New Techniques of Structure Elucidation for Sesquiterpenes
281
showed an intense negative Cotton effect at 208 nm (ε = − 18.04 mol
–1 dm
3
cm
−1 ), which resulted from the π x → π x
* electronic transition of the
1(6) double
bond of the cyclohexene ring, rather than the
11 double bond. The ECD spectrum
of 158 was calculated for the four possible enantiomers of this sesquiterpenoid
using the B3LYP/6-31G(d) level of theory. The experimental ECD spectrum of 158
showed a good agreement with the calculated spectrum of the (2R,4S,8S,10R)-isomer
considering the sign and the intensity of the analyzed transition [77]. The mixture of
artaboterpenoids B (159 and 160) was resolved on a chiral column and their absolute
configuration was established as (−)-(8R)-159 and (+)-(8S)-160 by application of
helicity rules [77]. Enantiomer (−)-(8R)-159 displayed cytotoxic effects toward the
HCT-116, HepG2, A2780, NCI-H1650, and BGC-823 cell lines with IC 50 values
between 1.38–8.19 μM.
HO
OH
O
O
O
158 ((2R,4S,8S,10R)artaboterpenoid A)
159 ((—)-(8R)artaboterpenoid B)
160 ((+)-(8S)artaboterpenoid B)
1
7
2
3
4
5
6
8
9
10
11
12
13
14
15
1
7
6
5
4
3
2
8
9
10
11
12
13
14
15
O
O
O
Two sesquiterpenoid glucosides of the guaiane-type (161 and 162) were isolated
from the fruits of Gardenia jasminoides, a medicinal plant of the Rubiaceae family
widely used in China [78]. The methodology for the determination of the absolute configuration of 161 was done by means of an ECD analysis. Its ECD spectrum showed a positive Cotton effect at 313.0 nm and a negative Cotton effect at
232.8 nm, suggesting that C-1 has the (R)-configuration. The DFT ECD calculation
of a model compound without the sugar moiety was performed at the B3LYP/6311++G(2d,p) level. The shapes of the computed and experimental spectra were
almost identical, indicating that the structure and absolute configuration of 161 corresponded to (1R,7R,10S)-11-O-β-d-glucopyranosyl-4-guaien-3-one. The structure of
162 was determined by comparison of the NOESY and ECD spectroscopic data with
those of 161 [78].
O O
OH
OH
HO
HO
O
1
2
3
4
5
6 7
8
9
10
11
12
13
14
15
1'
2'
3'
4'
5'
6'
O O
OH
OH
HO
HO
O
HO
161
162
The chemical study of the fruits of Illicium simonsii, a medicinal bush of the
Illiciaceae family, has revealed the presence of a unique pentacyclic structure with
a 5/5/5/5/5 caged 2-oxatricyclononane ring system fused to a five-membered carbocyclic ring and a five-membered lactone [79]. This novel compound received the
281
showed an intense negative Cotton effect at 208 nm (ε = − 18.04 mol
–1 dm
3
cm
−1 ), which resulted from the π x → π x
* electronic transition of the
1(6) double
bond of the cyclohexene ring, rather than the
11 double bond. The ECD spectrum
of 158 was calculated for the four possible enantiomers of this sesquiterpenoid
using the B3LYP/6-31G(d) level of theory. The experimental ECD spectrum of 158
showed a good agreement with the calculated spectrum of the (2R,4S,8S,10R)-isomer
considering the sign and the intensity of the analyzed transition [77]. The mixture of
artaboterpenoids B (159 and 160) was resolved on a chiral column and their absolute
configuration was established as (−)-(8R)-159 and (+)-(8S)-160 by application of
helicity rules [77]. Enantiomer (−)-(8R)-159 displayed cytotoxic effects toward the
HCT-116, HepG2, A2780, NCI-H1650, and BGC-823 cell lines with IC 50 values
between 1.38–8.19 μM.
HO
OH
O
O
O
158 ((2R,4S,8S,10R)artaboterpenoid A)
159 ((—)-(8R)artaboterpenoid B)
160 ((+)-(8S)artaboterpenoid B)
1
7
2
3
4
5
6
8
9
10
11
12
13
14
15
1
7
6
5
4
3
2
8
9
10
11
12
13
14
15
O
O
O
Two sesquiterpenoid glucosides of the guaiane-type (161 and 162) were isolated
from the fruits of Gardenia jasminoides, a medicinal plant of the Rubiaceae family
widely used in China [78]. The methodology for the determination of the absolute configuration of 161 was done by means of an ECD analysis. Its ECD spectrum showed a positive Cotton effect at 313.0 nm and a negative Cotton effect at
232.8 nm, suggesting that C-1 has the (R)-configuration. The DFT ECD calculation
of a model compound without the sugar moiety was performed at the B3LYP/6311++G(2d,p) level. The shapes of the computed and experimental spectra were
almost identical, indicating that the structure and absolute configuration of 161 corresponded to (1R,7R,10S)-11-O-β-d-glucopyranosyl-4-guaien-3-one. The structure of
162 was determined by comparison of the NOESY and ECD spectroscopic data with
those of 161 [78].
O O
OH
OH
HO
HO
O
1
2
3
4
5
6 7
8
9
10
11
12
13
14
15
1'
2'
3'
4'
5'
6'
O O
OH
OH
HO
HO
O
HO
161
162
The chemical study of the fruits of Illicium simonsii, a medicinal bush of the
Illiciaceae family, has revealed the presence of a unique pentacyclic structure with
a 5/5/5/5/5 caged 2-oxatricyclononane ring system fused to a five-membered carbocyclic ring and a five-membered lactone [79]. This novel compound received the