Pro-Amb reverse turn restricted bioactive peptide analogues

Abstract

The present invention discloses novel peptides acting as angiotensin II analog for therapeutic applications. Said peptides can be used for treatment of Alzheimer's and other neurological and cognitive disorders.

Claims

1. A peptide or a fragment thereof having the Formula I: ##STR00005## wherein R.sub.1 is selected from the group consisting of aspartate (Asp), tyrosine (Tyr) and alanine (Ala), or R.sub.1 is absent; R.sub.2 is arginine (Arg); R.sub.3 is isoleucine (Ile); R.sub.4 is selected from the group consisting of tyrosine (Tyr), histidine (His) and glutamate (Glu), or R.sub.4 is absent; R.sub.5 is selected from the group consisting of leucine (Leu), proline (Pro) and threonine (Thr), or R.sub.5 is absent; R.sub.6 is selected from the group consisting of glutamate (Glu) and phenylalanine (Phe), or R.sub.6 is absent, wherein proline-3-amino-2-methoxy-2-benzoic acid (Pro-Amb) has a -turn configuration between R.sub.2 and R.sub.3.

2. The peptide according to claim 1, wherein a -turn configuration is between 3-amino-2-methoxy benzoic acid (Amb) and R.sub.2 through hydrogen bonding which is stable under aqueous conditions.

3. The peptide according to claim 1, wherein the peptide of formula I is analogue 1 ##STR00006##

4. The peptide according to claim 1, wherein the peptide of formula I is analogue 2 ##STR00007##

5. The peptide according to claim 1, wherein the peptide of formula I is analogue 3 ##STR00008##

6. A pharmaceutical composition comprising a peptide or a fragment thereof having the Formula 1: ##STR00009## wherein R.sub.1 is selected from the group consisting of aspartate (Asp), tyrosine (Tyr) and alanine (Ala), or R.sub.1 is absent; R.sub.2 is arginine (Arg); R.sub.3 is isoleucine (Ile); R.sub.4 is selected from the group consisting of tyrosine (Tyr), histidine (His) and glutamate (Glu), or R.sub.4 is absent; R.sub.5 is selected from the group consisting of leucine (Leu), proline (Pro) and threonine (Thr), or R.sub.5 is absent; R.sub.6 is selected from the group consisting of glutamate (Glu) and phenylalanine (Phe), or R.sub.6 is absent, wherein proline-3-amino-2-methoxy-2-benzoic acid (Pro-Amb) has a -turn configuration between R.sub.2 and R.sub.3; and a pharmaceutically acceptable carrier.

7. The pharmaceutical composition according to claim 6, wherein the pharmaceutically acceptable carrier is a physiologically compatible buffer selected from the group consisting of: Phosphate buffer saline (PBS), a mixture of saline and glucose, and heparinized sodium-citrate-citric acid-dextrose solution.

Description

DETAILED DESCRIPTION OF DRAWINGS

(1) FIG. 1(a) represents the chemical structure and characteristic ROE excerpts for -turn conformation [H.sub.2O:D.sub.2O, (9:1), 700 MHz, 298K] of Arg-Pro-Amb-Ile (Analogue 3) (SEQ ID NO: 3). *The C7H proton signals were not distinctly visible due to water suppression.

(2) FIG. 1(b) represents the chemical structure and characteristic ROE excerpts for -turn conformation [H.sub.2O:D.sub.2O, (9:1), 700 MHz, 298K] of Asp-Arg-Pro-Amb-Ile-His-Pro (Analogue 2) (SEQ ID NO: 2). *The C11H proton signals were not distinctly visible due to water suppression.

(3) FIG. 1(c) represents the chemical structure and characteristic ROE excerpts for -turn conformation [H.sub.2O:D.sub.2O, (9:1), 700 MHz, 298K] of Asp-Arg-Pro-Amb-Ile-His-Pro-Phe (Analogue 1) (SEQ ID NO: 1). *The C11H proton signals were not distinctly visible due to water suppression.

(4) FIG. 2 depicts the circular dichroism spectra of Angiotensin II and SEQ ID NOs.1, 2 and 3 (0.2 mM in water)

(5) FIG. 3(a) depicts representative phase contrast images of NG108-15 cells displaying neurite outgrowth after 3 days treatment by control.

(6) FIG. 3(b) depicts representative phase contrast images of NG108-15 cells displaying neurite outgrowth after 3 days treatment by PD 123319 (10 M).

(7) FIG. 3(c) depicts representative phase contrast images of NG108-15 cells displaying neurite outgrowth (highlighted by white arrows) after 3 days treatment by Ang II (100 nM).

