Torsten Bruhn - Academia.edu (original) (raw)

Papers by Torsten Bruhn

Tetrahedron Letters, 2002

... JW Steed and JL Atwood, Supramolecular Chemistry, John Wiley & Sons, Chichester (... more ... JW Steed and JL Atwood, Supramolecular Chemistry, John Wiley & Sons, Chichester (2000). 3. Some reviews and books: (a) Gutsche, CD Calixarenes; Royal Society of Chemistry: Cambridge, 1989; (b) Vicens, J.; Böhmer, V., Eds.; Calixarenes. ...

Journal of Natural Products, 2015

Myrtucommulone A (MC A) (1), isolated from Myrtus communis (myrtle), shows the same pharmacologic... more Myrtucommulone A (MC A) (1), isolated from Myrtus communis (myrtle), shows the same pharmacological activity for inhibition of inflammation and induction of apoptosis as synthetic MC A, which consists of three stereoisomers, i.e., two enantiomers and one meso form. This led to the question of whether the natural MC A is a pure stereoisomer or a mixture of stereoisomers. The specific rotation and electronic circular dichroism (ECD) data of natural MC A (1) as well as of a pentacyclic derivative 4 revealed that naturally occurring MC A (1) consists of the racemate and the meso form in a 1:1 ratio. A probable precursor of MC A (1), nor-semimyrtucommulone (5), was also isolated from myrtle as a racemate. The absolute configurations of the enantiomers of 1 and 5 were determined using a combination of experimental and quantum-chemical calculated ECD spectra.

The Journal of organic chemistry, Jan 12, 2016

The single-electron oxidative dimerization of basket-handle porphyrins (BHPs) with different coor... more The single-electron oxidative dimerization of basket-handle porphyrins (BHPs) with different coordinated metal ions [Cu(II), Ni(II), Pd(II), Zn(II)] yielded directly meso-meso linked dimers in excellent yields. The synthetic protocol is suited for coupling substrates with different meso-substituents (H, Br, aryl, alkyl) opposite to the coupling site. Experimental findings concerning reactivities and selectivities were in good agreement with theoretical investigations using ALIE calculations. The dimers, which all are axially chiral, were resolved into their enantiomers by HPLC on a chiral phase. ECD spectra were measured in the stopped-flow mode and compared with results from quantum-chemical ECD calculations to assign the absolute configuration. One directly linked dimer was further oxidized to a fused system, which possessed a stable helical chirality. Its absolute configuration was again assigned by ECD investigations. Furthermore, functionalized BHPs and tetraarylporphyrins were...

Tetrahedron 66 Pp 9894 9901, 2010

Three novel natural products, sorbifuranones AeC (4e6), were isolated from a Penicillium chrysoge... more Three novel natural products, sorbifuranones AeC (4e6), were isolated from a Penicillium chrysogenum fungus isolated from the marine sponge Ircinia fasciculata. Sorbifuranones B (5) and C (6) and 2 0 ,3 0 -dihydrosorbicillin, a putative precursor to sorbifuranone B, were also found in the culture of another Penicillium strain, which was isolated from the sponge Tethya aurantium. Their constitutions were elucidated mainly by 2D NMR. NOE correlations in combination with quantum chemical calculations and comparison of experimental and calculated electronic circular dichroism (CD) spectra permitted assignment of the absolute configuration of sorbifuranone C. The structures hint at a two-step cleavage-cyclization sequence of sorbifuranone A (4) leading to the spiro compound sorbifuranone C, while sorbifuranone B is likely to be the respective cleavage product of a putative 2 0 ,3 0 -dihydrosorbifuranone A, which cannot cyclize further.

J Mol Struc Theochem, 2004

The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been e... more The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.

Bioorganic & Medicinal Chemistry, 2015

Biliverdin IXα is a naturally occurring linear tetrapyrrolic product of the enzymatic oxidative r... more Biliverdin IXα is a naturally occurring linear tetrapyrrolic product of the enzymatic oxidative ring cleavage of heme. Evidence is mounting that biliverdin possesses antioxidant properties in mammals but its mode of action is unclear. We present the single crystal X-ray structure analysis of two regioisomeric biladien-1,19-diones-ab that are derived from biliverdin IXα dimethyl ester by addition of two vicinal trans-methoxy groups to the 4,5- or 15,16-double bonds, respectively. The compounds were likely formed by photosensitized singlet oxygen addition, followed by Lewis acid-catalyzed methanol-induced ring-opening of the intermediate epoxide, and OH-to-OMe substitution. We thus present structural evidence for a possible reaction mechanism by which biliverdin can act as an antioxidant.

