New Techniques of Structure Elucidation for Sesquiterpenes
269
O
O
O
O
OH
O
O
O
OH
OH
O
O
O
O
O
O
O
O
OH
O
O
5
8
4
8
86
9
8
8
8
7
8
6α,7α-epoxy
90 6β,7β-epoxy
91 8β-hydroxy
92 8α-hydroxy
93
The soft coral Lemnalia flava collected near Xisha Island, China, afforded six
new sesquiterpenoids (94−99), for which their structures were established by NMR
spectroscopy, X-ray diffraction analysis, chemical transformations, and comparison
with theoretical NMR data and DFT electronic circular dichroism calculations [40].
The RDCs analysis was employed to evaluate the relative configuration of 96, which
was aligned in an oligopeptide phase (AAKLVFF) that was compatible with MeOH
[40]. RDCs were measured using the [
1 H–
13 C]-CLIP-HSQC experiment [41] that
allowed extraction of nine values with high accuracy.
On the other hand, a molecular modeling search protocol followed by DFT optimization at the B3LYP/6-31G(d) level of theory of 96 and three of its stereoisomers
revealed group structures to be analyzed according to NOE and RDC values [40]. The
alignment tensor of each structure was calculated using the singular value decomposition method as implemented in the RDC module of the MSpin program [42]. The
predicted RDCs were compared with the experimental ones providing the Q-factor as
a quantitative evaluation for each stereoisomer, supporting the (4S*5S*6S*7S*11S*)
configuration for 96 [40].
O
O
O
OH
O
O
O
O
O
O
OH
NH
O
OH
OH
O
O
O
94
6
9
5
9
97
98
99
269
O
O
O
O
OH
O
O
O
OH
OH
O
O
O
O
O
O
O
O
OH
O
O
5
8
4
8
86
9
8
8
8
7
8
6α,7α-epoxy
90 6β,7β-epoxy
91 8β-hydroxy
92 8α-hydroxy
93
The soft coral Lemnalia flava collected near Xisha Island, China, afforded six
new sesquiterpenoids (94−99), for which their structures were established by NMR
spectroscopy, X-ray diffraction analysis, chemical transformations, and comparison
with theoretical NMR data and DFT electronic circular dichroism calculations [40].
The RDCs analysis was employed to evaluate the relative configuration of 96, which
was aligned in an oligopeptide phase (AAKLVFF) that was compatible with MeOH
[40]. RDCs were measured using the [
1 H–
13 C]-CLIP-HSQC experiment [41] that
allowed extraction of nine values with high accuracy.
On the other hand, a molecular modeling search protocol followed by DFT optimization at the B3LYP/6-31G(d) level of theory of 96 and three of its stereoisomers
revealed group structures to be analyzed according to NOE and RDC values [40]. The
alignment tensor of each structure was calculated using the singular value decomposition method as implemented in the RDC module of the MSpin program [42]. The
predicted RDCs were compared with the experimental ones providing the Q-factor as
a quantitative evaluation for each stereoisomer, supporting the (4S*5S*6S*7S*11S*)
configuration for 96 [40].
O
O
O
OH
O
O
O
O
O
O
OH
NH
O
OH
OH
O
O
O
94
6
9
5
9
97
98
99