(8) FIG. 3(d) depicts representative phase contrast images of NG108-15 cells displaying neurite outgrowth (highlighted by white arrows) after 3 days treatment by SEQ ID No.1 (1 M). The cells in FIGS. 3(a)-3(d) were plated at an initial density of 3.610.sup.4 cells/petri dish (35 mm).

(9) FIG. 4 depicts the quantification of neurite outgrowth experiment, the effect of analogues 3, 2 and 1 on neurite outgrowth in NG108-15 cells.

DETAILED DESCRIPTION OF THE INVENTION

(10) The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

(11) For the purposes of the present invention, the designations SEQ ID NO: 1, 2 and 3 can be interchangeably used with analogue 1, analogue 2, and analogue 3, respectively.

(12) An embodiment of the present invention provides a peptide or a fragment thereof having the formula I:

(13) ##STR00002##

(14) wherein R.sub.1 is selected from the group consisting of aspartate (Asp), tyrosine (Tyr) and alanine (Ala), or R.sub.1 is absent;

(15) R.sub.2 is selected from the group consisting of serine (Ser), arginine (Arg) and isoleucine (Ile);

(16) R.sub.3 is selected from the group consisting of tyrosine (Tyr), isoleucine (Ile) and serine (Ser);

(17) R.sub.4 is selected from the group consisting of tyrosine (Tyr), histidine (His) and glutamate (Glu), or R.sub.4 is absent;

(18) R.sub.5 is selected from the group consisting of leucine (Leu), proline (Pro) and threonine (Thr), or R.sub.5 is absent;

(19) R.sub.6 is selected from the group consisting of glutamate (Glu) and phenylalanine (Phe), or R.sub.6 is absent,

(20) wherein proline-3-amino-2-methoxy benzoic acid scaffold (Pro-Amb) as a turn is incorporated between R.sub.2 and R.sub.3.

(21) Another embodiment of the present invention provides the sequence of peptide having formula I selected from the group consisting of SEQ ID NO: 1 (Asp-Arg-Pro-Xaa-Ile-His-Pro-Phe), SEQ ID NO: 2 (Asp-Arg-Pro-Xaa-Ile-His-Pro) and SEQ ID NO: 3 (Arg-Pro-Xaa-Ile), wherein Xaa represents 3-amino-2-methoxybenzoic acid, a non-coded amino acid abbreviated as Amb.

(22) Still another embodiment of the present invention provides a peptide or a fragment thereof having sequence selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 2 and SEQ ID NO: 3, wherein the peptide or a fragment thereof is an analogue of angiotensin II.

(23) For the purpose of the present invention, Xaa has been replaced with Amb in the sequence of analogue 1, analogue 2 and analogue 3 in the description and figures.

(24) Angiotensin II is an octapeptide hormone that plays a central role in cardiovascular homeostasis and its native sequence is Asp.sup.1-Arg.sup.2-Val.sup.3-Tyr.sup.4-Ile.sup.5-His.sup.6-Pro.sup.7-Phe.sup.8 (SEQ ID NO: 4).

(25) Analogue 1 is designed by replacement of Val.sup.3-Tyr.sup.4 residue of the native sequence of angiotensin II (Ang II) with Pro-Amb scaffold. Similarly, analogue 2 is designed by replacement of Val.sup.3-Tyr.sup.4 residues of Ang II by Pro-Amb scaffold and removal of Phe.sup.8. Analogue 3 comprises minimum amino acids wherein the Pro-Amb scaffold is introduced by merely extending one residue on N-terminus as well as C-terminus.

(26) Water clusters are dynamic in nature and hence, mimicking and characterization of peptidic secondary structure in aqueous solution can be challenging. Therefore, peptidic reverse turn scaffold, i.e. the Pro-Amb scaffold developed from unnatural amino acids with distinct secondary structure in an aqueous solution has wide applications in development of potential therapeutic agents.

(27) The choice of NMR solvent was decided mainly due to water solubility of the modified peptides and bio-activity testing in aqueous solution. Extensive solution-state NMR studies were carried out in H.sub.2O:D.sub.2O (9:1). The complete assignments of NMR spectra were done using COSY, TOCSY, HMBC and HSQC. Further, the ROESY spectrum of analogue 3 was examined for signatures of anticipated -turn between proline and Amb residues. The Nuclear Overhauser Effect (NOE) between Amb-NH and -hydrogen of proline (C7H) confirms -turn formed between AmbNH and carbonyl group of arginine [FIG. 1(a)]. The NOE observed between AmbNH and hydrogens (C18H) of the proline further supports this -turn conformation. The methyl from methoxy group of Amb showed NOE interactions with Amb NH and IleuNHconfirming extended 5- and 6-membered hydrogen bonds, respectively [FIG. 1(a)].

