- Email: [email protected]
Neo-clerodane diterpenoids from Scutellaria orientalis subsp. sintenisii
PII: S0031-9422(98)00291-X
Phytochemistry Vol. 49, No. 6, pp. 1825±1827, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0031-9422/98/$ - see front matter
NEO-CLERODANE DITERPENOIDS FROM SCUTELLARIA ORIENTALIS SUBSP. SINTENISII NURTEN EZER,$ YELDA AKCOS% and BENJAMIÂN RODRIÂGUEZ}* $Department of Pharmaceutical Botany, Faculty of Pharmacy, Hacettepe University, TR-06100 Ankara, Turkey, %Department of Pharmacognosy, Faculty of Pharmacy, Hacettepe University, TR06100 Ankara, Turkey and }Instituto de QuõÂ mica OrgaÂnica, CSIC, Juan de la Cierva 3, E-28006 Madrid, Spain (Received 25 February 1998)
Key Word IndexÐScutellaria orientalis subsp. sintenisii; Labiatae; neo-clerodane diterpenoids; scutalpin J; scutenisin. AbstractÐThe previously known neo-clerodane scutalpin J has been isolated from Scutellaria orientalis subsp. sintenisii together with a new diterpenoid, scutenisin, whose structure was established as (13R*)6a,7b-diisobutyryloxy-4a,18;8b, 13-diepoxy-19-hydroxy-neo-clerodan-15,16-olide by spectroscopic means. # 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION
A large number of neo-clerodane diterpenoids have been isolated from Scutellaria species in the last few years [1±3]. Interest in neo-clerodanes from Scutellaria has been stimulated because the most potent insect antifeedant substances discovered until now have been found in these plants [4, 5]. In a continuation of our studies on neo-clerodanes from Scutellaria species [3, 5±7], we have now investigated S. orientalis subsp. sintenisii, a plant endemic to Turkey [8].
dierences between the 1H and 13C NMR spectra of scutenisin (1, Table 1) and 2 [11] were consistent with the presence in 1 of a free hydroxyl group at the C-19 position [dc 62.2 t; dH 4.09 br t, J = 12.2 Hz (HA-19) and 4.38 dd, J = 12.2 and 2.7 Hz (HB-19), both signals collapsed into d,
RESULTS AND DISCUSSION
Repeated chromatography of an acetone extract of the aerial parts of S. orientalis subsp. sintenissi (see Section 3, Experimental) provided scutalpin J, previously isolated from S. alpina [9, 10], together with a new substence, scutanisin (1). Scutenisin (1, C28H42O9) showed IR absorptions consistent with the presence of a g-lactone, hydroxyl and ester groups and its 1H and 13C NMR spectra (Table 1) were very similar to those of scutalpin E (2, a neo-clerodane diterpenoid previously isolated from S. alpina [11]) and other related 4a,18,8b, 13diepoxy-neo-clerodan-15,16-olide derivatives possessing esteri®ed hydroxyl groups at the C-6a, C-7b and C-19 positions [5, 12]. In fact, the observed *Author to whom correspondence should be addressed. 1825
1826
Short Report Table 1. 1H and
H 1a 1b 2a 2b 3a 3b 6b 7a 10b 11A 11B 12A 12B 14A% 14B} 16A} 16B% Me-17 18A} 18B** 19A 19B Me-20 19-OH}} Isobutyrates 2', 20 Me-3', Me-30 Me-4', Me-40
d 01.70$ 01.60$ 2.00 m 01.45$ 2.28 tdd 01.10$ 5.23 br d 5.32 d 2.12 dd 01.60$ 01.60$ 01.55$ 01.55$ 2.53 d 2.67 d 4.11 d 4.28 d 1.17 s 2.25 d 3.01 dd 4.09 br t$$ 4.38 dd%% 0.86 s 2.33 dd
13
C NMR spectral data of compound 1* JH,H
Hz
C
1a,10b 1b,10b 2a,3a 2b,3a 3a,3b 3a,18B 6b,7a 14A,14B 16A,16B 18A,18B 19A,19B 19A,6b 19A,OH 19B,OH 2',3'(4')
11.0 4.6 4.1 13.4 13.4 2.3 10.2 17.1 9.0 3.9 12.2 <0.6 11.0 2.7 7.1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Isobutyrates 1',10 2',20 3',30 4',40
2.50 sept, 2.43 sept 1.15 d, 1.10 d 1.13 d, 1.04 d
d 20.8 25.1 32.2 65.5 46.9 71.1 73.1 81.1 37.8 41.4 27.2 28.9 75.6 42.7 174.6 79.6 20.1 48.0 62.2 18.9
t t t s s d d s s d t t s t sa t qb t t q
176.6 34.1 20.0 19.3
s, 174.4 sa d, 34.0 d qb, 18.7 q q, 18.6 q
* At 500 MHz (1H) and 125.7 MHz (13C) in CDCl3 solution; chemical shifts (d values) are reported with respect to residual CHCl3 (d 7.25) for 1H and to the solvent signals (d 77.00) for 13C. All these assignments were in agreement with the HMQC spectrum. $ Overlapped signal. % Pro-R hydrogen, distinguished by NOE experiments. } Pro-S hydrogen. } Exo hydrogen with respect to ring B. ** Endo hydrogen with respect to ring B. $$ Collapsed into a br d after addtion of D2O. %% Collapsed into a d after addition of D2O. }} Disappeared after addition of D2O. a,b Interchangeable assignments.
