2.1. Characterization
The aerial parts of
Salvia ballotiflora afforded, after extensive chromatographic purification, eleven diterpenoids: the icetexanes
1–
4,
6–
9, and the abietanes
5,
10,
11 (
Figure 1). While icetexanes
1,
2,
7 and
9 are related to anastomosine (
6), metabolites
3 and
4 are considered as icetexone (
8) derivatives. Diterpenoids
6–
11 are known natural products and have been identified by spectroscopic methods, mainly high field (700 MHz) NMR, and comparisons with the literature; icetexone (
8) and conacytone (
10) were described originally as constituents of the aerial parts of
S. ballotiflora [
15], as well as of other
Salvia spp. [
28,
33]; anastomosine (
6) was from
S. anastomosans [
27]; 7,20-dihydroanastomosine (
7) was from
S. ballotiflora [
23]; compound
9 was from
S. candicans [
28]; and 7α-acetoxy-19-hydroxyroyleanone (
11) was from
S. regla [
29]. The complete assignments of the NMR data of
6,
7,
9, and
11 are included in this paper, since some discrepancies have been found among the literature assignments. It is noteworthy that although icetexone (
8), the first 9(10→20)-
abeo-abietane diterpenoid, and conacytone (
10) were originally isolated from
S. ballotiflora [
15] 41 years ago, and have since then been obtained from several
Salvia spp., they lacked complete
1H- and
13C-NMR assignments, and absolute configuration determinations which were recently accomplished by single crystal X-ray and VCD determinations [
34]. Compounds
1–
5 are new diterpenoids whose structures were established based on the following considerations.
Compound
1 was isolated as a yellow oil which showed IR bands due to hydroxyl groups (3597 and 3412 cm
−1), γ-lactone (1778 cm
−1), quinone carbonyl groups (1654 and 1621 cm
−1), and conjugated double bonds (1583 cm
−1). The UV spectrum showed bands at 213, 243, and 332 nm, indicating the presence of an
ortho-hydroxy-
p-benzoquinone moiety [
15,
28]. In the
1H-NMR spectrum of
1 (
Table 1) characteristic signals of an isopropyl group bonded to a quinone system were observed at δ
H 3.25 (1H, sept,
J = 7.1 Hz), and δ
H 1.26 (6H, d,
J = 7.1 Hz). These signals were ascribed to H-15 and the C-16/C-17 methyl groups, respectively. The presence of an isopropyl group at the C-13 position is a common feature in all diterpenoids isolated from this population of
S. ballotiflora. The
13C-NMR of
1 (
Table 1) is consistent with the presence of the
ortho-hydroxy-
p-benzoquinone system and the isopropyl group, since the expected signals for these moieties were observed at δ
C 132.2 (C-8), 137.7 (C-9), 184.3 (C-11), 150.3 (C-12), 126.8 (C-13), 187.3 (C-14), 24.7 (C-15), 19.9 (C-16), and 20.0 (C-17). A signal at δ
C 179.8 was ascribed to the carbonyl of a γ-lactone as in anastomosine (
6) [
27]. The hydrogen atom at the lactone closure, i.e., H-6, was observed at δ
H 4.29 as a double doublet (
J = 10.3 and 2.3 Hz), the large value indicated a
pseudo-axial orientation for H-6. In the COSY spectrum, H-6 correlated to a doublet at δ
H 3.41 (
J = 10.2) that has been ascribed to H-5, and also with a broad singlet at δ
H 5.53 (H-7) assigned to the geminal hydrogen atom of a hydroxyl group, which must be attached to C-7. The adjacent quinone ring influences the chemical shift of H-7, thus explaining the lower chemical shift of H-7 in comparison to H-6, which is geminal to the lactone moiety. The H-7 signal collapsed to a doublet (
J = 2.2 Hz) upon the addition of D
2O. The coupling constant observed for H-7 was consistent with an α-orientation for the hydroxy group, as observed in other icetexanes and abietanes with an oxygenated function at C-7 isolated from
Salvia spp. [
29].