(28) Similar NOE interactions were observed between Amb-NH and -hydrogen of proline in heptapeptide (Analogue 2) and octapeptide (Analogue 1), confirming the -turn in these peptides. Further, methyl from methoxy group of Amb showed NOE interactions with Amb-NH and IleuNH confirming extended 5- and 6-membered hydrogen bonds in Analogue 2 and Analogue 1, respectively (FIGS. 1(b) and (c)).

(29) The observed NOEs under aqueous condition were in agreement with the earlier reported Pro-Amb oligomers in deuterated chloroform displaying -turn (i+2i) stabilized by bifurcated hydrogen bonding (P. K. Baruah, et al, J. Org. Chem., 2007, 72, 636). It is described for the first time in the present invention through extensive solution state NMR and CD studies that the Pro-Amb adopts a stable -turn like conformation under aqueous conditions. None of the prior arts have reported hydrogen-bonding-restricted angiotensin II analogues with -turn like conformation stable under aqueous condition. From these findings, the stability of -turn-like secondary structure which is stabilized by bi-furcated hydrogen bonding in analogues 1, 2 and 3 in aqueous solution was confirmed.

(30) Further, circular dichroism (CD) spectra of Pro-Amb analogues 2-3 in FIG. 2 indicated maxima around 195 nm and 235 nm and minima at 213 and 209 nm, respectively, in water. These finding suggests that peptides exist in turn-like conformation with content of -sheet-like secondary structure in analogue 1. Analogue 2 has maxima at 235 nm followed by minima at 207 nm suggesting random coiled structure. These results are in agreement with 2D NMR data.

(31) The chemical structures of the analogues are as follows:

(32) ##STR00003##

(33) In another embodiment of the present invention, the peptide or fragments thereof having Formula 1 are not cytotoxic upto concentrations ranging from 50 M upto 150 M.

(34) Accordingly, the cytotoxicity of the analogues 1-3 were determined by MTT assay using HeLa cell lines (ATCC CCL-2) and HepG2 (ATCC HB-8065) cell lines at various concentrations and it was observed that these molecules were not cytotoxic upto 100 M concentrations (data not shown).

(35) The functional activity of the analogues of the present invention was evaluated at the AT.sub.2 receptor, applying a neurite outgrowth assay in NG108-15 [108CC15] (ATCC HB12317) cells. It was earlier reported by Blankley et al (J. Med. Chem., 1991, 34, 3248) that NG108-15 cells in their undifferentiated state express only the AT.sub.2 receptor and that a 3-day treatment with Ang II or selective peptidic AT.sub.2 receptor agonist CGP-42112A induces neurite outgrowth. The signaling pathways involve a sustained increase in Rap1/BRaf/p42/p44mapk activity and activation of the nitric oxide/guanylyl cyclase/cGMP pathway. NG108-15 cells were treated in absence or presence of Ang II and PD 123319, an AT.sub.2 receptor antagonist. The cells were plated at the initial density of 3.610.sup.4 cells/petri dish (35 mm) and were cultured for 3 days in the absence () or presence (+) of 100 nM Ang II, 1 M analogue 3, analogue 2 and analogue 1 alone or in combination with 10 M antagonist PD 123,319 or 100 nM AngII. After 3 days of treatment, the cells were examined under a phase contrast microscope and micrographs were taken. Cells with at least one neurite longer than a cell body were counted as a positive neurite outgrowth. Antagonistic effect was established through co-incubation with Ang II resulting in reduced Ang II-induced neurite outgrowth, verifying blockage of the AT.sub.2 receptor. Agonistic effect was verified through co-incubation with selective AT.sub.2 receptor antagonist PD 123319, which reduced neurite outgrowth, verifying that the effect was mediated through the AT.sub.2 receptor (FIG. 4). The number of cells with neurites was expressed as the percentage of the total number in the micrographs (at least 260 cells according to the experiment). The results are significant according to two-way ANOVA whenever compared to control: ***, p<0.001. Treatment with PD 123319 alone did not alter the morphology compared to untreated cells. In case of Pro-Amb analogues 1, 2 and 3, there was enhancement in neurite outgrowth in NG108-15 cells when compared to control (FIG. 3. and FIG. 4). Further, there was no reduction in neurite outgrowth of Ang II when co-incubated with the analogues 1, 2 and 3 (FIG. 4). However, there was reduction in neurite outgrowth of analogues 1, 2, and 3 when co-incubated with PD123319 (10 M). These observations confirm that analogues 1, 2 and 3 are acting as AT.sub.2 receptor agonists and analogue 3 is preferably used in the present invention.

