# Patent

## Title
Methods and compositions for the treatment of non-IgE-mediated diseases

## Abstract

its salts and hydrates, as well as a therapeutic composition containing at least one of the enkephalin analogs, as an effective component.

## Background
1. Field of the Invention

The present invention relates to novel enkephalin analogs, salts and hydrates thereof, as well as a therapeutic composition containing at least one of the enkaphalin analogs.

2. Related Arts

Opiate alkaloids such as morphine induce a strong analgesic effect, but they also cause physical and psychological dependence and addiction as side effects.

Early in 1970, it was confirmed that opiate receptors are localized in mammalian brain; since then, numerous studies have been done to discover endogenous morphine-like substances which can not cause physical and psychological dependence and addiction. Hughes et al. have isolated two pentapeptides as endogenous opioid peptides [Hughes et al., "Nature" 258, 577 (1975)]. Enkephalins produce a weak and short-lived analgesia following intracerebroventricular (i.c.v.) or intravenous (i.v.) administration to mice and rats. .beta. -Endorphin, which consists of 31 amino acid residues and is a fragment of .beta. -lipotropin, has marked and long-lived analgesic activity following i.c.v. or i.v. administration. However, it is very difficult to massproduce .beta. -endorphin, because it is a high molecular weight polypeptide. Therefore, .beta. -endorphin has not been employed for an analgesic drug.

Shimohigashi et al. have reviewed the studies on synthetic enkephalins [Shimohigashi et al. "Protein, Nucleic acid, Enzyme" 28, 1321 (1983)]. The molecular structure of synthetic enkephalins has been designed to yield enkephalins with the following characteristics: a) lower molecular weight compounds which can be easily prepared, b) higher affinity for the receptors, c) resistance to degradation by enzymes such as aminopeptidase, carboxypeptidase, enkephalinase, and the like, d) easy absorption and diffusion in vivo, e) ability to pass through the blood-brain barrier, f) administration in oral dosage form, g) minimal side effects, and so on. For the chemical modifications in Met- and Leu-enkephalins each amino acid residue in the sequence has been replaced by others or chemically modified, or the enkephalin has been shortened or cyclized; however, no enkephalin analogs have been applied to patients as the analgesic drugs.

In 1980, Rodbard et al. reported symmetrical dimers of enkephalin analogs of the following formula as new synthetic enkephalins (U.S. Pat. No. 4,468,383). ##STR2## or an alkylene group having from 1 to 22 carbon atoms or a direct bond, and ##STR3##

The compounds in which R is H-Tyr-D-Ala-Gly and X is C.sub.1 -C.sub.22 -alkylene show more selectivity for .mu. than for to .delta. -receptors, particularly, DTRE.sub.2 in which X is C.sub.2 -alkylene, shows about 400-fold greater selectivity for .mu. than for .delta. in receptor binding assay [Lutz et al., "Eur. J. Pharmacol." 111, 257 (1985)]. When this compound was assayed using bioassays for opiate activity (GPI and MVD assays), it showed morphine-like activities and greater selectivity for .mu. than for .delta. [Shimohigashi et al., "Peptide Chemistry 1985" p. 51 (1986)].

The main object of the invention is to provide novel enkephalin analogs which are easily mass-produced, exhibit opioid activity, and are useful for an analgesic drug.

The concomitant object is to provide novel enkephalin analogs that can exhibit an analgesic effect without influence of dosage form.

According to this invention, the objects can be achieved by providing the enkephalin analogs of the following formula: ##STR4## wherein in case of

X is D-Val, D-Phe, Pro, D-Met, D-Met(O), D-Leu, D-Glu, D-Glu(OBzl), D-Lys, D-Lys(Z), or D-Arg,

Y is Gly or Phe; and

R is

wherein in case of

X is D-Ala,

Y is Phe; and

R is

its salts and hydrates.