Other relevant signals observed in the
1H-NMR spectrum of
1 were a broad triplet at δ
H 4.73 (
J = 7.7 Hz), which was ascribed to a H-1 geminal to an additional hydroxy group, and a triplet at δ
H 7.07 (
J = 2.5 Hz). While the chemical shift of the former suggested that it must be an allylic methyne supporting an oxygenated function, the second must be a vinylic one adjacent to the quinone ring to explain the observed chemical shifts. These facts led us to locate these hydrogen atoms at C-1 and C-20, respectively, as depicted in
1. A double resonance experiment confirmed the above assumption, since by irradiation at δ
H 4.73 (1H, brt,
J = 7.7 Hz, H-1), two multiplet signals of a methylene group at δ
H 1.70 and 2.49 (δ
C 29.0) collapsed, thus these signals were ascribed to the C-2 methylene hydrogen atoms. The
13C-NMR spectrum was consistent with the previous discussion, since the signals for C-1 and C-7 were observed at δ
C 68.2 and 65.0, respectively. A non-protonated carbon observed at δ
C 153.1 and a methine at δ
C 112.3 were assigned to C-10 and C-20, respectively. The HMBC spectrum supports the previous assignments, since H-1 showed correlation cross peaks with C-10, C-20, and C-5. In addition, H-20 correlated with C-1, C-5, C-6, C-9, and C-11, while H-6 showed cross peaks with C-5, C-7, and C-10; and H-7 correlated with C-6, C-8, and C-9. Other relevant HMBC correlations that confirmed the structure of
1 are shown in
Table 1 and
Figure 2. A three hydrogen atoms signal at δ
H 1.47 was also observed in the
1H-NMR spectrum of
1 and was ascribed to the C-18 methyl group. The relative stereochemistry of
1 was established with the aid of the coupling constants and the NOESY spectrum (
Figure 2), which showed a correlation between H-6 and H-7, both β-oriented. Meanwhile H-5, which must be
anti-periplanar to H-6, showed a nOe with methyl hydrogen atoms at C-4, which in turn correlated with H-1, thus indicating that H-5, Me-18, and H-1 had the same orientation. The large coupling constant value of H-1 indicated an
axial orientation, thus the hydroxy group attached to C-1 must be β-
equatorial oriented. Compound
1 is related to anastomosine (
6), and is a novel icetexane derivative that we named ballotiquinone (
1).
The mass spectrum of
2 indicated a molecular formula of C
20H
20O
6 and a high degree of unsaturation. The
1H- and
13C-NMR spectra indicated it was a 6,7-anhydro derivative of ballotiquinone (
1). In the
13C-NMR spectrum of
2 (
Table 1), the signals for an
ortho-hydroxy-
p-benzoquinone and an isopropyl group were observed at δ
C 140.0 (C-8), 149.9 (C-9), 182.8 (C-11), 151.2 (C-12), 126.5 (C-13), 185.3 (C-14), 24.8 (C-15), 20.0 and 20.1 (C-16 and C-17). A singlet at δ
C 179.3 was ascribed to the carbonyl of a γ-lactone like that found in anastomosine (
6) and ballotiquinone (
1); however, the hydrogen atom at the ring closure of this lactone (C-6) was not observed in the
1H-NMR spectrum of
2. This fact, in addition to the presence of two additional signals for
sp2 carbons in the
13C-NMR of
2 (
Table 1) at δ
C 130.2 and 100.5 in comparison with those observed in
1, indicated the presence of a C-6 = C-7 double bond. The
1H-NMR spectrum showed one hydrogen atom doublet at δ
H 6.77 (
J = 1.1), which was ascribed to H-7 since in the HSQC spectrum it correlated with a signal at δ
C 100.5 (C-7), and in the HMBC spectrum with a signal at δ
C 130.2 (C-6). In agreement with the previous consideration, in the IR spectrum of
2, the band for the C-19 carbonyl shifted to 1811 cm
−1 in agreement with an enol-γ-lactone [
35]. In the
1H-NMR, a broad singlet and a doublet at δ
H 2.85 and 6.91 (
J = 1.8 Hz), respectively, were ascribed to H-5 and H-20, since H-5 showed a correlation with H-20 and with the signal assigned to H-7 in the COSY spectrum. The B-ring of compound
2 is therefore a cycloheptatriene system, where one double bond is also part of the
ortho-hydroxy-
p-benzoquinone, thus explaining the UV absorptions observed at 213, 243, and 332 nm in agreement with the high degree of instauration deduced from the mass spectrum. Other relevant signals in the
1H-NMR spectrum of
2 were due to the hydrogen atoms of the C-18 methyl group at δ
H 1.44, and a triplet at δ
H 4.57 (
J = 2.9 Hz) ascribed to the geminal hydrogen atom of an allylic hydroxyl moiety at C-1, as in compound
1. Inspection of a Dreiding model and molecular mechanics (MM2) calculations of compound
2 indicated that the A-ring could adopt two distorted chair conformations due to the presence of the C-6 = C-7 double bond. In the more stable conformation, H-1 is α-
