Peter Lassen | Technical University of Denmark (DTU) (original) (raw)

Papers by Peter Lassen

Research paper thumbnail of Synthesis and vibrational circular dichroism of enantiopure chiral oxorhenium(V) complexes containing the hydrotris(1-pyrazolyl)borate ligand

Inorganic chemistry, Jan 11, 2006

The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complex... more The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complexes, bearing a hydrotris(1-pyrazolyl)borate (Tp) ligand, have been investigated. These complexes are promising candidates for observation of parity violation (symmetry breaking due to the weak nuclear force). New chiral oxorhenium complexes have been synthesized, namely, [TpReO(eta2-O(CH3)CH2CH2O-O,O)] (4a and 4b) diastereomers and [TpReO(eta2-N(CH3)CH2CH2O-N,O)] (5) and [TpReO(eta2-N(tBu)CH2CH2O-N,O)] (6) enantiomers. All compounds could be obtained in enantiomerically pure form by using either column chromatography or HPLC over chiral columns. VCD spectroscopy of these compounds and of [TpReO(eta2-N(CH3)CH(CH3)CH(Ph)O-N,O)] (2) and [TpReO(eta2-N(CH2)3CHCO2-N,O)] (3) (with chiral bidentate ligands derived, respectively, from ephedrine and proline) were studied. This allowed the absolute configuration determination of all compounds together with their conformational analysis, by comparing...

Research paper thumbnail of Stereochemical determination and bioactivity assessment of (S)-(+)-curcuphenol dimers isolated from the marine sponge Didiscus aceratus and synthesized through laccase biocatalysis

Bioorganic & medicinal chemistry, 2005

Electrospray ionization mass spectrometry-guided isolation of extracts from Didiscus aceratus led... more Electrospray ionization mass spectrometry-guided isolation of extracts from Didiscus aceratus led to the discovery of several new derivatives of the bioactive bisabolene-type sponge metabolite (S)-(+)-curcuphenol (1). The compounds obtained by this method included a mixture of known (2) and new (3) dihydroxylated analogs as well as a novel family of dimeric derivatives, dicurcuphenols A-E (4-8), and dicurcuphenol ether F (9). Dimers 4-9 were also subsequently obtained through a hemisynthetic method in which 1 was incubated with the enzyme laccase. Atropisomeric dimers 5 and 6 were subjected to vibrational circular dichroism analysis thereby establishing their absolute biaryl axial chirality as P and M, respectively. In contrast to 1, metabolites 2-9 exhibited weak or no cytotoxic or lipoxygenase inhibitory effects.

Research paper thumbnail of Direct determination of absolute configuration: a vibrational circular dichroism study on dimethyl-substituted phenyloxiranes synthesized by Shi epoxidation

Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (8... more Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++G**, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and related to the physical structure of the compounds. The absolute configuration could be established directly in each case by comparing experimental and theoretical spectra. In addition, we have been able to document the changes that occur both in structures and in the VA and VCD spectra due to substituent effects on the oxirane ring.

Research paper thumbnail of Structure and absolute configuration of nyasol and hinokiresinol via synthesis and vibrational circular dichroism spectroscopy

Journal of natural products, 2005

The absolute configuration of the norlignan (+)-nyasol was determined to be S by comparison of th... more The absolute configuration of the norlignan (+)-nyasol was determined to be S by comparison of the experimental vibrational circular dichroism data with first-principle calculations taking into account the eight lowest energy conformations. The established absolute configuration of (+)-nyasol enables establishment of the absolute configuration of (-)-hinokiresinol, which is concluded to be S. A total synthesis and resolution of hinokiresinol has been performed to resolve the conflicting reports of the coupling constant of the vinylic protons of the disubstituted double bond in this molecule. Racemic hinokiresinol was resolved. Both enantiomers possess the same antiplasmodial activity.

Research paper thumbnail of Synthesis and Vibrational Circular Dichroism of Enantiopure Chiral Oxorhenium(V) Complexes Containing the Hydrotris(1-pyrazolyl)borate Ligand

Inorganic Chemistry, 2006

The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complex... more The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complexes, bearing a hydrotris(1-pyrazolyl)borate (Tp) ligand, have been investigated. These complexes are promising candidates for observation of parity violation (symmetry breaking due to the weak nuclear force). New chiral oxorhenium complexes have been synthesized, namely, [TpReO(η 2 -O(CH 3 )CH 2 CH 2 O-O,O)] (4a and 4b) diastereomers and [TpReO(η 2 -N(CH 3 )CH 2 CH 2 O-N,O)] (5) and [TpReO(η 2 -N(tBu)CH 2 CH 2 O-N,O)] (6) enantiomers. All compounds could be obtained in enantiomerically pure form by using either column chromatography or HPLC over chiral columns. VCD spectroscopy of these compounds and of [TpReO(η 2 -N(CH 3 )CH(CH 3 )CH(Ph)O-N,O)] (2) and [TpReO(η 2 -N(CH 2 ) 3 CHCO 2 -N,O)]

