SUBSTITUTED DIPEPTIDES, METHODS FOR THEIR PRODUCTION, PHARMACEUTICAL COMPOSITIONS CONTAINING THEM, METHOD FOR MAKING SUCH PHARMACEUTICAL COMPOSITIONS

Abstract: Dipeptides are disclosed having the formula I R₁C*(HCOR₂)-NH-C*(HR₃)-CONH(CH₂) p -C*(R₄R₅)-COR₆ in which R₁, R₂, R₃, R₄, R₅ and R₆ are various substituents, p is 0,1 or 2 and the asterisks indicate chiral centres. The compounds inhibit the aciton of enkephalinase in mammals. Pharmaceutical compositions containing the above com­ pounds are described.

Description: SUBSTITUTED DIPEPTIDES, METHODS FOR THEIR PRODUCTION, PHARMACEUTICAL COMPOSITIONS CONTAINING THEM, METHOD FOR MAKING -SUCH PHARMACEUTICAL COMPOSITION Enkephalin is a natural opiate receptor agonist and is believed to be a mixture of two pentapeptides: H-Tyr-Gly-Gly-Phe-Met-OH (methionine-enkephalin), and H-Tyr-Gly-Gly-Phe-Leu-OH (leucine-enkephalin). Hereinafter, the name enkephalin is used generically to embrace all such compounds. It has been reported by Beluzzi et al., Nature, 2607 625 (1976), that when enkephalin is injected into the brain ventricle of rats, a profound analgesia is obtained. It is also known in the art that enkephalin is acted upon by a group of enzymes known generically as enkephalinases, which are also naturally occurring and is inactivated thereby. European Patent Application No. 79105015.6, publication No. 12401 discloses certain dipeptide derivatives which are described as possessing antihypertensive effects. European Patent Application No. 81110337.3 publication No. 54862 discloses certain dipeptide compounds which possess an enkephalinase inhibitory activity. The present invention comprises compounds having the formula I R1C* (HCOR2)-NH-C* (HR3 )-CONH(CH2)p-C* (R4R5)-COR6 or a mixture of enantiomers or diasterioisomers containing the same, and the pharmaceutically acceptable salts thereof wherein: : R1 is alkyl having from 1 to 6 carbon atcms, ada- mantylmethyl, cycloalkylmethyl having frOm 4 to 8 carbon atoms or A-Xm-CnH2n - wherein X is oxygen or sulfur, A is phenyl which may be substituted with the group Y, wherein Y is halogen, hydroxy, trifluoromethyl, alkoxy having from 1 to 6 carbon atoms, alkyl having from 1 to 6 carbon atoms, 2- or 3-furanyl, 2or 3-thienyl, or phenyl [which may be substituted with halogen, hydroxy, trifluoromethyl, alkoxy having from 1 to 6 carbon atoms or alkyl having fror I to 6 carbon atoms3, benzyl [the phenyl ring of which may be substituted with the group Y, as defined above, 1- or 2-naphthyl, 2- or 3-furanyl or 2- or 3-thienyl; m is O or I anc n is C, , 2, 2, 3, or 4; ; R2 and R 6 may be the same or different and are hydroxy, alkoxy having from 1 to 8 carbon atoms, B-Xm-CnH2n-O- wherein B is phenyl [which may be substituted with the group Y, as defined herein] or 1or 2-naphthyl, X, m, and a are as defined herein provided that when n=0, m=C, -OCH2OCO-alkyl in which the alkyl group has 1 to 6 carbon atoms, -OCH2CO-phenyl [the phenyl In of which may be substituted with the group Y, as defined above), 1-glyceryl, EMI3.1 wherein R7 is hydrogen, alkyl having from 1 to 6 carbon atoms, or pnyl which may be substituted with t group Y, as defined above, and R8 is hydrogen or alkyl having from 1 to 6 carbon atoms; R2 may also be -NR7R8 wherein R7 and R8 are as defined above; ; R3 is alkyl having from 1 to 6 carbon atoms, cycloalkylmethyl having from 4 to 8 carbon atoms, 2or 3- thienylmethyl, 2- or 3-furanylmethyl, 1- or 2naphthylmethyl, or benzyl the phenyl ring of which may be substituted with the group Y, as defined above; R4 is D-CnH2n-Om- wherein D is hydrogen, alkyl having from 1 to 4 carbon atoms or phenyl which may be substituted with the group Z, wherein Z is halogen, hydroxy, trifluoromethyl, alkoxy having from I to 6 carbon atoms, or alkyl having from 1 to 6 carbon atoms; m and n are as defined above: R5 is hydrogen or alkyl having from 1 to 6 carbon atoms; and p is 0, 1 or 2; subject to the following provisos (i) that when R and R, are both hydrogen, and p is 1 or 2 then, a) R1 is chosen from adamantyl methyl, 4-phenylphenyl ethyl, A-Xm-CnH2n- wherein m is 1, X is as defined above and n is 1,2,3 or 4, 1- or 2-naphthyl, 2- or 3-furanyl and 2- or 3 thienyl; and/or b) R2 and/or R6 are chosen from B-Xm-CnH 2n-O- wherein B is as defined above, m is one, X is as defined above and n is 1,2,3 or 4, -OCH2OCO-alkyl in which the alkyl group has 1 to 6 carbon atoms, -OCH2CO-phenyl (in which the phenyl group may be substituted by the group Y, as defined herein), 1-glyceryl, EMI4.1 and R2 may also be -NR7R8 wherein R7 and R8 are as defined herein; and/or c) R3 is 2- or 3-furanylmethyl or 4-phenyl phenylethyl; (ii) when P is zero then R1 is benzyl or benzylthiomethyl; R3 is benzyl or maybe leucyl when 1 is benzyl; R4 is benzyl when R1 is benzyl, and is methyl when R1 is benzylthiomethyl; R5 is hydrogen In formula I, the asterisks denote those carbon atoms which may be asymmetric (chiral) centres. The invention contemplates all isomers at these centres both in pure form and in admixture. One group of compounds of formula I of interest are those in which R4 represents a group D-Cn H2n-Om- as defined above in which the sum of n and m is at least one, that is R4 does not represent hydrogen. Examples of such R4 groups are hydroxy, methoxy, methyl and benzyl with preferred values being methyl and benzyl. Preferred values for the other groups represented in formula I when R4 has such value are as follows: R1 is benzyl optionally para substituted by chlorine, methoxy, methyl or phenyl, 2-phenylethyl or 1- or 2-naphthylmethyl and is most preferably benzyl or p-phenylbenzyl, R2 and R6 are the same or different and are hydroxy, methoxy r ethoxy, benzyloxy, 2-phenoxyethoxy, 1- glyceryl, EMI6.1 or (2,2-dimethyl-1--: :oxopropoxyl methoxy and are most preferably chosen from hydroxy, 2-phenoxyethoxy, 1-glyceryl, EMI7.1 and (2,2-dimethyl-l-oxypropoxy) methoxy1 R3 is benzyl, P -methylbenzyl, p- phenylbenzyl, l-naphthylmethyl or 3-thienylmethyl and is most preferably benzyl or p-phenylbenzyS, and R5 is hydrogen. Another group of compounds of interest are those in which one of R2 and R6 is essentially chosen from 2-phenoxyethoxy, l-glyceryl, EMI7.2 or (2,2-dimethyl-1-oxopropoxy)methoxy and the other is chosen from the foregoing groups or is hydroxy, methoxy, ethoxy or benzyloxy: when R2 and R6 have such values, the preferred values for R1 R3 and R5 are as set forth in the preceding paragraph, and preferred values for R4 are hydrogen, methyl and benzyl. p is preferably one. As used herein, unless stated otherwise, the terms alkyl and alkoxy denote suc groups having straight cr branched carbon chains of from 1 to 6 carbon atoms. The term pivaloyl- oxymethyl is the trivial or common name for the (2,2-dimethyl1-oxopropoxy)methyl group. Balogen includes fluorine, chlorlne, bro-ine anc iodine, Certain of the compounds having structural formula I form salts with pharmaceutically acceptable acids, Hydrochloric, sulfuric, acetic, maleic, fumaric and the like rats be utilized. Compounds having structural formula I wherein R2 and/ or R6 are hydroxy form salts with pharmaceutically acceptable bases. Sodium, potassium and calcium hydroxide as well as sodium and potassium carbonate are examples of suitable bases for this purpose. In addition, salts formed with pharmaceu- tically acceptable aimines such as, for example, ammonia, Nmethylglucamine, benzylamine and morpholine are also contemplated. Specific compounds haying structural formula I within the scope of invention are those having the names: 1. N-[N-[L-1-(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]2-phenylethyl]-L-phenylalanyl]-ss-alanine, (2,2-dimethyl-1 oxopropoxy)methyl ester; 2. N-[N-[L-1-[phenylmethoxy]carbonyl]-2-phenylethyl] L-phenylalanyl]-ss-alanine, (2,2-dimethyl-1-oxopropoxy]methyl ester, 3. N-[N-[L-1-carboxy-2-(4-phenyl)phenylethyl]-Lphenylalanyl]-ss-alanine; 4. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine (2,2-dlmethyl-l-oxopropoxy)metl ester; 5. N-[N-[L-1-carboxy-2-phenylethyl]-L-(4-phenyl) phenylalanyl) --alanine; 6. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; 7. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine, (2,2-imethyl-l-oxoropoxv)methyl ester; 8. N-[N-[L-1-carboxy-2-phenylethyl]-L-phenylalanyl] L-(&alpha;-methyl)-ss-alanine; 9. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-L-(&alpha;-methyl)- ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; 10. N-[N-[L-1-carboxy-2-phenylethyl)]-L-phenylalanyl] ss-alanine, 2-phenoxyethyl ester; 11. N-[N-[(D-1-carboxy-2-phenylethyl)]-L-leucyl)-Lphenylalanine; 12. N-[N-[L-1-carboxy-2-phenylpropyl)]-L-phenylalanyl] L-phenylalanine; 13. N-[N-[L-1-carboxy-3-phenylpropyl)]-L-phenylalanyl] ss-alanine; 14. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-phenylalanyl]-ss-alanine; 15. N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2phenylethyl]-L-phenylalanyl]-ss-alanine; 16. N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]2-phenylethyl]-L-phenylalanyl-ss-alanine; 17. N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2phenylethyl]-L-phenyl]-ss-alanine; 18. N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-phenylethyl]-L-phenylananyl]-ss-alanine; 19. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; 20. n-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; 21. N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]-2 (4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; 22. N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 (4-phenyl)phenylethyl]-L-phenylalanyl)-ss-alanine; 23. N- [N- [L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)tnethoxy)- carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl)-ss-alanine; 24. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylethyl]-ss-alanine; 25. N-[N-[L-[1-[(2-phenoxy)ethoxy)carbonyl]-2phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; 26. N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl] 2-phenylethyl]-L-(4-phenyl)phenylalanyl]-f-alanine; 27. N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; 28. N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; 29. N- IN- [L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]- carbonyl]-2-(4-phenyl)phenylethyl)-L-(4-phenyl)phenylalanyl)- ss-alaine; 30. N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; 31. N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]-2 (4-phenyl)phenylethyl]-L-(4-phenyl)phenylaianyl)-B-alanine; 32. N-[N-[L-[1-[(2,3-dihydroxy]-1-propoxy]carbonyl]-2 l4-phenyl)phenylethyl]-L-(4-phenylOphenylalanyl)-kµ-alanine; 33. N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl0methoxy] carbonyl)-2-(4-phenyl)phenylethyl)-L-(4-phenyl)phenylalanyl)- ss-alanine 34. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl- B-alanine; 35. N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2 phenylethylJ-L-phenylalanyl)-D,L-a-methyl-ss-alaninei 36. N-[N-[L-[1-[(1-oxo-3-isobenxofuranyloxy)]carbonyl] 2-phenylethyl}-L-phenylaIanyl3-D,L-c-methyl-R-alanine; 37. N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 phenylethylJ-L-phenylalanyl)-DrL-a-methyl-B-alaninei 38. N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-phenylethyl]-phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; 39. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalayl]-D,L-&alpha;methyl-B-alanine; 40. N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl) phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl ss-alanine; 41. N-[N-[L-[1-[(1-oxo-3-isobenxofuranyloxy)]carbonyl] 2-(4-phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; 42. N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2-(4 phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methylss-alanine; 43. N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyll-2-(4-phenylwphenylethvll-L-phenylalanyll-D,L- - methyl- 13-alanine; 44. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy] carbonyl]-2-phenylethyl}-L-(4-phenyl)phenylalanyl]-D,L-&alpha;methy1--alanine; 45. N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2 phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; 46. N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl] 2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; 47. N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl] 2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; 48. N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]-carbonyl]-2-phenylethyl]-L-(4-phenyl)phenyl alanyl]-D,L-&alpha;-methyl-ss-alanine; 49. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenyl alanyl]-D,L-&alpha;-methyl-ss-alanine; 50. N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4 phenyl)-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; 51. N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-D, L-&alpha;-methyl-ss-alanine; 52. N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl] 2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; 53. N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]-carbonyl]-2-(4-phenyl)phenylethyl]-L-94-phenyl) phenylalanyl]-D,L-&alpha;-methyl-ss-alanine; 54. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-2-thienylalanyl]-ss-alanine; 55. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropooxy)methoxy] carbonyl]-2-phenylethyl]-L-3-thienylalanyl]-ss-alanine; 56. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-2-furoalanyl]-ss-alanine; 57. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylthyl]-L-phenylalanyl]-&alpha;-methylalanine; 58. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-L-&alpha;-hydroxy- ss-alanine; 59. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D-&alpha;-hydroxy- ss-alanine; 60. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-L-&alpha;-methoxy- ss-alanine; 61. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D-&alpha;-methoxy- ss-alanine; 62. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl- ss-alanine benzyl ester; and 63. N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-(4-methoxy)phenylethyl]-L-phenylalanyl-ss- alanine Also within the scope of the invention are the pharmaceutically acceptable salts of the above listed specific compounds. The compounds having structural formula I may be utilized to exert their analgesic effect in the many dosage forms known to the art, such as tablets, capsules or elixirs for oral administration or in sterile solutions or suspensions for parenteral administration. The foregoing pharmaceutical dosage forms are advantageously prepared using, in addition to a compound of this invention, pharmaceutically acceptable and compatible excipients, binders, preservatives, stabilizers, flavours and the like. In each of the dosage forms the active compound will be administered in a dosage in the range of from about 1 to 100 mg/kg. The doses are to be administered at intervals of from 3 to 8 hours. However, the quantity and frequency of dosage will depend upon such factors as the severity of the pain, the general physical condition of the patient, including the age and weight of the patient and other factors which a person skilled in the art will recognize. The compounds of this invention may be prepared by using reactions and reagents well known in the polypeptide art. Broadly speaking the compounds of formula I are prepared by an appropriate one of the following methods (in which in the following formula p, R 1' R2,R3,R4,R5 and R6 are as defined above including suitable protection of any reactive groups); a} reducing a compound of formula XX at the C=N double bond EMI16.1 b) condensing a keto acid or ester of formula II with an amino acid of formula III in a reactive medium containing a reducing agent EMI16.2 c) coupling an amino acid of formula VIII with an amino acid of formula V EMI16.3 d) reducing a compound of the formula XXI at the C=N double bond EMI16.4 e) condensing a keto acid or ester of formula X with an amino acid in <RTI ID=17.1> G reactive medium containing a reducing agent EMI17.1 in 2 reactive medium containing a reducing agent; f) alkylating an amine of formula III with a compound of formula Y.XII EMI17.2 in whicn X is a halogen atom; followed by removal of any protecting groups if necessary to obtain the