14-O-p-CHLOROBENZOYLACONINE AND ANALGESIC/ANTIINFLAMMATORY AGENT

Abstract: 14-O-p-Chlorobenzoylaconine, salt thereof and analgesic/antiinflammatory agent containing the same as the active ingredient. This compound is a novel substance which is highly safe, develops an analgesic action on inflammatory and noninflammatory pains, and is antiinflammatory.

Description: Technical Field This invention relates to novel compound 14-O-p-chlorobenzoylaconine or salts thereof, as well as to a novel analgesic/anti-inflammatory composition containing the 14-O-p-chlorobenzoylaconine or salts thereof as active ingredient. Background Art Aconitine alkaloids contained in the tuberous root of plants of the genus Aconitium have already been reported to have a potent analgesic and anti-inflammatory activity; see Tohoku J. exp. Med., 128, (1979), 175-187; J. Pharm. Dyn., 2, (1979), 78-83; J. Pharm. Dyn., 3, (1980), 514-525; European J. of Pharmacology, 82, (1982), 65-71; European J. of Pharmacology, 101, (1984), 29-36; European J. of Pharmacology, 108, (1985), 19-23; Br. J. Pharmac., 85, (1985), 575-580; They, however, are supposed to show a narrow safety margin because of their high toxicity. From JP-A-63211268 aconitine compounds of the general formula are known wherein R₁ is benzoyl or anisoyl; R₂ is methyl or ethyl; provided that if R₁ is benzoyl, then R₂ is methyl, and that if R₁ is anisoyl, then R₂ is ethyl, for use as an analgesic/anti-inflammatory agent. Disclosure of Invention As a result of extensive studies in an attempt to develop novel aconitine alkaloid derivatives which are low in toxicity but maintain the analgesic/anti-inflammatory activity that aconitine alkaloids have, we have already succeeded in providing "novel aconitine compounds and analgesic/anti-inflammatory agent comprising the same" (Japanese patent application No. 2-283553, application date : October 23, 1990). As a result of further studies, we have now succeeded in providing 14-O-p-chlorobenzoylaconine, a compound with excellent pharmacological effects coupled with high safety. Thus, the present invention provides a new compound, 14-O-p-chlorobenzoylaconine of the formula: as well as salts thereof. It also provides an analgesic/anti-inflammatory agent containing 14-O-p-chlorobenzoylaconine or a salt thereof as active ingredient together with an excipient. The present invention will now be described in detail in the following. The compound according to the invention of the formula (I) shown above may be prepared by using as starting material aconitine compounds described in the literature, such as aconitine, mesaconitine, jesaconitine, 14-O-benzoylaconine, 14-O-benzoylmesaconine and 14-O-anisoylaconine shown below by the formulas (II), (III), (IV), (V), (VI) and (VII), respectively. Where the compounds of the formulas (II), (IV), (V) and (VII) are used as starting material, the compound of the formula (I) may be prepared by hydrolytic cleavage of the ester group, at the position 14 or 8 such as alkaline hydrolysis, followed by reaction with p-chlorobenzoyl chloride in an appropriate solvent such as pyridine. Where the compounds of the formulas (III) and (VI) are used as starting material, the compound of the formula (I) may be prepared by following the same steps as in the case where the compounds of the formulas (II), (IV), (V) and (VII) are used as starting material, i.e. hydrolytic cleavage of the ester group, at the position 14 or 8 such as alkaline hydrolysis, followed by reaction with p-chlorobenzoyl chloride in an appropriate solvent such as pyridine, to give 14-O-p-chlorobenzoylmesaconine; reacting the product with an appropriate oxidizing agent such as potassium permanganate in an appropriate solvent such as acetone to give N-demethylated product; and reacting the N-demethylated product with an ethylating agent such as ethyl iodide. R₁ R₂ R₃ II Bz CH₂CH₃ OAc III Bz CH₃ OAc IV An CH₂CH₃ OAc V Bz CH₂CH₃ OH VI Bz CH₃ OH VII An CH₂CH₃ OH Bz: COC₆H₅, An: COC₆H₄OCH₃, Ac: COCH₃ The compound of the invention is a basic substance capable of forming salts with inorganic acids such as hydrochloric acid, sulfuric acid and