ANTIHYPERTENSIVE AGENTS COMPRISING 2-ALKYNYLADENOSINES AS ACTIVE INGREDIENTS

Abstract: A 2-alkynyladenosine represented by general formula [I]: wherein n is an integer of from 2 to 15, has been found to have excellent properties as an antihypertensive agent. On the basis of this finding, the present invention has provided an antihypertensive agent comprising an antihypertensive ef­ fective amount of a compound of the above formula [I] and a pharmaceutically acceptable carrier. The present invention also discloses a novel compound 2-alkynyladenosine of for­ mula [I] shown above wherein n is 6 to 15.

Description: BACKGROUND OF THE INVENTION The present invention relates to an antihypertensive agent comprising a 2-alkynyladenosine as an active ingredient. Heretofore, adenosine has been used for the treatment of cardiac incompetency, myocardial infarction, arterial sclerosis and angina pectoris. This compound, however, exhibits a strong transient pharmacological effect when taken up into organisms and is known to be rapidly deaminated by adenosine deaminase or taken up into red blood cells and tissues to lose its activity. Adenosine also exhibits a strong suppressive effect on the heart as a side effect. In order to improve the pharmacological activity of adenosine, impart thereto resistance to adenosine deaminase and mitigate undesirable side effects, a variety of adenosine analogues have been prepared synthetically. With respect to 2-substituted adenosines, various compounds have been synthesized. For example, 2-alkylthioadenosines, 2-phenylaminoadenosines and the like exhibiting such physiological activities as adenosine deaminase inhibitor effect, coronary vasodilator effect, platelet aggregation inhibitor effect and antiviral effect have so far been obtained. The inventors had previously synthesized 2-alkynyladenosines of the following formula as 2-substituted adenosine derivatives each having a substituent introduced by a carbon-carbon bond in the 2 position of adenosine: wherein R is Si(CH₃)₃, H, Ph, CH₂OH, CH₂CH₂OH, CH(OH)CH₃, (CH₂)₂CH₃, (CH₂)₃CH₃, (CH₂)₄CH₃ or (CH₂)₅CH₃, and had found that some of these compounds have an inhibitory effect on the I g E-mediated 48-hr. passive cutaneous anaphylaxis reaction in rats. (Nucleic Acids Research Symposium Series No.12, pp. 5 ∼ 8 (1983) and Chem. Pharm. Bull. Vol. 33, pp. 1766 ∼ 1769 (1985)) The inventors had also reported at the 105th Meeting of the Pharmaceutical Society of Japan (see "Proceedings" (1985), p.541,5K 1-5) that derivatives of that formula wherein R has the meaning of Ph and -(CH₂) n CH₃ with n of from 3 to 15 had no inhibitory activity on the above-mentioned reaction in rats, even at a dose of 4 mg/kg (i.v.). Numerous pharmaceutical preparations have been developed to date as antihypertensive agents. In view of the nature of the disease, pharmaceutical preparations must be administered over a long period of time in many cases. The intake of pharmaceutical preparations over a long period of time may sometimes induce drug resistance therefor or side effects. For this reason, stepwise pharmacotherapy is generally so adopted that a particular pharmaceutical is selected with due consideration for age, severity of hypertension, complications and the like and another pharmaceutical preparation having a different function mechanism is further used in combination depending upon the symptoms. At present, no pharmaceutical preparations comprising compounds having adenosine skeletons are used as antihypertensive agents, and it would thus be highly profitable for the treatment of hypertension to provide antihypertensive agents comprising adenosine derivatives. SUMMARY OF THE INVENTION As a result of the inventors' intensive researches directed to the development of novel 2-substituted adenosine derivatives useful as antihypertensive agents, they have found quite unexpectedly that 2-alkynyladenosines having an alkynyl group in the 2 position exhibit excellent properties as antihypertensive agents. On the basis of this finding, they arrived at the present invention. More specifically, this invention is directed to the use of a 2-alkynyladenosine represented by general formula [1]: wherein n is an integer of from 2 to 15, for the manufacture of an antihypertensive agent. DETAILED DESCRIPTION OF THE INVENTION The 2-alkynyladenosine of the formula [I] shown supra which is used as an active ingredient for the manufacture of an antihypertensive agent according to the present invention can be synthesized by reacting a 2-halogenoadenosine of general formula [II]: wherein X is iodine or bromine, with an alkyne of general formula [III]: CH≡C[CH₂] n CH₃ [III] wherein n is an integer of from 2 to 15, in a solvent in the presence of bis(triphenylphosphine) palladium dichloride and cuprous iodide. Depending upon the desired compound among those used according to the present invention, an alkyne having the corresponding "n" is selected. For the solvent, basic solvents such as a solvent mixture of triethylamine and N,N-dimethylformamide are used. Triethylamine can be replaced by another tertiary amine such as tributylamine, trioctylamine, N,N,N',N'-tetramethyl-1,8-naphthalenediamine, dimethylaniline, diethylaniline or pyridine, while N,N-dimethylformamide can be replaced by a non-proton polar solvent such as