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 - Buyinza, Daniel A1 - Derese, Solomon A1 - Ndakala, Albert A1 - Heydenreich, Matthias A1 - Yenesew, Abiy A1 - Koch, Andreas A1 - Oriko, Richard T1 - A coumestan and a coumaronochromone from Millettia lasiantha JF - Biochemical systematics and ecology N2 - The manuscript describes the phytochemical investigation of the roots, leaves and stem bark of Millettia lasiantha resulting in the isolation of twelve compounds including two new isomeric isoflavones lascoumestan and las-coumaronochromone. The structures of the new compounds were determined using different spectroscopic techniques. KW - Millettia lasiantha KW - Leguminosae KW - Coumestan KW - Coumaronochromone Y1 - 2021 U6 - https://doi.org/10.1016/j.bse.2021.104277 SN - 0305-1978 SN - 1873-2925 VL - 97 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 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Dative or coordinative carbon-boron bond in boron trapped N-heterocyclic carbenes (NHCs)? BT - an answer given on the magnetic criterion JF - Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of isolated as well as B-C bond length varied model compounds (BR3 trapped NHCs) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the present dative vs. coordinative bond character of the boron-carbon bond in the trapped NHCs. Results are confirmed by bond lengths and B-11/C-13 chemical shift variations in the BR3 trapped NHCs. KW - NHCs KW - Dative vs. coordinative NHC -> BR3 bond KW - Through-space NMR KW - shieldings (TSNMRS) KW - NICS KW - Anisotropy effect Y1 - 2021 U6 - https://doi.org/10.1016/j.tet.2020.131787 SN - 0040-4020 SN - 1464-5416 VL - 80 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Quantification of sigma-acceptor and pi-donor stabilization in O, S and Hal analogues of N-heterocyclic carbenes (NHCs) 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 (TSNMRSs), of stable O, S and Hal analogues of N-heterocyclic carbenes (NHCs) have been calculated using the GIAO perturbation method employing the nucleus-independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSSs) of various sizes and directions. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the position of the present mesomeric equilibria (carbenes <-> ylides). The results are confirmed by geometry (bond angles and bond lengths), IR spectra, UV spectra, and C-13 chemical shifts of the electron-deficient carbon centers. Y1 - 2021 U6 - https://doi.org/10.1021/acs.jpca.1c05257 SN - 1089-5639 SN - 1520-5215 VL - 125 IS - 33 SP - 7235 EP - 7245 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Intramolecular carbene stabilization via 3c,2e bonding on basis of the magnetic criterion JF - Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of bent cyclobutylcarbene 8, 1,2-diboretane-3-ylidene 9, and some carbene analogues of boron 14-18 as most intriguing examples of carbenes, which can be stabilized as homoaromatic systems with 3c,2e bonding, have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values (actually, ring current effect/anisotropy effects as measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the degree of present 3c,2e-homoaromaticity. Results are confirmed by geometry (bond angles and bond lengths) and spectroscopic data, the delta(B-11)/ppm data and the C-13 chemical shifts of the carbene electron-deficient centre. KW - Cyclobutylcarbene KW - 1,2-diboretane-3-ylidene KW - 3c,2e-bonding KW - Through-space NMR shieldings (TSNMRS) KW - NICS Y1 - 2021 U6 - https://doi.org/10.1016/j.tet.2021.132357 SN - 0040-4020 SN - 1464-5416 VL - 95 PB - Elsevier Science CY - Amsterdam 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 - 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 - Cyclazines-structure and aromaticity or antiaromaticity on the magnetic criterion JF - European journal of organic chemistry N2 - Structure and spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of all ten cycl[2.2.2]azine to cycl[4.4.4]azine, hetero-analogues and the corresponding hydrocarbons have been calculated at the B3LYP/6-311G(d,p) theory level using the GIAO perturbation method and employing the nucleus independent chemical shift (NICS) concept. The TSNMRS values (actually, the ring current effect as measurable in H-1 NMR spectroscopy) are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction, and employed to readily qualify and quantify the degree of (anti)aromaticity. Results are confirmed by NMR [delta(H-1)/ppm, delta(N-15)/ppm] and geometry (planar, twisted, bow-shaped) data. The cyclazines N[2.2.2](-) up to N[2.4.4](-) are planar or at most slightly bowl-shaped and, due to coherent peripheral ring currents (except in N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+)), develop aromaticity or anti-aromaticity of the whole molecules dependent on the number of peripheral conjugated pi electrons. The cyclazines N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+) develop two ring currents of different direction within the same molecule, in which the dominating ring current proves to be paratropic (in N[3.3.4](+) diatropic) including the nodal N p(z) lone pair into the conjugation. The residual cyclazines N[3.4.4], N[4.4.4](-) and N[4.4.4](+) are heavily twisted and, therefore, are not developing peripheral or diverse ring currents. The TSNMRS information about cyclazines and the parent tricyclic annulene analogues is congruent subject to structure and number of peripheral or internal conjugated pi electrons, the corresponding (anti)aromaticity is in unequivocal accordance with Huckel's rule. KW - Aromaticity KW - Cyclazines KW - NMR spectroscopy KW - Peripheral ring current Y1 - 2022 U6 - https://doi.org/10.1002/ejoc.202101362 SN - 1434-193X SN - 1099-0690 VL - 2022 IS - 8 PB - Wiley-VCH CY - Weinheim 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 -