NOVEL TETRAPEPTIDE DERIVATIVE

Abstract: A tetrapeptide derivative represented by general formula (I) or its salt, having a higher cytostatic activity than dolastatin 10, thus being useful as an antitumor drug wherein R₁, R₂, R₃ and R₄ may be the same or different from one another and each represents hydrogen, lower alkyl or aralkyl; and Q represents (a) or -A₂-R₇, wherein A₁ represents a direct bond or -CHR₅-, Y represents hydrogen or -COR₆, R₅ represents hydrogen, lower alkyl or aralkyl, R₆ represents hydroxy, lower alkoxy, aralkyloxy or -NR₈R₉ wherein R₈ and R₉ may be the same or different from each other and each represents hydrogen, lower alkyl, phenyl or a 4- to 7-membered heterocyclic group bearing one or two heteroatoms selected among S, O and N, or alternatively R₈ and R₉ may form together with the nitrogen atom to which they are bonded a 4- to 7-membered heterocyclic ring which may further bear one heteroatom selected among S, O and N, A₂ represents a direct bond or lower alkylene, and R₇ represents cycloalkyl, aryl orindolyl, provided that the case where both R₁ and R₂ represent isopropyl, R₃ represents sec-butyl, R₄ represents methyl, and Q represents α-(2-thiazolyl)phenethyl is excluded.

Description: Technical Field This invention relates to a novel tetrapeptide derivative having an antitumor activity, and relates more detailedly to a tetrapeptide derivative represented by the following formula or a salt thereof: wherein, R 1 , R 2 , R 3 and R 4 are the same or different and each represent a hydrogen atom, a lower alkyl group or an aralkyl group; Q represents or a group of -A 2 -R 7 , wherein, A 1 represents a direct bond or Y represents -COR 6 , R 5 represents a hydrogen atom, a lower alkyl group or an aralkyl group, R 6 represents a hydroxyl group, a lower alkoxy group, an aralkyloxy group or wherein, R 8 and R 9 are the same or different and each represent a hydrogen atom, a lower alkyl group, a phenyl group or a 4- to 7-membered heterocyclic group containing one or two hetero atoms selected from S, O and N, or alternatively R 8 and R 9 may combine together with the nitrogen atom to which they are bonded to form a 4- to 7-membered heterocyclic ring optionally further containing one hetero atom selected from S, O and N, A 2 represents a direct bond or a lower alkylene group, and R 7 represents a cycloalkyl group, an aryl group or an indolyl group. Background Art Peptides having a cytostatic activity and/or an antineoplasm activity have been isolated from marine molluscs, sea hare Dolabella auricularia and these peptides are called dolastatins 1 to 15. Among them, dolastatin 10 is a pentapeptide extracted from Dolabella auricularia from the Indian Ocean in 1987 by G. R. Pettit, et al. and having the following structural formula, and is said to be the strongest cytostatic substance presently known (see G. R. Pettit, et al., J. Am. Chem. Soc., 109 , 6883 (1987) and Japanese Laid-Open Patent Publication No. 167278/1992). Further, recently, publication was made on the total synthesis of dolastatin 10 itself (see, US Patent No. 4,978,744), but its derivatives have not so far been known at all. The present inventors had intensely studied about derivatives of dolastatin 10, and as a result they found that certain dolastatin analogs represented by the above formula (I) have a higher cytostatic activity than dolastatin 10. They further found that many of these compounds have a larger therapeutic ratio (maximum effective dose/dose at 30% prolongation of life) and a lower toxicity than dolastatin 10, and are thus excellent as an antitumor agent. Namely, they found not only that amino acid analogs of dolastatin 10 exhibit a higher activity than the native dolastatin 10, but that the activity is, unexpectedly, extremely increased by introducing a carboxyl derivative into the thiazole ring. Further, they found, throughly astoundingly, that derivatives wherein the thiazole ring is eliminated show extremely higher activity than dolastatin 10. The document R. Bai et al. (Biochem. Pharmacal., Vol. 40, No. 8 (1990), pp. 1859-1864) mentions the inhibitory action of dolastatin 10 and its chiral isomers against both tubulin polymerization and the growth of L1210 leukemia cells. The document G.R. Pettit et al. (J. Med. Chem., Vol. 33, No. 12 (1990), pp. 3132-3133) refers to the cytostatic activity of dolastatin 10 and its chiral isomers (isodolastatin 10) against lymphocytic leukemia P388 cells. Derivatives of dolastatin 10 are, however, not mentioned in either of the above documents. Disclosure of Invention The embodiments of this invention completed based on these findings can be classified into the following three categories. (1) Amino acid-substituted compounds of dolastatin 10 and synthesis thereof (2) Carboxyl derivatives of the thiazole ring and synthesis thereof (3) Tetrapeptide derivatives wherein the thiazole ring is eliminatd and synthesis thereof The synthesis of compounds belonging to category (1) is described in the later-shown Flow sheet 1, and synthesis of compounds belonging to category (2) is described in the later-shown Flow sheets 2 and 3. Further, synthesis of compounds belonging to category (3) is described in the later-shown Flow sheet 4. In the present description, the term "lower" means that the number of the carbon atoms of a group or compound to which this term is attached is 6 or less, preferably 4 or less. In the above formula (I), the "lower alkyl group" may be either of straight-chain and branched-chain, and there can, for example, be mentioned a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl or isohexyl group, or the like and the "aralkyl group" means an aryl-lower alkyl group, and there can, for example, be mentioned a benzyl or phenethyl group, or the like. Further, the "lower alkoxy group" means a lower alkyl-O-group wherein the lower alkyl part has the above meaning, an there can, for example, be mentioned a methoxy, ethoxy, n-propoxy, isopropoxy or tert-butoxy group, or the like, and the "aralkyloxy group" means an aralkyl-O-group wherein the aralkyl part has the above meaning, and there can, for example, be mentioned a benzyloxy or phenethyloxy group, or the like. Further, the "lower alkylene group" may be either of straight-chain and branched-chain, and there can, for example, be mentioned a