Cyclic CRF analogs

Abstract

Improved CRF peptide antagonists have the formula: ##STR1## wherein R.sub.20 is Cys or Glu; R.sub.23 is Cys, Lys or Orn; provided that when R.sub.20 is Cys, R.sub.23 is Cys and when R.sub.20 is Glu, R.sub.23 is Lys or Orn; or a nontoxic addition salt thereof. Specific CRF antagonists disclosed include (cyclo 20-23) [D-Phe.sup.12, Lys.sup.23, Nle.sup.21,38, ]rCRF(12-41); (cyclo 20-23) [D-Phe.sup.12, Orn.sup.23, Nle.sup.21,38 ]rCRF(12-41) and (cyclo 20-23) [D-Phe.sup.12, Cys.sup.20, Cys.sup.23, Nle.sup.21,38 ]rCRF(12-41).

Description

This invention is directed to peptides and to methods for pharmaceutical treatment of mammals using such peptides. More specifically, the invention relates to analogs of the hentetracontapeptide CRF, particularly antagonists thereof, to pharmaceutical compositions containing such CRF analogs and to methods of treatment of mammals using such CRF analogs.

BACKGROUND OF THE INVENTION

Experimental and clinical observations have supported the concept that the hypothalamus plays a key role in the regulation of adenohypophysial corticotropic cells' secretory functions. Over 25 years ago it was demonstrated that factors present in the hypothalamus would increase the rate of ACTH secretion by the pituitary gland when incubated in vitro or maintained in an organ culture. However, a physiologic corticotropin releasing factor (CRF) was not characterized until ovine CRF (oCRF) was characterized in 1981. As disclosed in U.S. Pat. No. 4,415,558, the disclosure of which is incorporated herein by reference, oCRF was found to be a 41-residue amidated peptide. oCRF lowers blood pressure in mammals when injected peripherally and stimulates the secretion of ACTH and .beta.-endorphin.

Rat CRF (rCRF) was later isolated, purified and characterized; it was found to be a homologous, amidated hentetracontapeptide as described in U.S. Pat. No. 4,489,163, the disclosure of which is incorporated herein by reference. It is sometimes referred to as rat amunine. The formula human CRF has now been determined to be the same as that of rCRF, and the terms rCRF and hCRF are used interchangeably.

A CRF analog was subsequently developed having a high alpha-helical foxing potential which is also a 41-residue amidated peptide. It is commonly referred to as AHC (alpha-helical CRF) and is described in U.S. Pat. No. 4,594,329, the disclosure of which is incorporated herein by reference.

Synthetic rCRF, oCRF and AHC stimulate ACTH and .beta.-endorphin-like activities (.beta.-END-Li) in vitro and in vivo and substantially lower blood pressure when injected peripherally. Antagonists of these compounds are disclosed in U.S. Pat. No. 4,605,642, issued Aug. 12, 1986, the disclosure of which is incorporated herein by reference.

Since the foregoing discoveries, the search for improved CRF analogs has continued.

SUMMARY OF THE INVENTION

Analogs of these CRF peptides have been discovered which exhibit longer lasting and improved biological activity. Certain analogs which are of particular interest are novel CRF antagonists that have improved biological properties in comparison to known CRF antagonists. These peptides have a cyclizing bond between the residues in the 20- and 23-positions. The bond is either a disulfide linkage between two Cys residues or preferably an amide bond (or lactam bridge) between a side chain carboxyl group on the residue in the 20-position, preferably Glu, and a side chain amino group on the 23-position residue, preferably Lys or Orn. oCRF, rCRF and AHC all have Glu as the 20-position residue, and oCRF and AHC have Lys as the 23-position residue.

The peptides also have the preferred optional substitutions of D-Phe in the 12-position and norleucine in the 21 and 38 positions. Other optional substitutions may also be made throughout the molecule as previously taught, and these are considered to be functional equivalents thereof. For example, the Leu residue in the 37-position can be substituted with a methyl group on its .alpha.-carbon atom, as can be other Leu residues throughout the molecule, and such substitutions, both alone and in combination with the aforementioned substitutions, are considered to enhance biopotency. The 41-residue peptide is shortened at the N-terminus to produce the antagonists, preferably by deletion of a sequence of 11 residues. Advantages also flow from the employment of these substitutions in the entire 41-residue peptide, i.e improved CRF agonists.

Pharmaceutical compositions in accordance with the invention include such CRF analogs, including the antagonists, or nontoxic addition salts thereof that are dispersed in a pharmaceutically or veterinarily acceptable liquid or solid carrier. The administration of such peptides or pharmaceutically or veterinarily acceptable addition salts thereof to mammals, particularly humans, in accordance with the invention may be carried out for the regulation of secretion of ACTH, .beta.-endorphin, .beta.-lipotropin, corticosterone and other products of the pro-opiomelanocortin gene and/or for affecting mood, behavioral and gastrointestinal functions and autonomic nervous system activities.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The nomenclature used to define the peptides is that specified by Schroder & Lubke, "The Peptides", Academic Press (1965) wherein, in accordance with conventional representation, the amino group appears to the left and the carboxyl group to the right. The standard 3-letter abbreviations are used to identify the alpha-amino acid residues, and where the amino acid residue has isomeric forms, it is the L-form of the amino acid that is represented unless otherwise expressly indicated, e. g. Ser=L-serine, Orn=L-ornithine, Nle=L-norleucine, Nva=L-norvaline, Abu=L-2-aminobutyric acid, Dbu=L-2,4-diaminobutyric acid, Dpr=L-2,3-diaminopropionic acid, and Har=L-homoarginine. In addition the following abbreviations are used: CML=C.sup..alpha. CH.sub.3 -L-leucine; Aib=C.sup..alpha. CH.sub.3 -L-alanine or 2-aminoisobutyric acid; Nal=L-.beta.-(1- or 2-naphthyl) alanine and Pal=L-.beta.-(2-, 3- or 4-pyridyl ) alanine.

