Polypeptide, a process for preparing the same, a pharmaceutical composition containing said polypeptide as well as the use thereof

Abstract: There is disclosed a novel polypeptide, a process for preparing the same, a pharmaceutical composition contain­ ing the same as well as the use thereof. The novel polypeptide which is useful as an analgesic corresponds to the formula given below: wherein the meaning of R¹ and R², A, B, C, D, E, and F is the same defined in the claims.

Description: The present invention relates to polypeptides having excellent medicinal effects, a process for preparing the same, a pharmaceutical composition containing the same as well as the use thereof. More particularly, the invention relates to polypeptides of the following general formula (I): wherein R¹ and R² can be the same or different and each is selected from hydrogen, lower alkyl groups having 1 to 6 carbon atoms or lower alkenyl groups having 2 to 6 carbon atoms, A is selected from D-Met, D-Ser or D-Thr, C is selected from L-Leu, L-Ile, L-Nle, L-tert.Leu, L-Met, L-Met(O), L-Ser or L-Val, D and E can be the same or different and each is selected from L-Arg, L-Lys, L-homoArg or L-Orn, and F is selected from -OH or -NH₂. or pharmacologically acceptable salts of said polypeptides, and medicines containing them. The amino acids constituting the peptides herein include D- and L-amino acids. Unless otherwise stated, the amino acids are L-amino acids. The symbols used herein have the same meanings as is the general practice in the field of peptide chemistry. Namely, they are as follows: Tyr: tyrosine Gly: glycine Phe: phenylalanine Arg: arginine Leu: leucine Ile: isoleucine Nle: norleucine Met: methionine Met(O): methionine sulfoxide Ser: serine Thr: threonine Lys: lysine Val: valine homo-Arg: homoarginine Orn: ornithine BOC: tert-butoxycarbonyl Z: benzyloxycarbonyl Cl₂Bzl: 2,6-dichlorobenzyl CH₃Bzl: 4-methylbenzyl Tos: p-toluenesulfonyl, and Bzl: benzyl Prior Art The findings obtained in investigations of the mechanism of analgesic effects of morphine suggest that the living body contains so-called endogenous morphine-like substances which control various vital sensations, such as those of pain and mental action. After a series of studies, enkephalin and endorphin were isolated as opioid peptides and the structures of them were determined. Thereafter, intensive investigations were made further in this art and various new opioid peptides such as β-neoendorphin, β-casomorphin, kyotorphin, dermorphin and dynorphin were found. Among them, dynorphin is an opioid peptide of the following structural formula found by some of the inventors of the present invention: Dynorphin is a natural opioid peptide having specific effects on a K-receptor and, therefore, the use of it as an analgesic having no side effects, such as tolerance or dependency, is expected. Problems to be solved by the Invention However, dynorphin has the defect that it cannot exhibit an analgesic effect, as such, when it is administered by intravenous injection, because it is unstable in the blood. Further, a highly active peptide having a shorter chain is demanded, since dynorphin is a heptadecapeptide having a relatively long chain. Disclosure of the Invention The inventors have made intensive investigations of peptides having chains shorter than that of dynorphin and capable of exhibiting an analgesic effect, when administered by both intravenous and subcutaneous injection, and finally have discovered that this object can be attained by using peptides of the following formula (I) comprising 7 amino acids. The present invention provides polypeptides of the following general formula: wherein R¹ and R² can be the same or different and each is selected from hydrogen, lower alkyl groups having 1 to 6 carbon atoms or lower alkenyl groups having 2 to 6 carbon atoms, A is selected from D-Met,D-Ser or D-Thr, C is selected from L-Leu, L-Ile, L-Nle, L-tert.Leu, L-Met, L-Met(O), L-Ser or L-Val, D and E can be the same or different and each is selected from L-Arg, L-Lys, L-homoArg or L-Orn, and F is selected from -OH or -NH₂, or pharmacologically acceptable salts of those polypeptides. Examples of the pharmacologically acceptable salts herein include inorganic acid salts, such as hydrochloride, sulfate, hydrobromide and hydroiodide, as well as organic acid salts, such as maleate, fumarate, succinate, acetate, malonate, citrate and benzoate. Accordingly, an object of the present invention is to provide new peptides useful as medicines, particularly analgesics. Another object of the invention is to provide a process for producing new peptides useful as medicines. Still another object of the invention is to provide new analgesics containing the new peptides. The term "lower alkyl group" in the above-mentioned definition of R¹ to R¹³ refers to straight-chain, branched, cyclic or ring-containing alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, 1-methylpropyl, tert-butyl, cyclopropylmethyl, n-pentyl, 1-ethylpropyl, isoamyl and n-hexyl groups. The term "lower alkenyl group" in the above-mentioned definition of R¹ and R² refers to those corresponding to the above-mentioned