Cross-Re erence to Related Application

This application is a continuation-in-part of co-pending application Serial Number 921,295,filed July 3, 1978.

This invention relates to N-[3-(lower)alky1- aminopropyl]-N'-(disubstituted)phenylureas which are useful in the treatment of cardiac arrhythmias. Heretofore the treatment of arrhythmias has been li- mited by drug toxicity, undesirable side-effects, or variable ef ectiveness. Accordingly, a great need exists for an anti-arrhythmic agent which is effica¬ cious and less toxic and which has a lower incidence of undesirable side-effects than known anti-arrhy- th ic agents.

In particular, the invention comprises chemical compounds of the formula:

0 H

Y-NHCNH-CH ₂ CH ₂ CH ₂ -NH-X

wherein: Y is 2, 6-dimethylphenyl , 2, 5-dimethylphenyl ,

5-bromo-2-methylphenyl , or 5-chloro-2- methylphenyl ; and X is propyl , isopropyl , n-butyl , or isobutyl; or a non-toxic pharmaceutically acceptable acid ad- dition salt thereof .

The compounds of Formula I wherein X is iso- propyl are preferred. Also preferred are those compounds of Formula I wherein Y is 2,6-dimethyl- phenyl or 5-chloro-2-methylphenyl. The compounds of Formula I exhibit cardiac anti-arrhythmic activity as demonstrated in labora¬ tory tests involving a variety of arrhythmic animal models. The compounds are therefore useful in treating both atrial and ventricular arrhythmias re- suiting from various ufnderlying conditions, such as ischemic heart disease, myocardial infarction, con¬ genital cardiac defects, digitalis overdose, myo¬ carditis, or other pathological or toxic processes which may alter the electrical excitability of the heart.

The compound of Formula I wherein Y is 2,6-di- methylphenyl and X is isopropyl offers particularly significant advantages over known anti-arrhythmic agents because of its low toxicity, longer duration ■ of activity, and low incidence of undesirable side- effects. In particular, said compound at therapeu¬ tic doses has been found to produce little or no ef¬ fect on the central nervous system (such as sedation, muscle weakness, or ataxia). Moreover, anti-chlo- linergic effects were not observed and undesirable cardiac effects (such as depressed cardiac contrac¬ tility or cardiac output), were minimal at effective dosages.

The compound of Formula I wherein Y is 5-chloro- 2-methylphenyl and X is isopropyl also offers parti¬ cularly significant advantages over known anti-arrhy¬ thmic agents because of its high efficacy, particu¬ larly long duration of activity, and low incidence of undesirable side-effects.

The compounds of Formula I can be prepared by conventional synthetic methods. The preferred method is by the reaction of an appropriate disubstituted phenyl isocyanate with an N-(lower)-alkylamino-l,3-di- aminopropane in an inert organic solvent, such as di¬ chloromethane. In order to optimize the yield, the reaction should be carried out with an excess of the diaminopropane and at a low temperature. A molar ratio of about 3 to 1 (diamine to isocyanate) is pre- ferred and a temperature of about -5 to +5° C. is desirable.

In an alternative method, an appropriate disub¬ stituted phenyl isocyanate is first reacted with an N-protected-N'-(lower)alkyl-l,3-diaminopropane in an inert solvent, (such as chloroform, dichloromethane, or benzene) to form the protected intermediate (II):

Y-NHC0N-CH _o CH _o CH _o -NH-Z I 2 2 2

II

wherein Y and X have the meanings hereinbefore defined and Z is a conventional protecting group for an amino group. The protecting group is then removed to afford the deprotected intermediate III:

Y-NHC0N-CH ₂ CH ₂ CH ₂ -NH ₂

III

If the deprotection step is performed under the in¬ fluence of heat, the intermediate (III) undergoes an intramolecular aminolysis of the amide ij situ result¬ ing in substitution of the (lower)alkyl group (X) at

the terminal position of the chain. The initial reac¬ tion between the isocyanate and the protected diamine is carried out in an inert solvent, such as chloroform dichloromethane, or benzene. If the deprotection re- action is carried out at room temperature, the depro- tected intermediate III can be isolated, and it can thereafter be converted to the final product by heat¬ ing the intermediate in a suitable solvent, such as chloroform. Protecting groups for an amino group- are known in the art. Suitable groups are those which will prevent undesirable side reactions from occurring at the amino group during the initial reaction and which will be easily removed under mild conditions after the initial reaction.