The compound of this invention can be prepared by the method described in EXAMPLES (Examples 1 to 12) given later or by the general method as described by Izumiya et al. [                translated as "Basis and experiments for peptide synthesis" Maruzen Co., Ltd. Japan (1985)]. The compound of this invention can be administered as pharmaceutically acceptable salts such as the hydrochloride, sulfate, sulfonate, phosphate, citrate, benzoate, acetate, propionate, lactate, maleate, malate, succinate, or tartrate.

All of the pharmaceutically acceptable dosage forms may be suitable to prepare a drug containing the compound of this invention, its salt, or hydrate as an active ingredient. The compound can be administered in such oral dosage forms as tablets, capsules, powders, granules, suspensions, or solutions. They can be administered in such non oral dosage forms as sterilized solutions or suspensions. To the compound may be added pharmaceutically acceptable bulking agents, smoothing agents, antiseptics, stabilizers or other additives for dosage forms.

The dosage regimen of the compound according to the invention is selected by taking various factors including the type and severity of symptoms, age, weight, and other conditions of patients, into consideration.

The following abbreviations are used: Tyr, tyrosine; Ala, alanine; Gly, glycine; Met, methionine; Ser, serine; Thr, threonine; Phe, phenylalanine; Pro, proline; Leu, leucine; NMePhe, N-methylphenylalanine; Gly-ol, glycinol; Boc, tert-butoxycarbonyl; Bzl, benzyl; EDC.HCl, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride; HOBt, 1-hydroxybenzotriazole; DMF, N,N-dimethylformamide; Z, carbobenzoxy; TFA, trifluoroacetic acid; EtOAc, ethyl acetate; Et.sub.3 N, triethylamine; HF, hydrogen fluoride. ##STR5##

To a solution of Boc-Tyr-D-Ala-Gly-OH (1.1 mmol) and o-, m-, or p-phenylenediamine (0.5 mmol) in DMF were added HOBt (1.3 mmol) and EDC.HCl (1.2 mmol) at -10.degree. C., followed by reaction at room temperature for 2 days. The solvent was evaporated in vacuo. The residual oil was solidified by adding cold water, washed with 4% NaHCO.sub.3, 5% KHSO.sub.4, and water, and dried over P.sub.2 O.sub.5 in a desiccator. The dried powder was dissolved in DMF (1 ml) and subjected to gel filtration on a column (1.8.times.100 cm) of Sephadex LH-20 in DMF. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo. The residue was dissolved in 1 ml of CHCl.sub.3 -MeOH (9:1, v/v) and subjected to a silica gel column (2.2.times.65 cm), followed by elution with the same solvent. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo. The desired compound was crystallized from DMF-EtOAc-diethyl ether and recrystallized from the same solvent. ##STR6##

Boc-DTRE-.phi. (o-, m-, or p-)(0.2 mmol) was dissolved in TFA at 0.degree. C. After 30 min, the solvent was evaporated in vacuo. The residue was dissolved in 30% AcOH, and subjected to gel filtration on a Sephadex G-15 column (2.0.times.140 cm) in the same solvent. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo. The residue was dissolved in distilled water and the solvent was evaporated in vacuo. This procedure was repeated to remove AcOH from the solution. The residue was dissolved in distilled water. The desired compound was obtained by lyophilization. ##STR7##

To a solution of Boc-Tyr-D-Ala-Gly-OH (1.1 mmol) and trans-1,2-diaminocyclohexane (0.5 mmol) in DMF were added HOBt (1.3 mmol) and EDC.HCl (1.2 mmol) at -10.degree. C., followed by stirring at room temperature for 2 days. The solvent was evaporated in vacuo. The residual oil was dissolved in 30 ml of EtOAc and washed with 5% KHSO.sub.4, 4% NaHCO.sub.3, and a saturated NaCl solution. The residue was dried over Na.sub.2 SO.sub.4 . Na.sub.2 SO.sub.4 was removed by filtration and the filtrate was evaporated to dryness in vacuo. The residue was dissolved in 1 ml of CHCl.sub.3 -MeOH (9:1, v/v), subjected to a silica gel column (0.9.times.40 cm), and aluted with the same solvent. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo to dryness. The desired compound was crystallized from EtOAc-diethyl etherpetroleum ether. ##STR8##

