A CRYSTALLINE PROSTAGLANDIN SALT

Abstract: Crystalline 9-deoxo-16,16-dimethyl-9-methylene-PGE₂ potassium salt.

Description: A CRYSTALLINE PROSTAGLANDIN SALT The present invention relates to a novel crystalline salt of 9-deoxo-16,16-dimethyl-9-methylene-PGE2. 9-Deoxo-16,16-dimethyl-9-methylene-PGE2 was described in U.S. Patent 3,950,363, issued 13 April 1976, as a useful gastric antisecretory agent. This compound was disclosed in both its free acid and lower alkyl ester forms. Subsequently, U.S. Patent 4,060,534, issued 29 November 1977, described this compound and various salt forms thereof, e.g., the tris (hydroxymethyl)aminomethane salt. This patent also describes pharmacologically acceptable salts with pharmacologically acceptable metal cations, indicating especially preferred metal cations are those derived from the alkali metals, e.g., lithium, sodium, and potassium, and from the alkaline earth metals, e.g., magnesium and calcium. Prostaglandins are known generally to be oily materials, which complicates handling and formulation for pharmaceutical purposes. Crystalline forms or derivatives of certain prostaglandins are, however, known to exist. For example, PGF2a (prostaglandin F2a) is known to be an oily material which is difficult to purify and formulate pharmaceutically. However, U.S. Patent 3,657,327, issued 18 April 1972, describes a method for the preparation of freeflowing crystalline THAM or tris (hydroxymethyl)aminomethane salt of PGF2a. Other solid PGF2a salts include the L-arginine salt described in U.S. Patent 4,005,133, issued 25 January 1977. For relatively unstable prostaglandin free acids, the preparation of crystalline salts thereof is known to markedly increase stability. For example, U.S. Patent No. 4,338,325, issued 6 July 1982, describes the crystalline sodium salt of prostacyclin or PG12. In summary, the free acid and potassium salt of 9-Deoxo- 16, 16-dimethyl - 9-methyl ene- PGE2 are known, while certain oily prostaglandins are also known. See the references cited above. SUMMARY OF THE INVENTION The present invention particularly provides: a pharmaceutically elegant crystalline solid consisting essentially of 9-deoxo-16,16-dRmethyl-9'methylene-PGE2, potassium salt. The composition of matter in accordance with the present invention exhibits surprising and unexpected pharmaceutical elegance. As indicated above, the free acid of 9-deoxo-16,16-dirnethyl-9-methylene- PGE2 is a viscous oil. As a result, purification and pharmaceutical formulation of this free acid are complicated by these physical characteristics. In contrast, the novel composition of matter disclosed herein is pharmaceutically elegant. For example, this material is easily and simply prepared using conventional crystallization techniques. Moreover, the crystallinity of this material facilitates handling and chemical analysis, and improves chemical stability. Moreover, the crystalline potassium salt of the present invention is non-hygroscopic. This characteristic is of importance and significance In handling and formulation for pharmaceutical purposes. The pharmaceutical elegance of the present Invention is further embodied in its facility in formulation, especially in suppositories and Its bloavailability therefrom. Accordingly, the crystalline potassium salt of the present invention Ss readily formulated in suppositories by mixing with conventional suppository bases and drug release rates therefrom when administered to a patient or animal blo- equivalently provide the useful pharmacological effects of the free acid. Finally, with regard to the pharmaceutical elegance of the present invention, the biological profile of the crystalline potassium salt is essentially equivalent to that of the free acid, thereby enhancing the usefulness of the crystalline potassium salt for the known pharmacological purposes for which the free acid is employed. Thus, inasmuch as the crystalline potassium salt disclosed herein is readily bloavallable and bioequivalent to the free acid when used in place of the free acid, the present Invention provides an especially useful and unexpectedly Improved means whereby 9-deoxo-16,16-dimethyl- g methylene-PGE2 is employed for pharmaceutical purposes. DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention is more completely understood by the operation of the following examples: Example 1 All solvents used in this example are degassed with nitrogen using a gas dispersion tube for 15 min prior to use. To a stirred solution of 4.82 