J = 12.2 Hz, after addition of D2O; d19-OH 2.33 dd, J = 11.0 and 2.7 Hz] and two isobutyryloxy groups at the C-6a and C-7b equatorial positions [dc 71.1 d (C-6) and 73.1 d (C-7); dH 5.23 br d, J = 10.2 Hz (H-6b) and 5.32 d, J = 10.2 Hz (H-7a); for the 1H and 13C NMR signals of the two isobutyrates see Table 1] instead of the C-7b and C-19 acetates and the C-6a tiglate of 2 [dc 69.2 d (C-6), 73.9 d (C-7) and 62.4 t (C-19); dH 5.23 d (H-6b), 5.45 d (H-7a), J6b.7a=10.3 Hz, 4.55 d (HA-19) and 4.69 d (HB-19), Jgem=12.1 Hz] [11]. The relative stereochemistry of all the stereogenic centres of 1 was in complete agreement with NOE experiments. In particular, the 13R* con®guration was ®rmly supported by the following NOE observations. Irradiation at d 1.17 (Me-17 protons) caused NOE enhancement in the signals of the HB14 (d 2.67), H-7a (d 5.32) and Me-20 (d 0.86) protons, whereas on irradiating at d 2.67 (HB-14 proton), NOE enhancements were observed in the HB16 (d 4.28), Me-17 (d 1.17) and HA-14 (d 2.53) proton signals. These results established that the H-7a, Me-17, Me-20 and C-14 methylene groups are aoriented, possessing a cis spatial relationship with respect to the tetrahydropyran ring of scutanisin.
The NOE experiments also provided information for distinguishing both methylene protons at positions C-14 and C-16, because irradiation of the Me-17 protons caused a NOE enhancement in HB14 and, irradiating this proton, the HB-16 signal was enhanced (see above and Table 1). The absolute stereochemistry of 1 was not ascertained by direct methods but, on biogenetic grounds, we suppose that it possesses a neo-clerodane absolute con®guration [13] like other clerodanes isolated from Scutellaria plants [3, 5, 7, 12, 14]. EXPERIMENTAL
General Mp uncorr.: Plant material was collected in July 1993 at GoÈlbasi, GoÈlbasi±Bala, near Ankara, Turkey, and voucher specimens are deposited in the Herbarium of the Faculty of Pharmacy, Hacettepe University at Ankara (HUEF No. 93002). Extraction and isolation of the diterpenoids Dried and powdered aerial parts of Scutellaria orientalis L. subsp. sintenisii (Hausskn. ex Bornm.) Edmondson (500 g) were extracted with Me2CO
Short Report
(5 2 l) at room temp. for 1 week. After ®ltration, the solvent was evapd in vacuo to dryness, yielding a residue (22 g), which was subjected to CC (silica gel Merck No. 7734, deactivated with 10% H2O, w/ v, 400 g) eluting with a petrol±EtOAc gradient. The fractions eluted with petrol±EtOAc (3:2) contained a complex mixture of diterpenoids (765 mg) which, on repeated CC (silica gel) eluting with CH2Cl2± MeOH (30:1) allowed the isolation of pure scutalpin J (12 mg, most polar constituent) [9, 10] and another fraction (98 mg) which gave only one spot on TLC with several eluents. The 1H NMR spectrum of this material revealed that it was a mixture of diterpenoids and crystallization from EtOAc-nhexane yielded pure scutenisin (1, 10 mg). Attempts