From the bark of Cassia reingera 1,5,6-trihydroxy-3-methyl- anthraquinone-8-O-α-L-glucoside has been isolated and its structure elucidated with the help of ...
Indian Journal of Chemistry Vol. 44B, September 2005, pp. 1970-1971
Note
Anthraquinone glycoside from stem bark, fatty acids and sterols from seeds of Cassia reingera Lalita Ledwani & Mukhtar Singh*† Department of Chemistry, Agra College, Agra, India Received 5 April 2004; accepted (revised) 17 May 2005 From the bark of Cassia reingera 1,5,6-trihydroxy-3-methylanthraquinone-8-O-α-L-glucoside has been isolated and its structure elucidated with the help of chemical studies and spectral data. The dyeing property of crude anthraquinone has been studied to develop variety of shades on wool by using different mordants. Sterols and fatty acids have been isolated from the seeds of Cassia reingera and are identified by using GLC techniques by comparison with authentic sample. Keywords: Anthraquinone glycoside, Stem-bark, fatty acids, sterols, Cassia reingera IPC: Int.Cl.7 A 61 K 35/00
Most of the plants of the genus Cassia1,2 are wellknown in Indian system of medicine for their cathartic, purgative and antibiotic properties. Many compounds of structural significance and medicinal importance have been reported from different species of this genus. Cassia reingera (Caesalpinoidae) is known as rich source of anthraquinones3 and flavonoids. But no systematic work has been reported on anthraquinones obtained from this plant. Anthraquinones are main source of natural dye, which are gaining importance in recent years due to environmental pollution caused by synthetic dyes. Natural dyes are useful for human health because they have antibacterial, insecticidal and healthy properties. No systematic work has been reported so far on fixed oils from the seeds. Phytochemical screening of seed oil is a subject of intensive research to explore new alternative source for conventional oils. It was therefore considered of interest to isolate sterols and fatty acids from seeds of this plant. Stem-bark The stem-bark of Cassia reingera was collected from natural sources and identified by taxonomist. ⎯⎯⎯⎯⎯⎯ † Address of Correspondence: HIG 142, Phase-A, Shastri Puram, Sikandra, Agra 282 007
The bark was dried under shade and pulverized in wiley mill to powder form. The air-dried and crushed stem-bark (3 kg) of Cassia reingera was repeatedly extracted with boiling ethanol in soxhlet extractor and concentrated under reduced pressure in a rotatory evaporator till the weight of concentrated extract became 5 g. It was then pored into an excess of icecold water to give water soluble and water insoluble portions. The water soluble portion was extracted successively with different solvents. The ethyl acetate extract on concentration gave reddish brown pigment. Thin layer chromatography by silica gel plate using solvent system, chloroform-ethyl acetate-methanol (4:4:12, v/v) gave compound 1 (2 g). This compound was found to be glycoside by positive Molisch's test and did not reduce Fehling solution. Compound 1. Crystallised from EtOAc-petrol (3:1), M+ 448, m.p. 190°C (Found: C, 56.25; H, 4.40. Calcd for C21H20O11: C, 56.25; H, 4.46%); UV; 235, 255, 300 and 470 nm; IR: 3420, 3300, 2920, 1640, 1550, 1475, 1450, 1375, 1360, 1300, 1230, 1220, 1100, 1030, 990, 890, 870, 835 and 770 cm-1; 1 H NMR (250 MHz, CDCl3): δ 3.85 (6H, sugar protons), 5.02 (H-1' glucosyl), 2.26 (3H, s, Me), 7.00 (s, 1H, C7-H), 7.25 (br, 1H, C2-H), 7.75 (br, 1H, C4H). This compound was characterized as 1,5,6trihydroxy-3-methyl-8-O-glucoside. Acid hydrolysis of compound 1 Compound 1 was refluxed in MeOH with 7% H2SO4 at 65°C for 6 hr on a water-bath to obtain aglycon. The aglycon thus obtained was crystallised from C6H6EtOAc (4:1), m.p. 220° (Found: C, 62.80; H, 3.54. Calcd for C15H10O6: C, 62.90, H, 3.49%). It responded to positive colour test for an anthraxquinone4-6 (appearance of red colour with methanolic sodium hydroxide as well as with methanolic magnesium acetate). UV: 235, 255, 310, 475 nm; IR: 3450, 3272, 2920, 1610, 1545, 1475, 1450, 1375, 1360, 1230, 1100, 1030 cm–1; 1H NMR (250 MHz, CDCl3): 2.26 (3H, s, Me), 7.00 (s, 1H, C7-H), 7.20 (br, 1H, C1-H), 7.80 (br,1H,C4-H), Mass: m/z: 286 (M)+, 268, 258, 240, 230, 183, 110, 108. Ethanol and water extract of this pigment was taken to obtain variety of shades7,8 on wool. These extracts were used to dye the wool samples on dye bath at 70-80°C for 1 hr. Many