Boc-DTRE-CH (50 .mu.mol) was dissolved in TFA at 0.degree. C. After 30 min, the solvent was evaporated in vacuo. The residue was dissolved in 1 ml of 30% AcOH, subjected to gel filtration on a Sephadex G-15 column (2.0.times.100 cm) in the same solvent. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo. The residue was dissolved in distilled water and the solvent was evaporated in vacuo. This procedure was repeated to remove AcOH from the solution. The residue was dissolved in distilled water. The desired compound was obtained by lyophilization.

Physical properties of the substance obtained Examples 1 to 4 by each were given in following Table 1 and 2. __________________________________________________________________________ Melting Specific   Elemental analysis Yield point rotation   observed calculated Peptides  (%)  (.degree.C.) [.alpha.] .sub.D.sup.20 Rf.sup.1 Rf.sup.2 C  H  N  C  H   N __________________________________________________________________________ Boc--DTRE-.phi.-(o) 53   156-158 -3.4.sup.(a) 0.62 0.74 58.70 6.86 12.35 58.72 6.61 12.45 (0.5 H.sub.2 O) Boc--DTRE-.phi.-(m) 58   157-159 -18.1.sup.(a) 0.56 0.63 58.12 6.72 12.15 58.13 6.65 12.33 (H.sub.2 O) Boc--DTRE-.phi.-(p) 43   158-159 -27.1.sup.(a) 0.54 0.59 58.36 6.63 12.26 58.13 6.65 12.33 (H.sub.2 O) Boc--DTRE--CH 17   146-148 -17.9.sup.(b) 0.63 0.73 57.69 7.28 12.20 57.75 7.27 12.25 (H.sub.2 O) __________________________________________________________________________ .sup.(a) c 1.0, DMF; .sup.(b) c 1.0, MeOH Rf.sup.1 : CHCl.sub.3 --MeOH (5:1, v/v) Rf.sup.2 : CHCl.sub.3 --MeOH--AcOH (50:10:2, v/v) __________________________________________________________________________ Specific.sup.(a) Melting rotation   Amino acid composition Peptides Yield (%) point (.degree.C.) [.alpha.] .sub.D.sup.20 Rf.sup.3 Rf.sup.4 Tyr Ala Gly __________________________________________________________________________ DTRE-.phi.  (o) 78    128-129 +47.2 0.54 0.56 1.96 2.00 2.02 DTRE-.phi. (m) 57    143-145 +24.2 0.52 0.55 1.98 2.00 2.00 DTRE-.phi. (p) 83    160-161 +35.8 0.48 0.54 1.96 2.00 2.06 DTRE--CH 98    131-133 +42.3 0.55 0.58 2.00 2.00 2.08 __________________________________________________________________________ .sup.(a) c 0.5, 95% AcOH Rf.sup.3 : nBuOH--AcOH--pyridine--H.sub.2 O (4:1:1:2, v/v) Rf.sup.4 : 0.1% AcOHn-BuOH--pyridine (11:5:3, v/v, upper layer)

To a solution of Boc-Phe-OH (11 mmol) and ethylene diamine (NH.sub.2 -CH.sub.2 -CH.sub.2 -NH.sub.2) (5 mmol) in DMF were added HOBt (13 mmol) and EDC.HCl (12 mmol), followed by stirring at room temperature for 2 days. The solvent was evaporated in vacuo. The residual oil was solidified by adding cold water, washed with 4% NaHCO.sub.3, 5% KHSO.sub.4, and water on a glass filter and dried over P.sub.2 O.sub.5 in a desiccator. The dried powder was dissolved in 5 ml of DMF and subjected to gel filtration on a Sephadex LH-20 column (5.times.110 cm) in DMF. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo to dryness. The desired compound was crystallized from DMF-MeOH-diethyl ether and recrystallized from the same solvent.

