N.sup.2 -Arylsulfonyl-L-argininamides and the pharmaceutically acceptable salts thereof

Abstract

N.sup.2 -arylsulfonyl-L-argininamides and the pharmaceutically acceptable salts thereof have been found to be effective as pharmaceutical agents for the inhibition and suppression of thrombosis in mammals.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the discovery of certain new and useful N.sup.2 -arylsulfonyl-L-argininamides and the pharmaceutically acceptable salts thereof, which are of especial value in view of their outstanding antithrombotic properties and low toxicities.

2. Description of the Prior Art

In the past, there have been many attempts to obtain new and improved agents for the treatment of thrombosis. The N.sup.2 -(p-tolysulfonyl)-L-arginine esters have been found to be one type of agent which can be used and these have been found to be effective in dissolving blood clots. (U.S. Pat. No. 3,622,615, issued Nov. 23, 1971). One family of compounds which have been found to be particularly useful as highly specific inhibitors of thrombin for the control of thrombosis is the N.sup.2 -dansyl-L-arginine ester or amide. (Our pending U.S. Application Ser. No. 496,939, filed Aug. 13, 1974 now U.S. Pat. No. 3,978,045). However, there is a continuing need for a highly specific inhibitor of thrombin for the control of thrombosis, which exhibits lower toxicity.

SUMMARY OF THE INVENTION

It has now been discovered that N.sup.2 -arylsulfonyl-L-argininamides exhibit antithrombotic activity and even lower toxicity levels at the same relative potencies, as compared with the N.sup.2 -dansyl-L-arginine ester or amide.

The present invention provides an N.sup.2 -arylsulfonyl-L-argininamide of the formula (I): ##STR1## wherein R is ##STR2## wherein R.sub.1 is hydrogen or C.sub.1 -C.sub.5 alkyl; and Ar is 1,2,3,4-tetrahydro-8-quinolyl optionally substituted with at least one C.sub.1 -C.sub.3 alkyl.

Also encompassed within this invention are pharmaceutically acceptable salts thereof.

This invention also relates to a method for inhibiting activity and suppressing activation of thrombin in vivo in mammals which comprises administering to a mammal a pharmaceutically (antithrombotically) effective amount of an N.sup.2 -arylsulfonyl-L-argininamide or the pharmaceutically acceptable salts thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention relates to a group of N.sup.2 -arylsulfonyl-L-argininamides of the formula (I): ##STR3## wherein R is ##STR4## wherein R.sub.1 is hydrogen or alkyl of 1-5 (preferably 1-3) carbon atoms; and Ar is 1,2,3,4-tetrahydro-8-quinolyl optionally substituted with at least one (preferably one or two) alkyl of 1-3 (preferably 1-2) carbon atoms.

Typical compounds of this invention include:

1-[N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid 1-[N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-ethyl-2-piperidinecarboxylic acid 1-[N.sup.2 -(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid 1-[N.sup.2 -(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-ethyl-2-piperidinecarboxylic acid 1-[N.sup.2 -(3-ethyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid 1-[N.sup.2 -(3-ethyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-ethyl-2-piperidinecarboxylic acid The pharmaceutically acceptable salts of the above compounds are of course also included within the scope of this invention.

For the preparation of the compounds of this invention, various methods can be employed depending upon the particular starting materials and/or intermediates involved. Successful preparation of these compounds is possible by way of a synthetic route which is outlined below. ##STR5## In the above formulas, R, Ar and R.sub.1 are as defined herein above; X is halogen; R'" is a protective group for the .alpha.-amino group, such as benzyloxycarbonyl or tert-butoxycarbonyl; R' and R" are selected from the group consisting of hydrogen and protective groups for the guanidino group, such as nitro, tosyl, trityl, oxycarbonyl and the like; and at least one of R' and R" is a protective group for the guanidino group; R.sub.2 is lower alkyl such as methyl and ethyl; and Q is 8-quinolyl optionally substituted with at least one C.sub.1 -C.sub.3 alkyl, which is corresponding to Ar.

