J. Nat. Prod. 1997, 60, 1229-1235
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Neoclerodane Diterpenoids from Scutellaria polyodon† Marı´a C. de la Torre,‡ Benjamı´n Rodrı´guez,*,‡ Maurizio Bruno,§,⊥ Nadia Vassallo,⊥ Maria Luisa Bondı`,⊥ Franco Piozzi,§ and Orietta Servettaz| Instituto de Quı´mica Orga´ nica, Consejo Superior de Investigaciones Cientı´ficas (CSIC), Juan de la Cierva 3, E-28006 Madrid, Spain, Dipartimento di Chimica Organica “E. Paterno` ”, Universita` di Palermo, Archirafi 20, 90123 Palermo, Italy, Istituto di Chimica e Tecnologia dei Prodotti Naturali-Consiglio Nazionale delle Ricerche (ICTPN-CNR), Archirafi 26, 90123 Palermo, Italy, and Dipartimento di Biologia, Universita` di Milano, Celoria 3, 20132 Milano, Italy Received April 21, 1997X
Nine new neoclerodane diterpenoids, scupolins A-I, have been isolated from an Me2CO extract of the aerial parts of Scutellaria polyodon (3-11), together with the known neoclerodanes jodrellin B (1) and scutecolumnin A (2). Structures 3-11 were established by spectroscopic means and by comparison with closely related compounds. A large number of neoclerodane1 diterpenoids have been isolated from plants and microorganisms in the past few years.2-4 These compounds have attracted interest because of their biological activities, especially as antifeedants against some economically important lepidopterous pests,2,5 and as antifungal, antitumor, antimicrobial, and molluscicidal agents.2 The species of the genus Scutellaria (family Labiatae) are the source of the most potent neoclerodane insect antifeedants known so far.6-8 In continuation of our studies on Scutellaria plants8-10 we report here on the isolation and structure elucidation of nine new neoclerodane derivatives isolated from Scutellaria polyodon Juz. Results and Discussion An Me2CO extract of the aerial parts of S. polyodon was subjected to extensive chromatography to yield the known neoclerodanes jodrellin B6 (1) and scutecolumnin A11 (2), together with nine new diterpenoids, scupolins A-I, whose structures (3-11, respectively) were established as follows. Scupolin A (3) had the molecular formula C27H40O9, and its 1H- and 13C-NMR spectra (see Tables 1 and 2, respectively) were almost identical with those of scutorientalin B (12, C26H38O9), a neoclerodane diterpene recently isolated from Scutellaria orientalis subsp. pinnatifida.12 The observed differences between the 1Hand 13C-NMR spectra of 3 and 12 were consistent with the presence in the former of a 2-methylbutanoyloxy substituent at the C-6R position11 [δH 2.31, 1H, sext (H2′), 1.68 and 1.46, 1H each, both ddq (HA-3′ and HB-3′), 0.90, 3H, t (Me-4′), and 1.12, 3H, d (Me-5′); δC 175.1 s (C-1′), 41.4 d (C-2′), 26.4 t (C-3′), 11.4 q (C-4′), and 16.5 q (C-5′)] instead of the isobutyrate ester of the latter12 [δH 2.49, 1H, sept (H-2′), and 1.15 and 1.18, 3H each, both d (Me-3′ and Me-4′); δC 174.1 s (C-1′), 34.1 d (C2′), 20.2 q (C-3′), and 21.0 q (C-4′)]. In particular, the location of the acetate group at the C-11 position is in agreement with the chemical shifts and coupling con* To whom correspondence should be addressed. Phone: 34 1 5622900. FAX: 34 1 5644853. † Dedicated to the memory of the late Prof. Ignacio Ribas (19011996), University of Santiago de Compostela, Spain. ‡ Instituto de Quı´mica Orga ´ nica, CSIC, Madrid. § Dipartimento di Chimica Organica, Universita ` di Palermo. ⊥ Istituto di Chimica e Tecnologia dei Prodotti Naturali-CNR, Palermo. | Dipartimento di Biologia, Universita ` di Milano. X Abstract published in Advance ACS Abstracts, November 1, 1997.
