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Labdane acids from polar extracts of Juniperus thurifera
Phytochmzstry, Vol. 31, No. 5, pp. 1719-1722,1992 Printedin GreatBritain.
003I --9422f92 $5.00+ 0.00 @ 1992Pergamon Pressplc
LABDANE ACIDS FROM POLAR EXTRACTS OF ~U~~~ERU~ ARTURO SAX FELICIANO,” JOSE M. MIGUEL DEL CORRAL, JOSE L. LOPEZ Department of Organic and
THURIFERA
and BEATRIZDE PASCUAL-TERESA
Pharmaceutical Chemistry, Faculty of Pharmacy, 37007 Saiamanca, Spain (ReceiueH16 September 1991)
Key Wd
Index-Juniperus thur@fera; Cupressaceae; leaves; diterpenes; labdane acids.
Abstract-Seven new labdane acids: 3a,15-dihydroxy-labd-8(17)-en-19-oic; (14R) and (14s) 14,15_dihydroxy-8,13epoxy-labdan-19-oic; 3a-hydroxy-13-oxo-l4,15-dinorlabd-8(17)-en-l9-oic; 3cr,l5-dihydroxy-14-oxo-labd-8(17),13(16)dien-19-oic; (14R) and (14s) 3~,14,1S-trihydroxy-labd-8( 17),13(16)-dien-19-oic acids, have been isolated as acetates and methyl esters from a chloroform extract of the leaves of Juniperus thurifira. INTRODUCTION
We have recently reported the isolation of several lignans and 8-hydroxylabdanes Cl, 21 from a chloroform extract of Junipertis tr?uriferla. This paper deals with the isolation and structural elucidation of seven new labdanes (la-7a) from an acid fraction of the same extract. RESULTSANDDISCUSSION The acid part, obtained as reported in a recent work [l], after methylation and acetylation of the different fractions, afforded five diterpenoids (la, 3a, 4a, 6a and 7a) with a labdane structure, all of them having a Aaf17) double bond, a 19-methyl ester group and a 3a-acetoxy group as common characteristics, and two Iabdanes (2a and 5a) with a manoyl oxide acid-related structure [3]. The common structure of the five new compounds was deduced from their spectral data, i.e. IR bands of double bonds (3080, 1630,990,895 cm- ’ ) and ester and acetate groups (1730 and 1250-1200 cm-‘); ‘HNMR signals of two methyIs around Cs1.16 and 0.53 corresponding to H18 and H-20, respectively, two broad singlets at 64.5 and 4.80 of the vinylidenic protons H-17, another methyl signal at 6 3.63 from the methyl ester (Table l), and a triplet at 6 5.32 and a singlet at 6 2.10 assignable to an acetoxy1 group which must be located at C-3 in equatorial disposition. The configuration of the acetate was deduced from the coupling constant of its gemina1 proton (J =2.6 Hz) and confirmed by comparison with other diterpenoids previously isolated from the n-hexane extract of this plant [4], having a 3a-acetoxyl group. A 13CNMR signal near 623.8, assignable to the C-18 methyl group, and another around 6 176.0, assignable to the carboxyl group (Table 2) confirmed the axial disposition of the ester group [5,6]; the rest of the signals present in the 13C NMR spectra led us to establish the already mentioned bicyclic structure for these five new diterpenoids, all of them thus differing in the side chain at C-9. Compound la showed [&ID= + 13.7”and CM]” (EIMS) at m/z 436 in agreement with the molecular formula C25H,00,. The *HNMR spectrum displayed signals similar to those presented by methyl imbricatolate [7]. *Author to whom correspondence should be addressed.