desired compound of formula I, and thereafter, if desired converting the compound of formula I into another compound of formula I and/or forming a salt thereof, and if desired isolating a preferred isomer. The following overall procedures may be used to prepare the compounds of this invention from readily available or easily prepared starting material: Procedure 1 EMI18.1 In the foregoing reaction sequence, the amino function of Compound VI is protected by an amino protecting group commonly used in the art (G) such as benzyloxycarbonyl, t-butyl- oxycarbonyl or the like. Compound VI is condensed with an aminoester derivative V wherein G' is benzyloxy, t-butyloxy, Tower-alkoxy or the like. Condensing agents such as dicyclohexyl carbodiimide, or diphenylphosphoryl azide may be employed. Also, activating agents such as l-hydroxybenzotriazole may be employed in the reaction. The resulting dipeptide IV is deprotected at the amine terminus by treatment with acids or by hydrogenation using for example, hydrogen and a metal catalyst. The resulting product (III), is then condensed (according to method (b) as defined above) with a ketoacid or ketoester (II) in a suitable solvent such as water or acetonitrile at a substantially neutral pH in the presence of a reducing agent such as sodium cyanoborohydride or other equivalently functioning reducing agent. Alternatively, the Schiff base resulting from the initial condensation of II and III may be reduced (according to method (a) as defined above) e.g. by catalytic reduction to give I using hydrogen at a pressure of 1 - 4 atmospheres. The catalytic reduction may be effected using Raney nickel catalyst or 10% palladium on carbon or the like. The compounds of formula 1 having a terminal carboxyl group may be prepared from a corresponding ester by hydrolysis or hydrogenolysis. In the foregoing reaction sequence, substituents R1 R2,R3,R4,R5 and R6; and p are as previously defined, G and G' are suitable protecting groups, e.g. benzyloxy carbonyl or t-butyloxy carbonyl Procedure 2 EMI20.1 Procedure 2 is commenced by condensing an R3 substituted amino acid with a ketoester II by procedures substan tially as described in Procedure 1. The resulting inter mediate (VIII) Is then coupled (according to method (c) as defined above) with an R4,R5 substituted amino acid wherein the carboxy group is derivatized by a lower alkoxy, or a dialkylamino group, or an equivalently acting carboxy protective group Gt to form compounds which after removal of protecting groups which may be present will produce products of this invention wherein substituents R1,R2,R3,R4,R5 and R6; and p are as defined above Procedure 3 EMI21.1 An amino acid or ester (IX) wherein R1 and R 2 are defined as above is condensed with a carbonyl compound (X) under conditions described in Procedures 1 and 2 to prepare I (according to methods (d) or (e) as defined above). Substituents R3, R4,R5 and R6; and p are as previously described. Procedure 4 EMI21.2 Intermediate III, whose preparation is shown in Procedure 1, is reacted with a substituted halo ester under conventional alkylating conditions, preferably in the presence of a base (a tertiary amine or an inorganic hydroxide, carbonate or bicarbonate) The reaction is usually carried out in water or in an organic solvent, such as N,N-dimethylformamide or acetonitrile. Substituents R1,R2,R3,R4,R5 and R6; and p are as previously described. In the foregoing reaction sequences wherein water is generated by the reactants (e.g. the condensation of compounds II and III in Method 1), the reaction may be effected by azeotropic distillation of the formed water with suitable high boiling solvents such as toluene or xylene. Alternatively, the reactions may be effected in the presence of dehydrating agents such as molecular sieves or the like. Various of the intermediates for use in the methods and procedures described above can be obtained by following directly or analogously procedures described in European Patent Application publication No. 54862. Further a number of the intermediates for preparing the compounds of this invention are commercially available or they may be readily prepared by art recognized methods. Intermediates for preparing a substantial number of the compounds of this invention are described or the preparation thereof is embodied in publications and treatises relating to peptide chemistry such as, J'H. Jones, in "Comprehensive Organic Chemistry", Vol.2, D. Barton and W.D. Owls, Editors, Pergamon Press, 1979 pp 819-823 and references 2, and 29-31 cited therein. The relevant portions of this publication are incorporated by reference herein. The following exampTes illustrate the preparation of the compounds of the invention. EXAMPLE 1 N-CN-[L-1-CARBOXY-2-(4-PHENYL)PHENYLETHYL]-L-PHENYL- ALANYL--ALANINE BENZYL ESTER A. 4-Phenylphenylpyruvic Acid 40g of Potassium t-butoxide was added to 150 ml of diethyl oxalate in small portions with stirring. After the initial exothermic reaction subsided, the reaction mixture was heated on a steam bath under nitrogen in order to dissolve solids. After cooling down to room temperature, 799 of 4-biphenyl acetic acid methyl ester was added in one portion. The mixture was stirred at 60-70"C., for 2 hours while low boiling material was removed under vaccum. On cooling to room temperature, the viscous residue was stirred with 200 ml of ether and 350 ml of water with cooling. The ether layer was separated and extracted once with 100 ml of water. The aqueous layers were combined, extracted once with ether, made acidic with concentrated HC1 (cooling) and extracted with 2 x 300 ml of ether. Some solids did not dissolve in the ether layer and were filtered. The ether layer was then evaporated to dryness and the semi-solid residue was combined with the preceeding solids. A mixture of 160 ml of conc. HC1 and 350 ml of acetic acid was added to the solids/semi-solid residue mixture, and the resulting mixture was heated under reflux for 2 1/2 hours. On cooling down to 50dC., a solid precipitated, which was filtered and washed with 150 ml of water. The wet solid was stirred with 150 ml of acetonitrile for five minutes, then filtered and dried under high vacuum at room temperature for 3 hours. 42.2 g of the title compound m.p. 215-218"C., were obtained. B. N-[N-[N-tert.-butyloxycarbonyl]-L-phenylalanyl] ss-alanine benzyl ester To a stirred mixture of 0.023 mole each of di-t-butyldicarbonate, L-phenylalanine ss-alanine benzyl ester p-toluenesulfonate, hydroxybenzotriazole, N-dimethylaminopropyl-N'-ethylcarbodimide hydrochloride in 75 ml of dry N,N-dimethylformamide in an ice bath was added 5 ml of N-ethyl-morpholine and the mixture stirred at room temperature for 3 hours, then poured into 600 ml of ice water and extracted with 3 x 150 ml of ether. The ether layers were combined and extracted once with 150 ml of 0.3N HC1, then twice with 300 ml of water, and then dried over Na2S04, filtered and evaporated down to dryness at 28 C in vacuo. 