Methods for making the protected amino compounds and for removing the protecting groups are well-known inthe art. Preferred protecting groups are the carbo- benzoxy group and the anisylidene group. The anisyli- dene group can be removed by treating the protected amine intermediate with hydroxylamine ] -toluene-sulfo- nate in refluxing dioxane or ethyl alcohol. Under suc conditions aminolysis takes place ±n situ. The carbo- benzoxy group can be removed by treatment with hydroge bromide in acetic acid at room temperature. The depro tected amine (III) can be isolated and thereafter con¬ verted to the final product by mild heating.

The compounds of Formula I can be isolated in the form of the free base or in the form of a non-toxic acid addition salt prepared by reaction of the free base with a pharmaceutically acceptable organic or in¬ organic acid. Suitable acids will be apparent to thos skilled in the art. Examples of such acids are p_-tolu ene sulfonic (tosyl), hydrochloric, or phosphoric. Th tosyl and hydrochloric salts are generally preferred.

In another aspect, the invention provides a method of suppressing cardiac arrhythmias in warm-blooded ani¬ mals which comprises administering to said animal oral¬ ly or parenterally an effective amount of a compound of Formula I, w ^r herein X and Y are as hereinabove defined, or a non-toxic, pharmaceutically acceptable acid addi¬ tion salt thereof. The anti-arrhythmic dosage of a compound of Formula I will vary according to the parti¬ cular subject being treated, the severity and nature of the arrhythmia, and the particular subject being treat¬ ed. Therapy should be initiated at a low dosage, the dosage thereafter being increased until the desired anti-arrhythmic effect is obtained. In general, with large warm-blooded animals (about 70 kg. body weight) effective results can be achieved by the oral route at a daily dosage level of from about 0.5 g. of about 1.5 g. (about 7-20 mg/kg. of body weight) given as needed.

In yet another aspect, the invention provides a pharmaceutical composition comprising: (a) a compound o f Formula I, wherein X and Y have the meanings here¬ inbefore defined, or a non-toxic, pharmaceutically ac- • ceptable acid addition salt thereof, and (b) a pharma¬ ceutically acceptable carrier.

The active substances may be administered alone or in combination with pharmaceutically acceptable car¬ riers, the proportion and nature of which are deter¬ mined by the solubility and chemical properties of the compound selected, the chosen route of administration, and standard pharmaceutical practice. For example, the compounds of Formula I may be administered orally in solid dosage forms, e.g. capsules, tablets, or powders, or in liquid forms, e.g. solutions or suspensions. The compounds may also be injected parenterally in the form of sterile solutions or suspensions. Solid oral forms may contain conventional excipients, for instance: lac¬ tose, sucrose, magnesium stearate, resins, and like

materials. Liquid oral forms may contain various fla¬ voring, coloring, preserving, stabilizing, solubilizin or suspending agents. Parenteral preparations are ste rile aqueous or non-aqueous solutions or suspensions which may contain various preserving, stabilizing, buf fering, solubilizing, or suspending agents. If desire additives, such as saline or glucose may be added to make the solutions isotonic. The tosyl salt of the co pound of -Example 2 is preferred for oral administratio and the hydrochloride salt thereof is preferred for ad ministration by injection.

The following examples are illustrative of the processes of the invention. All temperatures are in centigrade.