Research paper thumbnail of Structure and absolute configuration of ginkgolide B characterized by IR- and VCD spectroscopy

Chirality, 2009

Experimental and calculated (B3LYP/6-31G(d)) vibrational circular dichroism (VCD) and IR spectra ... more Experimental and calculated (B3LYP/6-31G(d)) vibrational circular dichroism (VCD) and IR spectra are compared, illustrating that the structure and absolute configuration of ginkgolide B (GB) may be characterized directly in solution. A conformational search for GB using MacroModel and subsequent DFT optimizations (B3LYP/6-31G(d)) provides a structure for the lowest energy conformer which agrees well with the structure determined by X-ray diffraction. In addition, a conformer at an energy of 7 kJ mol 21 (B3LYP/6-3111G(2d,2p)) with respect to the lowest energy conformer is predicted, displaying different intramolecular hydrogen bonding. Differences between measured and calculated IR and VCD spectra for GB at certain wavenumbers are rationalized in terms of interactions with solvent, intermolecular GB-GB interactions, and the potential presence of more than one conformer. This is the first detailed investigation of the spectroscopic fingerprint region (85021300 cm 21 ) of the natural product GB employing infrared absorption and VCD spectroscopy. Chirality 22:217-223, 2010. V V C 2009 Wiley-Liss, Inc.

Research paper thumbnail of A configurational and conformational study of aframodial and its diasteriomers via experimental and theoretical VA and VCD spectroscopies

In this work we present the experimental and theoretical vibrational absorption (VA) and the theo... more In this work we present the experimental and theoretical vibrational absorption (VA) and the theoretical vibrational circular dichroism (VCD) spectra for aframodial. In addition, we present the theoretical VA and VCD spectra for the diasteriomers of aframodial. Aframodial has four chiral centers and hence has 2 4 = 16 diasteriomers, which occur in eight pairs of enantiomers. In addition to the four chiral centers, there is an additional chirality due to the helicity of the entire molecule, which we show by presenting 12 configurations of the 5S,8S,9R,10S enantiomer of aframodial. The VCD spectra for the diasteriomers and the 12 configurations of one enantiomer are shown to be very sensitive not only to Festschrift in Honor of Philip J. Stephens' 65th Birthday.

Research paper thumbnail of Direct determination of absolute configuration of methyl-substituted phenyloxiranes: Combined experimental and theoretical approach

The Journal of Physical Chemistry A, Jul 27, 2006

Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (8... more Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++ G**, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and ...

Research paper thumbnail of Synthesis and vibrational circular dichroism of enantiopure chiral oxorhenium(V) complexes containing the hydrotris(1-pyrazolyl)borate ligand

Inorganic chemistry, Jan 11, 2006

The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complex... more The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complexes, bearing a hydrotris(1-pyrazolyl)borate (Tp) ligand, have been investigated. These complexes are promising candidates for observation of parity violation (symmetry breaking due to the weak nuclear force). New chiral oxorhenium complexes have been synthesized, namely, [TpReO(eta2-O(CH3)CH2CH2O-O,O)] (4a and 4b) diastereomers and [TpReO(eta2-N(CH3)CH2CH2O-N,O)] (5) and [TpReO(eta2-N(tBu)CH2CH2O-N,O)] (6) enantiomers. All compounds could be obtained in enantiomerically pure form by using either column chromatography or HPLC over chiral columns. VCD spectroscopy of these compounds and of [TpReO(eta2-N(CH3)CH(CH3)CH(Ph)O-N,O)] (2) and [TpReO(eta2-N(CH2)3CHCO2-N,O)] (3) (with chiral bidentate ligands derived, respectively, from ephedrine and proline) were studied. This allowed the absolute configuration determination of all compounds together with their conformational analysis, by comparing...

Research paper thumbnail of Stereochemical determination and bioactivity assessment of (S)-(+)-curcuphenol dimers isolated from the marine sponge Didiscus aceratus and synthesized through laccase biocatalysis

Bioorganic & medicinal chemistry, 2005

Electrospray ionization mass spectrometry-guided isolation of extracts from Didiscus aceratus led... more Electrospray ionization mass spectrometry-guided isolation of extracts from Didiscus aceratus led to the discovery of several new derivatives of the bioactive bisabolene-type sponge metabolite (S)-(+)-curcuphenol (1). The compounds obtained by this method included a mixture of known (2) and new (3) dihydroxylated analogs as well as a novel family of dimeric derivatives, dicurcuphenols A-E (4-8), and dicurcuphenol ether F (9). Dimers 4-9 were also subsequently obtained through a hemisynthetic method in which 1 was incubated with the enzyme laccase. Atropisomeric dimers 5 and 6 were subjected to vibrational circular dichroism analysis thereby establishing their absolute biaryl axial chirality as P and M, respectively. In contrast to 1, metabolites 2-9 exhibited weak or no cytotoxic or lipoxygenase inhibitory effects.