The Journal of Organic Chemistry, 2015

Chiral and achiral basket-handle porphyrins (BHPs) with different p-xylene straps and peripheral ... more Chiral and achiral basket-handle porphyrins (BHPs) with different p-xylene straps and peripheral solubilizing groups were synthesized using a previously established synthetic approach. Subsequent modification, functionalization, and metalation of the tetrapyrrolic macrocycle yielded more than 80 BHPs. The chiral representatives were resolved into their enantiomers, whose absolute configurations were determined by comparison of their ECD spectra with other experimental or quantum chemically calculated spectra. NMR studies and coupled-cluster calculations proved that the free base BHPs, although highly symmetric, exhibited the phenomenon of "arrested tautomerism". Comparison of the solid-state structures of three metalated BHPs offered detailed insight into their three-dimensional shape. Finally, directly linked dimeric porphyrins with a BHP subunit were synthesized from functionalized BHPs to prove their value as synthetic building blocks.

European Journal of Organic Chemistry, 2015

ABSTRACT Indaphyrins and indachlorins possess large chiral porphyrinoid π-systems with particular... more ABSTRACT Indaphyrins and indachlorins possess large chiral porphyrinoid π-systems with particularly long-wavelength absorption properties. All indaphyrin derivatives, including the indaphyrin MII complexes (M = NiII, CuII, ZnII, and PtII), adopt strongly ruffled conformations incorporating a helimeric twist, thus forming two stereochemically stable helimeric enantiomers. Their degree of ruffling is modulated by the coordination to metal ions or pyrrole ring modifications. Resolution of the racemic mixtures of the helimers of all derivatives was achieved by HPLC on a chiral phase and their absolute stereostructures were assigned. The much altered UV/Vis spectra of the indaphyrin derivatives, when compared to those of porphyrins, were rationalized using excited state calculations. The conformational stability of the conformers toward thermally induced racemization was also shown. The report forms the basis for future applications that exploit the chiral properties of the chromophores.

Journal of Molecular Structure: THEOCHEM, 2004

The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been e... more The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.

Journal of natural products, Jan 26, 2015

Eight new khayanolides, named thaixylomolins G-N (1-8), two new phragmalins (9 and 10), and two n... more Eight new khayanolides, named thaixylomolins G-N (1-8), two new phragmalins (9 and 10), and two new mexicanolides (11 and 12) were obtained from the seeds of the Trang mangrove plant Xylocarpus moluccensis. The absolute configurations of these limonoids, except for the stereocenter at C-6 of 11 and 12, were assigned by experimental and TDDFT calculated electronic circular dichroism spectra. The khayanolides may be classified into two subclasses, one of which has a C-2 carbonyl and a 3β-acetoxy group, whereas the other possesses a 2β-acetoxy and a C-3 carbonyl function. Khayanolides, rearranged phragmalin-type limonoids, are reported for the first time from plants of the mangrove genus Xylocarpus. The structure of moluccensin J, a known 30-ketophragmalin containing a Δ(8(14)) double bond, was revised to be a khayanolide, named thaixylomolin K. The antiviral activities of the isolates against pandemic influenza A virus (subtype H1N1) were tested by the assay of cytopathic effect inhib...

Chemical communications (Cambridge, England), Jan 16, 2015

Apparent exceptions to the exciton chirality method may arise for chromophores undergoing transit... more Apparent exceptions to the exciton chirality method may arise for chromophores undergoing transitions which are both electric- and magnetic-dipole allowed, for example bis-phenanthrenes. We present a computational approach to calculate exciton-coupled CD spectra based on a quantum-mechanical description of the excitonic parameters, which also includes the solvent effects.

The Journal of organic chemistry, Jan 6, 2015

The reduction of a free-base chlorin generally forms a bacteriochlorin (BC), while the reduction ... more The reduction of a free-base chlorin generally forms a bacteriochlorin (BC), while the reduction of the corresponding metallochlorin forms a metalloisobacteriochlorin (M-iBC). This regioselectivity has been long known but was never fully rationalized. In the free-base case, this regioselectivity can be explained using resonance arguments, but the explanations for the regioselectivity in the metallochlorin reactions requires a more sophisticated approach. A combination of DFT-calculated average local ionization energies (ALIEs), thermodynamics of the products, and the transition-state trajectories of reduction reactions of meso-tetraaryl- and β-octaethylchlorins, as their free bases and zinc complexes, now fully delineate the theoretical basis of the reduction regioselectivity. The reactions are kinetically controlled. Steric effects originating in the conformational flexibility of the chlorin macrocycle direct the reactions toward the formation of iBCs. Only when electronic effects ...