equatorial, forming a dihedral angle of approximately 60 degrees with the hydrogen atoms of the methylene at C-2, thus accounting for the coupling constant values observed, and in consequence forming a β-orientation for the hydroxy group. The relative stereochemistry of
2 was established with the aid of the coupling constants and the NOESY spectrum (
Figure 3) that showed a correlation between H-5 and the α-methyl at C-4, thus indicating that they were on the same side of the molecule. In agreement with the proposed α-
equatorial orientation for H-1, the NOESY spectrum correlation cross peaks were observed with H-20 and both C-2 methylene hydrogen atoms (δ
H 2.01 and 1.41). Compound
2 could originate from ballotiquinione (
1) by the loss of a water molecule from the C-6:C-7 positions, and was named 6,7-anhydroballotiquinone. Compounds
1 and
2 are new icetexane derivatives closely related to anastomosine (
6), 7,20-dihydroanastomosine (
7), and compound
9, which co-exist in this population of
S. ballotiflora. The yet unnamed icetexane
9, known from
S. candicans, turned out to be 1,2-anhydroballotiquinone.
Compound
3 was isolated as a yellow powder. The HR-DART-MS indicated a C
22H
26O
7 molecular formula. Its IR spectrum showed bands due to hydroxyl (3414 cm
−1), saturated γ-lactone (1771 cm
−1), ester carbonyl (1744 cm
−1), and quinone carbonyl groups (1646 cm
−1). The
13C-NMR spectrum displayed signals for 22 carbons, accounting for four methyl groups, five methylene units, three methines, and 10 quaternary carbons, which included two quaternary
sp3, four carbonyls, and four olefinic carbons, according to the HSQC experiment. Signals for the typical isopropyl-
ortho-hydroxy-
p-benzoquinone were observed, as in
1 and
2, as well as signals for an acetate group at δ
C 169.6, and 20.7 (
Table 2). Other relevant signals in the spectrum were observed at δ
C 179.6 (C), 81.8 (C), 17.2 (CH
3), and 30.2 (CH
2). The former was ascribed to the carbonyl of a γ-lactone with a high degree of ring strain, as in
1 and
2; however, the presence of the singlet at δ
C 81.8 and the chemical shift of the methyl at δ
C 17.2 indicated a γ-lactone system related to icetexone (
8). In agreement with this conclusion, the triplet at δ
C 30.2 was ascribed to the C-20 methylene group, characteristic of an icetexone-type derivative, while the signals at δ
C 179.6, 81.8, and 17.2 were assigned to C-19, C-10, and C-18, respectively. The
1H-NMR spectrum of
3 (
Table 2) confirmed the above conclusions since an AB system at δ
H 3.43 and 3.01 (
J = 15.7 Hz), ascribed to the hydrogen atoms at C-20, and a singlet at δ
H 1.11, assigned to the hydrogen atoms of the C-18 methyl group, were observed. A singlet at δ
H 2.09 due to the presence of an acetate group, whose geminal hydrogen atom was observed at δ
H 6.21 as a doublet (
J = 7.0 Hz), was also evident. The COSY spectrum of
3 indicated that the acetoxy geminal hydrogen atom was coupled to one methylene hydrogen atom observed at δ
H 2.27 (1H, ddd,
J = 15.0, 7.2, 5.5 Hz, H-6α) which was coupled to its geminal hydrogen atom at δ
H 1.43 (1H, brdd,
J = 15.0, 12.0 Hz, H-6β). In turn, the methylene hydrogen atoms were coupled to a double doublet at δ
H 2.37 (1H,
J = 12.0, 5.4 Hz, H-5). Since the acetoxy germinal hydrogen atom was shown to be coupled only to one hydrogen atom of the methylene group (δ
H 2.27), we can infer that it must form a 90-degree dihedral angle with the other methylene hydrogen atom at δ
H 1.43, thus accounting for the observed multiplicity of H-7. The chemical shift of the acetate geminal hydrogen atom and the correlations observed in the COSY spectrum led us to locate the ester group at C-7 with an α-
pseudoaxial orientation, and to assign the signals at δ
H 2.27 and 1.43 to H-6α and H-6β, respectively, and therefore the signal at δ
H 2.37 to H-5, which must be α-
axially oriented. Inspection of the Drieding molecular model and MM2 calculations confirmed the spatial relation of H-7 with the H-6β, which formed a 90-degree dihedral angle in the most stable conformation. In the
13C-NMR spectrum of
3, the signal for C-7 was observed at δ
C 65.9, and the methylene carbon at δ
H 27.2 was ascribed to C-6. The HMBC spectrum of
3 supported the previous assignments, since correlation cross peaks were observed between H-7 and the signal ascribed to the acetate carbonyl, as well as with C-5, C-6, C-8, C-9 and C-14 (
Table 2 and
Figure 3). In addition, H-5 showed correlations with C-3, C-4, C-6 and C-19. While both hydrogen atoms at the C-6 position showed correlation cross peaks with C-10 and C-5, the hydrogen atoms of the C-20 methylene correlated with C-5, C-8, C-9, C-10, and C-11. Other relevant HMBC correlations observed for
3 are included in
Table 2 and
Figure 4.
