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6-Hydroxyplumbagin, a naphthoquinone from Plumbago indica
Phytochemistry, Vol.31,No. 10,pp. 3652-3653,1992 Printedin Great Britam.
0031.-9422/92 $5.00+0.00 t>: 1992 Pergamon Press Ltd
6_HYDROXYPLUMBAGIN, A NAPHTHOQUINONE PLUMBAGO INDICA
FROM
B. DINDA* and G. CHEL Department of Chemistry, Tripura University, Agartala 799004, India (Received in reoisedform 7 February 1992) Key Word Index-Plumbago
indica;
Plumbaginaceae; naphthoquinone; 6-hydroxyplumbagin.
Abstract-From the aerial parts of Plumbago indica, a new naphthoquinone, as well as plumbagin, sitosterol, stigmasterol and campesterol were isolated. The structure of the new compound is 5,6-dihydroxy-2-methyl-1,4naphthoquinone or 6-hydroxyplumbagin
INTRODUCTION Plumbago indica L. (syn. P. rosea L.) [l] is a branched herb, which is grown in India and other tropical countries as an ornamental plant. In West Bengal and Tripura, it is known locally as ‘lalchita’ [ 11. Harborne reported [2] the presence of plumbagin in root, leucodelphinidin in leaf and delphinidin, cyanidin and pelargonidin 3-rhamnosides, kaempferol-3-rhamnoside, galloylglucose and digalloylglucose in petal. We have reinvestigated the aerial parts of the plant and now report the isolation of 1, plumbagin (3), sitosterol, stigmasterol and campesterol and the structure elucidation of 1.
RESULTSAND DISCUSSION Compound 1, C, 1HB04 ([Ml’ 204), was isolated as a minor component from the petrol extract of P. indica. It showed UV/VIS absorption, 1::$215,274,488, Slosh and 545 sh nm (log ~3.60,3.32,2.89,2.87 and 2.66) and IR bands at 1660 and 1615 cm-’ strikingly similar to those of naphthazarins [3,4]. It showed a bathochromic shift in band I of about 30 nm with AlCl,, a~~H+A1C’3224, 314, 536 and 575 nm, suggesting the presence of peri hydroxyl group in the molecule. The compound showed also a bathochromic shift in band I of about 50 nm in alkaline methanolic solution (blue solution), J&FH+Ho- 215,276, 555 and 595 nm. The methanolic solution of the compound produced a violet coloured chelate as a precipitate with H,BO, and anhydrous NaOAc. The ‘HNMR spectrum exhibited signals at 62.22 (d, J= 1.5 Hz) for one vinylic methyl group, 66.88 (q, J= 1.5 Hz) for one vinylic proton, 6 7.20 (d, J = 8.5 Hz, H-7) for one aromatic proton, 6 7.30 (d, J = 8.5 Hz, H-8) for one aromatic proton, S 12.44 and 12.56 (two lH, s, HO-6 and HO-5, respectively, exchangeable with DzO) for two phenolic hydroxyl groups suggesting the structure 1 for the compound. An alternative structure, 7,8-dihydroxy-2-methyl-1,4naphthoquinone of it was discarded on biogenetic ground since only 5-hydroxy-2-methyl-1,4-naphthoquinones have been reported so far from the genus Plumbago.
*Author to whom correspondence should be addressed.