(36) Ang II is not selective and is well known to bind and activate both the AT.sub.1 and AT.sub.2 receptors. However, analogues 1, 2 and 3 of the present invention, constrained into -turn-like conformation, may bind selectively to AT.sub.2 receptor.

(37) Yet another embodiment of the present invention provides a process for synthesis of the peptide or a fragment thereof having the Formula I by Fmoc-based solid-phase peptide synthesis using 2-chlorotritylchloride resin.

(38) For the synthesis of Pro-Amb analogues 1, 2 and 3 of the present invention, 3-amino-2-methoxybenzoicacid (Amb) was Fmoc-protected using Fmoc-Cl in dioxane:water with sodium bicarbonate as a base and used further without purification. The Fmoc-Amb-OH was used for solid phase peptide synthesis, similar to other commercial Fmoc protected -amino amino acids.

(39) Purity of all peptide analogues was analysed by RP-HPLC using C-18 analytical column using 5% ACN to 90% ACN gradient in water and both the solvents containing 0.001% TFA and was estimated to be >90%.

(40) Still another embodiment of the present invention provides a pharmaceutical composition comprising therapeutically effective amount of a peptide or a fragment thereof having the Formula I:

(41) ##STR00004##

(42) wherein R.sub.1 is selected from the group consisting of aspartate (Asp), tyrosine (Tyr) and alanine (Ala), or R.sub.1 is absent;

(43) R.sub.2 is selected from the group consisting of serine (Ser), arginine (Arg) and isoleucine (Ile);

(44) R.sub.3 is selected from the group consisting of tyrosine (Tyr), isoleucine (Ile) and serine (Ser);

(45) R.sub.4 is selected from the group consisting of tyrosine (Tyr), histidine (His) and glutamate (Glu), or R.sub.4 is absent;

(46) R.sub.5 is selected from the group consisting of leucine (Leu), proline (Pro) and threonine (Thr), or R.sub.5 is absent;

(47) R.sub.6 is selected from the group consisting of glutamate (Glu) and phenylalanine (Phe), or R.sub.6 is absent,

(48) wherein proline-3-amino-2-methoxy benzoic acid (Pro-Amb) as a turn is incorporated between R.sub.2 and R.sub.3

(49) and a pharmaceutically acceptable carrier.

(50) In another embodiment of the present invention, there is provided a pharmaceutical composition comprising a peptide having SEQ ID NO: 1 (Asp-Arg-Pro-Amb-Ile-His-Pro-Phe) in a concentration of upto 150 M.

(51) The pharmaceutical composition of the present invention comprises pharmaceutically acceptable carriers selected from physiologically compatible buffers selected from the group consisting of physiological saline, i.e. Phosphate buffer saline (PBS), a mixture of saline and glucose, heparinized sodium-citrate-citric acid-dextrose solution, and other such acceptable carriers.

(52) The pharmaceutical composition of the present invention can be administered intraperitoneally or intrathecally. The pharmaceutical composition of the present invention can be prepared in water mixed with a surfactant, such as hydroxypropylcellulose. Dispersions comprising said composition can also be prepared in glycerol and liquid polyethylene glycols or mixtures thereof. The composition can additionally comprise preservatives to prevent the growth of microorganisms when stored.

(53) In case of sterile powders for preparation of sterile injectable solutions, methods of preparation of sterile powder include vacuum drying and freeze-drying techniques that yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof.

(54) The route of administration of the pharmaceutical composition of the present invention is in accordance with procedure for protein therapeutic delivery to the central nervous system (CNS) described by conventional methods. The intracerebroventricular (ICV) route involves delivery of the pharmaceutical composition comprising the peptide of a fragment thereof having the formula I directly into the ventricle. ICV delivery is facilitated via an access port which is implanted in a pocket between the scalp and periosteum on top of the head, with a catheter placed directly into the ventricle. Further, intrathecal (IT) delivery is either performed by lumbar puncture or via port-catheter delivery systems. An implanted catheter is connected to an infusion pump, either implanted or external between the laminae of the lumbar vertebrae and the tip is threaded up the thecal space to the desired level.

(55) Yet another embodiment of the present invention provides a method of treating a cognitive or a neurological disease comprising administration of a therapeutically effective concentration of a peptide or fragment thereof having the 1 formula I to a subject diagnosed with said cognitive or neurological disease or to a subject exhibiting symptoms of said cognitive or neurological disease.

(56) Accordingly, the preferred peptide administered to a subject suffering from a cognitive disease is SEQ ID NO: 1.

