Ever since the isolation of sennosides A and B from senna, the presence of several other constituents has been demonstrated. The purgative action of the leaf drug is attributed to the synergistic effect of several active principals chief among which are sennosides. The total leaf sennosides constituting largely of sennosides A and B are isolated from senna leaves and or pods and then converted to calcium salts.

Isolation of sennosides involves producing purer fractions of anthraquinone glycosides, both free and in the form of glycosides. These are present both free and as magnesium, potassium and sodium salts combined either through a hydroxyl or a carboxylic acid group. The differential solubility of the glycosides, their aglycones and other anthracene derivatives of senna in chloroform is used for their isolation. While the glycosides are chloroform insoluble, the aglycones and others are soluble in it.

A. Method I

1. 300 g of powdered senna are macerated with 850 ml of 5% acetic acid for 24 h in a 2 l stoppered conical flask. Acidification liberates the free aglycones from their glycosides and from their potassium, magnesium and calcium salts.
2. The maceration mixture is then air-dried and extracted exhaustively with chloroform (10 × 600 ml) to remove free anthraquinones as well as many impurities. The absence of a red colour imparted to a small portion of the chloroform filtrate on the addition of a few drops of 5% alcoholic potassium hydroxide indicates complete extraction of hydroxyanthraquinones.
3. The chloroform extracts are combined, evaporated to dryness and weight recorded.
4. The chloroform exhausted marc is air-dried and extracted exhaustively with 600-ml portions (10 times) of warm ethanol until successive extracts show no red or pink colouration with a few drops of 5% alcoholic potassium hydroxide solution.
5. The combined filtrates are evaporated at 40°C in a rotary vacuum evaporator to about one-third the original volume. To this solution, 5% alcoholic potassium hydroxide is added until no further precipitation occurs.
6. The solution is then filtered and the residue washed with cold ethanol to remove last traces of potassium hydroxide and then dried by suction on a Buchner funnel.
7. The residue consisting of the potassium salts of the glycosides is suspended in warm ethanol and the glycosides liberated by slow addition of glacial acetic acid with stirring.
8. The solution is filtered hot and the residue further extracted with warm ethanol. The combined filtrates are evaporated to dryness in vacuo at 40°C, the residue recrystallized from isopropyl alcohol and weight noted.

Preparation of calcium sennosides

The residues from the chloroform and the ethanol extracts are pooled together and slurried in 150 ml water. A mixture of 2 g of calcium hydroxide in 5 ml water is added to the slurry to solubilize the glycosides. The pH of the solution is brought to 6.7 using dilute HCl. Add 75 ml of 90% methanol and 200 ml of 100% methanol solution and stir the solution. Filter to separate the formed precipitate of calcium sennosides. Carefully separate the residue on the filter after washing it with a little methanol and dry it in vacuo.

B. Method II

1. 25 g of powdered senna leaflets are extracted with 75 ml benzene for 15 min on and electric shaker, filtered in vacuum and solvent distilled off.
2. The leftover marc is dried at room temperature and extracted with 75 ml of 70% methanol for 30 min on an electric shaker and filtered under vacuum.
3. The marc is reextracted with 50 ml of 70% methanol for 15 min, filtered and the methanolic extracts combined.
4. The methanolic extract is then concentrated to one-eighth volume, acidified to pH 3.2 by adding HCl with constant stirring.
5. It is set aside for 15 min at 5°C, filtered under vacuum and 1g of anhydrous calcium chloride in 12.5 ml of denatured spirit is added with constant stirring.
6. The pH of the solution is adjusted to 8 by addition of ammonia and set aside for 15 min. The precipitate obtained is dried.

Identification