The N.sup.2 -arylsulfonyl-L-argininamide (I) is prepared by removing the N.sup.G -substituent from an N.sup.G -substituted-N.sup.2 -quinolylsulfonyl-L-argininamide (IX) by means of hydrogenolysis and, at the same time, hydrogenating the quinolyl moiety to the corresponding 1,2,3,4-tetrahydroquinolyl moiety.

The removal of the nitro group and the oxycarbonyl group, e.g., benzyloxycarbonyl, p-nitrobenzyloxycarbonyl, is readily accomplished by the hydrogenolysis.

The hydrogenolysis and hydrogenation are effected in a reaction-inert solvent, e.g., methanol, ethanol, tetrahydrofuran or dioxane, in the presence of a hydrogen-activating catalyst, e.g., Raney nickel, palladium, or platinum, ruthenium, rhodium, in a hydrogen atmosphere at a temperature of 0.degree. C. to 200.degree. C. and preferably 50.degree. C. to 150.degree. C. for a period of 2 hours to 120 hours.

In general, the hydrogen pressure is in the range of 1 to 100 kg/cm.sup.2, and preferably in the range of 5 to 50 kg/cm.sup.2. It is necessary to continue the hydrogenolysis and hydrogenation until a stoichiometric amount of hydrogen is absorbed. The N.sup.2 -arylsulfonyl-L-argininamides (I) are isolated by filtration of the catalyst followed by evaporation of the solvent, and then purified by trituration or recrystallization from a suitable solvent, such as diethyl ether-tetrahydrofuran, diethyl ether-methanol and water-methanol, or may be chromatographed on silica gel or alumina.

1-(N.sup.G -substituted-N.sup.2 -quinolylsulfonyl-L-arginyl)-2-piperidinecarboxylic acids (IX) can be prepared by hydrolyzing an alkyl 1-(N.sup.G -substituted-N.sup.2 -quinolylsulfonyl-L-arginyl)-2-piperidinecarboxylate (VIII) by a conventional procedure well known in the art.

The alkyl 1-(N.sup.G -substituted-N.sup.2 -quinolylsulfonyl-L-arginyl)-2-piperidinecarboxylate (VIII) can be prepared by condensing an N.sup.G -substituted-N.sup.2 -substituted L-arginine (III) (generally the N.sup.G -substituent is nitro or acyl, and the N.sup.2 -substituent is a protective group for the amino group, such as benzyloxycarbonyl, tert-butoxycarbonyl, or the like) and a corresponding amino acid derivative (IV), selectively removing only the N.sup.2 -substituent of an N.sup.G -substituted-N.sup.2 -substituted L-argininamide (V) by means of catalytic hydrogenolysis or acidolysis, and then condensing the thus obtained N.sup.G -substituted-L-argininamide (VI) with a quinolinesulfonyl halide (VII), preferably a chloride in the presence of a base in a solvent.

The N.sup.2 -arylsulfonyl-L-argininamide (I) of this invention forms acid addition salts with any of a variety of inorganic and organic acids. They also form salts with any of a variety of inorganic and organic bases.

The product of the reactions described above can be isolated in the free form or in the form of salts. In addition, the product can be obtained as pharmaceutically acceptable acid addition salts by reacting one of the free bases with an acid, such as hydrochloric, hydrobromic, hydroiodic, nitric, sulfuric, phosphoric, acetic, citric, maleic, succinic, lactic, tartaric, gluconic, benzoic, methanesulfonic, ethanesulfonic, benzenesulfonic, p-toluenesulfonic acid or the like. In a similar manner, the product can be obtained as pharmaceutically acceptable salts by reacting one of the free carboxylic acids with a base, such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, triethylamine, procaine, dibenzylamine, 1-ephenamine, N,N'-dibenzylethylenediamine, N-ethylpiperidine or the like.

Likewise, treatment of the salts with a base or acid results in a regeneration of the free amide.