Example 1

N-Anisylidene-N'-Isopropyl-1, -Diaminopropane

A solution of 25 ml. of N-isopropyl-1,3-diaminopro- pane, 20.5 g. of p_-anisaldehyde and 100 ml. of toluene was refluxed in a flask equipped with a water separator. After 4 hours the solution was cooled and extracted with λvater. After drying over magnesium sulfate, the solu¬ tion was evaporated to dryness to obtain 34.5 g. of N- anisylidene-N'-isopropyl-l,3-diaminopropane. Infrared absorption (film) at 5300 cm. , 2960 cm. , 2830 cm. , 1650 cm. , 830 cm.- . Nuclear magnetic resonance spec- trum (CDC1„) : 8.18 δ (S, 1H) , 7.70 (d, 2H, J=9 Hz),

6.90 (d, 2H, J=9 Hz), 3.73 (S, 3H), 3.66 (m, 2H), 2.75 (m, 3H), 1.87 ( , 2H), 1.05 (d, 6H) , 1.05 (m, 1H ex¬ changes on deuteration).

Example 2

N-[5-( Isopropylamino)Propyl]-N ' -( 2, 6-Dimethylphenyl)Urea

Method A:

A solution of 7.4 g. of 2,6-dimethylphenylisocynate and 50 ml. of dichloromethane was added to 12 g. of N- anisylidene-N'-isopropyl-l,3-diaminopropane dissolved in 100 ml. of dichloromethane. The solution was refluxed one-half hour, then cooled and extracted with water and with saturated sodium carbonate solution. After drying over magnesium sulfate, the dichloromethane was evapora¬ ted to dryness. The residue was dissolved in 100 ml. of

ethanol. Eleven grams of hydroxylamine-p-toluenesul- fonate were added and refluxed one-half hour. The so¬ lution was evaporated to dryness. The residue was tri turated with hot ether, then dissolved in hot ethanol. Precipitate separated on standing. Recrystallization from ethanol afforded N-[3(isorpopylamino)propyl]-N ^! - (2,6-dimethylphenyl)urea, 4-methylphenyl sulfonate, m.p. 152-155° C.

Analysis for: C ₁₅ H ₂₅ N ₃ 0 • C ₇ HgSG ₃ Calculated: C, 60.66; H, 7.64; N, 9.65; S, 7.36 Found: C, 60.61; H, 7.85; N, 9.70; S, 7.07.

IR (KBr) 3380 cm. ^"1 , 3280 cm. ^-1 , 2650-3100 cmT ¹ , 1670 cm. ^-1 , 1550 cm. ^-1 ; NMR (DMS0) 8.18-8.68 δ (m, 2H, ex¬ change with D ₂ 0), 7.78 (S, 1H, exchanges with D ₂ 0), 6.90-7.65 (m, 7H), 6.48 (m, 1H, exchanges with D ₂ 0), 2.60-3.50 (m, 5H), 2.30 (S, 3H) , 2.17 (S, 6H) , 1.55- 2.05 (m, 2H), 1.19 (d, 6H).

Method B:

A solution of 73 g. of 2,6-dimethylphenylisocya- nate and 150 ml. of dichloromethane was added to a stirred, cooled solution of 150 g. of N-isopropyl-1,3- diaminopropane in 400 ml. of dichloromethane. The tem perature was kept between -3 and 3° C. during the addi tion. Stirring was continued at room temperature for an additional 3 hours. The mixture was extracted with water, then with a total of 500 ml. of 20% hydrochlori acid (v/v). The acid solution was made basic with sa¬ turated sodium carbonate solution. The mixture was ex tracted with dichloromethane. The dichloromethane sol tion was dried over magnesium sulfate, then evaporated dryness. The residue was treated with p_-toluenesulfon acid to obtain the salt. Recrystallization from EtOH

afforded N-[ -(isopropylamino) ropyl]-N'-(2,6-dimethyl- phenyl)urea, 4-methylphenyl sulfonate, m.p. 152-154° C. Analysis for: C, ₅ H ₂₅ N ₃ 0 • C-HgSO^ Calculated: C, 60.66; H, 7.64; N, 9.65; S, 7.36 Found: C, 60.53; H, 7.69; N, 9.45; S, 7.53.