Generally the CRF antagonists have the formula: ##STR2## wherein Y is Ac or hydrogen; R.sub.13 is His, Tyr or Glu; R.sub.14 is CML or Leu; R.sub.15 is CML or Leu; R.sub.17 is Cys or CML, Glu, Asn or Lys; R.sub.18 is Val, Nle or Met; R.sub.19 is CML, Leu, Ile, Ala or Aib; R.sub.20 is Cys or Glu; R.sub.22 is Ala, Aib, Thr, Asp or Glu; R.sub.23 is Cys, Orn or Lys; R.sub.24 is Ala or Aib; R.sub.25 is Asp or Glu; R.sub.26 is Gln, Asn or Lys; R.sub.27 is CML or Leu; R.sub.28 is Ala or Aib; R.sub.29 is Gln, Aib or Glu, R.sub.31 is Ala or Aib; R.sub.32 is His, Aib, Gly, Tyr or Ala; R.sub.33 is Ser, Aib, Asn, Leu, Thr or Ala; R.sub.34 is Asn or Aib; R.sub.36 is Lys, Orn, Arg, Har or Leu; R.sub.37 is CML, Leu or Tyr; R.sub.39 is Glu, Aib or Asp; R.sub.40 is Ile, Aib, Thr, Glu, Ala, Val, Leu, Nle, Phe, Nva, Gly or Gln; and R.sub.41 is Ala, Ile, Gly, Val, Leu, Nle, Phe, Nva or Gln, provided that when R.sub.20 is Glu, R.sub.23 is Lys or Orn and when R.sub.20 is Cys, R.sub.23 is Cys.

A preferred group of antagonists are those having the formula: ##STR3## wherein R.sub.18 is Val Nle or Met; R.sub.20 is Cys or Glu; R.sub.22 is Ala or Thr; R.sub.23 is Cys, Orn or Lys; R.sub.25 is Asp or Glu; R.sub.29 is Gln or Glu; R.sub.32 is His or Ala; R.sub.33 is Ser or Leu; R.sub.34 is Asn or Aib; R.sub.36 is Lys or Leu; R.sub.39 is Glu or Asp; R.sub.40 is Ile or Glu; and R.sub.41 is Ile or Ala; provided that when R.sub.20 is Cys, R.sub.23 is Cys; and when R.sub.20 is Glu, R.sub.23 is Orn or Lys; or a nontoxic addition salt thereof.

A more preferred group of CRF antagonists are those having the formula: ##STR4## wherein Y is Ac or hydrogen; R.sub.18 is Val or Nle; R.sub.19 is CML, Leu, Ile, Ala or Aib; R.sub.20 is Cys or Glu; R.sub.21 is Nle or Met; R.sub.22 is Ala, Aib or Thr; R.sub.23 is Cys, Orn or Lys; R.sub.24 is Ala or Aib; R.sub.25 is Asp or Glu; R.sub.27 is Leu or CML; R.sub.28 is Ala or Aib; R.sub.31 is Ala or Aib; R.sub.34 is Aib or Asn; R.sub.39 is Glu or Asp; and R.sub.41 is Ala or Ile; or a nontoxic addition salt thereof.

Still another group of preferred CRF peptide antagonists are those having the formula: ##STR5## wherein Y is Ac or hydrogen; R.sub.13 is His, Tyr or Glu; R.sub.17 is Glu or CML; R.sub.18 is Val, Nle or Met; R.sub.20 is Cys or Glu; R.sub.22 is Ala, Aib, Thr, Asp or Glu; R.sub.23 is Cys, Orn or Lys; R.sub.24 is Ala or Aib; R.sub.25 is Asp or Glu; R.sub.26 is Gln, Asn or Lys; R.sub.28 is Ala or Aib; R.sub.29 is Gln, Aib or Glu, R.sub.31 is Ala or Aib; R.sub.32 is His, Aib, Gly, Tyr or Ala; R.sub.33 is Ser, Aib, Asn, Leu, Thr or Ala; R.sub.34 is Asn or Aib; R.sub.36 is Lys, Orn, Arg, Har or Leu; R.sub.37 is CML, Leu or Tyr; R.sub.39 is Glu, Aib or Asp; R.sub.40 is Ile, Aib, Thr, Glu, Ala, Val, Leu, Nle, Phe, Nva, Gly or Gln; and R.sub.41 is Ala, Ile, Gly, Val, Leu, Nle, Phe, Nva or Gln, provided that when R.sub.20 is Glu, R.sub.23 is Lys or Orn and when R.sub.20 is Cys, R.sub.23 is Cys.

A particularly preferred group of CRF antagonists are those having the formula: ##STR6## wherein R.sub.20 is Cys or Glu; R.sub.23 is Cys, Lys or Orn; provided that when R.sub.20 is Cys, R.sub.23 is Cys and when R.sub.20 is Glu, R.sub.23 is Lys or Orn; or a nontoxic addition salt thereof. Two analogs of this group which have been found to be particularly biopotent are: cyclo(20-23)[D-Phe.sup.12, Lys.sup.23, Nle.sup.21,38 ]rCRF(12-41), and cyclo(20-23)[D-Phe.sup.12, Orn.sup.23, Nle.sup.21,38 ]rCRF(12-41).

The peptides are synthesized by a suitable method, such as by exclusively solid-phase techniques, by partial solid-phase techniques, by fragment condensation or by classical solution addition.

Common to chemical syntheses of peptides is the protection of the labile side chain groups of the various amino acid moieties with suitable protecting groups which will prevent a chemical reaction from occurring at that site until the group is ultimately removed. Usually also common is the protection of an alpha-amino group on an amino acid or a fragment while that entity reacts at the carboxyl group, followed by the selective removal of the alpha-amino protecting group to allow subsequent reaction to take place at that location. Accordingly, it is common that, as a step in the synthesis, an intermediate compound is produced which includes each of the amino acid residues located in its desired sequence in the peptide chain with various of these residues having side-chain protecting groups.

For example, chemical synthesis of a peptide analog from one preferred group may include the initial formation of an intermediate of the following formula: X.sup.1 -D-Phe-R.sub.13 (X.sup.7 or X.sup.5)-Leu-Leu-Arg(X.sup.3)-R.sub.17 (X.sup.5)-R.sub.18 -Leu-R.sub.20 (X.sup.5 or X.sup.8)-Nle-R.sub.22 (X.sup.2 or X.sup.5)-R.sub.23 (X.sup.3 or X.sup.6)-R.sub.24 -R.sub.25 (X.sup.5)-R.sub.26 (X.sup.4 or X.sup.6)-Leu-R.sub.28 -R.sub.29 (X.sup.4 or X.sup.5)-Gln(X.sup.4)-R.sub.31 -R.sub.32 (X.sup.7)-R.sub.33 (X.sup.2 or X.sup.4)-R.sub.34 (X.sup.4)-Arg(X.sup.3)-R.sub.36 (X.sup.3 or X.sup.6)-R.sub.37 (X.sup.7)-Nle-R.sub.39 (X.sup.5)-R.sub.40 (X.sup.2, X.sup.4 or X.sup.5)-R(X.sup.4)-X.sup.9 wherein: the R-groups are as hereinbefore defined.