As stated above, the N.sup.2 -arylsulfonyl-L-argininamides, and the salts thereof of this invention are characterized by their highly specific inhibitory activity in mammals against thrombin as well as by their substantial lack of toxicity, and therefore these compounds are useful in the determination of thrombin in blood as diagnostic reagents, and/or for the medical control or prevention of thrombosis.

The compounds of this invention are also useful as an inhibitor of platelet aggregation.

The antithrombotic activity of the N.sup.2 -arylsulfonyl-L-argininamide of this invention was compared with that of a known antithrombotic agent, N.sup.2 -(p-tolylsulfonyl)-L-arginine methyl ester, by determining the fibrinogen coagulation time. The measurement of the fibrinogen coagulation time was conducted as follows:

An 0.8 ml aliquot of a fibrinogen solution, which had been prepared by dissolving 150 mg of bovine fibrinogen (Cohn fraction I) supplied by Armour Inc. in 40 ml of a borate saline buffer (pH 7.4), was mixed with 0.1 ml of a borate saline buffer, pH 7.4, (control) or a sample solution in the same buffer, and 0.1 ml of a thrombin solution (5 units/ml) supplied by Mochida Pharmaceutical Co., Ltd. was added to the solutions in an ice bath.

Immediately after mixing, the reaction mixture was transferred from the ice bath to a bath maintained at 25.degree. C. Coagulation times were taken as the period between the time of transference to the 25.degree. C. bath and the time of the first appearance of fibrin threads. In the cases where no drug samples were added, the coagulation time was 50-55 seconds.

The experimental results are summarized in Table 1. The term "concentration required to prolong the coagulation time by a factor of two" is the concentration of an active ingredient required to prolong the normal coagulation time 50-55 seconds to 100-110 seconds.

The concentration required to prolong the coagulation time by a factor of two for the known antithrombotic agent, N.sup.2 -(p-tolylsulfonyl)-L-arginine methyl ester, was 1,100 .mu.m. The inhibitors are shown in Table 1 by indicating R and Ar in the formula (I) and the addition moiety.

When a solution containing an N.sup.2 -arylsulfonyl-L-argininamide of this invention was administered intravenously into animal bodies, the high antithrombotic activity in the circulating blood was maintained for from one to three hours. The halflife for decay of the anti-thrombotic compounds of this invention in circulating blood was shown to be approximately 60 minutes; the physiological conditions of the host animals (rats, rabbit, dog and chimpanzee) were well maintained. The experimental decrease of fibrinogen in animals caused by infusion of thrombin was satisfactorily controlled by simultaneous infusion of the compounds of this invention.

The acute toxicity values (LD.sub.50) determined by intravenous administration of substances of formula (I) in mice (male, 20 g) range from about 100 to 500 milligrams per kilogram of body weight.

Representative LD.sub.50 values for 1-N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl-4-methyl-2-piperidinecarboxylic acid, 1-N.sup.2 -(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl-4-methyl-2-piperidinecarboxylic acid, 1-N.sup.2 -(3-ethyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl-4-methyl-2-piperidinecarboxylic acid and 1-N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl-4-ethyl-2-piperidinecarboxylic acid are 191, 264, 322 and 132 milligrams per kilogram, respectively.

On the other hand, LD.sub.50 values for N.sup.2 -dansyl-N-butyl-L-argininamide and N.sup.2 -dansyl-N-methyl-N-butyl-L-argininamide are 10 and 5 milligrams per kilogram, respectively.

The therapeutic agents in this invention may be administered to mammals, including humans, alone or in combination with pharmaceutically acceptable carriers, the proportion of which is determined by the solubility and chemical nature of the compound, chosen route of administration and standard pharmaceutical practice.

For example, the compounds may be injected parenterally, that is, intramuscularly, intravenously or subcutaneously. For parenteral administration, the compounds may be used in the form of sterile solutions containing other solutes, for example, sufficient saline or glucose to make the solution isotonic. The compounds may be administered orally in the form of tablets, capsules, or granules containing suitable excipients such as starch, lactose, white sugar and the like.