However, it showed additional signais of two acetate groups, one of them being that already mentioned at C-3. The location of the second acetate group at C-15 was deduced from the presence of a methylene signal at 6 63.1 in the 13CNMR spectrum. The configuration at C-13 was determined by comparing the physical and spectroscopic data with those of methyl imbricatolate [S, 91. All this led us to propose structure la for this compound. Compound 2a, [IX&,= + 8.3”, was aiso isolated from an acetyfated fraction. The EIMS displayed the highest peak at m/z 393, which corresponded, after loss of acetate, to the molecular formula C&H,,O,. The ‘HNMR speo trum (Table 1) showed no signals assignable to the 8(17) vinylidene, whereas it displayed seven singlets of methyl groups, one of a methyl ester (6 3.62), two of acetates (6 2.01 and 2.08), another one characteristic of the C-18 methyl group (6 1.17) and the last two assignable to two methyl groups attached to an oxygenated carbon (6 1.21 and 1.25). The IR spectrum did not show free hydroxyl bands; however, the 13CNMR spectrum showed two signals for non-protonated oxygenated carbons (6 75.0 and 73.4), all this suggesting a manoyl oxide acid-related structure. The absence of vinyl group signals, characteristic of the last structure, and the presence of two acetates prompted us to locate these acetate groups at C-14 and C15, which was confirmed by the 13CNMR spectrum. The stereochemistry at C-14 was established by comparison with the data reported in the literature for compounds having the same structure at the C-13 side chain [lo]. Thus, we propose structure 2a for this compound. Compound 3a presented [a&, = + 8.2”. As the ‘f-I NMR signals assignable to the C-9 chain displayed a double intensity singlet at S2.10, and the Ir3C NMR spectrum showed only 21 peaks, this suggested a dinorlabdane structure for this compound. The spectroscopic data were similar to those shown by methyl 13-0x0-14,15dinorlabd-8(17)-en-19-oate isoIated from berries of this plant [ 111, the only difference being the presence of the C3 acetoxyl group. All this confirms the proposed structure 3a for this compound. Compound 4s~showed [a],,= + 7.5”, and a UV maximum at 220 nm, characteristic of a conjugated carbony group; this was confirmed by the presence in the IR spectrum of a band at 1645 cm- ‘. The EIMS showed CMI’ at m/z 448, in agreement with the molecular
1719
A. SAN FELICIANO et al.
1720
Table H
la
3 14a 14b 15a 15b 16a 16b 17a 17b 18 20 COOCEJ, 3-OCOCIS, 14-OCOW, 1%OCOCEI,
5.32
1. ‘HNMR
2a
t (2.6)
data for compounds
la-7a (J in Hz)
3a
4a
5.32 br t
5.32 br t
4.10 dd (12.0, 8.9) 4.08 br t (6.7) 0.91 d (5.9) 4.50 4.85 1.16 0.52 3.64 2.09 2.03
br s
4.51 dd (2.2, 12.0) 4.95 dd (2.2, 8.9) 1.21 s 1.25 s
br s
s s s s s
1.17 s 0.58 s 3.62 s
4.46 4.87 1.16 0.53 3.64 2.10
5.38 5.31 4.62 4.89 1.16 0.50 3.63 2.10
br s br s
s s s s
2.01 s 2.08 s
4.18 dd (12.0, 9.0)
5.34 5.37
5.32 dd (9.0, 12.0) 1.31 s
br s br s br s
1.12 s
br s s s s s
1.17 s 0.60 s 3.63 s 2.03 s 2.07 s
2.18 s
formula C25H3607. The ‘H NMR spectrum displayed as main signals: an acetate group (6 2.18) and a vinylidenic double bond (two broad singlets at 6 5.31 and 5.38). This was confirmed by the data afforded by the 13CNMR spectrum (6 124.0 and 147.3) which also contained a signal at 6 193.6 for a conjugated carbonyl, whose location at C-14 could justify the deshielding of the already mentioned olefinic protons which would be at C-16. This allowed us to assign a 2H singlet at 6 5.82 to the 15methylene bearing an acetate group. All the foregoing led us to propose structure 4a for this compound.
6a+7a
4.60 dd (1.9, 2.0)
5.82 s
2.10 s
5a
t (3.2) t (3.2)
4.08 m
4.25 m 4.98 5.08 4.52 4.88 1.17 0.53 3.64 2.11 2.05 2.09
br s br s br s br s
s s s s s s
Compound Sa showed [aIn = + 26.7”. The IR,‘H NMR and i3C NMR data were similar to those of 2a, the NMR data differing only in the chemical shifts of the iH NMR signals corresponding to the methyl groups attached to the oxygenated carbons (61.31 and 1.12 instead of 1.21 and 1.12) and the “C NMR signal of C-14 (674.6 instead of 78.3). All this showed that compound 5a was the C-14 epimer of the already mentioned compound, thus having the S configuration, which was also confirmed by comparison of these two compounds with data in the literature [lo].
