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Ab initio optical rotations have been obtained for allene, 1,3-dichloroallene, H2O2, and H2S2 as a function of dihedral angles, both at SCF and post-SCF levels. The results have been used to test (a) the concept that the molecular...
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Ab initio optical rotations have been obtained for allene, 1,3-dichloroallene, H2O2, and H2S2 as a function of dihedral angles, both at SCF and post-SCF levels. The results have been used to test (a) the concept that the molecular optical rotation can be written as a Sigma(i) M-i sin theta(i), where theta(i) is the dihedral angle of the ith X-A-A-X type segment and M-i is a parameter associated with that segment; and (b) Kirkwood's polarizability model. The predicted ab initio optical rotation was found to depend strongly on the level of ab initio theory used, so highest levels of theory are required for accurate predictions. The optical rotation patterns obtained using high-level ab initio theory for H2O2, H2S2 and allene, as a function of dihedral angles, are found to be in line with Kirkwood's polarizability model predictions but not with the Sigma(i) M-i sin theta(i) predictions. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 35]
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Enolate of Wieland-Miescher ketone 1 has reacted with methyl acrylate to give methyl (1S*,2S*,4R*,6S*)-6-methyltricyclo[6.2.2(1,6)]-dodecan-7,12-dion-2-carboxy late 5 whose structure has been determined by Xray crystallography aft...
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Enolate of Wieland-Miescher ketone 1 has reacted with methyl acrylate to give methyl (1S*,2S*,4R*,6S*)-6-methyltricyclo[6.2.2(1,6)]-dodecan-7,12-dion-2-carboxy late 5 whose structure has been determined by Xray crystallography after transformation of 5 into sultamamide 8a. [References: 12]
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Fractionation of the ethyl acetate extract of a Cladosporium sp., isolated from the Red Sea sponge Niphates rowi, yielded a new hexaketide, pandangolide 1a (1), together with its known diastereomer pandangolide 1 (2) and the known...
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Fractionation of the ethyl acetate extract of a Cladosporium sp., isolated from the Red Sea sponge Niphates rowi, yielded a new hexaketide, pandangolide 1a (1), together with its known diastereomer pandangolide 1 (2) and the known iso-cladospolide B (3). The structures of the compounds were determined by 1D and 2D NMR techniques and mass spectrometric data. The absolute configurations of the stereocenters in these compounds were determined by Riguera's method and circular dichroism.
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Chiral N-substituted porphyrin free bases having a conformationally locked asymmetric nitrogen atom catalyzed Michael addition of thiophenols to cycloalkenones, where the reaction proceeded enantioselectively when the catalyst hav...
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Chiral N-substituted porphyrin free bases having a conformationally locked asymmetric nitrogen atom catalyzed Michael addition of thiophenols to cycloalkenones, where the reaction proceeded enantioselectively when the catalyst having a xylylene strap anchored via two secondary amido linkages (2) was employed. Copyright (C) 1995 Elsevier Science Ltd [References: 15]
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A bicyclic goniofupyranone core was synthesized from argentilactone using epoxide as an intermediate. The absolute stereochemistry of all asymmetric centers of a compound possessing the 2,6-dioxabicyclo [3.2.1]-octan-3-one moiety ...
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A bicyclic goniofupyranone core was synthesized from argentilactone using epoxide as an intermediate. The absolute stereochemistry of all asymmetric centers of a compound possessing the 2,6-dioxabicyclo [3.2.1]-octan-3-one moiety were unambiguously determined directly from X-ray data for the first time. Additionally, the absolute stereochemistry of the major epoxide was reported.
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A collection of the marine sponge Dysidea herbacea, containing cyanobacterial symbionts, from Papua New Guinea yielded a new ketide amino acid, herbamide A (1), along with the previously reported polychlorinated tetrapeptide, dysi...
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A collection of the marine sponge Dysidea herbacea, containing cyanobacterial symbionts, from Papua New Guinea yielded a new ketide amino acid, herbamide A (1), along with the previously reported polychlorinated tetrapeptide, dysidenin (2). The structure of 1 was determined by spectroscopic methods. [References: 24]
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Two novel norlignans, gymnothedelignans A and B were isolated from the whole plants of Gymnotheca chinensis. These norlignans possess a rare 2/5 epoxy benzocycloheptanone skeleton. Their structures were established on the basis of...
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Two novel norlignans, gymnothedelignans A and B were isolated from the whole plants of Gymnotheca chinensis. These norlignans possess a rare 2/5 epoxy benzocycloheptanone skeleton. Their structures were established on the basis of ID and 2D NMR spectral data analysis, and the absolute stereochemistry of gymnothedelignans A and B was further confirmed by single crystal X-ray diffraction analysis.
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Two novel lignans, gymnothespirolignans A (1) and B (2), possessing a rare polycyclic spiro skeleton, were isolated from the endemic plant of Gymnotheca involucrata Pei. Their structures were determined by spectroscopic evidences ...
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Two novel lignans, gymnothespirolignans A (1) and B (2), possessing a rare polycyclic spiro skeleton, were isolated from the endemic plant of Gymnotheca involucrata Pei. Their structures were determined by spectroscopic evidences and the absolute configurations were confirmed by single crystal X-ray diffraction analysis. Compounds 1 and 2 showed promising antiviral activities against RSV with an IC_(50) value of 31.87 and 17.51 uM, respectively.
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We describe the total synthesis and structural determination of (+)-akaterpin (1), an inhibitor of phosphatidylinositol- specific phospholipase C (PI-PLC). The key features of the synthetic strategy include the resolution of β,γ...
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We describe the total synthesis and structural determination of (+)-akaterpin (1), an inhibitor of phosphatidylinositol- specific phospholipase C (PI-PLC). The key features of the synthetic strategy include the resolution of β,γ-unsaturated ketone (±)-2a with chiral sulfoximine 6. The absolute stereochemistry was determined by comparison of the specific optical rotation data of (+)-1 and (-)-1 with that of natural akaterpin.
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The absolute configurations at five chiral centers, except for C-32(S) reported previously, in iejimalides A, C, and D, potent cytotoxic 24-membered macrolides isolated from a tunicate Eudistoma cf. rigida, were assigned as 4R, 9S...
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The absolute configurations at five chiral centers, except for C-32(S) reported previously, in iejimalides A, C, and D, potent cytotoxic 24-membered macrolides isolated from a tunicate Eudistoma cf. rigida, were assigned as 4R, 9S, 17S, 22S, and 23S on the basis of detailed analysis of NMR data and chemical means. Furthermore, the structures proposed for iejimalides A, C, and D were revised to their 13Z-isomers. Iejimalides A-D (1-4) exhibited antitumor activity in vivo.
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