9.0 g of gummy solid residue were obtained. C. N-(L-Phenylalanyl)-ss-alanine benzyl ester hydrochloride 4.0 g of the material from Example IB in 25 ml of ethyl acetate at 05C was stirred with gaseous HC1 for 10 min. Stir at 0 C for I 1/2 hours then at 100C for 30 min. A stream of N2 was passed into the solvent to expel excess HC1. The solution was poured into 200 ml of ether with vigourous stirring, and the precipitated solid filtered, and then dried at room temperature under high vacuum for 2 hours to give 3.35 g of product. D. N-[N-[L-1-Carboxy-2-(4-phenyl)phenylethyl]-Lphenylalanyl]-ss-alanine benzyl ester. A mixture of 9.10 g of N-(L-phenyIalamyl)--alanine benzyl ester hydrochloride and 8.40 g of the compound of Example IA in 500 ml of a mixture of tetrahydrofuran ether (9:1) was treated with triethylamine to pH 6.6 and stirred at room temperature for 1 1/2 hours. A solution of 2.0 g of sodium cyanoborohydride in a mixture of 100 ml of tetrahydrofuranethanol was added dropwise over a period of 2 hours with stirring. Stirring was continued at room temperature overnight. The reaction mixture was concentrated to 75 ml at 40 C in vacuo. The residue was stirred with 400 ml each of 0.5N HC1 and ether for one hour. The ether layer was dried over sodium sulfate, filtered and evaporated to dryness in vacuo. A yellow viscous syrup was obtained which was dissolved in 25 ml of ethanol. Solids were formed, on refrigeratiqn over-night, and were filtered off, washed with cold ethanol (4.2 g) and chromatographed on a column of 300 g of silica gel using a solvent mixture consisting of CHC13:CH30H:CH3C02H (200:10:2). The effluent was divided into fractions which were evaporated to dryness in vacuo. In this manner, 600 mg of a solid product consisting of the title compound, m.p. 192-194 C., were obtained. EXAMPLE 2 N-[N-[L-1-CARBOXY-2-(4-PHENYL)PHENYLETHYL]-L-PHENYL ALANYLJ--ALANINE. A suspension of 590 mg of the product from Example 1 in 100 ml of ethanol was shaken overnight with 200 mg of 10% Pd/C in a Parr apparatus. The resulting mixture was diluted with 40 ml of ethanol and 10 ml of water then heated on a steam bath briefly until all white precipitate dissolved. After cooling, the catalyst was filtered off. The filtrate was evaporated at 500C under vacuum to 5 ml. The solid was filtered, washed with ethanol, and dried at room temperature under high vacuum for 6 hours to yield 155 mg of the title compound m.p. 226 2280C. [&alpha;]D26 = 16.8 (c-0.5, DMF). Analysis Calculated: C, 70.40; H, 6.13; N, 6.08. Found: C, 70.54; H, 6.26; N, 5.97. EXAMPLE 3 N-[N-[L-[1-[PIVALOYLOXYMETHOXY[CARBONYL[-2-PHENYLETHYL)] L-PHENYLALANYL]-ss-ALANINE, PIVALOYLOXYMETHYL ESTER. A. N-(tert.-Butyloxycarbonyl)-ss-alanine, pivaloyloxymethyl ester Triethylamine (32.4 ml) is added to N-tert.-butyloxy- carbonyl ss-alanine (40 g) in N,N'-dimethylformamide at room temperature under a nitrogen atmosphere in a 7 1 round bottom flask. The solution is stirred 15 minutes and chloromethyl pivalate (36.6 g) EM. Rasmussen & BR< N.J. Leonard, J. Amer. Chem. Soc., 89, 5439 (1967)] is added dropwise at 0 C. The solution is stirred at room temperature overnight. The mixture is then diluted with ethyl acetate, filtered, washed with water, then brine, and evaporated to give 70g crude material which was chromatographed (silica gel) eluting with 15% ethyl acetate-hexane to give 62.5 g of product. B. ss-Alanine, pi-valoyloxymethyl ester, trifluoroacetate Trifluoroacetic acid (100 ml) is added to a solution of the product from Example 3A (62 g) in methylene chloride (180 ml) at 0 C. The mixture is stirred at room temperature for two hours, and solvent removed in vacuum to give 100 g product as a pale yellow oil. C. N-[L-l-(Phenylmethoxy)carbonyl-2-phenylethyl )-L- phenylalanine L-Phenylalanine benzyl ester hydrochloride, 190.4 g (0.652 mole) is suspended in 960 mls absolute methanol, 6.7 1 dry (3A sieves) tetrahydrofuran added and the slurry is stirred while adding about 50 ml triethylamine to bring the pH to 6.5-7.0. The pH is checked with EM Reagents ColorpHast indicator sticks, range pH 5-10, moistened with water before use. To the neutral slurry is added 200 9 (0.98 mole) sodium phenyl pyruvate hydrate (Sigma), followed by 240 g crushed 3A molecular sieves. (Sieves may be gound in a mortar and need not be finely powdered. If too fine, they are difficult to remove by filtration). The slurry is stirred at ambient temperature while adding a solution of 61.6 g (0.98 mole) sodium cyanoborohydride in 40 ml methanol plus 300 ml dry tetrahydrofuran dropwise over 5 hours. The reaction is stirred at ambient temperature for 48 to 72 hours while monitoring the disappearance of benzyl ester by thin layer chromatography. The reaction mixture is filtered to remove sieves, washing sieves well with hot methanol, as some product precipitates out on them. The filtrate is concentrated on a rotary evaporator at 50 C to a syrup. This syrup is dissolved in 2.4 1 ether in a 12 1 round bottomed flask and stirred in an ice bath while adding 2.4 1 2.5 aqueous HC1. The large volume of HCN which is generated is passed into a sodium hydroxide trap. The mixture is allowed to stir for 2.5 to 3 hours while a white solid gradually forms at the interface and evolution of HCN stops. The 2-phase mixture is filtered (most of the aqueous phase may be drawn off in a separator before filtering as the product remains at the interface) and the solid is washed well with ether and dried in vacuo below 50 ; yield 80-90 g, m.p. 175-180 C. This material is 90-95% pure L,L isomer as estimated by thin layer chromatography. The crude product is re-dissolved in about 10 1 boiling, absolute methanol, some fine white inorganic insolubles filtered and the filtrate concentrated to 5 1 at the boiling point, when flocculent white crystals appear. The product is allowed to cool slowly to room temperature and then to 0 C for 2-3 hours. The solid is collected and dried in vacuo at 50 C; yield wt 57-60 g, m.p. 185-l860C, [a]D26 5.9 to 6.30C* (DMSO, C=l). The product is greater than 98% L,L isomer as estimated by thin layer chromatography and high pressure liquid chromatography analysis. *(results of several runs) D. N-(L-1-Benzyloxycarbonyl-2-phenylethyl)-L-phenylalanine pivaloyloxymethyl ester. A solution of 4.03 g (10 m mole) of the product from Example 3C and 1.5 ml (llmmole) triethylamine in 20 ml DMF is treated at ambient temperature with 1.6 ml (11 mmole) of chloromethyl-pivalate, stirred at 50 600C for 24 hours, and the resulting slurry poured into water and extracted with 3 x 100 ml ether. Some insoluble are filtered off, and the ether phase washed with water, dried and concentrated to an oil; yield 4.8 g; NMR consistent with structure of title compound. E. N-(L-Carboxy-2-phenylethyl )-L-phenylalanine, piva loyloxymethyl ester The crude ester from Example 3D (4.8 g) is hydrogenated in a Parr apparatus at 60 psig in 50 ml methanol + 5 ml H20 in the presence of 0.4 g of 10% Pd/C for 3 hours, The resulting reaction mixture is filtered and concentrated to a damp solid which was re-crystallized from methanol/ H20. White fluffy needles are filtered off and dried in vacuo; yield 3.0 9, m.p. 122-124 C. TLC showed essentially one spot, Rf 0.2, in CHC13/MeOH/HOAc 100: 1:0.0.5. F. N-(L-l-Pivaloyloxymethylcarbonyl-2-phenylethyl)-L- phenyl-alanine-ss-alanine, pivaloyloxymethyl ester A mixture of 1.0 g (2.3 mmole) of the product from Example 3E and 0.89 g (2.3 mmole) of the product from Example 3B in 25 ml DMF is treated with 1.01 ml (8 mmole) N-ethyl-morpholine followed by 352 mg (2.3 mmole) 1hydroxybenzotriazole hydrate and 439 mg (2.3 mmole) l-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride, and allowed to stir at ambient temperature overnight. Thin layer chromatography still shows starting material present. The reaction mixture is heated to 40-50 C., for 6 hours and allowed to stand at room temperature overnight. The mixture is poured into water and extracted with several portions of ether, then the ether phase is washed well with water, dried and concentrated to an oil (1.2 g). The oil is chromatographed on Merck thin layer chromatography grade silica gel 60-G to yield 0.9 g of oil showing a single spot, R 0.4 in EtOAc/Hexane 1:2 (same system as used for column chromatography.) Analysis: Calculated for C33H44N209: C, 64.69; H, 7.24; N, 4.57. Found: C, 64.47; H, 7.20; N, 4.29. La026 -21.7 (DMF, C=l .0). EXAMPLE 4 N-[N-[L-[1-[(2,2-DIMETHYL-1-OXOPROPOXY)METHOXY]CARBONYL]2-(4-PHENYL)-PHENYLETHYL]-l-PHENYLALANYL]-ss-ALANINE A. N-[D,L-1-Carboxy-2-(4-phenyl)phenylethyl]-L-phenyl alanine, benzyl ester. A stirred suspension of 4-phenylphenylpyruvic acid (24.0 g) and L-phenylalanine benzyl ester hydrochloride (23.2 g) in 1 1. of THF/ethanol (9:1) was brought to pH 6.6 by gradual addition of triethylamine. In the course of this process, all solids dissolved. After stirring the resulting solution for 2 hours at room temperature, a solution of sodium cyanoborohydride (3.5 g) in the same solvent was added dropwise with stirring. The reaction mixture was allowed to stir overnight at room temperature. The reaction mixture was then concentrated to 200 ml under reduced pressure. The residue was poured into 600 ml of 0.3N HC1 with cooling and stirring. A gummy solid separated. The aqueous material was decanted off, anu the remaining solid stirred with 120 ml of ethanol. The resulting solids were filtered, and the wet solids stirred with 100 ml of fresh ethanol. After standing overnight, the solids were filtered and dried to give 22.3 g of solid product. B. N-[D,L-[1.