X.sup.1 is either hydrogen or an alpha-amino protecting group. The alpha-amino protecting groups contemplated by X.sup.1 are those known to be useful in the art in the step-wise synthesis of polypeptides. Among the classes of alpha-amino protecting groups covered by X.sup.1 are (1) acyl-type protecting groups, such as formyl, acrylyl(Acr), benzoyl(Bz) and acetyl(Ac) which are preferably used only at the N-terminal; (2) aromatic urethan-type protecting groups, such as benzyloxycarbonyl(Z) and substituted Z, such as p-chlorobenzyloxycarbonyl, p-nitrobenzyloxycarbonyl, p-bromobenzyloxycarbonyl, p-methoxybenzyloxycarbonyl; (3) aliphatic urethan protecting groups, such as t-butyloxycarbonyl (BOC), diisopropylmethoxycarbonyl, isopropyloxycarbonyl, ethoxycarbonyl, allyloxycarbonyl; (4) cycloalkyl urethan-type protecting groups, such as fluorenyl methyloxycarbonyl (FMOC), cyclopentyloxy-carbonyl, adamantyloxycarbonyl, and cyclohexyloxy-carbonyl; and (5) thiourethan-type protecting groups, such as phenylthiocarbonyl. The preferred alpha-amino protecting group is BOC.

X.sup.2 is a protecting group for the hydroxyl group of Thr and Ser and is preferably selected from the class consisting of acetyl(Ac), benzoyl(Bz), tert-butyl, triphenylmethyl(trityl), tetrahydropyranyl, benzyl ether(Bzl) and 2,6-dichlorobenzyl (DCB). The most preferred protecting group is Bzl. X.sup.2 can be hydrogen, which means there is no protecting group on the hydroxyl group.

X.sup.3 is a protecting group for the guanidino group of Arg or Har preferably selected from the class consisting of nitro, p-toluenesulfonyl(Tos), Z, adamantyloxycarbonyl and BOC, or is hydrogen. Tos is most preferred.

X.sup.4 is hydrogen or a protecting group, preferably xanthyl(Xan), for the amido group of Asn or Gln. Asn or Gln is preferably coupled without side chain protection in the presence of hydroxybenzotriazole (HOBt).

X.sup.5 is hydrogen or an ester-forming protecting group for the .beta.- or .gamma.-carboxyl group of Asp or Glu, preferably selected from the esters of cyclohexyl (OChx) benzyl (OBzl). 2,6-dichlorobenzyl, methyl, ethyl and t-butyl (Ot-Bu). OChx is preferred for a BOC strategy.

X.sup.6 is hydrogen or a protecting group for the side chain amino substituent of Lys or Orn. Illustrative of suitable side chain amino-protecting groups are Z, 2-chlorobenzyloxycarbonyl(2-Cl-Z), Tos, t-amyloxycarbonyl(Aoc), BOC and aromatic or aliphatic urethan-type protecting groups as specified hereinbefore. 2-Cl-Z is preferred for a BOC strategy.

When His is present, X.sup.7 is hydrogen or a protecting group for the imidazole nitrogen such as Tos or 2,4-dinitrophenyl(DNP), and when Tyr is present, X.sup.7 is hydrogen or a protecting group for the hydroxyl group such as DCB. When Met is present, the sulfur may be protected, if desired, with oxygen.

X.sup.8 is a protecting group for the sulfhydryl group of Cys, preferably p-methoxybenzyl(MeOBzl), p-methylbenzyl, acetamidomethyl, trityl or Bzl; or a suitable protecting group for an amino side chain which is removable without simultaneously removing the protecting group X.sup.6, e.g. a base-labile group such as Fmoc; or a suitable labile protecting group for a carboxyl side chain which is removable without simultaneously removing the protecting group X.sup.5, e.g., a base-labile group such as OFm (fluorenylmethyl ester); or is a direct bond between the residues in the 20- and 23-positions when the cyclic form results from a carba or dicarba bond.

The selection of a side chain amino protecting group is not critical except that it should must be one which is not removed during deprotection of the alpha-amino groups during the synthesis. Hence, the alpha-amino protecting group and the side chain amino protecting group cannot be the same.

X.sup.9 is NH.sub.2, a protecting group such as an ester or an anchoring bond used in solid phase synthesis for linking to a solid resin support, preferably one represented by the formula: -NH-benzhydrylamine (BHA) resin support and -NH-paramethylbenzhydrylamine (MBHA) resin support. Cleavage from a BHA or MBHA resin directly gives the CRF analog amide. By employing a methyl-derivative of such a resin, a methyl-substituted amide can be created, which is considered to be the equivalent thereof.

In the formula for the intermediate, at least one of X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.5, X.sup.6, X.sup.7 and X.sup.8 is a protecting group or X.sup.9 includes resin support. The particular amino acid chosen for each R-group determines whether there will also be a protecting group attached as specified hereinbefore and as generally known in the art. In selecting a particular side chain protecting group to be used in the synthesis of the peptides, the following rules are followed: (a) the protecting group should be stable to the reagent and under the reaction conditions selected for removing the alpha-amino protecting group at each step of the synthesis, (b) the protecting group should retain its protecting properties and not be split off under coupling conditions and (c) the side chain protecting group must be removable, upon the completion of the synthesis containing the desired amino acid sequence, under reaction conditions that will not alter the peptide chain.

If an acyl group is present at the N-terminus, as represented by Y, acetyl, formyl, acrylyl and benzoyl are preferred.

Thus, in one aspect, there is also provided a process for the manufacture of compounds comprising (a) forming a peptide intermediate, as defined hereinbefore, having at least one protective group wherein: X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.5, X.sup.6, X.sup.7 and X.sup.8 are each either hydrogen or a protective group, and X.sup.9 is either a protective group or an anchoring bond to resin support or NH.sub.2 and (b) splitting off the protective group or groups or the anchoring bond from said peptide intermediate and (c) if desired, converting a resulting peptide into a nontoxic addition salt thereof.

