstrom, c = 12.6566(12) angstrom, beta = 112.095(7)degrees. Oxidation and reductions potentials of one of the host complexes, [Ni(tBu2bpy)(mnt)], were obtained by cyclovoltammetric measurements.
KW  - 1
KW  - 2-Dithiosquarate
KW  - 1
KW  - 2-Dithiooxalate
KW  - 1
KW  - 2-Dicyanoethene-1
KW  - 2-dithiolate
KW  - 4
KW  - 4'-Bis(tert-butyl)-2
KW  - 2'-bipyridine
KW  - X-ray structure
KW  - EPR
KW  - Copper
KW  - Nickel
KW  - Zinc
Y1  - 2012
U6  - https://doi.org/10.1002/zaac.201100517
SN  - 0044-2313
VL  - 638
IS  - 6
SP  - 965
EP  - 975
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kolocouris, Antonios
A1  - Zervos, Nikolaos
A1  - De Proft, Frank
A1  - Koch, Andreas
T1  - Improper Hydrogen Bonded Cyclohexane C-H-ax center dot center dot center dot Y-ax Contacts theoretical predictions and experimental Evidence from H-1 NMR Spectroscopy of Suitable Axial Cyclohexane Models
JF  - The journal of organic chemistry
N2  - C-H-ax center dot center dot center dot Y-ax are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts is investigated in this work. MP2/6-31+G(d,p) calculations predicted the presence of improper hydrogen bonded C-H-ax center dot center dot center dot Y-ax of different strength in substituted cyclohexane rings. To support the theoretical predictions with experimental evidence, several synthetic 2-substituted adamantane analogues (1-24) with suitable improper H-bonded C-H-ax center dot center dot center dot Y-ax contacts of different strength were used as models of a substituted cyclohexane ring. The H-1 NMR signal separation, Delta delta(gamma-CH2), within the cyclohexane ring gamma-CH(2)s is raised when the MP2/6-31+G(d,p) calculated parameters, reflecting the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact, are increased. In molecules with enhanced improper H-bonded contacts C-H-ax center dot center dot center dot Y-ax, like those having sterically crowded contacts (Y-ax = t-Bu) or contacts including considerable electrostatic attractions (Y-ax = O-C or O=C) the calculated DFT steric energies of the gamma-axial hydrogens are considerably reduced reflecting their electron cloud compression. The results suggest that the proton H-ax electron cloud compression, caused by the C-H-ax center dot center dot center dot Y-ax contacts, and the resulting increase in Delta delta(gamma-CH2) value can be effected not just from van der Waals spheres compression, but more generally from electrostatic attraction forces and van der Waals repulsion, both of which are improper H-bonding components.
Y1  - 2011
U6  - https://doi.org/10.1021/jo102353f
SN  - 0022-3263
VL  - 76
IS  - 11
SP  - 4432
EP  - 4443
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - THES
A1  - Koch, Andreas
T1  - Quantenchemische Untersuchungen von Tautomeriegleichgewichten und von Rotationsbarrieren um partielle C,N- Doppelbindungen
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Kallies, Bernd
A1  - Koch, Andreas
A1  - Mitzner, Rolf
T1  - Competitive resonance at the carbonyl group as visualized by the natural bond orbital analysis
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Muiva-Mutisya, Lois
A1  - Macharia, Bernard
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Akala, Hoseah M.
A1  - Derese, Solomon
A1  - Omosa, Leonidah K.
A1  - Yusuf, Amir O.
A1  - Kamau, Edwin
A1  - Yenesew, Abiy
T1  - 6 alpha-Hydroxy-alpha-toxicarol and (+)-tephrodin with antiplasmodial activities from Tephrosia species
JF  - Phytochemistry letters
N2  - The CH2Cl2/MeOH (1: 1) extract of the roots of Tephrosia villosa showed good antiplasmodial activity against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum with IC50 values of 3.1 +/- 0.4 and 1.3 +/- 0.3 mu g/mL, respectively. Chromatographic separation of the extract yielded a new rotenoid, 6 alpha-hydroxy-alpha-toxicarol, along with five known rotenoids, (rotenone, deguelin, sumatrol, 12 alpha-hydroxy-alpha-toxicarol and villosinol). Similar treatment of the extract of the stem of Tephrosia purpurea (IC50 = 4.1 +/- 0.4 and 1.9 +/- 0.2 mu g/mL against D6 and W2 strains of P. falciparum, respectively) yielded a new flavone having a unique substituent at C-7/C-8 [trivial name (+)-tephrodin], along with the known flavonoids tachrosin, obovatin methyl ether and derrone. The relative configuration and the most stable conformation in (+)-tephrodin was determined by NMR and theoretical energy calculations. The rotenoids and flavones tested showed good to moderate antiplasmodial activities (IC50 = 9 +/- 23 mu M). Whereas the cytotoxicity of rotenoids is known, the flavones (+)-tephrodin and tachrosin did not show significant cytotoxicity (IC50 > 100 mu M;) against mammalian African monkey kidney (vero) and human larynx carcinoma (HEp2) cell lines. (C) 2014 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
KW  - Tephrosia villosa
KW  - Tephrosia purpurea
KW  - 6 alpha-Hydroxy-alpha-toxicarol
KW  - (+)-Tephrodin
KW  - Plasmodium falciparum
Y1  - 2014
U6  - https://doi.org/10.1016/j.phytol.2014.09.002
SN  - 1874-3900
SN  - 1876-7486
VL  - 10
SP  - 179
EP  - 183
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Muiva-Mutisya, Lois M.
