New Techniques of Structure Elucidation for Sesquiterpenes
257
O
O HO
O
O
HO
O
O
O HO
O
O
O HO
O
HO
O
O
O
O
O
7 (mexicanin I)
8 (helenalin)
9 (6-hydroxydihydroaromaticin)
10 (geigerinin)
11 (badkhysin)
Two new germacranes named ketopelenolides C (12) and D (13) were isolated
from Artemisia arborescens, collected in Cagliari, Italy. Crucial points in their structure elucidation were solved by NMR spectroscopy in combination with molecular modeling and quantum–mechanical calculations including comparisons between
experimental and DFT-calculated
13 C NMR data [8]. For the configurational assignment of these structures, which comprise highly flexible medium-sized rings, a
detailed conformational analysis was undertaken. The calculation protocol involved
geometry optimization of all possible conformers followed by calculation of chemical shifts with the GIAO approach using the DFT MPW1PW91/6-31G(d,p) method
[8].
O
HO
O
O
O
O
O
O
12 (ketopelenolide C)
13 (ketopelenolide D)
The guaiane-type sesquiterpenoids 14–18 were isolated from Daphne genkwa
collected in Xingyi City, Guizhou Province, People’s Republic of China [9]. Calculation of their
13 C NMR chemical shifts was achieved using the GIAO method
at the mPW1PW91/6-311+G(d,p) level of theory, while application of the statistical method DP4+ [10] was an effective strategy for the assignment of the correct
diastereoisomers. Additionally, the absolute configurations were determined by
comparing the experimental and calculated electronic circular dichroism spectra [9].
257
O
O HO
O
O
HO
O
O
O HO
O
O
O HO
O
HO
O
O
O
O
O
7 (mexicanin I)
8 (helenalin)
9 (6-hydroxydihydroaromaticin)
10 (geigerinin)
11 (badkhysin)
Two new germacranes named ketopelenolides C (12) and D (13) were isolated
from Artemisia arborescens, collected in Cagliari, Italy. Crucial points in their structure elucidation were solved by NMR spectroscopy in combination with molecular modeling and quantum–mechanical calculations including comparisons between
experimental and DFT-calculated
13 C NMR data [8]. For the configurational assignment of these structures, which comprise highly flexible medium-sized rings, a
detailed conformational analysis was undertaken. The calculation protocol involved
geometry optimization of all possible conformers followed by calculation of chemical shifts with the GIAO approach using the DFT MPW1PW91/6-31G(d,p) method
[8].
O
HO
O
O
O
O
O
O
12 (ketopelenolide C)
13 (ketopelenolide D)
The guaiane-type sesquiterpenoids 14–18 were isolated from Daphne genkwa
collected in Xingyi City, Guizhou Province, People’s Republic of China [9]. Calculation of their
13 C NMR chemical shifts was achieved using the GIAO method
at the mPW1PW91/6-311+G(d,p) level of theory, while application of the statistical method DP4+ [10] was an effective strategy for the assignment of the correct
diastereoisomers. Additionally, the absolute configurations were determined by
comparing the experimental and calculated electronic circular dichroism spectra [9].