[(2,2-Dimethyl-1-ocopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanine, benzyl ester. Triethylamine (3.05 ml) was added to a solution of N-[D,L1-carboxy-2-(4-phenyl)phenylethyl]-L-phenylalanine, benzyl ester (9.6 g) in 30 ml of dimethylformamide. The mixture was stirred at room temperature for 20 min. and chloromethyl pivalate (3.15 ml) was added. The resulting mixture was heated in a bath at 45-55"C for 4 hours with stirring, then allowed to stir at room temperature overnight. The resulting mixture was diluted with 300 ml of water and extracted with three 150 ml portions of ether. The combined ether layers were extracted twice with 100 ml portions of water, and the ether solution dried over anhydrous Na2S04. Filtration and evaporation in vacuo gave 7.5 g of syrupy product. This material was chromotographed on 135 g of silica gel eluting with a mixture of ethylacetate-cyclohexane (85:15). Fractions containing the desired diastereomeric mixture of products were identified by thin-layer chromotography, combined, and evaporated to dryness in vacuo to give 5.9 g of product as a syrup. C. N-[D,L-[1-[(2,2-Dimethyl-l-oxopropoxy)methoxy]- carbonyl -2-(4-phenyl )phenylethyl3-L-phenylalanine A solution of the above product (5.9 g) in 175 ml of ethanol was hydrogenated at 15-30 psig over 750 mg. of 10%.Pd/C for 2 hours. The reaction mixture was diluted with an additional 250 ml of ethanol and warmed to 45"C to dissolve the precipitated product. Catalyst was filtered from the warm solution, and the filtrate evaporated to give a total of 4.4 9 product. D. N-[N-[L-Ç1-[(2,2-Dimethyl-l-oxopropoxymethoxy]- carbonyl]-2-(4-phenyl)phenylethy13-L-phenylalanyl3- D-alanine, benzyl ester. N-ethylmorpholine (1.2 ml) was added to a stirred mixture of the above product (3.25 g), N-(N,N-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (1.7 g), of hydroxybenzotriazole (1.3 g) and -alanine benzyl ester p-toluenesulfonate (3.0 9) in 25 ml of dimethyl formamide. The mixture was stirred at room temperature for 3 hours, diluted with 200 ml of ice-water and extrac ted with two 125 ml portions of ether. The combined extracts were washed with 250 ml of water and dried over anhydrous MgS04. Filtration and evaporation gave 5.25 g of residue. Thin-layer chromotography (silica gel, CHC13/EtOAc - 10:1) showed two major products, Rf=0.36 and Rf=0.32 (partially overlapping). This material was chromotographed on 350 9 of silica gel (thin-layer chromotography grade), eluting with CHC13-EtOAc (100:5). Fractions containing the pure individual components were identified by thin layer chromatography, combined and evaporated. In this manner 650 mg of faster moving component (L,L-diastereoisomer) was obtained along with 590 mg of L,D-diastereoisomer. The final product was obtained by hydrogenating a solution of 650 mg of L, L-diastereoisomer above in 50 ml ethanol over 50 mg of 10% Pd/C at 15-45 psig for 3 hours. Catalyst was filtered off, and the filtrate evaporated to dryness in vacuo at 300C. The residue was chroma tographed on 50 9 of t.l.c. grade silica gel, eluting initially with 300 ml of CHC13/EtOAc (10:1), then with CHCl3/CH3OH/AcOH (600:10:2). Fractions containing pure product were identified by thin layer chromatography silica gel)CHCl3/CH3OH/AcOH (600:10:2), Rf = 0.31. These fractions were combined, evaporated, and the resiude dried at room temperature in high vacuum over night. The residue was recrystallized from ether and the product dried at 45 C for 3 1/2 hours in high vacuum. Obtain 250 mg. solid, m.p. 101-103 C, ±0D26 -22 (c = 0.5, DMF). EXAMPLE 5 N-[N-[L-[1-[(2,2-DIMETHYL-1-OXOPROPOXY)METHOXY]CARBONYL]2-PHENYLETHYL]-l-PHENYLALANYL]-ss-ALANINE A mixture of 0.9 g (2.1 mmole) of N-(L-l-carboxy-2phenylethyl)-L-phenylalanine, pivaloyloxymethyl ester (Example 3E) and equimolar amounts of g-alanine benzyl ester p-toluenesulfonate (73) mg), l-hydroxybenzotriazole hydrate (321 mg) and l-(3-dimethylaminopropyl)-3- ethyl-carbodiimide HC1 (401 mg) were dissolved in 20 ml DMF containing 0.8 ml (6.3 mmole) N-ethylmorpholine and the mixture stirred at ambient temperature overnight. The yellow solution was poured into water (150 ml) and extracted with 3 x 100 ml ether. The ether phase was washed with water, dried and concentrated to an oil, 1.1 g showing one major spot with minor impurity on thinlayer chromatography. The total product was chromatographed on 150 g silica gel eluting with ethyl acetate/hexane (30:70). The fractirns were combined and concentrated to an oil, Ca3D26 - 20.0 (DMF, c = 1). The above-described product (1.5 g) was hydrogenated at 40 psig in 100 ml absolute EtOH over 0.2 9 10% Pd/C for 3 hours. The catalyst was filtered and the filtrate concentrated to an oil which crystallized, upon drying in high vacuum, overnight. On standing under hexane fine colourless crystals were obtained, which on filtration and drying gave 1.2 9 of product, m.p. 93-95"C, LaJ26 - 27.3 (DMF, c = 1). By following the procedures described in the preceding description and examples, using appropriate intermediates, each of the specific compounds 1-63 listed above can be prepared. In the following table, the shorthand notations C6H5CH2 and C H indicate the benzyl groups; and C H indicates the phenyl group. By way of example utilizing the above described methods, the following compounds of the invention were prepared. Except where indicated all compounds have the L absolute stereochemistry at the chiral centres, and R5 equal to hydrogen. R1 C*HCOR2 NH C*HR3 CONH(CH2)p C*R4R5 COR6 Compound R1 R2 R3 R4 R6 p m.p. c [&alpha;]0 (C,Solv.) A C6H5CH2- -OCH2C6H5 C7H7- H -OCH2OCOC(CH3)3 1 oil -25.0 (0.5, MeOH) B C6H5CH2- -OCH2OCOC(CH3)3 C7H7- H -OCH2OCOC(CH3)3 1 oil -21.7 (1.0, DMF) C C6H5CH2- -OCH2OCOC(CH3)2 C7H7- H -OCH2CH3 1 oil -23.8 (1.0, DMF) D C6H5CH2- -OCH2OCOC(CH3)3 C7H7- H -OCH2C6H5 1 oil -20.0 (1.0, DMF) E C6H5CH2- OH C7H7- H -O(CH2)2O-C6H5 1 141-4 -5.7 (0.4, MeOH) F C6H5CH2- OH C7H7- H -OCH2OCOC(CH3)3 1 180-1 - Ga C6H5CH2- OH C7H7- CH3 OH 1 224-6 - Ha C6H5CH2- -OCH2C6H5 C7H7- CH3 -OCH2OCOC(CH3)3 1 oil -- Compound R1 R2 R3 R4 R6 p m.p. c [&alpha; ;]0 (C,Solv.) Ia C6H5CH2- OH C7H7- -CH2C6H5 OH 1 235-7 -23.7 (1.0, DMF) J p-C6H5-C6H4CH2- OH C7H7- H OH 1 226-8 -16.8 (0.5 DMF) K C6H5CH2- OH p-C6H5-C6H4CH2- H OH 1 229-30 -7.5 (0.5, DMF) L C6H5CH2- -NHC6H4-o-CH3 C7H7- H -OCH2OCOC 1 amorphous - M C6H5CH2- OH (CH3)2CHCH2 C7H7 OH 0 178-80 - AMb C6H5CH2- OH C7H7 C7H7 OH 0 191-92 - N C6H5CH2- OH C7H7 C7H7 OH 0 O C6H5CH2SCH2 OH C7H7 CH3 OH 0 152-4 b D stereochemistry at chiral centre bonded to R1 a 1:1 mixture of D&alpha;L stereoisomers The compounds having structural formula I inhibit the activity of enzymes designated enkephalinases. The compounds are particularly useful for the inhibition of enkephalinase A, which is derived form the striata of both rats and humans. In in vitro tests, selected compounds having structural formula I in a concentra -9 -6 tion range from 10 9 to 10 M have been found to inhibit the activity of the aforementioned enzyme by 50% or more. The following test procedure was utilized to assy the enkephalinase A inhibition of the compounds having structural formula I. Enkephalin (ENK) degrading activity was separated into the following three fractions according to the method of Gorenstein and Snyder, [Life Sci., 25, 2065 (1979): Enk'ase A (Gly3-Phe4), Aminopeptidase, (AP) (try 1 Gly2), and Enktase B (Gly2-Gly3). Enzyme activity was separated by taking the brain tissue (minus cerebellum) from Sprague-Dawley rats and homogenizing it in 30 volumes of 50 mM Tris buffer, pH 7.4, using a Brinkmann Polytron. The resulting homogenate is