The relative configuration of
3 was established with the aid of a NOESY spectrum (
Figure 4), while VCD [
36,
37] allowed the establishment of the absolute configuration.
The experimental section details the calculation procedures performed to obtain the theoretical IR and VCD spectra, while the left portion of
Figure 5 shows a comparison of the experimental and calculated spectra of
3. These allowed us to determine the absolute configuration. The comparison parameters, determined using the Compare
VOA software [
38], are given in
Table 3, where it can be observed that the determination was accomplished with 100% confidence. The thermochemical parameters associated with the VCD calculations of the conformers contributing to this determination are summarized in
Table 4.
Compound 3 is a new icetexane (8) derivative herein named 7α-acetoxy-6,7-dihydroicetexone.
Compound
4 was obtained as a yellow powder and its molecular formula was established as C
20H
24O
6 by HR-DART-MS. In the
13C-NMR spectrum of
4 (
Table 5) a signal at δ
C 204.7 was observed, indicating the presence of a conjugated ketone carbonyl. Aside from the signals for the γ-lactone (δ
C 179.1), the methyl group (δ
C 17.4), and the γ-lactone closure i.e., C-10 at δ
C 85.2, the characteristics of an icetexone-type derivative were also observed. In addition, the spectrum showed six non-protonated
sp2 carbon signals at δ
C 113.1, 120.0, 134.9, 150.3, 119.9 and 159.2, indicating that
4, instead of the
ortho-hydroxy-
p-benzoquinone, possessed a fully substituted aromatic ring, where one of the substituents was an isopropyl group. In the IR spectrum of
4, several bands due to hydroxyl groups were observed at 3602, 3564 and 3514 cm
−1, suggesting that the other substituents of the aromatic ring were hydroxy groups. Other relevant bands were those observed at 1771 and 1612 cm
−1, which were ascribed to the γ-lactone carbonyl and the conjugated ketone deduced from the
13C-NMR data.
In the
1H-NMR spectrum of
4, the signals for an AB system at δ
H 3.59 and 2.95 (
J = 13.9 Hz) were assigned to the C-20 methylene group hydrogen atoms characteristic of this type of icetexane diterpenoid [
28]. An ABX system at δ
H 2.84 (1H, dd,
J = 17.4, 12.0 Hz), 2.80 (1H, dd,
J = 17.4, 2.0 Hz), and 2.00 (1H, dd,
J = 12.0, 2.0 Hz) was also observed. The magnitude of the geminal coupling constant of the AB methylene signals at δ
H 2.84 and 2.80 (
J = 17.4 Hz) indicated its vicinity to a carbonyl group and was therefore ascribed to C-6, which in turn meant that C-7 must be a carbonyl group. The presence of a singlet at δ
H 13.0 corresponded to a hydrogen bonded hydroxy group (-C14-O-H-O=C7), confirming the above assumption. The signal at δ
H 2.00 (1H, dd,
J = 12.0, 2.0 Hz) was attributed to H-5, which must be α-
axially oriented. The HMBC spectrum of
4 agreed with the previous discussion, since the expected correlation cross peaks were observed (
Table 5). The relative stereochemistry of
4 was established with the aid of coupling constant values and was based on the nOe observed in the NOESY spectrum (
Figure 6). This is the first isolation of
4 as a natural product, although its derived diacetyl and triacetyl analogues have been isolated from
S. candicans [
28]. Compound
4 is also an icetexone-type derivative and is therefore named 6,7,11,14-tetrahydro-7-oxo-icetexone.