S0163-3864(97)00213-9 CCC: $14.00
stants shown by the C-11 and C-12 protons of 3 (see Table 1), which were identical with those reported12-15 for other neoclerodanes having an 11S-acetoxyl substituent and an R,β-unsaturated 15,16-γ-lactone moiety, previously isolated from Scutellaria plants. The 1H-NMR spectrum of scupolin B (4, C26H36O10) showed characteristic signals for a neoclerodane diterpenoid possessing a 4R,18-oxirane, an R,β-unsaturated 15,16-γ-lactone, and a hydroxyl group at the C-8β position. The proton spectrum of 4 was very similar to that of 3 (see Table 1), except for three acetoxyl groups (δ 2.09, 2.00, and 1.93, 3H each, singlets) and no 2-methylbutanoyloxy group. The acetates must be attached to the C-6R, C-11, and C-19 positions, because the signals of their geminal protons appeared at identical field and with the same coupling values (δH-6β 5.14 dd, J6β,7R ) 11.9 Hz, J6β,7β ) 4.7 Hz; δH-11 5.53 dd, J11,12A ) 10.7 Hz, J11,12B ) 1.5 Hz; δH-19 4.39 and 4.85 d, Jgem ) 12.0 Hz) as those observed for other (11S)-6R,11,19tris(acyloxy)-4R,18-epoxy-8β-hydroxyneoclerod-14-en15,16-olide derivatives found in Scutellaria species.12,14,15 Scupolin C (5) had the molecular formula C36H40O10, and its IR spectrum showed hydroxyl (3450 cm-1), R,βunsaturated γ-lactone (3105, 1780, 1640 cm-1), acetate (1740, 1240 cm-1), and benzoate group (3060, 1720 br, 1600, 1580 cm-1) absorptions.9,10,15 The UV spectrum of 5 [λmax nm (log ) 225 (4.38), 273 (3.29)] corroborated the presence of benzoate esters in this diterpenoid.9,10,15 The 1H- and 13C-NMR spectra of 5 (see Tables 1 and 2) described the presence of an acetoxyl group, two benzoates, and a neoclerodane framework with the same functionalities as those found in 3 and 4. The attachment of the acetoxyl group at the C-11 position and the two benzoates at the C-6R and C-19 positions was in agreement with the chemical shifts of the geminal protons of the ester groups, as compared with those of the 6R,11S,19-triacetoxy derivative 4 [∆δ ) δ(4) - δ(5), +0.34 (H-6β), +0.07 (H-11), +0.43 (HA-19), and +0.17 ppm (HB-19)], because the C-6 and C-19 protons are shifted downfield in 5 and the C-11 proton resonates at an almost identical chemical shift in both compounds. Thus, scupolin C had structure 5. Scupolins D (6) and E (7) had the same molecular formula C27H40O10, and their 1H- and 13C-NMR spectra (see Tables 1 and 2) were almost identical, showing characteristic signals for a neoclerodane structure having a 4R,18-oxirane, an R,β-unsaturated 15,16-γ-lactone,
© 1997 American Chemical Society and American Society of Pharmacognosy
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Journal of Natural Products, 1997, Vol. 60, No. 12
Table 1.
1H-NMR
proton(s) H-1R H-1β H-2R H-2β H-3R H-3β H-6β H-7R H-7β H-10β H-11 HA-12 HB-12 H-14 HA-16 HB 16 Me-17 HA-18b HB-18c HA-19 HB-19 Me-20 OAc-6R OAc-11 OAc-19 H-2′ HA-3′ HB-3′ Me-4′ Me-5′ OBz H-2′,6′ H-3′,5′ H-4′ H-2′′,6′′ H-3′′,5′′ H-4′′ OH-6R OH-7β OH-8β OH-19
de la Torre et al.