g of 9-deoxo-16,16-dimethyl-9-methylene-PGE2 in 50 ml of methanol is added a solution of 880 mg of potassium carbonate in 15 ml of water. The reaction mixture is then allowed to stand for 5 min at 25"C and then concentrated under reduced pressure at 35"C. Eight 250 ml portions of anhydrous tetrahydrofuran are added and evaporated to insure complete removal of water. The residue, a pale yellow foam, is dissolved in 15 ml of methanol and added dropwise under a nitrogen atmosphere with vigorous stirring to one liter of diethyl ether. The initial cloudy suspension yields a gum-like residue on the walls of the reaction vessel after about 1 hr. Continued vfgorous stirring for 24 hr leads to gradual crystallization and resuspension as a uniform, easily filterable solid. This suspension is then filtered using a medium porosity sintered glass funnel. The solids are washed with 15 ml of fresh diethyl ether at 250C. After drying for 2 hr in a vacuum desiccator at 250C, a colorless free-flowing crystalline solid, 5.13 g, is obtained, pure crystalline 9-deoxo-16,16-dimethyl-9-methylene- PGE2 potassium salt. IR absorptions (cm 1) are observed at 3134, 1652, 1572, 1467, 1392, 1337, 1364, 1344, 1102, 1024, 974, and 883. Water content is 0.16% after 5 days at amblent humidity. Melting range is 130-132"C. Example 2 9-Deoxo-16,16-dlmethyl-9-methylene-PGE2 (57.03 g) is dissolved in methanol. Thereafter the resulting mixture is stirred in an ice bath and a solution of 10.11 g of potassium carbonate In water is added. The water and methanol are then removed by concentration under reduced pressure at 35"C and thereafter 500 ml of dry tetrahydrofuran is added and evaporated under reduced pressure. Five additional 500 ml portions of dry tetrahydrofuran are similarly added and evaporated. Thereafter a pale yellow foam is obtained and dissolved in 75 ml of methanol. This methanolic solution is then added dropwise to 4 liters of anhydrous diethyl ether and the potassium salt formed an oily or gummy mixture on the walls of the reaction vessels. After crystallization, induced by stirring for 4 hr, the product is scraped from the walls of the reaction vessel and the resulting suspension Is stirred vigorously for 64 hr. After filtration and washing of the solids with 500 ml of diethyl ether, pure crystalline product is then dried over nitrogen and desiccated under reduced pressure for 16 hr. Pure crystalline 9-deoxo-16, 16-dimethyl-9-methyl ene-PGE2 potassium salt (59.12 g) is obtained. Example 3 9-Deoxo-16,16-dimethyl-9-methylene PGE2, methyl ester (110 g) in 169 ml of methanol is added to 149 ml of 1N aqueous potassium hydroxide to yield a cloudy mixture. This mixture is then heated to 65 C for 15 min and diluted with 2 liters of tetrahydrofuran. Concentration on a rotary evaporator at 41-450C is undertaken concomitently with the addition of additional tetrahydrofuran until a total of 15.2 liters of tetrahydrofuran has been removed. The resulting residue is then dissolved in 125 ml of warm methanol and 1,250 ml of anhydrous tetrahydrofuran. The resulting mixture is then stirred and 1 liter of hexane is added. Seed crystals are then added (the product of Example 1 or Example 2) and an additional 375 ml of hexane is added dropwise. The resulting mixture is then stirred for 15 hrs, while adding dropwise an additional 500 ml of hexane. After stirring for 2 hrs and filtering, the resulting crystalline 9-deoxo 16,16-dimethyl.9-methylene PGE2 potassium salt is washed in 25X tetrahydrofuran in hexane to yield 61.6 g of pure crystalline product. Optionally, recrystallization from methanol, tetrahydrofuran and hexane (1:10:30) yields pure title product. Also, additional pure crystalline product can be obtained by concentration of mother liquors to an oil followed by recrystallization from methanol, tetrahydrofuran and hexane (1:10:18). Example 4 A. Midtrimester pregnant female Rhesus monkeys (Macaca mulatta) are used. (The first day of menstrual bleeding is designated Day 1 of the menstrual cycle; the first day a female is placed with a male for breeding is designated Day 1 of pregnancy. Pregnancy is confinned by abdominal palpation of the uterus.) B. A fluid-filled open-ended polyethylene tubing (PElO* Clay Adams) inserted transabdominally into the amniotic sac is used to monitor uterine muscle activity in pregnant animals. The polyethylene tubing is attached to transducers which are in turn connected to a polygraph. Animals are anesthetized when recordings are made. Animals are