hydrobromic acid or with organic acids such as oxalic acid, succinic acid, tartaric acid, citric acid and ascorbic acid. In the following will now be given examples for illustration of the present invention. Physicochemical parameters and analytical data of the compound of the formula (I) are given. Pharmacological activity, toxicity etc. of compounds are shown in Tables 1-6. Example 1 100 mg of aconitine was dissolved in 5 ml of 5 % KOH in methanol. This solution was stirred at room temperature for 10 hours. The solvent was evaporated off under reduced pressure and the resulting residue was dissolved in 5ml of ice water. This solution was chromatographed on Amberlite XAD2 (20 ml, product of Nippon Organo) which had been washed with methanol and water in that order. After this column was washed by water until the washings were free from alkalinity, it was eluted with methanol (300 ml). The eluate was dried under reduced pressure to afford 96 mg of residue containing aconine. This residue was dissolved in 2 ml of distilled pyridine. To this solution, 0.06ml of p-chlorobenzoyl chloride was added and the mixture was stirred at -18 °C for 10 minutes. After reaction, the reaction mixture was chromatographed on a silica gel (10 g) column, eluting with CHCl₃ (30 ml), 10 % methanol in CHCl₃ (30 ml), 15% methanol in CHCl₃ and 20 % methanol in CHCl₃ in that order. The eluates with 10 % methanol in CHCl₃ and 15 % methanol in CHCl₃ were mixed and dried under reduced pressure. The residue was subjected to column chromatography on silica gel (30 g), eluting with ammonia-saturated chloroform. The eluate was evaporated. The so purified residue was recrystallized from acetone - hexane to afford 14-O-p-chlorobenzoylaconine (83 mg). Example 2 77 mg of 14-O-p-chlorobenzoylaconine was obtained in the same manner as in Example 1, except for the use of 100 mg of jesaconitine as a substitute for aconitine in Example 1. Example 3 85 mg of 14-O-p-chlorobenzoylaconine was obtained in the same manner as in Example 1, except for the use of 100 mg of 14-O-benoylaconine as a substitute for aconitine in Example 1. Example 4 84 mg of 14-O-p-chlorobenoylaconine was obtained in the same manner as in Example 1, except for the use of 100 mg of 14-O-anisoylaconine as a substitute for aconitine in Example 1. Example 5 80 mg of 14-O-p-chlorobenzoylmesaconine was obtained in the same manner as in Example 1, except for the use of 100 mg of mesaconitine as a substitute for aconitine in Example 1. 80 mg of 14-O-p-chlorobenzoylmesaconine were dissolved in 10 ml of acetone. To this solution, 4 ml of aqueous KMnO₄ solution (887 mg in 25 ml of water) and 0.7ml of aqueous K₂CO₃ solution were added and the mixture was stirred at room temperature for 30 minutes. The reaction mixture was concentrated under reduced pressure until the odor of acetone was no longer apparent. To the residual solution, 5 ml of 2N H₂SO₄ and 3.5 ml of aqueous Na₂S₂O₃ solution (887 mg in 22 ml of water) were added and the mixture was washed with CH₂Cl₂. The aqueous layer was adjusted to pH 8 - 9 with Na₂CO₃. This solution was extracted with CH₂Cl₂. The CH₂Cl₂ layer was dried over Na₂SO₄ and concentrated to dryness in vacuo . The residue was subjected to column chromatography on silica gel, eluting with 5 % methanol in ammonia-saturated CHCl₃ to afford de-N-methyl-14-O-p-chlorobenzoylmesaconine (58 mg). 58 mg of de-N-methyl-14-O-p-chlorobenzoylmesaconine was dissolved in 2 ml of a mixture of methanol and ether (1 : 1). To this solution, 65 mg of CaCO₃ and 0.5 ml of CH₃CH₂I were added and the mixture was refluxed for 2 hours. The reaction mixture was filtered off to remove insolubles and concentrated to dryness under reduced pressure. The residue was subjected to column chromatography on silica gel for separation and purification, eluting with 5 % methanol in ammonia-saturated CHCl₃ to afford 14-O-p-chlorobenzoylaconine (33 mg). Example 6 35 mg of 14-O-p-chlorobenzoylaconine was obtained in the same manner as in Example 5, except for the use of 14-O-benzoylmesaconine as a substitute for mesaconitine in Example 5. Example 7 10 mg of 14-O-p-chlorobenzoylaconine was