Physical chemistry chemical physics : PCCP, Jan 7, 2015

meso-Tetraphenylporphyrin N-oxide (1) and meso-tetraphenyl-21,23-dithiaporphyrin S-oxide (3) poss... more meso-Tetraphenylporphyrin N-oxide (1) and meso-tetraphenyl-21,23-dithiaporphyrin S-oxide (3) possess optical spectra that are distinctly different from their parent porphyrins, meso-tetraphenylporphyrin (2) and meso-tetraphenyl-21,23-dithiaporphyrin (4), respectively. The hyperporphyrin spectra were reproduced and classified using TD CAM-B3LYP and SCS-CC2 computational methods. Calculations revealed the electronic and conformational influences of the N- and S-oxide functionalities. While the N-oxide under acidic conditions forms a dication with a UV-vis spectrum that is nearly indistinguishable from that of the diprotonated parent porphyrin, the diprotonated S-oxide possesses a much different UV-vis spectrum from diprotonated parent dithiaporphyrin. A computational study of the protonation events revealed the site and degree of protonation and rationalized the regular and hyperporphyrin UV-vis spectra of the neutral and protonated species, respectively. The study illuminates the ele...

Chemical communications (Cambridge, England), Jan 7, 2014

Upon irradiation a mixed-valence (MV) state is formed in a donor-iridium(III)-acceptor triad by a... more Upon irradiation a mixed-valence (MV) state is formed in a donor-iridium(III)-acceptor triad by a photoinduced electron transfer process. The resulting radical and intervalence charge transfer (IV-CT) absorptions cover a wide spectral range (3200-400 nm). These results were supported by spectroelectrochemistry, fs-time resolved pump-probe spectroscopy and assisted by TD-DFT calculations.

Tetrahedron Letters, 2002

... JW Steed and JL Atwood, Supramolecular Chemistry, John Wiley & Sons, Chichester (... more ... JW Steed and JL Atwood, Supramolecular Chemistry, John Wiley & Sons, Chichester (2000). 3. Some reviews and books: (a) Gutsche, CD Calixarenes; Royal Society of Chemistry: Cambridge, 1989; (b) Vicens, J.; Böhmer, V., Eds.; Calixarenes. ...

Journal of Natural Products, 2015

Myrtucommulone A (MC A) (1), isolated from Myrtus communis (myrtle), shows the same pharmacologic... more Myrtucommulone A (MC A) (1), isolated from Myrtus communis (myrtle), shows the same pharmacological activity for inhibition of inflammation and induction of apoptosis as synthetic MC A, which consists of three stereoisomers, i.e., two enantiomers and one meso form. This led to the question of whether the natural MC A is a pure stereoisomer or a mixture of stereoisomers. The specific rotation and electronic circular dichroism (ECD) data of natural MC A (1) as well as of a pentacyclic derivative 4 revealed that naturally occurring MC A (1) consists of the racemate and the meso form in a 1:1 ratio. A probable precursor of MC A (1), nor-semimyrtucommulone (5), was also isolated from myrtle as a racemate. The absolute configurations of the enantiomers of 1 and 5 were determined using a combination of experimental and quantum-chemical calculated ECD spectra.

The Journal of organic chemistry, Jan 12, 2016

The single-electron oxidative dimerization of basket-handle porphyrins (BHPs) with different coor... more The single-electron oxidative dimerization of basket-handle porphyrins (BHPs) with different coordinated metal ions [Cu(II), Ni(II), Pd(II), Zn(II)] yielded directly meso-meso linked dimers in excellent yields. The synthetic protocol is suited for coupling substrates with different meso-substituents (H, Br, aryl, alkyl) opposite to the coupling site. Experimental findings concerning reactivities and selectivities were in good agreement with theoretical investigations using ALIE calculations. The dimers, which all are axially chiral, were resolved into their enantiomers by HPLC on a chiral phase. ECD spectra were measured in the stopped-flow mode and compared with results from quantum-chemical ECD calculations to assign the absolute configuration. One directly linked dimer was further oxidized to a fused system, which possessed a stable helical chirality. Its absolute configuration was again assigned by ECD investigations. Furthermore, functionalized BHPs and tetraarylporphyrins were...