When the peptides are prepared by chemical synthesis, they are preferably prepared using solid phase synthesis, such as that described by Merrifield, J. Am. Chem. Soc., 85, p 2149 (1964), although other equivalent chemical syntheses known in the art can also be used as previously mentioned. Solid-phase synthesis is commenced from the C-terminus of the peptide by coupling a protected alpha-amino acid to a suitable resin as generally set forth in U.S. Pat. No. 4,244,946 issued Jan. 21, 1981 to Rivier et al., the disclosure of which is incorporated herein by reference. Such a starting material for an antagonist based upon human CRF can be prepared by attaching alpha-amino-protected Ile to a BHA resin.

Ile protected by BOC is coupled to the BHA resin using methylene chloride and dimethylformamide (DMF). Following the coupling of BOC-Ile to the resin support, the alpha-amino protecting group is removed, as by using trifluoroacetic acid(TFA) in methylene chloride, TFA alone or with HCl in dioxane. Preferably 50 volume % TFA in methylene chloride is used with 0-5 weight % 1,2 ethanedithiol. The deprotection is carried out at a temperature between about 0.degree. C. and room temperature. Other standard cleaving reagents and conditions for removal of specific alpha-amino protecting groups may be used as described in Schroder & Lubke, "The Peptides", 1 pp 72-75 (Academic Press 1965).

After removal of the alpha-amino protecting group of Ile, the remaining alpha-amino- and side chain-protected amino acids are coupled step-wise in the desired order to obtain the intermediate compound defined hereinbefore. As an alternative to adding each amino acid separately in the synthesis, some of them may be coupled to one another prior to addition to the solid phase reactor. The selection of an appropriate coupling reagent is within the skill of the art. Particularly suitable as coupling reagents are N,N'-dicyclohexyl carbodiimide(DCC) and N,N'-diisopropyl carbodiimide(DICI).

Activating or coupling reagents for use in the solid phase synthesis of the peptides are well known in the peptide art. Examples of suitable activating reagents are carbodiimides, such as N,N'-diisopropyl carbodiimide and N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide. Other activating reagents and their use in peptide coupling are described by Schroder & Lubke, supra, in Chapter III and by Kapoor, J. Phar. Sci., 59, pp 1-27 (1970). P-nitrophenyl ester (ONp) can also be used to activate the carboxyl end of Asn or Gln for coupling. For example, BOC-Asn(ONp) can be coupled overnight using one equivalent of HOBt in a 50% mixture of DMF and methylene chloride.

Each protected amino acid or amino acid sequence is introduced into the solid phase reactor in about a threefold excess, and the coupling is carried out in a medium of dimethylformamide(DMF):CH.sub.2 Cl.sub.2 (1:1) or in CH.sub.2 Cl.sub.2 alone. In instances where the coupling is carried out manually, the success of the coupling reaction at each stage of the synthesis is monitored by the ninhydrin reaction, as described by E. Kaiser et al., Anal. Biochem. 34, 595 (1970). In cases where incomplete coupling occurs, the coupling procedure is repeated before removal of the alpha- amino protecting group prior to the coupling of the next amino acid. The coupling reactions can be performed automatically, as on a BECKMAN 990 automatic synthesizer, using a program such as that reported in Rivier et al., Biopolymers, 1978, 17, pp. 1927-1938.

After the desired amino acid sequence has been completed, the intermediate peptide is removed from the resin support unless it is desired to form the cyclizing bond while attached to the resin, as described hereinafter. Removal is effected by treatment with a reagent, such as liquid hydrogen fluoride (HF), which not only cleaves the peptide from the resin but also cleaves all remaining side chain protecting groups X.sup.2, X.sup.3, X.sup.4, X.sup.5, X.sup.6 and X.sup.7 and the alpha-amino protecting group X.sup.1, if still present (unless it is an acyl group which is intended to be present in the final peptide), to obtain the peptide. When using hydrogen fluoride for cleaving, anisole or cresol and methylethyl sulfide are included in the reaction vessel as scavengers. When Met is present in the sequence, the BOC protecting group may be cleaved with trifluoroacetic acid(TFA)/ethanedithiol prior to cleaving the peptide from the resin to eliminate S-alkylation.

The cyclizing step for the CRF peptide analog depends, of course, upon the type of linkage which is desired between the residues in the 20- and 23-positions. When residues of L-Cys are included in both the 20- and 23-positions, it is often more convenient to carry out the cyclizing step following the cleavage from the resin and the removal of all of the protecting groups from the peptide. The cyclic form of the peptide is obtained by oxidization using a ferricyanide solution, preferably as described in Rivier et al., Biopolymers, Vol. 17 (1978), 1927-38, or by air oxidation, or in accordance with other known procedures.

To effect an amide cyclizing linkage, cyclization may be carried out while the partially protected peptide remains attached to the resin as disclosed in A. M. Felix et al., "Synthesis, biological activity and conformational analysis of cyclic GRF analogs", Int. J. Pep. Prot. Res, Vol. 32 (1988), 441-54. Such a procedure effectively creates an amide cyclizing bond between the two desired side chains while other residues, such as Asp, Glu and/or Lys, retain their side-chain protection.

When cyclizing via an amide bond between a side-chain amino group of the 20-position residue and a side-chain carboxyl group of the 23-position residue, or vice-versa, it is preferable to synthesize the protected peptide on an MBHA or BHA resin and to derivatize the benzyl ester of the particular carboxyl acid side chain to the hydrazide while the peptide is still attached to the resin and then react it with a selectively deprotected amino-side chain as set forth in U.S. Pat. No. 4,661,472, issued Apr. 28, 1987. Preferably cyclization is accomplished by using a base-labile protecting group, e.g., OFm, for the carboxyl side-chain of the residue to be involved in the amide-bond bridge and using Fmoc as a protecting group for the amino side chain on the other residue that is to be involved. The .alpha.-amino protecting group on the 1-position residue, whether or not it is to be acylated, and all of the other side-chain protecting groups remain in place while the two base-labile groups are removed using piperidine or the like. Following this selective removal, the reaction to accomplish cyclization is carried out by treating with BOP which effects substantially complete generation of the amide bond. Following cyclization, the peptide is completely deprotected and cleaved from the resin using a reagent, such as HF. Optionally a BOC-protecting group can be first removed using TFA.