A1  - Atilaw, Yoseph
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Akala, Hoseah M.
A1  - Cheruiyot, Agnes C.
A1  - Brown, Matthew L.
A1  - Irungu, Beatrice
A1  - Okalebo, Faith A.
A1  - Derese, Solomon
A1  - Mutai, Charles
A1  - Yenesew, Abiy
T1  - Antiplasmodial prenylated flavanonols from Tephrosia subtriflora
JF  - Natural Product Research
N2  - The CH2Cl2/MeOH (1:1) extract of the aerial parts of Tephrosia subtriflora afforded a new flavanonol, named subtriflavanonol (1), along with the known flavanone spinoflavanone B, and the known flavanonols MS-II (2) and mundulinol. The structures were elucidated by the use of NMR spectroscopy and mass spectrometry. The absolute configuration of the flavanonols was determined based on quantum chemical ECD calculations. In the antiplasmodial assay, compound 2 showed the highest activity against chloroquine-sensitive Plasmodiumfalciparum reference clones (D6 and 3D7), artemisinin-sensitive isolate (F32-TEM) as well as field isolate (KSM 009) with IC50 values 1.4-4.6M without significant cytotoxicity against Vero and HEp2 cell lines (IC50>100M). The new compound (1) showed weak antiplasmodial activity, IC50 12.5-24.2M, but also showed selective anticancer activity against HEp2 cell line (CC50 16.9M). [GRAPHICS] .
KW  - Tephrosia subtriflora
KW  - Leguminosae
KW  - prenylated flavanonol
KW  - subtriflavanonol
KW  - antiplasmodial
KW  - cytotoxicity
Y1  - 2018
U6  - https://doi.org/10.1080/14786419.2017.1353510
SN  - 1478-6419
SN  - 1478-6427
VL  - 32
IS  - 12
SP  - 1407
EP  - 1414
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Deyou, Tsegaye
A1  - Marco, Makungu
A1  - Heydenreich, Matthias
A1  - Pan, Fangfang
A1  - Gruhonjic, Amra
A1  - Fitzpatrick, Paul A.
A1  - Koch, Andreas
A1  - Derese, Solomon
A1  - Pelletier, Jerry
A1  - Rissanen, Kari
A1  - Yenesew, Abiy
A1  - Erdelyi, Mate
T1  - Isoflavones and Rotenoids from the Leaves of Millettia oblata ssp teitensis
JF  - Journal of natural products
N2  - A new isoflavone, 8-prenylmilldrone (1), and four new rotenoids, oblarotenoids A-D (2-5), along with nine known compounds (6-14), were isolated from the CH2Cl2/CH3OH (1:1) extract of the leaves of Millettia oblata ssp. teitensis by chromatographic separation. The purified compounds were identified by NMR spectroscopic and mass spectrometric analyses, whereas the absolute configurations of the rotenoids were established on the basis of chiroptical data and in some cases by single-crystal X-ray crystallography. Maximaisoflavone J (11) and oblarotenoid C (4) showed weak activity against the human breast cancer cell line MDA-MB-231 with IC50 values of 33.3 and 93.8 mu M, respectively.
Y1  - 2017
U6  - https://doi.org/10.1021/acs.jnatprod.7b00255
SN  - 0163-3864
SN  - 1520-6025
VL  - 80
SP  - 2060
EP  - 2066
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Spatial magnetic properties subject to lone pair and pi electron delocalization in benzenoid and quinoid structures : are quinoid tautomers really nonaromatic?
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzenoid and quinoid tautomeric structures such as benzodifurantrione and phenazine-type molecules have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Rague Schleyer and visualized as iso- chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the partial aromaticity of the studied compounds. In the case of the surprisingly more stable quinoid tautomers, the aromaticity-synonymous with stability due to the conjugation of p electrons and lone pairs-was not found to be particularly reduced.