centrifuged at 50,000xg for 15 min. The pellet, constituting the membrane bound enzyme material, is washed by re-suspending it in Tris and re-centrifuging it 4 times. Following washing, solubilization of the membrane pellet is achieved by incubating it for 45 min. at 37"C in the presence of 15 volumes (based on initial brain weight) of 50mM Tris-1 ,' Triton X-100 buffer, pH 7.4. After centrifugation at l00,00Oxg for 60 minutes to remove non-solubilized material, the Triton soluble supernatant is layered on a 1.5 x 30 cm DEAE Sephacel column previously equilibrated with SO mM Tris-O.lX Triton, pH 7.4. Material is eluted from the column using a 1 liter linear NaC1 gradient running from 0.0 to 0.4 M. Eluant is collected in 7 ml fractions, each of which is assayed for enkephalin degrading activity. Under these conditions Enktase A activity is found to elute between 120 and 200 ml. followed by AP activity (260 to 400 ml) and finally by Enk'ase B activity between 420 and 450 ml. Enkephalin degrading activity is monitored using a radiometric assay. The substrate is 3H-Met5 -ENK (50.1 Ci/mmol, New England Nuclear) diluted in 0.05 M Tris buffer, pH 7.4, such that the final reaction mixture concentration is 40 riM. Total reaction mixture volume including enzyme and substrate is 250 yl. Incubation is carried out for 90 min at 370C. To stop the reaction, tubes are transferred to a boiling water bath for 15 min Assay products are separated from one another using thin layer chromatography. A 4yul aliquot of the reaction mixture is spotted on a Baker-flex Silica Gel 1B plate (20 x 20 cm) along with unlabeled standards (Met5 ENK, tyrosine, tyrosylglycine, tyrosyl -glycyl-glyci ne) and the components co-chromatographed in an isopropanyl: ethyl acetate: 5% acetic acid-solvent system (2:2:1) which is capable of resolving Met5-ENK from its breakdown products. Total running time is approximately 17 hours. TLC tanks are gassed with nitrogen prior to starting the run. Following the run, markers are visualized with ninhydrin spray. These spots, along with remaining plate regions, are cut from the plate and the radioactivity corresponding to each monitored using liquid scintillation counting. IC SOEs are determined using linear regression techniques. Utilizing this procedure, the following nanomolar (nM) concentrations for the specified compounds were found to inhibit the action of enkephalinase A by 50% (IC50). TABLE A Compound Enkephalinase A Inhibition IC50 nM A N.A. B N.A. C N.A. D N.A. E 230 F 580 G 6.4 H N.A.1 I 6.3 J 2.5 K 0.9 L N.A. 1 M 140 AM 12 N 6Q 0 170 Ko activity at 4105nM The following test procedure was utilized to assess the noted compounds1 potentiatiation of the analgesic effects of (DAla2-Met )-enkephalinamide (DAEAM). Background for the use of this procedure is given in Chipkin, R.E., Iorio, L.C., Barnett, A., Berger, J., and Billard, W., Regulatory Peptides: From Molecular Biology to Function, edited by E. Costa and M. Trabucchi, Raven Press, New York, 1982, pp. 235-242. Male CF1 mice (19-239) from Charles River Breeding Labs, Mass., are used (N=lO/dose or dose combination). Tailflick testing is done similar to that of Dewey and Harris, Methods in Narcotic Research, Eds., S. Ehrenpreis and A. Neidle, pp. 101-109, Marcel Dekker, Inc., New York, 1975 using a radiant heat noxious stimulus. Following determination of control latencies (typically 2-3 sec), the mice are first injected (sc or po) with either vehicle or drug and after an appropriate interval injected intracerebroventricularly (icv) with either vehicle (10so1 of saline) or DAEAM according to Haley and McCormic, Br., J. Pharmacol., 12,12 (1957). Tail flick latencies are re-determined 30 min. later, as this has previously been determined to be the time of peak analgesia for DAEAM, a cut-off of 10 seconds is employed. Utilizing this procedure, the following ED50 values (the dose at which half the test animals displayed analgesia) were obtained for selected compounds. TABLE B DAEAM Potentatiation Compound ED50 (route) A 155 mg/k (po) B 37 mg/k (po) C 100 mg/k (po) D 100 mg/k (po) E 30-60 mg/k (po) F 100 mg/k (sc)ê G 50 g (icv) H 100 mg/k (po) I 50 g (icv)ê K 50 g (icv)ê L 100 mg/k (po) 2ED1 00 It should be noted that compounds A, B, C, F and H are ester derivatives; compound H being an ester derivative of compound G, and compound L is an amide derivative. Such derivatization is found to confer oral activity to the parent entity which show poor absorption from the gastrointestinal tract. These derivatives, which show no activity in vitro at 105nM (see Table A), are bioactivated in vivo to deliver the parent (in vivo enkephalinase A inhibitors) to a site of action within the central nervous system (see Table B).

Claims: CLAIMS 1. A compound having the formula I R1C*(HCOR2)-NH-C*(HR3)-CONH(CH2)p-C*(R4R5)-COR6 or a mixture of enantiomers or diasterioisomers containing the same, and the pharmaceutically acceptable salts thereof wherein: R1 is alkyl having from 1 to 6 carbon atoms7 adamantylmethyl, cycloalkylmethyl having from 4 to 8 carbon atoms or A-X -C H 2n - wherein X is oxygen or it n sulfur, A is phenyl which may be substituted with the group Y, wherein Y is halogen, hydroxy, trifluoromethyl, alkoxy having from 1 to 6 carbon atoms, alkyl having from 1 to 6 carbon atoms, 2- or 3-furanyl, 2or 3-thienyl, or phenyl [which may be substituted with halogen, hydroxy, trifluoromethyl, alkoxy having from 1 to 6 carbon atoms or alkyl having from 1 to 6 carbon atoms r benzyl [the phenyl ring of which may be substituted with the group Y, as defined above3, 1- or 2-naphthyl, 2- or 3-furanyl or 2- or 3-thienyl; m is O or 1 and n is 0, 1, 2, 3, or 4; R2 and R may be the same or different and 6 are hydroxy, alkoxy having from 1 to 8 carbon atoms7 B-X -C H -0- wherein B is phenyl [which may be sub m n 2n stituted with the group Y, as defined herein] or 1or 2-naphthyl, X, m, and n are ds defined herein provided that when n=O, m=O, -OCH20CO-alkyl in which the alkyl group has 1 to 6 carbon atoms, -OCH2CO-phenyl [the phenyl ring of which may be substituted with the group Y, as defined above], l-glyceryl, EMI44.1 wherein R7 is hydrogen, alkyl having from 1 to 6 carbon atoms, or phenyl which may be substituted with the group Y, as defined above, and R8 is hydrogen or alkyl having from 1 to 6 carbon atoms; ; R2 may also be -NR7R8 wherein R7and R8 are as defined above; R3 is alkyl having from 1 to 6 carbon atoms, cycloalkylmethyl having from 4 to 8 carbon atoms, 2or 3- thienylmethyl, 2- or 3-furanylmethyl, 1- or 2 naphthylmethyl, or benzyl the phenyl ring of which may be substituted with the group Y, as defined above; R4 is D-C H -O - wherein D is hydrogen, n 2n m alkyl having from 1 to 4 carbon atoms or phenyl which may be substituted with the group Z, wherein Z is halogen, hydroxy, trifluoromethyl, alkoxy having from 1 to 6 carbon atoms, or alkyl having from 1 to 6 carbon atoms; m and n are as defined above: R5 is hydrogen or alkyl having from 1 to 6 carbon atoms; and p is 0, 1 or 2; subject to the following provisos (i) that when R4 and R5 are both hydrogen, and p is 1 or 2 then; a) R1 is chosen from adamantyl, 4-phenyiphenyl- ethyl, A-X -C H - wherein m is 1, X is as m n 2n defined above and n is 1,2,3 or 4, 1- or 2-naphthyl, 2- or 3-furanyl and 2- or 3 thienyl; and/or b) R2 and/or R6 are chosen from B-Xm-CNH O- wherein B is as defined above, m is one, X is as defined above and n is 1,2,3 or 4, -OCH2OCO-alkyl in which the alkyl group has 1 to 6 carbon atoms, -OCH2CO-phenyl (in which the phenyl group may be substituted by the group Y, as defined herein), l-gylceryl, EMI45.1 and R2 may also be -NR7R8 wherein R7 and R8 are as defined herein; and/or c) R3 is 2- or 3-furanylmethyl or 4-phenyl phenylethyl; (ii) when P is zero then R1 is benzyl or benzylthiomethyl; R3 is benzyl or maybe leucyl when 01 is benzyl; R4 is benzyl when R1 is benzyl, and is methyl when R1 is benzylthiomethyl; R5 is hydrogen. 