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 - 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 - 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 - 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 - 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 -