(57) For the purposes of the present invention, the cognitive diseases is described as those diseases associated with a significant impairment of cognition or memory that represents a marked deterioration from a previous level of function according to Guerrero, Anthony (2008) New York: Springer. pp. 367-79. The three main areas of cognitive disorders are delirium, dementia, Alzheimer's disease, and amnesia. Neurological disorders include dysfunctions of the central nervous system and the peripheral nervous system.

(58) In another embodiment of the present invention, there is provided a method for treating a subject having a cognitive or a neurological diseases, said method comprising administering a therapeutically effective amount of a peptide or a fragments thereof having formula 1 selected from the group consisting of SEQ ID NO: 1, 2 and 3 or mixture thereof to a subject diagnosed with said disease or to a subject exhibiting symptoms of said disease followed by administering a Angiotensin II receptor (AT.sub.2R) antagonist either simultaneously with the peptide or after a time interval.

(59) The known AT.sub.2 receptor antagonist is PD123319 while AT.sub.2 receptor agonists are CGP42112A and C21. Further, the present invention also provides a combination product comprising a peptide or fragments thereof having Formula I and an AT.sub.2 receptor agonist.

(60) Administration of an AT.sub.2 agonist along with an AT.sub.2 receptor antagonist/AT.sub.1 receptor antagonist either simultaneously or concomitantly after a time interval addresses the modulation of the renin-angiotensin system (RAS), related hypertension and diabetic nephropathy by means of said antagonist, as well as it provides beneficial protective effects of the AT2 agonist of the present invention.

(61) In yet another embodiment of the present invention there is provided a use of the peptide or a fragment thereof having formula I for other therapeutic applications. The peptide or a fragment thereof having the formula I of the present invention can be further used in treatment of disorders of the central and peripheral nervous system, cardiovascular system, respiratory system gastro-intestinal tract, reproductive system, and renal system.

(62) Cardiovascular diseases treated by the peptide having formula I of the present invention is characterised by hypertension, vasoconstriction, cardiomyopathy, cardiomegaly, ischemic lesions, thrombosis, increased cell growth and/or differentiation, increased cardiovascular hypertrophy, angiogenesis and several other related diseases. Respiratory diseases treated by the peptide having the formula I of the present invention include emphysema, extrinsic and intrinsic asthma, malignant pulmonary neoplasms, cell carcinoma of the lung and active sarcoidosis. Gastrointestinal diseases include inflammatory bowel disease, functional gut disorders, mucosal inflammation gastrointestinal malignancy and intestinal ischaemia.

(63) Peptide or a fragment thereof having formula I of the present invention can also be used to regulate the process of growth metabolism and differentiation of cells in treatment of carcinomas, modulation of cell differentiation, tissue healing, neuronal lesions and in organ transplants.

EXAMPLES

(64) Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.

Example 1: General Methods

(65) 2-Chlorotritylchloride resin and Fmoc protected amino acid derivatives were obtained from Novabiochem, Switzerland. DMF (lab reagent grade) was obtained from Merck and distilled twice over pthalic anhydride under reduced pressure. Dichloromethane-DCM (lab reagent grade) was obtained from Merck and distilled after overnight suspension over anhydrous K.sub.2CO.sub.3 (Merck). 3-Amino-2-methoxy-benzoic acid, N,N-diisopropylcarbodiimide (DIC) and dicyclohexylcarbodiimide (DCC) were obtained from Sigma-Aldrich. 1-hydroxybenzotriazole (HOBt) was purchased from Anaspec. All other reagents were obtained from commercial sources and were used as received. The purity of synthesized peptides was analyzed using analytical RP-HPLC as described in example 2 (SPPS section). The characterization of synthesized peptides was performed using circular dichroism (CD), fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), high resolution mass-spectroscopy (HRMS), etc. The NMR studies were performed on 700 MHz Bruker instrument using H.sub.2O:D.sub.2O (9:1) as a solvent. In the .sup.1H NMR spectra, it was not possible to integrate the peaks due to water suppression; hence the number of protons in NMR peak was assigned using HSQC (heteronuclear single quantum coherence spectroscopy) and HMBC (heteronuclear multiple bond correlation).

Example 2: Solid-Phase Peptide Synthesis (SPPS)

(66) Designed peptides were synthesized using solid phase peptide synthesis (SPPS) on semi-automatic peptide synthesizer act-90 from Advanced Chemtec using Fmoc/tert-butyl protection. The starting polymer was 2-chlorotritylchloride resin (1.6 mmol/g) and for the Fmoc amino acids, the side chain protecting groups were Asp(OtBu), Arg(Pbf) and His(Trt). Removal of the F-moc group was achieved by reaction with 20% piperidine in DMF for 10 min thrice. Coupling of the amino acids (4 equiv.) were performed in DCM:DMF (1:1) (10 ml) using DIC:HOBt (1:1) (4 equiv.) for 90 min Completion of coupling was confirmed by positive and negative Kaiser test.

