Novel peptide derivatives and their pharmaceutical use

Abstract: Peptide derivatives of the following formula wherein R¹ and R² are the same or different and respectively mean hydrogen atom, a C₁₋₅ alkyl group or phenyl, X is -NH-or -CH₂-, Y is hydrogen atom, a benzyl group wherein phenyl may be substituted by hydroxyl, or a C₁₋₅ alkyl group which may be substituted by -SH, -SR³, -SO₂R³, -CONH₂, -OR⁶ or (wherein R³ means a C₁₋₅ alkyl group or an aryl group, R⁴ and R⁵ are the same or different and respectively mean hydrogen atom, a C₁₋₅ alkyl group or an amino protecting group and R⁶ is hydrogen atom, a C₁₋₅ alkyl group or a hydroxyl protecting group), Z is -CH₂- or -S-, and n is 1 or 2, provided that when X is -NH-, R¹ and R² are not hydrogen atoms at the same time, pharmaceutically acceptable acid addition salts thereof and pharmaceutical use thereof. Since the compounds of the present invention possess stronger actions on central nervous system, they are of use as a therapeutic medicament for central nervous disorders.

Description: BACKGROUND OF THE INVENTION This invention relates to peptide derivatives of the following formula [I] and pharmaceutically acceptable acid addition salts thereof which exhibit more potent stimulant activities in central nerve system such as an antagonistic action against hypothermia, a locomoter stimulant action, a spinal reflex stimulant action, etc., as compared with other pharmaceuticals, particularly thyrotropin releasing hormone (TRH) and its derivatives, and thus are useful as a therapeutic medicament for central nervous disorders: wherein R¹ and R² are the same or different and respectively mean a hydrogen atom, a C₁₋₅ alkyl group or a phenyl group, X is -NH- or -CH₂-, Y is a hydrogen atom, a benzyl group wherein phenyl may be substituted by hydroxyl, or a C₁₋₅ alkyl group which may be substituted by -SH, -SR³, -SO₂R³, -CONH₂, -OR⁶ or (wherein R³ means a C₁₋₅ alkyl group or an aryl group, R⁴ and R⁵ are the same or different and respectively mean a hydrogen atom, a C₁₋₅ alkyl group or an amino protecting group and R⁶ is a hydrogen atom, a C₁₋₅ alkyl group or a hydroxyl protecting group), and Z is -CH₂- or -S-, provided that when X is -NH-, R¹ and R² are not hydrogen atoms at the same time. TRH is a tripeptide (L-pyroglutamyl-L-histidyl-L-prolinamide; pGlu-His-Pro-NH₂) synthesized in cerebral hypothalamus. TRH is known to have thyroid stimulating hormone (TSH)-releasing activity and is also known to be useful as a therapeutic medicine for disturbance of consciousness caused by cerebral function disturbances. However, TRH has defects such that it is poorly stable in vivo, easily decomposed by pyroglutamylpeptidase, TRH amidase and other enzymes [Progress of Medicines (Igaku no Ayumi), vol. 134, No. 4, p. 252] and deactivated in a short period, necessitating frequent administration when used, which results in excessive secretion of TSH. For the improvement of the above-mentioned defects of TRH, studies from various aspects have been conducted for TRH derivatives which on the one hand reduce TSH secretion-inducing action as the side effect and on the other hand possess more potent central nerve-stimulant actions such as an antihypnotic action, an anti-reserpine action (antagonistic action against hypothermia), a locomoter stimulant action, a spinal reflex stimulant action, a dopamine potentiating action and an anesthesia antagonism, and have more excellent durability in action than TRH. For example, there have been knowm TRH derivatives in which the pGlu-moiety of TRH is converted into a heterocyclic group such as or the like. Also, TRH derivatives wherein the His moiety is converted to leucine (Leu) have been reported in US 4299821 and others. Inventors of the present invention previously invented TRH derivatives wherein the pGlu-moiety was converted. As a result of further intensive studies on TRH derivatives, the inventors have found that the TRH derivatives obtained by converting the pGlu-L-His-moiety overcome the defects of TRH, and possess more potent stimulant actions on central nervous system and longer durability than other known TRH derivatives, which resulted in completion of the invention. SUMMARY OF THE INVENTION The object of the present invention is to provide novel peptide derivatives and pharmaceutically acceptable acid addtion salts thereof which are obtained by converting the pGlu-L-His-moiety of TRH into a structure of the following formula [II] wherein n, R¹, R², X and Y are as defined above, and have marked characteristic feature in terms of chemical structure. According to the present invention, the novel peptide derivatives and pharmaceutically acceptable acid addition salts thereof are represented by the following formula [I]: wherein R¹ and R² are the same or different and respectively mean a hydrogen atom, a C₁₋₅ alkyl group or a phenyl group, X is -NH- or -CH₂-, Y is a hydrogen atom, a benzyl group wherein phenyl may be substituted by hydroxyl, or a C₁₋₅ alkyl group which may be substituted by -SH, -SR³, -SO₂R³, -CONH₂, -OR⁶ or (wherein R³ means a C₁₋₅ alkyl group or an aryl group, R⁴ and R⁵ are the same or different and respectively mean a hydrogen atom, a C₁₋₅ alkyl group or an amino protecting group and R⁶ is a hydrogen atom, a C₁₋₅ alkyl group or a hydroxyl protecting group), and Z is -CH₂- or -S-, provided that when X is -NH-, R¹ and R² are not hydrogen atoms at the same time. DETAILED DESCRIPTION OF THE INVENTION In the present specification, the C₁₋₅ alkyl group means a straight or branched carbon-chain having, preferably, one through four carbon atoms, which is exemplified by methyl group, ethyl group, propyl group, butyl group, isopropyl group, and sec-butyl group. The aryl group means, for example, phenyl, and tolyl, the amino protecting group means, for example, acetyl, benzoyl, benzyl, tosyl, benzyloxycarbonyl, tert-butoxycarbonyl, and 2,4-dinitrophenyl, and the hydroxyl protecting group means, for example, benzyl, acetyl, and benzoyl. The objective compounds [I] of this invention are capable of forming pharmaceutically acceptable salts thereof with an acid. Examples of the acid include inorganic acids such as hydrochloric acid and sulfuric acid or organic acids such as citric acid, acetic acid and tartaric acid. These salts are also encompassed