Y1  - 2012
SN  - 1551-7004
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Spatial magnetic properties subject to lone pair and pi electron delocalization in benzenoid and quinoid structures are quinoid tautomers really nonaromatic?
JF  - Arkivoc : free online journal of organic chemistry
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzenoid and quinoid tautomeric structures such as benzodifurantrione and phenazine-type molecules have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Rague Schleyer and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the partial aromaticity of the studied compounds. In the case of the surprisingly more stable quinoid tautomers, the aromaticity-synonymous with stability due to the conjugation of p electrons and lone pairs-was not found to be particularly reduced.
KW  - Through-space NMR shieldings (TSNMRS)
KW  - GIAO
KW  - NICS
KW  - benzenoid structures
KW  - quinoid structures
KW  - aromaticity
Y1  - 2012
SN  - 1551-7004
SP  - 94
EP  - 108
PB  - ARKAT
CY  - Gainesville
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Paramagnetic ring current effects in anti-aromatic structures subject to substitution/annelation quantified by spatial magnetic properties (TSNMRS)
JF  - Tetrahedron
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of the typically anti-aromatic cyclopentadienyl cation, cyclobutadiene, pentalene, s-indacene and of substituted/annelated analogues of the latter structures have been calculated using the CIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to visualize and quantify the dia(para) magnetic ring current effects in the studied compounds. The interplay of dia(para)magnetic ring current effects due to substitution/annelation caused by heavy exo-cyclic n,pi-electron delocalization can be qualified.
KW  - Aromaticity
KW  - Anti-aromaticity
KW  - Through-space NMR shieldings (TSNMRS)
KW  - GIAO
KW  - NICS
KW  - Annelation effect
Y1  - 2018
U6  - https://doi.org/10.1016/j.tet.2017.12.020
SN  - 0040-4020
VL  - 74
IS  - 7
SP  - 700
EP  - 710
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Koch, Andreas
A1  - Thomas, Steffen
A1  - Kleinpeter, Erich
T1  - Ab-initio study, semi-empirical calculation and NMR spectroscopy of keto-enol tautomerism of triazolopyrimidines
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Shainyan, Bagrat A.
A1  - Ushakov, Igor A.
A1  - Meshcheryakov, Vladimir I.
A1  - Schilde, Uwe
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - The stereodynamics of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane and 1,3,5- tris(trifluoromethylsulfonyl)-1,3,5-triazinane- an experimental and theoretical study
N2  - Multinuclear dynamic NMR spectroscopy of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane (3) revealed the existence of two conformers with differently oriented CF3 groups with respect to the ring, and two dynamic processes: ring inversion and restricted rotation about the N-S bond. Two transition states connecting the two conformers and corresponding to clockwise and counterclockwise rotations about the N-S bond were found; the calculated activation barriers of about 12 kcal/mol are in excellent agreement with those measured experimentally for the related molecule 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane (1). X-ray analysis proved the existence of the symmetric isomer of 3, which is the minor isomer in solutions but the only one in the crystal due to packing effects. The normal Perlin effect (JCHax < JCHeq)observed for 2(6)-CH2 in 3, whereas the reversed Perlin effect was found for the 4-CH2 group in 3 as well as for all CH2 groups in 1 both experimentally and theoretically. The latter effect in compounds 1, 3, and 1- (methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane (2) can be considered as a genuine reverse Perlin effect since larger values of 1JCH are observed for longer C-H bonds.
Y1  - 2007
UR  - http://www.sciencedirect.com/science/article/pii/S0040402007016389
U6  - https://doi.org/10.1016/j.tet.2007.09.041
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Is the term "Carbene" justified for remote N-heterocyclic carbenes (r-NHCs) and abnormal N-heterocyclic carbenes (aNHCs/MICs)?
JF  - Tetrahedron
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of typical N-heterocyclic carbenes NHCs, r-NHCs, a-NHCs and MICs have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. Prior to that both structures and 13C chemical shifts were calculated and in case of isolated carbenes the computed δ(13C)/ppm values compared (as a quality criterion for obtained structures) with the experimental ones. The TSNMRS values of the studied carbenes, which are in mesomeric equilibrium with zwitterionic (ylide/betaine/mesoionic) resonance contributors, are employed to qualify and quantify the present electronic structure and if the term carbene is still justified to denote the compounds studied. The results, thus obtained from spatial magnetic properties (TSNMRS), are compared with the geometry of the compounds, the corresponding WIBERG's bond index values, and the 13C chemical shifts especially of the carbene electron-deficient centre.
