The 4-amino-6,7-dimethoxy-2-[4-(5-lower alkylthio-1,3,4-oxadiazole-2-carbonyl)-piperazin-1-yl]-quinazolines are potent antihypertensive drugs which have little or no .alpha.-adrenergic blocking activity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to 4-amino-6,7-dimethoxy-2-[4-(5-lower 
alkylthio-1,3,4-oxadiazole-2 carbonyl)-piperazin-1-yl]-quinazolines. 
2. Description of the Prior Art 
U.S. Pat. Nos. 3,511,386; 3,635,979; and 3,663,706 disclose various 
4-amino-6,7-dimethoxy-2-[4-(heterocyclic-2-carbonyl)-piperazin-1-yl] 
quinazolines. One of these compounds, i.e., 
2-[4-(2-furoyl)-piperazin-1-yl]-4-amino-6,7-dimethoxyquinazoline described 
in Example LXXII of these patents is a clinically useful anti-hypertensive 
agent and is marketed as such in many countries of the world under the 
generic name prazosin. It is well established that the antihypertensive 
efficacy of prazosin results from a dual mechanism of action: (i) a direct 
peripheral vasodilation effect on vascular smooth muscle, and (ii) a 
functional peripheral .alpha.-adrenergic receptor blockade, H. Adriaensen, 
The Practitioner, 214, 268 (1975); Mroczek, et al., Current Therapeutic 
Research, 16, 769 (1974); Scriabine, et al., Experientia, 24, 1150 (1968); 
Constantine, et al., "Hypertension: Mechanisms and Management", ed. by 
Onesti, Kim and Moyer; Grune and Stratton, 1973 pp. 429-44; and Zacest, 
Med. J. of Austral. Special Supplement, 1,4 (1975). Although initial 
clinical assessments on prazosin indicated an almost complete absence of 
side effects, recent reports have revealed severe adverse reactions of 
postural hypotension in some patients, Bendall, et al., Brit. Med. J., 727 
(June 28, 1975); Rees, Brit. Med. J., 593 (Sept. 6, 1975); Gabriel, et 
al., The Lancet, 1095 (May 10, 1975 ); and Bloom, et al., Current 
Therapeutic Research, 18, 144 (1975). It is generally felt that this type 
of side effect results from the .alpha.-blockade component of prazosin. 
Indeed, it has been stated by R. Zacest in the Med. J. of Austral., 
Special Supplement, 1, 4 (1975) that "if the alpha adrenergic `blocking` 
activity does prove to be significant with high doses it may lead to 
postural hypotension". 
U.S. Pat. Nos. 3,669,968 and 3,769,286 cover trialkoxyquinazolines, such as 
those having the formula: 
##STR1## 
wherein R may be a number of different groups including furyl and thienyl. 
These patents claim to have certain advantages over the corresponding 
6,7-dialkoxy compounds such as those disclosed in the patents previously 
discussed. Thus, it is stated that such compounds "have a more favorable 
pharmacological profile (e.g., they are non-adrenolytic in dogs) and 
possess greatly improved solubility characteristics (particularly in 
water) as contrasted to the corresponding 6,7-dialkoxy compounds reported 
in the prior art". One of the compounds disclosed in these patents is 
known by the generic name trimazosin and has the formula: 
##STR2## 
Trimazosin is reported to be active in humans as an antihypertensive 
agent, DeGuia, et al., Current Therapeutic Research, 15, 339 (1973); 
Vlachakis, et al., Current Therapeutic Research, 17, 564 (1975). However, 
it is a much weaker drug than prazosin, the respective clinical daily dose 
ranges being approximately 150 to 500 mg. for trimazosin as compared to 
1.5 to 15 mg. for prazosin. Trimazosin is therefore 100-fold weaker than 
prazosin at the lower end of the dosage range. 
U.S. Pat. Nos. 3,517,005; 3,594,480; and 3,812,127 describe certain 
piperazinyl quinazolines having both bronchodilator and antihypertensive 
activity, e.g., a compound having the formula: 
##STR3## 
wherein A and B may each be alkoxy, etc., R.sup.1 may be hydrogen or alkyl 
and R.sup.2 may be hydrogen or a radical such as alkyl, benzoyl, etc. 