at isolating other diterpene constituents from the plant extract were unsuccessful. The previously known compound, scutalpin J, was identi®ed by its physical (mp, [a]D) and spectroscopic (IR, 1H NMR, MS) data and by comparison (mmp, TLC) with an authentic sample. Scutenisin (1) Mp 252±2548 (EtOAc-n-hexane); a18 D ÿ25.58 ÿ1 (CHCl3; c 0.141). KBr cm : 3600 (OH), 3070 (oximax rane), 1785 (spiro g-lactone), 1745, 1735 (esters), 2980, 2950, 2880, 1460, 1415, 1390, 1370, 1190, 1170, 1150, 1080, 1030, 1010, 995, 960, 910, 880, 860, 850, 750; 1H and 13C NMR: Table 1; EI±MS (70 eV, direct inlet) m/z (rel. int.): [M]+ absent, 491 [M±CH3O]+ (4), 421 (28), 404 (15), 403 (17), 389 (15), 351 (20), 334 (100), 316 (80), 301 (62), 275 (31), 201 (15), 174 (23), 159 (11), 121 (13), 91 (15), 71 [C4H7O]+ (56), 55 (11). (Found: C, 64.47; H, 8.16. C28H42O9 requires: C, 64.35; H, 8.10%.) Acknowledgements ÐThis work was supported by the `DireccioÂn General de EnsenÄanza Superior' (grants No. PB94-0104, PB96-0830, Spain) and the `ConsejerõÂ a de EducacioÂn y Cultura de la Comunidad de Madrid' (project No. 06G/001/96). REFERENCES
1. Merritt, A. T. and Ley, S. V., Natural Product Reports, 1992, 9, 243.
1827
2. RodrõÂ guez-Hahn, L., Esquivel, B. and CaÂrdenas, J., Progress in the Chemistry of Organic Natural Products, 1994, 63, 107. 3. RodrõÂ guez, B., de la Torre, M. C., Jimeno, M.L., Bruno, M., Vassallo, N., BondõÂ , M. L., Piozzi, F. and Servettaz, O., Journal Natural Products, 1997, 60, 348. 4. Anderson, J. C., Blaney, W. M., Cole, M. D., Fellows, L. L., Ley, S. V., Sheppard, R. N. and Simmonds, M. S. J., Tetrahedron Letters, 1989, 30, 4737. 5. MunÄoz, D. M., de la Torre, M. C., RodrõÂ guez, B., Simmonds, M. S. J. and Blaney, W. M., Phytochemistry, 1997, 44, 593. 6. RodrõÂ guez, B., de la Torre, M. C., RodrõÂ guez, B. and GoÂmez-Serranillos, P., Phytochemistry, 1996, 41, 247. 7. Hussein, A. A., de la Torre, M. C., Jimeno, M.-L., RodrõÂ guez, B., Bruno, M., Piozzi, F. and Servettaz, O., Phytochemistry, 1996, 43, 835. 8. Davis, P. H., Flora of Turkey and East Aegean Islands. Vol. 7, University Press, Edinburgh, 1982, p. 78. 9. de la Torre, M. C., RodrõÂ guez, B., Bruno, M., Piozzi, F., Savona, G., Vassallo, N. and Servettaz, O., Phytochemistry, 1995, 38, 181. 10. Miyaichi, Y., Kizu, H., Yamaguchi, Y. and Tomimori, T., Yakugaku Zasshi, 1994, 114, 264. 11. Bozov, P. I., Papanov, G. Y. and Malakov, P. Y., Phytochemistry, 1994, 35, 1285. 12. Bozov, P. I., Malakov, P. Y., Papanov, G. Y., de la Torre, M. C., RodrõÂ guez, B. and Perales, A., Phytochemistry, 1993, 34, 453. 13. Rogers, D., Unal, G. G., Williams, D. J., Ley, S. V., Sim, G. A., Joshi, B. S. and Ravindranath, K. R., Journal of the Chemical Society, Chemical Communications, 1979, 97. 14. RodrõÂ guez, B., de la Torre, M.C., RodrõÂ guez, B., Bruno, M., Piozzi, F., Savona, G., Simmonds, M. S. J., Blaney, W. M. and Perales, A., Phytochemistry, 1993, 33, 309.
