Synthesis and evaluation of 2-[(5-methylbenz-1-ox-4-azin-6- yl)imino]imidazoline, a potent, peripherally acting α2 adrenoceptor agonist

Article abstract of DOI:10.1021/jm960359r

We have synthesized 2-[(5-methylbenz-1-ox-4-azin-6- yl)imino]imidazoline, 3, a potent, peripherally acting α₂ adrenoceptor agonist. The agent is conveniently prepared in five steps from 2-amino-m- cresol. The agent has demonstrated good selectivity for α₂ adrenoceptors in binding and functional studies. When applied topically to eyes, the agent is efficacious for the reduction of intraocular pressure. The agent does not penetrate the blood-brain barrier and, as a consequence, does not lower blood pressure or induce sedation when administered topically or intravenously. We have determined the pK(a) and log P in water versus both octanol and dodecane of 3 and a set of related agents. The best physical parameter to explain its lack of central nervous system penetration appears to be log P measured in octanol versus water.

Full text of DOI:10.1021/jm960359r

J . Med. Chem. 1996, 39, 3533-3538
3533
Syn th esis a n d Eva lu a tion of 2-[(5-Meth ylben z-1-ox-4-a zin -6-yl)im in o]im id a zolin e,
a P oten t, P er ip h er a lly Actin g r Ad r en ocep tor Agon ist†
2
Stephen A. Munk,* Dale Harcourt, Gy o¨ rgy Ambrus, Lydia Denys, Charles Gluchowski, J ames A. Burke,
Alexander B. Kharlamb, Cynthia A. Manlapaz, Edwin U. Padillo, Eileen Runde, Linda Williams,
Larry A. Wheeler, and Michael E. Garst
Allergan Pharmaceuticals, 2525 Dupont Drive, Irvine, California 92612
X
Received May 16, 1996
We have synthesized 2-[(5-methylbenz-1-ox-4-azin-6-yl)imino]imidazoline, 3, a potent, peripher-
ally acting R
2
adrenoceptor agonist. The agent is conveniently prepared in five steps from
adrenoceptors in binding
2
-amino-m-cresol. The agent has demonstrated good selectivity for R
2
and functional studies. When applied topically to eyes, the agent is efficacious for the reduction
of intraocular pressure. The agent does not penetrate the blood-brain barrier and, as a
consequence, does not lower blood pressure or induce sedation when administered topically or
a
intravenously. We have determined the pK and log P in water versus both octanol and
dodecane of 3 and a set of related agents. The best physical parameter to explain its lack of
central nervous system penetration appears to be log P measured in octanol versus water.
In tr od u ction
Agents stimulating R2 adrenoceptors have been dem-
onstrated to mediate a variety of physiologic functions
including reduction of blood pressure, sedation, and
inhibition of fluid secretion.1 We have been interested
in designing novel R2 adrenoceptor agonists to reduce
elevated intraocular pressure (IOP). This is a condition
often associated with glaucoma.3 Reduction of IOP is a
peripherally mediated R2 adrenoceptor process in both
rabbit and human. This class of agents was first used
to reduce IOP in 1966, when Makabe demonstrated that
clonidine (1), a potent R2 adrenoceptor agonist, lowered
IOP in man.4 A major limitation of peripheral applica-
tion of clonidine for the treatment of elevated IOP is
the ability of this agent to cross the blood-brain barrier.
This property leads to centrally mediated side effects
including sedation and reduction in blood pressure upon
topical administration of the agent.5 Polar compounds
including p-aminoclonidine (2) have been introduced as
,2
F igu r e 1.
bonding capacity, log P, and membrane penetration.12,13
Herein, we describe full details of our studies with 2-[(5-
methylbenz-1-ox-4-azin-6-yl)imino]imidazoline (AGN
6
,7
central nervous system (CNS)-limited agents.
One
drawback of p-aminoclonidine is its potency at R1
receptors. That agent proved to be less than 100-fold
selective for R2 versus R1 adrenoceptors under our assay
conditions. An agent possessing enhanced selectivity
for R2 relative to R1 adrenoceptors would minimize R1
adrenoceptor-mediated effects including ocular vaso-
constriction and mydriasis and would have a distinct
1
93080, 3), a potent, selective R2 adrenoceptor agonist
that does not cross the blood-brain barrier. Agent
structures are shown in Figure 1.