U.S. Pat. No. 3,920,636 describes homopiperazino quinazolines as 
antihypertensive agents, e.g., the compound: 
##STR4## 
U.S. Pat. No. 3,780,040 discloses compounds useful as antihypertensive 
agents such as the compound: 
##STR5## 
Netherlands application 72 06,067 (CA, 78, 72180s) describes a process for 
preparing aminoquinazolines, such as prazosin, by treating the 
corresponding o-aminobenzonitrile in the presence of phenyl lithium 
according to the following mechanism: 
##STR6## 
wherein R.sub.2 N may be the group 4-(2-furoyl)-1-piperazinyl. 
SUMMARY OF THE INVENTION 
Compounds having the formula: 
##STR7## 
in which R is (lower)alkyl having from 1 to 6 carbon atoms and 
pharmaceutically acceptable acid addition salts thereof, possess 
antihypertensive potency comparable to prazosin but have little or none of 
the peripheral .alpha.-adrenergic blocking properties shown by prazosin. 
These compounds are potent antihypertensive agents which have little or no 
potential for side effect as reflected by their lack of adrenolytic 
activity. 
The preferred compound of this invention is 
4-amino-6,7-dimethoxy-2-[4-(5-methylthio-1,3,4-oxadiazole-2-carbonyl)-pipe 
razin-1-yl]-quinazoline or the acid salts thereof. 
COMPLETE DISCLOSURE 
The compounds of this invention may be prepared by several different 
methods. The preferred method, which will be exemplified in the examples 
appearing hereinafter, involves the following reaction: 
##STR8## 
wherein R is a (lower)alkyl group of from 1 to 6 carbon atoms and X is a 
carbonyl activating group of the type typically used in amidation 
reactions, e.g., halo, azido, ethoxycarbonyloxy, 1-imidazo, etc. The 
preparation of compounds I and II will be described hereinafter. The 
reaction of compound I with compound II is preferably conducted in an 
inert solvent such as dioxane, chloroform, methylene chloride, glyme and 
the like at room temperature, with heating at reflux briefly to insure 
completion of the reaction. 
A preferred embodiment of this invention is the compound 
##STR9## 
or the hydrochloride salt thereof. 
The process for the preparation of the compounds of this invention is also 
new and novel. The preferred process for preparing compounds having the 
formula 
##STR10## 
wherein R is a (lower)alkyl group comprises acylating a compound having 
the formula 
##STR11## 
with a compound having the formula 
##STR12## 
wherein R is a (lower)alkyl group and X is a carbonyl activating group. In 
a preferred embodiment, the reaction is conducted in the presence of an 
inert solvent such as dioxane, methylene chloride, glyme and the like. 
The most preferred process comprises acylating a compound having the 
formula 
##STR13## 
with a compound having the formula 
##STR14## 
in dioxane to provide a product having the formula 
##STR15## 
A second method which may be employed to prepare the compounds of this 
invention is illustrated by the following equation. 
##STR16## 
wherein R is a (lower)alkyl group. 
Another method for the preparation of the compounds of this invention 
involves the following reaction sequence: 
##STR17## 
wherein R'.sub.2 is a conventional amine protecting group (e.g., a 
t-butoxycarbonyl group) and wherein R is a (lower)alkyl group. The amine 
protecting group may then be removed from compound C by conventional means 
to provide the desired product, compound III. 
Another procedure for the preparation of compounds of this invention is 
illustrated by the following reaction sequence: 
##STR18## 
wherein R" is a group such as F.sub.3 CC(O), CH.sub.3 SO.sub.2, F.sub.3 
CSO.sub.2, aryl SO.sub.2, etc. 
Still another method for the preparation of compounds of this invention is 
illustrated in the following reaction sequence: 
##STR19## 
wherein R is a (lower)alkyl group. 
The following experiments illustrate the preparation of intermediate 
compound II. Experiment A shows the reaction equation for the formation of 
compound II wherein R is methyl and X is Cl. Each individual step in the 
reaction is described. 
##STR20## 
Ethyl 5-methylthio-1,3,4-oxadiazole-2-carboxylate 
A mixture of ethyl-1,3,4-oxadiazole-2-thione-5-carboxylate potassium salt 
dimethylsulfoxide solvate (45.0 g.; 0.122 mole; D. E. Horning et al., Can. 
