TY  - JOUR
A1  - Kolocouris, Antonios
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
A1  - Stylianakis, Ioannis
T1  - 2-Substituted and 2,2-disubstituted adamantane derivatives as models for studying substituent chemical shifts and C-H-ax center dot center dot center dot Y-ax cyclohexane contacts-results from experimental and theoretical NMR spectroscopic chemical shifts and DFT structures
JF  - Tetrahedron
N2  - The complete H-1 and C-13 NMR chemical shifts assignment for various 2-substituted and 2,2-disubstituted adamantane derivatives 1-38 in CDCl3 solution was realized on the basis of NMR experiments combined with chemical structure information and DFT-GIAO (B3LYP/6-31+G(d,p)-GIAO) calculations of chemical shifts in solution. Substituent-induced C-13 NMR chemical shifts (SCS) are discussed. C-H-ax center dot center dot center dot Y-ax contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts will be further investigated in this work on basis of new adamantane derivatives, which are substituted at C-2 to provide models for 1,4-C-H-ax center dot center dot center dot Y-ax and 1,5-C-H-ax center dot center dot center dot Y-ax contacts. The B3LYP/6-31+G(d,p) calculations predicted the presence of NBO hyperconjugative attractive interactions between C-H-ax and Y-ax groups along C-H-ax center dot center dot center dot Y-ax contacts. The H-1 NMR signal separation, Delta delta(gamma-CH2), reflects the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact. (C) 2015 Elsevier Ltd. All rights reserved.
KW  - 2-Substituted adamantane derivatives
KW  - 2,2-Disubstituted adamantane derivatives
KW  - H-1 NMR
KW  - C-13 NMR
KW  - B3LYP/6-31+G(d,p) calculations
KW  - GIAO calculations
KW  - Substituent chemical shifts
Y1  - 2015
U6  - https://doi.org/10.1016/j.tet.2015.01.044
SN  - 0040-4020
VL  - 71
IS  - 16
SP  - 2463
EP  - 2481
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Kriiger, Stefanie
A1  - Koch, Andreas
T1  - Anisotropy Effect of Three-Membered Rings in H-1 NMR Spectra: Quantification by TSNMRS and Assignment of the Stereochemistry
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - The spatial magnetic properties (through Space NAIR shieldings, TSNMRSs) of cyclopropane; of the heteroanalogous oxirane, thiirane, and aziridine; and of various substituted dis-, and tris-cyclic analogues have been computed by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs) of various size and direction. The TSNMRS values, thus obtained, can be employed to visualize the anisotropy (ring current) effect of I the cyclopropane ring moiety. This approach has been employed to qualify and quantify substituent influences and contributions of appropriate ring heteroatoms O, NH, and S on the anisotropy (ring current) effect of three-mernbered ring moieties, and to assign the stereochemistry of mono-, bis-, and tris cyclic structures containing cyclopropane as a structural element. Characteristic examples are included.
Y1  - 2015
U6  - https://doi.org/10.1021/acs.jpca.5b03078
SN  - 1089-5639
VL  - 119
IS  - 18
SP  - 4268
EP  - 4276
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Michaelis, Marcus
A1  - Koch, Andreas
T1  - Are para-nitro-pyridine N-oxides quinonoid or benzenoid? An answer given by spatial NICS (TSNMRS)
JF  - Tetrahedron
N2  - The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of a number of substituted para-nitro-pyridine N-oxides have been computed, visualized as Iso-Chemical-Shielding-Surfaces (ICSS) of various size and direction, and were examined subject to the present quinonoid or benzenoid pi-relectron distribution of the six-membered ring. (C) 2015 Elsevier Ltd. All rights reserved.
KW  - para-Nitro-pyridine N-oxides
KW  - Quinonoid structure
KW  - Benzenoid structure
KW  - Ring current effect
KW  - Anisotropy effect
KW  - Theoretical calculations
Y1  - 2015
U6  - https://doi.org/10.1016/j.tet.2015.02.043
SN  - 0040-4020
VL  - 71
IS  - 15
SP  - 2273
EP  - 2279
PB  - Elsevier
CY  - Oxford
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  - Balci, K.
A1  - Akkaya, Y.
A1  - Akyuz, S.
A1  - Collier, W. B.
A1  - Stricker, M. C.
A1  - Stover, D. D.
A1  - Ritzhaupt, G.