Agen t Syn th esis
The synthesis of 6-amino-5-methylbenz-1-ox-4-azin-
3-one (10), the amine intermediate for assembly of 3, is
shown in Scheme 1. Treatment of 2-amino-m-cresol (6)
with chloroacetyl chloride afforded the cyclic amide 7.
This amide provided a convenient protecting group for
the 4-nitrogen during the subsequent nitration reaction
and during installation of the imidazoline subunit. This
material was carefully nitrated in cold sulfuric acid to
obtain the desired 6-nitro isomer 8 as the major product.
Compound 8 and the 8-nitro isomer 9 proved difficult
to separate. We therefore reduced the nitrated products
directly to obtain the mixture of amines which proved
easier to separate. The reduction, accomplished with
hydrogen and palladium, afforded the key intermediate
8
advantage over existing agents in this class. A second
drawback of 2 is the allergy induced upon topical
9
administration. We have recently proposed that the
induced allergic response to 2 is a consequence of its
facile oxidation to an electrophilic p-quinonediimide
followed by addition of thiol nucleophiles.10 This process
1
1
models well-known hapten formation reactions. Oxi-
dative instability is also a potential liability of long term
use for 5. It is a useful compound to assess hydrogen-
†
A preliminary account of these studies has been presented: Munk,
S. A.; Harcourt, D.; Burke, J .; Lai, R.; Roberts, D.; Small, D.;
Gluchowski, C.; Manlapaz, C.; Padillo, E.; Kharlamb, A.; Runde, E.;
Wheeler, L.; Garst, M. Synthesis and Biological Evaluation of AGN
1
93080. A Potent and Selective Ocular Antihypertensive Agent. 209th
1
0 for the assembly of 3. The regiochemistry of the
American Chemical Society National Meeting, Anaheim, CA, April
major product 10 was confirmed by NOE-NMR analy-
sis.
1
995; MEDI 193.
X
Abstract published in Advance ACS Abstracts, August 1, 1996.
S0022-2623(96)00359-7 CCC: $12.00 © 1996 American Chemical Society

3
534 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 18
Munk et al.
Sch em e 1a
Sch em e 3a
a
Reagents and conditions: (i) imidazoline-2-sulfonic acid, tri-
ethylamine, acetonitrile, reflux; (ii) borane-dimethyl sulfide
complex, tetrahydrofuran, reflux.
azoline ring, conformational preorganization of both the
imidazoline ring and the substituents appended to the
aromatic core, and hydrogen bonding, as well as steric
effects on R2A adrenoceptor activity.
a
Reagents and conditions: (i) triethylamine, 4-(dimethylamino)-
pyridine, chloroacetyl chloride, methylene chloride; (ii) concen-
trated nitric acid, concentrated sulfuric acid, -15 °C; (iii) saturated
sodium bicarbonate, ice; (iv) 10% palladium-carbon, H2, methanol-
tetrahydrofuran (1:1).
In Vitr o Eva lu a tion . The agent was evaluated in
a variety of binding assays. The R1 adrenergic mem-
brane preparation was from human brain and has a
mixed population of subtypes. Binding studies were
conducted using R2 adrenergic membrane preparations
from cloned receptors transfected into Chinese hamster
ovary (CHO) cells to determine the subtype selectivity.
The R2A preparation was the human C-10 receptor; the
R2B preparation was the rat RNG receptor; the R2C
Sch em e 2a
a
Reagents and conditions: H2O2, Na2MoO4‚2H2O, NaCl, -10
to -5 °C.
1
9
preparation was the human C-2 receptor.
Preliminary in vitro functional studies were conducted
using tissue baths. The rabbit vas deferens was used
to assess R2 adrenergic activity, and the rabbit aorta
was used to assess R1 adrenergic activity. Prostatic
ends of the vas deferens from albino rabbits were
mounted between platinum electrodes and field stimu-
lated. Cumulative concentration-response curves in
Methods for the synthesis of amidino-2-sulfonic acids,
potential reagents for the construction of guanidines,
1
4,15
have been reported.
The synthesis of imidazoline-
2
-sulfonic acid (13), the primary reagent for the as-
sembly of aminoimidazolines including 3, proved incon-
sistent in our hands initially. We therefore investigated
the reaction to define a reproducible procedure for the
preparation of reagent 13. Internal temperature of the
reaction mixture was found to be the critical variable
after considering a variety of reaction conditions. The
molybdenum-promoted H2O2 oxidation of the thiourea
to imidazoline-2-sulfonic acid proved very exothermic.
