MULTIMERIC POLYVALENT ANTITHROMBOTIC AGENTS

Abstract: This invention relates to antithrombotic agents and uses thereof. Specifically, the invention relates to chemical moieties that specifically bind to platelets and inhibit their aggregation, including linear and cyclic peptides. The invention provides methods for using these antithrombotic agents to prevent the formation of thrombi at sites in a mammalian body. In particular, the platelet-specific binding moieties including linear and cyclic peptides of the invention are covalently linked to a polyvalent linker moiety, so that the polyvalent linker moiety is covalently linked to a multiplicity of the platelet-specific binding moieties including linear and cyclic peptides. Efficacious antithrombotic agents are thereby provided.

Description: MULTIMERIC POLYVALENT ANTITHROMBOTIC AGENTS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to antithrombotic agents and uses thereo Specifically, the invention relates to compounds that bind to platelets, specificall compounds that bind to the platelet receptor molecule GPIIb/IIIa. Suc compounds include peptides and cyclic peptides that bind to platelets and inhib their aggregation. In particular, the platelet-specific antithrombotic agents of th invention are covalently linked to a polyvalent linker moiety, so that th polyvalent linker moiety is covalently linked to a multiplicity of the platelet specific moieties, particularly peptides and cyclic peptides, thereby providing th multimeric polyvalent antithrombotic agents of the invention. The invention als provides methods for using such compounds to prevent the formation of throm at sites in a mammalian body. 2. Description of the Prior Art Thrombosis and thromboembolism, in particular deep vein thrombosi (DVT) and pulmonary embolism (PE), are common clinical conditions that ar associated with significant morbidity and mortality. It has been estimated that i the U.S. approximately 5 million patients experience one or more episodes o DVT per year and that over 500,000 cases of pulmonary embolism occur resulting in 100,000 deaths (J. Seabold, Society of Nuclear Medicine Annu Meeting 1990). In addition, myocardial infarction (heart attack) is usually caused b thrombosis in a coronary artery, often at the site of an atherosclerotic plaque Conventional therapies for heart attack involve removing such thrombi, eithe surgically by angioplasty and/or by adminstration of thrombolytic drugs, such a recombinant tissue plasminogen activator or streptokinase. Following suc therapy, however, re-stenosis or even re-occlusion of the affected coronary arter frequently occurs due to formation of another thrombus at the site of the origin thrombus. Preventing such re-occurrence of coronary artery thrombi is thus a important goal of all post-infarct therapy. The physiological processes involved in the formation of thrombi ar initiated by the accumulation of platelets at sites of damage or insult to th endothelial cell wall of a blood vessel, such as an atheroschlerotic plaqu Platelets normally accumulate at such sites after stimulation by local mediato signalling the injury. Subsequently, such platelets become aggregated at suc sites by binding serum fibrinogen via GPIIb/IIIa receptors expressed on th platelet surface. It is with the binding of fibrinogen that such an aggregation platelets becomes a thrombus. The amino acid sequence of the fibrinogen molecule recognized b GPIIb/IIIa receptors is the sequence -Arg-Gly-Asp- (RGD), which sequence i present four times in each fibrinogen molecule. Platelet aggregation can b inhibited using fibrinogen antagonists that bind to the GPIIb/IIIa receptors. Thu compounds that are fibrinogen antagonists and bind to GPIIb/IIIa are useful i preventing thrombosis, particularly in post-angioplasty or post-thrombolyti treatment regimes. Peptides having the ability to bind to platelets and inhibit their aggregatio are known in the prior art. Ruoslahti & Pierschbacher, U.S. Patent No. 4,578,079 describe peptid of sequence X-Arg-Gly-Asp-R-Y, wherein X and Y are either H or an amin acid, and R is Thr or Cys, the peptides being capable of binding to platelets. Ruoslahti & Pierschbacher, U.S. Patent No. 4,792.525 describe peptid of sequence Arg-Gly-Asp-X, wherein X is Ser, Thr or Cys, the peptides bein capable of binding to platelets. Pierschbacher et al, 1989, PCT/US 88/04403 disclose conformationall restricted RGD-containing peptides for inhibiting cell attachment to a substratu Hawiger et al., 1989, PCT/US 89/01742 relates to peptides comprisin sequences for two binding sites of a protein. Nutt et al., 1990, European Patent Application 90202015.5 disclose cycl RGD peptides that are fibrinogen receptor antagonists. Nutt et al., 1990, European Patent Application 90202030.4 disclose cycl RGD peptides that are fibrinogen receptor antagonists. Nutt et al., 1990, European Patent Application 90202031.2 disclose cycli RGD peptides that are fibrinogen receptor antagonists. Nutt et al, 1990, European Patent Application 90202032.0 disclose cycli RGD peptides that are fibrinogen receptor antagonists. Nutt et al., 1990, European Patent Application 90311148.2 disclose cycli peptides that are fibrinogen receptor antagonists. Nutt et al., 1990, European Patent Application 90311151.6 disclose cycli peptides that are fibrinogen receptor antagonists. Ali et al., 1990, European Patent Application 90311537.6 disclose cycli peptides that are fibrinogen receptor antagonists. Barker et al, 1991, PCT/US90/03788 disclose cyclic peptides fo inhibiting platelet aggregation. Maraganore et al. 1991, PCT/US90/04642 disclose a radiolabele thrombus inhibitor comprising (a) an inhibitor moiety; (b) a linker moiety; and (c and an "anion binding exosite (ABE)" binding site moiety. Pierschbacher et al, 1991, PCT/US91/02356 disclose cyclic peptides th are fibrinogen receptor antagonists. Ojima et al., 1992, 204th Meeting, Amer. Chem. Soc. Abst. 44 disclos synthetic multimeric RDGF peptides useful in inhibiting platelet aggregation. Although it is possible to prepare cyclic peptides that specifically bind t platelets, some such peptides exhibit low binding site affinity whereby the strengt of peptide binding to platelets is insufficient to prevent platelet aggregation an thereby have an antithrombotic effect. Peptides comprised of linear arrays o thrombus-specific peptide binding units have been described in the prior art. Rodwell et al, 1991 , PCT/US91/03116 disclose linear arrays of th peptide sequence RGD. Alternative arrangements of specific binding peptide units are preferabl The present invention provides multimeric polyvalent antithrombotic agents, on embodiment of which are reagent comprised of a multiplicity of cyclic peptid that specifically bind to platelets and have a sufficient affinity for platelets t