N,N-dimethylacetamide, dimethyl sulfoxide or acetonitrile. The reaction terminates in several hours in a temperature range of from : room temperature to solvent reflux temperature. The compounds used according to the present invention can be isolated by any conventional separation and purification method. For example, adsorption chromatography, ion exchange chromatography, extraction or recrystallization is applied for the isolation. The antihypertensive agents manufactured according to this invention are administered to patients orally, by injection, intrarectally or via topical administration. These antihypertensive active preparations, when administered, are made by a conventional method into dosage forms suited for the desired route of administration. For example, solid form preparations such as tablets, powders, dragées, granules, sublingual tablets and capsules or liquid form preparations such as syrups, suspensions and elixirs are suitable for oral administration, injections for administration by means of a syringe, suppositories and ointments for intrarectal administration, and poultices for topical administration. In the process of manufacture, suitable additives such as binders, vehicles, lubricants, disintegrators, emulsifiers, suspending agents, antiseptics, stabilizers, solubilizing agents, taste conditioners, and sweeteners can be selected and used as necessary from a pharmaceutical point of view. The optimum doses of the antihypertensive active preparations are determined according, for example, to the dosage form, severity of diseases, age and body weight. For example, a preparation comprising a short-chain 2-alkynyladenosine of the formula [I] wherein n is an integer of from 2 to 5 as an active ingredient is administered orally to an adult generally at a dose level of the order of 0.1 to 5 mg/kg/day while that comprising a long-chain 2-alkynyladenosine of the formula [I] wherein n is an integer of from 6 to 15 as an active ingredient is administered orally at a dose level of the order of 0.1 to 10 mg/kg/day. The long-chain 2-alkynyladenosines, especially the compounds of the formula [I] wherein n is an integer of from 11 to 15, exhibit a mild hypotensive effect of a long duration coupled with relatively low toxicity and minimal side effects. As a result of animal tests with normotensive rats (NR) and spontaneously hypertensive rats (SHR), the antihypertensive agents manufactured according to the invention were further found to act on SHR selectively and barely affect normotension. It has also been found that short-chain 2-alkynyladenosines show a more drastic hypotensive effect than the long-chain alkynyl substituent compounds and act equally on normotension but have a higher toxicity. In view of the foregoing, the long-chain 2-alkynyladenosine used according to the present invention can be said to be endowed with overall excellent properties. It can also be said that preferably the short-chain 2-alkynyladenosines are used at lower dose levels than those for the long-chain alkynyl substituent compounds. EXAMPLES Preparation of compounds to be used according to the present invention 6.0 g of 6-chloro-2-iodo-9-(2,3,5-tri-0-acetyl-β-D-ribofuranosyl) purine was added to 60 ml of methanol plus ammonia (saturated at 0°C) and the mixture was reacted at a temperature of 60°C for 17 hours in a sealed tube. The reaction solution was cooled, then degassed, and concentrated under reduced pressure. Crystallization of the residue from water afforded 3.94 g of 2-iodoadenosine (90% yield) having a melting point of 141°C to 144°C. 393 mg (1 mmole) of the 2-iodoadenosine was dissolved in 10 ml of dimethylformamide plus 3 ml of triethylamine, and to the solution obtained were added 21 mg of bis(triphenylphosphine) palladium dichloride and 12 mg of cuprous iodide. To the resulting solution was added an alkyne (1.1 equivalent) in an argon stream, and the mixture was heated and stirred under heat at 80°C. The reaction solution was then concentrated under reduced pressure, the residue was dissolved in methanol, and hydrogen sulfide was passed through the solution for one minute. The precipitate formed was filtered off, and the filtrate was concentrated to dryness under reduced pressure. The residue was purified by column chromatography on silica gel and recrystallized from methanol or methanol-water to obtain a 2-alkynyladenosine. The alkynyl groups of the alkyne reactants, the reaction time, yield, melting point and infrared absorption spectrum of the compounds prepared are shown in TABLE 1. Test Examples Test 1: Effect of the test compounds on the blood pressure in SHR To twelve- to fifteen-week old male SHRs were orally administered some of the test compounds of table 1 each suspended in 0.5% CMC/physiological saline at a rate of 2 ml/kg. The blood pressure of the thus treated SHRs was measured by means of a tail artery sphygmomanometer (supplied by Nalco Co., Model PE-300) prior to the oral administration and at 2, 4, 6 and 8 hours thereafter. Reduction in blood pressure was calculated on the basis of the values thus obtained, and the maximum reduction levels attained by the respective compounds are summarized in TABLE 2. Each test compound was evaluated with a group of 4 rats. As is apparent from TABLE 2, all of the 2-alkynyladenosines exhibited a