The rate of addition of H2O2 determined the internal
temperature. The rate must be sufficiently slow to
prevent the internal reaction temperature from rising
above -4 °C. Careful monitoring of the internal tem-
perature afforded reproducible yields of the reagent. A
detailed procedure for the reaction shown in Scheme 2
is provided below.
0
.25 log units were obtained for each agent. Contractile
responses from aortic rings from albino rabbit were
determined in 0.5 log units. The EC50 was determined
as the concentration that produced a 50% contractile
response relative to the maximum response to nor-
epinephrine.
Agent 3 (AGN 193080) proved to be 400-fold selective
for the R2A adrenoceptor subtype relative to the R1
adrenoceptor in both binding and function assay sys-
tems. Functional evaluation of the agents demonstrated
that 3 was a full agonist in the vas deferens assay and
proved more selective than p-aminoclonidine (90-fold
selective) or clonidine (66-fold selective) for the R2A
receptor versus the R1 receptor. Table 1 summarizes
the results of the in vitro evaluation of 3 (AGN 193080)
and several analogs.
In Vivo Eva lu a tion . A single drop of either cloni-
dine or 3 was applied unilaterally to rabbit eyes and
the IOP was monitored for 6 h postadministration. The
concentration was 0.001% for each agent. The results
of the study are presented in Figure 3. From this study,
both agents proved effective for the reduction of intra-
ocular pressure; however, 3 proved to have enhanced
efficacy compared to clonidine. Agent 3 decreased IOP
25% at the peak (2 h) compared to a peak reduction of
only 10% for clonidine. The duration of action of 3 was
superior to that of clonidine. The IOP had not returned
to the base-line level at 6 h postadministration of 3 in
contrast to clonidine, where a return to base line was
The final assembly of 3 is shown in Scheme 3. The
imidazoline subunit was installed in a single step upon
treatment of the amine with imidazoline-2-sulfonic acid
in acetonitrile and triethylamine. Amide 14 was re-
duced with borane-dimethyl sulfide to afford the agent
for biological evaluation.
P h a r m a cologic Eva lu a tion
Structure-activity studies within this series based on
R2 adrenergic receptor binding affinities have been
communicated previously.1
6-18
The earlier data allowed
us to develop a summary of the key functional features
of the agent that are responsible for agent-R2A adreno-
ceptor binding. The summary is presented in Figure
2
. Those studies revealed the importance of the imid-

2
-[(5-Methylbenz-1-ox-4-azin-6-yl)imino]imidazoline
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 18 3535
2
F igu r e 2. Functional features of agent 3 designed to be a peripherally acting R agonist.
Ta ble 1
binding affinities (Ki, nM)
functional response (EC50, nM)
agent
clonidine
R1
R2A
R2B
R2C
R1
R2
510 ( 110
180 ( 18
470 ( 21
1400 ( 200
8700 ( 320
3.8 ( 0.41
2.9 ( 0.25
1.2 ( 0.19
2.0 ( 0.58
9.6 ( 1.2
8.3 ( 0.21
4.8 ( 1.2
30 ( 2.1
17 ( 1.9
140 ( 7.7
30 ( 2.0
30 ( 7.7
8.9 ( 2.1
27 ( 7.0
120 ( 9.6
290 ( 47
180 ( 9.5
480 ( 75
4700 ( 100
790 ( 100
4.4 ( 0.43
1.9 ( 0.19
1.2 ( 0.10
0.26 ( 0.016
3.5 ( 1.7
p-NH2-clonidine
3
4
5
F igu r e 3. Intraocular pressure upon topical, unilateral administration of a single drop of a 0.001% solution of the agent to
rabbit eye. The untreated (fellow) eye served as the control. The mean values reported are the result of six animals in each group.
observed at 3 h. While the data are not presented,
topical administration of 4 lowered IOP in the rabbit
while 5 had little effect on IOP in that species at
comparable concentrations.
These results are in sharp contrast to those obtained
when either clonidine or 3 was injected directly into the
fourth ventricle of the rabbit brain, Figure 5, panel B.
Clonidine lowered blood pressure 20% relative to control
Figure 4 details the effect that the agents had on
blood pressure in the cynomolgus monkey following
intravenous (peripheral) administration of the agents.