0
&
R’ 1H 2 Me 3H 4 Me
R2 OH OMe H H
The EI mass spectrum also corroborated [S] structure 1 by revealing significant mass peaks, besides the molecular peak, at m/z 189 [M-Me]‘, 176 [M-CO]+, 165 [CsH404]‘, 161 [176-Me], 148 [176-CO], 147 [148 -H], 137 [C7H50J]+, 136 [161-C&H], 131,130,109 [137-CO] and 108 [136-CO]. The structure was confirmed by converting it to the dimethyl ether (2) C13H1204 ([Ml’ 232), with MeI in CHCl, in the presence of Ag,O [6]. The ‘HNMR spectrum of this derivative was similar to that of the parent compound except that two hydroxyl signals were replaced by two methoxyls at 63.88 (3H, s,) and 4.06 (3H, s). Therefore, the new compound is 5,6-dihydroxy-2-methyl-1,4-naphthoquinone or 6-hydroxyplumbagin (1). The petrol extract of the aerial parts of the plant afforded plumbagin (3), as a major constituent, identified on the basis of UV/VIS, IR, ‘HNMR and EI mass spectral data of the compound and its methyl ether and by comparison with literature data [7, 81. From the petrol extract, a crystalline solid, mp 138-140” was also isolated. It was identified as a mixture of sitosterol, stigmasterol and campesterol by comparison of the GC of its acetate with the reported [9] relative retention times of the acetates of standard samples, sitosterol was the major constituent in the mixture. EXPERIMENTAL General. UV/VIS and IR spectra were recorded in MeOH and KBr respectively, unless otherwise stated. ‘H spectra were
Short Reports measured in CDCl, at 100 with TMS as reference. CC and TLC were carried out with silica gel (Qualigen, 60-120 mesh) and silica gel G (Merck), respectively. Plant material was collected from Hooghly and Jampai areas in December 1988 (Herbarium Sample No. 998 in Shibpur Botanical Garden, Howrah). Extraction of P. Mica aerial part. The dried and powered aerial part (1 kg) of P. indica was extracted with hot petrol (bp &SO”) and after removal of solvent under red. pres. a semi-solid dark brown residue (7.41 g) was obtained. Isolation of compound 1. The residue was subjected to CC using petrol containing increasing proportions of EtOAc as eluents. The fraction eluted with petrol-EtOAc (9: 1) yielded a solid, which on repeated CC afforded 1 (20 mg, 2 x lo-“%) as dark red needles, mp 134-135”; (Found: C, 64.62; H, 3.91. C, iHs04 requires C, 64.71; H, 3.95%). Dimethyl ether (Z), dark brown needles mp 158”; (Found: C, 67.17; H, 5.16. Ci3Hiz0, requires C, 67.23; H, 5.21%). IR v,,,cm-r: 1660 and 1608; ‘HNMR: 62.02 (3H, d, J= 1.5 Hz, Me-2), 3.88 (3H, s, MeG-6), 4.06 (3H, s, MeO-5), 6.62 (lH, q. .J= 1.5 Hz, H-3), 7.06 (lH, d, J=8 Hz, H-7) and 7.14 (lH, d, J=8 Hz, H-8). Isolation of plumbagin (3). The fraction eluted with petrol-EtOAc (10: 1) yielded a residue, which on crystallization from a petrol-EtOAc mixture gave plumbagin (1.5 g, 0.15%) as bright orange needles, mp 76” (lit. [lo] mp 78”). Methyl ether (4), yellow needles, mp 93” (lit. [l l] mp 94”). Acknowledgements-We
thank RSIC, CDRI, Lucknow for providing mass spectra; IICB, Calcutta for ‘HNMR spectra; and
3653
RSIC (Bose Institute, Calcutta) for GC analysis of the compounds. One of us (GC) thanks DST (Tripura) for the award of a Junior Research Fellowship.
REFERENCES 1. Deb, D. B. (1983) in Flora of Tripura State, Vol. 2, pp. 184-187. Today and Tomorrow, New Delhi. 2. Harborne, J. B. (1967) Phytochemistry 6, 1415. 3. Thomson, R. H. (1986) in Naturally Occurring Quinones, p. 215. Chapman & Hall, London. 4. Gunaherath, G. M. K. B., Gunatilaka, A. k L. and Thomson, R. H. (1988) J. Chem. Sot., Perkin Trans. 1,407. 5. Bowie, J. H., Cameron, D. W. and Williams, D. H. (1965) J. Am. Chem. Sot. 87,5094. 6. Garden, J. F. and Thomson, R. H. (1957) J. C/tern Sot. 2483. 7. Thomson, R. H. (1971) in Naturully Occurring Quinones 2nd Edn, p. 228. Academic Press, London. 8. Sidhu, G. S. and Sankaram, A. V. B. (1971) Tetrahedron Letters 26, 2385. 9. Itoh, T., Tani, H., Fukushima, K., Tamura, Matsumoto, T. (1982) J. Chromatog. 234, 65.
T. and
10. Sankaram, A. V. B., Rao, A. S. and Sidhu, G. S. (1976) Phytochemistry 15,237. 11. Sidhy G. S., Sankaram, A. V. B. and Ali, S. M. (1968) Indian J. Chem 6, 68 1.