The compounds may be administered sublingually in the form of troches or lozenges in which each active ingredient is mixed with sugar or corn syrups, flavoring agents and dyes, and then dehydrated sufficiently to make the structure suitable for pressing into solid form. The compounds may be administered orally in the form of solutions which may contain coloring and flavoring agents. Physicians will determine the dosage of the present therapeutic agents which will be most suitable for humans, and dosages vary with the mode of administration and the particular compound chosen. In addition, the dosage will vary with the particular patient under treatment.

When the composition is administered orally, a larger quantity of the active agent will be required to produce the same effect as caused with a smaller quantity given parenterally.

The therapeutic dosage is generally 10-50 mg/kg of active ingredient parenterally, 10-500 mg/kg orally per day.

Having generally described the invention, a more complete understanding can be obtained by reference to certain specific examples, which are included for purposes of illustration only and are not intended to be limiting unless otherwise specified.

It is to be understood that the present invention includes pharmaceutical compositions containing a compound of the invention as an active ingredient. Such compositions may be in the forms described above. In particular, the invention includes such compositions in unit dose form.

EXAMPLE 1

(A) Ethyl 1-[N.sup.G -nitro-N.sup.2 -(tert-butoxycarbonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylate

To a stirred solution of 28.3 g of N.sup.G -nitro-N.sup.2 -(tert-butoxycarbonyl)-L-arginine in 450 ml of dry tetrahydrofuran were added in turn 9.0 g of triethylamine and 12.2 g of isobutyl chloroformate while keeping the temperature at -20.degree. C. After 10 minutes, to this was added 15.2 g of ethyl 4-methyl-2-piperidinecarboxylate and the mixture was stirred for 10 minutes at -20.degree. C. At the end of this period, the reaction mixture was warmed to room temperature. The solvent was evaporated and the residue taken up in 400 ml of ethyl acetate, and washed successively with 200 ml of water, 100 ml of 5% sodium bicarbonate solution, 100 ml of 10% citric acid solution and 200 ml of water. The ethyl acetate solution was dried over anhydrous sodium sulfate.

The solution was evaporated to give 31.5 g (75 percent) of ethyl 1-[N.sup.G -nitro-N.sup.2 -(tert-butoxycarbonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylate in the form of a syrup.

I.R. (KBr): 3,300, 1,730, 1,680 cm.sup.-1

(B) Ethyl 1-[N.sup.G -nitro-L-arginyl]-4-methyl-2-piperidinecarboxylate hydrochloride

To a stirred solution of 30 g of ethyl 1-[N.sup.G -nitro-N.sup.2 -(tert-butoxycarbonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylate in 50 ml of ethyl acetate was added 80 ml of 10% dry HCl-ethyl acetate at 0.degree. C. After 3 hours, to this solution was added 200 ml of dry ethyl ether to precipitate a viscous oily product.

This was filtered and washed with dry ethyl ether to give ethyl 1-[N.sup.G -nitro-L-arginyl]-4-methyl-2-piperidinecarboxylate hydrochloride as an amorphous solid.

(C) Ethyl 1-[N.sup.G -nitro-N.sup.2 -(3-methyl-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylate

To a stirred solution of 25 g of ethyl 1-(N.sup.G -nitro-L-arginyl)-4-methyl-2-piperidinecarboxylate hydrochloride in 200 ml of chloroform were added in turn 18.5 g of triethylamine, and 14.7 g of 3-methyl-8-quinolinesulfonyl chloride at 5.degree. C., and stirring was continued for 3 hours at room temperature. At the end of this period, the solution was washed twice with 50 ml of water.

The chloroform solution was dried over anhydrous sodium sulfate. Upon evaporation of the solvent, the residue was chromatographed on 50 g of silica gel packed in chloroform, washed with chloroform and eluted with 3% methanol-chloroform. The fraction eluted from 3% methanol-chloroform was evaporated to give 32.1 g (91 percent) of ethyl 1-[N.sup.G -nitro-N.sup.2 -(3-methyl-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylate in the form of an amorphous solid.