Spectral Data of Compounds 3-8 3
4
∼1.65a 1.89 (dddd) ∼2.00a ∼1.50a 2.37 (dddd) ∼1.15a 5.20 (ddd) 2.05 (dd) 1.55 (dd) 2.15 (dd) 5.52 (dd) 2.54 (dd) 3.50 (dd 5.84 (br t) 4.65 (dd) 4.85 (dd) 1.30 (3H, s) 2.29 (d) 2.98 (dd) 4.11 (td)d 4.28 (dd)e 0.70 (3H, s)
a ∼1.90a a a a ∼1.15a 5.14 (br dd) a 1.51 (dd) a 5.53 (dd) 2.53 (dd) 3.52 (dd) 5.84 (br t) 4.64 (dd) 4.86 (dd) 1.30 (3H, s) 2.25 (d) 3.01 (dd) 4.39 (br d) 4.85 (d) 0.76 (3H, s) 1.93 (3H, s) 2.00 (3H, s) 2.09 (3H, s)
2.00 (3H, s)
5
6
7
a a a a a a 5.48 (dd) a 1.76 (dd) 2.40 (dd) 5.60 (dd) 2.60 (dd) 3.62 (dd) 5.87 (br t) 4.68 (dd) 4.89 (dd) 1.34 (3H, s) 2.34 (d) 3.18 (dd) 4.82 (d) 5.02 (d) 0.86 (3H, s)
1.66 (dddd) 1.88 (dddd) ∼2.03a 1.50 (ddddd) 2.29 (tdd) 1.16 (ddd) 3.83 (dd) 5.41 (d) 2.06 (dd) 5.53 (dd) 2.54 (dd) 3.46 (dd) 5.84 (br t) 4.63 (dd) 4.84 (dd) 1.23 (3H, s) 2.49 (d) 3.21 (dd) 4.12 (dd)e 4.29 (dd)e 0.84 (3H, s)
2.14 (dd) 5.57 (dd) 2.55 (dd) 3.54 (dd) 5.85 (br t) 4.65 (dd) 4.87 (dd) 1.36 (3H, s) 2.28 (d) 3.04 (dd) 4.12 (dd)e 4.22 (dd)e 0.74 (3H, s)
2.03 (3H, s)
2.01 (3H, s)
2.01 (3H, s)
2.43 (sext) 1.48 (ddq) 1.72 (ddq) 0.92 (3H, t) 1.18 (3H, d)
2.38 (sext) ∼1.50a ∼1.70a 0.94 (3H, t) 1.18 (3H, d)
2.31 (sext) 1.46 (ddq) 1.68 (ddq) 0.90 (3H, t) 1.12 (3H, d)
a ∼1.90a a a a ∼1.10a 5.04 (d) 3.78 (dd)
8 a a a a 2.97 (tdd) a 5.37 (dd) a a a a a a 5.81 (br t) 4.72 (2H, d) 1.21 (3H, s) 2.58 (d) 3.17 (dd) 1.01 (3H, s)
2.35 (sext) a a 0.91 (3H, t) 1.14 (3H, d)
8.12 (2H, dd) 7.31 (2H, td) 7.49 (tt) 7.77 (2H, dd) 6.90 (2H, td) 7.26 (tt) 3.15 (d) a 2.46 (dd)
a
a
2.68 (s) a a
2.00 (s) 2.69 (dd)
a a
JH,H (Hz)
3
4
5
6
7
8
1R,1β 1R,2R 1R,2β 1R,10β 1β,2R 1β,2β 1β,10β 2R,2β 2R,3R 2R,3β 2β,3R 2β,3β 3R,3β 6β,7R 6β,7β 7R,7β 11,12A 11,12B 12A,12B 14,16A 14,16B 16A,16B 18A,18B 18B,3R 19A,19B 19A,6β 6β,OH-6R 19A,OH-19 19B,OH-19 7R,OH-8β 2′,3′ 2′,5′ 3′A,3′B 3′,4′ OBz 2′,3′(2′′,3′′) 2′,4′(2′′,4′′) 3′,4′(3′′,4′′)
13.4 a a 11.7 2.7 4.2 2.8 a 4.1 a 13.4 a 13.4 11.4 4.8 14.3 10.7 1.4 15.4 1.8 1.8 17.4 3.8 2.4 11.5 0.9
a a a a a a a a a a a a a 11.9 4.7 14.3 10.7 1.5 15.3 1.8 1.8 17.4 4.0 2.2 12.0