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - The effects of conformation and zwitterionic tautomerism on the structural and vibrational spectral data of anserine
JF  - Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy
N2  - In this study, the stable conformers of neutral anserine were searched by molecular dynamics simulations and energy minimization calculations using the MM2 force field. Thermochemical calculations at B3LYP/6-31G(d) level of theory followed these preliminary calculations. The results confirmed that neutral anserine has quite a flexible structure and many stable gauche and trans conformers at room temperature. Nevertheless, two are considerably more favourable in energy than the others and expected to dominate the gas-phase and matrix IR spectra of the molecule. The corresponding structural and vibrational spectral data for these two conformers of neutral anserine, whose relative stabilities were also examined by high-accuracy energy calculations carried out using G3MP2B3 method, and for the most stable conformer of anserine in zwitterion form were calculated at B3LYP/6-311++G(d,p) level of theory. The calculated harmonic force constants were refined using the Scaled Quantum Mechanical Force Field (SQM-FF) method and then used to produce the refined wavenumbers, potential energy distributions (PEDs) and IR and Raman intensities. These refined data together with the scaled harmonic wavenumbers obtained using another method, Dual Scale factors (DS), enabled us to correctly analyse the observed IR and Raman spectra of anserine and revealed the effects of conformation and zwitterionic tautomerism on its structural and vibrational spectral data. (C) 2016 Elsevier B.V. All rights reserved.
KW  - Anserine
KW  - Matrix IR spectrum
KW  - Tautomerism
KW  - SQM-FF
KW  - Dual scale factors
Y1  - 2016
U6  - https://doi.org/10.1016/j.vibspec.2016.08.003
SN  - 0924-2031
SN  - 1873-3697
VL  - 86
SP  - 277
EP  - 289
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Barta, Petra
A1  - Szatmari, Istvan
A1  - Fueloep, Ferenc
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Synthesis and stereochemistry of new naphth[1,3]oxazino[3,2-a] benzazepine and naphth[1,3]oxazino[3,2-e]thienopyridine derivatives
JF  - Tetrahedron
N2  - Through the reactions of 1- or 2-naphthol and 4,5-dihydro-3H-benz[c]azepine or 6,7-dihydrothieno[3,2-c]pyridine, new aminonaphthol derivatives were prepared. The syntheses were extended by using N-containing naphthol analogues such as 5-hydroxyisoquinoline and 6-hydroxyquinoline. The ring closures of the novel bifunctional compounds were also achieved, resulting in new naphth[2,1-e][1,3]oxazines, naphth[1,2-e][1,3]oxazines, isoquinolino[5,6-e][1,3]oxazines and quinolino[5,6-e][1,3]oxazines. H-1 NMR spectra of the target heterocycles 16, 20 and 21 were sufficiently resolved to indentify the present stereochemistry; therefore, beside computed structures, spatial experimental (dipolar coupling-NOE) and computed (ring current effect of the naphthyl moiety-TSNMRS) NMR studies were employed. The studied heterocycles exist exclusively as S(14b),R(N), R(14b),S(N), and S(16b)S(N) isomers, respectively. The flexible moieties of the studied compounds prefer. (C) 2016 Elsevier Ltd. All rights reserved.
KW  - Modified Mannich reaction
KW  - Thienopyridine
KW  - Benzazepine
KW  - NMR spectroscopy
KW  - Stereochemistry
KW  - Theoretical calculations
Y1  - 2016
U6  - https://doi.org/10.1016/j.tet.2016.03.058
SN  - 0040-4020
VL  - 72
SP  - 2402
EP  - 2410
PB  - Elsevier
CY  - Oxford
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  - 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  - Identification of mesomeric substructures by through-space NMR shieldings (TSNMRS). Trimethine cyanine/merocyanine-like or aromatic pi-electron delocalization?
JF  - Tetrahedron
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of amino-substituted heteraromatic six-membered ring systems such as pyrylium/thiopyrylium analogues 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. The TSNMRS values were employed to quantify and visualize the existing aromaticity of the studied compounds. Due to strong conjugation of six-membered ring pi-electrons and lone pairs of the exo-cyclic amino substituents (restricted rotation about partial C,N double bonds) the interplay of still aromatic and already dominating trimethine cyanine/merocyanine-like substructures can be estimated. (C) 2017 Elsevier Ltd. All rights reserved.
KW  - Through-space NMR shieldings (TSNMRS)
KW  - GIAO
KW  - NICS
KW  - Benzenoid structures
KW  - Cyanine/merocyanine-like structures
KW  - Aromaticity
Y1  - 2017
U6  - https://doi.org/10.1016/j.tet.2017.05.062
SN  - 0040-4020
VL  - 73
SP  - 4265
EP  - 4274
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Krtitschka, Angela
A1  - Krüger, Tobias
A1  - Linker, Torsten
T1  - NMR spectroscopic conformational analysis of 4-methylene-cyclohexyl pivalateThe effect of sp(2) hybridization
JF  - Magnetic resonance in chemistry
N2  - The conformational equilibrium of the axial/equatorial conformers of 4-methylene-cyclohexyl pivalate is studied by dynamic NMR spectroscopy in a methylene chloride/freon mixture. At 153K, the ring interconversion gets slow on the nuclear magnetic resonance timescale, the conformational equilibrium (-G degrees) can be examined, and the barrier to ring interconversion (G(#)) can be determined. The structural influence of sp(2) hybridization on both G degrees and G(#) of the cyclohexyl moiety can be quantified.