I.R. (KBr): 3,250, 1,725, 1,640 cm.sup.-1

(D) 1-[N.sup.G -nitro-N.sup.2 -(3-methyl-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid

A solution of 30 g of ethyl 1-[N.sup.G -nitro-N.sup.2 -(3-methyl-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylate in 100 ml of ethanol and 100 ml of 1 N sodium hydroxide solution was stirred for 24 hrs at room temperature. At the end of this period, the solution was neutralized with 1 N hydrochloric acid and then concentrated to 70 ml.

The solution was adjusted to pH 11 with 1 N sodium hydroxide solution, washed three times with 100 ml of ethyl acetate, acidified with 1 N hydrochloric acid and then extracted three times with 100 ml of chloroform. The combined chloroform solution was dried over anhydrous sodium sulfate and evaporated to give 28.0 g (97 percent) of 1-[N.sup.G -nitro-N.sup.2 -(3-methyl-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid as an amorphous solid.

IR (KBr): 3,300, 1,720, 1,630 cm.sup.-1 Analysis Calcd. for C.sub.23 H.sub.31 N.sub.7 O.sub.7 S (percent): C, 50.26; H, 5.69; N, 17.84 Found (percent) C, 50.00; H, 5.50; N, 17.49

(E) 1-[N.sup.2 -(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid

To a solution of 3.00 g of 1-[N.sup.G -nitro-N.sup.2 -(3-methyl-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid in 50 ml of ethanol was added 0.5 g of palladium black and then the mixture was shaken under 10 kg/cm.sup.2 hydrogen pressure at 100.degree. C. for 8 hrs. At the end of this period, the ethanol solution was filtered to remove the catalyst and evaporated to give 2.50 g (90 percent) of 1-[N.sup.2 -(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid as an amorphous solid.

IR (KBr): 3,400, 1,620, 1,460, 1,380 cm.sup.-1 NMR: 100 MHz in CD.sub.3 OD .delta.-value; 6.5 (triplet 1H) 7.1 (doublet 1H), 7.4 (doublet 1H)

Analysis Calcd. for C.sub.23 H.sub.36 N.sub.6 O.sub.5 S (percent): C, 54.31; H, 7.13; N, 16.52 Found (percent) C, 54.01; H, 6.98; N, 16.61

Various other N.sup.2 -arylsulfonyl-L-argininamides were synthesized in accordance with the procedure of the above example, and the test results are summarized in Table 1.

