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Glaucolides, piptocarphins and cadinanolides from Lepidaploa remotiflora
Biochemical Systematics and Ecology 26 (1998) 685 — 689
Glaucolides, piptocarphins and cadinanolides from ¸epidaploa remotiflora Diego Alvares Valde´s!, Alicia Bardo´n!, Ce´sar A. N. Catala´n!, Thomas E. Gedris", Werner Herz",* ! Instituto de Quı´ mica Orga´ nica, Falcultad de Bioquı´ mica, Quı´ mica y Farmacia, Universidad Nacional de Tucuma´ n, Ayacucho 491, 4000 S. M. de Tucuma´ n, Argentina " Department of Chemistry, The Florida State University, Tallahassee, FL 32306-4390, U.S.A. Received 5 January 1998; accepted 18 February 1998 Keywords: ¸epidaploa remotiflora; Vernoniinae; Vernonieae; Asteraceae; Sesquiterpene lactones; Glaucolides; Piptocarphins; Cadinanolides
1. Subject and source Aerial parts of ¸epidaploa remotiflora (L. C. Rich) H. Robinson were collected at the flowering stage in October 1992 in Montero, Departamento Santa Cruz, Bolivia. A voucher specimen (Lil d595749) is present in the herbarium of the Fundacio´n Miguel Lillo, Tucuma´n.
2. Previous work The Lepidaploa complex of Western hemisphere »ernonia species has been dissected into a number of separate genera (Robinson, 1987a—c, 1988a—c, 1990, 1992) and various additions and transfers have been made since then (Robinson, 1994, 1995). One of the segregates is the genus ¸epidaploa (Robinson, 1990). The literature contains references to the chemistry of several of its members under the old »ernonia binomials (Abdel-Baset et al., 1971; Mabry et al., 1975; Bohlmann et al., 1981, Bohlmann and Zdero, 1982, 1988; Bohlmann et al., 1982; Jakupovic et al., 1986; Jakupovic et al., 1987). Commonly occurring terpenoid constituents in the herb are sesquiterpene lactones of a type generally found in »ernonia sensu, particularly
* Corresponding author. 0305-1978/98/$19.00 ( 1998 Elsevier Science Ltd. All rights reserved. PII: S 03 0 5-1 9 78 ( 9 8) 0 0 02 6 - X
686
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689
glaucolides and goyazensolides and in two instances, i.e. ¸. cotoneaster (Willd. ex Spreng) H. Robinson (Bohlmann, Gupta et al., 1980; Bohlmann et al., 1982) and ¸. lilacina (Mart. ex DC.) H. Robinson (Bohlmann et al., 1981) unusual allenic sesquiterpene lactones related to glaucolides were found.
3. Present study In the course of our study of Vernoniinae of northern Argentina and adjacent regions (Borkoski et al., 1997 and references therein) we examined ¸epidaploa remotiflora (L. C. Rich) H. Robinson (old synonym »ernonia remotiflora L. C. Rich) (Cabrera, 1978). Air-dried flowers and leaves (630 g) were extracted with CHCl3 (2]3 l) at room temperature for 4 days to give 22 g of residue (3.5%) which was suspended in 190 ml of EtOH at 55°C, diluted with 140 ml of H2O and extracted successively with hexane (2]165 ml), C6H6 (2]165 ml), CHCl3 (2]165 ml) and EtOAc (2]165 ml). Evaporation of the C6H6 extract at reduced pressure gave 2.13 g of residue which was flash chromatographed on Si gel with C6H6 and increasing amounts of EtOAc (0—50%) and finally MeOH to give 44 fractions. Fractions containing sesquiterpene lactones (IR band at 1765 cm~1) were further purified by HPLC, using (A) a Beckman Ultrasphere C8 (5 lm, 10]250 mm) and (B) a Phenomenex C 18 (5 lm, 10]250 mm) column. Retention times were measured from the solvent peak. Eluted fractions were identified by 1H NMR spectrometry at 500 MHz (CDCl3), MS, and compared with spectra of known samples. A 140 mg portion of frs 13—18 (220 mg) was processed by HPLC (column B, MeOH—H2O 3 : 2, 1.5 ml min~1) to give 10.8 mg of glaucolide B (1a, R5 10 min) (Abdel-Baset et al., 1971; Padolina et al., 1974; Mabry et al., 1975) and a mixture which on further HPLC (column A, MeOH—H2O 4 : 3, 1.5 ml min~1) gave 3.8 mg of mikanolide (4, R5 13 min) (Herz