NOTES
mordants such as alum, pot. dichromate, tartaric acid, were used for dyeing to obtain number of colourful shades on wool. This aglycone 1a was characterized as 1,5,6,8-tetrahydroxy-3-methyl-anthraquinone. OH
O
OH
O
HO
OH
CH3
1a
Seeds Seeds of Cassia reingera were purchased from local market. Cleaned and dried seeds (500 g) were crushed and extracted exhaustively with light petroleum ether (60-80°C) until a colourless extract was obtained. Evaporation of solvent yielded a yellowish oil which was saponified with 10% methanolic KOH for 2 hr in the atmosphere of nitrogen. The solvent was removed under reduced pressure and the residue was diluted with water. The unsaponifiable material was extracted with ether and dried over anhyd. Na2SO4. The ether layer was dried and evaporated to afford residue of unsaponifiable matter (8.28 g). The unsaponifiable matter was column chromatographed over silica gel (40 g) and eluted with increasing concentration of pet. ether (5, 10, 15, 20%) to afford a solid foam, the last elute which was crystallized from methanol-ether. This gave the positive Libermann-Buchard colour test for sterols. This sterol mixture was dissolved in 2 mL of acetic anhydride-pyridine mixture (2:1) and kept for two nights. The solvent was evaporated in vacuo and the residue was crystallized from methanol. The crystalline sterol acetate was obtained. The gas liquid chromatography of the residue showed three peaks indicating the presence of 3 sterols. These sterols were identified as cholesterol, stigmosterol and β-sistosterol by comparison with authentic samples9-11 (Table I). The mixed fatty acids were obtained by acidification of aqueous layer left after extraction of unsaponifiable matter with diethyl ether. The aqueous layer was acidified with dil. HCl to pH 2-3. This was then extracted with diethyl ether. The ethereal layer was washed with water and dried over sodium sulphate. The dried extract was concentrated in presence of nitrogen to afford an oily viscous mass. This was esterified with methanol in the presence of conc. H2SO4 for 2-3 hr. The esters so formed were
1971
Table I ⎯ Characteristics, sterol and fatty acid composition of the oil Yield of oil (%) 5 0.916 Specific gravity (at 30°) Refractive Index (at 40°) Moisture content (%) Acid value Saponification value Unsaponifiable matter (%)
1.468 3.9 1.8 192 4.12
Sterols (%) Cholesterol Stigmosterol -Sistosterol
6.716 18.60 67.50
Fatty acids (%) Palmitic acid Stearic acid Oleic acid Linoleic acid
0.734 3.837 34.913 59.071
extracted with ether. Ethereal layer was washed with water and dried over anhydrous sodium sulphate. The solvent was concentrated under the steam of nitrogen. Mixed fatty acids were converted to methyl ester. GLC of methyl ester showed four peaks, confirming the presence of four fatty acids12,13 (Table I). GLC of the sample were carried out on model, 4890 II series on GLC gas chromatogram equipped with flame ionization detector using stainless steel column (3mm × 2m) packed with 20% DEGS on chromosorb and using nitrogen as carrier gas. The injection port column and flame ionization detector block were maintained at 210°C, 170°C and 220°C respectively. The samples were identified by co-GLC with authentic samples. References 1 Tiwari R D & Singh J, Phytochemistry, 10, 1979, 906. 2 Honghu G, Zhenzhan C, Rujun D G & Junhua Z, Phytochemistry, 49, 1998, 1923. 3 Susumu K & Michio T, Phytochemistry, 39, 1995, 717. 4 Thomson R H, Naturally occurring quinones, Vol.73, 2nd edn, (Butterworths Publication, London), 1971. 5 Robinson T, The organic constituents of higher plants, Vol. 107, (Bargles Publishing Co, USA),1963. 6 Feigl S & Jungries E, Michrochem J, 2, 1959, 216. 7 Gulrajni M L, Gupta D B & Agarwal V, The Indian Textile Journal, 102(4), 1992, 50. 8 Brain G, J Soc Dyers Col, 4, 1998, 114. 9 Klyne W, The Chemistry of Steroids, (Methuen, London), 1957. 10 Singh H & Sinha R P, Oil seeds and their utilization,(Rohini Publishing, House, Dehradun), 1984. 11 Shoppee C, Chemistry of Steroids, (Academic Press, New York), 1958. 12 Chalvardgian J, Biochem J, 90, 1964, 510. 13 Christic W W, Lipid Analysis, 2nd edn, (Pergamon, New York), 1982.