Phytochemistry Vol. 49, No. 6, pp. 1825±1827, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0031-9422/98/$ - see front matter
NEO-CLERODANE DITERPENOIDS FROM SCUTELLARIA ORIENTALIS SUBSP. SINTENISII NURTEN EZER,$ YELDA AKCOS% and BENJAMIÂN RODRIÂGUEZ}* $Department of Pharmaceutical Botany, Faculty of Pharmacy, Hacettepe University, TR-06100 Ankara, Turkey, %Department of Pharmacognosy, Faculty of Pharmacy, Hacettepe University, TR06100 Ankara, Turkey and }Instituto de QuõÂ mica OrgaÂnica, CSIC, Juan de la Cierva 3, E-28006 Madrid, Spain (Received 25 February 1998)
Key Word IndexÐScutellaria orientalis subsp. sintenisii; Labiatae; neo-clerodane diterpenoids; scutalpin J; scutenisin. AbstractÐThe previously known neo-clerodane scutalpin J has been isolated from Scutellaria orientalis subsp. sintenisii together with a new diterpenoid, scutenisin, whose structure was established as (13R*)6a,7b-diisobutyryloxy-4a,18;8b, 13-diepoxy-19-hydroxy-neo-clerodan-15,16-olide by spectroscopic means. # 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION
A large number of neo-clerodane diterpenoids have been isolated from Scutellaria species in the last few years [1±3]. Interest in neo-clerodanes from Scutellaria has been stimulated because the most potent insect antifeedant substances discovered until now have been found in these plants [4, 5]. In a continuation of our studies on neo-clerodanes from Scutellaria species [3, 5±7], we have now investigated S. orientalis subsp. sintenisii, a plant endemic to Turkey [8].
dierences between the 1H and 13C NMR spectra of scutenisin (1, Table 1) and 2 [11] were consistent with the presence in 1 of a free hydroxyl group at the C-19 position [dc 62.2 t; dH 4.09 br t, J = 12.2 Hz (HA-19) and 4.38 dd, J = 12.2 and 2.7 Hz (HB-19), both signals collapsed into d,
RESULTS AND DISCUSSION
Repeated chromatography of an acetone extract of the aerial parts of S. orientalis subsp. sintenissi (see Section 3, Experimental) provided scutalpin J, previously isolated from S. alpina [9, 10], together with a new substence, scutanisin (1). Scutenisin (1, C28H42O9) showed IR absorptions consistent with the presence of a g-lactone, hydroxyl and ester groups and its 1H and 13C NMR spectra (Table 1) were very similar to those of scutalpin E (2, a neo-clerodane diterpenoid previously isolated from S. alpina [11]) and other related 4a,18,8b, 13diepoxy-neo-clerodan-15,16-olide derivatives possessing esteri®ed hydroxyl groups at the C-6a, C-7b and C-19 positions [5, 12]. In fact, the observed *Author to whom correspondence should be addressed. 1825
1826
Short Report Table 1. 1H and
H 1a 1b 2a 2b 3a 3b 6b 7a 10b 11A 11B 12A 12B 14A% 14B} 16A} 16B% Me-17 18A} 18B** 19A 19B Me-20 19-OH}} Isobutyrates 2', 20 Me-3', Me-30 Me-4', Me-40
d 01.70$ 01.60$ 2.00 m 01.45$ 2.28 tdd 01.10$ 5.23 br d 5.32 d 2.12 dd 01.60$ 01.60$ 01.55$ 01.55$ 2.53 d 2.67 d 4.11 d 4.28 d 1.17 s 2.25 d 3.01 dd 4.09 br t$$ 4.38 dd%% 0.86 s 2.33 dd
13
C NMR spectral data of compound 1* JH,H
Hz
C
1a,10b 1b,10b 2a,3a 2b,3a 3a,3b 3a,18B 6b,7a 14A,14B 16A,16B 18A,18B 19A,19B 19A,6b 19A,OH 19B,OH 2',3'(4')
11.0 4.6 4.1 13.4 13.4 2.3 10.2 17.1 9.0 3.9 12.2 <0.6 11.0 2.7 7.1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Isobutyrates 1',10 2',20 3',30 4',40
2.50 sept, 2.43 sept 1.15 d, 1.10 d 1.13 d, 1.04 d
d 20.8 25.1 32.2 65.5 46.9 71.1 73.1 81.1 37.8 41.4 27.2 28.9 75.6 42.7 174.6 79.6 20.1 48.0 62.2 18.9
t t t s s d d s s d t t s t sa t qb t t q
176.6 34.1 20.0 19.3
s, 174.4 sa d, 34.0 d qb, 18.7 q q, 18.6 q
* At 500 MHz (1H) and 125.7 MHz (13C) in CDCl3 solution; chemical shifts (d values) are reported with respect to residual CHCl3 (d 7.25) for 1H and to the solvent signals (d 77.00) for 13C. All these assignments were in agreement with the HMQC spectrum. $ Overlapped signal. % Pro-R hydrogen, distinguished by NOE experiments. } Pro-S hydrogen. } Exo hydrogen with respect to ring B. ** Endo hydrogen with respect to ring B. $$ Collapsed into a br d after addtion of D2O. %% Collapsed into a d after addition of D2O. }} Disappeared after addition of D2O. a,b Interchangeable assignments.