dissolved in 0.5 ml of ethanol . To this solution, 0.5 ml of an ethanolic solution of L(+)-tartaric acid (23 mg in 5 ml of ethanol) was added and the mixture was well mixed. Then, N₂ gas was blowed against this solution to evaporate off the ethanol in the solution to dryness. The residue was placed in a desiccator under reduced pressure to afford the tartaric acid salt of 14-O-p-chlorobenzoylaconine (11.4 mg). Example 8 12.9 mg of the citric acid salt of 14-O-p-chlorobenzoylaconine was obtained in the same manner as in Example 7, except for the use of 32 mg of citric acid as a substitute for L(+)-tartaric acid in Example 7. Example 9 12 mg of the L(+)-ascorbic acid salt of 14-O-p-chlorobenzoylaconine was obtained in the same manner as in Example 7, except for the use of 26 mg of L(+)-ascorbic acid as a substitute for L(+)-tartaric acid in Example 7. Example 10 10.8 mg of the hydrobromic acid salt of 14-O-p-chlorobenzoylaconine was obtained in the same manner as in Example 7, except for the use of 27 mg of hydrobromic acid as a substitute for L(+)-tartaric acid in Example 7. Physicochemical parameters and analytical data of 14-O-p-chlorobenzoylaconine 1) Analysis of IR spectra (KBr) IR ν KBr / max: 3500, 1720 cm⁻¹. 2) Analysis of UV spectra (ethanol) UV λ EtOH / max (log ε) nm: 240 (3.98). 3) Analysis of ¹H-NMR spectra (CDCl₃) The following signals are shown (δ , ppm). 7.99 and 7.40 (each 2H, d, J=8.9 Hz, p-chlorobenzoyl group), 4.97 (1H, d, J=5.4 Hz, C14-H), 3.71, 3.31, 3.30 and 3.26 (each 3H, s, OCH₃ at C1, C6, C16 and C18), 1.10 (3H, t, J=7.0 Hz, CH₃ of C₂H₅ at the nitrogen atom). 4) Analysis of ¹³C-NMR spectra (CDCl₃) The following signals are shown (δ , ppm). 165.3 (carbonyl of p-chlorobenzoyl group at C14), 139.6, 131.1, 128.8 and 128.2 (p-chlorobenzoyl group), 90.7, 83.0, 82.4, 81.8, 79.9, 78.5, 77.1, 74.6 and 71.6 (C16, C6, C1, C15, C14, C8, C18, C13 and C3), 60.8, 59.1, 58.0 and 55.7 (OCH₃ at C16, C18, C6 and C1), 48.9 (CH₂ of C₂H₅ at the nitrogen atom), 13.0 (CH₃ of C₂H₅ at the nitrogen atom). 5) Analysis of Mass spectra m/z: 637, 639 (M⁺ ). 6) Property and solubility Colorless and odorless needles. m.p. 221-222 °C. Soluble in ether, chloroform, benzene, methanol, ethanol, acetone, ethyl acetate, pyridine and dimethyl sulfoxide. Insoluble in hexane and water. Examples of experiment with respect to the pharmacological property and acute toxicity of the compound shown in formula (I) mentioned above are described below. Example 11 Measurement of analgesic activity by the acetic acid-induced writhing method. Male mice of the Std:ddY Strain (20 - 25g), which were fasted for one night before the initiation of the experiment, were used. Test compound hardly soluble in water gas used in 3 % suspension in gum arabic. Test compound taking a salt form was used in aqueous solution. 0.7 % acetic acid in 0.9 % physiological saline solution was injected i.p. (10 ml / kg) at 2 hours and 50 minutes after the test compound was administered p.o. After 10 minutes, the number of writhing movements was counted for a period of 10 minutes. The results are shown in Table 1. It was demonstrated in Table 1 that the compounds of this invention had a dose-dependent potent analgesic activity. Example 12 Measurement of analgesic activity by the phenylquinone-induced writhing method. Male mice of the Std:ddY Strain (20 - 25g), which were fasted for one night before the initiation of the experiment, were used. Test compound hardly soluble in water was used in 3 % suspension in gum arabic. Test compound taking a salt form was used in aqueous solution. 