Novel Peptides Having Plateler Aggregation Inhibitory Activity

The following examples illustrate the preparation of the peptide derivatives corresponding to Formula I.

This peptide was synthesized on a solid phase starting from a presubstituted resin of the PAM type (4-(oxymethyl)-phenylacetamidomethyl), Boc-Trp(CHO)-PAM-resin, which is substituted with 0.34 mmol Trp/g. The protected amino acids used and the solvents in which they were dissolved were the following:

Each coupling was carried out using dicyclohexylcarbodiimide (DCC) catalyzed by hydroxybenzotriazole (HOBT), the reaction being allowed to proceed for 2 hours, and was followed by acetylation using acetic anhydride for 30 minutes.

During the synthesis, the deprotections were performed using trifluoroacetic acid (TFA) and the completeness of coupling was checked by the Kaiser test.

The final cleavage was carried out using HF (10 ml HF/g) in the presence of ethanedithiol (1 ml/10 ml HF) for 1 hour at 0.degree. C. in order to cleave the tryptophan residue. After being washed with ether, the peptide was extracted by means of 45% acetic acid, then 10% acetic acid and lyophilized.

However, the formyl group (--CHO) used to protect the Trp during synthesis is resistant to hydrogen fluoride (HF). In order to cleave it a second treatment of the peptide is necessary:

For this purpose, the peptide RGDW (For) is treated for several hours with 75 ml of 0.03M hydroxylamine (H.sub.2 N--OH.HCl) adjusted to pH 9 by ammonia solution, the disappearance of the absorption due to the formyl group at 300 nm and the appearance of free tryptophan absorbing at 280 nm being monitored spectrometrically.

After being filtered through a Millex SR-0.5 u, the peptide obtained was purified on a column of Sephadex G 10 using 25% acetic acid as eluant, then it was lyophilized twice.

The amino acid analysis and the absorption spectrum of RGDW as well as thin layer chromatography and HPLC reveal a pure peptide product, free of other organic material but contaminated with a large amount of salt. This is explained by the prior deprotection treatment of tryptophan with H.sub.2 N--OH.HCl in the presence of NH.sub.4 OH which leads to the formation of ammonium chloride which cannot be lyophilized. It is therefore necessary to remove the chlorides by anion exchange on a column of AGl-X.sub.2 (acetate form) and the peptide is eluted by 0.1% acetic acid (pH 3.5). The ammonium acetate obtained can be lyophilized.

1. Thin layer chromatography on silica with detection by:

ninhydrin (NH.sub.2)

TDM (NH)

Ehrlich reagent (paradimethylaminobenzaldehyde) (specific for Trp).

2. HPLC on an analytical column of Spherisorb OD5.2 5 u Eluant: gradient of acetonitrile (0.1% TFA) in water (0.1% TFA) from 0 to 80% in 25 mn at a flow rate of 1 ml/mn.

Detection: Optical density at 205-215 nm (peptide bond) and at 270-290 nm (Trp).

Retention T RGDW: 15 mn, i.e. at 48% acetonitrile (0.1% TFA).

3. Amino acid analysis

After hydrolysis at 110.degree. C. for 27 hours by means of HCl/propionic acid (50/50) in the presence of mercaptoethanol (0.1%).

This peptide was synthesized on a solid phase using the following procedures:

support: chloromethylated Merrifield resin (0.7 mmol Cl/g) containing 2% of divinylbenzene.

To 7.5 mmoles (2 g) of Boc-Phe-OH dissolved in 10 ml of ethanol are added 3.75 mmoles (1.22 g) of Cs.sub.2 CO.sub.3 in 2 ml of water. The cesium salt formed (Boc-Phe-OCs, 7.5 mmol) after several minutes of stirring was evaporated to dryness and stored in a vacuum in a dessicator for 48 h. It was then redissolved in 80 ml of DMF and mixed with 10.7 g of resin (0.7 mmol Cl). The reaction was carried out with stirring in a bath heated to 50.degree. C. for 24 h. The derivatized resin (Boc-Phe-resin) was then filtered off and washed with DMF, DMF/H.sub.2 O, DMF, EtOH, then dried in a vacuum for 3 h. The degree of substitution of the resin was calculated by amino acid analysis after hydrolysis at 150.degree. C. for 3 h. by means of the HCl/propionic acid (50/50) mixture. The degree of substitution obtained was about 0.24 mmol Phe/g resin.

coupling:

All of the amino acid derivatives incorporated were coupled by the carbodiimide DCC method in the presence of the catalyst HOBT (2 equivalents of amino acid, DCC and HOBT with respect to the Phe).

