[CONTRIBUTICIN FROM THE
MALLINCKRODT CHEMIC4L W O R K S ]
ISOLATION AND PURIFICATIOK OF KEOPINE A . H. HOMEYER A N D W. L. SHILLISG' Received November 14, 1946
The only record of the isolation of the rare opium alkaloid neopine is a sample from T. & H. Smith and Co., Edinburgh, used by Dobbie and Lauder (1) and Van Duin, Robinson, and Smith (2) in determining its structure, and one prepared by A. C. Boylston of this company used by D. E. Jackson (3) in studying its pharmacological action. The methods used for its separation and purification by earlier investigators have not been published. It seems appropriate therefore to describe the procedures we have employed to isolate neopine and to record our observations on its properties. Neopine was first observed during attempts to evaluate tarry mother liquors from the isolation of codeine from opium. Its hydrobromide was much more soluble than codeine hydrobromide and its sulfate failed to crystallize. After purification, its physical properties agreed closely with the reports of previous workers, and its reduction to dihydrocodeine was confirmed. Neopine sulfate was prepared and found to differ markedly from codeine sulfate. It did not crystallize from water and indeed seemed to be unstable in the presence of moisture. It was much more soluble in alcohol than was codeine sulfate, and this property makes possible the relatively easy separation of these alkaloids. Since neopine differs structurally from codeine only in the position of the double bond, it seemed possible to us that it might be formed by isomerization of codeine during crystallization operations. Accordingly a search for neopine was made in the mother liquors of codeine prepared from morphine. KO evidence for the presence of neopine was found and it was concluded that neopine occurs as such in opium. We wish to express our appreciation t o Dr. Lyndon Small for his interest and encouragement. EXPERIMENTAL
Isolation. The starting material for isolation of neopine was the last mother liquor from crystallization of crude natural codeine sulfate or hydrobromide from Turkish opium. -4 typical procedure was as follows: Twenty-seven liters of concentrated black tarry hydrobromide mother liquor from which no more crystals separated after three months storage was diluted with 76 1. of boiling water in which 500 g. of sodium chloride had been dissolved. The solution was filtered with the aid of diatomaceous earth, and the filtrate was extracted three times with 23-1. portions of chloroform to remove tars, which were discarded. The aqueous phase was stirred with 38 I . of benzene and made alkaline t o phenolphthalein by addition of 10 N sodium hydroxide solution. The benzene layer was separated and extraction was repeated three times more 1 Present address: Department of Chemistry, University of Kotre Dame, South Bend, Indiana. 356
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with 38-1. portions of benzene. The solvent was removed from the combined extracts by distillation; the residue, still containing some solvent, amounted t o 5.4 kg. of a thick brown syrup. This was dissolved in 14.1. of acetone and acidified t o Congo Red by adding 3.5 1. of 40% aqueous hydrobromic acid. The crude neopine hydrobromide separated in crystalline form. It waa centrifuged, washed with acetone and dried a t 100". The product was a light tan powder weighing 2.2 kg. I t s specific rotationin water was [a]:+14" (c, 3.738). Neopine hydrobromide. The crude hydrobromide was purified by dissolving one part by weight in four parts of boiling water, decolorizing the solution with activated carbon (Darco G60) and cooling t o 2". The first crop of crystals amounted to a 60% recovery. Three or four recrystallizations gave a colorless product. When heated in a capillary tube in a Berl and Kullmann block i t turned pink at 235", darkened a t 240" and decomposed at 280-285'. The specific rotation in water was [a]:f16.99' (c, 3.806). Dobbie and Lauder reported darkening a t 240" and decomposition at 282-283", [a]: $17.07" (c, 5.188), f17.4' (c, 5.074); Van Duin and co-workers gave [CY]: +17.32" (c, 3.696). Keopine hydrobromide is about 7 times as soluble in cold water as codeine hydrobromide. Recrystallization from water of a mixture containing about 85% neopine hydrobromide results in little change in the proportions. If the per cent of neopine hydrobromide is less than 85%, i t will concentrate in the mother liquors, while if greater, pure neopine hydrobromide may be obtained by several recrystallizations. Neopine alkaloid. A water solution of the hydrobromide, 10 g. i n 100 cc. of warm water, was made alkaline with potassium carbonate and extracted 5 times with equal volumes of ether. Evaporation of the solvent left a syrup which crystallized on standing, or more rapidly if seeded. The alkaloid was purified by dissolving 6.5 g. in 100 ml. of boiling cyclohexane, decolorizing with activated carbon (Darco G60)and cooling t o 20°, which gave an 80% recovery of the base in the form of long needles. Cooling the cyclohexane solution below 20" gave a thick opalescent gel which remelted on warming. A similar gel formed with methylcyclohexane. The alkaloid