J = 12.2 Hz, after addition of D2O; d19-OH 2.33 dd, J = 11.0 and 2.7 Hz] and two isobutyryloxy groups at the C-6a and C-7b equatorial positions [dc 71.1 d (C-6) and 73.1 d (C-7); dH 5.23 br d, J = 10.2 Hz (H-6b) and 5.32 d, J = 10.2 Hz (H-7a); for the 1H and 13C NMR signals of the two isobutyrates see Table 1] instead of the C-7b and C-19 acetates and the C-6a tiglate of 2 [dc 69.2 d (C-6), 73.9 d (C-7) and 62.4 t (C-19); dH 5.23 d (H-6b), 5.45 d (H-7a), J6b.7a=10.3 Hz, 4.55 d (HA-19) and 4.69 d (HB-19), Jgem=12.1 Hz] [11]. The relative stereochemistry of all the stereogenic centres of 1 was in complete agreement with NOE experiments. In particular, the 13R* con®guration was ®rmly supported by the following NOE observations. Irradiation at d 1.17 (Me-17 protons) caused NOE enhancement in the signals of the HB14 (d 2.67), H-7a (d 5.32) and Me-20 (d 0.86) protons, whereas on irradiating at d 2.67 (HB-14 proton), NOE enhancements were observed in the HB16 (d 4.28), Me-17 (d 1.17) and HA-14 (d 2.53) proton signals. These results established that the H-7a, Me-17, Me-20 and C-14 methylene groups are aoriented, possessing a cis spatial relationship with respect to the tetrahydropyran ring of scutanisin.
The NOE experiments also provided information for distinguishing both methylene protons at positions C-14 and C-16, because irradiation of the Me-17 protons caused a NOE enhancement in HB14 and, irradiating this proton, the HB-16 signal was enhanced (see above and Table 1). The absolute stereochemistry of 1 was not ascertained by direct methods but, on biogenetic grounds, we suppose that it possesses a neo-clerodane absolute con®guration [13] like other clerodanes isolated from Scutellaria plants [3, 5, 7, 12, 14]. EXPERIMENTAL
General Mp uncorr.: Plant material was collected in July 1993 at GoÈlbasi, GoÈlbasi±Bala, near Ankara, Turkey, and voucher specimens are deposited in the Herbarium of the Faculty of Pharmacy, Hacettepe University at Ankara (HUEF No. 93002). Extraction and isolation of the diterpenoids Dried and powdered aerial parts of Scutellaria orientalis L. subsp. sintenisii (Hausskn. ex Bornm.) Edmondson (500 g) were extracted with Me2CO
Short Report
(5 2 l) at room temp. for 1 week. After ®ltration, the solvent was evapd in vacuo to dryness, yielding a residue (22 g), which was subjected to CC (silica gel Merck No. 7734, deactivated with 10% H2O, w/ v, 400 g) eluting with a petrol±EtOAc gradient. The fractions eluted with petrol±EtOAc (3:2) contained a complex mixture of diterpenoids (765 mg) which, on repeated CC (silica gel) eluting with CH2Cl2± MeOH (30:1) allowed the isolation of pure scutalpin J (12 mg, most polar constituent) [9, 10] and another fraction (98 mg) which gave only one spot on TLC with several eluents. The 1H NMR spectrum of this material revealed that it was a mixture of diterpenoids and crystallization from EtOAc-nhexane yielded pure scutenisin (1, 10 mg). Attempts