Method of preparing delta-9-tetrahydrocannabinol

Details Method of preparing delta-9-tetrahydrocannabinol Method of preparing delta-9-tetrahydrocannabinol

1998-10-26

2002-04-02

Ludlow, Jan (Department: 1743)

Chemistry: analytical and immunological testing

Including sample preparation

Liberation or purification of sample or separation of...

C436S093000, C436S161000, C436S177000, C436S178000, C436S901000, C514S454000, C549S388000

Reexamination Certificate

active

06365416

ABSTRACT:

BACKGROUND OF THE INVENTION
Delta-9-tetrahydrocannabinol (THC, also known as dronabinol) is the main biologically active component in the Cannabis plant which has been approved by the Food and Drug Administration (FDA) for the control of nausea and vomiting associated with chemotherapy and, more recently, for appetite stimulation of AIDS patients suffering from the wasting syndrome. The drug, however, shows other biological activities which lend themselves to possible therapeutic applications, such as in the treatment of glaucoma (1), migraine headaches (2,3), spasticity (4), anxiety (5), and as an analgesic (4). It is because of these-promising biological activities of THC that marijuana has been brought into a public debate relative its medicinal value. The balance between medicinal use of a drug and the abuse potential is a delicate balance. One of the main points brought by the medicinal marijuana proponents is the fact that the currently available soft gelatin capsule formulation is very expensive and lacks consistency in its effects. The latter point could be explained based on the fact that oral THC has erratic absorption from the gastrointestinal tract, is subject to the first-pass effect resulting in heavy metabolism with production of high levels of 11-OH-THC, and undesirable side effects. Another THC formulation which is currently under development is a pro-drug consisting of THC hemisuccinate formulated in a suppository base (6). This formulation appears to overcome the problems associated with the oral preparation and has been shown to produce consistent bioavailability in animal studies (7). Preliminary clinical investigations show promise for this formulation (8, 9, 10). It is anticipated that other THC formulations will be forthcoming in light of the current interest in the therapeutic activities of cannabis.
Regardless of which formulation is to be used for THC or a pro-drug thereof, a source for the raw material is critical. The currently-approved capsule formulation is prepared from synthetic THC which is extremely expensive to produce. It is thought that should an economic process be developed for isolation of THC from the natural material (cannabis), then the cost of the raw material could be brought down significantly, making it possible to develop such formulations at a reasonable cost to the public. The consequence of this would be the availability of alternative therapies involving THC (or a prodrug thereof) which would help in suppressing the public outcry for approval of marijuana as a medicine.
Several investigations have been carried out over the years to isolate THC from the plant material, mostly to determine its chemical structure or to investigate the phytochemistry of the plant. In 1942, Wollner, et al., (11) reported the isolation of tetrahydrocannabinol from cannabis extract “red oil”. Red oil was prepared by extraction of the plant material with ether, followed by distillation of the concentrated extract at room pressure followed by redistillation under reduced pressure (15-50 mm Hg). The oil was acetylated with acetic anhydride, and the acetylated product was subjected to fractional distillation in vacuo. Six fractions were collected. The head and tail fractions were removed. The remaining four fractions which represented the principal fractions (fractions 2, 3, 4, and 5) were combined and passed over silica gel column in benzene and then passed over activated alumina in carbon tetrachloride solution. The product was hydrolyzed by acid, alkali, or ammonia in alcoholic solution. The authors reported that the deacetylated product has, in each case, a different physiological potency than the acetate. All fractions were not pure compounds.
DeRopp, in 1960 (12), described the isolation of THC from the flowering tops of
Cannabis sativa.
His method involved adsorption chromatography of the methanolic extract of cannabis followed by partition chromatography on Celite using N,N-dimethyl formamide/cychlohexane mixture and high vacuum distillation. The purity of THC was based on paper chromatographic evidence.
The first isolation of the naturally occurring THC in its pure form was reported by Gaoni and Mechoulam in 1964 (13). THC was isolated from the hexane extract of hashish by repeated column chromatography on florisil and alumina. Further purification was carried out by the preparation of the crystalline 3,5-dinitrophenylurethane of THC followed by mild basic hydrolysis to get the pure THC. The purity of THC was proven by thin layer chromatography (TLC) and spectroscopic analysis (IR and NMR).
Korte, et al., in 1965 (14) reported the isolation of THC from the crude extracts of the female inflorescence of
Cannabis sativa
indica and
Cannabis sativa
non indica. The crude extracts were chromatographed over activated alumina in order to remove the coloring impurities like carotinoids, chlorophylls, and xanthophylls. All the cannabinolic fractions were combined and concentrated to give a brownish-red oil. The oil was further purified by a countercurrent distribution method to get THC which was proved to be identical with that described by Gaoni and Mechoulam (13).
In 1967, Mechoulam and Gaoni (15) reported the isolation of THC from the acidic fraction of the hexane extract of hashish. The hexane extract of hashish was separated into acidic and neutral fractions. The acidic fraction was chromatographed on florisil or acid washed alumina. The column was eluted with pentane-ether mixtures in a manner of increasing polarities. THC was eluted with 15% ether in pentane. Repeated chromatography was carried out by the preparation of crystalline derivative (3,5-dinitrophenylurethane THC, m.p., 115-116° C.) followed by hydrolysis.
In 1972, Verwey and Witte (16) reported a method for the preparation of THC by isolation of THC acid from hashish. The hexane extract was shaken with 2% NaOH solution as well as 2% sodium sulphite in an extraction funnel. The alkaline layer was rendered acidic with H
2
SO
4
(pH<2), thus precipitating the cannabinoid acids. The oily layer as well as the oily deposits on the wall were extracted with ether. The acid-base extraction process was repeated. THC was obtained from the impure acids by heating the ether solution containing the acids on a sand bath with a temperature of 300° C. The ether being evaporated, the evaporating dish was for a moment kept on the sand bath, in this way causing decarboxylation of THC acid. The THC was cleaned by preparative TLC.
In summary, for isolation of THC and other cannabinoid constituents, generally the alcoholic or the petroleum ether or benzene or hexane extract of the plant is separated into neutral and acidic fractions. These fractions are further purified by repeated column chromatography and countercurrent distribution or a combination of these methods. Various adsorbents have been used in column chromatography, especially silica gel, silicic acid, silicic acid-silver nitrate, florisil, acid washed alumina, and acid washed alumina-silver nitrate. Most of the above-discussed methods were used for the preparation of a small amount of THC and not for large-scale production.
If THC is to be prepared in large-scale (kilogram) quantities, an efficient and economic method is needed. Such a method would require an efficient isolation procedure.
SUMMARY OF THE INVENTION
The present invention is for the preparation of THC from Cannabis plant material. Simple, high yielding steps are developed which reduce the cost of preparation of THC several fold over the synthetic route
The present invention comprises a process wherein Cannabis plant material is extracted with a non-polar organic solvent to provide an extract containing THC and the extract is subjected to fractional distillation under reduced pressure to provide a distillation fraction (distillate) having a high content of THC. The instant process further comprises subjecting the extract from the plant material to column chromatography prior to fractional distillation. A still further aspect of the instant process comprises subjecting the di

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