(67) For proline (Pro) and 3-amino-2methoxy-benzoic acid (Amb), isatin and chloranil tests were used, respectively. After the introduction of each amino acid, excess amino acids were washed by DMF, four times. The final peptide resins were cleaved by a cleavage cocktail:TFA/H.sub.2O/TIS/EDT/phenol (250:2.5:1:1:1), for 4 h. The filtrate was concentrated on rota-vapour at reduced pressure and later co-evaporated with distilled diethyl ether, twice. The residue obtained was dissolved in minimum volume of methanol and desalted by eluting through sephadex LH-20 chromatography using methanol as mobile phase. The desired fractions were confirmed by LCMS and lyophilized to obtain peptide as a white amorphous powder. The purity of the peptides was examined by analytical RP-HPLC using LiChrosolv C-18 column with a flow-rate of 0.8 ml/min and the pressure was 1400 psi. The mobile phases for HPLC were 0.001% TFA in ACN (solvent A) and 0.001% TFA in H.sub.2O (solvent B). The gradients of solvent A to solvent B were varied as follows: 0 to 5 min (10%), 5 to 40 min (10% to 90%), 40 to 45 min (90% to 10%) and 45 to 50 min (10%).

Example 3: Synthesis of 3-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-2-methoxybenzoicacid

(68) 3-Amino-2-methoxybenzoic acid (1 equiv.) was dissolved in dioxane (2:1) and an aqueous solution of sodium bicarbonate (2 eq) was added with stirring. The resulting solution was cooled to 5 C. and Fmoc-Cl (1.05 eq) was added slowly as a solution in dioxane (cooled). The resulting mixture was stirred at 0 C. for 1 h and allowed to warm to room temperature overnight. Dioxane was evaporated on rota vapour. The concentrate was precipitated using 2N HCl. Then, it was filtered and the residue was washed several times with water. The off-white powder obtained from residue was air dried for two days and used further on SPPS without any further purification.

2-(3-{[1-(2-Amino-5-guanidino-pentanoyl)-pyrrolidine-2-carbonyl]-amino}-2-methoxy-benzoylamino)-3-methyl-pentanoic acid

(69) The peptide having SEQ ID NO: 3 (analogue 3) was prepared as mentioned in example 2 of SPPS. [].sup.25.3.sub.D: 4.1 (c 0.002, CH.sub.3OH). IR (nujol) (cm.sup.1): 3376.96, 3087.66, 3062.93, 3027.69, 2925, 2856.17, 2729.31, 1854.86, 1700.76, 1652.98, 1605.34, 1496.08, 1489.41, 1461.52, 1377.61, 1312.3, 1209.32, 1155.41, 1081.56, 1030.54, 893.73, 843.5, 727.8, 694.26. .sup.1H NMR.sup.1 (700 MHz, H.sub.2O:D.sub.2O (9:1)) : 9.84 (s, 1H), 8.70 (d, J=7.9 Hz, 1H), 8.07 (broad, 1H), 7.61 (dd, J=8.11, 1.5 Hz, 1H), 7.44 (dd, J=7.9, 1.4 Hz, 1H), 7.20 (t, J=7.9 Hz, 1H), 7.09 (t, J=5.9 Hz, 1H), 6.55 (broad, 1H), 4.65 (m, 1H), 4.41 (m, 1H), 4.36 (t, J=6.1(2)Hz, 1H), 3.75-3.69 (m, 5H), 3.60-3.57 (m, 2H), 3.15-3.12 (m, 2H), 2.41-2.37 (m, 1H), 2.08-1.88 (m, 5H), 1.68-1.57 (m, 2H), 1.48-1.43 (m, 1H), 1.24-1.19 (m, 1H), 0.93 (d, J=6.9 Hz, 3H), 0.84 (t, J=7.5 Hz, 3H). .sup.13C NMR (176 MHz, H.sub.2O:D.sub.2O (9:1)) : 176.9, 174.2, 170.0, 169.4, 158.2, 158.1, 152.2, 130.9, 130.3, 129.2, 128.7, 126.0, 63.5, 62.2, 59.7, 59.6, 52.7, 49.3, 41.7, 41.6, 37.7, 30.6, 28.2, 26.0, 26.0, 24.2, 16.3, 11.8. HRMS C.sub.25H.sub.40O.sub.3N.sub.7 [M+H].sup.+ calculated mass 534.3035, observed mass 534.3026.