et al., 1970; Cox et al., 1973). A 300 mg portion of frs 19—20 (400 mg) was similarly processed (column B, MeOH—H2O, 4 : 3, 1.5 ml min~1). Fr 1 was again 1a, (12 mg, R5 12 min~1), fr 2 was rechromatographed (column A, MeOH-H2O 1 : 1, 1.5 ml min~1) to give 2a (3.4 mg R5 35 min) (Borkosky and Valde´s et al., 1996) and a mixture (12 mg, R5 12 min~1), and fr 3 was rechromatographed (column A, MeOH—H2O, 4 : 3, 1.5 ml min~1) to give an additional 7.4 mg of 2a (R5 23 min~1) and a mixture. HPLC of a 200 mg portion of frs 21—30 (310 mg) using column B (MeOH—H2O, 1 : 1, 1.5 ml min~1) furnished mixtures, 38.8 mg of 2a (R5 23 min) 12.7 mg of 1a (R5 31 min) and 1.5 mg of 2b (R5 34 min) (Catala´n et al., 1986). HPLC of a 150 mg portion of frs 31—44 (250 mg column A, MeOH-H2O 1 : 1, 1.5 ml min~1) gave 3a (4.7 mg, R5 13 min) contaminated with a small amount of 3b (Bardo´n and Montanaro et al., 1993), 2.1 mg of 1b (R5 24 min) (Borkosky and Valde´s et al., 1996), 6.5 mg of a lactone mixture (R5 23 min) and a further 4.2 mg of 2a (R5 26 min). Evaporation of the CHCl3 extract gave 300 mg of residue which was subjected to HPLC (column B, MeOH—H2O 1 : 1, 1.5 ml min~1) to give 2.1 mg of a lactone mixture (R5 24 min), 5.5 mg of 2a (R5 28 min) and 27 mg of glaucolide B (1a, R5 32 min). Evaporation of EtOAc extract gave 42 mg of a mixture which furnished no identifiable products.
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689
687
(1S*, 4R*, 5S*, 6S*, 8S*, 10R*)-1,4,5-Trihydroxy-8,10,13-triacetoxycadin-7(11)-en6,12-olide (3a). Gum admixed with a small amount of 5-acetoxy derivative 3b previously reported from Chrysolaena verbascifolia (Less.) H. Robinson (syn. »ernonia verbascifolia Less.) (Bardo´n and Montanaro et al., 1993); MS PCI (isobutane) m/z (rel. int.) 499 (32.8 [M # H]` of 3b), 481 (10.7 [M # H]`—H2O of 3b), 457 (100 [M # H]` of 3a), 439 (35.1 [M#H]` - H2O of 3a); 1H NMR (CDCl3, 500 MHz) 6.06 (dd, J"4, 2.5 Hz, H-8), 5.14 (d, J"13 Hz, H-13a) 4.78 (d, J"13 Hz, H-13b), 4.36 (s, H-5), 3.38 (dd, J "16, 2.5 Hz, H-9b), 2.26 (m, H-3a), 2.21 (m, 2a), 2.06 (dd, J"16, 4 Hz, H-9a), 2.04, 2.03, 2.01 (all s and 3p, Ac), 1.88 (m, H-3b), 1.75 (m, H-2b), 1.68 (s, 3p, H-14), 1.36 (s, 3p, H-15). The absence of a b-orientated acetate on C-5 shifts H-5 upfield by &1.6 ppm, H-8 downfield by &0.25 ppm and H-15 upfield by &0.1 ppm.
4. Chemotaxonomic significance A survey of the large amount of extant chemical information reveals that glaucolides, goyazensolides and cadinanolides carrying an a-orientated acetate function on C-8 identical with or similar to 1a,b, 2a,b and 3a,b (Fig. 1) are concentrated in but by no means limited to members of the Lepidaploa complex of »ernonia. Otherwise there is little distinction between members of the complex and other Vernoniinae. However, the occurrence of mikanolide (4) which has so far been found only in members of the large genus Mikania (Eupatorieae) (Herz, 1986) in ¸. remotiflora is perplexing. No
Fig. 1
688
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689
Mikania species were within or near the site of our collection of ¸. remotiflora and contamination with extracts of M. dusenii and M. ypacarayensis which were studied in our laboratories several years ago and contained mikanolide (Zamorano et al., 1994, 1995) seems highly unlikely, as no Mikania extracts remained from the earlier work. Repetition of the HPLC fractionation with the CC fractions remaining after completion of the work described above again yielded mikanolide. Among the few germacradienolides with a trans-fused lactone ring closed to C-8 so far encountered within Vernoniinae, only one from Mattfeldanthus nobilis (H. Robinson) H. Robinson (Bohlmann et al., 1980) possesses additional oxygenation at C-6 and C-15 which could represent a transitional stage leading to dilactones of the mikanolide type.
