Extract from Ginkgo biloba leaves, its method of preparation and pharmaceuticals containing the extract

A method of preparing an extract from the leaves of Ginkgo biloba which is substantially free of alkylphenol compounds and having a high content of flavone glycosides and comprising substantially all of the ginkgolides and bilobalide originally present in the leaves, the method comprising the steps of

• a) extracting the leaves with an organic solvent selected from the group consisting of aqueous acetone, an aqueous alkanol having one to three carbon atoms and anhydrous methanol;
• b) separating most of the organic solvent from the extract of step (a) to form an aqueous solution;
• c) diluting the aqueous solution with water to a solids content of 5 to 25 weight percent;
• d) cooling the diluted aqueous solution to precipitate and separate lipophilic components from the diluted aqueous solution;
• e) treating the aqueous solution from step (d) with ammonium sulfate and and then extracting the aqueous solution with methylethylketone, acetone, or a mixture of methylethylketone and acetone;
• f) diluting the extract from step (e) with water and alcohol to form an aqueous alcohol solution;
• g) treating the aqueous alcohol solution with a lead compound or an insoluble polyamide;
• h) extracting the treated aqueous alcohol solution with an aliphatic or cycloaliphatic solvent having a boiling point of about 60.degree.-100.degree. C. to further remove the alkylphenol compounds;
• and
• i) recovering a dry extract.

A method of preparing an extract from Ginkgo biloba leaves, containing 20 to 30 weight percent flavone glycosides, 2.5 to 4.5 weight percent of ginkgolides selected from ginkgolide A, B, C and J or mixtures thereof, 2.0 to 4.0 weight percent bilobalide, less than 10 ppm alkylphenol compounds and less than 10 weight percent proanthocyanidins comprising the steps of:

• (a) extracting fresh or dried green leaves of Ginkgo biloba at a temperature of approximately 40.degree. to 100.degree. C. with an organic solvent selected from the group consisting of aqueous acetone, an aqueous alkanol of 1 to 3 C-atoms and anhydrous methanol,
• (b) distilling the extract from step (a) to remove the organic solvent to a maximum content of 10 weight percent to form a concentrated aqueous solution,
• (c) diluting the concentrated aqueous solution with water to a solids content of 5 to 25 weight percent and then cooling the diluted aqueous solution to a temperature below 25.degree. C. to precipitate and separate the lipophilic components from the diluted aqueous solution,
• (d) adding ammonium sulfate to the aqueous solution from step (c) to a concentration of 30 weight percent and extracting said solution with methylethylketone or a mixture containing methylethylketone and acetone in a ratio from about 9:1 to 4:6,
• (e) concentrating the extract from step (d) to a solids content of 50 to 70% and then diluting with water and ethanol to form an aqueous alcohol solution containing about 50 weight percent of water and about 50 weight percent of ethanol with a solids content of about 10 weight percent,
• (f) adding an aqueous solution of a lead salt or an aqueous suspension of lead hydroxide to the aqueous alcohol solution of step (e) until a change in color from brown to umber takes place and precipitate is formed and separated,
• (g) extracting the aqueous alcohol solution from step (f) with an aliphatic or cycloaliphatic solvent having a boiling point of about 60.degree. to 100.degree. C. to further remove alkylphenol compounds,
• (h) concentrating the aqueous alcohol solution from step (g) under reduced pressure to a maximum ethanol content of about 5% and then adding ammonium sulfate up to about 20 weight percent,
• (i) extracting the aqueous alcohol solution from step (h) with a mixture of methylethylketone and ethanol in a ratio from about 8:2 to 5:5 to form an organic phase extract,
• (j) concentrating the organic phase extract to a solids content of 50 to 70 weight percent, and
• (k) drying the resultant concentrate from step (j) under reduced pressure at a maximum temperature of 60.degree. to 80.degree. C. to form a dry extract with a water content of less than 5%.