In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-in... more In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-indolinone alkaloids, thomandersine and isothomandersine, have been isolated from a methanol extract of the leaves of Thomandersia laurifolia. Their structures were elucidated by spectroscopic methods and chemical correlations.
The relative reactivities of six polycyclic iodomethylarenes toward reduction by triphenyltin hyd... more The relative reactivities of six polycyclic iodomethylarenes toward reduction by triphenyltin hydride in deuterobenzene at 70°C have been obtained. While a limited range of reactivities is observed, a trend does exist. Data are best correlated with calculated energy differences between transition states, based on adding an electron to the antibonding carbon-iodine orbitals, and parent arenes. These results agree with those obtained from substituent effect and isotope effect studies on other organic iodides which apparently undergo electron transfer with trialkyl or triaryltin radicals. *Dedicated to Prof. M. J. S. Dewar on the occasion of his 70th birthday.
... n TETROLIDE PENTALIDE Cst)Rbt)Kt)Nat)Lit Figure 6. Metal ion selectivity sequences of natural... more ... n TETROLIDE PENTALIDE Cst)Rbt)Kt)Nat)Lit Figure 6. Metal ion selectivity sequences of natural antibiotics (beau-vericinI3 and nonactin18) and ... the tri-n-butyltin radical.' Within the past year, this system has been reexamined and elaborated upon by Blackburn and Tanner in a ...
Abstract A series of monochloromethylated polycyclic benzenoid hydrocarbons have been treated wit... more Abstract A series of monochloromethylated polycyclic benzenoid hydrocarbons have been treated with triphenyltin hydride and AIBN initiator at 70°C. Under these conditions the only observable reaction is reduction of the starting materials to methylarenes. A significant range of relative rates (factor of 40) has been found among the compounds studied. All relative rates yielded an excellent correlation when plotted against PPP-SCF calculated energy differences. The present works shows the ability of such calculations to treat processes involving nucleophilic radicals.
Pycnanthus anglonensis is known for its medicinal value. This paper deals with a phytochemical in... more Pycnanthus anglonensis is known for its medicinal value. This paper deals with a phytochemical investigation of this species, from which pycnangloside (1), a new cerebroside has been isolated. Its structure was determined by comprehensive analyses of its 1D and 2D NMR spectroscopic, and ESI mass spectrometric data. Four known compounds were also isolated and identified as biochanin A, formonentin, β-sitosterol, and β-sitosterol glucopyranoside.
The twigs of Dorstenia poinsettifolia yielded poinsettifolactone\ a new dihydro!3!phenylcoumarin\... more The twigs of Dorstenia poinsettifolia yielded poinsettifolactone\ a new dihydro!3!phenylcoumarin\ and dorspoinsettifolin\ a new 6\7!"1\1!dimethylpyrano#!3?!methoxy~avanone[ Three known prenylated~avonoids\ 3!hydroxylonchocarpin\ 3!methoxylonchocarpin and 3?!hydroxyisolonchocarpin\ were also isolated and identi_ed[ Structures were established by spectroscopic analysis and chemical correlations[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
Hosloppin [l], a new pyrone-substituted flavonoid, was isolated from the MeOH extract of the leav... more Hosloppin [l], a new pyrone-substituted flavonoid, was isolated from the MeOH extract of the leaves of Hoslundia opposita. The structure of 1 was established as 3"-0demethylhoslundin from an analysis of its spectroscopic data.
Investigation of the twigs of Dorstenia mannii gave 6,8-diprenyl-5,7,3 H 4 H-tetrahydroxy¯avanone... more Investigation of the twigs of Dorstenia mannii gave 6,8-diprenyl-5,7,3 H 4 H-tetrahydroxy¯avanone and four new prenylated avanones, named dorsmanins E-H and characterized as 5,6-7,8-bis-(2,2-dimethylchromano)-3 H ,4 H-dihydroxy¯avanone, 7,8-[20-(1hydroxy-1-methylethyl)-dihydrofurano]-6-prenyl-5,3 H ,4 H-trihydroxy¯avanone, 6,7-[20-(1-hydroxy-1-methylethyl)dihydrofurano]-8prenyl-5,3 H ,4 H-trihydroxy¯avanone and 6-prenyl-8-(2-hydroxy-3-methylbut-3-enyl)-5,7,3 H ,4 H-tetrahydroxy¯avanone, respectively, on the basis of spectral analysis and chemical evidence for the chromano derivative.
Using DFT calculations, we have studied the C-N vibration of dicyanobenzenes in different solvent... more Using DFT calculations, we have studied the C-N vibration of dicyanobenzenes in different solvents. The effects of solvent polarity and hydrogen bonding were evaluated. The frequency is decreased by 4 cm-1 when the solvent polarity increases. In the current study, the red shift due to the solvent polarity was underestimated by PCM. For hydrogen bonding, the frequency is increased by 10 cm-1 because of the charge transfer from the lone pair of nitrogen in C≡N to water, which slightly increases the bond strength of C-N. The C-N vibration of dicyanobenzenes is calculated to be sensitive to solvation.
In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-in... more In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-indolinone alkaloids, thomandersine and isothomandersine, have been isolated from a methanol extract of the leaves of Thomandersia laurifolia. Their structures were elucidated by spectroscopic methods and chemical correlations.