KW  - Carbene or zwitterions
KW  - Ylide
KW  - Mesomeric equilibrium of carbene/zwitterion
KW  - Through-space NMR shieldings (TSNMRS)
KW  - NICS
Y1  - 2019
U6  - https://doi.org/10.1016/j.tet.2019.02.005
SN  - 0040-4020
VL  - 75
IS  - 11
SP  - 1548
EP  - 1554
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - The multiple bond character of the carbon-boron bond in boron trapped N-heterocyclic carbenes (NHCs) and cyclic(alkyl)(amino) carbenes (CAACs) on the magnetic criterion
JF  - Tetrahedron
N2  - Geometry, 11B, 13C chemical shifts and the spatial magnetic properties (Through-Space NMR Shieldings -TSNMRS) of both cations and anions of boron-trapped N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) and of the corresponding diborane/diborene/diboryne dis-carbene adducts have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept; the TSNMRS results are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The ICSS of the TSNMRS (actually the anisotropy effects measurable in 1H NMR spectroscopy) are employed to qualify and quantify the present multiple bond character of the Carbene-Boron bond in the trapped NHCs and CAACs. Results are confirmed by bond length and 11B/13C chemical shift variations. Thus the partial multiple bond character of the Carbene-Boron bond cannot be expressed by the arrow of weak, much longer dative bonds and should be omitted as in other covalent lone pair-it or triel bonds. & COPY; 2023 Elsevier Ltd. All rights reserved.
KW  - NHCs
KW  - CAACs
KW  - Multiple NHC(CAAC)-Boron bonds
KW  - Through -space NMR
KW  - shieldings (TSNMRS)
KW  - NICS
KW  - Anisotropy effect
KW  - Ring current effect
Y1  - 2023
U6  - https://doi.org/10.1016/j.tet.2023.133469
SN  - 0040-4020
SN  - 1464-5416
VL  - 140
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Bent Allenes or Di-1,3-betaines-An Answer Given on the Magnetic Criterion
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of bent allene 1, the corresponding C-extended 1,3-butadiene derivative 2, and a number of related compounds 3 -20 have been calculated using the gauge-independent atomic orbital perturbation method, employing the nucleus-independent chemical shift concept and visualized as isochemical shielding surfaces of various sizes and directions. Prior to that, both structures and C-13 chemical shifts were calculated and compared with available experimental bond lengths and delta(C-13)/ppm values (also, as a quality criterion for the computed structures). Bond lengths, the delta(C-13)/ppm, and the TSNMRS values are employed to qualify and quantify the electronic structure of the studied compounds in terms of dative or classical electron-sharing bonds.
Y1  - 2020
U6  - https://doi.org/10.1021/acs.jpca.0c01392
SN  - 1089-5639
SN  - 1520-5215
VL  - 124
IS  - 16
SP  - 3180
EP  - 3190
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Y-aromaticity - existing: yes or no? An answer given on the magnetic criterion (TSNMRS)
JF  - Tetrahedron
N2  - The spatial magnetic properties (Through Space NMR Shieldings - TSNMRS) of a number of Y-shaped structures possessing 4n+2 pi-electrons (i.a. the trimethylenemethane ions TMM2+, TMM2-, the guanidinium cation, substituted and hetero analogues) have been computed, visualized as Isochemical Shielding Surfaces (ICSS) of various size and direction, were examined subject to present Y-aromaticity and the results compared with energetic and geometric criteria obtained already. (C) 2016 Elsevier Ltd. All rights reserved.
KW  - Y-aromaticity
KW  - pi-Electron delocalization
KW  - Theoretical calculations
KW  - ICSS
KW  - TSNMRS
Y1  - 2016
U6  - https://doi.org/10.1016/j.tet.2016.02.020
SN  - 0040-4020
VL  - 72
SP  - 1675
EP  - 1685
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Belasri, Khadija
A1  - Topal, Leila
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
A1  - Fulop, Ferenc
A1  - Szatmari, Istvan
T1  - Synthesis and conformational analysis of naphthoxazine-fused phenanthrene derivatives
JF  - Molecules
N2  - The synthesis of new phenanthr[9,10-e][1,3]oxazines was achieved by the direct coupling of 9-phenanthrol with cyclic imines in the modified aza-Friedel-Crafts reaction followed by the ring closure of the resulting bifunctional aminophenanthrols with formaldehyde. Aminophenanthrol-type Mannich bases were synthesised and transformed to phenanthr[9,10-e][1,3]oxazines via [4 + 2] cycloaddition. Detailed NMR structural analyses of the new polyheterocycles as well as conformational studies including Density Functional Theory (DFT) modelling were performed. The relative stability of ortho-quinone methides (o-QMs) was calculated, the geometries obtained were compared with the experimentally determined NMR structures, and thereby, the regioselectivity of the reactions has been assigned.