Yield: 89%

Melting point: 197.degree.-198.degree. C.,

Specific rotation: [.alpha.].sub.D =-2.67.degree. (c 0.53, DMF),

HPTLC: Rf.sup.1 value; 0.91 (CHCl.sub.3 -MeOH=9:1, v/v), Rf.sup.2 value; 0.72 (CHCl.sub.3 -MeOH-AcOH=95:5:1, v/v),

Elemental analysis: calculated; C, 64.96; H, 7.63; N, 10.10, observed; C, 64.98; H, 7.62; N, 10.03.

(Boc-Phe-NH-CH.sub.2 -).sub.2 (3 mmol) was dissolved in TFA at 0.degree. C. After 30 min, the solvent was evaporated in vacuo. The residue was solidified by adding diethyl ether and dried over KOH in a desiccator.

Yield: 99%,

Melting point: 213.degree.-217.degree. C. (decomposition)

Specific rotation: [.alpha.].sub.D =+63.8.degree. (c 0.16, 95% AcOH),

HPTLC: Rf.sup.3 value; 0.05 (n-BuOH-AcOH-H.sub.2 O=4:1:5, v/v, upper layer), Rf.sup.4 value; 0.56 (n-BuOH-AcOH-pyridine-H.sub.2 O=4:1:1:2, v/v), Rf.sup.5 value; 0.60 (0.1% AcOH-n-BuOH-pyridine=11:5:3, v/v, upper layer),

Elemental analysis: calculated; C, 49.49; H, 4.85; N, 9.62, observed; C, 49.60; H, 4.91; N, 9.56.

To a solution of Boc-Tyr-D-Ala-OH (1.1 mmol), (H-Phe-NH-CH.sub.2 -).sub.2.2TFA(0.5 mmol), and Et.sub.3 N (1.0 mmol) in DMF were added HOBt (1.3 mmol) and EDC.HCl (1.2 mmol) at -10.degree. C., followed by stirring at room temperature for 2 days. The solvent was evaporated in vacuo. The residual oil was solidified by adding cold water, washed with 4% NaHCO.sub.3, 5% KHSO.sub.4, and water on a glass filter and dried over P.sub.2 O.sub.5 in a desiccator. The dried powder was dissolved in 1 ml of DMF and subjected to gel filtration on a Sephadex LH-20 column (2.times.140 cm) in DMF. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo to dryness. The desired compound was crystallized from DMF-EtOAc-diethyl ether and recrystallized from the same solvent. D-Met(O), or D-Glu(OBzl))

To a solution of Boc-Xxx--OH (1.1 mmol), (H-Phe-NH-CH.sub.2 -.sub.2.2TFA (0.5 mmol) and Et.sub.3 N (1.0 mmol) in DMF were added HOBt (1.3 mmol) and EDC.HCl (1.2 mmol) at -10.degree. C., followed by stirring at room temperature for 2 days. The solvent was evaporated in vacuo. The residual oil was solidified by adding cold water, washed with 4% NaHCO.sub.3, 5% KHSO.sub.4, and water on a glass filter and dried over P.sub.2 O.sub.5 in a desiccator. The dried powder was dissolved in 1 ml of DMF and subjected to gel filtration on a Sephadex LH-20 column (2.times.140 cm) in DMF. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo to dryness. The desired compound was crystallized from DMF-EtOAc-diethyl ether and recrystallized from the same solvent. D-Leu, D-Met(O), or D-Glu(OBzl)

(Boc-Xxx-Phe-NH-CH.sub.2 -).sub.2 (2 mmol) was dissolved in TFA at 0.degree. C. After 30 min, the solvent was evaporated in vacuo. The residue was solidified by adding diethyl ether and dried over KOH in a desiccator. D-Val, D-Leu, D-Met(O), or D-Glu(OBzl))