methylene, ethylene, trimethylene, tetramethylene, methylmethylene, propylene, ethylethylene or 1,2-dimethylethylene group, or the like, and as the "cycloalkyl group", there can be mentioned a cycloalkyl group having 3 to 7 carbon atoms such as, for example, a cyclopropyl, cyclopentyl, cyclohexyl or cycloheptyl group, and as the "aryl group", there can, for example, be mentioned a phenyl or naphthyl group, or the like. When R 8 and R 9 represents "a 4- to 7-membered heterocyclic group containing one or two hetero atoms selected from S, O and N", as examples of the heterocyclic group, there can be mentioned azetidinyl, furyl, thienyl, pyridyl, piperidinyl, azepinyl, thiazolyl, imidazolyl, oxazolyl, pyrimidinyl and pyridazinyl groups, etc. Further, when R 8 and R 9 "combine together with the nitrogen atom to which they are bonded to form a 4- to 7-membered heterocyclic ring optionally further containing one hetero atom selected from S, O and N", as examples of the heterocyclic ring, there can be mentioned azetidino, pyrrolidino, piperidino, 1-perhydroazepinyl, piperazino, morpholino and thiomorpholino groups, etc. Thus, as examples of the group of there can be mentioned amino, methylamino, ethylamino, isopropylamino, tert-butylamino, dimethylamino, diethyl-amino, phenylamino, N-methyl-N-phenylamino, furylamino, pyridylamino, 2-thiazolylamino, imidazolylamino, pyrimidinylamino, pyrrolidino, piperidino and morpholino group, etc. A group of preferred compounds are the compounds of the case where R 1 and R 2 represent isopropyl groups, R 3 represents a sec-butyl group, R 4 represents a methyl group and Q represents wherein R 5 represents a benzyl group and R 6 has the same meaning as defined above. Further, another group of preferred compounds are compounds of the case where Q represents -A 2 -R 7 wherein A 2 represents a lower alkylene group and R 7 has the same meaning as defined above, and particularly preferable among them are compounds wherein both R 1 and R 2 represent isopropyl groups, R 3 represents a sec-butyl group, R 4 represents a methyl group and R 7 represents an aryl group. In the compounds of the aforesaid formula (I) of this invention, the carbon atoms to which the substituents R 1 , R 2 , R 3 , R 4 , R 5 and methoxy groups are bonded are asymmetric carbon atoms, and can take arbitrary R or S configurations, and all these are included in the scope of this invention, but in view of the point of pharmacological activities, compounds which have the same configuration as dolastatin 10 are preferable. As representative examples of the compounds of the above formula (I) provided by this invention, there can be mentioned the following ones besides those mentioned in the later-described Examples. In the above groups, Me, Et, Pr, Bu, Bzl, Ph and Np mean a methyl group, an ethyl group, a propyl group, a butyl group, a benzyl group, a phenyl group and a naphthyl group, respectively. The tetrapeptide derivatives of the above formula (I) can exist as a salt, and examples of such salts, there can be mentioned hydrochlorides, hydrobromides, trifuloroacetates, p-toluenesulfonates and acetates. According to this invention, a tetrapeptide derivative of the above formula (I) can be prepared by condensing amino acid or peptide fragments, for example according to the liquid phase synthesis method (see, E. Schröder and K. Lübke, "The Peptides", volume 1, pages 76-136, 1965, published by Academic Press) well known in the field of peptide chemistry. However, it is most preferable to synthesize these tetrapeptide derivatives by condensing a tripeptide fragment of the following formula (II) wherein R 1 , R 2 and R 3 have the same meanings as defined above, with a fragment of the following formula (III) wherein R 4 has the same meaning as defined above, Q 1 represents a group of or -A 2 -R 7 wherein Y 1 represents a methoxycarbonyl group, and A 1 , A 2 and R 7 have the same meanings as defined above, because each fragments of the formulae (II) and (III) is easy to synthesize and is free from racemization at their condensation step. A compound in the case where, in the group Q, the substituent Y at the 4-position of the thiazole ring represents the group -COR 6 other than a methoxycarbonyl group, can be obtained by preparing a compound of the formula (I) wherein Y represents a methoxycarbonyl group and then converting the methoxycarbonyl group to a group -COR 6 . The reaction can generally be carried out by treating the above fragments (II) and (III) with a condensing agent, e.g. dicyclohexylcarbodiimide (DCC), diphenyl phosphoryl azide (DPPA) or diethyl phosphorocyanidate (DEPC), a so-called BOP reagent, or the like in an inert solvent such as, for example, chloroform, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF) or acetonitrile, if necessary in the presence of an organic base such as, for example, triethylamine, N-methylmorpholine or diisopropylethylamine (DIEA). The reaction temperature is usually -10°C to room temperature, preferably around 0°C, and as for use rates of the compound of the formula (III), the organic base and the condensing agent based on the compound of the formula (II), it is advantageous to use the compound of the formula (III) of at least one mole, preferably of the order of 1.0 to 1.1 moles, the organic base of the order of 2 moles, and the condensing agent of the equimolar order, respectively per mole of the compound of the formula (II). The conversion of a compound wherein the substituent Y at the 4-position of the thiazole ring in the group Q represents a methoxycarbonyl group to a compound wherein the substituent Y represents a group -CO-R 6 can easily be carried out, for example, when R 6 represents a hydroxyl group, by hydrolyzing the former compound with an alkali; when R 6 represents a lower alkoxy group or aralkyloxy group, by esterifying a compound wherein R 6 represents a hydroxyl group according to a conventional method; and when R 6 represents by treating the compound wherein the substituent Y represents a methoxycarbonyl group with ammonia, a primary amine or a secondary amine. Thus, the desired tetrapeptide derivatives of the formula (I) are formed, and the isolation and purification thereof from the reaction mixtures can be carried out by recrystallization, ion exchange chromatography, gel filtration, high performance