alkyl groups but having a double bond in some position. The term "alkyl" in the 'α-N-alkyl derivatives' in the definition of the amino acids has the same meaning as that of the above-mentioned lower alkyl group. The compounds of the present invention in which at least one of the constituent amino acids is an α-N-alkylamino acid or a D-amino acid are free from the serious defects of dynorphin and its derivatives, namely, that they cannot exhibit any analgesic effects, as such, when they are administered by intravenous injection, because they are unstable in the blood. The compounds of the invention are highly valuable because they have a high stability in vivo and they are practically useful as analgesics. The peptides of the present invention can be synthesized by any suitable process. The protected peptides can be synthesized by a conventional liquid phase process or solid phase process. It is usually preferred that functional groups present in side chains of the amino acids are protected. All the protective groups are removed in the final stage. The protective groups for the functional groups in the side chains of the amino acids include all the protective groups reported in the prior art. Typical examples of them include tosyl (Tos), nitro (NO₂), benzyl (Bzl), tert-butyl (But), benzyloxycarbonyl (Z) and tert-butoxycarbonyl (BOC) groups. As the protective groups for the α-amino groups in the amino acids, all of the protective groups reported in the prior art can be used. It is preferred, however, to select the combination of the protective groups so that the protective groups for only the α-amino groups can be removed selectively without exerting any influence on the protective groups for the functional groups in the side chains. For example, when a tert-butoxycarbonyl group is used as the protective group for the α-amino group, a benzyl or benzyloxycarbonyl group is preferred for protecting the functional group(s) in the side chain(s). When a benzyloxycarbonyl group is used for protecting the α-amino group, a tert-butyl or tert-butoxycarbonyl group is preferred for protecting the functional group(s) in the side chains(s). When the amino group of Tyr at the N-terminal is dialkylated, the amino group can be left as it is without any further protection. To inhibit racemization, the protected peptide is synthesized preferably by a stepwise process wherein all the amino acids are bonded in sequence starting from the C-terminal, or a process wherein the fragment condensation is conducted at the position of Gly. It is also possible to conduct the fragment condensation at any desired position. In either the solid phase process or liquid phase process, according to the present invention, the protective groups are removed from the peptide and the latter is purified by repeating the reactions of the following schemes to synthesize the peptide. The steps of this process will be illustrated with reference to the liquid phase process: wherein X¹ and X² each represent H or an alkyl group, Y¹ and Y² each represent an amino acid side chain and R' and R" represent a protective group or a peptide residue. (1) Reaction of forming a peptide bond: The peptide bond can be formed by any of the processes reported heretofore. A conventional process comprises activating the carboxyl group of an acid component of the general formula: by a conventional method, such as the azide method, dicyclohexylcarbodiimide (DCC) method, mixed anhydride method or active ester method and reacting the activated compound with an amine component of the general formula: The reaction conditions, such as reaction solvent and temperature, can vary depending on the method chosen for activating the carboxyl group. The mixed anhydride method, which is one of typical condensation methods, is carried out as follows: an acid component of the general formula: is dissolved in an aprotic solvent, such as dimethylformamide, tetrahydrofuran or ethyl acetate, the resulting solution is cooled to about -20°C and then equimolar amounts of N-methylmorpholine and ethyl chlorocarbonate are added successively to the solution. After 5 min, an amine component of the general formula: in an equimolar amount is added thereto and the mixture is stirred at -15 to 0°C for 2 to 5 h and then treated in a conventional manner to obtain a protected peptide of the general formula: (2) Removal of a protective group from an α-amino group: The removal of a protective group is carried out by a conventional process, such as a catalytic reduction process, a process wherein an acid is used, a process wherein a base is used and a process wherein hydrazine is used. A preferred process is selected from among these processes depending on the type of the protective group employed for the α-amino group. Typical processes include one wherein the protective group is removed by the catalytic reduction of the benzyloxycarbonyl group and one wherein the tert-butoxycarbonyl group is removed with trifluoroacetic acid. Now, an embodiment of the process for removing the tert-butoxycarbonyl group with trifluoroacetic acid will be described in detail: 0.25 ml of anisole and 5 ml of trifluoroacetic acid