Tetrahedron 66 Pp 9894 9901, 2010

Three novel natural products, sorbifuranones AeC (4e6), were isolated from a Penicillium chrysoge... more Three novel natural products, sorbifuranones AeC (4e6), were isolated from a Penicillium chrysogenum fungus isolated from the marine sponge Ircinia fasciculata. Sorbifuranones B (5) and C (6) and 2 0 ,3 0 -dihydrosorbicillin, a putative precursor to sorbifuranone B, were also found in the culture of another Penicillium strain, which was isolated from the sponge Tethya aurantium. Their constitutions were elucidated mainly by 2D NMR. NOE correlations in combination with quantum chemical calculations and comparison of experimental and calculated electronic circular dichroism (CD) spectra permitted assignment of the absolute configuration of sorbifuranone C. The structures hint at a two-step cleavage-cyclization sequence of sorbifuranone A (4) leading to the spiro compound sorbifuranone C, while sorbifuranone B is likely to be the respective cleavage product of a putative 2 0 ,3 0 -dihydrosorbifuranone A, which cannot cyclize further.

J Mol Struc Theochem, 2004

The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been e... more The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.

Bioorganic & Medicinal Chemistry, 2015

Biliverdin IXα is a naturally occurring linear tetrapyrrolic product of the enzymatic oxidative r... more Biliverdin IXα is a naturally occurring linear tetrapyrrolic product of the enzymatic oxidative ring cleavage of heme. Evidence is mounting that biliverdin possesses antioxidant properties in mammals but its mode of action is unclear. We present the single crystal X-ray structure analysis of two regioisomeric biladien-1,19-diones-ab that are derived from biliverdin IXα dimethyl ester by addition of two vicinal trans-methoxy groups to the 4,5- or 15,16-double bonds, respectively. The compounds were likely formed by photosensitized singlet oxygen addition, followed by Lewis acid-catalyzed methanol-induced ring-opening of the intermediate epoxide, and OH-to-OMe substitution. We thus present structural evidence for a possible reaction mechanism by which biliverdin can act as an antioxidant.

The Journal of Organic Chemistry, 2015

Chiral and achiral basket-handle porphyrins (BHPs) with different p-xylene straps and peripheral ... more Chiral and achiral basket-handle porphyrins (BHPs) with different p-xylene straps and peripheral solubilizing groups were synthesized using a previously established synthetic approach. Subsequent modification, functionalization, and metalation of the tetrapyrrolic macrocycle yielded more than 80 BHPs. The chiral representatives were resolved into their enantiomers, whose absolute configurations were determined by comparison of their ECD spectra with other experimental or quantum chemically calculated spectra. NMR studies and coupled-cluster calculations proved that the free base BHPs, although highly symmetric, exhibited the phenomenon of "arrested tautomerism". Comparison of the solid-state structures of three metalated BHPs offered detailed insight into their three-dimensional shape. Finally, directly linked dimeric porphyrins with a BHP subunit were synthesized from functionalized BHPs to prove their value as synthetic building blocks.

European Journal of Organic Chemistry, 2015

ABSTRACT Indaphyrins and indachlorins possess large chiral porphyrinoid π-systems with particular... more ABSTRACT Indaphyrins and indachlorins possess large chiral porphyrinoid π-systems with particularly long-wavelength absorption properties. All indaphyrin derivatives, including the indaphyrin MII complexes (M = NiII, CuII, ZnII, and PtII), adopt strongly ruffled conformations incorporating a helimeric twist, thus forming two stereochemically stable helimeric enantiomers. Their degree of ruffling is modulated by the coordination to metal ions or pyrrole ring modifications. Resolution of the racemic mixtures of the helimers of all derivatives was achieved by HPLC on a chiral phase and their absolute stereostructures were assigned. The much altered UV/Vis spectra of the indaphyrin derivatives, when compared to those of porphyrins, were rationalized using excited state calculations. The conformational stability of the conformers toward thermally induced racemization was also shown. The report forms the basis for future applications that exploit the chiral properties of the chromophores.