In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-in... more In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-indolinone alkaloids, thomandersine and isothomandersine, have been isolated from a methanol extract of the leaves of Thomandersia laurifolia. Their structures were elucidated by spectroscopic methods and chemical correlations.
The relative reactivities of six polycyclic iodomethylarenes toward reduction by triphenyltin hyd... more The relative reactivities of six polycyclic iodomethylarenes toward reduction by triphenyltin hydride in deuterobenzene at 70°C have been obtained. While a limited range of reactivities is observed, a trend does exist. Data are best correlated with calculated energy differences between transition states, based on adding an electron to the antibonding carbon-iodine orbitals, and parent arenes. These results agree with those obtained from substituent effect and isotope effect studies on other organic iodides which apparently undergo electron transfer with trialkyl or triaryltin radicals. *Dedicated to Prof. M. J. S. Dewar on the occasion of his 70th birthday.
... n TETROLIDE PENTALIDE Cst)Rbt)Kt)Nat)Lit Figure 6. Metal ion selectivity sequences of natural... more ... n TETROLIDE PENTALIDE Cst)Rbt)Kt)Nat)Lit Figure 6. Metal ion selectivity sequences of natural antibiotics (beau-vericinI3 and nonactin18) and ... the tri-n-butyltin radical.' Within the past year, this system has been reexamined and elaborated upon by Blackburn and Tanner in a ...
Abstract A series of monochloromethylated polycyclic benzenoid hydrocarbons have been treated wit... more Abstract A series of monochloromethylated polycyclic benzenoid hydrocarbons have been treated with triphenyltin hydride and AIBN initiator at 70°C. Under these conditions the only observable reaction is reduction of the starting materials to methylarenes. A significant range of relative rates (factor of 40) has been found among the compounds studied. All relative rates yielded an excellent correlation when plotted against PPP-SCF calculated energy differences. The present works shows the ability of such calculations to treat processes involving nucleophilic radicals.
Pycnanthus anglonensis is known for its medicinal value. This paper deals with a phytochemical in... more Pycnanthus anglonensis is known for its medicinal value. This paper deals with a phytochemical investigation of this species, from which pycnangloside (1), a new cerebroside has been isolated. Its structure was determined by comprehensive analyses of its 1D and 2D NMR spectroscopic, and ESI mass spectrometric data. Four known compounds were also isolated and identified as biochanin A, formonentin, β-sitosterol, and β-sitosterol glucopyranoside.
The twigs of Dorstenia poinsettifolia yielded poinsettifolactone\ a new dihydro!3!phenylcoumarin\... more The twigs of Dorstenia poinsettifolia yielded poinsettifolactone\ a new dihydro!3!phenylcoumarin\ and dorspoinsettifolin\ a new 6\7!"1\1!dimethylpyrano#!3?!methoxy~avanone[ Three known prenylated~avonoids\ 3!hydroxylonchocarpin\ 3!methoxylonchocarpin and 3?!hydroxyisolonchocarpin\ were also isolated and identi_ed[ Structures were established by spectroscopic analysis and chemical correlations[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
Hosloppin [l], a new pyrone-substituted flavonoid, was isolated from the MeOH extract of the leav... more Hosloppin [l], a new pyrone-substituted flavonoid, was isolated from the MeOH extract of the leaves of Hoslundia opposita. The structure of 1 was established as 3"-0demethylhoslundin from an analysis of its spectroscopic data.
Investigation of the twigs of Dorstenia mannii gave 6,8-diprenyl-5,7,3 H 4 H-tetrahydroxy¯avanone... more Investigation of the twigs of Dorstenia mannii gave 6,8-diprenyl-5,7,3 H 4 H-tetrahydroxy¯avanone and four new prenylated avanones, named dorsmanins E-H and characterized as 5,6-7,8-bis-(2,2-dimethylchromano)-3 H ,4 H-dihydroxy¯avanone, 7,8-[20-(1hydroxy-1-methylethyl)-dihydrofurano]-6-prenyl-5,3 H ,4 H-trihydroxy¯avanone, 6,7-[20-(1-hydroxy-1-methylethyl)dihydrofurano]-8prenyl-5,3 H ,4 H-trihydroxy¯avanone and 6-prenyl-8-(2-hydroxy-3-methylbut-3-enyl)-5,7,3 H ,4 H-tetrahydroxy¯avanone, respectively, on the basis of spectral analysis and chemical evidence for the chromano derivative.
Using DFT calculations, we have studied the C-N vibration of dicyanobenzenes in different solvent... more Using DFT calculations, we have studied the C-N vibration of dicyanobenzenes in different solvents. The effects of solvent polarity and hydrogen bonding were evaluated. The frequency is decreased by 4 cm-1 when the solvent polarity increases. In the current study, the red shift due to the solvent polarity was underestimated by PCM. For hydrogen bonding, the frequency is increased by 10 cm-1 because of the charge transfer from the lone pair of nitrogen in C≡N to water, which slightly increases the bond strength of C-N. The C-N vibration of dicyanobenzenes is calculated to be sensitive to solvation.
In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-in... more In addition to the usual phytosterol mixture, taraxeryl palmitate and maslinic acid, two new 2-indolinone alkaloids, thomandersine and isothomandersine, have been isolated from a methanol extract of the leaves of Thomandersia laurifolia. Their structures were elucidated by spectroscopic methods and chemical correlations.
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Papers by HELENE TAMBOUE