liquid chromatography, etc. The compounds of the above formulae (II) and (III) used as starting materials in the above reaction are novel compounds not disclosed in prior literatures, and can easily be prepared by condensing amino acids, which are constituents thereof, according to a liquid phase synthesis method. The tetrapeptide derivatives of the formula (I) of this invention have a higher cytostatic activity than dolastatin 10, and are useful for treatment of acute myelocytic leukemia, acute lymphocytic leukemia, chronic melanoma, pulmonary adenocarcinoma, neuroblastoma, pulmonary small cell carcinoma, breast cancer, colon cancer, ovary cancer, bladder cancer, etc. The screening of cytostatic activity was made using lymphocytic leukemia P388 cells. The results are shown in the following Table. Example No. of Compound ED 50 (µg/ml) 1 2.4 × 10 -7 2 2.7 × 10 -5 9 < 1.0 × 10 -6 11 < 1.0 × 10 -6 12 < 1.0 × 10 -6 14 2.9 × 10 -6 Dolastatin 10 7.0 × 10 -4 The compounds of this invention, when used as a drug, can be used by formulating then into any dosage form of solid forms (e.g., tablets, hard capsules, soft capsules, granules, powders, fine granules, pills, troches, etc.), semi-solid forms (e.g., suppositories, ointments, etc.) and liquid forms (e.g., injections, emulsions, suspensions, lotions, sprays, etc.). As nontoxic additives usable in the above formulations, there can, for example, be mentioned starches, gelatin, glucose, lactose, fructose, maltose, magnesium carbonate, talc, magnesium stearate, methylcellulose, carboxymethylcellulose or salts thereof, gum arabic, polyethylene glycol, p-hydroxybenzoic acid alkyl esters, syrups, ethanol, propylene glycol, vaseline, carbowax, glycerol, sodium chloride, sodium sulfite, sodium phosphate, citric acid, etc. The drug can also contain another therapeutically effective drug. The content of the compound of this invention in the drug varies depending on the dosage form, but it is generally preferable that the drug contains the compound at a concentration of 0.1 to 50 wt% in the case of solid and semi-solid forms, and at a concentration of 0.05 to 10 wt% in the case of liquid form. The dose of the compound of this invention can widely be varied depending on the kind of warm-blooded animals including human beings and a subject, administration routes, the seriousness of symptoms, the diagnoses of doctors, etc., but can generally be on the order of 0.01 to 50 mg/kg per day. However, it is of course be possible to administer the compound in an amount smaller than the lower limit of the above range or in an amount larger than the upper limit thereof in accordance with the seriousness of the symptom of the patient and the diagnosis of the doctor as mentioned above. The above dose can be administered once a day or in divided several portions per day. This invention is further described below according to Referential Examples and Examples. As for the structure of compounds corresponding to compound numbers used in Referential Examples and Examples, please refer to the following Flow sheets 1 to 4. Therein, Z, Me, Bu t , Boc and Bzl represent a benzyl-oxycarbonyl group, a methyl group, a tert-butyl group, a tert-butoxycarbonyl group and a benzyl group, respectively, and R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and -A 2 -R 7 have the aforesaid meanings. Referential Example 1-A Preparation of compound 1-A (Compound 1 wherein R 3 =CH 3 ) 11.15 g (50 mmoles) of Z-alanine is dissolved in 140 ml of tetrahydrofuran, 9.72 g (60 mmoles) of carbonyldiimidazole is added, and the mixture is stirred at room temperature for 4 to 5 hours. On the other hand, 17.16 g (110 mmoles) of malonic acid monomethyl ester potassium salt and 7.60 g (80 mmoles) of anhydrous magnesium chloride are suspended in 150 ml of tetrahydrofuran and is stirred for 6 hours with heating on a water bath of 55°. The reaction mixture is cooled with ice, the above reaction solution is poured thereinto all at once, the cooling bath is immediately removed, and the mixture is stirred at room temperature for 24 to 48 hours. A small amount of water is added to the reaction solution, and a clear supernatant is decanted from the deposited waxy precipitate, and concentrated under reduced pressure to obtain an oily matter. Ethyl acetate and ice-cooled 4N hydrochloric acid are added to each of the above waxy residue and this oily matter, each of the mixtures is shaken to dissolve, the two solutions are combined, the layers are separated, and the aqueous layer is extracted again with ethyl acetate. The ethyl acetate layer is washed with ice-cooled 2N hydrochloric acid and saturated aqueous sodium bicarbonate and dried, and the solvent is distilled off to obtain 13.50 g of a pale yellow oily matter. This is purified by silica gel column chromatography (eluent : ethyl acetate-n-hexane (1 : 1)) to obtain the desired compound 1-A as a colorless - pale yellow oily matter. 12.96 g (92.9%). [α] D 26 -17.7° (c=1.01, MeOH) 1 H―NMR (CDCl 3 , δ) 1. 38(3H, d, J=7. 1 Hz), 3. 55(2H, s), 3. 72(3 H, s), 4. 45(1H, m, J=7. 1 Hz), 5. 11(2H, s), 5. 25∼5. 55(1H, m), 7. 34(5H, s) Referential Examples 1-B, 1-C, 1-D and 1-E were carried out in all the same manner as in Referential Example 1-A to obtain compounds 1-B, 1-C, 1-D and 1-E as oily matters, respectively. Referential Example 2-A Preparation of compound 2-A (Compound 2 wherein R 3 =CH 3 ) 12.96 g (46.45 mmoles) of compound 1-A obtained in Referential Example 1-A is dissolved in 380 ml of methanol, and 3.56 g (93.67 mmoles) of sodium borohydride is added thereinto all at once under stirring at -78°. Cooling and stirring are continued for 6 hours, ice-cooled 1N hydrochloric acid is added gradually, and when it is confirmed that the mixture becomes acidic, the mixture is concentrated under reduced pressure, and the deposited oily matter is extracted with ethyl acetate. The ethyl acetate layer is washed with saturated aqueous sodium bicarbonate and dried, and the solvent is distilled off to obtain 12.93 g of crystals. The crystals are recrystallized from isopropyl ether to obtain the desired compound 2-A as colorless needles of a melting point of 78°. 11.09g (85.0%). [α] D 28 -4. 4° (c=1. 00, MeOH) As C 14 H 19 NO 5 Calculated C=59. 77% H=6. 81% N=4. 98% Found C=59. 83% H=6. 92% N=5. 07% 1 H―NMR (CDCl 3 , δ ) 1. 