Journal of Molecular Structure: THEOCHEM, 2004

The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been e... more The 13C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C3O2, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.

Journal of natural products, Jan 26, 2015

Eight new khayanolides, named thaixylomolins G-N (1-8), two new phragmalins (9 and 10), and two n... more Eight new khayanolides, named thaixylomolins G-N (1-8), two new phragmalins (9 and 10), and two new mexicanolides (11 and 12) were obtained from the seeds of the Trang mangrove plant Xylocarpus moluccensis. The absolute configurations of these limonoids, except for the stereocenter at C-6 of 11 and 12, were assigned by experimental and TDDFT calculated electronic circular dichroism spectra. The khayanolides may be classified into two subclasses, one of which has a C-2 carbonyl and a 3β-acetoxy group, whereas the other possesses a 2β-acetoxy and a C-3 carbonyl function. Khayanolides, rearranged phragmalin-type limonoids, are reported for the first time from plants of the mangrove genus Xylocarpus. The structure of moluccensin J, a known 30-ketophragmalin containing a Δ(8(14)) double bond, was revised to be a khayanolide, named thaixylomolin K. The antiviral activities of the isolates against pandemic influenza A virus (subtype H1N1) were tested by the assay of cytopathic effect inhib...

Chemical communications (Cambridge, England), Jan 16, 2015

Apparent exceptions to the exciton chirality method may arise for chromophores undergoing transit... more Apparent exceptions to the exciton chirality method may arise for chromophores undergoing transitions which are both electric- and magnetic-dipole allowed, for example bis-phenanthrenes. We present a computational approach to calculate exciton-coupled CD spectra based on a quantum-mechanical description of the excitonic parameters, which also includes the solvent effects.

The Journal of organic chemistry, Jan 6, 2015

The reduction of a free-base chlorin generally forms a bacteriochlorin (BC), while the reduction ... more The reduction of a free-base chlorin generally forms a bacteriochlorin (BC), while the reduction of the corresponding metallochlorin forms a metalloisobacteriochlorin (M-iBC). This regioselectivity has been long known but was never fully rationalized. In the free-base case, this regioselectivity can be explained using resonance arguments, but the explanations for the regioselectivity in the metallochlorin reactions requires a more sophisticated approach. A combination of DFT-calculated average local ionization energies (ALIEs), thermodynamics of the products, and the transition-state trajectories of reduction reactions of meso-tetraaryl- and β-octaethylchlorins, as their free bases and zinc complexes, now fully delineate the theoretical basis of the reduction regioselectivity. The reactions are kinetically controlled. Steric effects originating in the conformational flexibility of the chlorin macrocycle direct the reactions toward the formation of iBCs. Only when electronic effects ...

Physical chemistry chemical physics : PCCP, Jan 7, 2015

meso-Tetraphenylporphyrin N-oxide (1) and meso-tetraphenyl-21,23-dithiaporphyrin S-oxide (3) poss... more meso-Tetraphenylporphyrin N-oxide (1) and meso-tetraphenyl-21,23-dithiaporphyrin S-oxide (3) possess optical spectra that are distinctly different from their parent porphyrins, meso-tetraphenylporphyrin (2) and meso-tetraphenyl-21,23-dithiaporphyrin (4), respectively. The hyperporphyrin spectra were reproduced and classified using TD CAM-B3LYP and SCS-CC2 computational methods. Calculations revealed the electronic and conformational influences of the N- and S-oxide functionalities. While the N-oxide under acidic conditions forms a dication with a UV-vis spectrum that is nearly indistinguishable from that of the diprotonated parent porphyrin, the diprotonated S-oxide possesses a much different UV-vis spectrum from diprotonated parent dithiaporphyrin. A computational study of the protonation events revealed the site and degree of protonation and rationalized the regular and hyperporphyrin UV-vis spectra of the neutral and protonated species, respectively. The study illuminates the ele...

Chemical communications (Cambridge, England), Jan 7, 2014

Upon irradiation a mixed-valence (MV) state is formed in a donor-iridium(III)-acceptor triad by a... more Upon irradiation a mixed-valence (MV) state is formed in a donor-iridium(III)-acceptor triad by a photoinduced electron transfer process. The resulting radical and intervalence charge transfer (IV-CT) absorptions cover a wide spectral range (3200-400 nm). These results were supported by spectroelectrochemistry, fs-time resolved pump-probe spectroscopy and assisted by TD-DFT calculations.