Alternatively, cyclizations of peptides by such amide linkages can also be effected using teachings of U.S. Pat. Nos. 4,115,554, (Sep. 19, 1978); 4,133,805 (Jan. 9, 1979); 4,140,767 (Feb. 20, 1979); 4,161,521 (Jul. 17, 1979); 4,191,754 (Mar. 4, 1980); 4,238,481 (Dec. 9, 1980); 4,244,947 (Jan. 13, 1981); and 4,261,885 (Apr. 14, 1981).

The following Example I sets forth a preferred method for synthesizing CRF antagonists by the solid-phase technique.

Example I

The synthesis of the (cyclo 20-23) [D-Phe.sup.12, Lys.sup.23, Nle.sup.21,38 ]-human CRF(12-41) having the formula: ##STR7## is conducted in a stepwise manner on a MBHA hydrochloride resin, such as available from Bachem, Inc., having a substitution range of about 0.43 to 0.46 mequiv/gm resin. The synthesis is performed on an automatic Beckman 990B peptide synthesizer using a suitable program, preferably as follows:

______________________________________ MIX TIMESSTEP REAGENTS AND OPERATIONS MIN.______________________________________1 CH.sub.2 Cl.sub.2 wash-80 ml. (2 times) 32 Methanol(MeOH) wash-30 ml. (2 times) 33 CH.sub.2 Cl.sub.2 wash-80 ml. (3 times) 34 50 percent TFA plus 5 percent 1,2-ethane- 12 dithiol in CH.sub.2 Cl.sub.2 -70 ml. (2 times)5 Isopropanol wash-80 ml. (2 times) 36 TEA 12.5 percent in CH.sub.2 Cl.sub.2 -70 ml. 5 (2 times)7 MeOH wash-40 ml. (2 times) 28 CH.sub.2 Cl.sub.2 wash-80 ml. (3 times) 39 Boc-amino acid (10 mmoles) in 30 ml. of either 30-300 DMF or CH.sub.2 Cl.sub.2, depending upon the solu- bility of the particular protected amino acid, (1 time) plus DCC (10 mmoles) in CH.sub.2 Cl.sub.2______________________________________

Coupling of BOC-Ile results in the substitution of about 0.35 mmol. Ile per gram of resin. All solvents that are used are carefully degassed, preferably by sparging with an inert gas, e.g. helium or nitrogen.

After deprotection and neutralization, the peptide chain is built step-by-step on the resin. Generally, one to two mmol. of BOC-protected amino acid in methylene chloride is used per gram of resin, plus one equivalent of 2 molar DCC in methylene chloride, for two hours. When BOC-Arg(Tos) is being coupled, a mixture of 50% DMF and methylene chloride is used. Bzl is used as the hydroxyl side-chain protecting group for Ser. BOC-Asn or BOC-Gln is coupled in the presence of one equivalent of DCC and two equivalents of HOBt in a 50% mixture of DMF and methylene chloride. 2-Cl-Z is used as the protecting group for the Lys side chain. Tos is used to protect the guanidino group of Arg and the imidazole group of His, and the side chain carboxyl group of Glu is protected by OChx or OFm. At the end of the synthesis, the following composition is obtained: BOC-D-Phe-His(Tos)-Leu-Leu-Arg(Tos)-Glu(OChx)-Val-Leu-Glu(OFm)-Nle-Ala-Lys(Fmoc)-Ala-Glu(OChx)-Gln-Leu-Ala-Gln-Gln-Ala-His(Tos)-Ser(Bzl)-Asn-Arg(Tos)-Lys(2Cl-Z)-Leu-Nle-Glu(OChx)-Ile-Ile-MBHA resin support.

Next cyclization (lactamization) of residues 20 and 23 is performed by the method of A. M. Felix et al., referred to hereinbefore and described more fully as follows. After washes with dichloromethane (DCM) (2.times.) and dimethylformamide (DMF) (2.times.), the OFmc/Fmoc groups of Glu.sup.20 and Lys.sup.23, respectively, were removed by 20% piperidine in DMF (1.times.1 min. and 2.times.10 min.), followed by washing with (DMF) (2.times.), methanol (MeOH) (2.times.) and dichloromethane (DCM) (2.times.). The peptide-resin was cyclized by reaction at room temperature with threefold excess of benzotriazol-1-yl-oxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP) in presence of excess diisoproplyethylamine (DIEA) in dimethylformamide (DMF). After washing, the cyclization was repeated two more times for four hours and once for twelve hours. The reaction was followed by Kaiser ninhydrin test (E. Kaiser et al., Color test for detection of free terminal amino groups in the solid-phase synthesis of peptides, Anal Biochem (1970) 34:595-98) and in general was completed after 24 hours.

After removal of the N.sup..alpha. -Boc protecting group, the fully protected peptide-resin was dried. A total of 4.8 g was obtained; 2 g was cleaved by anhydrous HF (20 mL) in the presence of anisole (0.6 mL) at 0.degree. C. for 90 min. The crude peptide was precipitated and washed with anhydrous diethyl ether (450 mL in 3 portions), filtered, extracted from the resin with 380 mL (4 portions) of 0.1% TFA in CH.sub.3 CN/H.sub.2 O (60:40) and lyophilized to give 1.02 g of crude product.

The crude lyophilized peptide was purified by preparative reverse-phase HPLC (RHPLC) on a system composed of a Waters Associates (Milford, Mass.) Prep LC 3000 System, a Waters Associate 600E System Controller, a SHIMADZU SPD-6A UV Spectrophotometric variable-wavelength detector (detection was 230 nm), Waters 1000 PrepPak Module, and a Fisher (Lexington, Mass.) Recordall Series 5000 strip chart recorder (chart speed 0.25 cm/min.). Peptide purification was made in two steps (TEAP 2.25 and 0.1% TFA). The crude peptide was dissolved in 400 mL buffer A: triethylammonium phosphate (TEAP) (pH 2.25) (1:4 v/v), loaded on a preparative reversed phase HPLC cartridge (5.times.30 cm) packed in the laboratory using Waters polyethylene sleeves and frits and Vydac C.sub.18 slica gel (The Separations Group, Hesperia, Calif.; 300 .ANG. pore size, 15 to 20 .mu.-m particle size). The peptide was eluted using buffer B: 60% CH.sub.3 CN in buffer A with a gradient from 30 to 60% B. Buffers A (triethlyammonium phosphate (TEAP), pH 2.25) and B (CH.sub.3 CN in A) were pumped at a flow rate of 95 mL/min for 90 minutes (retention time of about 36 min.). A total of 20 fractions containing 50-100 mL were screened under isocratic conditions (61% B, retention time about 4.2 min.), and 3 good fractions (numbers 30 to 32) containing the compound were identified and pooled.