J. Chem., 50, 3079 (1972)) and methyl iodide (52.0 g., 0.366 mole) in 
absolute ethanol (400 ml.) was stirred at reflux for 45 minutes. The 
cooled reaction mixture was concentrated to a semi-solid. Water (about 600 
ml.) was added, the mixture was filtered and the precipitated solid washed 
with water and dried to yield the title compound (15.6 g., M.P. 
77.degree.-79.degree. C.). An additional 4.08 g., M.P. 
70.degree.-76.degree. C. was obtained from the filtrate and water washings 
to provide a total yield of 19.68 g. (70%). 
Potassium 5-methylthio-1,3,4-oxadiazole-2-carboxylate 
A solution of ethyl 5-methylthio-1,3,4-oxadiazole-2-carboxylate (4.31 g., 
0.023 mole) in absolute ethanol (50 ml.) was treated dropwise with 2.87 g. 
(0.023 mole) of 45 wt.% potassium hydroxide solution. The resultant white 
precipitate was isolated by filtration, washed with ethanol and dried to 
yield 3.92 g. (86%) of the title compound; M.P. 176.degree.-177.degree. C. 
with decomposition after recrystallization from ethanol. 
______________________________________ 
Anal. Calcd for C.sub.4 H.sub.3 N.sub.2 O.sub.3 SK: 
C, 24.23; H, 1.53; N, 14.13. 
Found: C, 24.33; H. 1.66; N, 14.26. 
______________________________________ 
5-methylthio-1,3,4-oxadiazole-2-carbonyl chloride 
A solution of oxalyl chloride (2.57 ml., 0.03 mole) in benzene (15 ml.) was 
added dropwise to a refluxing suspension of potassium 
5-methylthio-1,3,4-oxadiazole-5-carboxylate (3.96 g., 0.02 mole) in 
benzene (50 ml.). After the addition, the mixture was stirred at reflux 
for one hour. Filtration and evaporation left the acid chloride; 
distillation gave 1.86 g. (52%); B.P. 65.degree.-69.degree. C. at 0.05 mm. 
of mercury. 
Experiments B, C and D describe the preparation of compounds having other 
(lower)alkyl groups as the R substituent on compound II. 
EXPERIMENT B 
Ethyl 5-ethylthio-1,3,4-oxadiazole-2-carboxylate 
A mixture of ethyl 1,3,4-oxadiazole-2-thione-5-carboxylate potassium salt 
dimethylsulfoxide solvate (11 g., 0.03 mole) and ethyl iodide (7 g., 0.045 
mole) in absolute ethanol (100 ml.) was heated at reflux for 45 minutes 
and then worked up as described previously in Experiment A to yield the 
title compound (5.59 g.). 
5-Ethylthio-1,3,4-oxadiazole-2-carbonyl chloride 
The title compound was prepared from the above ester analogously to the 
procedure described in Experiment A, B.P. 86.degree. C. at 0.04 mm. of 
mercury. 
EXPERIMENT C 
Ethyl 5-isopropylthio-1,3,4-oxadiazole-2-carboxylate 
The title compound was prepared from ethyl 
1,3,4-oxadiazole-2-thione-5-carboxylate potassium salt dimethylsulfoxide 
solvate (11 g., 0.03 mole) and isopropyl iodide (5.6 g., 0.03 mole) 
analogously to the procedure described in Experiment A. The yield was 4.1 
g. (63%). 
5-Isopropylthio-1,3,4-oxadiazole-2-carbonyl chloride 
The title compound was prepared from the above ester analogously to the 
procedures described under Experiment A. The yield was 2.04 g. (66%). The 
product had a B.P. of 70.degree.-74.degree. C. at 1 mm. of mercury. 
EXPERIMENT D 
Ethyl 5-n-propylthio-1,3,4-oxadiazole-2-carboxylate 
The title compound was prepared from ethyl 
1,3,4-oxadiazole-2-thione-5-carboxylate potassium salt dimethylsulfoxide 
solvate (10 g., 28.5 mmole) and n-propyliodide (4.17 ml., 42.8 mmole) 
analogously to the procedure described in Experiment A. The yield was 4.99 
g. (81%). The product had a B.P. of 108.degree.-118.degree. C. at 0.65 mm. 
of mercury. 
