The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Yue-wei Guo - One of the best experts on this subject based on the ideXlab platform.
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Sarcophytrols A–C, new capnosane diterpenoids from the South China Sea soft coral Sarcophyton trocheliophorum
Tetrahedron Letters, 2015Co-Authors: Wen-ting Chen, Li-gong Yao, Yue-wei GuoAbstract:Three new capnosane type diterpenoids, sarcophytrols A–C (1–3), were isolated from the South China Sea soft coral Sarcophyton trocheliophorum. Among them, 1 and 2 share a dodecahydrocyclopenta[6,7]cycloundeca[1,2-b]Oxirene ring system with an unusual 1Z-configuration, whereas 1 and 3 encompass a peculiar isopropyl alcohol moiety. Their structures were elucidated by extensive spectroscopic analysis and the absolute configuration of 1 was determined by an X-ray diffraction analysis with Cu Kα radiation on a single crystal.
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Unprecedented diterpenoids as a PTP1B inhibitor from the Hainan soft coral Sarcophyton trocheliophorum Marenzeller.
Organic letters, 2012Co-Authors: Lin-fu Liang, Li-gong Yao, Tibor Kurtán, Attila Mándi, Wen Zhang, Yue-wei GuoAbstract:Methyl sarcotroates A and B (3 and 4), two unprecedented diterpenoids possessing a tetradecahydrocyclopenta[3′,4′]cyclobuta[1′,2′:4,5]cyclonona[1,2-b]Oxirene ring system, along with their probable biogenetic precursor, sarcophytonolide M (1), were isolated from the Hainan soft coral Sarcophyton trocheliophorum. Their structures were elucidated by detailed spectroscopic analysis, and the absolute configuration of compound 3 was determined by TDDFT ECD calculations. Compound 4 exhibited significant inhibitory activity against protein tyrosine phosphatase 1B (PTP1B), being similar to that of positive control oleanolic acid.
Henry F. Schaefer - One of the best experts on this subject based on the ideXlab platform.
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the wolff rearrangement the relevant portion of the Oxirene ketene potential energy hypersurface
Journal of the American Chemical Society, 1994Co-Authors: Anthony P Scott, Ross H Nobes, Henry F. Schaefer, Leo RadomAbstract:The portion of the C[sub 2]H[sub 2]O potential energy hypersurface that includes Oxirene, formylmethylene, and ketene has been studied with ab initio methods incorporating high levels of electron correlation and basis sets that include up to f and g functions. Our best geometries were determined at the CCSD(T)/6-3 UG(df,p) level of theory. Single-point energies were then determined by using CCSD(T) and BD(T) calculations with the cc-pVTZ basis set augmented with additional f and g polarization functions. Our main conclusion is that there is little or no barrier separating formylmethylene from Oxirene, the potential energy surface linking these two species begin extremely flat. On the other hand, a more significant barrier (21-23 kJ mol[sup [minus]1]) separates formylmethylene or Oxirene from ketene. These results strongly support the previously postulated intermediacy of Oxirene in the Wolff rearrangement. Ketene is found to lie 325 kJ mol[sup [minus]1] lower in energy than Oxirene. Our predicted energy threshold for the scrambling of carbon atoms in ketene (348 kJ mol[sup [minus]1]) is in close agreement with a recent experimental value (340 kJ mol[sup [minus]1]). 42 refs., 5 figs., 3 tabs.
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Substituted Oxirenes (X2C2O, X = BH2, CH3, NH2, OH, F): Can They Be Made?
Journal of the American Chemical Society, 1994Co-Authors: Joseph E. Fowler, John Morrison Galbraith, George Vacek, Henry F. SchaeferAbstract:The Oxirene system has received much attention recently; most theoretical studies have concentrated on the unsubstituted molecule while most experimentation has involved substituted Oxirenes. In an effort to bridge the information gap between theory and experiment we have undertaken an ab initio study of substituted Oxirenes. Predictions at various levels of theory up to the double-[zeta] plus polarization single and double coupled cluster with perturbative triples correction [DZP CCSD(T)] are presented for the series of substituted Oxirenes with the formula X[sub 2]C[sub 2]O, where X = BH[sub 2], CH[sub 3], NH[sub 2], OH, and F. Predictions from this level of theory are thought to be quite dependable on the basis of earlier work. Stationary points are compared among themselves and with the parent Oxirene (X = H) and the molecular orbitals involved in ring bonding are analyzed, providing insight into the nature of the chemical bonding. Only the dimethylOxirene molecule (in addition to the earlier reported unsubstituted Oxirene) is predicted to be a minimum on the DZP CCSD(T) surface. All other substituted Oxirenes in the series are predicted to be transition states at that or lower levels of theory. Preliminary data from a benzoOxirene study are also included. 53 refs.,more » 9 figs., 11 tabs.« less
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Oxirene. To be or not to be
The Journal of Physical Chemistry, 1994Co-Authors: George Vacek, Anthony P Scott, Ross H Nobes, Henry F. Schaefer, John Morrison Galbraith, Yukio Yamaguchi, Leo RadomAbstract:The C{sub 2v}-symmetry structure of Oxirene has been examined using ab initio molecular orbital calculations with large basis sets and a variety of methods of including electron correlation. Different qualitative conclusions regarding the nature of Oxirene are reached, depending on the choice of basis set and method of electron correlation incorporation. With certain combinations of basis set and theoretical method, the symmetric Oxirene structure is found to be a saddle point on the potential energy surface, while for other combinations Oxirene is a local minimum. Inclusion of triple excitations in the correlation treatment has a large effect, tending to make the curvature of the surface corresponding to a ring-opening distortion of the C{sub 2v}-symmetry structure less positive (or more negative). This is counterbalanced by a basis set effect, with inclusion of functions making the curvature more positive. At our highest level of theory, CCSD(T) with basis sets of triple-{zeta} quality and including multiple d shells and an f shell on C and O and multiple p shells and a d shell on H, Oxirene is a genuine minimum under harmonic vibrational analysis, with a ring-opening frequency of 139-163 cm{sup -1}. 72 refs., 2 tabs.