In the second step, the pooled fractions (about 160 mL) were diluted with 160 mL of H.sub.2 O and eluted by using as buffer A: 0.1% TFA/H.sub.2 O and B: 0.1% TFA in CH.sub.3 CN/H.sub.2 O (60:40), with a gradient from 40 to 70% B in 90 minutes (retention time ca 60 min.). A total of 19 fractions containing 30-50 mL were screened, 5 fractions (160 mL, numbers 17 to 21) were pooled and lyophilized to yield the final product peptide (yield=70.9 mg: 3.6% of expected amount from the original substitution of the MBHA resin).

Specific optical rotation at the Sodium D line of the peptide synthesized and purified in this manner is measured on a Perkin Elmer Model 241 Polarimeter as [.alpha.].sub.D.sup.25 =-49.degree..+-.1.0 (c=1 in 50% acetic acid) (without correction for the presence of H.sub.2 O and TFA); it has a purity of about 98%. Purity is further confirmed by mass spectroscopy (MS) and capillary zone electrophoresis (CZE).

Amino acid analysis of the peptide [after 4N methanesulfonic acid hydrolysis at 110.degree. C. for 24 h] was performed on a Perkin-Elmer LC system (Norwalk, Conn.) comprising of two Series 10 LC pumps, an ISS-100 sample injector, an RTC 1 column oven, a Kratos Spectroflow 980 fluorescence detector, and an LCI-100 integrator. A Pierce AA511 ion-exchange column was maintained at 60.degree. C. and post column derivatization with o-phthalaldehyde was performed at 52.degree. C. Samples containing the internal standard .gamma.-aminobutyric acid were injected and, 5 minutes after injection, were subjected to a gradient of 0 to 100% B for 25 minutes and then 100% B for 15 minutes. The flow rate was 0.5 mL/min, and A and B buffers were Pierce Pico buffer (pH 2.20) and Beckman Microcolumn sodium citrate buffer (pH4.95), respectively. This analysis gave the expected amino acid ratios.

Biopotency of the product peptide was measured as follows. Rat anterior pituitary glands from male Sprague-Dawley rats were dissociated by collagenase and plated (0.16.times.10.sup.6 cells/well in 48-well plates) in medium containing 2% fetal bovine serum (FBS). Three days after plating, the cells were washed three times with fresh medium containing 0.1% bovine serum albumin (BSA) and incubated for 1 h. Following the 1 h preincubation, the cells were washed once more, and the test peptides were applied in the presence of 1 nM oCRF. At the end of a 3 h incubation period the media were collected and the level of ACTH was determined by radioimmunoassay (Diagnostic Products Corporation). The peptide product of the above described synthesis and purification was found to have three times the biopotency of the standard peptide, [D-Phe.sup.12, Nle.sup.21,38 ]rCRF(12-41).

Administration of the peptide inhibits the secretion of ACTH and .beta.-endorphin-like immuno-activities (.beta.-END-LI).

Example II

The synthesis of (cyclo 20-23) [D-Phe.sup.12, Orn.sup.23, Nle.sup.21,38 ]-human CRF(12-41) having the formula: ##STR8## is conducted as described in Example I above, except that residue 23 is Orn instead of Lys.

Specific optical rotation at the Sodium D line of the peptide is measured, as previously described, as [.alpha.].sub.D.sup.25 =-67.degree..+-.1.0 (c=1 in 50% acetic acid) (without correction for the presence of H.sub.2 O and TFA). It has a purity of about 98%, further confirmed by mass spectroscopy (MS) and capillary zone electrophoresis. The peptide's biopotency, determined as previously described, was twice that of the standard peptide, [D-Phe.sup.12, Nle.sup.21,38 ]rCRF(12-41).

Example III

The peptide (cyclo 20-23) [D-Phe.sup.12, Cys.sup.20, Cys.sup.23, Nle.sup.21,38 ]humanCRF(12-41) having the formula: ##STR9## is synthesized.

According to the synthesis protocol previously described herein, 1.9 g of the fully protected peptide-resin was cleaved by HF. After precipitation and washing with diethyl ether (ca 480 mL in 3 portions), the peptide was extracted with water (200 mL) and 5.0% AcOH (100 mL). The resulting solution was poured into 4.0 L of degassed water and the pH adjusted to 6.8-7.0 with NH.sub.4 OH. As the mixture became cloudy, CH.sub.3 CN (300 mL) was added to avoid precipitation. The mixture was then stirred at 4.degree. C. under air atmosphere, and after 48 h, the cyclization was completed (Ellman test). The pH was adjusted to 5.0 with AcOh and the resulting solution was loaded on a Bio-Rex-70 column (120 mL). The column was washed with 0.5% AcOH (200 mL) and the peptide eluted with 50% AcOH. Fractions were collected and those containing ninhydrin positive material were diluted and lyophilized (80 mg).

Purification was performed in three steps. First the peptide was dissolved in buffer A (TEAP pH 2.25, 300 mL) and eluted by using as buffer B: 60% CH.sub.3 CN in A, with a gradient from 30 to 60% B in 60 minutes (retention time was about 32 min.). A total of 10 fractions were screened under isocratic conditions (53% B, retention time 3.7 min.), and 3 good fractions containing the compound were pooled. In the second step, the pooled fractions (about 150 mL) were diluted with H.sub.2 O (150 mL) and eluted using buffer A: TEAP (pH 6.0) and B: 60% CH.sub.3 CN in A, with a gradient from 30 to 55% B in 60 minutes (retention time about 25 min.). A total of 24 fractions were screened under isocratic conditions (53% B). The pooled fractions (17 to 23) were diluted with H.sub.2 O and eluted using buffer A: 0.1 % TFA/H.sub.2 O and B: 0.1% TFA in CH.sub.3 CN/H.sub.2 O (60:40), with a gradient from 30 to 60% B in 20 minutes (retention time about 10 min.). A total of 5 (30-50 mL) fractions were screened, and 3 good fractions were pooled and lyophilized to yield the product peptide (89.5 mg, 4.4% ).