0031.-9422/92 $5.00+0.00 t>: 1992 Pergamon Press Ltd
6_HYDROXYPLUMBAGIN, A NAPHTHOQUINONE PLUMBAGO INDICA
FROM
B. DINDA* and G. CHEL Department of Chemistry, Tripura University, Agartala 799004, India (Received in reoisedform 7 February 1992) Key Word Index-Plumbago
indica;
Plumbaginaceae; naphthoquinone; 6-hydroxyplumbagin.
Abstract-From the aerial parts of Plumbago indica, a new naphthoquinone, as well as plumbagin, sitosterol, stigmasterol and campesterol were isolated. The structure of the new compound is 5,6-dihydroxy-2-methyl-1,4naphthoquinone or 6-hydroxyplumbagin
INTRODUCTION Plumbago indica L. (syn. P. rosea L.) [l] is a branched herb, which is grown in India and other tropical countries as an ornamental plant. In West Bengal and Tripura, it is known locally as ‘lalchita’ [ 11. Harborne reported [2] the presence of plumbagin in root, leucodelphinidin in leaf and delphinidin, cyanidin and pelargonidin 3-rhamnosides, kaempferol-3-rhamnoside, galloylglucose and digalloylglucose in petal. We have reinvestigated the aerial parts of the plant and now report the isolation of 1, plumbagin (3), sitosterol, stigmasterol and campesterol and the structure elucidation of 1.
RESULTSAND DISCUSSION Compound 1, C, 1HB04 ([Ml’ 204), was isolated as a minor component from the petrol extract of P. indica. It showed UV/VIS absorption, 1::$215,274,488, Slosh and 545 sh nm (log ~3.60,3.32,2.89,2.87 and 2.66) and IR bands at 1660 and 1615 cm-’ strikingly similar to those of naphthazarins [3,4]. It showed a bathochromic shift in band I of about 30 nm with AlCl,, a~~H+A1C’3224, 314, 536 and 575 nm, suggesting the presence of peri hydroxyl group in the molecule. The compound showed also a bathochromic shift in band I of about 50 nm in alkaline methanolic solution (blue solution), J&FH+Ho- 215,276, 555 and 595 nm. The methanolic solution of the compound produced a violet coloured chelate as a precipitate with H,BO, and anhydrous NaOAc. The ‘HNMR spectrum exhibited signals at 62.22 (d, J= 1.5 Hz) for one vinylic methyl group, 66.88 (q, J= 1.5 Hz) for one vinylic proton, 6 7.20 (d, J = 8.5 Hz, H-7) for one aromatic proton, 6 7.30 (d, J = 8.5 Hz, H-8) for one aromatic proton, S 12.44 and 12.56 (two lH, s, HO-6 and HO-5, respectively, exchangeable with DzO) for two phenolic hydroxyl groups suggesting the structure 1 for the compound. An alternative structure, 7,8-dihydroxy-2-methyl-1,4naphthoquinone of it was discarded on biogenetic ground since only 5-hydroxy-2-methyl-1,4-naphthoquinones have been reported so far from the genus Plumbago.
*Author to whom correspondence should be addressed.