1-[2-{2-[3-({1-[2-(2-Amino-3-carboxy-propionylamino)-5-guanidino-pentanoyl]-pyrrolidine-2-carbonyl}-amino)-2-methoxy-benzoylamino]-3-methyl-pentanoylamino}-3-(1H-imidazol-4-yl)-propionyl]-pyrrolidine-2-carboxylic acid

(70) The peptide having SEQ ID NO: 2 (analogue 2) was prepared as mentioned in example 2 of SPPS. [].sup.25.42.sub.D: 32.9067 (c 0.003, CH.sub.3OH). IR (nujol) (cm.sup.1): 3554.11, 3365.11, 3171.62, 3087.11, 2919.62, 2727.52, 2670.93, 2036.48, 1937.58, 1855.22, 1702.99, 1605.47, 1496.2, 1461.21, 1377.55, 1307.96, 1204.93, 1170.55, 1154.55, 1081.3, 1042.46, 1030.52, 973.78, 893.1, 842.74, 800.69, 727.72, 694.26, 666.04, 594.63. .sup.1H NMR.sup.1 (700 MHz, H.sub.2O:D.sub.2O (9:1)) : 9.79 (s, 1H), 8.65-8.61 (m, 5H), 8.50 (d, J=1.3 Hz, 1H), 7.6 (dd, J=8.1, 1.4 Hz, 1H), 7.37 (dd, J=7.8, 1.5 Hz, 1H), 7.26 (s, 1H), 7.2 (t, J=7.9(2) Hz, 2H), 7.08 (t, J=5.5(2) Hz, 2H), 5.98 (m, 1H), 4.64 (m, 1H), 4.57 (m, 1H), 4.31 (m, 1H), 4.27 (m, 2H), 3.8 (m, 2H), 3.71 (m, 2H), 3.65 (s, 3H), 3.62 (m, 2H), 3.53 (m, 2H), 3.19 (m, 1H), 3.1 (m, 3H), 2.93 (dd, J=17.9, 4.7 Hz, 1H), 2.83 (dd, J=17.9, 8.1 Hz, 1H), 2.35 (m, 1H), 2.21 (m, 1H), 2.02 (m, 3H), 1.91 (m, 3H), 1.78 (m, 2H), 1.68 (m, 1H), 1.61 (m, 2H), 1.4 (m, 1H), 1.15 (m, 1H), 0.82 (m, 3H), 0.79 (m, 3H). .sup.13C NMR (176 MHz, H.sub.2O+D.sub.2O) =177.7, 174.7, 174.6, 174.6, 174.4, 172.5, 170.6, 169.9, 169.9, 158.1, 158.1, 152.1, 134.8, 134.8, 131.0, 130.5, 129.4, 129.0, 128.6, 126.1, 118.9, 63.4, 62.2, 61.4, 60.0, 52.8, 52.7, 51.5, 51.0, 49.3, 49.0, 48.2, 41.9, 37.4, 36.7, 32.2, 30.7, 30.2, 28.7, 27.1, 26.0, 25.8, 25.7, 25.2, 16.0, 11.2. HRMS C.sub.40H.sub.59O.sub.11N.sub.12 [M+H].sup.+ calculated mass 883.4421, observed mass 883.4428; C.sub.40H.sub.58O.sub.11N.sub.12Na [M+Na].sup.+ calculated mass 905.4240, observed mass 905.4240.

3-Amino-N-{1-[2-(3-{1-[2-[2-(1-carboxy-2-phenyl-ethylcarbamoyl)-pyrrolidin-1-yl]-1-(1H-imidazol-4-ylmethyl)-2-oxo-ethylcarbamoyl]-2-methyl-butylcarbamoyl}-2-methoxy-phenylcarbamoyl)-pyrrolidine-1-carbonyl]-4-guanidino-butyl}-succinamic acid