Administration of the peptide inhibits the secretion of ACTH and .beta.-END-LI.

EXAMPLE IV

Using the procedure as generally set forth Example I, the following peptides are also prepared which are CRF antagonists:

______________________________________(c 20-23) [D--Phe.sup.12, Nle.sup.21,38 ]-AHC(9-41)" [Aib.sup.34 ]-AHC(12-41)" [D--Phe.sup.12, Lys.sup.23 ]-oCRF(10-41)" [Lys.sup.23, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, Lys.sup.23 ]-oCRF(12-41)" [Nle.sup.18,21 ]-AHC(10-41)" [D--Phe.sup.12, Lys.sup.13 ]-rCRF(12-41)" [D--Phe.sup.12, Nle.sup.21, Aib.sup.34 ]-oCRF(12-41)" [D--Phe.sup.12, Orn.sup.23 ]-AHC(12-41)" [D--Phe.sup.12, Aib.sup.22, Lys.sup.23, Nle.sup.21,38 ]-rCRF(12-41) 1" [D--Phe.sup.12, Lys.sup.23, Aib.sup.24, Nle.sup.21,38 ]-rCRF(12-41) q" [D--Phe.sup.12, Orn.sup.23, Aib.sup.28, Nle.sup.21,38 ]-rCRF(12-41) u" [D--Phe.sup.12, Orn.sup.23, Aib.sup.29, Nle.sup.21,38 ]-rCRF(12-41) i" [D--Phe.sup.12, Orn.sup.23, Aib.sup.31, Nle.sup.21,38 ]-rCRF(12-41) 8" [ D--Phe.sup.12, Lys.sup.23, Aib.sup.32, Nle.sup.21,38 ]-rCRF(12-41 )" [D--Phe.sup.12, Lys.sup.23, Aib.sup.34, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, Orn.sup.23, Aib.sup.39, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, Lys.sup.23, Aib.sup.40, Nle.sup.21,38 ]-rCRF(12-41)" [Nle.sup.18,21, D--His.sup.32 ]-AHC(11-41)" [D--Phe.sup.12, Orn.sup.23, Aib.sup.34 ]-rCRF(12-41)" [Lys.sup.23, Nle.sup.21,38 ]-rCRF(10-41)" [D--Phe.sup.12, Orn.sup.23, Nle.sup.21,38, Aib.sup.39 ]-oCRF(9-41)" [Lys.sup.23, Nle.sup.21,38, D--His.sup.32 ]-rCRF(9-41)" [D--Phe.sup.12, Nle.sup.18,21, Aib.sup.22 ]-AHC(12-41)" [Tyr.sup.13, Nle.sup.21, CML.sup.37 ]-oCRF(11-41)" [CML.sup.17, Nle.sup.21,38, Orn.sup.23, CML.sup.37 ]-oCRF(10-41)" [D--Phe.sup.12, Aib.sup.24, Nle.sup.21,38, CML.sup. 37 ]-oCRF(12-41)______________________________________

These peptides are biopotent in inhibiting the secretion of ACTH and .beta.-END-LI in response to various stimuli.

EXAMPLE V

Using the procedure as generally set forth in Example I, the following peptides are also prepared which are CRF antagonists:

______________________________________(c 20-23) [CML.sup.17 ]--AHC(12-41)" [CML.sup.17 ]-oCRF(10-41)" [D--Phe.sup.12, CML.sup.14, Lys.sup.23, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, CML.sup.14 ]-oCRF(12-41)" [Nle.sup.18,21, CML.sup.17 ]--AHC(10-41)" [D--Phe.sup.12, CML.sup.17, Orn.sup.23 ]-rCRF(12-41)" [D--Phe.sup.12, Nle.sup.21, CML.sup.17,37 ]-oCRF(12-41)" [D--Phe.sup.12, CML.sup.15 ]--AHC(12-41)" [D--Phe.sup.12, CML.sup.15, Orn.sup.23, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, CML.sup.17, Lys.sup.23, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, CML.sup.17,37, Lys.sup.23, Nle.sup.21,38 ]-rCRF(12- 41)" [Nle.sup.18,21, CML.sup.17,37, D--His.sup.32 ]-AHC(11-41)" [D--Phe.sup.12, CML.sup.17,37, Orn.sup.23, Aib.sup.34 ]-rCRF(12-41)" [CML.sup.17,37, Lys.sup.23, Nle.sup.21,38 ]-rCRF(10-41)" [D--Phe.sup.12, CML.sup.19, Orn.sup.23 ]-rCRF(12-41)" [D--Phe.sup.12, Nle.sup.21, CML.sup.27,37 ]-oCRF(12-41)" [D--Phe.sup.12, CML.sup.27 ]--AHC(12-41)" [D--Phe.sup.12, CML.sup.19, Lys.sup.23, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, Orn.sup.23, CML.sup.27, Nle.sup.21,38 ]-rCRF(12-41)" [D--Phe.sup.12, CML.sup.19,37, Lys.sup.23, Nle.sup.21,38 ]-rCRF(12- 41)______________________________________

These peptides are biopotent in inhibiting the secretion of ACTH and .beta.-END-LI in response to various stimuli.

EXAMPLE VI

Using the procedure set forth in Example I, the following peptides are also prepared:

______________________________________(c 20-23) [Acetyl-Ser.sup.1, D--Phe.sup.12, Lys.sup.23, Nle.sup.21,38 ]-rCRF" [D--Phe.sup.12, Orn.sup.23 ]-oCRF" [D--Phe.sup.12, Lys.sup.23, D--Ala.sup.24 ]-rCRF(4-41)" [D--Phe.sup.12, Nle.sup.21, Aib.sup.34 ]-oCRF" [Formyl-Ser.sup.1, D--Phe.sup.12, Lys.sup.23, Nle.sup.21,38 ]-rCRF" [CML.sup.17,37 ]-oCRF" [D--Phe.sup.12, CML.sup.17, Orn.sup.23 ]-rCRF(2-41)" [Orn.sup.23, Nle.sup.21,38 ]-oCRF" [D--His.sup.32, Aib.sup.34 ]-oCRF" [D--Phe.sup.12, Lys.sup.23, D--Ala.sup.24, D--His.sup.32 ]-rCRF(6-4 1)" [Nle.sup.21, Aib.sup.29, D--His.sup.32 ]-oCRF" [Acrylyl-Glu.sup.2, Nle.sup.21,38, Orn.sup.23, D--His.sup.32 ]-rCRF(2-41)" [Nle.sup.18,21, D--His.sup.32 ]-AHC" [D--Pro.sup.4, D--Phe.sup.12, Nle.sup.18,21 ]-AHC(4-41)" [D--Tyr.sup.3, Nle.sup.18, Nva.sup.21 ]-AHC" [CML.sup.17, Nle.sup.18,21 ]-AHC" [D--Phe.sup.12, CML.sup.17 ]-AHC" [D--Phe.sup.12, CML.sup.37 ]-AHC" [Nle.sup.18,21, CML.sup.37 ]-AHC" [CML.sup.17 ]-AHC" [Tyr.sup.13 ]-AHC" [Aib.sup.19, Nle.sup.21, CML.sup.37 ]-oCRF" [D--Phe.sup.12, Nle.sup.21,38, Aib.sup.29, CML.sup.37 ]-oCRF" [Nle.sup.21,38, Aib.sup.33, CML.sup.37 ]-oCRF______________________________________