15(3H, d, J=6. 8 Hz), 2. 35∼2. 55(2H, m), 3. 70(3H, s), 3. 85∼4. 15(1H, m), 5. 09(2H, s), 7. 34(5H, s) Referential Examples 2-B, 2-C, 2-D and 2-E were carried out in all the same manner as in Referential Example 2-A to obtain compounds 2-B, 2-C, 2-D and 2-E, respectively. Referential Example 3-A Preparation of compound 3-A (Compound 3 wherein R 3 =CH 3 ) 9.78 g (34.80 mmoles) of the compound obtained in Referential Example 2-A is dissolved in 100 ml of dimethylformamide, 40.0 g (172.41 mmoles) of silver oxide and 50 ml of methyl iodide are added, and the mixture is stirred for 5 hours in a water bath of 35°. The mixture is filtered, silver oxide is washed with dimethylformamide, and the filtrate and washings are combined and concentrated under reduced pressure at 50° or below. The residue is thoroughly extracted with ethyl acetate, the ethyl acetate layer is washed with 5% sodium thiosulfate and saturated aqueous sodium bicarbonate and dried, and the solvent is distilled off to obtain 10.43 g of a yellow oily matter. The oily matter is purified by silica gel column chromatography (eluent : benzene-ethyl acetate (5 : 1)) to obtain the desired Compound 3-A as a pale yellow oily matter. 7.63 g (71.0%). [α] D 25 -39. 8° (c=1. 03, MeOH) 1 H―NMR (CDCl 3 , δ) 1 .21(3H, d, J=6. 8 Hz), 2. 47(2H, d, J=6.2 Hz), 2. 80(3H, s), 3. 38(3H, s), 3. 64(3H, s), 5. 13(2H, s), 7. 34(5H, s) Referential Examples 3-B, 3-C, 3-D and 3-E were carried out in all the same manner as in Referential Example 3-A to obtain compounds 3-B, 3-C, 3-D and 3-E as oily matters, respectively. Referential Example 4-A Preparation of compound 4-A (Compound 4 wherein R 3 =CH 3 ) 6.60 g (21.36 mmoles) of the compound 3-A obtained in Referential Example 3-A is dissolved in 100 ml of dioxane, 23.5 ml (23.5 mmoles) of 1N sodium hydroxide is added, and the mixture is stirred at room temperature for 2 to 3 hours. 20% citric acid is added to the reaction solution to make the pH 4.0, the mixture is concentrated under reduced pressure, and the deposited oily matter is extracted with ethyl acetate. The ethyl acetate layer is washed with saturated saline and dried and the solvent is distilled off to give a colorless - pale yellow oily matter. This is dissolved in 60 ml of dichloromethane, 0.8 ml of concentrated sulfuric acid is added, and the mixture is shaken with 25 ml of isobutene in a pressure bottle at room temperature for 48 to 96 hours. The reaction solution is poured into saturated aqueous sodium bicarbonate, nitrogen gas is blown thereinto to remove isobutene and the greater part of dichloromethane, the deposited oily matter is extracted with ethyl acetate, and the ethyl acetate layer is washed with saturated aqueous sodium bicarbonate and dried. The solvent is distilled off, and the remaining yellow oily matter (7.32 g) is purified by silica gel column chromatography (eluent : benzene-ethyl acetate (10 : 1)) to obtain 6.31 g (84.1%) of the desired compound 4-A as a colorless - pale yellow oily matter. [α] D 27 -33. 0° (c=1. 02, MeOH) 1 H―NMR (CDCl 3 , δ) 1.21(3H, d, J=6. 8 Hz), 1.44(9H, s), 2. 38(2 H, d, J=6. 2 Hz), 2. 82(3H, s), 3. 38(3H, s), 3. 5∼ 3. 85(1H, m), 3. 85∼4. 4(1H, m), 5. 13(2 H, s), 7. 34(5H, s) Referential Examples 4-B, 4-C, 4-D and 4-E were carried out in all the same manner as in Referential Example 4-A to obtain compounds 4-B, 4-C, 4-D and 4-E as oily matters, respectively. Referential Example 5-A Preparation of compound 5-A (Compound 5 wherein R 3 =CH 3 ) 0.70 g (2.00 mmoles) of compound 4-A obtained in Referential Example 4-A is dissolved in 20 ml of t-butanol-water (9 : 1), 0.1 g of 5% palladium carbon is added, and the mixture is stirred under a hydrogen stream for 2 hours. After the reaction, the catalyst is filtered and washed, and the filtrate and the washings are concentrated under reduced pressure. The remaining oily matter is dissolved in 30 ml of benzene, the solution is concentrated again under reduced pressure, and the operation is repeated once more. The resultant oily matter is dissolved together with 0.56 g (2.23 mmoles) of Z-valine in 10 ml of acetonitrile, and 0.43 g (2.09 mmoles) of DCC is added under ice cooling and stirring. Soon, crystals appear. Stirring is continued at 0° for at least 3 hours, and then overnight during which time the temperature is allowed to rise as the ice melts, the reaction mixture is diluted with ethyl acetate, and the crystals are filtered and washed with ethyl acetate. The filtrate and the washings are concentrated under reduced pressure, the syrupy residue is dissolved in ethyl acetate, the insoluble matters, if any, are removed by filtration, the ethyl acetate solution is washed with ice-cooled -2N hydrochloric acid and saturated aqueous sodium bicarbonate and dried, and the solvent is distilled off to obtain 1.01 g of a colorless oily matter. This is purified by silica gel column chromatography (eluent : benzene-ethyl acetate (5 : 1)) to obtain 0.67 g (74.4%) of the desired compound 5-A as a colorless oily matter. [α] D 28 -31. 4° (c=1. 02, MeOH) 1 H―NMR (CDCl 3 , δ) 0.8∼1. 1(6H, m), 1. 17(3H, d, J=6. 8 Hz), 1. 45(9H, s), 2. 25∼2. 45(2H, m), 3. 00(3H, s), 3. 37(3H, s), 3. 68(1H, dd, J=12. 1 Hz, 6. 2 Hz), 4. 35∼4. 75(2H, m), 5. 09(2H, s), 5. 56 (1H, br, d), 7. 33(5H, s) The following compounds were obtained in all the same manner as in Referential Example 5-A. Referential Example 6-A Preparation of compound 6-A (Compound 6 wherein and R 3 =CH 3 -) 0.65 g (1.44 mmoles) of compound 5-A obtained in Referential Example 5-A is dissolved in 15 ml of t-butanol-water (9 : 1), 50 mg of 5% palladium carbon is added, and the mixture is stirred under a hydrogen stream for 2 hours. After the reaction, the catalyst is removed by filtration and washed, and the filtrate and the washings are concentrated under reduced pressure. The oily residue is dissolved in 30 ml of benzene and the solution is concentrated again under reduced pressure, and this operation is further repeated once more. The resultant oily matter is dissolved in 6 ml of dimethylformamide, 0.25 g (1.72 mmoles) of N,N-dimethylvaline and 0.29 g (1.78 mmoles) of DEPC are added, the mixture is stirred at room temperature until clear solution is obtained, then the solution is cooled with ice, and the solution of 0.17 g (1.68 mmoles) of triethylamine in 1 ml of dimethylformamide is added dropwise over a period of 4 minutes. Stirring is continued at 0° for at least 4 hours and then overnight during which time the temperature is allowed to rise as the ice melts, the resultant clear reaction mixture is diluted with ethyl acetate, and the ethyl acetate solution is thoroughly washed with saturated aqueous sodium bicarbonate and then dried. The solvent is distilled off, and 0.66 g of the remaining pale brown oily matter is purified by silica gel column chromatography (eluent : ethyl acetate-hexane (1 : 1)) to obtain 0.46 g (71.9%) of the desired compound 6-A as a colorless oily matter. [α] D 27- 56. 