Hydrochloride, m.p. 162-164° C. (Recrystallized from EtOH/Et ₂ 0).

Analysis for: C _ιg H ₂₅ N ₃ 0 • HC1

Calculated: C, 60.08; H, 8.74-; N, 14.02; Cl, 11.83 Found: C, 60.02; H, 8.97; N, '14.02; Cl, 11.83.

Phosphate, m.p. 194-196° C. (Recrystallized from EtOH).

Analysis for: C, H ₂₅ N_0 • H ₃ P0 ₄

Calculated: C, 49.85; H, 7.81; N, 11.63

Found: C, 4 _. 9.48; H, 7.89; N, 11.54.

Example 3

N-[3-(n.-Propylamino)Propyl-N'-(2,6-Dimethylphenyl)Urea

A solution of 14.7 g. of 2,6-dimethylphenylisocya- nate and 50 ml. of dichloromethane was added to a stirred, cooled solution of 40 grams of N-n-propyl-l,3-diamino- propane and 350 ml. of dichloromethane. The temperature was kept between -3 and 0° C. during addition. Stirring was continued at room temperature for 45 minutes. The solution was extracted with water, then extracted with a total of 200 ml. of 20% hydrochloric acid (v/v). The acid solution was made basic with saturated sodium car¬ bonate solution. The basic mixture was extracted with dichloromethane. The dichloromethane solution was dried over magnesium sulfate, then evaporated to dryness. The residue was .treated with p_-toluenesulfonic acid to ob- tain the salt. Recrystallization from Et0H/Et ₂ 0 afforded

N-[3-(ιι-propylamino)propyl-N'-(2_,6-dimethylphenyl)urea 4-methylphenylsulfonate, m.p. 157-159° C.

Analysis for: ^C ₁₅ ^H ₂ 5 ^N 3 ^{0 * C} 7 ^H 8 ^S0 3

Calculated: C, 60.66; H, 7.64; N, 9.65; S, 7.36 Found: C, 61.01; H, 7.47; N, 9.77; S, 7.09. ^'

Example 4

N-[3-(Isopropylamino)Propyl3-N'-(2,5-Dimethylphenyl)Ur

A solution of 14.7 grams of 2,5-dimethylphenyliso cyanate and 50 ml. of dichloromethane was added to a stirred, cooled solution of 35 g. N-isop opyl-l,3-di- aminopropane and 400 ml. fo dichloromethane. The tem¬ perature was kept between -5 and 0° C. during addition. Stirring was continued at room temperature for one hou The solution was extracted with water, then with 200 m of 15% hydrochloric acid (v/v). The acid extract was made basic with saturated sodium carbonate solution an extracted with dichloromethane. The dichloromethane so lution was dried over magnesium sulfate, then evaporat to dryness. The residue was dissolved in ether and sa- turated with hydrogen chloride. The solid was separat and recrystallized from EtOH/Et ₂ 0 to obtain N-[3-(iso- propylamino)propyl]-N'-(2,5-dimethylpheny1)urea, hydro¬ chloride, m.p. 152-154° C.

Analysis for: ^C ₁₅ ^H 25 ^N 3° ^{* HC1} Calculated: C, 60.08; H, 8.74; N, 14.02; Cl, 11.83 Found: C, 59.97; H, 8.77; N, 14.03; Cl, 11.74.