Research paper thumbnail of Direct determination of absolute configuration: a vibrational circular dichroism study on dimethyl-substituted phenyloxiranes synthesized by Shi epoxidation

Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (8... more Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++G**, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and related to the physical structure of the compounds. The absolute configuration could be established directly in each case by comparing experimental and theoretical spectra. In addition, we have been able to document the changes that occur both in structures and in the VA and VCD spectra due to substituent effects on the oxirane ring.

Research paper thumbnail of Structure and absolute configuration of nyasol and hinokiresinol via synthesis and vibrational circular dichroism spectroscopy

Journal of natural products, 2005

The absolute configuration of the norlignan (+)-nyasol was determined to be S by comparison of th... more The absolute configuration of the norlignan (+)-nyasol was determined to be S by comparison of the experimental vibrational circular dichroism data with first-principle calculations taking into account the eight lowest energy conformations. The established absolute configuration of (+)-nyasol enables establishment of the absolute configuration of (-)-hinokiresinol, which is concluded to be S. A total synthesis and resolution of hinokiresinol has been performed to resolve the conflicting reports of the coupling constant of the vinylic protons of the disubstituted double bond in this molecule. Racemic hinokiresinol was resolved. Both enantiomers possess the same antiplasmodial activity.

Research paper thumbnail of Synthesis and Vibrational Circular Dichroism of Enantiopure Chiral Oxorhenium(V) Complexes Containing the Hydrotris(1-pyrazolyl)borate Ligand

Inorganic Chemistry, 2006

The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complex... more The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complexes, bearing a hydrotris(1-pyrazolyl)borate (Tp) ligand, have been investigated. These complexes are promising candidates for observation of parity violation (symmetry breaking due to the weak nuclear force). New chiral oxorhenium complexes have been synthesized, namely, [TpReO(η 2 -O(CH 3 )CH 2 CH 2 O-O,O)] (4a and 4b) diastereomers and [TpReO(η 2 -N(CH 3 )CH 2 CH 2 O-N,O)] (5) and [TpReO(η 2 -N(tBu)CH 2 CH 2 O-N,O)] (6) enantiomers. All compounds could be obtained in enantiomerically pure form by using either column chromatography or HPLC over chiral columns. VCD spectroscopy of these compounds and of [TpReO(η 2 -N(CH 3 )CH(CH 3 )CH(Ph)O-N,O)] (2) and [TpReO(η 2 -N(CH 2 ) 3 CHCO 2 -N,O)]

Research paper thumbnail of Structure and absolute configuration of ginkgolide B characterized by IR- and VCD spectroscopy

Chirality, 2009

Experimental and calculated (B3LYP/6-31G(d)) vibrational circular dichroism (VCD) and IR spectra ... more Experimental and calculated (B3LYP/6-31G(d)) vibrational circular dichroism (VCD) and IR spectra are compared, illustrating that the structure and absolute configuration of ginkgolide B (GB) may be characterized directly in solution. A conformational search for GB using MacroModel and subsequent DFT optimizations (B3LYP/6-31G(d)) provides a structure for the lowest energy conformer which agrees well with the structure determined by X-ray diffraction. In addition, a conformer at an energy of 7 kJ mol 21 (B3LYP/6-3111G(2d,2p)) with respect to the lowest energy conformer is predicted, displaying different intramolecular hydrogen bonding. Differences between measured and calculated IR and VCD spectra for GB at certain wavenumbers are rationalized in terms of interactions with solvent, intermolecular GB-GB interactions, and the potential presence of more than one conformer. This is the first detailed investigation of the spectroscopic fingerprint region (85021300 cm 21 ) of the natural product GB employing infrared absorption and VCD spectroscopy. Chirality 22:217-223, 2010. V V C 2009 Wiley-Liss, Inc.

Research paper thumbnail of A configurational and conformational study of aframodial and its diasteriomers via experimental and theoretical VA and VCD spectroscopies

In this work we present the experimental and theoretical vibrational absorption (VA) and the theo... more In this work we present the experimental and theoretical vibrational absorption (VA) and the theoretical vibrational circular dichroism (VCD) spectra for aframodial. In addition, we present the theoretical VA and VCD spectra for the diasteriomers of aframodial. Aframodial has four chiral centers and hence has 2 4 = 16 diasteriomers, which occur in eight pairs of enantiomers. In addition to the four chiral centers, there is an additional chirality due to the helicity of the entire molecule, which we show by presenting 12 configurations of the 5S,8S,9R,10S enantiomer of aframodial. The VCD spectra for the diasteriomers and the 12 configurations of one enantiomer are shown to be very sensitive not only to Festschrift in Honor of Philip J. Stephens' 65th Birthday.

Research paper thumbnail of Direct determination of absolute configuration of methyl-substituted phenyloxiranes: Combined experimental and theoretical approach

The Journal of Physical Chemistry A, Jul 27, 2006

Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (8... more Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++ G**, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and ...