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Does Oxirene exist? A theoretical inquiry involving the coupled-cluster method
Chemical Physics Letters, 1991Co-Authors: George Vacek, Brenda Thies Colegrove, Henry F. SchaeferAbstract:Abstract The Oxirene isomer of C2H2O has been characterized at three levels of ab initio quantum-mechanical theory. At all three levels, Oxirene is shown to be a genuine minimum on the respective C2H2O potential energy hypersurfaces. However, the steep decrease in the predicted ring-deformation vibrational frequency (to 262 cm− with the double-zeta-plus-polarization basis set, single-and double-excitation coupled-cluster method) as a function of level of theory leaves open the possibility that Oxirene may be a transition state for the degenerate rearrangement of ketene.
Leo Radom - One of the best experts on this subject based on the ideXlab platform.
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the wolff rearrangement the relevant portion of the Oxirene ketene potential energy hypersurface
Journal of the American Chemical Society, 1994Co-Authors: Anthony P Scott, Ross H Nobes, Henry F. Schaefer, Leo RadomAbstract:The portion of the C[sub 2]H[sub 2]O potential energy hypersurface that includes Oxirene, formylmethylene, and ketene has been studied with ab initio methods incorporating high levels of electron correlation and basis sets that include up to f and g functions. Our best geometries were determined at the CCSD(T)/6-3 UG(df,p) level of theory. Single-point energies were then determined by using CCSD(T) and BD(T) calculations with the cc-pVTZ basis set augmented with additional f and g polarization functions. Our main conclusion is that there is little or no barrier separating formylmethylene from Oxirene, the potential energy surface linking these two species begin extremely flat. On the other hand, a more significant barrier (21-23 kJ mol[sup [minus]1]) separates formylmethylene or Oxirene from ketene. These results strongly support the previously postulated intermediacy of Oxirene in the Wolff rearrangement. Ketene is found to lie 325 kJ mol[sup [minus]1] lower in energy than Oxirene. Our predicted energy threshold for the scrambling of carbon atoms in ketene (348 kJ mol[sup [minus]1]) is in close agreement with a recent experimental value (340 kJ mol[sup [minus]1]). 42 refs., 5 figs., 3 tabs.
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Oxirene. To be or not to be
The Journal of Physical Chemistry, 1994Co-Authors: George Vacek, Anthony P Scott, Ross H Nobes, Henry F. Schaefer, John Morrison Galbraith, Yukio Yamaguchi, Leo RadomAbstract:The C{sub 2v}-symmetry structure of Oxirene has been examined using ab initio molecular orbital calculations with large basis sets and a variety of methods of including electron correlation. Different qualitative conclusions regarding the nature of Oxirene are reached, depending on the choice of basis set and method of electron correlation incorporation. With certain combinations of basis set and theoretical method, the symmetric Oxirene structure is found to be a saddle point on the potential energy surface, while for other combinations Oxirene is a local minimum. Inclusion of triple excitations in the correlation treatment has a large effect, tending to make the curvature of the surface corresponding to a ring-opening distortion of the C{sub 2v}-symmetry structure less positive (or more negative). This is counterbalanced by a basis set effect, with inclusion of functions making the curvature more positive. At our highest level of theory, CCSD(T) with basis sets of triple-{zeta} quality and including multiple d shells and an f shell on C and O and multiple p shells and a d shell on H, Oxirene is a genuine minimum under harmonic vibrational analysis, with a ring-opening frequency of 139-163 cm{sup -1}. 72 refs., 2 tabs.
George Vacek - One of the best experts on this subject based on the ideXlab platform.
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Substituted Oxirenes (X2C2O, X = BH2, CH3, NH2, OH, F): Can They Be Made?