The protected amino acid derivatives used and the solvent in which they were dissolved were the following:

The couplings were allowed to proceed in DCM for 2 h.

The deprotections by means of TFA and the completeness of coupling were all checked by the Kaiser test.

cleavage:

The cleavage of the synthesized peptide was carried out using HF (10 ml/g resin) in the presence of anisole (1 ml/g resin) for 1 h. at 0.degree. C. After being washed with ether, the peptide was then extracted with 15% acetic acid and lyophilized.

purification: on a column of Sephadex G10 using 10% acetic acid as eluant.

control:

amino acid analysis: after hydrolysis in HCl/propionic acid (50/50) for 30 mn at 150.degree. C.

thin layer chromatography on silica:

eluant: CH.sub.3 OH/CHCl.sub.3 /25% NH.sub.4 OH (60/40/20)

detection: phenanthroquinone (Arg), ninhydrin (NH.sub.2), TDM (NH)

R.sub.f =0.51

eluant 2: 2-butanone/CH.sub.3 COOH/H.sub.2 O (10/30/25)

R.sub.f =0.73

eluant 3: butanol/CH.sub.3 COOH/H.sub.2 O (75/10/24)

R.sub.f =0.16.

This peptide was synthesized, purified and analyzed using the same methods as those described for the peptide synthesized in Example 1.

Its analytical properties are as follows:

thin layer chromatography on silica:

eluant 1: CH.sub.3 OH/CHCl.sub.3 /25% NH.sub.4 OH (60/40/20).

R.sub.f =0.82

eluant 2: 2-butanone/CH.sub.3 COOH/H.sub.2 O (10/30/25)

R.sub.f =0.69

eluant 3: butanol/CH.sub.3 COOH/H.sub.2 O (75/10/24)

R.sub.f =0.21

Given below are the results of the pharmacological studies which demonstrate the properties of the peptide derivatives corresponding to Formula I

The platelets were isolated from 60 ml of human blood collected in the anticoagulant buffer ACD in a ratio of 1 volume of ACD to 6 volumes of blood.

The blood is then centrifuged for 20 mn at a 1,000 r/mn (JOUAN E 96 centrifuge) at room temperature.

The PRP (plasma rich in platelets) is decanted and treated with 0.1 .mu.M PGE.sub.1, then centrifuged for 15 mn at 2,000 r/mn.

The platelets obtained in the pellet are then taken up in 1 ml of Tyrode buffer-albumin, pH 7.2, prepared with the following composition:

The platelets are washed on a column of Sepharose CL 2B using Tyrode buffer-albumin, pH 7.2, then the platelets are recovered and diluted to a concentration of 2.times.10.sup.8 platelets/ml.

The assays are carried out on 4.times.10.sup.7 platelets in the presence of CaCl.sub.2 (0.5 mM), .sup.125 I-fibrinogen 0.1.times.10.sup.-6 M) and different concentrations of peptide, and the stimulation of the platelets is induced by ADP (5.times.10.sup.-6 M). After incubation for 15 mn and deposition on a 15% saccharose solution the .sup.125 I-fibrinogen-platelet complex is isolated by centrifugation at 12,000 r/mn for 2 mn.

The results are presented in Table II in the form of CI50. This table also presents the sequence of the peptides.

The effect of the synthetic peptides on platelet aggregation was studied on platelets isolated as previously described for the study of the binding to fibrinogen. The stimulation of the platelets was also brought about by 5.times.10.sup.-6 M ADP and the assay was carried out in the presence of 1.1.times.10.sup.-6 M fibrinogen and of 0.5.times.10.sup.-6 M CaCl.sub.2.

The results are presented in Table II and demonstrate an inhibitory activity of the peptides corresponding to Formula I on platelet aggregation.

The peptide derivatives corresponding to Formula I can be used in particular for the treatment and prevention of thromboses, in particular in prethrombotic states in order to block platelet aggregation.

They are also able to exert an inhibitory effect on:

the adhesion of blood platelets to endothelial cells of the vascular walls or of the sub-endothelium.

atherogenesis

the development of metastases

the inflammatory response.

The therapeutic compositions according to the invention may be administered to man and to animals by the oral or the parenteral route.

They can exist in the form of solid, semi-solid or liquid preparations. As examples may be cited tablets, gelatine capsules, injectable solutions or suspensions.

In these compositions the active principle is usually mixed with one or more of the usual, pharmaceutically acceptable excipients well-known to the specialist.

The therapeutic composition may contain in particular from 1 to 60% by weight of the active principle.

The amount of active principle administered obviously depends on the patient who is being treated, the route of administration and the severity of the disease. It usually varies from 1 to 5,000 mg.