R 12 13 G” 14
16
la 15 OAc
“c
-4
0
4a OAC
6a+7a OAC
2a 5a
R’= OAc, R2= H R’= H, R2= OAc
1722
A. SAN FELICIANO et al.
‘H NMR: h, cm-I: 3645,3460,1690,1370,1165,995,960,850; see Table 1; 13C NMR: see Table 2. Methyl (14R) and (14s) 31,14,15-triacetoxy-lahd-8(17),13(16)dien-19-oate (6a and 7n). Oil eluted with hexane-EtOAc (2:3); IR v,,, cm -‘:2850,1725,1640,1440,1360,1230,1160,1040,970, 890; ‘H NMR: see Table 1; 13C NMR: see Table 2. Acknowledgement-Financial support DGICYT, grant PB 89-0394.
for this work came from
REFERENCES 1. San Feliciano, A., Miguel de1 Corral, J. M., L6pez, J. L. and Pascual-Teresa, B. de (1992) Phytochemisrry 31, 267. 2. San Feliciano, A., Miguel de1 Corral, J. M., Lbpez, J. L. and Pascual-Teresa, B. de (1992) Phytochemistry 31, 1713. 3. Anderson, R., Gref, R. and Lundgre, N. (1990) Phytochemistry 29, 1320. 4. San Feliciano, A., Medarde, M., Lopez, J. L., Puebla, P., Miguel de1 Corral, J. M. and Barrero, A. F. (1988) Phytochemistry 27, 2241.
5. Wherly, F. W. and Nishida, T. (1979) Fortschr. Chem. Org. Naturstoffe 276, 55. 6. Aranda, J. and Bernassau, J. M. (1977) J. Org. Chem. 42, 4256. 7. Pascual Teresa, J. de, Barrero. A. F., Muriel, L., San Feliciano, A. and Grande, M. (1980)Phytochemistry 19, 899. 8. Pascual Teresa, J. de, Bellido, I. S., Basabe, P., Marcos, I. S., Ruano, L. F. and Urones. J. G. (1982) Phytochemistry 21, 1153. 9. Carman, R. M. (1966) Aust. J. Chem. 19, 629. 10. Garcia-Alvarez, M. C.. Rodriguez, B., Garcia-Granados, A. and S. de Buruaga, A. (1982) J. Org. Chem. 47, 3571. 11. Pascual Teresa, J. de, San Feliciano, A. and Egido, T. (1976) An. Quim. 72, 865. 12. San Feliciano, A., Caballero, E., Del Rey, B. and Sancho. I. (1991) Phytochemistry 30, 3134. 13. Urones, J. G., Marcos, I. S., Basabe. P., Sexmero, M. J., Diez, D. J., Garrido, N. M. and Prieto, J. E. S. (1990) Tetrahedron 46, 2495. 14. Urones, J. G.. Marcos, I. S., Sexmero, M. J., Basabe, P. and Lithgow, M. A. (1990) Phytochemistry 29, 1247.
003I --9422f92 $5.00+ 0.00 @ 1992Pergamon Pressplc
LABDANE ACIDS FROM POLAR EXTRACTS OF ~U~~~ERU~ ARTURO SAX FELICIANO,” JOSE M. MIGUEL DEL CORRAL, JOSE L. LOPEZ Department of Organic and
THURIFERA
and BEATRIZDE PASCUAL-TERESA
Pharmaceutical Chemistry, Faculty of Pharmacy, 37007 Saiamanca, Spain (ReceiueH16 September 1991)
Key Wd
Index-Juniperus thur@fera; Cupressaceae; leaves; diterpenes; labdane acids.
Abstract-Seven new labdane acids: 3a,15-dihydroxy-labd-8(17)-en-19-oic; (14R) and (14s) 14,15_dihydroxy-8,13epoxy-labdan-19-oic; 3a-hydroxy-13-oxo-l4,15-dinorlabd-8(17)-en-l9-oic; 3cr,l5-dihydroxy-14-oxo-labd-8(17),13(16)dien-19-oic; (14R) and (14s) 3~,14,1S-trihydroxy-labd-8( 17),13(16)-dien-19-oic acids, have been isolated as acetates and methyl esters from a chloroform extract of the leaves of Juniperus thurifira. INTRODUCTION
We have recently reported the isolation of several lignans and 8-hydroxylabdanes Cl, 21 from a chloroform extract of Junipertis tr?uriferla. This paper deals with the isolation and structural elucidation of seven new labdanes (la-7a) from an acid fraction of the same extract. RESULTSANDDISCUSSION The acid part, obtained as reported in a recent work [l], after methylation and acetylation of the different fractions, afforded five diterpenoids (la, 3a, 4a, 6a and 7a) with a labdane structure, all of them having a Aaf17) double bond, a 19-methyl ester group and a 3a-acetoxy group as common characteristics, and two Iabdanes (2a and 5a) with a manoyl oxide acid-related structure [3]. The common structure of the five new compounds was deduced from their spectral data, i.e. IR bands of double bonds (3080, 1630,990,895 cm- ’ ) and ester and acetate groups (1730 and 1250-1200 cm-‘); ‘HNMR signals of two methyIs around Cs1.16 and 0.53 corresponding to H18 and H-20, respectively, two broad singlets at 64.5 and 4.80 of the vinylidenic protons H-17, another methyl signal at 6 3.63 from the methyl ester (Table l), and a triplet at 6 5.32 and a singlet at 6 2.10 assignable to an acetoxy1 group which must be located at C-3 in equatorial disposition. The configuration of the acetate was deduced from the coupling constant of its gemina1 proton (J =2.6 Hz) and confirmed by comparison with other diterpenoids previously isolated from the n-hexane extract of this plant [4], having a 3a-acetoxyl group. A 13CNMR signal near 623.8, assignable to the C-18 methyl group, and another around 6 176.0, assignable to the carboxyl group (Table 2) confirmed the axial disposition of the ester group [5,6]; the rest of the signals present in the 13C NMR spectra led us to establish the already mentioned bicyclic structure for these five new diterpenoids, all of them thus differing in the side chain at C-9. Compound la showed [&ID= + 13.7”and CM]” (EIMS) at m/z 436 in agreement with the molecular formula C25H,00,. The *HNMR spectrum displayed signals similar to those presented by methyl imbricatolate [7]. *Author to whom correspondence should be addressed.