KW  - modified Mannich reaction
KW  - cyclic imines
KW  - [4+2] cycloaddition
KW  - NMR
KW  - spectroscopy
KW  - conformational analysis
KW  - DFT calculations
Y1  - 2020
U6  - https://doi.org/10.3390/molecules25112524
SN  - 1420-3049
VL  - 25
IS  - 11
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Szatmári, István
A1  - Fulop, Ferenc
A1  - Kleinpeter, Erich
T1  - Synthesis and conformational analysis of naphth[1,2-e][1,3]oxazino[4,3-a][1,3]isoquinoline and naphth[2,1- e][1,3]oxazino[4,3-a]isoquinoline derivatives
N2  - Through the cyclization of 1-(;-hydroxynaphthyl)-1,2,3,4-tetrahydroisoquinoline and 1-(;- hydroxynaphthyl)-1,2,3,4-tetrahydroisoquinoline with formaldehyde, phosgene, p-nitrobenzaldehyde or p-chlorophenyl isothiocyanate, 8-substituted 10,11-dihydro-8H,15bH-naphth[1,2-e][1,3]oxazino[4,3-a]isoquinolines (3 and 4) and 10,11- dihydro-8H,15bH-naphth[2,1-e][1,3]oxazino[4,3-a]isoquinolines (15 and 16) were prepared. Conformational analysis of both the piperidine and the 1,3-oxazine moieties of these heterocycles by NMR spectroscopy and an accompanying theoretical study revealed that these two conformationally flexible six-membered ring moieties prefer twisted chair conformers.
Y1  - 2008
UR  - http://www.sciencedirect.com/science/article/pii/S0040402008009150
U6  - https://doi.org/10.1016/j.tet.2008.05.025
ER  - 
TY  - JOUR
A1  - Csütörtöki, Renata
A1  - Szatmari, Istvan
A1  - Koch, Andreas
A1  - Heydenreich, Matthias
A1  - Kleinpeter, Erich
A1  - Fulop, Ferenc
T1  - Syntheses and conformational analyses of new naphth[1,2-e][1,3]oxazino[3,2-c] quinazolin-13-ones
JF  - Tetrahedron
N2  - The syntheses of naphth[1,2-e][1,3]oxazino[3,2-c]quinazolin-13-one derivatives (3a-f) were achieved by the solvent-free heating of benzyloxycarbonyl-protected intermediates (2a-f) with MeONa. For intermediates 2a-f, prepared by the reactions of substituted aminonaphthols with benzyl N-(2-formylphenyl)carbamate, not only the expected trans ring form B and chain form A(1), but also the rearranged chain form A(2) as a new tautomer were detected in DMSO at room temperature. The quantity of A(2) in the tautomeric mixture was changed with time.
 Conformational analyses of the target heterocycles 3a-f by NMR spectroscopy and accompanying theoretical calculations at the DFT level of theory revealed that the oxazine ring preferred a twisted chair conformation and the quinazolone ring was planar. Besides the conformations, both the configurations at C-7a and C-15 and the preferred rotamers of the 1-naphthyl substituent at C-15 were assigned, which allowed evaluation of the aryl substituent-dependent steric hindrance in this part of the molecules. Configurational assignments were corroborated by quantifying the ring current effect of 15-aryl in terms of spatial NICS.
KW  - Naphthoxazinoquinazolinones
KW  - Aminonaphthols
KW  - NMR spectroscopy
KW  - Conformational analysis
KW  - Theoretical calculations
KW  - Ring current effect
Y1  - 2012
U6  - https://doi.org/10.1016/j.tet.2012.04.026
SN  - 0040-4020
VL  - 68
IS  - 24
SP  - 4600
EP  - 4608
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
A1  - Schulz, Stefanie
A1  - Wacker, Philipp
T1  - Interplay of para- and diatropic ring currents [(anti)aromaticity] of macrocyclic rings subject to conformational influences, further annelation and hydrogenation of aromatic ring moieties
JF  - Tetrahedron
N2  - The spatial magnetic properties (Through Space NMR Shieldings-TSNMRS) of a variety of porphyrins, hemiporphyrazines and tetraoxo[8]circulenes have been computed, visualized as Iso-chemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to the interplay of present (para)-diatropic ring currents [(anti)aromaticity] and influences on the latter property originating from the macrocyclic ring conformation, further annelation and partial to complete hydrogenation of aromatic ring moieties. Caution seems to be indicated when concluding from a single NICS parameter to present (para)diatropic ring currents [(anti)aromaticity]. (C) 2014 Elsevier Ltd. All rights reserved.