in the present invention. The objective compounds [I] of the present invention have at least three asymmetric carbons, and there exist stereoisomers based on such asymmetric carbons. The objective compounds of the present invention include respective isolated stereoisomers and the mixtures of the stereoisomers. According to the present invention, the objective compounds [I] or their acid addition salts can be produced by the following methods: (A) a condensing compound of the formula [III] wherein R¹ and R² are as defined above and X¹ is imino group, a protected imino group or methylene group, or its reactive derivative with a compound of the formula [IV] wherein Y and Z are as defined above, or its salt; (B) condensing a compound of the formula [V] wherein R¹, R², X¹ and Y are as defined above, its salt or its reactive derivative with an amino acid amide of the formula [VI] wherein Z is as defined above, or its salt; or (C) subjecting a compound of the formula [VII] wherein R¹, R², X¹, Y and Z are as defined above, its salt or its reactive derivative to amidation, and (D) thereafter, when X¹ in the product thus obtained by the above step (A), (B) or (C) is a protected imino group, removing the protective group ; and (E) whereafter if desired, converting the thus-obtained product into an acid addition salt thereof, to yield the objective compound. The starting compounds [IV] - [VII] of the present invention can be subjected to the respective reaction either in the form of free base or in the form of salt. The salt can be preferably used in the form of acid addition salt, and as such acid addition salt, use can be made of, for example, an inorganic acid addition salt such as hydrochloride or hydrobromide, or an organic acid addition salt such as trifluoroacetate or p-toluenesulfonate. As the reactive derivative of the compounds [III], [V] and [VII], use can be made of an active ester (e.g. N-hydroxysuccinimido ester, pentachlorophenyl ester, N-hydroxybenzotriazole ester), an acid halide (e.g. acid chloride), an acid azide, an acid anhydride and an imidazolamide, corresponding to the respective compounds. The active ester may be subjected to peptide-synthesizing reaction after isolated or without being isolated. As the reactive derivative of the compound [VII], use can be preferably made of, for example, an ester (an alkyl ester such as ethyl ester or methyl ester; or an aralkyl ester such as benzyl ester). When the group X¹ in the above-mentioned starting compounds [III], [V] and [VII] is a protected imino group, use can be made of any protective group conventionally used in peptide synthesis as the protective group of the imino group. Examples of the suitable protective group include benzyloxycarbonyl group, benzyl group, tosyl group, tert-butoxycarbonyl group and 2,4-dinitrophenyl group. [Reaction Steps (A) and (B)] Both of the condensation reaction of a compound [III] or a reactive derivative thereof with a compound [IV] or a salt thereof and the condensation reaction of a compound [V] or a salt thereof or a reactive derivative thereof with a compound [VI] or a salt thereof, which are peptide synthetic reactions, can be carried out by a conventional means. For example, the condensation reaction of a compound [III] with a compound [IV] or a salt thereof and that of a compound [V] or a salt thereof with a compound [VI] or a salt thereof can be carried out in a suitable solvent in the presence of a condensing agent. Examples of the suitable condensing agent include dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, phosphorus oxychloride, phosphorus trichloride, thionyl chloride, oxalyl chloride, triphenylphosphine and Vilsmeier Reagent. The condensation reaction is carried out preferably at -50 - 50°C. When a salt of a compound [IV] is used, the reaction is conducted in the presence of a deacidifying agent. On the other hand, the condensation reaction of a reactive derivative of a compound [III] with a compound [IV] or a salt thereof and that of a reactive derivative of a compound [V] with a compound [VI] or a salt thereof can be carried out in a suitable solvent in the presence or absence of a deacidifying agent. As the deacidifying agent, mention can be made of, for example, trialkylamines (triethylamine and trimethylamine), N,N-dialkylanilines (N,N-dimethylaniline and, N,N-diethylaniline), pyridine, N-alkylmorpholines (N-methylmorpholine), alkali metal hydroxides (potassium hydroxide and sodium hydroxide), alkali metal carbonates (potassium carbonate) and alkali metal hydrogencarbonates (sodium hydrogencarbonate). This condensation reaction can be suitably carried out at -50 - 50°C, particularly -10 - 10°C. As the solvent for the condensation reaction usable in the reaction steps (A) and (B), use can be made of, for example, N,N-dimethylformamide, dichloromethane, dioxane, tetrahydrofuran, acetonitrile, ethyl acetate, pyridine, acetone and water. [Reaction Step (C)] The amidation reaction of a compound [VII], a salt thereof or a reactive derivative thereof can be carried out by reacting the compound with ammonia or an ammonia-donating compound. For example, the amidation reaction of a compound [VII] or a salt thereof with ammonia or an ammonia-donating compound can be preferably carried out in the presence of a dehydrating agent in a suitable solvent. As the dehydrating agent, use can be made of, for example, any compound mentioned above as the suitable condensing agent. As the ammonia-donating compound, use can be made of any compound capable of releasing ammonia in the reaction mixture, which is exemplified by ammonium chloride and ammonium carbonate. The amidation reaction is preferably carried out at -20°C - 20°C. As the suitable solvent, mention can be made of, for example, N,N-dimethylformamide, dimethylsulfoxide and tetrahydrofuran. Furthermore, the amidation reaction of a reactive derivative of a compound [VII] or a salt thereof with ammonia or an ammonia-donating compound can be carried out in the presence or absence of a deacidifying agent in a suitable solvent. As the deacidifying agent, use can be made of any of the deacidifying agents mentioned in the description of the above reaction steps (A) and (B). The amidation reaction is preferably carried out at -20°C - 20°C. As the suitable solvent, mention