fasted overnight prior to use. Blood samples are collected into heparinized syringes at specified times following insertion of a suppository in pregnant or non-pregnant monkeys. Plasma is extracted and assayed for 9-deoxo 16,16-dimethyl-9-methylene-PGE2 content by radi oimmunoassay. C. Six suppository lots are prepared (4), each containing 9deoxo-16,16-dimethyl-9-methylene-PGE2 or its crystalline potassium salt (Examples 1 and 2). Two lots are made with Witepsol H15 alone as the suppository base, two with Witepsol H15 wax plus 2% colloidal silicon dioxide (CSD) and two with Witepsol H15 plus 2% CSD plus 10% triacetin. Suppositories are prepared using Witepsol H15 suppository wax. Free acid or potassium salt is dispersed in the hot wax using a homogenizer. Two percent colloidal silicon dioxide (CSD) is mixed in by further homogenization. In the third formulation, trlacetin (10X) is added before the CSD and then homogenized for one minute. Suppositories are formed in 800 mg aluminum molds and are stored at 40C until used. D. The plasma levels of 9-deoxo-16, 16-dimethyl- 9-methylene- PGE2 in monkeys treated with 6 formulations containing either 9-deoxo 16,16-dimethyl-9-methylene-PGE2 free acid or potassium salt are shown in Tables 1-6. In general, higher blood levels are measured in pregnant Rhesus monkeys than in non-pregnant monkeys. Similar plasma drug levels are reached in monkeys treated with either free acid or potassium salt. The uterine activity of pregnant Rhesus monkeys treated with these formulations in all cases begins by increased uterine tone 2-3 minutes following insertion of the suppository into the vagina. After 8-10 min the pattern changes into high amplitude frequent contractions lasting the length of the recording period. E. Examination of the drug plasma levels and uterine activity in Rhesus monkeys following treatment with free acid and potassium salt at 30 mg (acid equivalents) per dose in three suppository formulations indicates that these two compounds are equally bloavailable. Table 1 Plasma Levels in Rhesus Monkeys Treated with 30 mg Free Acid in H15 Suppositories Drug Levels (ng/ml) Hours Monkey & um;1 Monkey & um;2 Monkey & um;3a O ND ND ND 0.25 5.14 0.61 142.16 .5 1. 69 ND 63.60 1.0 4.39 ND 93.90 1.5 7.89 3.35 66.84 2.0 4.16 5.56 60.76 3.0 0.23 12.99 56.09 4.0 7.43 14.70 35.66 6.0 10.08 17.26 13.67 24.0 7.68 4.97 5.67 Table 2 Plasma Levels in Rhesus Monkeys Treated with 30 mg Potassium Salt in H15 Suppositories Drug Levels (ng/ml) Hours Monkey 4 Monkey #5 Monkey $6a O ND ND ND 0.25 127. 99 10.88 76.56 0.5 3.72 ND 68.37 1 ND 1.42 29.59 1.5 0.41 5. 91 77.27 2 0.86 11.54 28.39 3 7.52 14.18 41.68 4 8.39 22. 91 42. 76 6 17.88 25.04 20.20 24 21.69 16.24 7. 77 apregnant animal with uterine recording Table 3 Plasma Levels in Rhesus Monkeys Treated with 30 mg Free Acid in H15 Plus 2% CSD Suppositories Drug Levels (ng/ml) Hours Monkey #7 Monkey #8 Monkey *9a O ND ND ND 0.25 39.17 51.44 60.72 0.5 44.46 133.94 52.17 1.0 63.93 88.18 63.06 1.5 42.17 61.10 62.77 2 36.95 78.35 62.85 3 16.94 29.05 40.16 4 13.25 12.36 57.77 6 6.50 2.49 32.03 24 4.01 15.72 20.98 Table 4 Plasma Levels in Rhesus Monkeys Treated with 30 mg Potassium Salt in H15 Plus 2% CSD Suppositories Drug Levels (ng/ml) Hours Monkey *10 Monkey #11 Monkey #12a O ND ND ND 0.25 20.41 19.84 103.77 .5 2.39 13.98 55.66 1 1.50 6.61 40.86 1.5 1.70 8.13 91.09 2 3.57 9.80 66.54 3 12. 38 9.48 51.46 4 20.66 18.66 36.12 6 53.76 28.67 22.51 24 15.97 23.37 6.04 apregnant animal with uterine recording Table 5 Plasma Levels in Rhesus Monkeys Treated with 30 mg Free Acid in H15 Plus 2% CSD + 10% Triacetin Suppositories Drug Levels (ng/ml) Hours Monkey #13 Monkey #14 Monkey #15a O ND ND ND 0.25 12.56 18.80 118.62 0.5 9.25 35.96 154.08 1 2.80 80 25.06 154. 1.5 3.09 32.01 26.82 2 5.46 28.73 44.83 3 15.10 20.19 65.87 4 22.54 16.61 22.05 6 23.81 16.25 13.00 24 25. 96 12.89 2. 76 Table 6 Plasma Levels in Rhesus Monkeys Treated with 30 mg Potassium Salt in H15 Plus 2X CSD + 10% Triacetin Suppositories Drug Levels (ng/ml) Hours Monkey *16 Monkey #17 Monkey #18 O ND ND ND 0.25 7.45 7.98 56.78 0.5 7.00 2.15 207.06 1 12.62 1. 27 64.39 1.5 19.88 1.86 38.30- 2 40.18 1.75 87.17 3 45.45 20.11 47.84 4 31.38 3.13 35.46 6 34.47 6.97 33.85 24 14.21 21.94 8.31

Claims: CLAIM Crystalline 9-deoxo-1 6, 16-d imethyl-9-methyl ene-PGE2 potassium salt.

Inventors: BUNDY, GORDON LEONARD
Applicants: THE UPJOHN COMPANY
Application year: 1983
Main classification: C07C177
IPC codes: C07C67, C07C401, A61K31, C07C405