are added to 1 g of an α-N-butoxycarbonylpeptide of the general formula: under cooling with ice. The mixture is stirred for 60 min and then treated with ether to obtain a trifluoroacetate of a peptide of the general formula: This product is dissolved in a solvent and neutralized with an amine, such as triethylamine, to obtain a compound to be subjected to the subsequent reaction. (3) Removal of all the protective groups: After repeating the above-mentioned condensation and removal of the protective groups for the α-amino groups in order to elongate the peptide chain, all the protective groups are removed to obtain the intended crude peptide. The protective groups are removed by a conventional process, such as a catalytic reduction process, a process wherein a liquid ammonia/alkali metal is used, a process wherein an acid is used, a process wherein a base is used or a process wherein hydrazine is used. In practice, the process is selected depending on the type of the protective group that is to be removed. One of the frequently employed processes comprises removing the protective group with hydrogen fluoride (HF) as follows: 1 g of a protected peptide is dissolved in about 30 ml of HF, in the presence of 0.5 ml of anisole, at -15 to 0°C, in a closed reaction vessel. The solution is stirred for 60 min and HF is distilled out of the reaction system. The residue is washed with ether and dissolved in water. The solution is treated with Amberlite IRA-93 (acetic acid type) and freeze-dried to obtain a crude peptide from which the protective groups have been removed. (4) Purification of crude peptide: The crude peptide may be purified by a conventional process such as ion exchange chromatography, gel filtration, partition chromatography, counter current distribution and high performance liquid chromatography. The purification is conducted by, for example, the following high performance liquid chromatography: 100 mg of the crude peptide is charged in a column having a diameter of 20 mm and a height of 250 mm containing Nucleosil 5 c 18 as the carrier and then eluted with 0.05% HCl (H₂O-CH₃CN). Fractions having peaks corresponding to the intended peptide were collected by detection at UV 210 nm and freeze-dried to obtain the intended peptide. The compounds of the present invention exhibit a very potent activity as compared with dynorphin A. Furthermore, they have strong activities of inhibiting the contraction of ileal longitudinal muscles of a guinea pig and deferential ducts of a mouse caused by the electric stimulation. The peptide compounds obtained by the present invention have opioid activities similar to those of dynorphin, their effects are quite strong and remarkable analgesic effects are exhibited by intravenous injection or subcutaneous injection. It is highly valuable that the compounds of the present invention exhibit strong analgesic effects upon systemic administration by intravenous or subcutaneous injection, whereas dynorphin and its derivatives so far reported, scarcely exhibit analgesic effects upon intravenous injection because they are unstable in the blood. The peptide compounds obtained by the process of the present invention have remarkable analgesic effects and they are useful as medicines in the therapeutical field. In using the compounds of the present invention as analgesics, they are given by peroral or parenteral administration. Usually, they are given parenterally in the form of intravenous, subcutaneous or intramuscular injection or suppositories or sublingual tablets. The dosage varies depending on the severity of the symptoms, age of the patient, sex, body weight, sensitivity, administration manner, stage of the disease, intervals, properties of the medical preparation, formulation, type of preparation and type of the active ingredient. Although the dosage is thus not particularly limited, it is usually about 0.1 to 1,000 mg/day, preferably about 1 to 300 mg/day, for adult human beings. The compounds of the present invention can be formulated into injections, suppositories, sublingual tablets, tablets and capsules by conventional processes used in the field of pharmacology. In the preparation of an injection, additives such as a pH controller, buffering agent, suspending agent, solubilizer, stabilizer, isotonizing agent and preservative are added to the active ingredient and the obtained mixture is formulated into an intravenous, subcutaneous or intramuscular injection liquid by a conventional method. If necessary, the mixture may be lyophilized by conventional methods. Examples of the suspending agents include methylcellulose, Polysorbate 60, hydroxyethylcellulose, acacia, tragacanth powder, sodium carboxymethylcellulose and polyoxyethylene sorbitan monolaurate. Examples of the solubilizers include polyoxyethylene hardened castor oil, Polysorbate 80, nicotinamide, polyoxyethylene sorbitan monolaurate, macrogol and ethyl esters of castor oil fatty acids. Examples of the stabilizers include sodium sulfite, sodium metasulfite and ethers. Examples of the preservatives include methyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, sorbic acid, phenol, cresol and chlorocresol.