at isolating other diterpene constituents from the plant extract were unsuccessful. The previously known compound, scutalpin J, was identi®ed by its physical (mp, [a]D) and spectroscopic (IR, 1H NMR, MS) data and by comparison (mmp, TLC) with an authentic sample. Scutenisin (1) Mp 252±2548 (EtOAc-n-hexane); a18 D ÿ25.58 ÿ1 (CHCl3; c 0.141). KBr cm : 3600 (OH), 3070 (oximax rane), 1785 (spiro g-lactone), 1745, 1735 (esters), 2980, 2950, 2880, 1460, 1415, 1390, 1370, 1190, 1170, 1150, 1080, 1030, 1010, 995, 960, 910, 880, 860, 850, 750; 1H and 13C NMR: Table 1; EI±MS (70 eV, direct inlet) m/z (rel. int.): [M]+ absent, 491 [M±CH3O]+ (4), 421 (28), 404 (15), 403 (17), 389 (15), 351 (20), 334 (100), 316 (80), 301 (62), 275 (31), 201 (15), 174 (23), 159 (11), 121 (13), 91 (15), 71 [C4H7O]+ (56), 55 (11). (Found: C, 64.47; H, 8.16. C28H42O9 requires: C, 64.35; H, 8.10%.) Acknowledgements ÐThis work was supported by the `DireccioÂn General de EnsenÄanza Superior' (grants No. PB94-0104, PB96-0830, Spain) and the `ConsejerõÂ a de EducacioÂn y Cultura de la Comunidad de Madrid' (project No. 06G/001/96). REFERENCES
1. Merritt, A. T. and Ley, S. V., Natural Product Reports, 1992, 9, 243.
1827
2. RodrõÂ guez-Hahn, L., Esquivel, B. and CaÂrdenas, J., Progress in the Chemistry of Organic Natural Products, 1994, 63, 107. 3. RodrõÂ guez, B., de la Torre, M. C., Jimeno, M.L., Bruno, M., Vassallo, N., BondõÂ , M. L., Piozzi, F. and Servettaz, O., Journal Natural Products, 1997, 60, 348. 4. Anderson, J. C., Blaney, W. M., Cole, M. D., Fellows, L. L., Ley, S. V., Sheppard, R. N. and Simmonds, M. S. J., Tetrahedron Letters, 1989, 30, 4737. 5. MunÄoz, D. M., de la Torre, M. C., RodrõÂ guez, B., Simmonds, M. S. J. and Blaney, W. M., Phytochemistry, 1997, 44, 593. 6. RodrõÂ guez, B., de la Torre, M. C., RodrõÂ guez, B. and GoÂmez-Serranillos, P., Phytochemistry, 1996, 41, 247. 7. Hussein, A. A., de la Torre, M. C., Jimeno, M.-L., RodrõÂ guez, B., Bruno, M., Piozzi, F. and Servettaz, O., Phytochemistry, 1996, 43, 835. 8. Davis, P. H., Flora of Turkey and East Aegean Islands. Vol. 7, University Press, Edinburgh, 1982, p. 78. 9. de la Torre, M. C., RodrõÂ guez, B., Bruno, M., Piozzi, F., Savona, G., Vassallo, N. and Servettaz, O., Phytochemistry, 1995, 38, 181. 10. Miyaichi, Y., Kizu, H., Yamaguchi, Y. and Tomimori, T., Yakugaku Zasshi, 1994, 114, 264. 11. Bozov, P. I., Papanov, G. Y. and Malakov, P. Y., Phytochemistry, 1994, 35, 1285. 12. Bozov, P. I., Malakov, P. Y., Papanov, G. Y., de la Torre, M. C., RodrõÂ guez, B. and Perales, A., Phytochemistry, 1993, 34, 453. 13. Rogers, D., Unal, G. G., Williams, D. J., Ley, S. V., Sim, G. A., Joshi, B. S. and Ravindranath, K. R., Journal of the Chemical Society, Chemical Communications, 1979, 97. 14. RodrõÂ guez, B., de la Torre, M.C., RodrõÂ guez, B., Bruno, M., Piozzi, F., Savona, G., Simmonds, M. S. J., Blaney, W. M. and Perales, A., Phytochemistry, 1993, 33, 309.