Example 5

N-[3-(Isopropylamino)Propyl]-N'- (5-Chloro- -Methylpheny1)Urea

A solution of 16.7 g. of 2-methyl-5-chlorophenylis cyanate and 50 ml. of dichloromethane was added to a stirred, cooled solution of 35 g. of N-isopropyl-1,3-

OM

, Sλ^*.. w WiI

diaminopropane and 250 ml. of dichloromethane. The tem¬ perature was kept at -5 to 0° C. during addition. Stir¬ ring was continued at room temperature for 20 minutes. The precipitated solid was separated by filtration. The filtrate was extracted with water, then with 200 ml. of 15% hydrochloric acid (v/v). The acid extract was made basic with saturated sodium carbonate solution, then extracted with dichloromethane. The dichlorometh¬ ane solution was dried over magnesium sulfate, then eva- porated to dryness. The residue was dissolved in etha¬ nol and saturated with hydrogen chloride. The solution was evaporated to dryness j-n vacuo. The residue was triturated with ether until it solidified. The solid was recrystallized from EtOH/Et ₂ 0 to obtain N-[3-(iso- propylamino)propyl]-N'-(5-chloro-2-methylphenyl)urea hydrochloride, m.p. 180-183° C. Analysis for: C ₁₄ H ₂₂ N ₃ C10 • HC1

Calculated: C, 52.50; H, 7.24; N, 13.12; Cl, 22.14 Found: C, 52.41; H, 7.08; N, 13.32; Cl, 21.98.

Example 6

N-[3-(Isopropylamino)Propyl]-N'- • (5-Bromo-2-Methylphenyl)Urea

A solution of 16.5 grams of 5-bromo-2-methyl ani¬ line and 100 ml. of ethylacetate was added with stir- ring to a solution of 20 grams of phosgene and 300 ml. of ethylacetate kept at 5° C. After the addition was completed, phosgene was bubbled through the mixture while refluxing for one-half hour. The reaction mix¬ ture was purged with nitrogen, then the solvent was removed jln vacuo to obtain 17 grams of 5-bromo-2- me- thylphenylisocyanate. This material was dissolved in 150 ml. of chloroform and added cautiously to a

m K i

solution of 18.2 grams of 3-chloropropylamine hydro¬ chloride, 150 ml. of chloroform, and 20 ml. of tri- ethylamine. The mixture was refluxed for one-half hour, then cooled and shaken with water. The precipi¬ tated solid was separated by filtration. Recrystalli¬ zation from ethylacetate afforded N-[3-(chloropropyl- amino)propyl]-N ^l -(5-bromo-2-methylphenyl)urea, m.p. 145-148° C. Analysis for: C _1:L H ₁₄ BrClN ₂ 0 Calculated: C, 43.23; H, 4.62; N, 9.16 Found: C, 43.06; H, 4.55 N, 9.26.

Fifteen grams of the above material were combined with 250 ml. of chloroform and 50 ml. of isopropylamine then refluxed for 18 hours. The solution was evaporate to dryness jLn vacuo. The residue was dissolved in di¬ chloromethane and shaken with saturated sodium carbonat solution and with water. The dichloromethane solution was extracted with 200 ml. of 20% hydrochloric acid. The acid extract was cooled and made basic with 50% so¬ dium hydroxide solution. The mixture was extracted wit dichloromethane. After drying over magnesium sulfate, the dichloromethane was removed _in vacuό. The residue was dissolved.in ethanol and saturated with hydrogen chloride. The solution was evaporated to dryness in vacuo. The residue was crystallized by trituration wit hot ethylacetate. The solid was recrystallized from ethanol/ether to obtain n-[3-(isopropylamino)propyl]-N' (5-bromo-2-methylphenyl)urea, hydrochloride, m.p. 180-2 C.

Analysis for: C, ₄ H ₂₂ N ₃ BrO • HC1 Calculated: C, 46.10; H, 6.35; N, 11.52 Found: C, 46.11; H, 6.10; N, 11.18.