2. A compound of formula I as defined in claim 1, charac terized in that R4 represents a group D-C H -O - as n 2n m defined in claim 1 in which the sum of n and m is at least one. 3. A corrpound of formula I as defined in claim 1 or 2 characterized in that one of R2 and R6 is 2-phenoxy ethoxy, l-glyceryl, EMI46.1 or (2,2-dimethyl-1-oxocropoxy)methoxy, and the other is chosen from the groups defined above or is hydroxy, methoxy1 ethoxy or benzyloxy. 4. A compound as defined in claim 2, characterized in that R1 is benzyl optionally para substituted by chlorine, methoxy, methyl, or phenyl, 2-phenylethyl or 1- or 2-naphthylmethyl R2 and R6 are the same or different and are hydroxy, methoxy, ethoxy, benzyloxy, 2-phenoxyethoxy, 1 glycerol EMI47.1 or (2,2-dimethyl -l-oxopropoxy)methoxy, and R3 is benzyl, p--methylbenzyl, p-phenylbenzyl, 1 naphthylmethyl or 3-thienylmethyl. 5. A compound as defined in claim 4, characterized in that R4 is methyl or benzyl and R5 is hydrogen. 6. A compound as defined in claim 3, characterized in that R1 and R3 are as defined in claim 4, R4 is hydrogen, methyl or benzyl, and R5 is hydrogen. 7. A compound as defined in claim 6, characterized in that R4 is hydrogen. 8. A compound as defined in any one of the preceding claims in which p is one. 9. N-[N-[L-1-(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]2-phenylethyl]-L-phenylalanyl]-G-alanine, (2,2-dimethyl-1oxopropoxy)methyl ester; N-[N-[L-1-[phenylmethoxy]carbonyl]-2-phenylethyl] L-phenylalanyl]-ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[L-1-carboxy-2-(4-phenyl)phenylethyl]-Lphenylalanyl]-ss-alanine; N-[N-[L-1-(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[L-1-carboxy-2-phenylethyl]-L-(4-phenyl) phenylalanyl]-ss-alanine; N-[N-[L-1-(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl])phenylethyl]-L-(4-phenyl)phenylalanyl ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[L-1-(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; ; N-[N-[L-1-carboxy-2-phenylethyl]-L-phenylalanyl] L-(&alpha;-methyl)-ss-alanine; N-[N-[L-1-(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-L-(&alpha;-methyl)- ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[(L-1-carboxy-2-phenylethyl)]-L-phenylalanyl] ss-alanine, 2-phenoxyethyl ester; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]2-phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-phenylethyl]-L-phenylalanyl]-ss-alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]-2 (4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 (4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; ; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl)-2-(4-pbenyl)pbenyletbyll-L-(4-pbenyl)phenylalanyll- ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxygcarbonyll-2-(4-phenyl)- phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]-2 (4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[1-[(2,3-dihydroxy)-1-propoxy)carbonyl]-2 (4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] ss-alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2 phenylethyl]-L-phenylalanyl]-D,L-a-methyl-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl] 2-phenylethyl]-L-phenylalanyl]-D,L-a-methyl-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 phenylethyl]-L-phenvlalanyl3-D,L-u-methyl-ss-21anine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; ; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl) phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenxofuranloxy)]carbonyl] 2-(4-phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2-(4 phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methylss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-phenylethyl] L-(4-phenyl)phenylethyl]-D,L-&alpha;-methyl-ss-alanine; ; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl] 2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl) phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; ; N-[N-[L-[1-[(1-oxo-3-isobenxofuranyloxy)]carbonyl] 2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy)carbonyl]-2-(4 phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-2-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-2-thienylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]2-phenylethyl]-L-3-thienylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]2-phenylethyl]-L-2-furoalanyl]-ss-alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-&alpha;-methylalanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-L-&alpha;-hydroxy-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-D-&alpha;-hydroxy-ss-alanine; N-[ [l-[(22- imethvl-l-oxopropoxy)methoxylc2rbony 2-phenylethyl]-L-phenylalanyl]-L-&alpha;-methoxy-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl}-L-phenylalanyl]-D-a-methoxy-E-alanine; N-[N-[L-[I-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss-alanine benxyl ester; ; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-(4-methoxy)phenylethylJ-L-phenylalanyl-ss-alanine; N-[(L)-1-carboxy-2 phenylethyl]-L-phenyl alanyl-Lphenylalanine; N-[(L)-l-carboxy-2-phenylethyl]-L-leucyl-L-phenylalanine; and/or a salt of one of the foregoing, which contains a free acid function, with a pharmaceutically acceptable base, or a salt of one of the foregoing with a pharmaceutically acceptable acid. 10. A composition which comprises a compound as defined in any one of the preceding claims in combination with a pharmaceutically acceptable carrier. CLAIMS A A method of preparing a compound having the formula I R1C*(HCOR2)-NH-C*(HR3)-CONH(CH2)p-C*(R4R5)-COR6 or e mixture of enantiomers or diasterioisomers con raining the same, and the pharmaceutically acceptable salts thereof wherein: R1 is alkyl having from 1 to 6 carbon atoms, ada mantylmethyl, cycloalkylmethyl having from 4 to 8 carbon atoms or A-Xm-CnH2n-wherein X is oxygen or sulfur, A is phenyl which may be substItuted with the group Y, wherein Y is halogen, hydroxy, trifluoro methyl, alkoxy having from 1 to 6 carbon atoms, alkyl having from 1 to 6 carbon atoms, 2- or 3-furanyl, 2 or 3-thienyl, or phenyl [which may be substituted with halogen, hydroxy, trifluoxomethyl, alkoxy having from 1 to 6 carbon atoms or alkyl having from 1 to 6 carbon atoms], benzyl ithe phenyl ring of which may be substituted wth the group Y, as defined above 1- or 2-naphthyl, 2- or 3-furanyl or 2- or 3-thienyl; it is C or 1 and n is 0, 1, 2, 3, or 4; ; R anc R R6 may be the same or different and are hydroxy, alkoxy having from 1 to 8 carbon atoms, B-Xm-CnH2n-O- wherein B is phenyl [which may be substituted with the group y, as defined herein] or 1or 2-naphthyl, X, m, and n are as defined herein provided that when n=0, m=0, -OCH2OCO-alkyl in which the alkyl group has I to 6 carbon atoms, -OCH2CO-phenyl [the phenyl ring of which may be substituted with the group Y, as defined above 1-glyceryl, EMI55.1 wherein R7 is hydrogen, alkyl having from 1 to 6 carbon atoms, or phenyl which may be substituted with the group y, , as defined above, and R8 is hydrogen or alkyl having from 1 to 6 carbon atoms; R2 may also be -NR7R8 wherein R7and R8 are as defined above; R3 is alkyl having from 1 to 6 carbon atoms, cycloalkylmethyl having from 4 to 8 carbon atoms, 2or 3- thienylmethyl, 2- or 3-furanylmethyl, 1- or 2napthylmethyl, or benzyl the phenyl ring of which may be substituted wit the group Y, as define above; R4 is D-CnH2n-Om- wherein D is hydrogen, alkyl having from i to L carbon atoms or phenyl which may be substituted with the croup Z, wherein Z is halogen, hydroxy, trifluoromethyl, alkoxy having from 1 to 6 carbon atoms, or alkyl having fro 1 to 5 carbon atoms m and n are as defined above; ; R5 is hydrogen or alkyl having fro 1 to 6 carbon atoms; ano p is 0, 1 or 2; subject to the following provisos (i) that when R4 and R5 are both hydrogen and p is 1 or 2 then; a) R1 is chosen from adamantyl, 4-phenylphenyl ethyl, A-Xm-CnH2n- wherein m is 1, X is as defined above and n is 1,2,3 or 4, 1- or 2-naphthyl, 2- or 3-furanyl and 2- or 3 thienyl; and/or b) R2 and/or R6 are chosen from B-Xm-CnH2n whereln B is as defined above, it Is one, X is as defined above and n is 1,2,3 or 4, -OCH2OCO-alkyl in which the alkyl group has 1 to 6 carbon atoms, -OCH2CO-phenyl (in which the phenyl group may be