Clonidine showed a dramatic, dose-dependent reduction
in blood pressure upon peripheral administration of the
agent, panel A. This centrally mediated effect observed
upon peripheral administration demonstrated that the
agent crossed the blood-brain barrier. In addition, a
similar dose-dependent decrease in blood pressure was
observed with agent 4, panel B. In sharp contrast, 3
did not demonstrate any appreciable hypotensive activ-
ity upon peripheral administration, panel C. A lack of
hypotensive activity was also observed upon adminis-
tration of agent 5, panel D.
Similarly, clonidine proved to be a potent hypotensive
agent following intravenous administration to rabbit.
Agent 3, in contrast, did not affect blood pressure
following intravenous administration to rabbit. These
results, presented in Figure 5, panel A, suggest that 3
did not cross the blood-brain barrier upon peripheral
administration to rabbit.
(
saline). Agent 3 showed a 70% reduction in blood
pressure compared to control. These results demon-
strated that 3 was very efficacious for the reduction of
blood pressure when administered directly to the site
of action, reflecting the enhanced potency and efficacy
of 3 in functional assays for R2 adrenergic activity
relative to clonidine. These experiments support the
premise that 3 does not cross the blood-brain barrier
in the rabbit.
Sedation is a commonly observed centrally mediated
response to R2 adrenergic agonists. Rat activity after
intravenous administration to the tail vein is a good
model to evaluate that response. Similar results to
those obtained for the peripheral administration result-
ing in centrally mediated processes were obtained using
this model. Clonidine and 4 cross the blood-brain
barrier and sedate the rat. Complete sedation upon
administration of clonidine intravenously to the rat was
observed at a concentration of 100 µg/kg. In contrast,
after treatment with 3 or 5 intravenously at a concen-

3
536 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 18
Munk et al.
F igu r e 4. Mean arterial blood pressure (MABP) versus time upon intravenous administration to cynomolgus monkey. Saline
served as a control. Each agent was evaluated at three concentrations specified in the given panel. Each reported percent change
is the mean result from six animals.
F igu r e 5. MABP versus time upon either intravenous or intracisternal administration of clonidine or agent 3 to rabbit. Saline
served as a control. Each agent was evaluated at the same concentration in the given model. The concentration is specified in the
given panel. Each reported percent change is the mean result of the specified number of separate animals.
Ta ble 2
tration of over 1000 µg/kg, the animals remained active.
log DCoct
pKa(guanidine
These results are not shown.
agent (pH ) 7.4) log Poct log Pdodecane ∆log P
subunit)
3
4
5
-3.4
-0.80
-3.9
0.35
0.90
0.04
-0.34
-3.00
-0.39
0.69
3.90
0.43
11.1
9.4
11.3
P h ysicoch em ica l Eva lu a tion of Agen ts
log P and log DC (the distribution coefficient at a
given pH) are physical properties employed in early
2
0
studies to assess blood-brain barrier penetration.
A
negative log DC does not, however, guaranty minimal
access to the CNS. A summary of the data that we
obtained is shown in Table 2. The measured pKas of
the aniline nitrogens are all well below 5. These
nitrogens are not protonated at physiologic pH, and the
pKas are therefore not reported. Agent 4 has a log DC
of -0.80 at pH 7.4 and proved centrally active in a
variety of animal models. This is one among many
examples of agents possessing a low log DC that does
2
1
penetrate the CNS.

2
-[(5-Methylbenz-1-ox-4-azin-6-yl)imino]imidazoline
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 18 3537
Seiler first applied the concept of ∆log P, the differ-
mol), and NaCl (7.5 g; to depress freezing point of the water)
in water (150 mL; deionized) was prepared and chilled to -10
to -5 °C internal temperature (bath temperature -20 to -15
ence of the log Ps determined in water versus octanol
and water versus a hydrocarbon, as an improved
parameter to explain CNS penetration.22 Agents pos-
sessing a large ∆log P should not penetrate the blood-
brain barrier. Later, in a series of elegant studies, a
group originally at Smith Kline used ∆log P in the
°
C). H
2 2
O (30% in water; 250 mL, 2.45 mol; density ) 1.110;
Aldrich, personal communication) was added to this mechani-
cally mixed slurry in a Morton flask. The first 125 mL was
added at a rate of 0.23 mL/min via syringe pump. This rate
insured that the internal temperature did not rise above -4
°C as the reaction is extremely exothermic. The second 125
mL was added via addition funnel at a rate of 10 drops/min
overnight and did not cause an exotherm (note the first 0.972
mol of peroxide should be sufficient to complete the oxidation).