UR

OM

. Wi

Example 7

N-(2,6-Dimethylphenyl)-N'-[3-(l-Methylethylamino)- Propyl]Urea, 4-Methylbenzenesulfonate

Triethylamine (56 grams, 0.55 mole) was added to a stirred suspension of 65 grams (0.50 mole) of 3-chloro- propylamine hydrochloride and 350 ml. of chloroform. The resulting solution was cooled in an ice bath while 73.6 grams (0.50 mole) of 2,6-dimethylphenylisocyanate was added cautiously in portions. After the addition was completed, the solution was refluxed for 20 minutes. The solution was cooled to 15-20° C. and 148 grams (2.5 moles) of isopropylamine were added. The solution was refluxed for 20 hours. The solvent and excess isopro¬ pylamine were removed j n vacuo. The residue was dis- solved in dichloromethane and extracted with 200 ml. of 15% sodium hydroxide solution. The dichloromethane solution was separated and extracted twice with 250 ml. of water. The dichloromethane portion was then ex¬ tracted with a total of 500 ml. of hydrochloric acid solution (100 ml. cone. HC1 and 400 ml. of water).

The acid extract was cooled and made basic with 50% so¬ dium hydroxide solution. The mixture was extracted with 350 ml. of dichloromethane. The dichloromethane solution was washed with water, then dried over magne- sium sulfate. The solvent was removed in vacuo to ob¬ tain 128 grams of waxy solid. This was dissolved in 200 ml. of ethanol and 95 grams (0.50 mole) of j^-toluene- sulfonic acid monohydrate was added and to ef¬ fect solution. The solvent was evaporated ill vacuo. The residue was redissolved in ethanol and again eva¬ porated to dryness. The solid residue was slurried with cold ethanol and separated by filtration. The solid was recrystallized from ethanol to obtain 144

OiV.PI \ViFO

grams (66.1%) of N-(2,6-dimethylphenyl)-N ^« -[3-(l-meth- ylethylamino)propyl]urea, 4-methylbenzenesul onate, m.p. 152-4° C.

Analysis for: ^C ₁₅ ^H 25- ^N 3° * C _? H ₇ S0 ₃ H (435.57) Calculated: C, 60.66; H, 7.64; N, 9.65; S, 7.36 Found: C, 60.61; H, 7.57; N, 9.69; S, 7.67.

Example 8

The suppression of arrhythmias by the compounds o Formula I can be elicited and demonstrated in the test procedures described below.

In each test, dogs of both sexes are anesthetized by administration of sodium pentobarbital injected I. at a dose of 35 mg/kg. Positive pressure artificial respiration with room air is utilized. Blood pressure is recorded from a femoral artery by means of a pres¬ sure transducer and oscillograph.

A. Suppression of electrical-stimulated ventri¬ cular fibrillations (fibrillatory threshold)

The "fibrillatory threshold" is the voltage at which ventricular fibrillation is produced by an exter¬ nal electrical stimuli delivered to the left ventrical during the repolarization phase of the myocardium. In this test, the anti-arrhythmic activity of a compound is assessed by its ability to increase the fibrillatory threshold in anesthetized dogs.

Ventricular fibrillation is produced in an anes¬ thetized dog by stimulating the left ventricular epicar dium for periods of 5 seconds with pulses of 3 msec, duration at a frequency of 60 Hz. The stimuli are ap- plied through bipolar platinum electrodes, 3.5 mm. apar embedded in plastic plaque measuring 7 x 12 mm. which

is sutured to the epicardium. The train of stimuli is triggered by the R-wave of the electrocardiogram and applied at increasing intensities (voltages) -at 1 min. intervals until fibrillation occurs. The animal ^' is de- fibrillated by a DC countershock and the sequence re¬ sumed after 10 min. Test drug is injected I. V. over a period of 5-10 min. Fibrillation threshold is de¬ termined before and starting at 10 min. after injection of each dose of drug. An increase in threshold of less than +.75 volts is considered inactive; +.75-.99 volts is considered borderline; +1.0-1.24 volts is considered slight; +1.25-1.99 volts is considered moderate; and +2.0 volts or more is considered marked.