However, it showed additional signais of two acetate groups, one of them being that already mentioned at C-3. The location of the second acetate group at C-15 was deduced from the presence of a methylene signal at 6 63.1 in the 13CNMR spectrum. The configuration at C-13 was determined by comparing the physical and spectroscopic data with those of methyl imbricatolate [S, 91. All this led us to propose structure la for this compound. Compound 2a, [IX&,= + 8.3”, was aiso isolated from an acetyfated fraction. The EIMS displayed the highest peak at m/z 393, which corresponded, after loss of acetate, to the molecular formula C&H,,O,. The ‘HNMR speo trum (Table 1) showed no signals assignable to the 8(17) vinylidene, whereas it displayed seven singlets of methyl groups, one of a methyl ester (6 3.62), two of acetates (6 2.01 and 2.08), another one characteristic of the C-18 methyl group (6 1.17) and the last two assignable to two methyl groups attached to an oxygenated carbon (6 1.21 and 1.25). The IR spectrum did not show free hydroxyl bands; however, the 13CNMR spectrum showed two signals for non-protonated oxygenated carbons (6 75.0 and 73.4), all this suggesting a manoyl oxide acid-related structure. The absence of vinyl group signals, characteristic of the last structure, and the presence of two acetates prompted us to locate these acetate groups at C-14 and C15, which was confirmed by the 13CNMR spectrum. The stereochemistry at C-14 was established by comparison with the data reported in the literature for compounds having the same structure at the C-13 side chain [lo]. Thus, we propose structure 2a for this compound. Compound 3a presented [a&, = + 8.2”. As the ‘f-I NMR signals assignable to the C-9 chain displayed a double intensity singlet at S2.10, and the Ir3C NMR spectrum showed only 21 peaks, this suggested a dinorlabdane structure for this compound. The spectroscopic data were similar to those shown by methyl 13-0x0-14,15dinorlabd-8(17)-en-19-oate isoIated from berries of this plant [ 111, the only difference being the presence of the C3 acetoxyl group. All this confirms the proposed structure 3a for this compound. Compound 4s~showed [a],,= + 7.5”, and a UV maximum at 220 nm, characteristic of a conjugated carbony group; this was confirmed by the presence in the IR spectrum of a band at 1645 cm- ‘. The EIMS showed CMI’ at m/z 448, in agreement with the molecular
1719
A. SAN FELICIANO et al.
1720
Table H
la
3 14a 14b 15a 15b 16a 16b 17a 17b 18 20 COOCEJ, 3-OCOCIS, 14-OCOW, 1%OCOCEI,
5.32
1. ‘HNMR
2a
t (2.6)
data for compounds
la-7a (J in Hz)
3a
4a
5.32 br t
5.32 br t
4.10 dd (12.0, 8.9) 4.08 br t (6.7) 0.91 d (5.9) 4.50 4.85 1.16 0.52 3.64 2.09 2.03
br s
4.51 dd (2.2, 12.0) 4.95 dd (2.2, 8.9) 1.21 s 1.25 s
br s
s s s s s
1.17 s 0.58 s 3.62 s
4.46 4.87 1.16 0.53 3.64 2.10
5.38 5.31 4.62 4.89 1.16 0.50 3.63 2.10
br s br s
s s s s
2.01 s 2.08 s
4.18 dd (12.0, 9.0)
5.34 5.37
5.32 dd (9.0, 12.0) 1.31 s
br s br s br s
1.12 s
br s s s s s
1.17 s 0.60 s 3.63 s 2.03 s 2.07 s
2.18 s
formula C25H3607. The ‘H NMR spectrum displayed as main signals: an acetate group (6 2.18) and a vinylidenic double bond (two broad singlets at 6 5.31 and 5.38). This was confirmed by the data afforded by the 13CNMR spectrum (6 124.0 and 147.3) which also contained a signal at 6 193.6 for a conjugated carbonyl, whose location at C-14 could justify the deshielding of the already mentioned olefinic protons which would be at C-16. This allowed us to assign a 2H singlet at 6 5.82 to the 15methylene bearing an acetate group. All the foregoing led us to propose structure 4a for this compound.