5° (c=1. 00, MeOH) 1 H―NMR (CDCl 3 , δ) 0.8∼1. 1(12H, m), 1. 15(3H, d. J=7. 0 Hz), 1. 45(9H, s), 2. 27(6H, s), 3. 05(3H, s), 3. 38(3H, s), 3. 55∼3. 85(1H, m), 4. 35∼ 4. 65(1H, m), 4. 65∼4. 95(1H, m), 0. 88(1H br, d) The following compounds were obtained in all the same manner as in Referential Example 6-A. Referential Example 7-A Preparation of compound 7-C (Compound 7 wherein R 6 =OCH 2 Ph) 870 mg (2.4 mmoles) of compound 7-A (compound 7 wherein R=OCH 3 ), known compound, is dissolved in 5 ml of ethanol, and 3 ml of 1N sodium hydroxide is added. The mixture is stirred at room temperature for 30 minutes, the solvent is distilled off under reduced pressure, water is added, the mixture is acidified with citric acid, and the mixture is extracted with ethyl acetate. The extract is washed with water and dried over anhydrous sodium sulfate, and the solvent is distilled off under reduced pressure to obtain 680 mg (83.3%) of crystals of compound 7-B (compound 7 wherein R 6 =OH). 70 mg (0.2 mmole) of the crystals are dissolved in 0.5 ml of dichloromethane, 2.4 mg (0.02 mmole) of 4-dimethylaminopyridine and 30 mg (2.4 mmoles) of benzyl alcohol are added, and 50 mg (2.4 mmoles) of DCC is added under ice cooling. The mixture is stirred under ice cooling for 1 hour and then overnight at room temperature. The deposited crystals are removed by filtration, and the filtrate is diluted with ethyl acetate, washed with saturated aqueous sodium bicarbonate and saturated saline, and dried. The solvents are distilled off under reduced pressure, and the resultant crude product is purified by preparative TLC (developing solvent, hexane : ethyl acetate = 2 : 1) to obtain 79.6 mg (91.0%) of crystals (compound 7-C having a melting point of 111.5 to 113.4°. [α] 26 D +8. 38° (c=0. 37, MeOH) MS 438(M + ), 382, 365 1 H―NMR (CDCl 3 , δ) 1. 38(9H, s), 3. 31(2H, br. d, J=5. 5 Hz), 5. 1∼5. 3(2H, m), 5. 4(2H, s), 7. 0∼7. 5(10H, m), 8. 04 (1H, s) Referential Example 7-B Preparation of compound 7-D (Compound 7 wherein R 6 -NHPh) 28.2 mg (0.0809 mmole) of compound 7-B is dissolved in 0.5 ml of dichloromethane, 35.8 mg (1.0 equivalent) of the BOP reagent and 9 mg (1.2 equivalents) of aniline are added, and 15.7 mg (1.5 equivalents) of diisopropylethylamine is added dropwise under water cooling. The reaction solution is stirred overnight at room temperature and then concentrated under reduced pressure. The residue is dissolved in dichloromethane, and the solution is washed successively with 10% aqueous citric acid, saturated aqueous sodium bicarbonate and saturated saline, and dried. The crude product is purified by preparative TLC using hexane-ethyl acetate (2 : 1) as a developing solvent to obtain 35 mg (100%) of the desired compound as crystals. [α] 26 D ― 15.7° (c=0. 305, MeOH) MS 423, 368 1 H―NMR (CDCl 3 , δ) 1. 42(9H, s),3. 31(2H, d J=6.4), 4. 9-5. 4 (2H, m), 7. 0∼7. 8(11H, m), 8. 09(1H, s) Referential Examples 7-C and 7-D are carried out in the same manner as above to obtain the following compounds. Referential Example 8-A Preparation of compound 9-A (Compound 9 wherein R 4 =CH 3 and R 6 =OCH 3 ) 330 mg (0.91 mmole) of compound 7-A known compound, is dissolved in 1.4 ml of dichloromethane, 0.6 ml of trifluoroacetic acid is added under ice cooling, and the mixture is stirred at room temperature for 1.5 hours. The solvent is distilled off under reduced pressure, and ether is added to cause crystallization. The white crystals are collected by filtration and dried. Yield : 339 mg (98.9%). 314 mg (0.835 mmole) of the crystals are dissolved in 4.2 ml of acetonitrile, 369 mg (0.835 mmole) of the BOP reagent and 240 mg (0.835 mmole) of compound 8-A (Compound 8 wherein R 4 =CH 3 ), known compound, are added, and 270 mg (2.09 mmoles) of diisopropylethylamine is added dropwise under ice cooling. The reaction solution is stirred overnight at room temperature, diluted with ethyl acetate, washed successively with 10% aqueous citric acid, saturated aqueous sodium bicarbonate and saturated saline, and dried. The crude product is purified by silica gel column chromatography using dichloromethane-methanol (50 : 1) as an eluent to obtain 431 mg (97.1%) of the desired compound 9-A as powder. [α] 29 D -61.5° (c=1. 02, MeOH) MS 499, 440 1 H―NMR (CDCl 3 , δ) 1. 12(3H, d, j=7. 0 Hz), 1. 47 (9H, s), 3. 35 (3H, s), 3. 95(3H, s), 5. 4∼5. 7(1H, m), 7. 22(6H, m), 8. 05(1H, s) The following compounds were obtained in the same manner as in Referential Example 8-A. In the following Referential Example 8-C, compound 8-C (compound 8 wherein R 4 =H) as a starting material was synthesized according to Referential Examples 7 and 8 of WO 93/03054 and the step of debenzylation (see Referential Example 11 of WO 93/03054). According to Referential Example 7 of WO 93/03054, a compound having the formula is prepared as follows: 7 ml (15.5 mmoles) of a 23.8% LDA tetrahydrofuran : hexane (1 : 1) solution is added dropwise to 10 ml of anhydrous tetrahydrofuran at -20°C under a nitrogen atmosphere and stirring. Then the mixture is cooled to -78°C in a dry ice-acetone bath. 2.3 g (15 mmoles) of benzyl acetate is added dropwise over a period of 30 minutes, the mixture is stirred at -78°C for 5 minutes, and a solution of 2.0 g (10 mmoles) of Boc-L-prolinal in 10 ml of tetrahydrofuran is added dropwise over a period of 1 hour. The mixture is stirred at -78% for 10 minutes, 30 ml of ice-cooled 1N hydrochloric acid is added, and the temperature is elevated up to room temperature. The mixture is extracted with ethyl acetate, the extract is washed with water and dried, the solvent is distilled off under reduced pressure, and the residue is purified by silica gel flash chromatography using hexane : ethyl acetate (5 : 1) as an eluent to obtain 1.12 g (32.0%) of the desired compound as an oily matter. [α] D 25 -23. 