(71) The peptide having SEQ ID NO: 1 (analogue 1) was prepared as mentioned in example 2 of SPPS. [].sup.25.3.sub.D: 21.2 (c 0.002, CH.sub.3OH). IR (nujol) (cm.sup.1): 3365.62, 3177.77, 2922.83, 2854.97, 2725.92, 2363.75, 2041.28, 1700.75, 1653.17, 1461.22, 1377.47, 1310.21, 1204.97, 1155.51, 1080.39, 973.4, 892.96, 847.48, 801.42, 727.55, 694.17, 667.8, 552.2, 540.09. .sup.1H NMR.sup.1 (700 MHz, H.sub.2O:D.sub.2O (9:1)) : 9.79 (s, 1H), 8.64 (d, J=7.52 Hz, 1H), 8.59 (d, J=7.5 Hz, 1H), 8.54 (d, J=8.11 Hz, 1H), 8.47 (m, 1H), 8.18 (d, J=7.52 Hz, 1H), 7.61 (m, 1H), 7.37 (m, 1H), 7.27 (m, 2H), 7.2 (m, 4H), 7.08 (t, J=5.88 Hz, 1H), 6.57 (broad, 1H), 4.98 (m, 1H), 4.63 (m, 1H), 4.56 (m, 1H), 4.54 (m, 1H), 3.8 (m, 2H), 3.65 (m, 3H), 3.52 (m, 1H), 3.11 (m, 4H), 3.02 (m, 2H), 2.94 (m, 1H), 2.83 (m, 1H), 2.35 (m, 1H), 2.12 (m, 1H), 2.0 (m, 3H), 1.86 (m, 2H), 1.78 (m, 3H), 1.68 (m, 1H), 1.6 (m, 2H), 1.38 (m, 1H), 1.14 (m, 1H), 0.79 (m, 6H). .sup.13C NMR (176 MHz, H.sub.2O:D.sub.2O(9:1)) : 176.4, 174.9, 174.7, 174.6, 174.4, 172.5, 170.8, 170.0, 169.9, 158.2, 158.1, 152.2, 137.8, 134.8, 131.0, 130.5, 129.9, 129.5, 129.0, 128.6, 128.3, 126.1, 118.9, 63.4, 62.2, 61.7, 60.1, 55.8, 52.8, 52.7, 51.5, 51.1, 49.3, 49.2, 41.9, 37.8, 37.4, 36.8, 30.7, 30.5, 28.7, 27.2, 26.0, 25.8, 25.7, 25.2, 16.0, 11.2. HRMS C.sub.49H.sub.68O.sub.12N.sub.13 [M+H].sup.+ calculated mass 1030.5105, observed mass 1030.5105; C.sub.49H.sub.67O.sub.12N.sub.13Na [M+Na].sup.+ calculated mass 1052.4924, observed mass 1052.4916.

Example 4: Cell Culture. To Study In Vitro Morphological Effects (AT2 Receptor Agonistic/Antagonistic Activity)

(72) NG108-15 [108CC15] (ATCC HB12317) cells were cultured in Dulbecco's modified Eagle's medium with 10% fetal bovine serum, HAT supplement (hypoxanthine, aminopterin and thymidine), and 50 mg/L gentamycin at 37 C. in 75 cm.sup.2 Nunclon Delta flasks in a humidified atmosphere of 95% air and 5% CO.sub.2. Subcultures were performed at sub-confluency. Under these conditions, cells express only the AT.sub.2 receptor subtype (Payet, FEBS Lett., 1992, 309, 161). Cells were stimulated during 3 days (once daily)(first stimulation 24 h after plating). Cells were cultured for 3 subsequent days under these conditions. For all experiments, cells were plated at the same initial density of 3.610.sup.4 cells/35 mm Petri dish and test concentrations for compounds used were 1 M and 0.1 M. Cells were then treated in the absence or presence of Ang II (100 nM), PD 123,319 (10 M) AT.sub.2 receptor antagonist. After 3 days of treatment, cells were examined under a phase contrast microscope and micrographs were taken. For determination of cells with Neurites, cells were examined under a phase contrast microscope, and micrographs were taken after 3 days under various experimental conditions. Cells with at least one neurite longer than a cell body were counted as positive for neurite outgrowth. The number of cells with neurites represents the percentage of the total amount of cells in the micrographs. At least two different experiments were conducted for each condition, each in duplicate. At least five images were taken per petri dish; hence, a total of 250-400 cells from each of the duplicate dishes were examined.

Advantages of the Present Invention

(73) Stimulation of the AT.sub.2 receptor (AT.sub.2R) by an AT.sub.2 receptor agonist prevents neural damage and cognitive impairment. The present invention provides a peptide or a fragment thereof having formula I which acts as an AT.sub.2 receptor agonist which can be used for treatment neurological disorders and other cognitive dysfunctions. AT.sub.2R stimulation by the peptide or a fragment thereof having formula I of the present invention can be exploited in treatment of hypertension, renal disease, stroke, Alzheimer's disease, myocardial infarction and in tissue protection in diseased conditions. Insertion of Pro-Amb scaffold in a bioactive peptide to mimic a turn like conformation in the secondary structure of a protein helps in designing analogues for different therapeutic proteins, thereby enhancing receptor or ligand binding affinity.