Journal of the American Chemical Society, 1994Co-Authors: Joseph E. Fowler, John Morrison Galbraith, George Vacek, Henry F. SchaeferAbstract:The Oxirene system has received much attention recently; most theoretical studies have concentrated on the unsubstituted molecule while most experimentation has involved substituted Oxirenes. In an effort to bridge the information gap between theory and experiment we have undertaken an ab initio study of substituted Oxirenes. Predictions at various levels of theory up to the double-[zeta] plus polarization single and double coupled cluster with perturbative triples correction [DZP CCSD(T)] are presented for the series of substituted Oxirenes with the formula X[sub 2]C[sub 2]O, where X = BH[sub 2], CH[sub 3], NH[sub 2], OH, and F. Predictions from this level of theory are thought to be quite dependable on the basis of earlier work. Stationary points are compared among themselves and with the parent Oxirene (X = H) and the molecular orbitals involved in ring bonding are analyzed, providing insight into the nature of the chemical bonding. Only the dimethylOxirene molecule (in addition to the earlier reported unsubstituted Oxirene) is predicted to be a minimum on the DZP CCSD(T) surface. All other substituted Oxirenes in the series are predicted to be transition states at that or lower levels of theory. Preliminary data from a benzoOxirene study are also included. 53 refs.,more » 9 figs., 11 tabs.« less
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Oxirene. To be or not to be
The Journal of Physical Chemistry, 1994Co-Authors: George Vacek, Anthony P Scott, Ross H Nobes, Henry F. Schaefer, John Morrison Galbraith, Yukio Yamaguchi, Leo RadomAbstract:The C{sub 2v}-symmetry structure of Oxirene has been examined using ab initio molecular orbital calculations with large basis sets and a variety of methods of including electron correlation. Different qualitative conclusions regarding the nature of Oxirene are reached, depending on the choice of basis set and method of electron correlation incorporation. With certain combinations of basis set and theoretical method, the symmetric Oxirene structure is found to be a saddle point on the potential energy surface, while for other combinations Oxirene is a local minimum. Inclusion of triple excitations in the correlation treatment has a large effect, tending to make the curvature of the surface corresponding to a ring-opening distortion of the C{sub 2v}-symmetry structure less positive (or more negative). This is counterbalanced by a basis set effect, with inclusion of functions making the curvature more positive. At our highest level of theory, CCSD(T) with basis sets of triple-{zeta} quality and including multiple d shells and an f shell on C and O and multiple p shells and a d shell on H, Oxirene is a genuine minimum under harmonic vibrational analysis, with a ring-opening frequency of 139-163 cm{sup -1}. 72 refs., 2 tabs.
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Does Oxirene exist? A theoretical inquiry involving the coupled-cluster method
Chemical Physics Letters, 1991Co-Authors: George Vacek, Brenda Thies Colegrove, Henry F. SchaeferAbstract:Abstract The Oxirene isomer of C2H2O has been characterized at three levels of ab initio quantum-mechanical theory. At all three levels, Oxirene is shown to be a genuine minimum on the respective C2H2O potential energy hypersurfaces. However, the steep decrease in the predicted ring-deformation vibrational frequency (to 262 cm− with the double-zeta-plus-polarization basis set, single-and double-excitation coupled-cluster method) as a function of level of theory leaves open the possibility that Oxirene may be a transition state for the degenerate rearrangement of ketene.
Li-gong Yao - One of the best experts on this subject based on the ideXlab platform.
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Sarcophytrols A–C, new capnosane diterpenoids from the South China Sea soft coral Sarcophyton trocheliophorum
Tetrahedron Letters, 2015Co-Authors: Wen-ting Chen, Li-gong Yao, Yue-wei GuoAbstract:Three new capnosane type diterpenoids, sarcophytrols A–C (1–3), were isolated from the South China Sea soft coral Sarcophyton trocheliophorum. Among them, 1 and 2 share a dodecahydrocyclopenta[6,7]cycloundeca[1,2-b]Oxirene ring system with an unusual 1Z-configuration, whereas 1 and 3 encompass a peculiar isopropyl alcohol moiety. Their structures were elucidated by extensive spectroscopic analysis and the absolute configuration of 1 was determined by an X-ray diffraction analysis with Cu Kα radiation on a single crystal.
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Unprecedented diterpenoids as a PTP1B inhibitor from the Hainan soft coral Sarcophyton trocheliophorum Marenzeller.
Organic letters, 2012Co-Authors: Lin-fu Liang, Li-gong Yao, Tibor Kurtán, Attila Mándi, Wen Zhang, Yue-wei GuoAbstract:Methyl sarcotroates A and B (3 and 4), two unprecedented diterpenoids possessing a tetradecahydrocyclopenta[3′,4′]cyclobuta[1′,2′:4,5]cyclonona[1,2-b]Oxirene ring system, along with their probable biogenetic precursor, sarcophytonolide M (1), were isolated from the Hainan soft coral Sarcophyton trocheliophorum. Their structures were elucidated by detailed spectroscopic analysis, and the absolute configuration of compound 3 was determined by TDDFT ECD calculations. Compound 4 exhibited significant inhibitory activity against protein tyrosine phosphatase 1B (PTP1B), being similar to that of positive control oleanolic acid.
