Concerning the enantiomerization barrier of hypericin
摘要:
The Syntheses of omega-(R)-menthyl and omega,omega-bis-(R)-menthyl derivatives 2 and 3 of hypericin were achieved, and the corresponding diastereomers could be separated. The equilibria between the respective diastereomers are slightly displaced in favor of the chromatographically faster moving ones. Kinetic measurements on these easily equilibrating diastereomers of 2 and 3 provided an Arrhenius activation energy for the interconversion barrier between the two propeller conformers of 83 and 89 kJ/mol. It could be shown that the omega-menthyl residues are of minor relevance to the height of this barrier, as is also the case for the bay hydroxyl ionization and quinone tautomerization equilibria. It was thus concluded that the intrinsic barrier for the propeller conformer enantiomerization of hypericin is in the order of 80 kJ/mol. These results are in accord with those obtained from semiempirical calculations.
Concerning the enantiomerization barrier of hypericin
摘要:
The Syntheses of omega-(R)-menthyl and omega,omega-bis-(R)-menthyl derivatives 2 and 3 of hypericin were achieved, and the corresponding diastereomers could be separated. The equilibria between the respective diastereomers are slightly displaced in favor of the chromatographically faster moving ones. Kinetic measurements on these easily equilibrating diastereomers of 2 and 3 provided an Arrhenius activation energy for the interconversion barrier between the two propeller conformers of 83 and 89 kJ/mol. It could be shown that the omega-menthyl residues are of minor relevance to the height of this barrier, as is also the case for the bay hydroxyl ionization and quinone tautomerization equilibria. It was thus concluded that the intrinsic barrier for the propeller conformer enantiomerization of hypericin is in the order of 80 kJ/mol. These results are in accord with those obtained from semiempirical calculations.
Concerning the enantiomerization barrier of hypericin
作者:R. Altmann、C. Etzlstorfer、H. Falk
DOI:10.1007/bf00810772
日期:1997.4
The Syntheses of omega-(R)-menthyl and omega,omega-bis-(R)-menthyl derivatives 2 and 3 of hypericin were achieved, and the corresponding diastereomers could be separated. The equilibria between the respective diastereomers are slightly displaced in favor of the chromatographically faster moving ones. Kinetic measurements on these easily equilibrating diastereomers of 2 and 3 provided an Arrhenius activation energy for the interconversion barrier between the two propeller conformers of 83 and 89 kJ/mol. It could be shown that the omega-menthyl residues are of minor relevance to the height of this barrier, as is also the case for the bay hydroxyl ionization and quinone tautomerization equilibria. It was thus concluded that the intrinsic barrier for the propeller conformer enantiomerization of hypericin is in the order of 80 kJ/mol. These results are in accord with those obtained from semiempirical calculations.