prevent their aggregation. The incorporation of a multiplicity of platelet-specifi cyclic peptides in the antithrombotic agents of the invention permits the use o particular platelet-specific cyclic peptides comprising platelet binding sequence whose individual binding affinity might not otherwise be sufficient to produce th desired inhibition of platelet aggregation resulting in an antithrombotic effect i vivo, but which have other desireable properties, such as improved in viv stability and half-life, which are evidenced for example by increased retentio times at thrombus sites in vivo, detected by Tc-99m scintigraphy. Improve inhibition of platelet aggregation by particular platelet-specific binding moietie including peptides and cyclic peptides is achieved using the multimeric polyvalen antithrombotic agents of this invention. SUMMARY OF THE INVENTION The present invention provides multimeric polyvalent antithrombotic agent useful for preventing thrombus formation in a mammalian body. In a first aspect, the invention provides a multimeric polyvalen antithrombotic agent comprising a multiplicity of platelet-binding moieties that ar ligands for a GPIIb/IIIa receptor molecule, covalently linked to a polyvalen linking moiety. In a preferred embodiment, such a multimeric polyvalen antithrombotic agent has a molecular weight of less than about 20,000 daltons. In a second aspect, the invention provides a multimeric polyvalen antithrombotic agent comprising a multiplicity of platelet binding peptides, eac peptide comprising an amino acid sequence of 3-100 amino acids, covalentl linked to a polyvalent linking moiety, wherein each of the platelet bindin peptides has the formula A-R'-X-Gly-Asp-(aa) n -Z-B wherein A is H, an amine protecting group or (aa) p , where (aa) p is a peptid comprising an amino acid sequence of length p, wherein whenever the amino aci is cysteine, said cysteine may be protected at its sidechain sulfur atom, and p i an integer from 0 to 97; R 1 is a lipophilic amino acid or H; X is an amino aci capable of being positively charged; (aa) n is a peptide comprising an amino aci sequence of length n, wherein whenever the amino acid is cysteine, said cystein may be protected at its sidechain sulfur atom, and n is an integer from 0 to 97 Z is either absent or cysteine, isocysteine or homocysteine; B is -OH, -NH 2 , -S or (aa) m , wherein (aa) m is a peptide comprising an amino acid sequence of lengt , wherein whenever the amino acid is cysteine, said cysteine may be protecte at its sidechain sulfur atom, and m is an integer from 0 to 94; and the sum of + m + p is less than or equal to 97. In a preferred embodiment, the lipophili amino acid is a phenylalanine, tyrosine, tryptophan, valine, leucine or isoleucin residue. Lysine, homolysine, arginine, homoarginine, or L-[S-(3-aminopropyl cysteine] are preferred as amino acid X in the formula. Each of the multiplicit of platelet binding peptides is preferably comprised of 3 to 20 amino acids. In another aspect, the invention provides multimeric polyvalen antithrombotic agents, each comprising a multiplicity of platelet binding cycli peptides, each peptide comprising an amino acid sequence of 5-100 amino acids covalently linked to a polyvalent linking moiety, wherein each of the platele binding cyclic peptides has the formula wherein A D is a lipophilic D-amino acid; X is an amino acid capable of bein positively charged; (aa) n is a peptide comprising an amino acid sequence oflengt n, wherein whenever the amino acid is cysteine, said cysteine may be protecte at its sidechain sulfur atom, and n is an integer from 0 to 95; Z is either absen or cysteine, isocysteine or homocysteine; and B is -OH, -NH 2 , -SH, or (aa) m wherein (aa) is any amino acid, wherein when the amino acid is cysteine, sai cysteine may be protected at its sidechain sulfur atom, or where (aa) m is a peptid comprising an amino acid sequence of length m, wherein whenever the amino aci is cysteine, said cysteine may be protected at its sidechain sulfur atom, and m i an integer from 0 to 95, and the sum of n + m is < 95. In a preferre embodiment, the lipophilic D-amino acid is selected from the group consisting o phenylalanine, tyrosine, tryptophan, valine, leucine and isoleucine. Lysine homolysine, arginine, homoarginine, or L-[S-(3-aminopropyl)cysteine] are preferred as amino acid X in the formula. In another preferred embodiment, each of the multiplicity of platelet binding cyclic peptides is comprised of 5 to 20 amino acids. The invention also provides a multimeric polyvalent antithrombotic agent comprising a multiplicity of platelet binding peptides, each peptide comprising an amino acid sequence of 3-100 amino acids, covalently linked to a polyvalent linking moiety, wherein each of the platelet binding peptides has the formula A-R , -X-Gly-Asp-(R)-Z-B wherein A is H, an amine protecting group or (aa) p , where (aa) p is a peptide comprising an amino acid sequence of length p, wherein whenever the amino acid is cysteine, said cysteine may be protected at its sidechain sulfur atom, and p is an integer from 0 to 97; R 1 is a lipophilic amino acid or H; X is an amino acid capable of being positively charged; (R) is a substituted or unsubstituted linear or branched chain lower alkyl group having 1-20 carbon atoms or a substituted or unsubstituted phenyl, aryl, polycyclic or heterocyclic group, optionally comprising at least one heteroatom selected from the group consisting of O, S, and N; Z is either absent or cysteine, isocysteine or homocysteine; and B is -OH, -NH 2 , -SH, or (aa) m , wherein (aa) m is a peptide comprising an amino acid sequence of length m, wherein whenever the amino acid is cysteine, said cysteine may be protected at its sidechain sulfur atom, and m is an integer from 0 to 97; and the sum of m + p is less than or equal to 97. In a preferred embodiment, the lipophilic amino acid is selected from the group consisting of phenylalanine, tyrosine, tryptophan, valine, leucine and isoleucine. Lysine, homolysine, arginine, homoarginine, or L-[S-(3-aminopropyl)cysteine] are preferred as amino acid X in the formula. I another preferred embodiment, each of the multiplicity of platelet binding cyclic peptides is comprised of 3 to 20 amino acids. In yet another aspect, the invention provides multimeric polyvalen antithrombotic agents, each comprising a multiplicity of platelet binding cyclic peptides, each peptide comprising an amino acid sequence of 5-100 amino acids, covalently linked to a polyvalent linking moiety, wherein each of the platele binding cyclic peptides has the formula CH 2 -co-A D -X-Gly-Asp-Cys-(R)-Z-B wherein A D is a lipophilic D-amino acid; X is an amino acid capable of bein positively charged; (R) is a substituted or unsubstituted linear or branched chai lower alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstitute phenyl, aryl, polycyclic or heterocyclic group optionally comprising at least on heteroatom selected from the group consisting of O, S, and N; Z is either absen or cysteine, isocysteine or homocysteine; and B is -OH, -NH 2 , -SH, or (aa) m wherein (aa) m is a peptide comprising an amino acid sequence of length m wherein whenever the amino acid is cysteine, said cysteine may be protected a its sidechain sulfur atom, and m is an integer from 0 to 95. In a preferre embodiment, the lipophilic D-amino acid is selected from the group consisting o phenylalanine, tyrosine, tryptophan, valine, leucine and isoleucine. Lysine homolysine, arginine, homoarginine, or L-[S-(3-aminopropyl)cysteine] ar preferred as amino acid X in the formula. In another preferred embodiment, eac of the multiplicity of platelet binding cyclic peptides is comprised of 5 to 2 amino acids. In each of the linear peptides comprising a multimeric polyvalen antithrombotic agent of the invention the amino terminus may be protected by a amine protecting group. Preferred amine protecting groups include but are no limited to aliphatic or aromatic acyl groups comprising lower alkyl having 1 t 6 carbon atoms, or phenyl or phenyl substituted with lower alkyl, hydroxy, lowe alkoxy, carboxy, or lower alkoxycarbonyl groups. In each of the cyclic peptides of the invention having an amino aci residue (aa) comprising a cysteine, the sulfur atom of such a cysteine residue ma be protected by a thiol protecting group. Preferably, such thiol protecting group have the formula -CH 2 -NH-CO-R wherein R is a lower alkyl having 1 to 6 carbon atoms, 2-,3-,4-pyridyl, phenyl or phenyl substituted with lower alkyl, hydroxy, lower alkoxy, carboxy, or low alkoxycarbonyl. The multimeric polyvalent antithrombotic agents of the invention compris polyvalent linking moieties. Such polyvalent linking moieties are comprised at least 2 linker functional groups capable of covalently bonding to the platel binding moieties and linear and cyclic peptides comprising the antithromboti agents of the invention. Preferably, at least 2 of the linker functional groups ar identical, and most preferably, the linker functional groups are primary o secondary amines, hydroxyl groups, carboxylic acid groups or thiol-reactiv groups. In a preferred embodiment, the polyvalent linking moieties are comprise of a multiplicity of polyvalent linking moieties covalently linked to form branched polyvalent linking moiety. Preferred polyvalent linking moieties are bi maleimidomethylether, tra(maleimidoethyl)amine and derivatives thereof, whic form bw-succinimidylmethylether and t (succinimidylethyl)amine peptid conjugates. Each peptide-containing embodiment of the invention is comprised of sequence of amino acids. The term amino acid as used in this invention intended to include all L- and D- amino acids, naturally occurring and otherwis Reagents comprising platelet-binding peptides provided by the invention includ but are not limited to peptides comprising the following sequences, including th following cyclic peptides: CH Q.YnRGDC CH O.Y ^ RGDCWGG CH O.Y^RGDCFGG CH O.YpRGDCGGG CH.co.Y n RGDCGG CH O.Yp.Apc.GDCGGG CH Q.YrJ GDCGGG GGRGDS GGRGDGGRGDS GGRGDGGRGDGGRGDS KRARGDDMDDY RRRRRRRRRGD GRGDVK GRGDV GRGDVRGDFK GRGDVRGDF GGGRGDF RGD GRGDGG GGRGDF GGGRGDF GRGDGGGG RGDF G . Ape . GD V . Ape . GDFKCamide SYNRGDSTC CH£θ i Y Di Apc 1 GDCGGC Acm GC Acm GGCamide CH θ.Yp.Apc.GDCKGC nτ GC r l11 GGCamide Single-letter abbreviations for amino acids can be found in G. Zubay, Biochemistry (2d. ed.), 1988 (MacMillen Publishing: New York) p.33; subscrip "D" means a D-amino acid; Apc= L-[S-(3-aminopropyl)cysteine]. It will b understood by those with skill in the art that the sequences underlined in th above structures and in all other structures included herein represent a covalen bond between the the first and the last so underlined molecules, and further tha when cysteine is either the first or the last underlined molecule, such a covalen bond will be to the sidechain sulfer atom of said cysteine. This invention provides methods for preparing peptides of the inventio by chemical synthesis in vitro. In a preferred embodiment, peptides ar synthesized by solid phase peptide synthesis. The invention also provides a method for preventing thrombosis within mammalian body. This method comprises administering an effective therapeuti amount of a multimeric polyvalent antithrombotic agent of the invention to a animal in a pharmaceutical carrier. Specific preferred embodiments of the present invention will becom evident from the following more detailed description of certain preferre embodiments and the claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the experiment described in Example 4. DETAILED DESCRIPTION OF THE INVENTION The present invention provides multimeric, polyvalent compounds whic inhibit platelet aggregation and thus exhibit antithrombotic properties in mammalian body, comprising a multiplicity of platelet-specific binding moieties including peptides and cyclic peptides having an amino acid sequence of 3-10 amino acids, covalently linked to a polyvalent linking moiety. For purposes of this invention, the term "multimeric" is defined t describe compounds having multiple copies of a platelet-binding moeity that is ligand for a platelet GPIIb/IIIa receptor molecule. Exemplary of such platele binding moieties are peptides and cyclic peptides having an amino acid sequenc comprising the sequence -Arg-Gly-Asp- (RGD), in linear or polyvalent arrays For the purposes of this invention, the term "polyvalent" is defined to describ compounds in which a multiplicity of platelet-specific binding moieties, includin peptides and cyclic peptides having an amino acid sequence having specifi platelet-binding properties, exemplified by the sequence -Arg-Gly-Asp- (RDG) are covalently linked to a moiety having at least 2 functional groups, each capabl of covalent linkage to platelet-binding moieties of the invention. The polyvalent multimeric antithrombotic agents of the invention hav advantageous properties that make them preferable to the linearly multimeri peptides known in the art. In particular, the antithrombotic agents of th invention exhibit IC 50 values of platelet aggregation inhibition (i.e., th concentration of each agent at which platelet aggregation is reduced by 50% lower than the IC 50 values for platelet aggregation inhibiting agents known in th art. In addition, such multimeric polyvalent antithrombotic agents of th invention exhibit increased retention times at thrombus sites in vivo, as detecte by technetium-99m (Tc-99m) scintigraphy. These results suggest that the multimeric polyvalent antithrombotic agents of the invention are capable of remaining in contact with thrombi or at sites of thrombus formation for