hypotensive effect: the shorter the alkynyl substituent chain, the more drastic was the hypotensive effect while the longer the chain, the milder was the effect. Further,a sedative effect was observed in the groups of rats treated with Compounds 2 to 4. Test 2: Effect of the test compounds on the blood pressure in SHR Thirty-two-week-old male SHRs (divided into groups of three rats each) were anesthetized with urethane (1.1 g/kg, i.p.), and the blood pressure of each of the rats delivered from the common carotid artery was recorded on a polygraph through a pressure transducer (Model MPU-0.5). The antihypertensive agent manufactured with the use of some of the test compounds of table 1 was administered through a cannula inserted into the femoral vein of the rat at a rate of 0.5 ml/kg, and the blood pressure was measured continuously from before administration to 30 minutes after administration. The maximum levels of reduction in blood pressure were as set forth in TABLE 3. Test 3: Effect of the test compounds on the blood pressure in NR The procedure of Test 2 was repeated with 10- to 12-week-old male Wistar rats (divided into groups of three rats each) to measure the hypotensive effects of the respective agents (100 µg/kg). Simultaneously, the change in the heart rate was measured by an ictometer based on the systolic blood pressure as a trigger. The results obtained were as shown in TABLE 4. From the data given in TABLE 4 it can be seen that the long-chain alkynyl substituent compounds wherein n is 11 or more have far less effect on the blood pressure of normotensive rats than the short-chain alkynyl substituent compounds wherein n is 5 or less. It can also be noted that the long-chain compounds have less influence on the heart rate than the short-chain compound. The overall results set forth in TABLES 3 and 4 show that Compound 6(n=9) exhibited a substantially equal hypotensive effect on SHR and NR while Compounds 7(n=11) and 8(n=13) acted selectively on SHR. Test 4: Effect of the test compounds on the blood pressure in SHR and NR To eighteen- to twenty-week-old male SHR (divided into groups of four rats each) and to eighteen- to twenty-week-old male Wistar rats (divided into groups of four rats each) Compound 8 (n=13) was orally administered in the same manner as in Test 2 at a dose of 10 mg/kg, and the blood pressure of each of the rats was measured. The results obtained are incorporated in TABLE 5. As is apparent from TABLE 5, the tendency of Compound 8(n=13) to act selectively on SHR was also observed in the case of oral administration. Test 5: Acute toxicity The acute toxicity of Compound 8(n=13) was tested with seven-week-old male Jcl:ICR mice. The physically allowable doses of Compound 8 for intraperitoneal administration and oral administration were 800 mg/kg and 1,300 mg/kg, respectively. None of the mice treated with the test compound at these maximum doses, and divided into groups of five mice each, died, so that the LD₅₀ values for intraperitoneal administration and oral administration were estimated respectively at more than 800 mg/kg and more than 1,300 mg/kg. When Compound 6(n=9) was tested by a similar procedure, on the other hand, all five mice forming one group died with intraperitoneal administration of 500 mg/kg of the test compound. As is seen from the above data, the effective amount of Compound 8 is 3 mg/kg while the LD₅₀ thereof is more than 1,300 mg/kg, indicating a 400-fold or higher safety coefficient. The longer-chain alkynyl substituent compound such as Compound 8 were thus found to be less toxic than the not so long-chain alkynyl substituent compounds such as Compound 6. Formulation Examples Formulation 1: Tablets A total of 150 mg of a mixture comprising 20 mg of a long-chain alkynyl substituent compound to be used according to the present invention, 90 mg of lactose, 24 mg of corn starch, 10 mg of hydroxypropyl cellulose, and 6 mg of magnesium stearate was kneaded with water, and the resulting mixture was granulated for tableting purposes by a conventional method. After drying, the granules thus obtained were mixed with magnesium stearate to make tablets which were then formed into desired shape. In the case of a short-chain alkynyl substituent compound, tablets were formed in the same manner except that the quantity of the compound used was 10 mg. Formulation 2: Granules 40 mg of a long-chain alkynyl substituent compound to be used according to the present invention, 200 mg of mannitol and 50 mg of lactose were mixed. The mixture was kneaded with an aqueous solution containing 10 mg of polyvinyl alcohol, granulated and dried to obtain granules. In the case of a short-chain alkynyl substituent compound, granules were prepared in the same manner except that the quantity of the compound used was 20 mg. Formulation 3: Capsules Capsules were formulated by encapsulating the granules prepared for tableting purposes in Formulation 1.

Claims: Use of a 2-alkynyladenosine represented by general formula [I] wherein n is an integer of from 2 to 15, for the manufacture of an antihypertensive agent.

Inventors: ABIRU, TOICHI, MACHIDA, HARUHIKO, MATSUDA, AKIRA 10-501 MINAMI SHINKAWA KOUMUIN, MIYASAKA, TADASHI
Applicants: YAMASA SHOYU KABUSHIKI KAISHA
Application year: 1986
Main classification: C07H19
IPC codes: A61K31, C07H19, A61P9