7° (c=1. 26, CHCl 3 ) MS 331, 276 1 H―NMR (CDCl 3 , δ) 1. 46(9H, s), 2. 47(2H, d, j=6. 8 Hz), 3. 7∼ 4. 3(2H, m), 5. 15(2H, s), 7, 2∼7. 4(5H, m) According to Referential Example 8 of WO 93/03054, a compound having the formula is prepared as follows: 560 mg (1.6 mmoles) of the compound obtained in Referential Example 7 is dissolved in 27 ml of dichloromethane, 202 µl (1.6 mmoles) of BF 3 .Et 2 0 is added thereto under cooling in ice-salt bath, and an ether solution of diazomethane (32 mmoles) is added dropwise over a period of 30 minutes. After stirring for further two hours under cooling in ice-salt bath, 2 ml of saturated aqueous sodium bicarbonate is added. The insoluble matter is removed by filtration, the filtrate is extracted with ethyl acetate, and the extract is washed with water and dried. The solvent is distilled off under reduced pressure, and the residue is purified by silica gel flash chromatography using hexane : ethyl acetate (5 : 1) as an eluent to obtain 378 mg (65.0%) of the desired compound as an oily matter. [α] D 25 -58. 7° (c=0. 52, CHCl 3 ) MS 241, 218 1 H―NMR (CDl 3 , δ) 1. 46(9H, s), 2. 47(2H, d, j=7. 5 Hz), 3. 34(3 H, s),3. 6∼4. 3(2H, m), 5. 14(2H, s), 7. 2∼ 7.4(5H, m) Referential Example 9-A Preparation of compound 11-A (Compound 11 wherein -A 2 -R 7 =CH 2 CH 2 -Ph) 30.5 mg (0.106 mmole) of a carboxylic acid obtained from the following known compound according to Referential Example 11 of WO 93/03054 is dissolved in 1 ml of acetonitrile, 51.6 mg (1.1 equivalents) of the BOP reagent and 14.1 mg (1.1 equivalents) of phenethylamine are added, and 20.6 mg (1.5 equivalents) of diisopropylethylamine is added dropwise under ice cooling. The reaction solution is stirred overnight at room temperature, and concentrated under reduced pressure. The residue is dissolved in dichloromethane, and the solution is washed successively with 10% aqueous citric acid, saturated aqueous sodium bicarbonate and saturated saline, and dried. The crude product is purified by preparative TLC using dichloromethane-methanol (10 : 1) as a developing solvent to obtain 38.3 mg (92.5%) of the desired compound 11-A as powder. [α] 26 D -21. 6° (c=1. 02, MeOH) MS 358, 317 1 H―NMR (CDCl 3 , δ) 1. 19(3H, d, J=7. 0 Hz), 1. 48(9H, s), 3. 37 (3H, s), 7. 1-7. 4(5H, m) The following compounds were obtained in all the same manner as in Referential Example 9-A. Referential Example 10 Preparation of compound 12-A (Compound 12 wherein Compound 12-A was obtained in the same manner as in Referential Example 9-A from tryptamine and a benzyloxycarbonylated carboxylic acid obtained from the following compound as a starting material through the steps of debenzylation (see Referential Example 11 of WO 93/03054), de-tert-butoxycarbonylation and benzyloxycarbonylation as shown in Flow sheet 4. [α] 28 D -6. 4° (c=1. 41, MeOH) MS 593, 560 1 H―NMR (CDCl 3 , δ) 1. 0-1. 3(3H, m), 3. 28(3H, s), 6. 9-8. 0(6H, m) Example 1 Preparation of compound 10-A (Compound 10 wherein R 4 =CH 3 and R 6 =OCH 3 ) 0.5 ml of concentrated hydrochloric acid is added to 93 mg (0.192 mmole) of compound 6-H under ice cooling, and the mixture is stirred for 1 hour. The mixture is evaporated to dryness under reduced pressure, the residue is dissolved in 2 ml of dimethylformamide, and 0.15 ml of triethylamine is added under ice cooling. Although triethylamine hydrochloride is deposited, the mixture is evaporated to dryness under reduced pressure and dried. On the other hand, 102 mg (0.192 mmole) of compound 9-A obtained in Referential Example 8-A is dissolved in 0.4 ml of ethyl acetate, and 3.3 ml of 2N hydrogen chloride/ethyl acetate is added under ice cooling. The mixture is stirred at room temperature for 1 hour, the solvent is distilled off under reduced pressure, and the residue is dried. The resultant hygroscopic crystals are dissolved in 0.8 ml of dimethylformamide, the solution is added to the above tripeptide carboxylic acid, and 35 mg (0.192 mmole) of 90% DEPC and 54 µl (0.384 mmole) of triethylamine are added under ice cooling. The mixture is stirred under ice cooling for 1 hour and then overnight at room temperature. The solvent is distilled off under reduced pressure, the residue is dissolved in dichloromethane, and the solution is washed with saturated aqueous sodium bicarbonate and saturated saline and dried. The solvent is distilled off, the residue is purified by silica gel flash chromatography using dichloromethane : methanol (30 : 1) as an eluent, and the fraction containing the desired product are further purified by Sephadex LH-20 chromatography using hexane : dichloromethane : methanol (2 : 7.5 : 2.5) as an eluent to obtain 100 mg (62.0%) of the desired compound 10-A as amorphous powder. [α] 27 D -64.7° (c=0. 66, MeOH) MS 799, 751 1 H―NMR (CDCl 3 , δ) 2. 33(6H, s), 3. 02(3H, s),3. 32(6H, s), 3. 95(3H, s), 5. 53(1H, m), 6. 8∼7. 5(7H, m), 8. 05(1H, s) Examples 2-8 The following compounds were obtained by carrying out Examples 2 to 8 according to Example 1. Example 9 Preparation of compound 10-I (Compound 10 wherein R 4 =CH 3 and R 6 =OBu t ) 1. 120 mg (0.142 mmole) of compound 10-A is dissolved in 5 ml of dimethylformamide, and 0.16 ml of 1N sodium hydroxide is added under ice cooling. The mixture is stirred under ice cooling for 30 minutes and then at room temperature for 90 minutes. 0.16 ml of 1N hydrochloric acid is added under ice cooling, the solvent is distilled off under reduced pressure, the residue is dissolved in dichloromethane, and the deposited sodium chloride is removed by filtration. The filtrate is purified by Sephadex LH-20 chromatography using hexane : dichloromethane : methanol (2 : 7.5 : 2.5) as an eluent. The desired product is dissolved again in water, and the solution is lyophilized to obtain 114 mg (96.5%) of compound 10 carboxylic acid (R 6 =OH) as powder. 2. 30 mg (0.024 mmole) of the above carboxylic acid is dissolved in 0.5 ml of dichloromethane, 10 µl of concentrated sulfuric acid and 1 ml of isobutene are added under cooling in dry ice-acetone bath, and the mixture is stirred for 2 days in a sealed tube. 5 ml of saturated aqueous sodium bicarbonate is added to the reaction solution, the mixture is extracted with dichloromethane, and the extract is washed with water and dried. The solvent is distilled off under reduced pressure, and the residue is purified by Sephadex LH-20 chromatography using hexane : dichloromethane : methanol (2 : 7.5 : 2.5) as an eluent to obtain 13 mg (62.5%) of the desired product compound 10-I as amorphous powder. [α] 25 D -60.6° (c=0.35, MeOH) MS 841, 840, 793 1 H―NMR (CD 2 Cl 2 , δ) 1. 