longer times than compounds known in the art. This indicates that the multimeric polyvalent antithrombotic agents of this invention bind to platelets with higher avidity than compounds known in the art. Polyvalent linking moieties provided by the invention are comprised of at least 2 linker functional groups capable of covalently bonding to platelet-specific moieties, including linear and cyclic peptides. Such functional groups include but are not limited to primary and secondary amines, hydroxyl groups, carboxylic acid groups and thiol reactive groups. Polyvalent linking moieties are comprised of preferably at least three functional groups capable of being covalently linked to platelet-specific moeties, including linear and cyclic peptides. Preferred polyvalent linking moieties include amino acids such as lysine, homolysine, ornithine, aspartic acid and glutamic acid; linear and cyclic amines and polyamines; polycarboxylic acids; activated thiols; and thiol-reactive reagents such as di- and tri-maleimides. Also preferred are embodiments wherein the polyvalent linking moieties comprise a multiplicity of polyvalent linking moieties covalently linked to form a branched polyvalent linking moiety. For the purposes of this invention, the term "branched" polyvalent linking moieties is intended to include but are not limited to polyvalent linking moieties having formula: I I I III Most preferred polyvalent linking moieties are bw-maleimidomethylethe tπ ' s(maleimidoethyl)amine and derivatives thereof, which form bi succinimidylmethylether and ' _s(succinimidylethyl)amine peptide conjugat Those with skill in this art will recognize that the polyvalent linking moieties a properly denoted as being "succinimidyl" moieties when they are referred to the chemical components of the reagents of the invention, and as bei "maleimido" moieties when they are referred to as the chemical compounds us to synthesize said reagents. Peptides of the present invention can be chemically synthesized in vit Peptides of the present invention can generally advantageously be prepared on amino acid synthesizer. The peptides provided by the invention are preferably administer intravenously in any conventional medium for intravenous injection such as aqueous saline medium. Such medium may also contain conventio pharmaceutical adjunct materials such as, for example, pharmaceutica acceptable salts to adjust the osmotic pressure, buffers, preservatives and the li Among the preferred media are normal saline and other isotonic buffers. The peptides provided by the invention may also be administered subcutaneous or intra-muscular injection or by mouth. The antithrombotic agents of the invention, and methods for making a using these compounds, are more fully illustrated in the following Exampl These Examples illustrate certain aspects of the above-described invention a advantageous results thereof. These Examples are shown by way of illustrati and not by way of limitation. EXAMPLE 1 Synthesis of TMEA ffπs(2-maleimidoethyl)amine1 * _y(2-aminoethyl)amine (1.49 mL, 10 mmol) dissolved in 50 mL saturate aqueous sodium bicarbonate and cooled in an ice bath, was treated with carbomethoxymaleimide (4.808 g, 31 mmol). The mixture was stirred for 30 mi on ice and then for another 30 min at room temperature. The mixture was the partitioned between dichloromethane and water, dried over magnesium sulfate filtered and evaporated to give 3.442 g of product. Reverse phase thin-laye chromatography (RP-TLC) yielded essentially 1 spot (R f = 0.63 in 1:1 acetonitril : 0.5 M sodium chloride). 3.94 mmol (1.817g) of this product was dissolved i 20 mL tetrahydrofuran and 20 mL saturated sodium bicarbonate and mixed for h. The reaction mixture was then partitioned between ethyl acetate and water The organic phase was washed with saturated sodium chloride, dried ove magnesium sulfate, and filtered. The ethyl acetate solution was diluted wit hexanes and cooled. Solid TMEA was collected by filtration and dried to a yiel of 832 mg. Chemical analysis of the product confirmed its identity as TMEA a follows: Η ΝMR (CDC1 3 ): 2.65 (tr. 2 H), 3.45 (tr.2 H). 6.64 (s. 2 H). 13 C ΝMR (CDC1 3 ), 35.5, 51.5, 133.9, 170.4. EXAMPLE 2 Solid Phase Peptide Synthesis Solid phase peptide synthesis (SPPS) was typically carried out on a 0.2 millimole (mmole) scale using an Applied Biosystems Model 431 A Peptid Synthesizer and using 9-fluorenylmethyloxycarbonyl (Fmoc) amino-terminu protection, coupling with dicyclohexyl- carbodiimide/hydroxybenzotriazole or 2 (lH-benzo-triazol-l-yl)-l, l,3,3-tetramethyluronium hexafluorophosphat hydroxybenzotriazole (HBTU/HOBT), and using -hydroxymethyl phenoxymethylpolystyrene (HMP) resin for carboxyl-terminus acids or Rin amide resin for carboxyl-terminus amides. Resin-bound products were routinel cleaved using a solution containing trifluoroacetic acid (TFA) and various amount of dichloromethane (DCM), water, thioanisole, ethanedithiol, and triethylsilan (TES), typically a solution of TFA : DCM : H 2 O : TES, prepared in ratios of 5 : 50 : 5 : 2 for 0.5 - 1.5 h at room temperature. Where appropriate, N-terminal acetyl groups were introduced by treatin the free N-terminal amino peptide bound to the resin with 20% v/v aceti anhydride in N-methyl- pyrrolidinone (NMP) for 30 min. Where appropriate, 2 chloroacetyl or 2-bromoacetyl groups were introduced either by using th appropriate 2-haloacetic acid as the last residue to be coupled during SPPS, or b treating the N-terminus free amino acid peptide bound to the resin with either th 2-haloacetic acid/diisopropylcarbodiimide/N-hydroxysuccinimide in ΝMP or th 2-haloacetic anhydride/diisopropylethylamine in ΝMP. Where appropriate, HPLC-purified 2-haloacetylated peptides were cyclize by stirring an 0.1-1.0 mg/mL solution in phosphate or bicarbonate buffer o ammonia solution (pH 8.0), which may also contain 0.5-1.0 mM EDTA, for 0.5 48 h followed by acidification with acetic acid, lyophilization and HPL purification. Where appropriate, TSEA adducts were prepared by reacting single thiol containing peptides (1 to 10 mg/mL in aqueous buffer, pH 7, with or witho added acetonitrile) with 0.33 molar equivalents of TMEA [tris l maleimidoethyl)amine] added in 0.2 to 1 mL dimethylformamine (DMF) at roo temperature for approximately 1 to 2 hours. The products were purified b HPLC. Where appropriate, BSME adducts were prepared by reacting single thiol containing peptides (1 to 10 mg/mL in aqueous buffer, pH 7, with or witho added acetonitrile) with 0.5 molar equivalents of BMME is maleimidomethylether) pre-dissolved in DMF at room temperature fo approximately 0.5 to 2 hours. The solution was concentrated and the produ were purified by HPLC. Where appropriate, BAT-BS adducts were prepared by reacting singl thiol-containing peptide (at concentrations of 2 to 50 mg/mL