can be made of methanol, ethanol, N,N-dimethylformamide and dimethylsulfoxide. [Reaction Step D] When X¹ in the compound produced in the above-mentioned reaction step (A), (B) or (C) is a protected imino, the deprotection of the protective group can be carried out easily, depending upon the species of the protective group, in accordance with a conventional method such as catalytic reduction, electrolytic reduction, acid treatment, base treatment or oxidation reaction. [Reaction Step (E)] The thus-obtained objective compound can be, if necessary, converted into an acid addition salt easily by treating with a stoichiometric amount of an acid in accordance with a conventional method. In the above-mentioned reactions, the staring compounds [III] - [VII], the intermediate products and the objective compounds contain 1-4 asymmetric carbon atom(s), and the above methods of the present invention can be carried out using the respective optically active isomers of the starting compounds [III] - [VII] or their respective mixture. Since the above-mentioned reactions of the present invention can be carried out without involving racemization, the intermediate products and the objective compounds can be obtained in the form of the corresponding optically active isomer when the respective optically active isomers of the starting compounds [III] - [VII] are used. The objective compounds [I] and pharmaceutically acceptable acid addition salts thereof can be administered orally or nonorally as they are or in the form of, for example, powders, granules, tablets, capsules, injections (intravenous, subcutaneous, intramuscular) or suppositories suitably in admixture with pharmacologically acceptable carriers, excipients and diluents. While the dosage of the objective compounds [I] or their pharmaceutically acceptable acid addition salts of the present invention varies depending on the administration route, the age, body weight or symptom of the patient, generally it is preferably 0.5 µg - 5 mg/kg/day. Particularly, in the case of oral administration, the dosage is preferably 10 µg - 5 mg/kg/day and in the case of parenteral administration (e.g. intravenous administration, intramuscular administration, subcutaneous administration), the dosage is preferably 1 - 1000 µg/kg/day. Since the compounds [I] or their pharmaceutically acceptable acid addition salts of the present invention possess more potent actions on central nervous system (e.g. antagonistic action against hypothermia, locomotor stimulant action, spinal reflex stimulant action), they are of use as a therapeutic medicament for central nervous disorders such as impaired consciousness, depression and hypomnesia, in association with schizophrenia, melancholia, senile dementia, sequelae of cerebrovascular disorders, head trauma, epilepsy, and spinocerebellar degeneracy. Below, the present invention is in further detail described by illustrating reference examples and working examples. The abbreviations used in the examples stand for the following meanings respectively. NMR nuclear magnetic resonance spectra (¹H-NMR) CIMS chemical ionization mass spectra DMF N,N-dimethylformamide HOBT 1-hydroxy-1,2,3-benzotriazole DCC 1,3-dicyclohexylcarbodiimide Hydrobromide of dipeptide of the formula [IV] which is used in the present invention was synthesized by the method of T. Szirtes et al [T. Szirtes et al, J. Med. Chem. , 27 , 741 (1984)]. Example 1 N-( cis -3-Methylpyroglutamyl)-L-leucyl-L-prolinamide (Compound 1A and 1B) L-Leucyl-L-prolinamide hydrobromide (517 mg) was dissolved in DMF (1.5 ml), to which was added triethylamine (0.35 ml) under cooling at -10°C. The mixture was stirred for 10 minutes under ice-cooling and the resultant precipitate was filtered off to give L-leucyl-L-prolinamide in DMF solution, which was immediately used for the next reaction. cis -3-Methylpyroglutamic acid [A. B. Mauger, J. Org. Chem. , 46 , 1032 (1981)] (200 mg) was dissolved in DMF (1.5 ml), to which was added HOBT (257 mg), followed by cooling to 0°C. DCC (317 mg) was added thereto and the mixture was stirred at 0°C overnight. To the mixture was added the above-mentioned L-leucyl-L-prolinamide in DMF, and the mixture was stirred at 5°C overnight. The resultant precipitate was filtered off and concentrated to dryness under reduced pressure. The residue was washed with water and purified by HP-20 column chromatography (1.0x40cm) with methanol as eluent. The eluted fraction was concentrated to dryness under reduced pressure, and the residue obtained was purified by silica gel column chromatography (developing solvent: chloroform:methanol:ammonia water=60:10:1) to give the title less polar compound 1A (188 mg) and the more polar compound 1B (177 mg) as powders. The compounds 1A and 1B have diastereomeric relationship to each other. Compound 1A NMR (CD₃OD) δppm: 0.90 - 1.10 (9H, m), 1.55 - 1.82 (3H, m), 1.89 - 2.29 (5H, m), 2.35 - 2.44 (1H, m), 2.72 - 2.88 (1H, m), 3.61 - 3.71 (1H, m), 3.86 - 3.98 (1H, m), 4.19 (1H, d), 4.35 - 4.45 (1H, m), 4.59 - 4.68 (1H, m) CIMS m/z: 353(M+1)⁺ Compound 1B NMR (CD₃OD) δ ppm: 0.90 - 1.10 (9H, m), 1.55 - 1.84 (3H, m), 1.55 - 1.84 (3H, m), 1.85 - 2.29 (5H, m), 2.30 - 2.44 (1H, m), 2.72 - 2.90 (1H, m), 3.61 - 3.72 (1H, m), 3.85 - 3.95 (1H, m), 4.15 (1H, d), 4.43 - 4.53 (1H, m), 4.60 - 4.69 (1H, m) Example 2 N-( cis -3-Methylpyroglutamyl)-L-methionyl-L-prolinamide (Compound 2A and 2B) In the same manner as in Example 1, the title less polar compound 2A (140 mg) and the more polar compound 2B (150 mg) were obtained each as a powder from L-methionyl-L-prolinamide hydrobromide (685 mg) and cis -3-methylpyroglutamic acid (300 mg). The compounds 2A and 2B have diastereomeric relationship to each other. Compound 2A NMR (CD₃OD) δ ppm: 1.00 (3H, d, J=7.0Hz), 1.86 - 2.30 (10H, m), 2.39 (1H, d, J=8.5Hz and 16.5Hz), 2.51 - 2.72 (2H, m), 2.73 - 2.88 (1H, m), 3.69 - 3.80 (1H, m), 3.90 - 3.99 (1H, m), 4.18 (1H, d, J=8.0Hz), 4.40 (1H, dd, J=4.8Hz and 8.3Hz) CIMS m/z: 371 (M+1)⁺ Compound 2B NMR (CD₃OD) δ ppm: 1.05 (3H, d, J=7.0Hz), 1.86 - 2.26 (10H, m), 2.37 (1H, d, J=8.5Hz and 16.5Hz), 2.52 - 2.72 (2H, m), 2.73 - 2.86 (1H, m), 3.68 - 3.70 (1H, m), 3.86 - 3.96 (1H, m), 4.15 (1H, d, J=8.1Hz), 4.41 (1H, dd, J=4.8Hz and 8.2Hz), 4.82 (1H, dd, J=5.2Hz and 8.9Hz) Example 3 N-( cis -3-Methylpyroglutamyl)-L-norvalyl-L-prolinamide (Compound 3A and 3B) In the same manner as in Example 1, the title less polar compound 3A (250 mg) and the more polar compound 3B (241 mg) were obtained each as a powder from L-norvalyl-L-prolinamide hydrobromide (618 mg) and cis -3-methylpyroglutamic acid (300 mg). The compounds 3A and 3B have diastereomeric relationship to each other. Compound 3A NMR (CD₃OD) δppm: 0.89 - 1.10 (6H, m), 1.35 - 1.55 (2H, m), 1.55 - 1.74 (1H, m), 1.74 - 2.29 (6H, m), 2.38 (1H, dd, J=8.5Hz and 16.4Hz), 2.71 - 2.88 (1H, m), 3.60 - 3.72 (1H, m), 3.85 - 3.97 (1H, m), 4.19 (1H, d, J=8.0Hz), 4.39 (1H, dd, J=4.7Hz and 8.2Hz), 4.64 (1H, dd, J=5.2Hz and 8.9Hz) CIMS m/z: 339(M+1)⁺ Compound 3B NMR (CD₃OD) δppm: 0.97 (3H, t, J=7.3Hz), 1.05 (3H, d, J=7.0Hz), 1.35 - 1.60 (2H, m), 1.60 - 1.73 (1H, m), 1.73 - 2.30 (6H, m), 2.35 (1H, dd, J=8.5Hz and 16.5Hz), 2.71 - 2.86 (1H, m), 3.61 - 3.72 (1H, m), 3.82 - 3.93 (1H, m), 4.16 (1H, d, J=8.1Hz), 4.39 (1H, dd, J=4.7Hz and 8.2Hz), 4.57 (1H, dd, J=4.9Hz and 9.1Hz) Example 4 N-( cis -3-Methylpyroglutamyl)-L-phenylalanyl-L-prolinamide (Compound 4A and 4B) In the same manner as in Example 1, the title less polar compound 4A (250 mg) and the more polar compound 4B (150 mg) were obtained each as a powder from L-phenylalanyl-L-prolinamide hydrobromide (719 mg) and cis -3-methylpyroglutamic acid (300 mg). The compounds 4A and 4B have diastereomeric relationship to each other. Compound 4A NMR (CD₃OD) δ ppm: 0.84 (2.4H, d, J=7.0Hz), 1.01 (0.6H, d, J=7.0Hz), 1.61 - 2.25 (5H, m), 2.33 (1H, dd, J=8.5Hz and 16.6Hz), 2.67 - 2.82 (1H, m), 2.86 - 3.20 (1H, m), 3.15 - 3.25 (1H, m), 3.47 - 3.68 (1H, m), 3.88 - 3.99 (1H, m), 4.11 (0.8H, d, J=8.1Hz), 4.15 (0.2H, d, J=8.0Hz), 4.35 - 4.46 (1H, m), 7.15 - 7.42 (5H, m) CIMS m/z: 387(M+1)⁺ Compound 4B NMR (CD₃OD) δ ppm: 0.57 (2.4H, d, J=7.0Hz), 0.94 (0.6H, d, J=7.0Hz), 1.62 - 2.41 (6H, m), 2.55 - 2.72 (1H, m), 2.81 - 3.03 (1H, m), 3.16 - 3.28 (1H, m), 3.58 - 3.77 (1H, m), 3.85 - 3.97 (1H, m), 4.08 (0.8H, d, J=8.0Hz), 4.16 (0.2H, d, J=8.0Hz), 4.35 - 4.45 (1H, m), 7.15 - 7.45 (5H, m) Example 5 N-( cis -3-Methylpyroglutamyl)-L-norleucyl-L-prolinamide (Compound 5A and 5B) In the same manner as in Example 1, the title less polar compound 5A (220 mg) and the more polar compound 5B (160 mg) were obtained each as a powder from L-norleucyl-L-prolinamide hydrobromide (647 mg) and cis -3-methylpyroglutamic acid (300 mg). The compounds 5A and 5B have diastereomeric relationship to each other. Compound 5A NMR (CD₃OD) δppm: 0.82 - 1.13 (6H, m), 1.25 - 1.55 (4H, m), 1.58- 1.77 (1H, m), 1.77 - 2.31 (6H, m), 2.38 (1H, dd, J=8.5Hz and 16.5Hz), 2.70 - 2.90 (1H, m), 3.57 - 3.72 (1H, m), 3.83 - 3.99 (1H, m), 4.19 (1H, d, J=8.0Hz), 4.39 (1H, dd, J=4.7Hz and 8.2Hz), 4.62 (1H, dd, J=5.1Hz and 9.0Hz) CIMS m/z: 353(M+1)⁺ Compound 5B NMR (CD₃OD) δppm: 0.94 (3H, t, J=6.9Hz and 7.1Hz), 1.05 (3H, d, J=7.0Hz), 1.29 - 1.55 (4H, m), 1.55 - 1.76 (1H, m), 1.76 - 2.31 (6H, m), 2.35 (1H, dd, J=8.5Hz and 16.5Hz), 2.69 - 2.89 (1H, m), 3.57 - 3.74 (1H, m), 3.80 - 3.96 (1H, m), 4.16 (1H, d, J=8.1Hz), 4.39 (1H, dd, J=4.7Hz and 8.2Hz), 4.56 (1H, dd, J=4.9Hz and 9.2Hz) Example 6 N-(3,3-Dimethylpyroglutamyl)-L-leucyl-L-prolinamide (Compound 6A and 6B) In the same manner as in Example 1, the title less polar compound 6A (85 mg) and the more polar compound 6B (63 mg) were obtained each as a powder from L-leucyl-L-prolinamide hydrobromide (432 mg) and 3,3-dimethylpyroglutamic acid [T. Yamazaki et al, Chem. Pharm. Bull. , 24 , 3011 (1976)] (200 mg). The compounds 6A and 6B have diastereomeric relationship to each other. Compound 6A NMR (CD₃OD) δppm: 0.96 (3H, d, J=6.0Hz), 0.98 (3H, d, J=6.0Hz), 1.02 (3H, s), 1.26 (3H, s), 1.60 - 1.70 (2H, m), 1.70 - 1.80 (1H, m), 1.90 - 2.30 (4H, m), 2.04 (1H, d, J=16.5Hz), 2.30 (1H, d, J=16.5Hz), 3.60 - 3.70 (1H, m), 3.83 (1H, s), 3.87 - 3.98 (1H, m), 4.39 (1H, dd, J=8.0Hz and 4.5Hz), 4.7 (21H, dd, J=9.0Hz and 5.0Hz) CIMS m/z: 367(M+1)⁺ Compound 6B NMR (CD₃OD) δppm: 0.96 (3H, d, J=6.5Hz), 0.99 (3H, d, J=6.5Hz), 1.08 (3H, s), 1.26 (3H, s), 1.55 - 1.70 (2H, m), 1.70 - 1.85 (1H, m), 1.85 - 2.30 (4H, m), 2.02 (1H, d, J=16.5Hz), 2.36 (1H, d, J=16.5Hz), 3.60 - 3.70 (1H, m), 3.80 (1H, s), 3.83 - 3.95 (1H, m), 4.39 (1H, dd, J=8.0Hz and 5.5Hz), 4.63 (1H, dd, J=10.0Hz and 4.5Hz) Example 7 N-(3,3-Dimethylpyroglutamyl)-L-norvalyl-L-prolinamide (Compound 7A and 7B) In the same manner as in Example 1, the title less polar compound 7A (215 mg) and the more polar compound 7B (175 mg) were obtained each as a powder from L-norvalyl-L-prolinamide hydrobromide (702 mg) and 3,3-dimethylpyroglutamic acid (250 mg). The compounds 7A and 7B have diastereomeric relationship to each other. Compound 7A NMR (CD₃OD) δ ppm: 0.96 (3H, t, J=7.0Hz), 1.02 (3H, s), 1.25 (3H, s), 1.35 - 1.55 (2H, m), 1.55 - 1.75 (1H, m), 1.75 - 1.90 (1H, m), 1.90 - 2.30 (4H, m), 2.04 (1H, d, J=16.5Hz), 2.30 (1H, d, J=16.5Hz), 3.60 - 3.70 (1H, m), 3.83 (1H, s), 3.85 - 3.95 (1H, m), 4.40 (1H, dd, J=8.0Hz and 4.0Hz), 4.64 (1H, dd, J=8.0Hz and 4.0Hz) CIMS m/z: 353(M+1)⁺ Compound 7B NMR (CD₃OD) δ ppm: 0.97 (3H, t, J=7.0Hz), 1.08 (3H, s), 1.26 (3H, s), 1.40 - 1.60 (2H, m), 1.60 - 1.75 (1H, m), 1.75 - 1.90 (1H, m), 1.90 - 2.30 (4H, m), 2.02 (1H, d, J=16.5Hz), 2.35 (1H, d, J=16.5Hz), 3.60 - 3.70 (1H, m), 3.80 (1H, s), 4.41 (1H, dd, J=7.5Hz and 4.0Hz), 4.57 (1H, dd, J=8.0Hz and 4.0Hz) Example 8 N-(3,3-Dimethylpyroglutamyl)-L-methionyl-L-prolinamide (Compound 8A and 8B) In the same manner as in Example 1, the title less polar compound 8A (212 mg) and the more polar compound 8B (195 mg) were obtained each as a powder from L-methionyl-L-prolinamide hydrobromide (778 mg) and 3,3-dimethylpyroglutamic acid (250 mg). The compounds 8A and 8B have diastereomeric relationship to each other. Compound 8A NMR (CD₃OD) δ ppm: 1.03 (3H, s), 1.26 (3H, s), 1.85 - 2.30 (6H, m), 2.04 (1H, d, J=16.5Hz), 2.11 (3H, s), 2.30 (1H, d, J=16.5Hz), 2.50 - 2.70 (2H, m), 3.70 - 3.80 (1H, m), 3.82 (1H, s), 3.90 - 4.00 (lH, m), 4.39 (1H, dd, J=8.0Hz and 4.5Hz) CIMS m/z: 385(M+1)⁺ Compound 8B NMR (CD₃OD) δppm: 1.08 (3H, s), 1.26 (3H, s), 1.85 - 2.30 (6H, m), 2.02 (1H, d, J=16.5Hz), 2.11 (3H, s), 2.36 (1H, d, J=16.5Hz), 2.55 - 2.75 (2H, m), 3.70 - 3.80 (1H, m), 3.79 (1H, s), 3.90 - 4.00 (1H, m), 4.40 (1H, dd, J=8.0Hz and 4.5Hz), 4.81 (1H, dd, J=9.0Hz and 5.0Hz) Example 9 