Acknowledgements Work in Tucuma´n was supported by grants from the Consejo de Investigaciones de la Universidad Nactional de Tucuma´n.
References Abdel-Baset, Z. H., Southwick, L., Padolina, W. G., Yoshioka, H., Mabry, T. J., Jones, S. B., 1971. Phytochemistry 10, 2201. Bardo´n, A., Montanaro, S., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1993. Phytochemistry 34, 253. Bohlmann, F., Gupta, R. K., Jakupovic, J., King, R. M., Robinson, H. 1980. Liebigs Ann. 1904. Bohlmann, F., Jakupovic, J., Gupta, R. K., King, R. M., Robinson, H. 1981 Phytochemistry 20, 473. Bohlmann, F., Mu¨ller, L., Gupta, R. K., King, R. M., Robinson, H., 1981. Phytochemistry 20, 2233. Bohlmann, F., Zdero, C., 1982. Phytochemistry 21, 2263. Bohlmann, F., Zdero, C., 1988. Rev. Latinoamer. Quim. 19, 63. Bohlmann, F., Zdero, C., Robinson, H., King, R. M., 1980. Phytochemistry 19, 2473. Bohlmann, F., Zdero, C., King, R. M., Robinson, H., 1982. Phytochemistry 21, 695. Borkosky, S., Bardo´n, A., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1997. Phytochemistry 44, 465. Borkosky, S., Valde´s, D. A., Dı´ az, J. G., Herz, W., 1996. Phytochemistry 42, 1637. Cabrera, A. L., 1978. Flora de la Provincia de Jujuy, Parte XI, Coleccion Cientifica de INTA, Buenos Aires, p. 38. Catala´n, C. A. N., de Inglesias, D., Kavka, J., Sosa, V. E., Herz, W., 1986. J. Nat. Prod. 49, 351. Cox, P. J., Sim, G. A., Roberts, J. S., Herz, W., 1973. J. C. S. Chem. Commun. 428. Herz, W., 1986. Stud. Org. Chem. (Amsterdam) 26, 143. Jakopovic, J., Schmeda-Hirschmann, G., Schuster, A., Zdero, C., Bohlmann, F., King, R. M., Robinson, H., Pickardt, J. 1986. Phytochemistry 25, 145. Jakupovic, J., Zdero, C., Boeker, R., Warning, V., Bohlmann, F., Jones, S. B., 1987 Liebigs Ann. 111. Mabry, T. J. Abdel-Baset, Z. H., Padolina, W. G., Jones, S. B., 1975 Biol. Syst. Ecol. 2, 185. Padolina, W. G., Yoshioka, H., Nakatani, N. Mabry, T. J., Monti, S. A., Davis, R. E., Cox, P. J., Sim, G. A., Watson, W. H., Wu, I. B., 1974. Tetrahedron 30, 1161. Robinson, H., 1987a. Proc. Biol. Soc. Wash. 100, 578. Robinson, H., 1987b. Proc. Biol. Soc. Wash. 100, 544. Robinson, H., 1987c. Proc. Biol. Soc. Wash. 100, 844. Robinson, H., 1988a. Proc. Biol. Soc. Wash. 101, 929. Robinson, H., 1988b. Proc. Biol. Soc. Wash. 101, 952 Robinson, H., 1988c. Proc. Biol. Soc. Wash. 101, 959.
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689 Robinson, H., 1990. Proc. Biol. Soc. Wash. 103, 464. Robinson, H., 1992. Novon 2, 169. Robinson, H., 1994. Phytologia 76, 27. Robinson, H., 1995. Phytologia 78, 384. Zamorano, G., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1994. Phytochemistry 37, 187. Zamorano, G., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1995. Phytochemistry 38, 1257.