KW  - Porphyrins
KW  - Hemiporphyrazines
KW  - Tetraoxo[8]circulenes
KW  - (Anti)aromaticity
KW  - Anisotropy effect
KW  - Theoretical calculations
Y1  - 2014
U6  - https://doi.org/10.1016/j.tet.2014.10.018
SN  - 0040-4020
VL  - 70
IS  - 48
SP  - 9230
EP  - 9239
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Kovacs, J.
A1  - Toth, G.
A1  - Kleinpeter, Erich
T1  - Electronic influences on (3)J(C,H) coupling constants via -S-, -S(O)- and -SO2--: their determination, calculation and comparison of detection methods
N2  - (3)J(C,H) coupling constants via a sulfur atom in two series of compounds, both including a sulfide, a sulfoxide and a sulfone, were detected experimentally and calculated by quantum mechanical methods. In the first series (1-3) the coupling between a hydrogen, bonded to an Sp(3) carbon, and an Sp(2) carbon is treated; the second series (4- 6) deals with the coupling between a hydrogen, bonded to an Sp3 carbon, and an Sp3 carbon. Different pulse sequences (broadband HMBC, SelJres, 1D HSQMBC, J-HMBC-2, selective J-resolved long-range experiment and IMPEACH-MBC) proved to be useful in determining the long-range (3)J(C,H) coupling constants. However, the dynamic behaviour of two of the compounds (4 and 6) led to weighted averages of the two coupling constants expected (concerning equatorial and axial positions of the corresponding hydrogens). DFT calculations proved to be useful to calculate not only the (3)J(C,H) coupling constants but also the different contributions of FC, PSO, DSO and SD terms; the calculation of the Fermi contact term (FC) was found to be sufficient for the correct estimation of (3)J(C,H) coupling constants. Copyright (C) 2004 John Wiley Sons, Ltd
Y1  - 2004
SN  - 0749-1581
ER  - 
TY  - JOUR
A1  - Koch, Andreas
A1  - Mikhova, Bozhana
A1  - Kleinpeter, Erich
T1  - Ab initio MP2/GIAO/NBO study of the delta-syn-axial effect in C-13 NMR spectroscopy
N2  - The C-13 chemical shifts of 20 rigid bicyclic compounds have been calculated with ab initio HF and MP2 methods. The calculations showed very good reproducibility of the experimental values. The molecular orbital interactions in the rigid, nearly planar delta-syn-axial fragments in the isomeric groups of norbornane derivatives 1.x-4.x were studied in detail and were employed to explain the deshielding delta-syn-axial effect in C-13 NMR spectroscopy. (C) 2004 Elsevier B.V. All rights reserved
Y1  - 2004
SN  - 0022-2860
ER  - 
TY  - JOUR
A1  - Szatmari, Istvan
A1  - Martinek, T. A.
A1  - Lazar, L.
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
A1  - Neuvonen, Kari
A1  - Fulop, Ferenc
T1  - Stereoelectronic effects in ring-chain tautomerism of 1,3-diarylnaphth[1,2-e][1,3]oxazines and 3-alkyl-1- arylnaphth[1,2-e][1,3]oxazines
N2  - The disubstitution effects of X and Y in 1-(Y-phenyl)-3-(X-phenyl)-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines on the ring-chain tautomerism, the delocalization of the nitrogen lone pair (anomeric effect), and the C-13 NMR chemical shifts were analyzed by using multiple linear regression analysis. Study of the three-component equilibrium B reversible arrow A reversible arrow C revealed that the chain reversible arrow trans (A reversible arrow B) equilibrium constants are significantly influenced by the inductive effect (sigma(F)) of substituent Y on the 1-phenyl ring. In contrast, no significant substituent dependence on Y was observed for the chain reversible arrow cis (A reversible arrow C) equilibrium. There was an analogous dependence for the epimerization (C reversible arrow B) constants of 1-(Y-phenyl)-3- alkyl-2,3-dihydro-1H-naphth[1,2-e] [1,3]oxazines. With these model compounds, significant overlapping energies of the nitrogen lone pair was observed by NBO analysis in the trans forms B (to sigma*(C1-C1'), sigma*(C1-C10b), and sigma*(C3-O4)) and in the cis forms C (to sigma*(C1-H), sigma*(C1-C10b), and sigma*(C3-O4)). The effects of disubstitution revealed some characteristic differences between the cis and trans isomers. However, the results do not suggest that the anomeric effect predominates in the preponderance of the trans over the cis isomer. When the C-13 chemical shift changes induced Y by substituents X and Y (SCS) were subjected to multiple linear regression analysis, negative rho(F)(Y) and rho(F)(X) values were observed at C-1 and C-3 for both the cis and trans isomers. In contrast, the positive rho(R)(Y) values at C-1 and the negative rho(R)(X) values at C-3 observed indicated the contribution of resonance structures f (rho(R) > 0) and g (rho(R) < 0), respectively. The classical double bond-no-bond resonance structures proved useful in explaining the substituent sensitivities of the donation energies and the behavior of the SCS values
Y1  - 2004
SN  - 0022-3263
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Hilfert, Liane
A1  - Koch, Andreas
T1  - GIAO-HF/DFT calculation of C-13 and N-15 chemical shifts for studying tautomerism and intramolecular hydrogen bonding in 2,3-disubstituted quinoxalines
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Scholl, S.