5-n-Propylthio-1,3,4-oxadiazole-2-carbonyl chloride 
The title compound was prepared from the above ester analogously to the 
procedures described under Experiment A. The product had a B.P. of 
75.degree.-84.degree. C. at 0.4 mm. of mercury. 
The following experiment shows the preparation of compound I: 
EXPERIMENT E 
4-amino-6,7-dimethoxy-2-(1-piperazinyl)quinazoline (I) 
Piperazine hydrobromide (168.0 g., 1.006 mole) was added to a suspension of 
4-amino-2-chloro-6,7-dimethoxyquinazoline (241.0 g., 1.006 mole) in 
2-methoxyethanol (3.6 l.) and the mixture was stirred at reflux for 1.25 
hours. The precipitate was separated by filtration, washed with hot 
2-methoxyethanol and dried. The material then was added to a stirred 
solution of sodium hydroxide (81.0 g., 2.01 mole) in water (3 l.) and the 
mixture was heated to 75.degree. C. The mixture then was cooled to 
40.degree. C., filtered, and the insoluble precipitate washed with water 
and dried. The material was triturated under refluxing absolute ethanol 
(6.0 l.) and the mixture was filtered. The filtrate was evaporated to 
dryness to yield the title compound, 180.0 g. (62%), M.P. 
224.degree.-228.degree. C. 
Compound I can exist in two polymorphic forms. In an earlier experiment 
similar to Experiment E with the exception that an excess of piperazine 
hydrobromide was used, a water soluble form (Isomorph A) of Compound I 
having a M.P. of 224.degree.-228.degree. C. was obtained. This product was 
recrystallized from nitromethane to give an analytical sample of Isomorph 
A having a M.P. of 227.degree.-229.degree. C. 
Anal. Calcd for C.sub.14 H.sub.19 N.sub.5 O.sub.2 : C, 58.12; H, 6.62; N, 
24.20. Found: C, 58.23; H, 6.75; N, 24.22. 
A 200 mg. sample of Isomorph A was dissolved in 10 ml. of water at 
20.degree. C. The solution was heated at 60.degree. C. for 3 minutes, then 
cooled to 35.degree. C. and filtered. The precipitate (157 mg.), M.P. 
228.degree.-230.degree. C. would not redissolve in boiling water. This 
product was termed Isomorph B of Compound I. 
Anal. Calcd for C.sub.14 H.sub.19 N.sub.5 O.sub.2 : C, 58.12; H, 6.62; N, 
24.20. Found: C, 57.77; H, 6.54; N, 24.05. 
The infrared spectra of Isomorph A and Isomorph B of Compound I show 
distinct differences. The product obtained from the large scale experiment 
-- i.e., Experiment E, is Isomorph B. 
As previously discussed, compounds of this invention are valuable 
antihypertensive agents, possessing comparable antihypertensive potency to 
prazosin. However, they have little or none of the peripheral 
.alpha.-adrenergic blocking properties shown by prazosin. The compounds 
may be used in the form of the free base or in the form of 
pharmaceutically acceptable acid salts thereof, such as salts of sulfuric 
acid, hydrochloric acid, succinic acid, tartaric acid, benzoic acid, etc. 
The compounds may be administered orally or parenterally with oral 
administration being preferred. Generally, dosages will range from 0.1 to 
10 mg. 3 to 4 times per day per human adult. As is usual in 
antihypertensive therapy, the particular optimum dosage may vary 
considerably depending upon the sensitivity of the patient to the drug and 
the severity of the hypertension.

EXAMPLES 
EXAMPLE 1 
4-Amino-6,7-dimethoxy-2-[4-(5-methylthio-1,3,4-oxadiazole-2-carbonyl)-piper 
azin-1-yl]-quinazoline hydrochloride 
A solution of 5-methylthio-1,3,4-oxadiazole-2-carbonyl chloride (0.601 g., 
3.36 mmole) in dioxane (10 ml.) was added to a solution of 
4-amino-6,7-dimethoxy-2-(1-piperazinyl)quinazoline (0.972 g., 3.36 mmole) 
in dioxane (100 ml.). The resultant mixture was stirred at room 
temperature for 65 hours, then was heated at reflux for 30 minutes. 