Compound
5 was also isolated as a yellow powder. Its IR spectrum exhibited bands at 3599 and 3534 cm
−1 for hydroxy groups, as well as at 1730 and 1672 cm
−1 for an ester and a conjugated ketone carbonyl group, respectively. The HR-DART-MS established the molecular formula C
22H
30O
5 for this product. The
13C-NMR spectrum of
5 (
Table 6) confirmed the presence of 22 carbons grouped, according to the HSQC spectrum, into five methyl groups, five methylene moieties, three methines (including an aromatic one), and nine non-protonated carbons (two
sp3, two carbonyl groups, and five aromatic signals). The
1H-NMR spectrum showed the presence of only one aromatic hydrogen atom singlet at δ 7.64, which correlated with the carbon signal at δ
C 118.1, indicating that ring C was a penta-substituted aromatic ring, one of the substituents being an isopropyl group. The chemical shifts of the non-protonated aromatic carbon atoms (δ
C 125.4, 138.3, 141.3, 146.2, and 131.8), suggested the presence of two hydroxyl groups as substituents, very likely at C-11 and 12, as in
4. Two carbonyl signals at δ
C 198.2 and 171.3 were assigned to a conjugated ketone and an ester, respectively, as indicated by the IR spectrum. The carbon chemical shift of the ketone carbonyl group at δ
C 198.1 was similar to that reported for 10-hydroxysugiol (demethylcryptojaponol), an abietane diterpenoid originally isolated from
S. phlomoides Asso [
39] and other plant sources [
40]. The ester group was identified as an acetate, since in the
1H-NMR spectrum of
5, a three-hydrogen atoms singlet was observed at δ
H 2.02, and located at C-18. Accordingly, the AB signals at δ
H 3.73 and 3.84 (
J = 11.3 Hz)—ascribed to geminal hydrogen atoms of the acetoxy group (
Table 6)—showed correlation cross peaks with the carbonyl signal at δ
C 171.1 in the HMBC spectrum. Other relevant signals in the
1H-NMR spectrum of
5 (
Table 6) were those due to the isopropyl group attached to the aromatic ring and two methyl groups at δ
H 1.43 and 0.99, which were ascribed to the C-20 and C-19 methyl hydrogen atoms, respectively. A double doublet at δ
H 2.22 (1H,
J = 11.9, 5.5 Hz) was ascribed to H-5, which must be α-
axially oriented, as are all diterpenoids isolated from this population of
S. ballotiflora. The relative stereochemistry of
5 was established based on the coupling constant values observed in the
1H-NMR (
Table 6) and the NOESY spectra (
Figure 7). The C-18 methylene moiety supporting the acetoxy group, must be α-
ecuatorial oriented since an nOe was observed between H
2-18 and H-5, H-6α and the C-19 methyl hydrogen atoms, which in turn showed intense correlation cross peaks with the C-20 methyl group, H-2β, and H-6β. Furthermore, the C-20 methyl hydrogen atoms showed nOe with H-2β, H-6β, and H-1β. Thus, it follows that
5 is a new abietane derivative named 18-acetoxy-11-hydroxysugiol.
Anastomosine (
6), an icetexane diterpenoid isolated from
S. anastomosans [
27], is also known from
S. candicans [
28] and from a population of
S. ballotiflora collected from a different geographical region of Mexico [
23]. Analysis of the
1H,
13C, HSQC, HMBC, and NOESY NMR spectra measured for the present work led to the complete and unambiguous assignment of all hydrogen and carbon atoms. Several discrepancies with the previous
13C-NMR data were found, and therefore all data are included in the experimental section. Through our research, crystals suitable for X-ray diffraction analysis were obtained, and therefore in the first instance, the structure was verified by this independent methodology, which also allowed us to determine the molecular absolute configuration.