peptide in 50m sodium phosphate (pH 1)1 acetonitrile or THF) with 0.5 molar equivalents BAT-BM (N-[2-(N',N'-bw(2-maleimidoethyl)aminoethyl)]-N-(t-butoxycarbonyl N 6 ,Λ/ 9 -bw(2-methyl-2-triphenylmethylthiopropyl)-6,9-diazanonanamide; see c pending U.S. Patent Application 08/044,825, incorporated by reference) pr dissolved in acetonitrile or THF, at room temperature for approximately l-18 The solution was then evaporated to dryness and [BAT-BS]-peptide conjugat deprotected by treatment with lOmL TFA and 0.2mL triethylsilane for lh. Th solution was concentrated, the product adducts precipitated with ether, and the purified by HPLC. Crude peptides were purified by preparative high pressure liqui chromatography (HPLC) using a Waters Delta Pak C18 column and gradie elution using 0.1 % trifluoroacetic acid (TFA) in water modified with acetonitril Acetonitrile was evaporated from the eluted fractions which were then lyophilize The identity of each product was confirmed by fast atom bombardment ma spectroscopy (FABMS). Illustrative peptides are shown in Table I. TABLE I Peptides (CH θ.Yp.Apc.GDCGGC Λrπι GC Λcπ ,GGCamideVBSME (CHXQ.Yp.Apc.GDCGGC Λrm GC Λrm GGCamideVTSEA (CH 2 co i Y Di Apc i GDCKGC Acm GC Acm GGCamide) 2 -BSME (CH 2 c Y Di Δpc i GDCGGC Acm GC Acm GGCamide) 2 -BSH (CH 2 COY Di Apc 1 GDCGGC Acm GC Acm GGCamide) 2 -[BAT-BS] (CH θ.Yp.Apc.GDCKGC^ m GC . m GGCamideyrBAT-BSl 10 a Molecular weight determined by 1: fast atom bombardment mass spectroscopy (MH + ) or 2: electrospray mass spectroscopy (M) b HPLC methods [in R τ (min)]: en solvent A = 0.1 % CF3COOH/H 2 O I solvent B^ = 0.1 % CF 3 COOH/90% CH 3 CN/H 2 O 15 solvent flow rate = 1 mL/min Waters column = Waters DeltaPure RP-18, 5μ, 150mm x 3.9mm analytical column Conditions: 10% A to 40% B^ in 20 min 20 Single-letter abbreviations for amino acids can be found in G. Zubay, Biochemistry (2d. ed.), 1988 (MacMillen Publishing: New York) p.33; Acm = acetamidomethyl; Ape = L-[S-(3-aminopropyl)cysteine]; Y D = D-tyrosine; BSME = bw- succinimidylmethylether;TSEA =t (succinimidylethyl)amine;[BAT-BS] = N-[2-(N',N'-bis(2-succinimidoethyl)aminoethyl]-N 6 ,f , f- bis(2-mercapto-2-methylpropyl)-6,9-diazanonanamide; BSH = 1 ,6-bw-succinimidylhexane Peptides are linked to BSME, TSEA or [BAT-BS] linkers via the free thi moiety of the unprotected cysteine residue (C) in each peptide. EXAMPLE 3 Platelet Aggregation Inhibition Assays Platelet aggregation studies were performed essentially as described b Zucker (1989, Methods in Enzymol. 169: 117-133). Briefly, platelet aggregatio was assayed with or without putative platelet aggregation inhibitory compoun using fresh human platelet-rich plasma, comprising 300,000 platelets p microlitre. Platelet aggregation was induced by the addition of a solution adenosine diphosphate to a final concentration of 15 micromolar, and the exte of platelet aggregation monitored using a Bio/Data aggregometer (Bio/Data Corp Horsham, PA). The concentrations of platelet aggregation inhibitory compoun used were varied from 0.1 to 500 μg/mL. The concentration of inhibitor th reduced the extent of platelet aggregation by 50% (defined as the IC 50 ) w determined from plots of inhibitor concentration versus extent of platel aggregation. An inhibition curve for peptide RGDS was determined for eac batch of platelets tested as a positive control. The results of these experiments are shown in Tables II and III. In Tabl II, the compounds tested are as follows: P96 = GRGDVC Acm GC Acm amide P143 = CHXQ-YpRGDCGGC Λrm GC Λcm amide P154 = CH,Cθ-YτvApcGDCGGGC Λrm GC Λrm amide P474 = fCH Q-Y P ApcGDCGGC Λπn GC Λcm GGC-amideyBSH P476 = ( CH Q -YpApcGDCKGC Λm GC Λcm GGC-amideyrBAT-BS] P280 = (CH 2 coJf D AE^GDCGGC Acm GC Acm GGC-amide) 2 -BSME P357 = (CH 2 co 1 Y D Air.3DCGGC Acm GC Acffi GGC-amide) 2 -[BAT-BS] P317 = rcH Q-Y ^ ADcGDCGGC Λrm GC Λrm GGC-amide^-TSEA (Abbreviations used herein are the same as the abbreviations used in Table chemical structures representing peptides P474, P476, P280, P357 and P317 a shown on pages 21-23). These results demonstrate that the IC 50 decreases for cyclic peptides compared with linear ones, and is even less for polyvalent peptide agents compared with monovalent peptide agents. These results illustrate the efficacy the multimeric polyvalent antithrombotic agents of the invention at reducin platelet aggregation. Table III shows the IC 50 values of the agents of the invention compare with some of the most potent antithrombotic agents known in the prior art. T compounds tested as shown in Table III are as follows (RGDS is given as positive control): Cytogen Pac-8 = αcety'SYGRGDVRGDFKCTCCA Monsanto = H 2 NC(N=H)NH(CH 2 ) 7 CO-GDF 1 Rhone-Poulenc-Rorer = H 2 NC(N =H)NH(CH 2 ) 3 co-Sar.DV 2 Genentech = (j-naphthviiCHCO-GRGDC 3 Diatech P280 = (CH θ-YpApcGDCGGC m GC Λ . m GGC-amideWBSM SmithKline Beckman = acgtv/CR (N . Mf) GDPenamide 4 Merck = flcgtv/CN-ββDiMeTzl(p-αm o)FGDCamide 5 Diatech P317 = (CH O-YpApcGDCGGC Λ -GC Λ _. n GGC-amide TSEA (Pen = L-penicillamine; Sar = sarcosine; other abbreviations are as in Table References for these peptides are all taken from the Proceedings of the 12 American Peptide Symposium, held in Cambridge, MA on June 16-21, 1991: Tjoeng et al, Abst. LTh8; 2 : Klein et al, Abst. P-492; 3 : Burnier et al., Abs LTh9; 4 : Ali et al, Abst. P-471; 5 : Nutt et al., Abst. LF11). These results demonstrate that the multimeric polyvalent antithrombot agents P280 and P317 provided by the invention have a capacity to inhibit platel aggregation with efficiencies comparable to and in some cases better than the mo potent peptides known in the prior art. TABLE II INHIBITION OF PLATELET AGGREGATION Structure ICsotøM) GRGDVC ■ Α A ,c m mGC A , m amide 121 C ϊL Cθ Y 0 R£DCGGC Acm GC Acm amide 1.3 CH 2 co I Y 0 AβcGDCGGGC Acm GC Acm amide 0.30 10 CH O-YpApcGDCGGC^GC ^ GC^camide 0.27 (CH 2 co 1 Y D AβcGDCGGC Acm GC Acm GGC-amide) 2 - BSH 0.14 (CH,co-YpApcGDCKGC A „ T GC A .