These peptides are biopotent in stimulating the secretion of ACTH and .beta.-END-LI and decreasing systemic blood pressure when administered intravenously.

CRF profoundly stimulates the pituitary-adrenalcortical axis, and CRF agonists should be useful to stimulate the functions of this axis in some types of patients with low endogenous glucocorticoid production. For example, CRF agonists should be useful in restoring pituitary-adrenal function in patients having received exogenous glucocorticoid therapy whose pituitary-adrenalcortical functions remain suppressed. CRF antagonists should be useful to inhibit the functions of this axis in some types of patients with high ACTH and endogenous glucocorticoid production. For example, CRF antagonists may be useful in regulating pituitary-adrenal function in patients having pituitary Cushings disease or any CRF-sensitive tumor.

Most other regulatory peptides have been found to have effects upon the endocrine system, the central nervous system and upon the gastrointestinal tract. Because ACTH and .beta.-END-LI secretion is the "sine qua non" of mammal's response to stress, it was not surprising that CRF has significant effects on the brain as a mediator of many of the body's stress responses. Accordingly, CRF antagonists delivered to the brain should also find application in modifying the mood, learning and behavior of normal and mentally disordered individuals. Furthermore, CRF antagonists in the brain could ameliorate stress-induced conditions to which endogenous CRF might contribute, including some types of hypertension, infertility, decreased libido, impotency and hyperglycemia. Because peripherally administered CRF antagonists reduce the levels of ACTH, .beta.-END, .beta.-lipotropin, other pro-opiomelanocortin gene products and corticosterone, administration of the antagonists may be used to reduce the effects of all of these substances on the brain to thereby influence memory, mood, pain appreciation, etc., and more specifically, alertness, depression and/or anxiety, as well as to modulate the immune system, gastrointestinal tract and adrenalcortical growth and function.

All CRF-related peptides have been shown to dilate the mesenteric vascular bed. CRF antagonists may also be of use for decreasing blood flow to the gastrointestinal tract of mammals, particularly humans. Also, oCRF influences gastric acid production, and CRF antagonists are expected to also be effective to modulate gastrointestinal functions.

CRF antagonists or the nontoxic addition salts thereof, combined with a pharmaceutically or veterinarily acceptable carrier to form a pharmaceutical composition, may be administered to mammals, including humans, either inravenously, subcutaneously, intramuscularly, percutaneously, e.g. intranasally, intracerebroventricularly or orally. The peptides should be at least about 90% pure and preferably should have a purity of at least about 98%; however, lower purities are effective and may well be used with mammals other than humans. This purity means that the intended peptide constitutes the stated weight % of all like peptides and peptide fragments present. Administration to humans may be employed by a physician to inhibit endogenous gluco-corticoid production or for possible uses outlined above. The required dosage will vary with the particular condition being treated, with the severity of the condition and with the duration of desired treatment. In order to block the stress-related effects of endogenous CRF within the central nervous system, it may be necessary to deliver the CRF antagonists into the cerebral ventricle or spinal fluid. Alternatively, a means of modifying the antagonists so that they could penetrate the blood-brain barrier should be found.

Such peptides are often administered in the form of pharmaceutically or veterinarily acceptable nontoxic salts, such as acid addition salts or metal complexes, e.g., with zinc, iron, calcium, barium, magnesium, aluminum or the like (which are considered as addition salts for purposes of this application). Illustrative of such acid addition salts are hydrochloride, hydrobromide, sulphate, phosphate, tannate, oxalate, fumarate, gluconate, alginate, maleate, acetate, citrate, benzoate, succinate, malate, ascorbate, tartrate and the like. If the active ingredient is to be administered in tablet form, the tablet may contain a binder, such as tragacanth, corn starch or gelatin; a disintegrating agent, such as alginic acid; and a lubricant, such as magnesium stearate. If administration in liquid form is desired, sweetening and/or flavoring may be used, and intravenous administration in isotonic saline, phosphate buffer solutions or the like may be effected.

The peptides should be administered under the guidance of a physician, and pharmaceutical compositions will usually contain the peptide in conjunction with a conventional, pharmaceutically or veterinarily-acceptable carrier. Usually, the dosage will be from about 0.01 to about 10 milligrams of the peptide per kilogram of the body weight of the host animal. As used herein all temperatures are .degree.C. and all ratios are by volume. Percentages of liquid materials are also by volume.

Although the invention has been described with regard to its preferred embodiments, which constitute the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention which is set forth in the claims appended hereto. For example, substitutions and modifications at other positions in the CRF peptide chain can be made in accordance with present or future developments without detracting from the potency of the antagonists. Instead of D-Phe at the N-terminus, L-Phe may be present and is considered to be an equivalent. The N-terminus can be extended by Thr, by Leu-Thr, or by Asp-Leu-Thr and/or can be acylated by an acyl group having 7 or less carbon atoms, e.g. acetyl, and such changes are considered to produce equivalent CRF antagonists. In addition, instead of the simple amide at the C-terminal, a lower alkyl-substituted amide, e.g. 1-4 carbon atoms, i.e. methylamide, ethylamide, etc, may be incorporated. Such peptides are considered as being within the scope of the invention.

Various features of the invention are emphasized in the claims which follow.

Claims

1. A cyclic CRF peptide antagonist having the formula: ##STR10##

2. A CRF cyclic peptide antagonist having the formula: ##STR11##