was recrystallized also from hexane (Skellysolve B, b p. 60-70") containing 2.5% by volume of ethanol; i t is soluble t o the extent of about 2 g. per 100 ml. of the boiling solution and separates on slow cooling as long glistening needlesin 75% yield. Xeopine is not sufficiently soluble in ether or petroleum ether for convenient recrystallization of large amounts. Neopine alkaloid melted a t 127.5-127.8' (corr.) and its specific rotation in chloroform was [a]: -28.13' (c, 7.767); -30.50" (c, 3.904). Van Duin and co-workers reported m.p. 127127.5' (corr.) and [a]:-28.10' (c, 7.4740). Neopine sulfate. A solution of 4 g. of neopine i n 400 ml. of acetone was acidified by adding st solution of sulfuric acid in anhydrous acetone (0.65 g. per 100 ml.) until a test drop reacted acid to litmus but alkaline to chlorophenol red. Neopine sulfate separated rapidly as very fine crystals, was collected with minimum exposure to moisture, and dried a t 60". When heated in a sealed capillary i t softened at 163-165' and melted with frothing a t 1 6 6 167" Its rotation in water was [a]:+16.38" (c, 3.000). The salt was soluble in 65-70 parts of 99% alcohol, 4-5 parts of 95% alcohol and 2.5-3 parts of 80% alcohol. It was very soluble in water, giving a sdution which was neutral to methyl red. However, after four months in a stoppered flask, the solution had become somewhat brown and its specific rotation had increased 2'. When the dry salt was exposed to the atmosphere i t turned brown and caked, but when sealed in an ampoule i t remained white and powdery. Reduction of neopine. Five g. of neopine hydrobromide dissolved i n 100 ml. of water was shaken with 0.2 g. of platinum oxide catalyst (Baker and Co.) and hydrogen a t atmospheric pressure. The reduction came to a stop after 50 minutes, when375 ml. of hydrogen had been absorbed. A4fterfiltering off the catalyst, the solution was made alkaline with sodium hydroxide and extracted four times with 50 mi. of chloroform. The syrup remaining after evaporation of the solvent was recrystallized from 25 ml. of petroleum ether (b.p. 30-60") containing 5 ml. of benzene. The crystals of dihydrocodeine which formed melted a t 112113", which is in agreement with the literature (4). The mother liquor from the recrystallization was evaporated; the syrupy residue was taken up in 20 ml. of hot alcohol and mixed
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with a solution of 5 g. of tartaric acid in 20 ml. of hot alcohol. On cooling and stirring dihydrocodeine acid tartrate crystallized; i t melted a t 187-139', which is in agreement with previous reports. Separation of codeine and c.eopine mixtures. A method was developed of separating nlixtures of codeine and neopine based on the difference in solubility of the sulfates in 95% alcohol. One part of codeine sulfate dissolves in about 1000 parts of 95% alcohol, while one part of neopine sulfate dissolves in 4 or 5 parts. The procedure may be illustrated by the following typical example: Ten g. of a 1-to-1 mixture of codeine and neopine alkaloids was dissolved i n 75 ml. of dry acetone and a solution of 2 g. of sulfuric acid in 150 ml. of dry acetone was added until the solution reacted neutral to bromophenol blue. The mixed sulfates crystallized out immediately; the solution was chilled and filtered and the salt was air-dried. The dry salts were triturated two times with 100-ml. portions of 95% alcohol; the supernatant solution was decanted each time through a filter. The insoluble crystalline codeine sulfate remaining wa,s dissolved in water, precipitated with potassium carbonate and extracted with several portions of chloroform. The dried chloroform extracts were evaporated and the residue converted to the hydrobromide from acetone. The rotation of the codeine hydrobromide was [a]:-91" (c, 2.0, water) compared to -96.6' given by Martin (5) * The combined alcoholic extracts of the mixed sulfates were evaporated to small volume, taken up in water, and the alkaloid extracted and converted t o the hydrobromide as before. The rotation of this hydrobromide was [a]: +4.5" ( c , 3.7, water). Assuming a straight line relationship between specific rotation and per cent composition for mixtures of codeine and neopine hydrobromides i t was estimated that the material remaining undissolved from the alcoholic trituration and giving a hydrobromide with a specific rotation of -91" was 96% codeine. The specific rotation of 4-4.5" corresponds t o 89% neopine in the material dissolved in the alcoholic extracts. From such material pure neopine can be prepared by the procedure described. SUMJlARY
Neopine has been isolated from the mother liquors after crystalIization of codeine. Neopine sulfate has been prepared and found t o afford a means of separating neopine from codeine. No neopine was found in the mother liquors of codeine prepared from morphine. ST. LOUIS7, MISSOURI REFERENCES (1) DOBBIE AND LAUDER, J . Chem. SQC.,99,34 (1911). (2) VANDUIN,ROBINSON ANI) SMITH, J . Chem. soc., 903 (1926). J . Pharmacol. E z p t l . Therap., 6,66 (1914). (3) JACKSON, (4) SMALL AND LUTZ,"Chemistry of the Opium Alkaloids", 1932, p. 1970 (5) MARTIN, J. pharm. chim., (7) 26,176 (1922).