6a+7a
4.60 dd (1.9, 2.0)
5.82 s
2.10 s
5a
t (3.2) t (3.2)
4.08 m
4.25 m 4.98 5.08 4.52 4.88 1.17 0.53 3.64 2.11 2.05 2.09
br s br s br s br s
s s s s s s
Compound Sa showed [aIn = + 26.7”. The IR,‘H NMR and i3C NMR data were similar to those of 2a, the NMR data differing only in the chemical shifts of the iH NMR signals corresponding to the methyl groups attached to the oxygenated carbons (61.31 and 1.12 instead of 1.21 and 1.12) and the “C NMR signal of C-14 (674.6 instead of 78.3). All this showed that compound 5a was the C-14 epimer of the already mentioned compound, thus having the S configuration, which was also confirmed by comparison of these two compounds with data in the literature [lo].
R 12 13 G” 14
16
la 15 OAc
“c
-4
0
4a OAC
6a+7a OAC
2a 5a
R’= OAc, R2= H R’= H, R2= OAc
1722
A. SAN FELICIANO et al.
‘H NMR: h, cm-I: 3645,3460,1690,1370,1165,995,960,850; see Table 1; 13C NMR: see Table 2. Methyl (14R) and (14s) 31,14,15-triacetoxy-lahd-8(17),13(16)dien-19-oate (6a and 7n). Oil eluted with hexane-EtOAc (2:3); IR v,,, cm -‘:2850,1725,1640,1440,1360,1230,1160,1040,970, 890; ‘H NMR: see Table 1; 13C NMR: see Table 2. Acknowledgement-Financial support DGICYT, grant PB 89-0394.
for this work came from
REFERENCES 1. San Feliciano, A., Miguel de1 Corral, J. M., L6pez, J. L. and Pascual-Teresa, B. de (1992) Phytochemisrry 31, 267. 2. San Feliciano, A., Miguel de1 Corral, J. M., Lbpez, J. L. and Pascual-Teresa, B. de (1992) Phytochemistry 31, 1713. 3. Anderson, R., Gref, R. and Lundgre, N. (1990) Phytochemistry 29, 1320. 4. San Feliciano, A., Medarde, M., Lopez, J. L., Puebla, P., Miguel de1 Corral, J. M. and Barrero, A. F. (1988) Phytochemistry 27, 2241.
5. Wherly, F. W. and Nishida, T. (1979) Fortschr. Chem. Org. Naturstoffe 276, 55. 6. Aranda, J. and Bernassau, J. M. (1977) J. Org. Chem. 42, 4256. 7. Pascual Teresa, J. de, Barrero. A. F., Muriel, L., San Feliciano, A. and Grande, M. (1980)Phytochemistry 19, 899. 8. Pascual Teresa, J. de, Bellido, I. S., Basabe, P., Marcos, I. S., Ruano, L. F. and Urones. J. G. (1982) Phytochemistry 21, 1153. 9. Carman, R. M. (1966) Aust. J. Chem. 19, 629. 10. Garcia-Alvarez, M. C.. Rodriguez, B., Garcia-Granados, A. and S. de Buruaga, A. (1982) J. Org. Chem. 47, 3571. 11. Pascual Teresa, J. de, San Feliciano, A. and Egido, T. (1976) An. Quim. 72, 865. 12. San Feliciano, A., Caballero, E., Del Rey, B. and Sancho. I. (1991) Phytochemistry 30, 3134. 13. Urones, J. G., Marcos, I. S., Basabe. P., Sexmero, M. J., Diez, D. J., Garrido, N. M. and Prieto, J. E. S. (1990) Tetrahedron 46, 2495. 14. Urones, J. G.. Marcos, I. S., Sexmero, M. J., Basabe, P. and Lithgow, M. A. (1990) Phytochemistry 29, 1247.