689
Glaucolides, piptocarphins and cadinanolides from ¸epidaploa remotiflora Diego Alvares Valde´s!, Alicia Bardo´n!, Ce´sar A. N. Catala´n!, Thomas E. Gedris", Werner Herz",* ! Instituto de Quı´ mica Orga´ nica, Falcultad de Bioquı´ mica, Quı´ mica y Farmacia, Universidad Nacional de Tucuma´ n, Ayacucho 491, 4000 S. M. de Tucuma´ n, Argentina " Department of Chemistry, The Florida State University, Tallahassee, FL 32306-4390, U.S.A. Received 5 January 1998; accepted 18 February 1998 Keywords: ¸epidaploa remotiflora; Vernoniinae; Vernonieae; Asteraceae; Sesquiterpene lactones; Glaucolides; Piptocarphins; Cadinanolides
1. Subject and source Aerial parts of ¸epidaploa remotiflora (L. C. Rich) H. Robinson were collected at the flowering stage in October 1992 in Montero, Departamento Santa Cruz, Bolivia. A voucher specimen (Lil d595749) is present in the herbarium of the Fundacio´n Miguel Lillo, Tucuma´n.
2. Previous work The Lepidaploa complex of Western hemisphere »ernonia species has been dissected into a number of separate genera (Robinson, 1987a—c, 1988a—c, 1990, 1992) and various additions and transfers have been made since then (Robinson, 1994, 1995). One of the segregates is the genus ¸epidaploa (Robinson, 1990). The literature contains references to the chemistry of several of its members under the old »ernonia binomials (Abdel-Baset et al., 1971; Mabry et al., 1975; Bohlmann et al., 1981, Bohlmann and Zdero, 1982, 1988; Bohlmann et al., 1982; Jakupovic et al., 1986; Jakupovic et al., 1987). Commonly occurring terpenoid constituents in the herb are sesquiterpene lactones of a type generally found in »ernonia sensu, particularly
* Corresponding author. 0305-1978/98/$19.00 ( 1998 Elsevier Science Ltd. All rights reserved. PII: S 03 0 5-1 9 78 ( 9 8) 0 0 02 6 - X
686
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689
glaucolides and goyazensolides and in two instances, i.e. ¸. cotoneaster (Willd. ex Spreng) H. Robinson (Bohlmann, Gupta et al., 1980; Bohlmann et al., 1982) and ¸. lilacina (Mart. ex DC.) H. Robinson (Bohlmann et al., 1981) unusual allenic sesquiterpene lactones related to glaucolides were found.
3. Present study In the course of our study of Vernoniinae of northern Argentina and adjacent regions (Borkoski et al., 1997 and references therein) we examined ¸epidaploa remotiflora (L. C. Rich) H. Robinson (old synonym »ernonia remotiflora L. C. Rich) (Cabrera, 1978). Air-dried flowers and leaves (630 g) were extracted with CHCl3 (2]3 l) at room temperature for 4 days to give 22 g of residue (3.5%) which was suspended in 190 ml of EtOH at 55°C, diluted with 140 ml of H2O and extracted successively with hexane (2]165 ml), C6H6 (2]165 ml), CHCl3 (2]165 ml) and EtOAc (2]165 ml). Evaporation of the C6H6 extract at reduced pressure gave 2.13 g of residue which was flash chromatographed on Si gel with C6H6 and increasing amounts of EtOAc (0—50%) and finally MeOH to give 44 fractions. Fractions containing sesquiterpene lactones (IR band at 1765 cm~1) were further purified by HPLC, using (A) a Beckman Ultrasphere C8 (5 lm, 10]250 mm) and (B) a Phenomenex C 18 (5 lm, 10]250 mm) column. Retention times were measured from the solvent peak. Eluted fractions were identified by 1H NMR spectrometry at 500 MHz (CDCl3), MS, and compared with spectra of known samples. A 140 mg portion of frs 13—18 (220 mg) was processed by HPLC (column B, MeOH—H2O 3 : 2, 1.5 ml min~1) to give 10.8 mg of glaucolide B (1a, R5 10 min) (Abdel-Baset et al., 1971; Padolina et al., 1974; Mabry et al., 1975) and a mixture which on further HPLC (column A, MeOH—H2O 4 : 3, 1.5 ml min~1) gave 3.8 mg of mikanolide (4, R5 13 min) (Herz et al., 1970; Cox et al., 1973). A 300 mg portion of frs 19—20 (400 mg) was similarly