N-(3,3-Dimethylpyroglutamyl)-L-phenylalanyl-L-prolinamide (Compound 9A and 9B) In the same manner as in Example 1, the title less polar compound 9A (206 mg) and the more polar compound 9B (140 mg) were obtained each as a powder from L-phenylalanyl-L-prolinamide hydrobromide (654 mg) and 3,3-dimethylpyroglutamic acid (300 mg). The compounds 9A and 9B have diastereomeric relationship to each other. Compound 9A NMR (CD₃OD) δppm: 0.85 (2.3H, s), 1.04 (0.7H, s), 1.21 (2.3H, s), 1.25 (0.7H, s), 1.64 - 2.13 (4H, m), 2.13 - 2.40 (2H, m), 2.91 - 3.15 (1H, m), 3.18 - 3.32 (1H, m), 3.51 - 3.72 (1H, m), 3.74 (0.8H, s), 3.84 (0.2H, s), 3.90 - 4.02 (1H, m), 4.38 - 4.50 (1H, m), 7.20 - 7.42 (5H, m) CIMS m/z: 401 (M+1)⁺ Compound 9B NMR (CD₃OD) δ ppm: 0.61 (2.4H, s), 0.97 (0.6H, s), 1.12 (2.4H, s), 1.23 (0.6H, s), 1.67 - 2.14 (4H, m), 2.14 - 2.42 (2H, m), 2.84 - 3.09 (1H, m), 3.21 - 3.32 (1H, m), 3.61 - 3.72 (1H, m), 3.73 (0.8H, s), 3.80 (0.2H, s), 3.91 - 4.02 (1H, m), 4.38 - 4.50 (1H, m), 7.19 - 7.43 (5H, m) Example 10 N-(3,3-Dimethylpyroglutamyl)-L-norleucyl-L-prolinamide (Compound 10A and 10B) In the same manner as in Example 1, the title less polar compound 10A (175 mg) and the more polar compound 10B (120 mg) were obtained each as a powder from L-norleucyl-L-prolinamide hydrobromide (588 mg) and 3,3-dimethylpyroglutamic acid (300 mg). The compounds 10A and 10B have diastereomeric relationship to each other. Compound 10A NMR (CD₃OD) δ ppm: 0.94 (3H, t, J=6.8Hz), 1.03 (3H, s), 1.07 (3H, s), 1.29 - 1.51 (4H, m), 1.58 - 1.76 (1H, m), 1.76 - 2.26 (6H, m), 2.30 (1H, d, J=16.5Hz), 3.59 - 3.71 (1H, m), 3.83 (1H, s), 3.84 - 3.96 (1H, m), 4.39 (1H, dd, J=4.8Hz and 8.2Hz), 4.62 (1H, dd, J=5.2Hz and 9.0Hz) CIMS m/z: 367(M+1)⁺ Compound 10B NMR (CD₃OD) δ ppm: 0.94 (3H, t, J=6.9Hz and 7.1Hz), 1.08 (3H, s), 1.26 (3H, s), 1.30 - 1.51 (4H, m), 1.59 - 1.77 (1H, m), 1.78 - 2.30 (6H, m), 2.36 (1H, d, J=16.4Hz), 3.58 - 3.72 (1H, m), 3.80 (1H, s), 3.81 - 3.93 (1H, m), 4.38 (1H, dd, J=4.7Hz and 8.1Hz), 4.55 (1H, dd, J=4.8Hz and 9.2Hz) Example 11 N-[(1R)-3-oxocyclopentanecarbonyl]-L-phenylalanyl-L-prolinamide (Compound 11) L-Phenylalanyl-L-prolinamide hydrobromide (480 mg) was dissolved in DMF (3 ml), to which was added triethylamine (0.29 ml) under cooling at -10°C. The mixture was stirred for 10 minutes under ice-cooling and the resultant precipitate was filtered off to give L-phenylalanyl-L-prolinamide in DMF solution, which was immediately used for the next reaction. (1R)-3-Oxocyclopentanecarboxylic acid [K. Toki et al, Bull. Chem. Soc. Jpn. , 31 , 333 (1958)] (150 mg) was dissolved in DMF (2 ml), to which was added HOBT (216 mg), followed by cooling to 0°C. DCC (265 mg) was added thereto and the mixture was stirred at 0°C overnight. To the mixture was added the above-mentioned L-phenylalanyl-L-prolinamide in DMF, and the mixture was stirred at 5°C overnight. The resultant precipitate was filtered off and concentrated to dryness under reduced pressure. The residue was washed with water and purified by HP-20 column chromatography (1.0x40cm) with methanol as eluent. Further, the eluted portion was concentrated to dryness under reduced pressure, and the residue obtained was purified by silica gel column chromatography (developing solvent/ chloroform:methanol:ammonia water=60:10:1) to give the title compound 11 (150 mg) as powders. NMR (CD₃OD) δ ppm: 1.62 - 2.46 (10H, m), 2.81 - 3.27 (3H, m), 3.46 - 3.66 (1H, m), 3.70 - 3.91 (1H, m), 4.40 - 4.51 (1H, m), 7.15 - 7.42 (5H, m) CIMS m/z: 372(M+1)⁺ Example 12 N-[(1R)-3-Oxocyclopentanecarbonyl]-L-leucyl-L-prolinamide (Compound 12) In the same manner as in Example 11, the title compound 12 (280 mg) was obtained as a powder from L-leucyl-L-prolinamide hydrobromide (675 mg) and (1R)-3-oxocyclopentanecarboxylic acid (200 mg). NMR (CD₃OD) δ ppm: 0.85 - 1.04 (6H, m), 1.53 - 1.82 (3H, m), 1.85 - 2.45 (10H, m), 3.04 - 3.20 (1H, m), 3.55 - 3.72 (1H, m), 3.76 - 3.92 (1H, m), 4.33 - 4.48 (1H, m), 4.55 - 4.70 (1H, m) CIMS m/z: 338(M+1)⁺ Example 13 N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-methionyl-L-prolinamide (Compound 13A and 13B) In the same manner as in Example 1, the title less polar compound 13A (152 mg) and a small amount of the more polar compound 13B were obtained as powders from L-methionyl-L-prolinamide hydrobromide (385 mg) and cis -2-methyl-4-oxocyclopentanecarboxylic acid [K. Kojima et al, Chem. Pharm. Bull., 33 , 2750 (1985)] (150 mg). The compounds 13A and 13B have diastereomeric relationship to each other. NMR (CD₃OD) δppm: 1.01 (3H, d, J=6.9Hz), 1.83 - 2.50 (13H, m), 2.50 - 2.74 (3H, m), 3.04 - 3.21 (1H, m), 3.67 - 3.81 (1H, m), 3.83 - 4.02 (1H, m), 4.40 (1H, dd, J=4.6Hz and 8.2Hz), 4.78 (1H, dd, J=5.5Hz and 8.5Hz) CIMS m/z: 370(M+1)⁺ Example 14 N-[ cis -(1S,2R)-2-Methyl-4-oxocyclopentanecarbonyl]-L-leucyl-L-prolinamide In the same manner as in Example 11, the title compound (342 mg) was obtained as a powder from L-leucyl-L-prolinamide hydrobromide (477 mg) and cis -(1S,2R)-2-methyl-4-oxocyclopentanecarboxylic acid [Haruta et al, Japanese Patent Application No. 188378/1991] (200 mg). NMR (CD₃OD) δppm: 0.90 -1.15 (9H, m), 1.55 - 1.80 (3H, m), 1.85 -2.50 (8H, m), 2.55 - 2.70 (1H, m), 3.10 - 3.20 (1H, m), 3.55 - 3.70 (1H, m), 3.85 -3.95 (1H, m), 4.35 - 4.45 (1H, m), 4.60 - 4.70 (1H, m) Example 15 N-[ cis -(1S,2R)-2-Methyl-4-oxocyclopentanecarbonyl]-L-phenylalanyl-L-prolinamide In the same manner as in Example 11, the title compound (450 mg) was obtained as a powder from L-phenylalanyl-L-prolinamide hydrobromide (529 mg) and cis -(1S,2R)-2-methyl-4-oxocyclopentanecarboxylic acid (200 mg). NMR (CD₃OD) δppm: 0.99 (2H, d, J=7Hz), 1.09 (2H, d, J=7Hz), 1.60 - 2.50 (8H, m), 2.50 - 2.67 (1H, m), 2.85 - 2.97 (1H, m), 2.97 - 3.10 (1H, m), 3.10 - 3.25 (1H, m), 3.45 - 3.57 (1H, m), 3.80 - 3.93 (1H, m), 4.35 - 4.45 (1H, m), 7.15 - 7.35 (5H, m) Example 16 N-[ cis -(1S,2R)-2-Methyl-4-oxocyclopentanecarbonyl]-L-norvalyl-L-prolinamide In the same manner as in Example 11, the title compound (345 mg) was obtained as a powder from L-norvalyl-L-prolinamide hydrobromide (400 mg) and cis -(1S,2R)-2-methyl-4-oxocyclopentanecarboxylic acid (200 mg). NMR (CD₃OD) δ ppm: 0.90 -1.15 (6H, m), 1.40 - 2.50 (12H, m), 2.55 - 2.70 (1H, m), 3.10 - 3.20 (1H, m), 3.60 - 3.70 (1H, m), 3.85 - 3.95 (1H, m), 4.35 -4.50 (1H, m), 4.50 - 4.65 (1H, m) Example 17 N-[ cis -(1S,2R)-2-Methyl-4-oxocyclopentanecarbonyl]-L-norleucyl-L-prolinamide In the same manner as in Example 11, the title compound (227 mg) was obtained as a powder from L-norleucyl-L-prolinamide hydrobromide (477 mg) and cis -(1S,2R)-2-methyl-4-oxocyclopentanecarboxylic acid (200 mg). NMR (CD₃OD) δ ppm: 0.90 -1.15 (6H, m), 1.25 - 2.50 (14H, m), 2.56 - 2.70 (1H, m), 3.10 - 3.20 (1H, m), 3.60 - 3.70 (1H, m), 3.85 - 3.95 (1H, m), 4.35 - 4.50 (1H, m), 4.50 - 4.60 (1H, m) Example 18 N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-phenylalanyl-L-prolinamide In the same manner as in Example 11, the title less polar compound 18A (38 mg) and the more polar compound 18B (38 mg) were obtained from L-phenylalanyl-L-prolinamide hydrobromide (99 mg) and 2,2-dimethyl-4-oxocyclopentanecarboxylic acid [W. H. Perkin, jun. and J. F. Thorpe, J. Chem. Soc. , 79 , 729 (1901)] (45 mg). The compounds 18A and 18B have diastereomeric relationship to each other. Compound 18A NMR (CD₃OD) δppm: 0.98 (2.4H, s), 1.07 (0.6H, s), 1.18 (2.4H, s), 1.23 (0.6H, s), 1.60 - 2.50 (8H, m), 2.72 - 2.85 (1H, m), 2.85 - 3.10 (1H, m), 3.10 - 3.25 (1H, m), 3.45 -3.55 (1H, m), 3.82 - 3.95 (1H, m), 4.35 - 4.45 (1H, m), 7.15 - 7.40 (5H, m) Compound 18B NMR (CD₃OD) δppm: 0.66 (2.4H, s), 0.97 (0.6H, s), 1.00 (2.4H, s), 1.16 (0.6H, s), 1.60 - 2.10 (4H, m), 2.10 - 2.50 (4H, m), 2.72 - 2.80 (1H, m), 2.80 - 2.95 (1H, m), 3.20 - 3.30 (1H, m), 3.60 - 3.70 (1H, m), 3.85 - 3.95 (1H, m), 4.31 - 4.45 (1H, m), 7.15 - 7.40 (5H, m) Example 19 N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-leucyl-L-prolinamide In the same manner as in Example 11, the title less polar compound 19A (50 mg) and the more polar compound 19B (50 mg ) were obtained from L-leucyl-L-prolinamide hydrobromide (99 mg) and 2,2-dimethyl-4-oxocyclopentanecarboxylic acid (45 mg). The compounds 19A and 19B have diastereomeric relationship to each other. Compound 19A NMR (CD₃OD) δ ppm: 0.95 (3H, d, J=6.5Hz), 0.98 (3H, d, J=6.5Hz), 1.01 (3H, s), 1.22 (3H, s), 1.55 -1.80 (3H, m), 1.90 -2.40 (6H, m), 2.45 - 2.55 (2H, m), 2.82 - 2.90 (1H, m), 3.57 -3.67 (1H, m), 3.82 - 3.97 (1H, m), 4.35 - 4.45 (1H, m), 4.60 - 4.73 (1H, m) Compound 19B NMR (CD₃OD) δ ppm: 0.97 (3H, d, J=6.5Hz), 1.00 (3H, d, J=6.5Hz), 1.07 (3H, s), 1.21 (3H, s), 1.50 -1.70 (2H, m), 1.70 - 1.87 (1H, m), 1.87 -2.30 (5H, m), 2.33 (1H, d, J=18Hz), 2.47 (2H, d, J=6.5Hz), 2.86 (1H, t, J=6.5Hz), 3.55 -3.70 (1H, m), 3.80 - 3.90 (1H, m), 4.35 - 4.45 (1H, m), 4.62 (1H, dd, J=10.5Hz, 4.2Hz) Example 20 N-[(1R)-3-Oxocyclopentanecarbonyl]-L-norvalyl-L-prolinamide In the same manner as in Example 11, the title compound (322 mg) was obtained as a powder from L-norvalyl-L-prolinamide hydrobromide (379 mg) and (1R)-3-oxocyclopentanecarboxylic acid (150 mg). NMR (CD₃OD) δ ppm: 0.96 (3H, t, J=7.2Hz), 1.30 - 1.50 (2H, m), 1.50 - 2.40 (12H, m), 3.05 - 3.20 (1H, m), 3.60 - 3.70 (1H, m), 3.78 - 3.90 (1H, m), 4.41 (1H, dd, J=8.2Hz, 4.6Hz), 4.56 (1H, dd, J=9.1Hz, 4.9Hz) Example 21 N-[(1R)-3-Oxocyclopentanecarbonyl]-L-norleucyl-L-prolinamide In the same manner as in Example 11, the title compound (243 mg) was obtained as a powder from L-norleucyl-L-prolinamide hydrobromide (397 mg) and (1R)-3-oxocyclopentanecarboxylic acid (150 mg). NMR (CD₃OD) δ ppm: 0.94 (3H, t, J=7Hz), 1.25 - 1.50 (4H, m), 1.50 - 2.40 (12H, m), 3.05 - 3.20 (1H, m), 3.57 - 3.70 (1H, m), 3.80 - 3.90 (1H, m), 4.41 (1H, dd, J=8.0Hz, 4.5Hz), 4.54 (1H, dd, J=9.0Hz, 4.8Hz) Needless to say, the present invention is not limited to these examples, and, for example, the following compounds are also encompassed in the present invention. 22. N-(3-Oxocyclopentanecarbonyl)-L-tyrosyl-L-prolinamide 23. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-tyrosyl-L-prolinamide 24. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-tyrosyl-L-prolinamide 25. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-isoleucyl-L-prolinanide 26. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-glutamyl-L-prolinamide 27. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-asparagyl-L-prolinamide 28. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-arginyl-L-prolinamide 29. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-lysyl-L-prolinamide 30. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-threonyl-L-prolinamide 31. N-( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-valyl-L-prolinamide 32. N-( cis -2-Ethyl-4-oxocyclopentanecarbonyl)-L-phenylalanyl-L-prolinamide 33. N-( cis -2-Phenyl-4-oxocyclopentanecarbonyl)-L-phenylalanyl-L-prolinamide 34. N-( 3-Oxo cyclopentanacarbonyl)-L-isoleucyl-L-prolinamide 35. N-( 3-Oxo cyclopantanecarbonyl)-L-glutamyl-L-prolinamide 36. N-( 3-Oxo cyclopentanecarbonyl)-L-asparagyl-L-prolinamide 37. N-( 3-Oxo cyclopentanecarbonyl)-L-arginyl-L-prolinamide 38. N-( 3-Oxo cyclopentanecarbonyl)-L-lysyl-L-prolinamide 39. N-( 3-Oxo cyclopentanecarbonyl)-L-seryl-L-prolinamide 40. N-( 3-Oxo cyclopentanecarbonyl)-L-threonyl-L-prolinamide 41. N-( 3-Oxo cyclopentanecarbonyl)-L-valyl-L-prolinamide 42. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-isoleucyl-L-prolinamide 43. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-glutamyl-L-prolinamide 44. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-asparagyl-L-prolinamide 45. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-arginyl-L-prolinamide 46. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-lysyl-L-prolinamide 47. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-seryl-L-prolinamide 48. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-threonyl-L-prolinamide 49. N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-valyl-L-prolinamide 50. N-[( cis -2-Methyl-4-oxocyclopentanecarbonyl)-L-phenylalanyl]-L-thiazoline-4-carboxamide 51. N-[(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-phenylalanyl]-L-thiazoline-4-carboxamide 52. 3-[N-(3-Methylpyroglutamyl)-L-leucyl]-L-thiazolidine-4-carboxamide 53. 3-[N-(3-Methylpyroglutamyl)-L-methionyl]-L-thiazolidine-4-carboxamide 54. 3-[N-(3-Oxocyclopentanecarbonyl)-L-leucyl]-L-thiazolidine-4-carboxamide 55. 3-[N-(2-Methyl-4-oxocyclopentanecarbonyl)-L-methionyl]-L-thiazolidine-4-carboxamide 56. 3-[N-(2,2-Dimethyl-4-oxocyclopentanecarbonyl)-L-methionyl]-L-thiazolidine-4-carboxamide 57. N-(3-Phenylpyroglutamyl)-L-leucyl-L-prolinamide 58. N-(3-Phenylpyroglutamyl)-L-methionyl-L-prolinamide 59. 