When tested by the procedure set forth above, the compounds described in Examples 2, 3, 4, 5, and 6 pro¬ duced a moderate to marked increase in fibrillatory threshold at a dose of 10-20 mg/kg. (In this specifi¬ cation, unless indicated otherwise, the compounds were tested in the acid addition salt form obtained in the preparative example for that compound). No material differences in fibrillatory threshold activity were noted between the tosylate and hydrochloride salts of the compound of Example 2. An increase in the P-R in¬ terval was observed with the compound of Example 5. The mean (+_ standard deviation) increase in fibrilla¬ tory threshold for the compounds of Examples 2-6 at doses of 10 and 20 mg/kg. is given in Table I below. The data for the compound of Example 2 is the combined data for the hydrochloride and tosyl salts thereof.

IJUREAC' . v'

Table I

Increase in Threshold (Volts)

Compound 10 mg/kg. 20 mg/kg.

2 1.9 +_ .4 2.9 + 3 3.4 ■+ .1 4 2.6 +.1.1* 2.5 +_ .5* 5 3.5 ■+ .8 8.8 _+ .5 6 1.7 + .9 6.0 + .7

4 dogs at 10 mg; 2 dogs given additional 10 mg.

B. Suppression of ventricular arrhythmias pro¬ duced by ouabain.

The I. V. injection of ouabain results in ventricu¬ lar arrhythmias. In this test, the anti-arrhythmic activity of a compound is assessed by its ability to restore normal sinus rhythm in ouabain-treated, pento¬ barbital anesthetized dogs. Ouabain is injected I. V. to an anesthetized dog in an initial dose of 50 μg/kg. and then in incremental doses until a ventricular ar¬ rhythmia (multiform ventricular beats or ventricular tachycardia) is produced. A total dose of 55 to 60 μg/kg. is usually sufficient to produce the arrhythmia. The test compound is then injected I. V. over approxi¬ mately 3-5 min., starting 20 min. after the injection of ouabain, and the effect on the arrhythmia is ob- served. Drug injection is terminated.when reversion to sinus rhythm is observed. In untreated dogs, the arrhythmia persists greater than 45 minutes.

^■ f .

When tested as set forth above, the compound of Example 2, as the tosyl salt, restored sinus rhythm in four of four dogs at a dose of 7.5 +_ 1.7 mg/kg., and, as the hydrochloride salt, restored sinus rhythm in seven of eight dogs at 6.8 +_ 1.1 mg/kg. In the remain¬ ing dog in the latter group, improvement of the arrhy¬ thmia was observed, but in view of the absence of a "P" wave in the ECG, a junctional rhythm was assigned. However, this dog received a higher than normal (70 μg/kg.) dose of ouabain.

When tested as described above, compounds of Ex¬ amples 3, 4, 5, and 6 gave the following results:

Table II

No. of Dose Compound Dogs (mg/k .) Results

3 2 7 Restoration of sinus rhythm (2 dogs)

1 7 Improvement of sinus rhythm (1 dog)

4 3 8 Restoration of sinus rhythm

5 2 10 Restoration of sinus rhythm

6 2 6.8 Restoration of sinus rhythm

1 7.5 Junctional rhythm

(improvement)