Filtration gave the title compound (1.56 g.). Recrystallization from 
methanol gave a product having a M.P. of 280.degree.-285.degree. C. with 
decomposition. 
Anal. Calcd for C.sub.18 H.sub.21 N.sub.7 O.sub.4 S.HCl: C, 46.20; H, 4.74; 
Cl, 7.58; N, 20.96; S, 6.85. Found: C, 46.34; H, 4.89; Cl, 7.59; N, 20.38; 
S, 6.58. 
EXAMPLE 2 
4-Amino-6,7-dimethoxy-2-[4-(5-ethylthio-1,3,4-oxadiazole-2-carbonyl)-pipera 
zin-1-yl]-quinazoline hydrochloride 
The title compound was prepared from 
5-ethylthio-1,3,4-oxadiazole-2-carbonyl chloride (0.79 g., 4.1 mmole) and 
4-amino-6,7-dimethoxy-2-(1-piperazinyl)quinazoline (1.19 g., 4.1 mmole) 
following the procedure described in Example 1. The product had a M.P. of 
246.degree.-248.5.degree. C. 
Anal. Calcd for C.sub.19 H.sub.23 N.sub.7 O.sub.4 S.HCl: C, 47.34; H, 5.02; 
N, 20.34; S, 6.65. Found: C, 47.37; H, 4.76; N, 20.15; S, 6.71. (corrected 
for 4.11% H.sub.2 O). 
EXAMPLE 3 
4-Amino-6,7-dimethoxy-2-[4-(5-isopropylthio-1,3,4-oxadiazole-2-carbonyl)-pi 
perazin-1-yl]-quinazoline hydrochloride 
The title compound was prepared from 
5-isopropylthio-1,3,4-oxadiazole-2-carbonyl chloride (1.54 g., 7.5 mmole) 
and 4-amino-6,7-dimethoxy-2-(1-piperazinyl)quinazoline (2.1 g., 7.5 mmole) 
following the procedure of Example 1. The product had a M.P. of 
260.degree.-263.degree. C. with decomposition. 
Anal. Calcd for C.sub.20 H.sub.25 N.sub.7 O.sub.4 S.HCl: C, 48.43; H, 5.28; 
N, 19.77. Found: C, 48.05; H, 5.20; N, 19.61. 
EXAMPLE 4 
4-Amino-6,7-dimethoxy-2-[4-(5-n-propylthio-1,3,4-oxadiazole-2-carbonyl)-pip 
erazin-1-yl]-quinazoline hydrochloride 
The title compound was prepared from 
5-n-propylthio-1,3,4-oxadiazole-2-carbonyl chloride (1.68 g., 8.16 mmole) 
and 4-amino-6,7-dimethoxy-2-(1-piperazinyl)quinazoline (2.36 g., 8.16 
mmole) following the procedure of Example 1. The product had a M.P. of 
230.degree.-245.degree. C. with decomposition. 
Anal. Calcd for C.sub.20 H.sub.25 N.sub.7 O.sub.4 S.HCl: C, 48.43; H, 5.25; 
N, 19.77. Found: C, 48.11; H, 5.35; N, 19.65. 
EXAMPLE 5 
4-Amino-6,7-dimethoxy-2-[4-(5-n-butylthio-1,3,4-oxadiazole-2-carbonyl)-pipe 
razin-1-yl]-quinazoline hydrochloride 
The title compound was prepared from 
5-n-butylthio-1,3,4-oxadiazole-2-carbonyl chloride and 
4-amino-6,7-dimethoxy-2-(1-piperazinyl)quinazoline following the procedure 
of Example 1. 
To determine the efficacy of the compounds of this invention as 
antihypertensive agents, tests were conducted comparing the product of 
Example 1 to prazosin. The results of these tests are set forth in Table 
1. As shown in Table 1, the product obtained in Example 1, above 
(hereinafter referred to as BL-5111) is of comparable antihypertensive 
potency to prazosin, but has little or none of the peripheral 
.alpha.-adrenergic blocking properties shown by prazosin. The compounds 
described and claimed in this application thus represent a significant and 
unexpected advance in the continuing quest for potent antihypertensive 
drugs which have little or no potential for side effects as reflected by 
their lack of .alpha.-adrenergic blocking activity. 