3-[N-(3-Phenylpyroqlutamyl)-L-methionyl]-L-thiazolidine-4-carboxamide 60. N-(3-Ethylpyroglutamyl)-L-leucyl-L-prolinamide 61. N-(3-Isopropylpyroglutamyl)-L-methionyl-L-prolinamide 62. 3-[N-(3-Ethylpyroglutamyl)-L-methionyl]-L-thiazolidine-4-carboxamide 63. N-(2-Phenyl-4-oxocyclopentanecarbonyl)-L-methionyl-L-prolinamide 64. N-(3-Methylpyroglutamyl)-L-lysyl-L-prolinamide 65. N-(3-Ethylpyroglutamyl)-L-lysyl-L-prolinamide 66. N-(3-Methylpyroglutamyl)-L-ornithyl-L-prolinamide 67. [(1S)-5-dimethylamino-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]propylcarbamoyl]-3-methylpyrrolidin-5-one 68. [(1S)-4-benzyloxycarbonylamino-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]butylcarbamoyl]-3-methylpyrrolidin-5-one 69. N-(3-Methylpyroglutamyl)-L-arginyl-L-prolinamide 70. N-(3-Methylpyroglutamyl)-L-threonyl-L-prolinamide 71. [(1S)-2-Methoxy-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]propylcarbamoyl]-3-methylpyrrolidin-5-one 72. N-(3-Methylpyroglutamyl)-L-cysteyl-L-prolinamide 73. [(1S)-2-Methylthio-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]ethylcarbamoyl]-3-methylpyrrolidin-5-one 74. [(1S)-2-Phenylthio-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]ethylcarbamoyl]-3-methylpyrrolidin-5-one 75. [(1S)-2-Methylsulfonyl-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]ethylcarbamoyl]-3-methylpyrrolidin-5-one 76. N-(3-Methylpyroglutamyl)-L-asparagyl-L-prolinamide 77. N-(3-Methylpyroglutamyl)-L-tyrosyl-L-prolinamide 78. N-(2-Methyl-4-oxocyclopentanecarbonyl)-L-seryl-L-prolinamide 79. N-(3,3-dimethylpyroglutamyl)-L-arginyl-L-prolinamide 80. [(1S)-4-Acetylamino-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]butylcarbamoyl]-3-methylpyrrolidin-5-one 81. [(1S)-2-Acetylamino-1-[(2S)-2-carbamoylpyrrolidin-1-ylcarbonyl]butylcarbamoyl]-3-methylpyrrolidin-5-one The evaluation tests for anti-reserpine action, anti-chlorpromazine action and spinal reflex stimulant action were conducted as regards the compounds of the present invention. For comparison, the same tests were conducted also as regards TRH and the hitherto-known DN1417 of the following formula: Test Example 1 Anti-reserpine action (Antagonistic action against hypothermia) ICR male mice weighing 35 - 40 g were subcutaneously administered with reserpine at the dose of 5 mg/kg. About 2 hours later, each of the mice was held by a mouse-holder, and a body temperature sensor was intrarectally inserted. Thereafter, the body temperature was automatically measured every 10 minutes. The test compound dissolved in saline was subcutaneously administered 3 or 3.5 hours after administration of reserpine. After the administration of the test compound, the body temperature was measured every 10 minutes over the period of 120 minutes. The area below the body temperature line during the period was calculated, from which the regression line was estimated based upon least square method, and estimated was the amount of the test compound necessary for raising the body temperature by 1°C on the average for 120 minutes from that just before the administration of the test compound (Table 1). Concentration of test compound necessary for raising body temperature by 1°C on the average for 120 minutes (mg/kg, SC) TRH 2.52 DN1417 2.06 Compound 1A 0.18 Compound 2A 0.48 Compound 3A 0.91 Compound 5A 0.33 Test Example 2 Anti-chlorpromazine action (Locomotor stimulant action) ICR male mice weighing 35 - 40 g (four animals per group) were subcutaneously administered with chlorpromazine HCl at the dose of 5 mg/kg and immediately set in the automatic locomotor-measuring apparatus (AUTOMEX). One hour later, the test compound dissolved in saline was subcutaneously administered, and the locomotor activity was measured every 15 minutes for 120 minutes. The total locomotor activity during the period of 120 minutes was calculated and the regression line was estimated based on the method of least squares, from which the amount of the test compound necessary for inducing 3000 locomotor-count was estimated (Table 2). Concentration of test compound necessary for inducing 3000 count of automatism quantity in 2 hours (mg/kg, SC) TRH 6.82 DN1417 4.34 Compound 1A 2.63 Compound 2A 1.64 Compound 5A 16.30 Test Example 3 Flexor reflex in spinalized rats Wistar male rats (weighing 450 - 520 g) were anesthetized with ether, and the cervical part of spinal cord was exposed, into which a tracheal cannula was inserted. The vagus nerves were severed bilaterally at the cervical region. Thereafter, the cervical vertebra C1 segment was transected, and rapidly, artificial ventilation was given with the use of an artificial respirator (Shinano Factory 60 rpm. 4 ml/stroke). The rat was placed on a thermostated apparatus in which water thermostated at 37°C was circulated and fixed thereto at forelimbs, right hindlimb, tooth and tail. A venous cannula was inserted into the femoral vein in the right hindlimb and two needle electrodes were subcutaneously inserted into the left skin of the toe, and a piece of thread was attached to the limb with the edge of the thread bonded to a force-displacement transducer. Tension of about 5 g was applied to the thread. Through the elctrodes, electric stimuli of 50 - 100 V were applied once per 30 seconds. The flexor reflex was recorded on the polygraph via a force-displacement transducer. After the reaction became constant in about one-hours' lapse for stabilization, the test compound dissolved in saline was intravenously administered. Thereafter, the reaction was recorded for 1 hour. In the data, taking the mean of the three reactions just before administration of the test compound for 100%, the reflex amplitude at 1-, 3-, 5-, 8-, 10-, 15-, 20-, 30-, 40-, 50- and 60- minutes' lapse after administration of the test compound were calculated. In Table 3, there are shown calculated area below the straight line linking the obtained reflex amplitude at the respective above-mentioned time covering 60 minutes in the case of administration of each test compounds at the dose of 0.1 mg/kg, and the reflex amplitude at 10- and 60-minutes' lapse after administration (Table 3). The hormone activity of every compound of the invention was found to be as equal to or less than that of TRH by colloid formation test in thyroid follicles.