KW  - 4-methylene-cyclohexyl pivalate
KW  - conformational analysis
KW  - dynamic NMR spectroscopy
KW  - exo-methylene conformational effect at cyclohexane
KW  - quantum chemical calculations
Y1  - 2017
U6  - https://doi.org/10.1002/mrc.4630
SN  - 0749-1581
SN  - 1097-458X
VL  - 55
SP  - 1073
EP  - 1078
PB  - Wiley
CY  - Hoboken
ER  - 
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  - 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  - 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  - 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  - Hansen, Poul Erik
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Ring current and anisotropy effects on OH chemical shifts in resonance-assisted intramolecular H-bonds
JF  - Tetrahedron letters
N2  - Ring current effects on resonance-assisted and intramolecularly bridged hydrogen bond protons for 10-hydroxybenzo[h]quinoline 1 and a number of related compounds were calculated and the through-space NMR shieldings (TSNMRS) obtained hereby visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. These calculations revealed that this through-space effect is comparably large (up to 2 ppm) dependent on the position of the intramolecularly bridged OH proton, and therefore, contribute considerably to the chemical shift of the latter making it questionable to use delta(OH)/ppm in the estimation of intramolecular hydrogen bond strength without taking this into account. Furthermore, the anisotropy effects of additional groups on the aromatic moiety (e.g. the carbonyl group in salicylaldehyde or in o-hydroxyacetophenone of ca. 0.6 ppm deshielding) should also be considered. These through-space effects need to be taken into account when using OH chemical shifts to estimate hydrogen bond strength.
KW  - RA-intramolecular hydrogen bond
KW  - Through-space NMR shieldings (TSNMRS)
KW  - Iso-chemical-shielding surfaces (ICSS)
KW  - Ring current effect
KW  - Anisotropy effect
Y1  - 2018
U6  - https://doi.org/10.1016/j.tetlet.2018.05.006
SN  - 0040-4039
VL  - 59
IS  - 23
SP  - 2288
EP  - 2292
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Stable Carbenes or Betaines?
JF  - European journal of organic chemistry
N2  - The anisotropy effect in H-1 NMR spectroscopy can be readily employed to indicate the position of carbene/betaine mesomeric equilibria. NR2 substituted carbene/betaines tend to adopt betaine structures, whereas in the absence of NR2 substituents, the betaine structures cannot stabilise the structure through both -donation effects of the NMe2 groups and the electronegativity of the nitrogen atoms, and the corresponding carbene-like structures are preferred. These conclusions are supported by calculated bond orders and (C-13)/ppm values. The spatial magnetic properties of isonitriles and carbon monoxide, which can be counted as stable carbenes or, at least, as carbene-analogues, also exist as stable betaine structures, which is again supported by structural and magnetic properties.
KW  - Carbenes
KW  - Betaines
KW  - Mesomerism
KW  - Through-space NMR shieldings (TSNMRS)
KW  - NMR spectroscopy
KW  - Conformation analysis
Y1  - 2018
U6  - https://doi.org/10.1002/ejoc.201800462
SN  - 1434-193X
SN  - 1099-0690
VL  - 2018
IS  - 24
SP  - 3114
EP  - 3121
PB  - Wiley-VCH
CY  - Weinheim
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  - 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 13 C chemical shift and the anisotropy effect of the carbene electron-deficient centre
BT  - simple means to characterize the electron distribution of carbenes
JF  - Magnetic resonance in chemistry
N2  - Both the C-13 chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and C-13 chemical shifts were calculated and compared with the experimental delta(C-13)/ppm values and geometry parameters (as a quality criterion for obtained structures).
KW  - C-13 chemical shift
KW  - carbenes
KW  - zwitterions
KW  - carbene electron deficiency
KW  - nucleus-independent chemical shifts (NICS)
KW  - through space NMR shieldings
KW  - (TSNMRS)
Y1  - 2019
U6  - https://doi.org/10.1002/mrc.4979
SN  - 0749-1581
SN  - 1097-458X
VL  - 58
IS  - 3
SP  - 280
EP  - 292
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Benzyne - an acetylene- or cumulene-like electronic structure?
JF  - Tetrahedron
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzyne 1 and analogues (benzene 2, 1,2,3-cyclohexatriene 3, cyclohexen-3-yne 4, cyclohexen-4-yne 5, cyclohexyne 6) 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. The TSNMRS values could be employed to compare the diatropic ring current effects of benzene and benzyne, and, when compared with the spatial magnetic properties of the analogues, to answer the question whether the benzyne electronic structure is more acetylene- or cumulene-like, supported by structural data and delta(C-13)/ppm values. (C) 2019 Published by Elsevier Ltd.
KW  - Benzyne-allene or cumulene-like structure
KW  - Trough-space NMR shieldings (TSNMRS)
KW  - NICS
KW  - Iso-chemical shielding surfaces (ICSS)
KW  - Ring current effect
Y1  - 2019
U6  - https://doi.org/10.1016/j.tet.2019.07.011
SN  - 0040-4020
VL  - 75
IS  - 33
SP  - 4663
EP  - 4668
PB  - Elsevier
CY  - Oxford
ER  -