In Table 1, antihypertensive activity was determined by oral administration 
to spontaneous hypertensive rats, and the in vitro and in vivo 
.alpha.-adrenergic receptor blocking effect was determined by tests 
described following Table 1. In the in vitro test, the inhibition by 
BL-5111 of norepinephrine induced contractions of rat seminal vesicles was 
measured; and in the in vivo test, the inhibition by BL-5111 of 
norepinephrine induced pressor responses in anesthetized dogs was 
measured. The in vivo tests were conducted using intravenous 
administration, each compound being assayed in 4 dogs with 2 dose response 
results in each dog. 
TABLE 1 
__________________________________________________________________________ 
##STR21## 
.alpha.-Adrenergic Receptor 
Antihypertensive Activity 
Blocking Effect 
% Blood 
ED50 In Vitro 
In Vivo 
IV LD.sub.50 
Dose 
Pressure 
mm Hg 
Activity 
Activity 
Activity 
in mice 
Compound 
R mg/kg 
Change 
mg/kg 
Ratio 
Ratio 
Ratio 
mg/kg 
__________________________________________________________________________ 
Prazosin 
##STR22## 
10 3 1 
-42 -29 -14 
2.1 1.0 1.0 1.0 36.1 
BL-5111 
##STR23## 
10 3 1 
-41 -26 -19 
2.3 0.91 0 0.04 45.7 
__________________________________________________________________________ 
ISOLATED RAT SEMINAL VESICLE ASSAY 
Dangan et al, Int. J. Neuropharmacol., 4:219 (1965) have shown that the 
seminal vesicle of the rat is a tissue which is notably responsive to 
compounds which activate .alpha.-receptors but is relatively insensitive 
to compounds which activate .beta.-receptors. Lietch et al, Brit. J. 
Pharmacol., 9:236 (1954), have employed the isolated rat seminal vesicle 
in the comparative assay of .alpha.-receptor blocking drugs and the 
present studies were carried out using a modification of their procedure. 
Male Long Evans rats weighing approximately 300 g. were sacrificed by a 
sharp blow on the head. Seminal vesicles were removed and transfered to a 
shallow dish containing modified Tyrode's solution. The vesicles were 
emptied of their contents by squeezing them gently with a pair of forceps. 
Silk thread (4-0) was attached to both ends of the vesicle and it was 
suspended in a 20 ml. muscle chamber containing modified oxygenated 
Tyrode's solution (g./liter: NaCl 8, KCl 0.2, CaCl.sub.2 0.26, NaHCO.sub.3 
1, Na.sub.2 HPO.sub.4 0.0575, glucose 0.5 and MgCl.sub.2 0.02). The 
bathing fluid was maintained at 37.degree. C. with a thermostatically 
controlled isolated organ tissue bath. Contractions were recorded 
isometrically by means of a force displacement transducer and recordings 
were made with a Beckman RP Dynograph. Norepinephrine (NE) was added to 
the muscle chamber in volumes ranging from 0.1 to 0.4 ml. with a one ml. 
syringe attached to a 3 inch 20 gauge needle. NE and test compounds were 
dissolved in deionized water. 
NE dose response curves were obtained alone and in the presence of test 
compounds. NE was allowed to remain in contact with the strip until a 
maximal contraction was obtained. The strip was then washed with the 
perfusion fluid for 15-30 seconds and the preparation was allowed to 
return to base line before a subsequent dose of NE was given. Increasing 
amounts of NE were injected into the bath in the same manner until a 
complete dose response was obtained. 
The seminal vesicles used to obtain the control NE dose response were 
discarded and new preparations were placed in the tissue bath for 
evaluation of the test compound. The test compound was added directly to 
the perfusion fluid (10 nanograms/ml.) and the strips were allowed to 
remain in contact with the bathing media for at least 10 minutes before 
the NE dose response was determined. 