58(9H, s), 2. 57(6H, br.), 3. 02(3H, s), 3. 31(6H, s), 5. 46(1H, m), 7. 0∼7. 4(7H, m), 7.93(1H, s) Example 10 Preparation of compound 10-J (Compound 10 wherein R 4 =CH 3 and 21.5 mg (0.026 mmole) of compound 10 carboxylic acid (R 6 =OH) is dissolved in 0.5 ml of acetonitrile, 11.5 mg (1 equivalent) of the BOP reagent and 2.6 mg (1 equivalent) of 2-aminothiazole and added, and 5 mg (1.5 equivalents) of diisopropylethylamine is added dropwise under ice cooling. The mixture is stirred overnight at room temperature, and the reaction solution is concentrated under reduced pressure. The concentrate is dissolved in dichloromethane, and the solution is washed successively with 10% aqueous citric acid, saturated aqueous sodium bicarbonate and saturated saline and dried. The crude product is subjected to preparative TLC using dichloromethane-methanol (10 : 1) as a developing solvent, and are further purified by Sephadex LH-20 chromatography using hexane : dichloromethane : methanol (2 : 7.5 : 2.5) as an eluent to obtain 13.7 mg (57.7%) of the desired compound 10-J as amorphous powder. [α] 28 D -48.8° (c=0.25, MeOH) MS 910, 867 1 H-NMR (CDCl 3 , δ) 3. 01(3H, s), 3. 33(3H, s), 3. 37(3H, s), 5. 52(1H, m), 7. 05(1H, d, J=3. 5Hz), 7. 2-7. 3 (6H, m), 7. 50(1H, d, J=3. 3Hz), 8. 16(1H, s) Example 11 Preparation of compound 10-K (Compound 10 wherein R 4 =CH 3 and R 6 =NH 2 ) 21 mg (0.025 mmole) of compound 10-A is dissolved in 3 ml of ammonia-saturated methanol, and the solution is allowed to stand at room temperature for 1 hour. The solvent is distilled off under reduced pressure, and the residue is purified by Sephadex LH-20 using hexane : dichloromethane : methanol (2 : 7.5 : 2.5) as an eluent to obtain 20 mg (96.0%) of the desired compound 10-K as amorphous powder. [α] 25 D -65. 8° (c=0. 41, MeOH) MS 784, 736 1 H―NMR (CDCl 3 , δ) 2. 48(6H, s), 3. 06(3H, s), 3. 33(6H, s), 5. 50(1H, m), 7. 0∼7.6 (7H, m), 8. 04(1H, s) Examples 12 and 13 Compounds shown in the following table were obtained in the same manner as in Example 11 except that 70% aqueous ethylamine solution or 5% aqueous dimethylamine solution was used in place of ammonia-saturated methanol. Example 14 Preparation of compound 13-A (Compound 13 wherein -A 2 -R 7 =CH 2 CH 2 Ph) 27.7 mg (0.057 mmole) of compound 6-H is dissolved in 0.3 ml of dichloromethane, and 0.3 ml of trifluoroacetic acid is added under ice cooling. The mixture is stirred at room temperature for 1 hour, the solvent is distilled off under reduced pressure, and the residue is sufficiently dried under reduced pressure. On the other hand, 22.3 mg (0.057 mmole) of compound 11-A is dissolved in 2N hydrogen chloride/ethyl acetate under ice cooling, and the mixture is stirred at room temperature for 1 hour. The solvent is distilled off under reduced pressure, the residue is dried and dissolved in 0.5 ml of dimethylformamide, the solution is added to the above tripeptide carboxylic acid, and 9.8 mg (1.0 equivalent) of 95% DEPC and 16 µl (2 equivalents) of triethylamine are added under ice cooling. The mixture is stirred under ice cooling for 1 hour and then overnight at room temperature. The solvent is distilled off under reduced pressure, and the residue is dissolved in dichloromethane, washed successively with saturated aqueous sodium bicarbonate and saturated saline, and then dried. The solvent is distilled off, the residue is subjected to preparative TLC using dichlorometane-methanol (10 : 1) as a developing solvent, and the fractions of the desired product are further purified by Sephadex LH-20 chromatography using hexane : dichloromethane : methanol (2 : 7.5 : 2.5) as an eluent to obtain 35.8 mg (89.5%) of the desired compound 13-A as amorphous powder. [α] 25 D -38.0° (c=0. 566, MeOH) MS 701, 658 1 H―NMR (CD 2 Cl 2 , δ) 1. 16(3H, d, J=7. 0Hz), 2. 23(6H, s), 3. 00 (3H, s), 3. 30(3H, s), 3. 34(3H, s) The following compounds were obtained in the same manner as in Example 14. Example 25 Preparation of compound 13-L (Compound 13 wherein and The desired compound 13-L is obtained by reacting a product obtained by removing of Z of compound 12-A according to Referential Example 5-A with compound 6-H according to Example 14. [α] 27 D -25. 9° (c=0. 255, MeOH) MS 740, 697 1 H―NMR (CDCl 3 , δ) 2. 64(6H, br.), 3. 03(3H, s), 3. 30(6H, s), 7. 0-7. 7(5H, m), 8. 4(1H, m)

Claims: Claims for the following Contracting States : AT, BE, CH, Li, DE, DK, FR, GB, iE, iT, LU, MC, NC, SE A tetrapeptide derivative represented by the following formula or a salt thereof wherein, R 1 , R 2 , R 3 and R 4 are the same or different and each represent a hydrogen atom, an alkyl group having 6 or less carbon atoms or an aralkyl group; Q represents or a group of -A 2 -R 7 , wherein, A 1 represents a direct bond or Y represents -COR 6 , R 5 represents a hydrogen atom, an alkyl group having 6 or less carbon atoms or an aralkyl group, R 6 represents a hydroxyl group, an alkoxy group having 6 or less carbon atoms, an aralkyloxy group or wherein, R 8 and R 9 are the same or different and each represent a hydrogen atom, an alkyl group having 6 or less carbon atoms, a phenyl group or a 4- to 7-membered heterocyclic group containing one or two hetero atoms selected from S, O and N, or alternatively R 8 and R 9 may combine together with the nitrogen atom to which they are bonded to form a 4- to 7-membered heterocyclic ring optionally further containing one hetero atom selected from S, O and N, A 2 represents a direct bond or an alkylene group having 6 or less carbon atoms, and R 7 represents a cycloalkyl group, an aryl group or an indolyl group. The tetrapeptide derivative or a salt thereof according to claim 1 wherein Q represents wherein R 5 and Y have the same meanings as in claim 1. The tetrapeptide derivative or a salt thereof according to claim 2 wherein both R 1 and R 2 represent isopropyl groups, R 3 represents a sec-butyl group, R 4 represents a methyl group, R 6 represents a benzyl group, and Y represents -COR 6 wherein