Claims: A peptide derivative of the following formula wherein R¹ and R² are the same or different and respectively mean a hydrogen atom, a C₁₋₅ alkyl group or a phenyl group, X is -NH- or -CH₂-, Y is a hydrogen atom, a benzyl group wherein phenyl may be substituted by hydroxyl, or a C₁₋₅ alkyl group which may be substituted by -SH, -SR³, -SO₂R³, -CONH₂, -OR⁶ or (wherein R³ means a C₁₋₅ alkyl group or an aryl group, R⁴ and R⁵ are the same or different and respectively mean a hydrogen atom, a C₁₋₅ alkyl group or an amino protecting group and R⁶ is a hydrogen atom, a C₁₋₅ alkyl group or a hydroxyl protecting group), and Z is -CH₂- or -S-, provided that when X is -NH-, R¹ and R² are not hydrogen atoms at the same time, or a pharmaceutically acceptable acid addition salt thereof. A peptide derivative or a pharmaceutically acceptable acid addition salt thereof as claimed in Claim 1, wherein Y is a C₁₋₅ alkyl which may be substituted by SR³ (wherein R³ is as defined in Claim 1) or a benzyl group. A peptide derivative or a pharmaceutically acceptable acid addition salt thereof as claimed in Claim 1, which is selected from the group consisting of N-(cis-3-methylpyroglutamyl)-L-leucyl-L-prolinamide, N-( cis -3-methylpyroglutamyl)-L-methionyl-L-prolinamide, N-( cis -3-methylpyroglutamyl)-L-norvalyl-L-prolinamide, N-( cis -3-methylpyroglutamyl)-L-phenylalanyl-L-prolinamide, N-( cis -3-methylpyroglutamyl)-L-norleucyl-L-prolinamide, N-(3,3-dimethylpyroglutamyl)-L-leucyl-L-prolinamide, N-(3,3-dimethylpyroglutamyl)-L-norvalyl-L-prolinamide, N-(3,3-dimethylpyroglutamyl)-L-methionyl-L-prolinamide, N-(3,3-dimethylpyroglutamyl)-L-phenylalanyl-L-prolinamide, N-(3,3-dimethylpyroglutamyl)-L-norleucyl-L-prolinamide, N-[(1R)-3-oxocyclopentanecarbonyl]-L-phenylalanyl-L-prolinamide, N-[(1R)-3-oxocyclopentanecarbonyl]-L-leucyl-L-prolinamide, N-( cis -2-methyl-4-oxocyclopentanecarbonyl)-L-methionyl-L-prolinamide, N-[ cis -(1S,2R)-2-methyl-4-oxocyclopentanecarbonyl)-L-leucyl-L-prolinamide, N-[ cis -(1S,2R)-2-methyl-4-oxocyclopentanecarbonyl]-L-phenylalanyl-L-prolinamide, N-[ cis -(1S,2R)-2-methyl-4-oxocyclopentanecarbonyl]-L-norvalyl-L-prolinamide, N-[ cis -(1S,2R)-2-methyl-4-oxocyclopentanecarbonyl]-L-norleucyl-L-prolinamide, N-(2,2-dimethyl-4-oxocyclopentanecarbonyl)-L-phenylalanyl-L-prolinamide, N-(2,2-dimethyl-4-oxocyclopentanecarbonyl)-L-leucyl-L-prolinamide, N-[(1R)-3-oxocyclopentanecarbonyl]-L-norvalyl-L-prolinamide and N-[(1R)-3-oxocyclopentanecarbonyl]-L-norleucyl-L-prolinamide. A method of producing a peptide derivative or a pharmaceutically acceptable acid addition salt thereof as claimed in Claim 1, which comprises the steps of (A) condensing a compound of the formula [III] wherein R¹ and R² are as defined in Claim 1 and X¹ is an imino group, a protected imino group or a methylene group, or its reactive derivative with a compound of the formula [IV] wherein Y and Z are as defined in Claim 1 or its salt; (B) condensing a compound of the formula [V] wherein R¹, R², X¹ and Y are as defined above, its salt or its reactive derivative with an amino acid amide of the formula [VI] wherein Z is as defined above, or its salt; or (C) subjecting a compound of the formula [VII] wherein R¹, R², X¹, Y and Z are as defined above, its salt or its reactive derivative to amidation, and (D) thereafter, when X¹ in the product thus obtained by the above step (A), (B) or (C) is a protected imino group, removing the protective group. A pharmaceutical composition containing a peptide derivatives or a pharmaceutically acceptable acid additon salt thereof as claimed in Claim 1 as an active ingredient.

Inventors: FURUKAWA NOBORU, HARA KATSUYOSHI, HARUTA JUNICHI, IWATA KUNIO, UCHIDA ITSUO, YASUDA AKIHIRO, FURUKAWA, NOBORU,, HARA, KATSUYOSHI,, HARUTA, JUNICHI,, IWATA, KUNIO,, UCHIDA, ITSUO,, YASUDA, AKIHIRO,, Furukawa, Noboru, c/o Toxicology Research, Hara, Katsuyoshi, c/o Pharmaceutical Research, Haruta, Junichi, c/o Pharmaceutical Research, Iwata, Kunio, c/o Toxicology Research, UCHIDA, ITSUO, C/O PHARMACEUTICAL RESEARCH, Yasuda, Akihiro, c/o Pharmaceutical Research
Applicants: JAPAN TOBACCO INC, JAPAN TOBACCO INC.
Application year: 1991
Main classification: C07K5
IPC codes: C07K5, A61K38