A1  - Koch, Andreas
A1  - Henning, Dietrich
A1  - Kempter, Gerhard
A1  - Kleinpeter, Erich
T1  - The influence of structure and lipophilicity of hydantoin derivatives on anticonvulsant activity
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Woller, Jochen
A1  - Wolf, Gunter
A1  - Koch, Andreas
A1  - Kempter, Gerhard
A1  - Pihlaja, Kalevi
T1  - Configuration and stereodynamics of exo/endoisomeric push-pull alkenes of pentadiene structure
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Kalder, L.
A1  - Koch, Andreas
A1  - Henning, Dietrich
A1  - Kempter, Gerhard
T1  - NMR spectroscopic and theoretical structural analysis of 5,5-disubstituted hydantoins in solution
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Hilfert, Liane
A1  - Koch, Andreas
T1  - NMR spectroscopic and ab-initio MO study of sterically hindered 2,3-disubstituted quinoxalines
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Ristau, Thomas
A1  - Knoll, Susanne
A1  - Heinicke, Jochen
A1  - Sieler, Joachim
A1  - Niemitz, Matthias
A1  - Mühlstädt, Manfred
A1  - Kleinpeter, Erich
T1  - Conformational analysis of sulfur-containing heterocycles ; part I: synthesis and structural determination of diastereomerically pure 4,6-bis(phenoxymethyl)-1,2,5-trithiepanes
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
A1  - Zimmermann, Thomas
T1  - Dynamic NMR study of the flexibility of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts
Y1  - 1997
UR  - http://www.springerlink.com/content/110258
U6  - https://doi.org/10.1007/s002160050205
SN  - 0937-0633
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
A1  - Fischer, G.
A1  - Askolin, C.-P.
T1  - 13 C NMR, 15 N NMR and quantum-chemical study of the tautomerism of 2-substituted 5-ME-7-OH-1,2,4-triazolo[1,5- a]pyrimidines
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Study of the tautomerism by experimentally and theoretically estimated 13C and 15N chemical shifts
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Restricted rotation about particial C, N Double Bond
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Kalder, L.
A1  - Koch, Andreas
A1  - Henning, Dietrich
A1  - Kempter, Gerhard
A1  - Benassi, Rois
A1  - Taddei, F.
T1  - NMR spectroscopic and theoretical structural analysis of 5,5-disubstituted hydantoins in solution
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Koch, Andreas
A1  - Starke, Ines
A1  - Kleinpeter, Erich
T1  - Conformational study of Dibenzo crown ethers and their complexation with Li+ and Na+
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Ab-initio study and semiempirical calculations of keto-enol tautomerism of triazolopyrimidines
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
A1  - Heydenreich, Matthias
A1  - Chatterjee, S. K.
A1  - Rudorf, Wolf-Dieter
T1  - Study of the pi-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy, IV : the conformation and dynamic behaviour of substituted N-Phenyl-2,3-dihydro-4(1H)-pyridones
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Starke, Ines
A1  - Koch, Andreas
A1  - Holdt, Hans-Jürgen
A1  - Kleinpeter, Erich
T1  - 1H, 13C, and 15N NMR study of the solution structure of metabridged bis(benzo-15-crown-5-ether)s
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Starke, Ines
A1  - Koch, Andreas
A1  - Uhlemann, Erhard
A1  - Kleinpeter, Erich
T1  - Nuclear-magnetic-resonance studies and molecular modelling of the solution structure of some dibenzo crown- ethers and their complexes
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Szatmári, István
A1  - Lázár, László
A1  - Koch, Andreas
A1  - Heydenreich, Matthias
A1  - Fulop, Ferenc
T1  - Visualization and quantification of anisotropic effects on the 1H NMR spectra of 1,3-oxazino[4,3- alpha]isoquinolines - indirect estimates of steric compression
N2  - The anisotropic effects of the phenyl, alpha- and beta-naphthyl moieties in four series of 1,3-oxazino[4,3- a]isoquinolines on the H-1 chemical shifts of the isoquinoline protons were calculated by employing the Nucleus Independent Chemical Shift (NICS) concept and Visualized as anisotropic cones by a through-space NMR shielding grid. The signs and extents of these spatial effects on the H-1 chemical shifts of the isoquinoline protons were compared with the experimental H-1 NMR spectra. The differences between the experimental delta (H-1)/ppm values and the calculated anisotropic effects of the aromatic moieties are discussed in terms of the steric compression that occurs in the Compounds studied.