C. Suppression of ventricular arrhythmias pro¬ duced by coronary ligation.

Ligation of the left anterior descending coronary artery in two stages over a 20 minutes period results in severe ventricular arrhythmias beginning at 5-7 hours and lasting about 48 hours. By the third day, arrhythmias spontaneously subside and normal rhythm is reestablished. The severity of the arrhythmia is greatest within 24 hours following ligation. In this test, the anti-arrhythmic activity of a test compound is assessed by the ability of the compound to restore normal sinus rhythm in the coronary ligated dog. The left anterior descending coronary artery of an anes¬ thetized dog is ligated in two stages at the level of the atrial appendage. The animals recover from anes¬ thesia and the test compound is administered to the conscious dog by I. V. injection or orally (via gas¬ tric tube) at 18 to 24 hours after ligation. The test compound is administered until reversion of si- nus rhythm occurs or until the intended dose is given. When tested by I. V. administration about 24 hours post ligation in the procedure set forth above, the compound of Example 2, either as the tosylate salt or the hydrochloride salt, restored complete sinus rhythm in six of six conscious dogs at a dose of 15-20 mg/kg. In two animals, additional compound was admin¬ istered so that the total dose of >40 mg/kg. Although the animals appeared weaker, no deaths were observed. The compound of Example 3, restored sinus rhythm in two of two dogs at a dose of 10 mg/kg. The compound of Example 4 restored normal sinus rhythm in three of four dogs when administered in 14-15 mg/kg. doses (I. V.). The fourth dog showed no improvement at

OfΛPI

doses up to 20 mg/kg. The compound of Example 5 re¬ stored sinus rhythm in four of four dogs at doses of 8-20 mg/kg. (I. V.). The compound of Example 6 re¬ stored sinus rhythm in two of two dogs when adminis- tered I. V. according to this procedure at doses of 20 mg/kg.

When tested in the procedure set forth above by oral administration about 24 hours post ligation, the compound of Example 2, as the tosylate salt, restored sinus rhythm at a dose of 40-50 mg/kg. in eight of nine dogs. Although transient weakness appeared in several animals, no prolonged or serious side-effects were observed in any of the eight dogs. At a dose of 35 mg/kg. in two of three animals a high degree (85- 100%) of sinus rhythm was restored with no side-effects observed.

Oral administration of the compound of Example 2, as the hydrochloride salt, at a single dose of 50 mg/kg. restored sinus rhythm but the compound produced general weakness and two out of eight dogs died.

Three of three dogs died at a single dose of 75 mg/kg. However, oral administration of the compound of Example 2 as the hydrochloride salt in 2 hourly divided doses totaling 50 mg/kg. restored sinus rhythm with no ad- verse effects. In one dog, transient improvement and brief restoration of sinus rhythm was seen at an ini¬ tial dose of 35 mg/kg. and prolonged restoration of sinus rhythm was seen after an additional dose of 15 mg/kg. In the second dog, and initial dose of 25 mg/kg. produced little improvement, but an additional dose of 25 mg/kg. produced prolonged restoration of sinus rhythm.

When tested in the procedure set forth above by oral administration given about 48 hours post ligation the compound of Example 2, as the tosylate or hydro¬ chloride salt, restored sinus rhythm in four of five dogs at a dose of 15 mg/kg. Significant improvement was observed in one dog at this dose. When adminis¬ tered as either the tosylate or hydrochloride salt at a dose of 25 mg/kg. , the compound of Example 2 restore sinus rhythm in six of seven dogs. Marked improvement was observed in one of the dogs at this dose, and re¬ storation of sinus rhythm was observed in the animal after administration of an additional dose of 15 mg/kg.

When administered orally according to this proce¬ dure in doses of 50 mg/kg. , the compound of Example 4 restored sinus rhythm in one of three dogs and showed no significant effect in the other two dogs.

Oral administration of the compound of Example 5 as the tosyl salt at a dose of 50 mg/kg. produced less than 50% sinus rhythm. The hydrochloride salt adminis- tered orally at the same dose produced sinus rhythm in six of six dogs, and in five of the six dogs this ef¬ fect was prolonged for from four hours to in excess of six and one-half hours. Oral administration of the com pound of Example 5 at a dose of 25 mg/kg. produced si- nus rhythm in two of three dogs and a marked improve¬ ment to predominantly -sinus rhythm in the third dog.

When administered orally at a dose of 50 mg/kg., the compound of Example 6 produced normal sinus rhythm the one dog upon which this procedure was performed. This dosage also caused the dog to wretch.