„GGC-amide),-rBAT-BS1 0.093 (CH P-YpApcGDCGGC^GC^GGC-amideyBSME 0.083 (CH 2 coJf D AβcGDCGGC Acm GC Acm GGC-amide) 2 -[BAT-BS] 0.079 15 (ciico D AEcGDCGGC A^ GC A^ GGC-amideyTSEA 0.036 to I TABLE m INHIBITION OF PLATELET AGGREGATION 5 Peptide soiμM RGDS 140 Cytogen Pac-8 12 Monsanto 1.6 10 Rhone-Poulenc Rorer 0.63 Genentech 0.15 Diatech P280 0.083 SmithKline Beckman 0.08 Diatech P317 0.036 15 Merck 0.022 echistatin 0.03 (CH 2 CO.Y D .Apc.GDCGGC Acm GC Acm GGC.amide) 3 TSEA 1 S ■ 15 (CH 2 CO.Y D .Apc.GDCGGC Acm GC Acm GGC.amide) 2 -[BAT-BS] I s 1 (CH 2 CO.Y D .Apc.GDCGGC Acm GC Acm GGC.amide) 2 BSH I S 1 EXAMPLE 4 Demonstration of Antithrombotic Activity In Vivo The Folts model of coronary thrombosis (Folts et ah, 1976, Circulatio 5.4: 365-370) was used to demonstrate the antithrombotic activity of P280 in viv The Folts model is a largely platelet dependent, fibrin independent model whic is characterized by the cyclic flow reductions (CFRs) produced by alternatin gradual vessel occlusion by platelet-rich thrombus and abrupt restoration of flo caused by dislodgement of the thrombus. This model has been used t demonstrate the antithrombotic activity of potent GPIIb/IIIa binding peptid derived from snake venom [e.g. Bush et al., 1989, Circulation 80: 11-23 (Abst) Three male mongrel dogs (12-19 kg) were anesthetized with sodiu pentobarbital (30 mg/kg i.v.), intubated with a cuffed endotracheal tube an respirated on room air delivered by a Harvard respirator. Catheters were place in the jugular and femoral veins to deliver drugs and fluids. A catheter was als placed in the carotid artery to measure arterial blood pressure (ABP). A le thoracotomy was made, exposing the heart, which was tented in a pericardi cradle. A segment of the left anterior descending (LAD) or left circumfle coronary artery (LCX) was gently isolated and a pulsed Doppler flow probe w placed on the coronary artery just proximal to the intended site of stenosis. I addition to ABP, pulsatile and mean Doppler flow and limb lead electrocardiogram (ECG) were recorded on a Grass Physiological recorder. Afte obtaining control measurements of the parameters indicated above, the vessel' inner surface was denuded by squeezing together apposing sides of the artery an thereafter a rigid plastic constrictor was placed on the artery. This resulted in th development of an occlusive thrombus within approximately 3 to 7 minute After approximately one hour of sustained CFRs, peptide P280, dissolved in 10 propylene glycol/water, was infused into a free-running i.v. saline drip at a rat of 10, 30 or 100 μg/kg/min. In all three dogs, infusion of P280 abolished the CFRs. The results fro one of the dogs are shown in Figure 1. Panel A shows CFRs in dog coronar arteries before administration of P280. Panel B shows partial reduction of CF upon administration of 10 μg/kg/min of P280, and Panel C shows comple abolition of CFRs in this dog on administration of 30 / tg/kg/min of P280. Th reversability of the effects of P280 administration is shown in Panel D, wher return of the first occlusive thrombus in the dog coronary arteries is indicated b detection of resumed CFRs. Comparable results were attained by using infuse doses of 100 μg/kg/min in the other two dogs. In all animals the CFRs returne within approximately 30 to 50 minutes after stopping the P280 infusion, as i expected for low molecular weight GPIIb/IIIa binding peptides of this type These experiments demonstrated that P280, as an example of peptides of thi invention, is an effective antithrombotic agent. It should be understood that the foregoing disclosure emphasizes certai specific embodiments of the invention and that all modifications or alternative equivalent thereto are within the spirit and scope of the invention as set forth i the appended claims.

Claims: WHAT WE IS CLAIM IS: 1. A multimeric polyvalent antithrombotic agent comprising multiplicity of platelet-binding moieties that are ligands for a platelet GPIIb/III receptor molecule, covalently linked to a polyvalent linking moiety wherein th molecular weight of the multimeric polyvalent antithrombotic agent is less tha about 20,000 daltons. 2. A multimeric polyvalent antithrombotic agent according to Clai 1 wherein the polyvalent linking moiety is comprised of at least 2 linke functional groups capable of covalently bonding to the platelet-binding moietie and wherein at least 2 of the linker functional groups are identical. 3. A multimeric polyvalent antithrombotic agent according to Clai 2 wherein the linker functional groups of the polyvalent linking moiety ar primary or secondary amines, hydroxyl groups, carboxylic acid groups or thiol reactive groups. 4. A multimeric polyvalent antithrombotic agent according to Clai 1 wherein the polyvalent linking moiety is comprised of a multiplicity o polyvalent linking moieties covalently linked to form a branched polyvalen linking moiety. 5. A multimeric polyvalent antithrombotic agent according to Clai 1 wherein the polyvalent linking moiety is bw-succinimidylmethylether tra(succinimidylethyl)amine or a derivative thereof. 6. A multimeric polyvalent antithrombotic agent according to Clai 1 wherein the multiplicity of platelet-binding moieties that are ligands for platelet GPIIb/IIIa receptor molecule are each covalently linked to the polyvalen linking moiety by a functional linker group, said functional linker group selecte from the group consisting of primary or secondary amines, hydroxyl groups carboxylic acid groups and thiol groups. 7. A method for preventing thrombosis within a mammalian bod comprising administering an effective therapeutic amount of the multimeri polyvalent antithrombotic agent of Claim 1 in a pharmaceutical carrier. 8. A multimeric polyvalent antithrombotic agent comprising multiplicity of platelet binding peptides, each peptide comprising an amino aci sequence of 3-100 amino acids, covalently linked to a polyvalent linking moiety wherein each of the platelet binding peptides has the formula A-R'-X-Gly-Asp-(aa) n -Z-B wherein A is H, an amine protecting group or (aa) p , where (aa) p is a peptid comprising an amino acid sequence of length p, wherein wheneve the amino acid is cysteine, said cysteine may be protected at it sidechain sulfur atom, and p is an integer from 0 to 97; R 1 is a lipophilic amino acid or H; X is an amino acid capable of being positively charged; (aa) n is a peptide comprising an amino acid sequence of length n wherein whenever the amino acid is cysteine, said cysteine may b protected at its sidechain sulfur atom, and n is an integer from to 97; Z is absent or cysteine, isocysteine or homocysteine; B is -OH, -NH 2 , -SH, or (aa) m , wherein (aa) is a peptid comprising an amino acid sequence of length m, wherein wheneve the amino acid is cysteine, said cysteine may be protected at it sidechain sulfur atom, or where (aa) m is a peptide comprised of multiplicity of amino acids, and m is an integer from 0 to 97; and n + m + p < 97, wherein the molecular weight of the multimeric polyvalent antithrombotic agen is less than about 20,000 daltons. 9. The multimeric polyvalent antithrombotic agent of Claim 8 wherei the lipophilic amino acid is selected from the group consisting of phenylalanine tyrosine, tryptophan, valine, leucine and isoleucine. 10. The multimeric polyvalent antithrombotic agent of Claim 8 wherei X is an amino acid that is lysine, homolysine, arginine, homoarginine, or L-[S-(3 aminopropyl)cysteine] . 11. The multimeric polyvalent antithrombotic agent of Claim 8 wherei each of the multiplicity of platelet binding peptides is comprised of 3 to 20 amin acids. 