processed (column B, MeOH—H2O, 4 : 3, 1.5 ml min~1). Fr 1 was again 1a, (12 mg, R5 12 min~1), fr 2 was rechromatographed (column A, MeOH-H2O 1 : 1, 1.5 ml min~1) to give 2a (3.4 mg R5 35 min) (Borkosky and Valde´s et al., 1996) and a mixture (12 mg, R5 12 min~1), and fr 3 was rechromatographed (column A, MeOH—H2O, 4 : 3, 1.5 ml min~1) to give an additional 7.4 mg of 2a (R5 23 min~1) and a mixture. HPLC of a 200 mg portion of frs 21—30 (310 mg) using column B (MeOH—H2O, 1 : 1, 1.5 ml min~1) furnished mixtures, 38.8 mg of 2a (R5 23 min) 12.7 mg of 1a (R5 31 min) and 1.5 mg of 2b (R5 34 min) (Catala´n et al., 1986). HPLC of a 150 mg portion of frs 31—44 (250 mg column A, MeOH-H2O 1 : 1, 1.5 ml min~1) gave 3a (4.7 mg, R5 13 min) contaminated with a small amount of 3b (Bardo´n and Montanaro et al., 1993), 2.1 mg of 1b (R5 24 min) (Borkosky and Valde´s et al., 1996), 6.5 mg of a lactone mixture (R5 23 min) and a further 4.2 mg of 2a (R5 26 min). Evaporation of the CHCl3 extract gave 300 mg of residue which was subjected to HPLC (column B, MeOH—H2O 1 : 1, 1.5 ml min~1) to give 2.1 mg of a lactone mixture (R5 24 min), 5.5 mg of 2a (R5 28 min) and 27 mg of glaucolide B (1a, R5 32 min). Evaporation of EtOAc extract gave 42 mg of a mixture which furnished no identifiable products.
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689
687
(1S*, 4R*, 5S*, 6S*, 8S*, 10R*)-1,4,5-Trihydroxy-8,10,13-triacetoxycadin-7(11)-en6,12-olide (3a). Gum admixed with a small amount of 5-acetoxy derivative 3b previously reported from Chrysolaena verbascifolia (Less.) H. Robinson (syn. »ernonia verbascifolia Less.) (Bardo´n and Montanaro et al., 1993); MS PCI (isobutane) m/z (rel. int.) 499 (32.8 [M # H]` of 3b), 481 (10.7 [M # H]`—H2O of 3b), 457 (100 [M # H]` of 3a), 439 (35.1 [M#H]` - H2O of 3a); 1H NMR (CDCl3, 500 MHz) 6.06 (dd, J"4, 2.5 Hz, H-8), 5.14 (d, J"13 Hz, H-13a) 4.78 (d, J"13 Hz, H-13b), 4.36 (s, H-5), 3.38 (dd, J "16, 2.5 Hz, H-9b), 2.26 (m, H-3a), 2.21 (m, 2a), 2.06 (dd, J"16, 4 Hz, H-9a), 2.04, 2.03, 2.01 (all s and 3p, Ac), 1.88 (m, H-3b), 1.75 (m, H-2b), 1.68 (s, 3p, H-14), 1.36 (s, 3p, H-15). The absence of a b-orientated acetate on C-5 shifts H-5 upfield by &1.6 ppm, H-8 downfield by &0.25 ppm and H-15 upfield by &0.1 ppm.
4. Chemotaxonomic significance A survey of the large amount of extant chemical information reveals that glaucolides, goyazensolides and cadinanolides carrying an a-orientated acetate function on C-8 identical with or similar to 1a,b, 2a,b and 3a,b (Fig. 1) are concentrated in but by no means limited to members of the Lepidaploa complex of »ernonia. Otherwise there is little distinction between members of the complex and other Vernoniinae. However, the occurrence of mikanolide (4) which has so far been found only in members of the large genus Mikania (Eupatorieae) (Herz, 1986) in ¸. remotiflora is perplexing. No
Fig. 1
688
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689
Mikania species were within or near the site of our collection of ¸. remotiflora and contamination with extracts of M. dusenii and M. ypacarayensis which were studied in our laboratories several years ago and contained mikanolide (Zamorano et al., 1994, 1995) seems highly unlikely, as no Mikania extracts remained from the earlier work. Repetition of the HPLC fractionation with the CC fractions remaining after completion of the work described above again yielded mikanolide. Among the few germacradienolides with a trans-fused lactone ring closed to C-8 so far encountered within Vernoniinae, only one from Mattfeldanthus nobilis (H. Robinson) H. Robinson (Bohlmann et al., 1980) possesses additional oxygenation at C-6 and C-15 which could represent a transitional stage leading to dilactones of the mikanolide type.