To a solution of Boc-Tyr-OH (1.1 mmol), (H-Xxx-Phe-NH-CH.sub.2 -).sub.2.2TFA(0.5 mmol) and Et.sub.3 N (1.0 mmol) in DMF were added HOBt (1.3 mmol) and EDC.HCl (1.2 mmol) at -10.degree. C., followed by stirring at room temperature for 2 days. The solvent was evaporated in vacuo. The residual oil was solidified by adding cold water, washed with 4% NaHCO.sub.3, 5% KHSO.sub.4, and water on a glass filter and dried over P.sub.2 O.sub.5 in a desiccator. The dried powder was dissolved in 1 ml of DMF and subjected to gel filtration on a Sephadex LH-20 column (2.times.140 cm) in DMF. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo to dryness. The desired compound was crystallized from DMF-EtOAc-diethyl ether and recrystallized from the same solvent. D-Leu, D-Met(O), or D-glu(OBzl))

(Boc-Tyr-Xxx-Phe-NH-CH.sub.2 -).sub.2 (0.4 mmol) was dissolved in TFA at 0.degree. C. After 30 min, the solvent was evaporated in vacuo. The residue was dissolved in 1 ml of 30% AcOH, subjected to a Sephadex G-15 column (2.0.times.100 cm), and eluted with the same solvent. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo. The residue was dissolved in distilled water and the solvent was evaporated. This procedure was repeated to remove AcOH. The residue was dissolved in distilled water. The desired compound was obtained by lyophilization.

(Boc-Tyr-D-Glu(OBzl)-Phe-NH-CH.sub.2 -).sub.2 (0.4 mmol) was dissolved in TFA at 0.degree. C. After 30 min, the solvent was evaporated in vacuo. The residue was solidified by adding diethyl ether. The powder was dried over KOH in a desiccator. The powder was treated with HF in the presence of 10% anisol at 0.degree. C. for 1 hr. The solvent was evaporated in vacuo. The residue was dried over KOH in a desiccator. The residual oil was dissolved in 10% AcOH, washed with diethyl ether, subjected to a Sephadex G-15 column (2.0.times.100 cm), and eluted with 30% AcOH. The fractions containing the desired compound were pooled and the solvent was evaporated in vacuo. The residue was dissolved in distilled water and the solvent was evaporated. This procedure was repeated to remove AcOH. The residue was dissolved in distilled water. The desired compound was obtained by lyophilization.