12. The multimeric polyvalent antithrombotic agent of Claim 8 wherei each protected cysteine has a thiol protecting group of formula -CH 2 -NH-CO-R wherein R is a lower alkyl having 1 to 6 carbon atoms, 2-,3-,4-pyridyl, phenyl or phenyl substituted with lower alkyl, hydroxy, lower alkoxy, carboxy, or lowe alkoxycarbonyl. 13. The multimeric polyvalent antithrombotic agent of Claim 8 wherei the polyvalent linking moiety is comprised of at least 2 linker functional group capable of covalently bonding to platelet binding peptides and wherein at least of the linker functional groups are identical. 14. The multimeric polyvalent antithrombotic agent of Claim 1 wherein the linker functional groups of the polyvalent linking moiety are primar or secondary amines, hydroxyl groups, carboxylic acid groups or thiol-reactiv groups. 15. The multimeric polyvalent antithrombotic agent of Claim 8 wherei the polyvalent linking moiety is comprised of a multiplicity of polyvalent linkin moieties covalently linked to form a branched polyvalent linking moiety. 16. The multimeric polyvalent antithrombotic agent of Claim 8 wherei the polyvalent linking moiety is bw-succinimidylmethylether tra(succinimidylethyl)amine or a derivative thereof. 17. A multimeric polyvalent antithrombotic agent according to Clai 8 wherein the multiplicity of platelet-binding peptides are each covalently linke to the polyvalent linking moiety by a functional linker group, said functiona linker group selected from the group consisting of primary or secondary amines hydroxyl groups, carboxylic acid groups and thiol groups. 18. The multimeric polyvalent antithrombotic agent according to Clai 8 wherein the platelet-binding peptides are chemically synthesized in vitro. 19. The multimeric polyvalent antithrombotic agent according to Clai 18 wherein the platelet-binding peptides are synthesized by solid phase peptid synthesis. 20. A method for preventing thrombosis within a mammalian bod comprising administering an effective therapeutic amount of the multimeri polyvalent antithrombotic agent of Claim 8 in a pharmaceutical carrier. 21. A multimeric polyvalent antithrombotic agent comprising multiplicity of platelet binding peptides, each peptide comprising an amino aci sequence of 5-100 amino acids, covalently linked to a polyvalent linking moiety wherein each of the platelet binding cyclic peptides has the formula CH co-A D -X-Gly-Asp-Cys-(aa) n -Z-B wherein A D is a lipophilic D-amino acid; X is an amino acid capable of being positively charged; (aa) n is a peptide comprising an amino acid sequence of length n wherein whenever the amino acid is cysteine, said cysteine may b protected at its sidechain sulfur atom, and n is an integer from to 95; Z is absent or cysteine, isocysteine or homocysteine; B is -OH, -NH 2 , -SH, or (aa) m , wherein (aa) m is a peptid comprising an amino acid sequence of length m, wherein wheneve the amino acid is cysteine, said cysteine may be protected at it sidechain sulfur atom, and m is an integer from 0 to 95; and n + m < 95, wherein the molecular weight of the multimeric polyvalent antithrombotic agen is less than about 20,000 daltons. 22. The multimeric polyvalent antithrombotic agent of Claim 2 wherein the lipophilic D-amino acid is selected from the group consisting o phenylalanine, tyrosine, tryptophan, valine, leucine and isoleucine. 23. The multimeric polyvalent antithrombotic agent of Claim 2 wherein X is an amino acid that is lysine, homolysine, arginine, homoarginine or L-[S-(3-aminopropyl)cysteine] . 24. The multimeric polyvalent antithrombotic agent of Claim 2 wherein each of the multiplicity of platelet binding cyclic peptides is comprise of 5 to 20 amino acids. 25. The multimeric polyvalent antithrombotic agent of Claim 2 wherein each protected cysteine has a thiol protecting group of formula -CH 2 -NH-CO-R wherein R is a lower alkyl having 1 to 6 carbon atoms, 2-,3-,4-pyridyl, phenyl or phenyl substituted with lower alkyl, hydroxy, lower alkoxy, carboxy, or lowe alkoxycarbonyl. 26. The multimeric polyvalent antithrombotic agent of Claim 2 wherein the polyvalent linking moiety is comprised of at least 2 linker functiona groups capable of covalently bonding to platelet binding cyclic peptides an wherein at least 2 of the linker functional groups are identical. 27. The multimeric polyvalent antithrombotic agent of Claim 2 wherein the linker functional groups of the polyvalent linking moiety are primar or secondary amines, hydroxyl groups, carboxylic acid groups or thiol-reactiv groups. 28. The multimeric polyvalent antithrombotic agent of Claim 2 wherein the polyvalent linking moiety is comprised of a multiplicity of polyvalen linking moieties covalently linked to form a branched polyvalent linking moiety 29. The multimeric polyvalent antithrombotic agent of Claim 2 wherein the polyvalent linking moiety is bw-succinimidylmethylether t (succinimidylethyl)amine or a derivative thereof. 30. A multimeric polyvalent antithrombotic agent according to Clai 21 wherein the multiplicity of platelet-binding peptides are each covalently linke to the polyvalent linking moiety by a functional linker group, said function linker group selected from the group consisting of primary or secondary amines hydroxyl groups, carboxylic acid groups and thiol groups. 31. The multimeric polyvalent antithrombotic agent according to Clai 21 wherein the platelet-binding cyclic peptides are chemically synthesized in vitro 32. The multimeric polyvalent antithrombotic agent according to Clai 31 wherein the platelet-binding cyclic peptides are synthesized by solid phas peptide synthesis. 33. A composition of matter having the formula fCH ? CO.Yp.Apc.GDCKGC Λrm GC Λfm GGCamideyBSME fCH,CO.Y P .Apc.GDCGGC Λrm GC Λrm GGCamideWBSME or (CH 2 CO i Y Di Apc i GDCGGC Acm GC Acm GGCamide) 3 -TSEA. 34. A method for preventing thrombosis within a mammalian bod comprising administering an effective therapeutic amount of the multimeri polyvalent antithrombotic agent of Claim 21 in a pharmaceutical carrier. 35. A multimeric polyvalent antithrombotic agent comprising multiplicity of platelet binding peptides, each peptide comprising an amino aci sequence of 3-100 amino acids, covalently linked to a polyvalent linking moiety wherein each of the platelet binding peptides has the formula A-R 1 -X-Gly-Asp-(R)-Z-B wherein A is H, an amine protecting group or (aa) p , where (aa) p is a peptid comprising an amino acid sequence of length p, wherein wheneve the amino acid is cysteine, said cysteine may be protected at it sidechain sulfur atom, and p is an integer from 0 to 97; R 1 is a lipophilic amino acid or H; X is an amino acid capable of being positively charged; (R) is a substituted or unsubstituted linear or branched chain lowe alkyl group having 1-20 carbon atoms or a substituted o unsubstituted phenyl, aryl, polycyclic or heterocyclic group optionally comprising at least one heteroatom selected from th group consisting of O, S, and N; Z is absent or cysteine, isocysteine or homocysteine; B is -OH, -NH 2 , -SH, or (aa) m , wherein (aa) m is a peptid comprising an amino acid sequence of length m, wherein wheneve the amino acid is cysteine, said cysteine may be protected at it sidechain sulfur atom, and m is an integer from 0 to 97; and m + p < 97, wherein the molecular weight of the multimeric polyvalent antithrombotic agen is less than about 20,000 daltons. 