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, IT, LI, NL, SE A polypeptide having the formula (I) wherein R¹ and R² can be the same or different and each is selected from hydrogen, lower alkyl groups having 1 to 6 carbon atoms or lower alkenyl groups having 2 to 6 carbon atoms, A is selected from D-Met, D-Ser or D-Thr, C is selected from L-Leu, L-Ile, L-Nle, L-tert.Leu, L-Met, L-Met(O), L-Ser or L-Val, D and E can be the same or different and each is selected from L-Arg, L-Lys, L-homoArg or L-Orn, and F is selected from -OH or -NH₂, or a pharmaceutically acceptable salt of said polypeptide. An analgesic composition comprising, as an active ingredient, a therapeutically effective amount of a polypeptide of the formula (I) of claim 1, or a pharmacologically acceptable salt of said polypeptide, in combination with a pharmacologically acceptable vehicle. The use of the polypeptides according to claim 1 for the preparation of a pharmaceutical composition useful as analgesic. Claims for the following Contracting State : AT A process for preparing a polypeptide having the formula (I) wherein R¹ and R² can be the same or different and each is selected from hydrogen, lower alkyl groups having 1 to 6 carbon atoms or lower alkenyl groups having 2 to 6 carbon atoms, A is selected from D-Met, D-Ser or D-Thr, C is selected from L-Leu, L-Ile, L-Nle, L-tert.Leu, L-Met, L-Met(O), L-Ser or L-Val, D and E can be the same or different and each is selected from L-Arg, L-Lys, L-homoArg or L-Orn, and F is selected from -OH or -NH₂, or a pharmaceutically acceptable salt of said polypeptide which comprises forming a polypeptide having a structure of the above formula but in which reactive groups are protected by protective groups, then removing the protective groups to obtain a polypeptide of the above formula. A process for preparing an analgesic composition characterized in that, as an active ingredient, a therapeutically effective amount of a polypeptide of the formula (I), wherein R¹ and R² can be the same or different and each is selected from hydrogen, lower alkyl groups having 1 to 6 carbon atoms or lower alkenyl groups having 2 to 6 carbon atoms, A is selected from D-Met, D-Ser or D-Thr, C is selected from L-Leu, L-Ile, L-Nle, L-tert.Leu, L-Met, L-Met(O), L-Ser or L-Val, D and E can be the same or different and each is selected from L-Arg, L-Lys, L-homoArg or L-Orn, and F is selected from -OH or -NH₂, or a pharmaceutically acceptable salt of said polypeptide, is combined with a pharmacologically acceptable vehicle. The use of the polypeptides obtained by the process according to claim 1 for the preparation of a pharmaceutical composition useful as analgesic.

Inventors: ARAKAWA YOSHIHIRO, ARAKI SHIN, IKEDA MASUHIRO, KANEKO TAKERU, NAKAZAWA TAKAHIRO, TACHIBANA SHINRO, TSUCHIYA YUTAKA, YAMATSU KIYOMI, YOSHINO HIROSHI, ARAKAWA, YOSHIHIRO, ARAKI, SHIN, IKEDA, MASUHIRO, KANEKO, TAKERU, NAKAZAWA, TAKAHIRO, TACHIBANA, SHINRO, TSUCHIYA, YUTAKA, YAMATSU, KIYOMI, YOSHINO, HIROSHI
Applicants: EISAI CO LTD, EISAI CO., LTD.
Application year: 1985
Main classification: C07K14
IPC codes: C07K7, C07K1, C07K14, A61K38, A61P25