The physical properties of the substances obtained by Examples 7-12 are shown in following Tables 3-6. __________________________________________________________________________ Specific rotation Melting [.alpha.] .sub.D.sup.20 Elemental analysis Yield point (c 0.49-0.59,  observed calculated Xxx     (%)  (.degree.C.) DMF)     Rf.sup.1 Rf.sup.2 C  H  N  C  H   N __________________________________________________________________________ Pro     96   139-140 -55.9    0.48 0.24 63.52 7.46 11.15 63.39 7.58 11.09 (0.5 H.sub.2 O) D--Val  98   236-237 -14.4    0.90 0.46 62.45 7.88 10.96 62.32 8.11 10.90 (H.sub.2 O) (dec.) D--Leu  96   215-216 -8.1    0.91 0.48 64.50 8.25 10.71 64.59 8.26 10.76 D--Met(O) 80   188-190 -16.7    0.33 0.09 55.86 7.15 9.87 55.99 7.17 9.79 (0.5 H.sub.2 O) D--Glu(OBzl) 97   200-202 -12.9    0.93 0.48 65.13 6.89 8.36 65.30 6.90 8.46 __________________________________________________________________________ Rf.sup.1 : CHCl.sub.3 --MeOH (9:1, v/v) Rf.sup.2 : CHCl.sub.3 --MeOH--AcOH (95:5:1, v/v) __________________________________________________________________________ Specific rotation Melting [.alpha.] .sub.D.sup.20 Elemental analysis point (c 0.46-0.63,      observed calculated Xxx     Yield (%) (.degree.C.) 95% AcOH) Rf.sup.3 Rf.sup.4 Rf.sup.5 C  H  N  C   H    N __________________________________________________________________________ Pro     100   175-177 -8.6     0.29 0.78 0.80 49.30 5.21 9.88 49.16 5.82 10.12 (3 H.sub.2 O) D--Val  100   110-111 -18.9     0.28 0.79 0.81 49.33 5.89 10.06 49.45 6.23 10.18 (2.5 H.sub.2 O) D--Leu   91   147-148 -18.0     0.05 0.56 0.63 52.43 6.40 10.23 52.29 6.34 10.16 (H.sub.2 O) D--Met(O) 100   212-213 -9.6     0.29 0.80 0.81 45.86 5.30 9.35 45.63 5.41 9.39 (H.sub.2 O) D--Glu(OBzl) 100   197-198 -15.0     0.16 0.61 0.62 55.78 5.36 8.09 55.97 5.38 8.16 (0.5 H.sub.2 O) __________________________________________________________________________ Rf.sup.3 : nBuOH--AcOH--H.sub.2 O (4:1:5, v/v, upper layer) Rf.sup.4 : nBuOH--AcOH--pyridine--H.sub.2 O (4:1:1:2, v/v) Rf.sup.5 : 0.1% AcOHn-BuOH--pyridine (11:5:3, v/v, upper layer) __________________________________________________________________________ Specific rotation Melting [.alpha.] .sub.D.sup.20 Elemental analysis Yield point (c 0.51-0.63,  observed calculated Xxx     (%)  (.degree.C.) DMF)     Rf.sup.6 Rf.sup.7 C  H  N  C  H   N __________________________________________________________________________ Pro     44   129-132 -42.8    0.63 0.68 63.05 7.00 10.46 63.20 7.04 10.17 (1.5 H.sub.2 O) D--Val  70   238-241 -28.8    0.62 0.68 63.63 7.48 10.31 63.48 7.35 10.21 (H.sub.2 O) D--Leu  82   151-153 -10.9    0.64 0.69 63.66 7.39 10.04 63.53 7.55 9.88 (1.5 H.sub.2 O) D--Met(O) 88   221-222 -11.0    0.50 0.50 58.33 6.77 9.41 58.37 6.76 9.39 (H.sub.2 O) D--Glu(OBzl) 94   189-190 -16.2    0.70 0.76 64.64 6.61 8.49 64.65 6.63 8.38 (H.sub.2 O) D--Ala  86   160-161 -13.2    0.59 0.78 62.52 6.89 10.75 62.29 6.97 10.76 (H.sub.2 O) __________________________________________________________________________ Rf.sup.6 : CHCl.sub.3 -- MeOH (5:1, v/v) Rf.sup.7 : CHCl.sub.3 --MeOH--AcOH (50:10:2, v/v) __________________________________________________________________________ Specific rotation Melting [.alpha.] .sub.D.sup.20 Yield point (c 0.49-0.58,     Amino acid composition Xxx      (%) (.degree.C.) 95% AcOH) Rf.sup.3 Rf.sup.4 Rf.sup.5 Tyr Xxx Phe __________________________________________________________________________ Pro     76   116-119 -22.7    0.03 0.42 0.42 1.96 2.02 2.00 D--Val  91   206-207 +40.4    0.16 0.70 0.66 1.98 2.04 2.00 D--Leu  100  162-165 +43.8    0.21 0.76 0.70 2.00 2.04 2.00 D--Met(O) 100  107-108 +32.9    0.04 0.37 0.33 1.94 2.00 2.00 D--Glu(OBzl) 100  114-115 +54.9    0.21 0.76 0.71 1.96 2.02.sup.(a) 2.00 D--Glu  95   189-190 +46.2    0.21 0.74 0.74 1.98 2.06 2.00 D--Ala  89   128-131 +52.0    0.04 0.57 0.62 2.00 2.02 2.00 __________________________________________________________________________ .sup.(a) Glu(OBzl): Glu was detected by hydrolysis. Rf.sup.3, Rf.sup.4, Rf.sup.5 : The composition of each solvent system was described in Table 4. guinea pig ileum (GPl) and the mouse vas deferens (MVD)