0
&
R’ 1H 2 Me 3H 4 Me
R2 OH OMe H H
The EI mass spectrum also corroborated [S] structure 1 by revealing significant mass peaks, besides the molecular peak, at m/z 189 [M-Me]‘, 176 [M-CO]+, 165 [CsH404]‘, 161 [176-Me], 148 [176-CO], 147 [148 -H], 137 [C7H50J]+, 136 [161-C&H], 131,130,109 [137-CO] and 108 [136-CO]. The structure was confirmed by converting it to the dimethyl ether (2) C13H1204 ([Ml’ 232), with MeI in CHCl, in the presence of Ag,O [6]. The ‘HNMR spectrum of this derivative was similar to that of the parent compound except that two hydroxyl signals were replaced by two methoxyls at 63.88 (3H, s,) and 4.06 (3H, s). Therefore, the new compound is 5,6-dihydroxy-2-methyl-1,4-naphthoquinone or 6-hydroxyplumbagin (1). The petrol extract of the aerial parts of the plant afforded plumbagin (3), as a major constituent, identified on the basis of UV/VIS, IR, ‘HNMR and EI mass spectral data of the compound and its methyl ether and by comparison with literature data [7, 81. From the petrol extract, a crystalline solid, mp 138-140” was also isolated. It was identified as a mixture of sitosterol, stigmasterol and campesterol by comparison of the GC of its acetate with the reported [9] relative retention times of the acetates of standard samples, sitosterol was the major constituent in the mixture. EXPERIMENTAL General. UV/VIS and IR spectra were recorded in MeOH and KBr respectively, unless otherwise stated. ‘H spectra were
Short Reports measured in CDCl, at 100 with TMS as reference. CC and TLC were carried out with silica gel (Qualigen, 60-120 mesh) and silica gel G (Merck), respectively. Plant material was collected from Hooghly and Jampai areas in December 1988 (Herbarium Sample No. 998 in Shibpur Botanical Garden, Howrah). Extraction of P. Mica aerial part. The dried and powered aerial part (1 kg) of P. indica was extracted with hot petrol (bp &SO”) and after removal of solvent under red. pres. a semi-solid dark brown residue (7.41 g) was obtained. Isolation of compound 1. The residue was subjected to CC using petrol containing increasing proportions of EtOAc as eluents. The fraction eluted with petrol-EtOAc (9: 1) yielded a solid, which on repeated CC afforded 1 (20 mg, 2 x lo-“%) as dark red needles, mp 134-135”; (Found: C, 64.62; H, 3.91. C, iHs04 requires C, 64.71; H, 3.95%). Dimethyl ether (Z), dark brown needles mp 158”; (Found: C, 67.17; H, 5.16. Ci3Hiz0, requires C, 67.23; H, 5.21%). IR v,,,cm-r: 1660 and 1608; ‘HNMR: 62.02 (3H, d, J= 1.5 Hz, Me-2), 3.88 (3H, s, MeG-6), 4.06 (3H, s, MeO-5), 6.62 (lH, q. .J= 1.5 Hz, H-3), 7.06 (lH, d, J=8 Hz, H-7) and 7.14 (lH, d, J=8 Hz, H-8). Isolation of plumbagin (3). The fraction eluted with petrol-EtOAc (10: 1) yielded a residue, which on crystallization from a petrol-EtOAc mixture gave plumbagin (1.5 g, 0.15%) as bright orange needles, mp 76” (lit. [lo] mp 78”). Methyl ether (4), yellow needles, mp 93” (lit. [l l] mp 94”). Acknowledgements-We
thank RSIC, CDRI, Lucknow for providing mass spectra; IICB, Calcutta for ‘HNMR spectra; and
3653
RSIC (Bose Institute, Calcutta) for GC analysis of the compounds. One of us (GC) thanks DST (Tripura) for the award of a Junior Research Fellowship.
REFERENCES 1. Deb, D. B. (1983) in Flora of Tripura State, Vol. 2, pp. 184-187. Today and Tomorrow, New Delhi. 2. Harborne, J. B. (1967) Phytochemistry 6, 1415. 3. Thomson, R. H. (1986) in Naturally Occurring Quinones, p. 215. Chapman & Hall, London. 4. Gunaherath, G. M. K. B., Gunatilaka, A. k L. and Thomson, R. H. (1988) J. Chem. Sot., Perkin Trans. 1,407. 5. Bowie, J. H., Cameron, D. W. and Williams, D. H. (1965) J. Am. Chem. Sot. 87,5094. 6. Garden, J. F. and Thomson, R. H. (1957) J. C/tern Sot. 2483. 7. Thomson, R. H. (1971) in Naturully Occurring Quinones 2nd Edn, p. 228. Academic Press, London. 8. Sidhu, G. S. and Sankaram, A. V. B. (1971) Tetrahedron Letters 26, 2385. 9. Itoh, T., Tani, H., Fukushima, K., Tamura, Matsumoto, T. (1982) J. Chromatog. 234, 65.
T. and
10. Sankaram, A. V. B., Rao, A. S. and Sidhu, G. S. (1976) Phytochemistry 15,237. 11. Sidhy G. S., Sankaram, A. V. B. and Ali, S. M. (1968) Indian J. Chem 6, 68 1.