Y1  - 2009
U6  - https://doi.org/10.1016/j.tet.2009.07.038
SN  - 0040-4020
ER  - 
TY  - JOUR
A1  - Böhm, Stanislav
A1  - Tomaszciková, Jana
A1  - Imrich, Ján
A1  - Danihel, Ivan
A1  - Kristian, Pavol
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
A1  - Klika, Karel D.
T1  - Computational study to assign structure, tautomerism, E/Z and s-cis/s-trans isomerism, pi-delocalization, partial aromaticity, and the ring size of 1,3-thiazolidin-4-ones and 1,3-thiazin-4-ones formed from thiosemicarbazides
N2  - A set of structures encompassing 1-(9-acridinyl)thiosemicarbazide and its 2-methyl derivative together with their various tautomeric structures; the 5-membered ring 1,3-thiazolidin-4-one products resulting from the reaction of 1- (9-acridinyl)thiosemicarbazide and its 2-methyl derivative with dimethyl acetylenedicarboxylate (DMAD) together with the alternative 6-membered ring isomeric reaction products as well as other potential isomeric structures; and the 6- membered ring 1,3-thiazin-4-one product resulting from the reaction of 2-methyl-1-(9-acridinyl)thiosemicarbazide with methyl propiolate (MP) together with the alternative 5-membered ring isomeric reaction product were all extensively studied by molecular modeling calculations using DFT at the B3LYP/6-31G(d,p) level of theory. The ring-chain tautomerism of the thiosemicarbazides, the regio- and stereoselectivity of the reactions, the adopted conformations and E/Z configurations of the products, the prototropic tautomerism of all the compounds, and the reasons for the predominance of the s-cis conformation of the Z configuration of the 1,3-thiazolidin-4-one product in particular were all extensively analyzed. Comparison of the modeled structures were also made to the 1,3-thiazolidin-4-one and 1,3-thiazin-4-one structures of the methyl derivative as well as 1-(9-acridinyl)thiosemicarbazide available from X-ray crystallographic analysis. Tactics utilizing spectroscopic methods {IR frequencies (;) and NMR chemical shifts (;), scalar coupling constants (J), and NOEs (;)} in conjunction with molecular modeling calculations of the spectral parameters {frequency calculations (;) and NMR ; using the GIAO method and J by calculation of the Fermi contact term} were evaluated in terms of proving 5- or 6-membered ring formation.
Y1  - 2009
SN  - 0166-1280
ER  - 
TY  - JOUR
A1  - Sarodnick, Gerhard
A1  - Linker, Torsten
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Starke, Ines
A1  - Fürstenberg, Sylvia
A1  - Kleinpeter, Erich
T1  - Quinoxalines XV : convenient synthesis and structural study of pyrazolo[1,5-alpha]quinoxalines
N2  - A series of aryloxymethylquinoxaline oximes, hitherto unknown and synthesized from the corresponding aldehydes, afforded in only one step pyrazolo[1,5-;]quinoxalines in the presence of acetic anhydride at high temperatures. A formal [3,5]-sigmatropic rearrangement was proposed as the mechanistic rationale for this unprecedented transformation. Saponification with potassium hydroxide furnished the free phenol derivatives which were studied by NMR spectroscopy and accompanying theoretical DFT calculations, establishing intramolecular hydrogen bonding and the spatial magnetic properties. Additionally, mass spectrometric fragmentation was investigated by B/E-linked scans and collision-induced dissociation experiments. The fragmentation pattern devoted a new gas phase rearrangement process, which proved to be unique and characteristic for pyrazolo[1,5-;]quinoxalines.
Y1  - 2009
UR  - http://pubs.acs.org/journal/joceah
U6  - https://doi.org/10.1021/Jo802398g
SN  - 0022-3263
ER  -