The GPl assay was carried out according to the method reported by Kosterlitz et al. ["Br. J. Pharmacol." 39, 398 (1970)]. A male Hartley guinea pig was sacrified by cutting its jugular vein and subjected to an abdominal operation to remove its ileum as a piece of about 40 cm in length from a region 10 cm apart from ileocecal region. Then it was immediately immersed in low Mg.sup.2+ modified Krebs-bicarbonate solution (118 mM NaCl, 4.75 mM KCl, 2.54 mM CaCl.sub.2, 1.19 mM KH.sub.2 PO.sub.4, 0.12 mM MgSO.sub.4, 25 mM NaHCO.sub.3, 11 mM glucose). The myenteric plexus-longitudinal muscle strips were prepared according to the method reported by Paton et al., ["J. Physiol." (London) 194, 13, (1968)]. The strip was mounted in a 7 ml bath in the above-mentioned solution gassed with 95% O.sub.2 -5% CO.sub.2 at 35.degree. C. and stimulated coaxially with rectangular pulses of 1-msec duration at a frequency of 0.1 Hz at supramaximal voltage (70 Volts) to record the resulting contraction through a trasducer. The concentration required to produce a half-maximal effect (lC.sub.50) was calculated for the morphine-like activity of the sample.

The MVD assay was carried out according to the method reported by Hughes et al. ["Br. J. Pharmacol." 53, 371 (1975)]. An albino ddY mouse was decapitated and phlebotomized. Then it was immediately subjected to an abdominal operation to remove its vas deferens. The latter was immersed in modified Krebsbicarbonate solution (118 mM NaCl, 4.75 mM KCl, 2.54 mM CaCl.sub.2, 1.19 mM KH.sub.2 PO.sub.4,25 mM NaHCO.sub.3, 11 mM glucose), and adhering fat and blood vessels were removed. After being washed with the above-mentioned solution, the tissue was mounted in a 7 ml bath in the same solution gassed with 95% O.sub.2 -5% CO.sub.2 at 35.degree. C. and stimulated electrically (70 V, 0.1 Hz, 1 msec) by passage of current between an intramural platinum wire and a ring (10 mm wide) of platinum foil fixed to the top of the organ bath to record the resulting contraction through a transducer.

The concentration required to produce a half-maximal effect (lC.sub.50) was calculated for the morphine-like activity of the sample.

Following Table 7 shows the biological activities of the compound of the present invention by the GPl and MVD assays. Table 7 suggests that the compound of the present invention can inhibit the contraction of GPl and MVD caused by an electric stimulation. The ratio of lC.sub.50 in MVD assay to that in GPl assay suggests that the compound of the present invention would have a higher affinity for the receptor which is bound preferentially by morphine. __________________________________________________________________________ Activity IC.sub.50 (.mu.M) ratio Materials              GPI  MVD   MVD/GPI __________________________________________________________________________ The compound of this invention DTRE-.phi. (o)         0.20 0.95  4.8 DTRE-.phi. (m)         51   265   5.2 DTRE-.phi. (p)         640  600   0.94 DTRE--CH (trans)       0.46 4.2   9.1 (H--Tyr--Xxx--Phe--NH--CH.sub.2 --).sub.2 Xxx = D--Ala           0.042 0.079 1.9 D--Val             0.24 0.13  0.54 D--Leu             1.7  0.25  0.15 Pro                0.11 1.2   11 D--Met (O)         0.051 0.21  4.1 D--Glu             0.49 2.4   4.9 Controls Morphiceptin           0.21 1.2   5.7 H--Tyr--Pro--Phe--Pro--NH.sub.2 DAGO                   0.0064 0.078 12 H--Tyr--D--Ala--Gly--NMePhe--Gly--ol Leu--enkephalin        0.13 0.006 0.046 H--Tyr--Gly--Gly--Phe--Leu--OH DADLE                  0.019 0.00036 0.019 H--Tyr--D--Ala--Gly--Phe--D--Leu--OH DTRE.sub.2 *           0.44 2.7   6.1 (H--Tyr--D--Ala--Gly--NH--CH.sub.2 --).sub.2 __________________________________________________________________________ *Shimohigashi et al., "Peptide Chemistry 1985"  p. 51 (1986).