A crystal of
6 was mounted on a glass fiber for data collection using graphite monochromated Cu
Kα radiation at room temperature in the ω/2θ scan mode. The orange crystal measuring 0.34 × 0.26 × 0.15 mm, C
20H
20O
5,
M = 340.36 turned out to be orthorhombic, space group
P2
12
12
1, Z = 4, ρ = 1.361 mg/mm
3. A total of 40,440 reflections were collected, which, after data reduction, left 3178 observed reflections. The structure was solved by direct methods using the SHELXS-97 program included in the WinGX v1.70.01 crystallographic software package. For structural refinement, the non-hydrogen atoms were treated anisotropically, and the hydrogen atoms, included in the structure factor calculations, were refined isotropically. The final
R indices were
R1 = 3.9% and w
R2 = 10.3%, and a PLUTO plot of the molecular structure is shown in
Figure 8. The absolute configuration followed from the use of the Olex2 v1.1.5 software [
41], which allowed us to calculate the Flack (x) [
42] and Hooft (y) parameters [
43,
44]. These parameters were x = 0.1(2) and y = 0.09(5), while for the inverted structure they were x = 0.9(2) and y = 0.91(5).
Independently, the absolute configuration was determined by VCD. In this case, the central portion of
Figure 5 compares the experimental and DFT B3PW91/DGDZVP calculated IR and VCD spectra of
6. The comparison parameters, determined using the Compare
VOA software [
38], are shown in
Table 6, where it can be observed that the determination was accomplished with 100% confidence. In turn, the thermochemical parameters associated with the VCD calculations of those conformers contributing to the final calculations are summarized in
Table 4.
The presence of anastomosine (
6) in
S. anastomosans,
S. candicans, and
S. ballotiflora is important from a chemotaxonomic point of view, since these three species are classified in section Tomentellae. Phylogenetic analyses of some New World salvias of subgenus Calospahce have indicated the existence of different clades inside section Tomentellae and reinforce the evolutionary proximity between
S. candicans and
S. ballotiflora [
45]. This conclusion is also supported by the presence of diterpenoids
9 and
4 in both species. The inclusion of
S. anastomosans in section Tomentellae is also supported by the presence of the anastomosine-type diterpenoids
1,
2,
7 and
9 in
S. ballotiflora. Unfortunately, no gene sequence data is available for
S. anastomosans to reinforce the evolutionary proximity indicated by the diterpenoid content.
Compound
7 (7,20-dihydroanastomosine), was previously isolated from a different population of
S. ballotiflora [
23]; however, the absolute configuration of this icetexane diterpenoid has not been established, and as in the case of anastomosine (
6), we found some mistakes in the reported
13C-NMR spectrum. The assignment, based on high field (700 MHz) NMR analysis in this work, is included in the experimental section.
Crystallization of
7 also afforded suitable crystals for X-ray diffraction analysis. A yellow crystal measuring 0.25 × 0.16 × 0.09 mm, C
20H
22O
5,
M = 342.38 turned out to be monoclinic, space group P2
1,
a = 10.1571(6) Å,
b = 7.7387(4) Å,
c = 10.6394(6) Å, β = 95.401(3) deg,
V = 832.57(8) Å
3, Z = 2, ρ = 1.366 mg/mm
3. This allowed the collection of a total of 7988 reflections, which, after data reduction, left 2552 observed reflections. The structure was solved, as in the previous case, to afford final
R indices
R1 = 3.1% and w
R2 = 7.1%, and again the absolute configuration followed from the Flack (x) and Hooft (y) parameters, which were x = 0.07(18) and y = 0.13(9), and for the inverted structure were x = 0.90(17) and y = 0.87(9). A PLUTO plot of the molecular structure is shown in
Figure 8.
Independently, the absolute configuration of
7 was also determined by VCD. This molecule was also quite rigid, similar to
6. Thus, the sole bond for conformational freedom is that holding the isopropyl group, which generated the two conformers used for the final spectra comparison process. The comparison parameters shown in
Table 6 were determined as per the previous cases, and allowed us to secure the absolute configuration in agreement with the drawn molecular formula. In turn, the thermochemical parameters are also summarized in
Table 3.
The complete NMR assignments of the abietane 7α-acetoxy-19-hydroxyroyleanone (
11), previously isolated from
S. regla [
29], are included in the experimental section since, as in the case of
6 and
7, some discrepancies with earlier assignations were found.
Since icetexanes 3, 6, 7, and 8, as well as abietane 10, were isolated in this work from S. ballotiflora and showed an α-axially oriented H-5, we assumed (based on biogenetic grounds) that the diterpenoids 1, 2, 4, 5 and 11 possessed the same absolute configuration at C-5.