substituted by the group Y, as defined herein), 1-glyceryl. EMI56.1 and R2 may also be -NR7R8 wherein R7 and R8 are as defined herein; and/or c) R3 is 2- or 3-furanylmethyl or 4-phenyl phenylethyl; (iii when P is zero then R1 is benzyl or benzylthiomethyl; R3 is benzyl or maybe leucyl when D1 is benzyl R4 is benzyl when R1 is benzyl, and is methyl when R1 is benzylthiomethyl; R5 is hydrogen; characterized in that the compound is prepared by an appropriate method selected from the following methods (wherein in the following formulae p,Rl,R2,R3,R4,R5, and R6 are as defined above including suitable pro tection of any reactive groups); ; a) reducing a compound of formula XX at the C=N double bond EMI57.1 b) condensing a keto acid or ester of formula II with an amino acid of formula III in a reactive medium containing a reducing agent EMI57.2 c) coupling an amino acid of formula VIII with an amino acid of formula V EMI58.1 d) reducing a compound of the formula XXI at the C=N double bond EMI58.2 e) condensing a keto acid or ester of formula X with an amino acid in a reactive medium containing a reducing agent EMI58.3 f) alkylating an amine of formula III with a compound of formula XXII EMI58.4 in which X is a halogen atom; ; followed by removal of any protecting groups if necessary to obtain the desired compound of formula I, and thereafter, if desired converting the compound of formula I into another compound of formula I and/or forming a salt thereof, and if desired isolating a preferred isomer. 2. A method as defined in claim I, characterized in that a compound of formula I is produced in which R4 represents the group D-C H -O - as defined in 4 - - - n 2n m claim I in which the sum of n and m is at least one. 3. A method as defined in claim 1 or 2, characterized in that a compound of formula I is produced in which one of R2 and R6 is 2-phenoxyethoxy, l-glyceryl, EMI59.1 or (2,2-dimethyl-1-oxopropoxy)methoxy, and the other is chosen from the groups defined above or is hydroxy, methoxy, ethoxy or benzyloxy. t. A method as defined in claim 1 or 2, characterized in that a compound is produced in which R1 is is benzyl optionally Dare substituted by chlorine, methoxy. methyl, or phenyl. 2-henylethyl or 1- or 2-naphthylmethyl R2 and R & are the same or different and are hydroxy methoxy, ethoxy, benzyloxy, 2-phenoxyethoxy, 1 glycerol, EMI60.1 or (2,2-dimethyl-1-oxypropoxy)methoxy, and R3 is benzyl, p-methylbenzyl, p-phenylbenzyl, 1naphthylmethyl or 3-thienylmethyl. 5. A method as defined in claim 4, characterized in that a compound is produced in which R4 is methyl or benzyl and R5 is hydrogen. 6. A method as defined in claim 3, characterized in that a compound is produced in which R1 and R3 are as defined in claim 4, R4 is hydrogen, methyl or benzyl, and R5 is hydrogen. 7. A method as defined in claim 6, characterized in that R4 is hydrogen. 8. A method as defined in any one of the preceding claims, characterized in that a compound is pro duced in which p is one. 9. A method as defined in claim 1, characterized in that the compound N-[N-[L-1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-ss-alanine, (2,2-dimethyl-1ocopropoxy)methyl ester; N-[N-[L-1-[phenylmethoxy)carbonyl]-2-phenylethyl] L-phenylalanyl]-ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[L-1-carboxy-2-(4-phenyl)phenylethyl)-Lphenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[L-1-carboxy-2-phenylethyl]-L-(4-phenyl) phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; ; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[L-1-carboxy-2-phenylethyl]-L-phenylalanyl] L-(&alpha;-methyl)-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-L-(&alpha;-methyl)- ss-alanine, (2,2-dimethyl-1-oxopropoxy)methyl ester; N-[N-[(L-1-carboxy-2-phenylethyl)]-L-phenylalanyl] ss-alanine, 2-phenoxyethyl ester; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]2-phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2phenylethyl]-L-phenylalanyl]-ss-alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]-2 (4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 (4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; ; N-[N-[L-[1-[(1-oxo-3-isobenxofuranylocy)]carbonyl]2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2phenylethyl]-(4-phenyl)L-phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl)-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl)-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl]-2 (4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 (4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-ss-alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2 phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl) 2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1-oropropoxy)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl) phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl] 2-(4-phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2-(4 phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;-methylss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-(4-phenyl)phenylethyl]-L-phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy]methoxy] carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha; ;- methyl-ss-alanine; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl)-2-phenylethyl] L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(1-oxo-3-isobenzofuranyloxy)]carbonyl] 2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2 phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy] carbonyl]-2-phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] D,L-&alpha;-methyl-ss-alanine; ; N-[N-[L-[1-[(2-phenoxy)ethoxy]carbonyl]-2-(4-phenyl] phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl-ss- alanine; N-[N-[L-[1-[(1-oxo-3-isobenxofuranyloxy)]carbonyl] 2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;- methyl-ss-alanine; N-[N-[L-[1-[(2,3-dihydroxy)-1-propoxy]carbonyl]-2-(4 phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl]-D,L-&alpha;-methyl- ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)methoxy]carbonyl]-2-(4-phenyl)phenylethyl]-L-(4-phenyl)phenylalanyl] D,L-&alpha;-methyl-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]-2-phenylethyl]-L-2-thienylalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy)carbonyl]2-phenylethyl]-L-3-thienylalanyl]-ss-alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl]2-phenylethyl]-L-2-furoalanyl]-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-&alpha;-methylalanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy]methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-L-&alpha;-hydroxy-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-D-&alpha;-hydroxy-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-L-&alpha;-methoxy-ss-alanine; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl]-L-phenylalanyl]-D-&alpha;-methoxy-ss-alanine; ; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-phenylethyl3-L-phenylalGnyl-3,L-tl-metnyl-ss-alAnine benzyl ester; N-[N-[L-[1-[(2,2-dimethyl-1-oxopropoxy)methoxy]carbonyl] 2-(4-methoxy)phenylethyl)-L-phenylalanyl-ss-alanine; N-|CL)-l-carhoxy-2 phenylethyl) -L-phenyl alanyl-L- phenylalanine; N-[(L)-1-carboxy-2-phenylethyl]-L-leucyl-L-phenylalanine; or a pharmaceutically acceptable salt is produced. 10. A method of making a pharmaceutical composition, characterized in that a compound of formula I as defined in claim 1 or a mixture of enantiomers or diastereoisomers containing the same or a pharma ceutically acceptable salt thereof, is mixed with a pharmaceutically acceptable carrier or excipient. 11. A method of making a pharmaceutical composition characterized in that a compound of formula I as defined in claim 1 or a mixture of enantiomers or diastereoisomers containing the same, or a pharma ceutically acceptable salt thereof, prepared by the process of any one of the preceding claims, is mixed with a pharmaceutically acceptable carrier or excipient.

Inventors: BERGER, JOEL G.
Applicants: SCHERING CORPORATION
Application year: 1983
Main classification: C07C103
IPC codes: C07C59, A61K38, C07K5, C07D317, C07D307, C07C51