R 6 represents the same meaning as in claim 1. The tetrapeptide derivative or a salt thereof according to claim 1 wherein Q represents a group -A 2 -R 7 wherein A 2 represents an alkylene group having 6 or less carbon atoms. The tetrapeptide derivative or a salt thereof according to claim 4 wherein both R 1 and R 2 represent isopropyl groups, R 3 represents a sec-butyl group, R 4 represents a methyl group, and R 7 represents an aryl group. An antitumor agent containing a tetrapeptide derivative or a salt thereof according to claim 1 as an effective ingredient. Claims for the following Contracting States ES and GR A tetrapeptide derivative represented by the following formula or a salt thereof wherein, R 1 , R 2 , R 3 and R 4 are the same or different and each represent a hydrogen atom, an alkyl group having 6 or less carbon atoms or an aralkyl group; Q represents or a group of -A 2 -R 7 , wherein, A 1 represents a direct bond or Y represents -COR 6 , R 5 represents a hydrogen atom, an alkyl group having 6 or less carbon atoms or an aralkyl group, R 6 represents a hydroxyl group, an alkoxy group having 6 or less carbon atoms, an aralkyloxy group or wherein, R 8 and R 9 are the same or different and each represent a hydrogen atom, an alkyl group having 6 or less carbon atoms, a phenyl group or a 4- to 7-membered heterocyclic group containing one or two hetero atoms selected from S, O and N, or alternatively R 8 and R 9 may combine together with the nitrogen atom to which they are bonded to form a 4- to 7-membered heterocyclic ring optionally further containing one hetero atom selected from S, O and N, A 2 represents a direct bond or an alkylene group having 6 or less carbon atoms, and R 7 represents a cycloalkyl group, an aryl group or an indolyl group. The tetrapeptide derivative or a salt thereof according to claim 1 wherein Q represents wherein R 5 and Y have the same meanings as in claim 1. The tetrapeptide derivative or a salt thereof according to claim 2 wherein both R 1 and R 2 represent isopropyl groups, R 3 represents a sec-butyl group, R 4 represents a methyl group, R 5 represents a benzyl group, and Y represents -COR 6 wherein R 6 represents the same meaning as in claim 1. The tetrapeptide derivative or a salt thereof according to claim 1 wherein Q represents a group -A 2 -R 7 wherein A 2 represents an alkylene group having 6 or less carbon atoms. The tetrapeptide derivative or a salt thereof according to claim 4 wherein both R 1 and R 2 represent isopropyl groups, R 3 represents a sec-butyl group, R 4 represents a methyl group, and R 7 represents an aryl group. An antitumor agent containing a tetrapeptide derivative or a salt thereof according to claim 1 as an effective ingredient. Use of a tetrapeptide derivative or a salt thereof as defined in claim 1 for the preparation of an antitumor agent. A process for the preparation of a tetrapeptide derivative represented by the following formula or a salt thereof wherein, R 1 , R 2 , R 3 and R 4 are the same or different and each represent a hydrogen atom, an alkyl group having 6 or less carbon atoms or an aralkyl group; Q represents or a group of -A 2 -R 7 , wherein, A 1 represents a direct bond or Y represents -COR 6 , R 5 represents a hydrogen atom, an alkyl group having 6 or less carbon atoms or an aralkyl group. R 6 represents a hydroxyl group, an alkoxy group having 6 or less carbon atoms, an aralkyloxy group or wherein, R 8 and R 9 are the same or different and each represent a hydrogen atom, an alkyl group having 6 or less carbon atoms, a phenyl group or a 4- to 7-membered heterocyclic group containing one or two hetero atoms selected from S, O and N, or alternatively R 8 and R 9 may combine together with the nitrogen atom to which they are bonded to form a 4- to 7-membered heterocyclic ring optionally further containing one hetero atom selected from S, O and N, A 2 represents a direct bond or an alkylene group having 6 or less carbon atoms, and R 7 represents a cycloalkyl group, an aryl group or an indolyl group, which comprises condensing a tripeptide fragment of the following formula (II) wherein R 1 , R 2 and R 3 have the same meanings as defined above, with a fragment of the following formula (III) wherein R 4 has the same meaning as defined above, Q 1 represents a group of or -A 2 -R 7 wherein Y 1 represents a methoxycarbonyl group, and A 1 , A 2 and R 7 have the same meanings as defined above, and optionally converting the obtained compound wherein the substituent Y at the 4-position of the thiazole ring in the group Q represents a methoxycarbonyl group to a compound wherein the substituent Y represents a group -CO-R 6 by hydrolyzing the former compound with an alkali, when R 6 represents a hydroxyl group; or when R 6 represents an alkoxy group having 6 or less carbon atoms or aralkyloxy group, by esterifying a compound wherein R 6 represents a hydroxyl group; and when R 6 represents by treating the compound wherein the substituent Y represents a methoxycarbonyl group with ammonia, a primary amine or a secondary amine followed by isolation and purification of the desired tetrapeptide derivative and optionally converting said tetrapeptide derivative into its salt. A process as claimed in claim 8, wherein a condensing agent selected from dicyclohexylcarbodiimide, diphenyl phosphoryl azide or diethyl phosphorocyanidate in an inert solvent optionally in the presence of an organic base is used. A process as claimed in claims 8 or 9, wherein the reaction temperature is from -10°C to room temperature. A process as claimed in claim 10, wherein the reaction temperature is 0°C. A process as claimed in claims 9 to 11, wherein the compound of the formula (III) is used in an amount of at least 1 mole, preferably 1.0 to 1.1 moles per mole of the compound of the formula (II) and wherein the organic base is used in an amount of 2 moles per mole of the compound of the formula (II) and wherein the condensing agent is used in an amount equimolar to the compound of the formula (II).

Inventors: GONDO MASAAKI, MIYAZAKI KOICHI, SAKAKIBARA KYOICHI, GONDO, MASAAKI, MIYAZAKI, KOICHI, SAKAKIBARA, KYOICHI, GONDO, MASAAKI 5-310 SUNSTAGE-RYOKUENTOSHI
Applicants: TEIKOKU HORMONE MFG CO LTD, TEIKOKU HORMONE MFG. CO., LTD.
Application year: 1992
Main classification: C07K5
IPC codes: C07K7, C07K5, A61K38