The reaction was warmed to 0-5 °C to melt ice that had
formed overnight. The white solid was collected via vacuum
filtration, washed with chilled deionized water, and dried
1
2
design of peripherally acting histamine antagonists.
We evaluated this parameter to explain the lack of CNS
activity observed with 3. Dodecane was used as the
hydrocarbon to minimize loss of the solvent through
evaporation during the titration studies. Agent 4, which
penetrated the blood-brain barrier, had a very large
log P in contrast to either 3 or 5. Those data suggest
that ∆log P cannot explain the lack of CNS activity for
1
∆
under vacuum to afford 20.4 g (48%) of 13: H NMR (DMSO)
3
.88 (s, 4H), 10.15 (br s, 1H); 13C NMR (DMSO) 45.0, 169.3;
mp 133-135 °C. Anal. (C
-Meth ylben zox-4-a zin -3-on e (7). To 2-amino-m-cresol
6; 14.7 g, 120 mmol), triethylamine (35.0 mL, 251 mmol) and
-(dimethylamino)pyridine (0.29 g, 2.39 mmol) in anhydrous
CH Cl (100 mL) at 0 °C was added chloroacetyl chloride (10.0
3 6 2 3
H N O S) C, H, N.
3
.
5
The most meaningful correlation to lack of CNS
penetration appears to be the log P in our series. Agent
is basic and has a negative log DC at pH ) 7.4 but a
(
4
4
2
2
log P ) 0.9. This agent had the most negative log P in
dodecane of any agent examined within our series
suggesting that it should not penetrate the CNS. This
agent penetrates the blood-brain barrier upon periph-
eral administration, which was surprising. Agents 3
and 5 are extremely basic, having pKas around 11.
Basicity alone does not appear to control peripheral
membrane penetration. Agent 3, which had a log Poct
of 0.35, was able to penetrate peripheral membranes
as shown by its efficacy for the reduction of IOP. That
agent did not, however, penetrate the blood-brain
barrier upon peripheral administration. Agent 5, which
had a log Poct close to zero, did not penetrate any
biological membranes well as shown by its poor ability
to lower IOP or elicit any other biological response in
vivo at doses comparable to those employed for the
evaluation of the other agents.
mL, 0126 mmol) dropwise via syringe. After the addition was
complete, the resulting solution was warmed at reflux for 24
h. The organic material was washed successively with phos-
phoric acid (0.5 M), saturated sodium bicarbonate, water, and
brine and then dried (MgSO
concentrated, and the solid was dissolved in THF to which
Et O was then added. The resulting crystals were collected
by filtration to afford pure 7 (12.3 g) in 63% yield: H NMR
(CDCl ) 2.27 (s, 3H), 4.59 (s, 2H), 6.80-6.92 (m, 3H), 8.05 (br
s, 1H); 13C NMR (CDCl
) 16.3, 67.1, 114.6, 123.5, 124.2, 124.3,
4
). The organic solution was
2
1
3
3
1
24.8, 143.9, 165.9.
Nitr a tion of 5-Meth ylben zox-4-a zin -3-on e (8 a n d 9). To
(14.64 g, 89.7 mmol) dissolved in concentrated H SO (65
(8.08 g,
89.7 mmol) in concentrated H SO (25 mL) with rapid me-
7
2
4
mL) at -10 °C was added 70% concentrated HNO
3
2
4
chanical stirring at a rate such that the internal temperature
was maintained below -5 °C. As soon as the addition was
complete, the mixture was poured onto crushed ice (500 mL),
and the resulting solids were collected by filtration and then
slurried in cold water (300 mL). Sufficient NaOH was added
to adjust the pH to 7. The resulting yellow powder was
collected by filtration. The solid was then dissolved in THF,
adhered to silica gel, and purified by flash chromatography
with 60% hexane in ethyl acetate to afford the nitrated product
as a mixture of two regioisomers: the desired 6-substituted
aromatic 8 (55%) and the 8-substituted byproduct 9 (22%).
These isomers could be separated with difficulty at this point.