The compound acording to the invention (Example 1, R=o-phenylene) (50 mg) was added to wheat starch (150 mg) to prepare granules in a conventional manner. The granules (200 mg) were filled in capsules (No. 2) made from gelation (1.0 kg), distilled water (1.5 kg), syrup (0.15 kg) and gum arabic (0.20 kg) to obtain capsuled drug.

Prescription: The compound (Example 1, R = o-phenylene) 10    (mg) D-Mannitol                 40 NaCl                       4 ______________________________________

The components were dissolved in a small amount of distilled water. The solution was aseptically charged in a vail, freeze dried to prepare dry powder sealed in the vail.

The dry powder shall be dissolved in distilled water (2 ml) and then injected to a patient. The solution for injection has an osmotic pressure substantially same with that of the physiological saline solution.

Prescription: The compound (Example 11) 10    (mg) D-Mannitol              40 NaCl                    4 ______________________________________

The components were dissolved in a small amount of distilled water. The solution was aseptically charged in a vial, freeze-dried to prepare dry powder sealed in the vial.

The dry powder shall be dissolved in distilled water (2 ml) and then injected to a patient. The solution for injection has an osmotic pressure substantially same with that of the physiological saline solution.

## Claims

1. An enkephalin analog of the formula ##STR9## wherein X is D-Ala,D-Val,D-Phe, Pro,D-Met,D-met(O), D-Leu, D-Glu, D-Glu(OBzl), D-Lys, D-Lys(Z) or D-Arg; and Y is Phe; Phe; and R is or a salt or hydrate thereof.

2. An enkephalin analog according to claim 1, wherein R is a direct bond.

3. An enkephalin analog according to claim 1, wherein R is ethylene.

4. An enkephalin analog according to claim 1, wherein R is o-phenylene.

5. An enkephalin analog according to claim 1, wherein R is m-phenylene.

6. An enkephalin analog according to claim 1, wherein R is p-phenylene.

7. An enkephalin analog according to claim 1, wherein R is cis-cyclopropane or trans-cyclopropane.

8. An enkephalin analog according to claim 1, wherein R is cis-1,2-cyclobutane, trans-1,2-cyclobutane, cis-1,3-cyclobutane or trans 1,3-cylobutane.

9. An enkephalin analog according to claim 1, wherein R is cis-1,2-cyclopentane, trans-1,2-cyclopentane, cis-1,3-cyclopentane or trans-1,3-cyclopentane.

10. An enkephalin analog according to claim 1, wherein R is cis-1,2-cyclohexane, trans-1,2-cyclohexane, cis-1,3-cyclohexane, trans-1,3-cyclohexane, cis-1,4-cyclohexane or trans-1,4-cyclohexane.

11. An pharmaceutical composition comprising an analgesic effective amount of an enkephalin analog of the formula ##STR10## wherein X is D-Ala D-Val,D-Phe, Pro,D-Met,D-met(O), D-Leu, D-Glu, D-Glu(OBzl), D-Lys, D-Lys(Z) or D-Arg; and Y is Phe; Phe; and R is