0.03 % phenylquinone in 0.5 % ethanol solution was injected i.p. (10ml / kg) at 2 hours and 55 minutes after the compound was administered p.o. After 5 minutes, the number of writhings was counted for a period of 15 minutes. The results are shown in Table 2 described below. It was demonstrated in Table 2 that the compounds of this invention had a dose-dependent, potent analgesic activity. Example 13 Measurement of analgesic activity by the tail-pressure method. Male mice of the Std:ddY Strain (20 - 25g), which were fasted for one night before the initiation of the experiment, were used. Test compound hardly soluble in water was used in 3 % suspension in gum arabic. Test compound taking a salt form was used in aqueous solution. Experiments were made with a tail-pressure apparatus. Before the administration of test compounds, the pain threshold was measured twice at intervals of 30 minutes and those mice indicating a pain threshold of 30 to 80 mmHg were selected and used. The pain threshold of each mouse was measured at 1, 3 and 5 hours after test compounds were administered p.o. The results were described as a percentage of the pain threshold after the treatment with test compound relative to that before the treatment with test compound. The results are shown in Table 3. It was demonstrated in Table 3 that the compounds of this invention had a dose-dependent, potent analgesic activity. Example 14 Measurement of analgesic activity by the hot plate method. Male mice of the Std:ddY Strain (20 - 25g), which were fasted for one night before the initiation of the experiment, were used. Test compound hardly soluble in water was used in 3 % suspension in gum arabic. Test compound taking a salt form was used in aqueous solution. Mice were placed on a cyrindric hot plate (diameter: 22 cm, height: 11 cm) made of copper which gas fixed in a water bath adjusted to 52 °C so that each animal's four paws came into contact with the plate and the time taken to show the nociceptive response (jumping and licking) as an index of pain was measured. Mice showing response times above 25 seconds were excluded from the experiment. The analgesic activity of the compound was measured at 1, 3 and 5 hours after test compound was administered p.o. The results are shown in Table 4. It was demonstrated in Table 4 that the compound of this invention had a dose-dependent, potent analgesic activity. Example 15 Measurement of antiinflammatory activity by the carrageenin-induced hind paw edema. Male rats of the Wistar strain (5 weeks old, 120 - 130 g), which were fasted for one night before the initiation of the experiment, were used. One hour after the oral administration of test compound, λ-carrageenin (1 %) was injected s.c. under the plantar surface of the right hind paw. Thereafter, at one hour intervals for 6 hours, the volume of the pain was measured using an apparatus therefor. The results were described as a swelling rate (%) calculated using the following equation: (R - L) × 100 / L = swelling rate (%) R : the volume of the right hind paw L : the volume of the left hind paw The results are shown in Table 5. It was demonstrated in Table 5 that the compound of this invention had an inhibitory action against the carrageenin-induced paw edema. Example 16 (Acute toxicity) Male mice of the Std:ddY Strain (20 - 25 g), which were fasted for one night before the initiation of the experiment, were used. Test compound hardly soluble in water was used in 3 % suspension in gum arabic. Test compound taking a salt form was used in aqueous solution. The LD₅₀ values were calculated using the method of Litchfield-Wilcoxon from the mortality during 72 hours after test compound was administered p.o. The results are shown in Table 6. As shown in Table 6, no death of mice was seen even at the p.o. administration of 1000 mg / kg of the compounds of this invention. The compounds of this invention were thus found to be very low in toxicity. Measurement of analgesic activity by the acetic acid - induced writhing method Test compound Dose (mg/kg) The number of writhings mean ± S.E. control 0 31.3 ± 3.5 8-deoxy-14-O-benzoylaconine 3 24.1 ± 2.7 10 21.9 ± 2.6 30 17.8 ± 2.5 14-O-p-chlorobenzoylaconine 3 19.8 ± 2.5 10 17.3 ± 2.4 30 12.9 ± 3.7 14-O-p-chlorobenzoylaconine tartrate 3 17.8 ± 2.5 10 15.5 ± 2.3 30 10.7 ± 2.1 n=10. Measurement of analgesic activity by the phenylquinone-induced writhing method Test compound Dose (mg/kg) The number of writhings mean ± S.E. control 0 33.1 ± 3.2 8-deoxy-14-O-benzoylaconine 3 27.1 ± 2.7 10 25.0 ± 3.0 30 24.0 ± 2.3 14-O-p-chlorobenzoylaconine 3 20.1 ± 3.6 10 17.3 ± 2.8 30 15.9 ± 3.5 14-O-p-chlorobenzoylaconine tartrate 3 21.1 ± 2.4 10 18.3 ± 2.2 30 15.7 ± 2.7 n=8 ∼ 10. Measurement of analgesic activity by the tail-pressure method Test compound Dose (mg/kg) Pain threshold (%, mean ± S.E.) 1 3 5 (h) control 0 90.7±2.9 95.2±2.9 92.2±2.8 8-deoxy-14-O-benzoylaconine 100 101.8±14.1 100.2± 7.2 105.6± 9.2 300 115.6±17.0 116.2±12.0 110.2± 7.0 14-O-p-chlorobenzoylaconine 100 100.4± 2.5 129.6±10.3 108.0± 6.0 300 120.0± 7.3 182.0±21.7 166.0±20.1 14-O-p-chlorobenzoylaconine tartrate 100 102.6± 3.4 141.1± 8.3 128.0± 4.9 300 147.0± 7.8 240.4±25.0 202.9±19.7 n=6 ∼ 34. Measurement of analgesic activity by the hot plate method Test compound Dose (mg/kg) Pain threshold (s, mean ± S.E.) 1 3 5 (h) control 0 14.3±0.8 16.6±0.9 18.9±1.4 8-deoxy-14-O-benzoylaconine 100 17.3± 1.7 17.9± 2.1 18.9± 1.7 300 18.6± 1.6 24.0± 2.3 19.6± 2.0 14-O-p-chlorobenzoylaconine 100 21.6± 2.2 21.6± 2.0 27.6± 0.9 300 22.2± 1.5 38.4± 3.3 24.0± 1.6 14-O-p-chlorobenzoylaconine tartrate 100 17.3± 2.2 26.7± 3.2 24.7± 2.1 300 18.7± 1.7 42.5±11.0 25.7± 2.7 n=7 ∼ 14. Toxicity Test compound LD₅₀ (mg/kg) 8-deoxy-14-O-benzoylaconine 100 < 14-O-p-chlorobenzoylaconine 1000 < 14-O-p-chlorobenzoylaconine tartrate 1000 < The aforementioned demonstrates that the compound of the formula (I) and its salts have an analgesic/anti-inflammatory activity as well as a low toxicity with the LD₅₀ being not lower than 1,000 mg/kg. The dose of the compound of the formula (I) for clinical use as analgesic/anti-inflammatory agent according to the invention is preferably 1-1,000 mg/day for adults. The agent according to the present invention is presented for actual application after being formulated into the desired dosage form by oonventional methods using customarily used carriers or excipients. Wherever appropriate or necessary, the compound of the present invention may be used in the form of a salt thereof for achieving its pharmaceutical effect or facilitating the preparation of dosage forms. Oral preparations such as tablets, powders, granules and capsules may contain conventional excipients such as calcium carbonate, magnesium carbonate, calcium phosphate, corn starch, potato starch, sugar, lactose, talc, magnesium stearate and gum arabic. Tablets may be coated by conventional methods. Oral liquid preparations may be aqueous or oily suspensions, solutions, syrups, elixirs etc. For injectable preparations, the compound of the formula (I) may be used in the form of a salt thereof, and dissolved for use. Such preparations may contain different adjuvants such as suspending, stabilizing or dispersing agents. They may contain sterilized distilled water, refined oils such as peanut oil and corn oil, non-aqueous solvents, polyethylene glycol, polypropylene glycol, etc. Preparations for rectal administration are in the form of suppositories and may contain pharmaceutical carriers well known in the art such as polyethylene glycol, lanolin and coconut oil. Preparations for topical application are presented in the form or compositions for ointment, plaster or poultice and may contain pharmaceutical carriers well known in the art such as vaseline, paraffin, hydrous lanolin, plastibase®, kaolin, bentonite, talc, aluminum silicate, propylene glycol, sorbitol, hydrophilic petrolatum, macrogols, wax, resin, purified lanolin, gum, glycerin, gelatin, polyacrylic acid, polyacrylic acid salt, polyvinyl alcohol, polyvinyl pyrrolidone and polyethylene oxide.

Claims: 14-O-p-chlorobenzoylaconine of the formula (I) and salts thereof. An analgesic/anti-inflammatory agent containing as active ingredient 14-O-p-chlorobenzoylaconine or a salt thereof together with an excipient. 14-O-p-Chlorobenzoylaconine of the formula (I) according to claim 1, or a salt thereof for use as an active therapeutic substance. The use of 14-O-p-chlorobenzoylaconine of the formula (I) according to claim 1, or a salt thereof for the preparation of a pharmaceutical composition having analgesic/anti-inflammatory effects.

Inventors: MURAYAMA MITSUO, MURAYAMA, MITSUO, MURAYAMA, MITSUO, 1-26, DAIKAN 2-CHOME
Applicants: SANWA SHOYAKU KK, SANWA SHOYAKU KABUSHIKI KAISHA
Application year: 1991
Main classification: C07D221
IPC codes: A61K36, C07D221, A61P25, A61P29, A61K31