36. The multimeric polyvalent antithrombotic agent of Claim 3 wherein the lipophilic amino acid is selected from the group consisting o phenylalanine, tyrosine, tryptophan, valine, leucine and isoleucine. 37. The multimeric polyvalent antithrombotic agent of Claim 3 wherein X is an amino acid that is lysine, homolysine, arginine, homoarginine or L-[S-(3-aminopropyl)cysteine] . 38. The multimeric polyvalent antithrombotic agent of Claim 3 wherein each of the multiplicity of platelet binding peptides is comprised of 3 t 20 amino acids. 39. The multimeric polyvalent antithrombotic agent of Claim 3 wherein each protected cysteine has a thiol protecting group of formula -CH 2 -NH-CO-R wherein R is a lower alkyl having 1 to 6 carbon atoms, 2-,3-,4-pyridyl, pheny or phenyl substituted with lower alkyl, hydroxy, lower alkoxy, carboxy, or lowe alkoxycarbonyl. 40. The multimeric polyvalent antithrombotic agent of Claim 3 wherein the polyvalent linking moiety is comprised of at least 2 linker function groups capable of covalently bonding to platelet binding peptides and wherein least 2 of the linker functional groups are identical. 41. The multimeric polyvalent antithrombotic agent of Claim 4 wherein the linker functional groups of the polyvalent linking moiety are primar or secondary amines, hydroxyl groups, carboxylic acid groups or thiol-reactiv groups. 42. The multimeric polyvalent antithrombotic agent of Claim 3 wherein the polyvalent linking moiety is comprised of a multiplicity of polyvale linking moieties covalently linked to form a branched polyvalent linking moiet 43. The multimeric polyvalent antithrombotic agent of Claim 3 wherein the polyvalent linking moiety is bw-succinimidylmethylethe t (succinimidylethyl)amine or a derivative thereof. 44. A multimeric polyvalent antithrombotic agent according to Clai 35 wherein the multiplicity of platelet-binding peptides are each covalently linke to the polyvalent linking moiety by a functional linker group, said function linker group selected from the group consisting of primary or secondary amine hydroxyl groups, carboxylic acid groups and thiol groups. 45. The multimeric polyvalent antithrombotic agent according to Clai 35 wherein the platelet-binding peptides are chemically synthesized in vitro. 46. The multimeric polyvalent antithrombotic agent according to Clai 45 wherein the platelet-binding peptides are synthesized by solid phase peptid synthesis. 47. A method for preventing thrombosis within a mammalian bod comprising administering an effective therapeutic amount of the multimeri polyvalent antithrombotic agent of Claim 35 in a pharmaceutical carrier. 48. A multimeric polyvalent antithrombotic agent comprising multiplicity of platelet binding cyclic peptides, each peptide comprising an amin acid sequence of 5-100 amino acids, covalently linked to a polyvalent linkin moiety, wherein each of the platelet binding cyclic peptides has the formula wherein A D is a lipophilic D-amino acid; X is lysine, homolysine, arginine, homoarginine, or L-[S-(3 aminopropyl)cysteine] ; (R) is a substituted or unsubstituted linear or branched chain lowe alkyl group or a substituted or unsubstituted phenyl, aryl, polycyclic or heterocyclic group, optionally comprising at least on heteroatom selected from the group consisting of O, S, and N; Z is absent or cysteine, isocysteine or homocysteine; and B is -OH, -NH 2 , -SH, or (aa) m , wherein (aa) m is a ^ peptid comprising an amino acid sequence of length m, wherein wheneve the amino acid is cysteine, said cysteine may be protected at it sidechain sulfur atom, and m = 0-95, wherein the molecular weight of the multimeric polyvalent antithrombotic agen is less than about 20,000 daltons. 49. The multimeric polyvalent antithrombotic agent of Claim 4 wherein the lipophilic D-amino acid is selected from the group consisting o phenylalanine, tyrosine, tryptophan, valine, leucine and isoleucine. 50. The multimeric polyvalent antithrombotic agent of Claim 4 wherein X is an amino acid that is lysine, homolysine, arginine, homoarginine or L-[S-(3-aminopropyl)cysteine]. 51. The multimeric polyvalent antithrombotic agent of Claim 4 wherein each of the multiplicity of platelet binding cyclic peptides is comprise of 5 to 20 amino acids. 52. The multimeric polyvalent antithrombotic agent of Claim 4 wherein the polyvalent linking moiety is comprised of at least 2 linker functiona groups capable of covalently bonding to platelet-binding cyclic peptides an wherein at least 2 of the linker functional groups are identical. 53. The multimeric polyvalent antithrombotic agent of Claim 5 wherein the linker functional groups of the polyvalent linking moiety are primary or secondary amines, hydroxyl groups, carboxylic acid groups or thiol-reactiv groups. 54. The multimeric polyvalent antithrombotic agent of Claim 4 wherein the polyvalent linking moiety is comprised of a multiplicity of polyvalen linking moieties covalently linked to form a branched polyvalent linking moiety. 55. The multimeric polyvalent antithrombotic agent of Claim 4 wherein the polyvalent linking moiety is bw-succinimidylmethylether, tra(succinimidylethyl)amine or a derivative thereof. 56. A multimeric polyvalent antithrombotic agent according to Clai 48 wherein the multiplicity of platelet-binding peptides are each covalently linke to the polyvalent linking moiety by a functional linker group, said functiona linker group selected from the group consisting of primary or secondary amines hydroxyl groups, carboxylic acid groups and thiol groups. 57. The multimeric polyvalent antithrombotic agent according to Clai 48 wherein the platelet-binding cyclic peptides are chemically synthesized in vitro 58. The multimeric polyvalent antithrombotic agent according to Clai 57 wherein the platelet-specific cyclic peptides are synthesized by solid phas peptide synthesis. 59. A method for preventing thrombosis within a mammalian bod comprising administering an effective therapeutic amount of the multimeri polyvalent antithrombotic agent of Claim 48 in a pharmaceutical carrier. 60. A composition of matter that is tra(maleimidoethyl)amine.

Inventors: DEAN RICHARD T, LISTER-JAMES JOHN, DEAN, RICHARD, T., LISTER-JAMES, JOHN
Applicants: DEAN RICHARD T, DIATECH INC, LISTER JAMES JOHN, DIATECH, INC.
Application year: 1993
Main classification: C07K15
IPC codes: A61K38, A61P7, C07K14