TABLE 1__________________________________________________________________________ Sample ##STR6## Concen- tration required to prolong the coagulation time by a factor of proper-Physical Lower: FoundUpper: CalculatedElemental I.R.valueN.M.R. (ppm).delta.No. Ar R (.mu.M) ties C H N (cm.sup.-1) (CD.sub.3__________________________________________________________________________ OD) ##STR7## ##STR8## 0.45 powder 54.31 54.21 7.13 6.98 16.52 16.38 3,380, 1,620 1,460, 1,375 6.5 (t, 1H) 7.1 (d, 1H) 7.4 (d, 1H)2 ##STR9## " 0.08 powder 54.31 54.01 7.13 6.98 16.52 16.61 3,400, 1,620 1,460, 1,380 6.5 (t, 1H) 7.1 (d, 1H) 7.4 (d, 1H)3 ##STR10## " 0.2 powder 54.31 54.50 7.13 7.01 16.52 16.29 3,380, 1,620 1,380, 1,160 6.5 (t, 1H) 7.2 (d, 1H) 7.4 (d, 1H)4 ##STR11## " 1.8 powder 54.31 54.28 7.13 7.13 16.52 16.40 3,380, 1,620 1,380, 1,285 6.9 (s, 1H) 7.3 (s, 1H)5 ##STR12## " 5.5 powder 55.15 55.20 7.33 7.29 16.08 16.00 3,350, 1,620 1,380, 1,150 6.5 (t, 1H) 7.1 (t, 1H) 7.4 (t, 1H)6 ##STR13## " 0.06 powder 55.15 55.11 7.33 7.40 16.08 15.88 3,375, 1,620 1,460, 1,380 6.6 (t, 1H) 7.2 (d, 1H) 7.4 (d, 1H)7 ##STR14## " 0.45 powder 53.42 53.12 6.93 6.63 16.99 16.59 3,380, 1,620 1,460, 1,380 6.6 (d, 1H) 7.1 (d, 1H) 7.4 (d, 1H)8 ##STR15## ##STR16## 0.45 powder 54.31 54.20 7.13 7.19 16.52 16.41 3,380, 1,620 1,460 1,380 6.6 (d, 1H) 7.1 (d, 1H) 7.4 (d, 1H)9 ##STR17## " powder 55.15 55.07 7.33 7.03 16.08 16.38 3,380, 1,620 1,460, 1,380 6.5 (t, 1H) 7.2 (d, 1H) 7.4 (d, 1H)10 ##STR18## " powder 55.95 55.69 7.51 7.28 15.66 15.51 3,380, 1,620 1,460, 1,380 6.5 (t, 1H) 7.2 (d, 1H) 7.4 (d, 1H)11 ##STR19## ##STR20## powder 53.42 53.28 6.93 6.63 16.99 16.69 3,380, 1,620 1,460, 1,380 6.6 (d, 1H) 7.1 (d, 1H) 7.4 (d, 1H)__________________________________________________________________________

EXAMPLE 2

Tablets suitable for oral administration

Tablets containing the ingredients indicated below may be prepared by conventional techniques.

______________________________________ Amount per tabletIngredient (mg)______________________________________1-[N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl- 2502-piperidinecarboxylic acidLactose 140Corn starch 35Talcum 20Magnesium stearate 5Total 450 mg______________________________________

EXAMPLE 3

Capsules for oral administration

Capsules of the below were made up by thoroughly mixing together batches of the ingredients and filling hard gelatin capsules with the mixture.

______________________________________ Amount per capsuleIngredient (mg)______________________________________1-[N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl- 2502-piperidinecarboxylic acidLactose 250Total 500 mg______________________________________

EXAMPLE 4

Sterile solution for infusion

The following ingredients are dissolved in water for intravenous perfusion and the resulting solution is then sterilized.

______________________________________Ingredients Amount (g)______________________________________1-[N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid 25Buffer system As desiredGlucose 25Distilled water 500______________________________________ Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit of the invention as set forth herein.

Claims

1. An N.sup.2 -arylsulfonyl-L-argininamide of the formula (I): ##STR21## wherein R is ##STR22## wherein R.sub.1 is hydrogen or C.sub.1 -C.sub.5 alkyl; and Ar is 1,2,3,4-tetrahydro-8-quinolyl optionally substituted with at least one C.sub.1 -C.sub.3 alkyl.

2. The compound of claim 1 wherein R.sub.1 is hydrogen or C.sub.1 -C.sub.3 alkyl and Ar is 1,2,3,4-tetrahydro-8-quinolyl optionally substituted with at least one C.sub.1 -C.sub.2 alkyl.

3. The compound of claim 2, which is 1-[N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid.

4. The compound of claim 2, which is 1-[N.sup.2 -(1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-ethyl-2-piperidinecarboxylic acid.

5. The compound of claim 2, which is 1-[N.sup.2 -(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid.

6. The compound of claim 2, which is 1-[N.sup.2 -(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-ethyl-2-piperidinecarboxylic acid.

7. The compound of claim 2, which is 1-[N.sup.2 -(3-ethyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-methyl-2-piperidinecarboxylic acid.

8. The compound of claim 2, which is 1-[N.sup.2 -(3-ethyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginyl]-4-ethyl-2-piperidinecarboxylic acid.