266
J. C. Pardo-Novoa and C. M. Cerda-García-Rojas
O
69 (valeranone)
O
70 (morelianone)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
2
3
4
5 6
7
8
9
10
11
12
13
14
15
The structure and conformation of the longipinene diester 71 isolated from Stevia
eupatoria (Fig. 2) [34] was studied by a Monte Carlo search protocol [30] followed
by DFT molecular modeling calculations at the B3LYP/6-31G* level of theory
that revealed the ester residue orientations and the preferred conformation of the
seven-membered ring. The results with respect to the sesquiterpene framework were
validated by the comparison between calculated and experimental vicinal
1 H–
1 H
coupling constant analytical data [34].
The conformational analysis of 11αH-dihydrozaluzanin (72) was carried out by
molecular dynamics to locate all possible conformations, followed by DFT calculations at the B3LYP/6-31G(d,p) level, to optimize the molecular geometry of the
minimum energy structures [35]. This molecular modeling approach also allowed
the calculation of the theoretical coupling constants, as well as the generation of the
molecular electrostatic potential map to rationalize the susceptibility of electrophilic
attack on the molecule [35]. The coupling constants, which were essential elements
Fig. 2 Inflorescence of Stevia eupatoria Willd. Photograph courtesy of Dr. J. Martín TorresValencia
J. C. Pardo-Novoa and C. M. Cerda-García-Rojas
O
69 (valeranone)
O
70 (morelianone)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
2
3
4
5 6
7
8
9
10
11
12
13
14
15
The structure and conformation of the longipinene diester 71 isolated from Stevia
eupatoria (Fig. 2) [34] was studied by a Monte Carlo search protocol [30] followed
by DFT molecular modeling calculations at the B3LYP/6-31G* level of theory
that revealed the ester residue orientations and the preferred conformation of the
seven-membered ring. The results with respect to the sesquiterpene framework were
validated by the comparison between calculated and experimental vicinal
1 H–
1 H
coupling constant analytical data [34].
The conformational analysis of 11αH-dihydrozaluzanin (72) was carried out by
molecular dynamics to locate all possible conformations, followed by DFT calculations at the B3LYP/6-31G(d,p) level, to optimize the molecular geometry of the
minimum energy structures [35]. This molecular modeling approach also allowed
the calculation of the theoretical coupling constants, as well as the generation of the
molecular electrostatic potential map to rationalize the susceptibility of electrophilic
attack on the molecule [35]. The coupling constants, which were essential elements
Fig. 2 Inflorescence of Stevia eupatoria Willd. Photograph courtesy of Dr. J. Martín TorresValencia