Acknowledgements Work in Tucuma´n was supported by grants from the Consejo de Investigaciones de la Universidad Nactional de Tucuma´n.
References Abdel-Baset, Z. H., Southwick, L., Padolina, W. G., Yoshioka, H., Mabry, T. J., Jones, S. B., 1971. Phytochemistry 10, 2201. Bardo´n, A., Montanaro, S., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1993. Phytochemistry 34, 253. Bohlmann, F., Gupta, R. K., Jakupovic, J., King, R. M., Robinson, H. 1980. Liebigs Ann. 1904. Bohlmann, F., Jakupovic, J., Gupta, R. K., King, R. M., Robinson, H. 1981 Phytochemistry 20, 473. Bohlmann, F., Mu¨ller, L., Gupta, R. K., King, R. M., Robinson, H., 1981. Phytochemistry 20, 2233. Bohlmann, F., Zdero, C., 1982. Phytochemistry 21, 2263. Bohlmann, F., Zdero, C., 1988. Rev. Latinoamer. Quim. 19, 63. Bohlmann, F., Zdero, C., Robinson, H., King, R. M., 1980. Phytochemistry 19, 2473. Bohlmann, F., Zdero, C., King, R. M., Robinson, H., 1982. Phytochemistry 21, 695. Borkosky, S., Bardo´n, A., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1997. Phytochemistry 44, 465. Borkosky, S., Valde´s, D. A., Dı´ az, J. G., Herz, W., 1996. Phytochemistry 42, 1637. Cabrera, A. L., 1978. Flora de la Provincia de Jujuy, Parte XI, Coleccion Cientifica de INTA, Buenos Aires, p. 38. Catala´n, C. A. N., de Inglesias, D., Kavka, J., Sosa, V. E., Herz, W., 1986. J. Nat. Prod. 49, 351. Cox, P. J., Sim, G. A., Roberts, J. S., Herz, W., 1973. J. C. S. Chem. Commun. 428. Herz, W., 1986. Stud. Org. Chem. (Amsterdam) 26, 143. Jakopovic, J., Schmeda-Hirschmann, G., Schuster, A., Zdero, C., Bohlmann, F., King, R. M., Robinson, H., Pickardt, J. 1986. Phytochemistry 25, 145. Jakupovic, J., Zdero, C., Boeker, R., Warning, V., Bohlmann, F., Jones, S. B., 1987 Liebigs Ann. 111. Mabry, T. J. Abdel-Baset, Z. H., Padolina, W. G., Jones, S. B., 1975 Biol. Syst. Ecol. 2, 185. Padolina, W. G., Yoshioka, H., Nakatani, N. Mabry, T. J., Monti, S. A., Davis, R. E., Cox, P. J., Sim, G. A., Watson, W. H., Wu, I. B., 1974. Tetrahedron 30, 1161. Robinson, H., 1987a. Proc. Biol. Soc. Wash. 100, 578. Robinson, H., 1987b. Proc. Biol. Soc. Wash. 100, 544. Robinson, H., 1987c. Proc. Biol. Soc. Wash. 100, 844. Robinson, H., 1988a. Proc. Biol. Soc. Wash. 101, 929. Robinson, H., 1988b. Proc. Biol. Soc. Wash. 101, 952 Robinson, H., 1988c. Proc. Biol. Soc. Wash. 101, 959.
D. A. Valde& s et al./Biochemical Systematics and Ecology 26 (1998) 685—689 Robinson, H., 1990. Proc. Biol. Soc. Wash. 103, 464. Robinson, H., 1992. Novon 2, 169. Robinson, H., 1994. Phytologia 76, 27. Robinson, H., 1995. Phytologia 78, 384. Zamorano, G., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1994. Phytochemistry 37, 187. Zamorano, G., Catala´n, C. A. N., Dı´ az, J. G., Herz, W., 1995. Phytochemistry 38, 1257.
689