ED50 values for NE were obtained by regression analysis as described by 
Finney, Probit. Analysis, 2d Ed., Cambridge (1964). A minimum of 4 strips 
and at least 4 doses were employed to calculate the regression lines. The 
ED50 value is defined as the concentration of NE which produces a 
contraction equal to 50% of the maximal contraction. 
The ratio of the .alpha.-adrenergic blocking activity of BL-5111 relative 
to that of prazosin was calculated as follows: 
##EQU1## 
The value obtained for BL-5111 was then expressed as a ratio of the value 
obtained for prazosin. 
##EQU2## 
The results obtained with NE, prazosin and BL-5111 are summarized in Table 
II. 
Table II 
__________________________________________________________________________ 
Effect of Prazosin and BL-5111 on NE Response 
in Isolated Rat Seminal Vesicles 
__________________________________________________________________________ 
NE Activity 
ED50 with 95% Ratio 
No. of 
Conf. Limits 
Percent Change 
Relative to 
Treatment 
Strips 
(.mu.g/ml) 
From Control 
Prazosin 
__________________________________________________________________________ 
Control 32 0.89 (0.84-0.94) 
-- -- 
Prazosin, 
8 6.03 (5.30-6.81) 
578 1.0 
10 nano/ml. 
BL-5111 7 0.93 (0.80-1.08) 
4.5 0.008 
10 nano/ml. 
__________________________________________________________________________ 
These data indicate rather clearly that at a concentration of 10 
nanograms/ml., prazosin caused nearly a six fold decrease in the 
sensitivity of isolated rat seminal vesicles to the stimulant activity of 
NE while BL-5111 was essentially inactive in this respect. It was 
concluded that BL-5111 possesses less than one percent of the 
.alpha.-adrenergic blocking activity of prazosin. 
ANESTHETIZED DOG ASSAY FOR .alpha.-ADRENERGIC BLOCKING AGENTS 
Nash, C. B., Pharmacological Research Communications, 4:423, (1969) and 
Maxwell, R. A., Drill's Pharmacology in Medicine, (1971) p. 683 have shown 
that in anesthetized dogs .alpha.-adrenergic blocking agents antagonize 
the blood pressure elevating effects of intravenous norepinephrine. Thus, 
blood pressure responses to norepinephrine (NE) in anesthetized dogs was 
used as a comparative assay for .alpha.-adrenergic receptor blocking 
properties of drugs. 
Experiments were done on mongrel dogs anesthetized with sodium 
pentobarbital, 30 mg./kg. iv. The left femoral artery was cannulated to 
record aortic blood pressure and a femoral vein was cannulated for 
administration of drugs. All animals underwent a bilateral vagotomy. A 
norepinephrine dose-response curve was obtained by administering 
increasing doses of iv. norepinephrine (0.01 - 1 .mu.g/kg). The test drug 
(prazosin, BL-5111) was then administered iv. at 3 mg/kg. Approximately 30 
minutes later a dose-response curve was again established for iv. 
norepinephrine (0.01-10 .mu.g/kg). The dose of norepinephrine (with 95% 
confidence limits) that increased blood pressure by 50 mm of Hg was 
obtained from dose-response curve analysis before and after prazosin and 
BL-5111. The ratio of the .alpha.-adrenergic blocking activity of BL-5111 
relative to that of prazosin was obtained as follows: 
##EQU3## 
The results obtained with norepinephrine, prazosin and BL-5111 are 
summarized in Table III. The results indicate that BL-5111 was 
approximately 30 times less active than prazosin in causing 
.alpha.-adrenergic blockade at 3 mg/kg iv. 
Table III 
Effect of Prazosin and BL-5111 on the Blood Pressure Response to 
Intravenous Norepinephrine 
Table III 
______________________________________ 
Effect of Prazosin and BL-5111 on the Blood Pressure 
Response to Intravenous Norepinephrine 
______________________________________ 
NE ED50 mm Hg Activity Ratio 
Treatment 
N w/95% Conf. Limits 
Relative to Prazosin 
______________________________________ 
Control 20 0.23 (0.19-0.28) 
-- 
Prazosin, 
4 6.90 (4.80-10.7) 
1.00 
3 mg/kg 
BL-5111 4 0.47(0.40-0.55) 
0.036 
______________________________________