It proved operationally easier to carry the mixture directly to
the next step: MS calcd for C H N O ) 208, m/ z obsd at 208
Con clu sion s
We have prepared 3 (AGN 193080) using a convenient
five-step process. The agent is a potent, selective
agonist at the R2 adrenergic receptor. The agent is
among the most efficacious R2 adrenergic agonists for
the reduction of intraocular pressure that we have
evaluated. The agent does not cross the blood-brain
barrier and, as a consequence, is not sedating, nor does
it affect blood pressure upon peripheral administration.
This agent will have utility for applications requiring
peripheral R2 adrenergic agonist activity.
9
8
2
4
+
(M ).
-Am in o-5-m eth ylben zox-4-a zin -3-on e (10). To a mix-
6
ture of 8 and 9 (2.41 g, 11.6 mmol) dissolved in a solution of
MeOH (300 mL) and THF (300 mL) under argon was added
1
0% palladium on carbon (1.20 g). The resulting mixture was
stirred under an atmosphere of H for 16 h. The catalyst was
removed by filtration, and the resulting solution was concen-
2
Exp er im en ta l Section
Gen er a l. Reagents used were the highest quality available
commercially. Reaction solvents were obtained from Aldrich
in Sure-Seal bottles. Unless otherwise noted, all reactions
were carried out under an argon atmosphere and temperatures
refer to the temperature of the bath. Organic extracts were
trated in vacuo and subjected to flash chromatography on silica
gel with 50% hexane/ethyl acetate to afford pure 10 (0.96 g)
1
in 46% yield along with a mixture of 10 and 11 (0.33 g):
H
NMR (DMSO) 1.95 (s, 3H), 4.31 (s, 2H), 4.57 (s, 2H), 6.24 (d,
1
3
J ) 8.5 Hz, 1H), 6.54 (d, J ) 8.5 Hz, 1H), 10.01 (s, 1H);
C
dried with magnesium sulfate (MgSO
CO ). Flash chromatography was conducted using the
procedure described by Still.
4
) or potassium carbonate
NMR (DMSO) 10.8, 67.0, 108.6, 109.0, 113.6, 126.1, 135.6,
142.2, 166.4.
(K
2
3
2
3
Proton and carbon NMR
2-[(5-Met h yl-3-oxob en z-1-ox-4-a zin -6-yl)im in o]im id -
a zolin e (14). A mixture of 10 (1.20 g, 6.74 mmol), imidazo-
line-2-sulfonic acid (13; 2.02 g, 13.5 mmol), and triethylamine
(2.35 mL, 16.9 mmol) was heated at reflux in anhydrous
acetonitrile (50 mL) under argon for 48 h. At that time,
additional amounts of imidazoline-2-sulfonic acid (1.01 g, 6.74
mmol) and triethylamine (1.41 mL, 10.1 mmol) were added,
and the resulting mixture was stirred an additional 24 h. This
solution was concentrated in vacuo, and the residue was
spectra were measured on either a Varian Gemini 300 or a
Varian Unity Plus 500 spectrometer in the solvents specified.
Chemical shifts are reported in ppm downfield from TMS as
an internal standard, and coupling constants are reported in
Hertz. Mass spectra (LRMS and HRMS) were recorded on a
VG 7070E Sector magnetic 70 eV mass spectrometer. Com-
bustion analyses were conducted by Robertson Microlit Labo-
ratories, Madison, NJ .
Im id a zolin e-2-su lfon ic Acid (13). A slurry of imidazo-
dissolved in a solution of 25% i-PrOH/CHCl
sively with NaOH (1 N) and brine, dried (MgSO
3
, washed succes-
), and
line-2-thione (33.2 g, 0.324 mol), Na
2
MoO
4
‚2H
2
O (2.50 g, 0.0103
4

3
538 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 18
Munk et al.
concentrated in vacuo. The resulting foam was purified by
flash chromatography with 20% MeOH (saturated with NH
in chloroform to give pure 14 (0.42 g) as a foam in 25% yield
(5) Hodapp, E.; Kolker, A. E.; Kass, M. A.; Goldberg, I.; Becker, B.;
Gordon, M. The Effect of Topical Clonidine on Intraocular
Pressure. Arch. Ophthalmol. 1981, 99, 1208-1211.
3
)
(6) Rouot, B.; LeClerc, G. Synthese et reactivite de la p-aminocloni-
dine. Bull. Soc. Chim. Fr. 1979, II-520-II-528.
along with 55% recovered starting material. The HCl salt was
2
recrystallized from EtOH/Et O to afford fine white needles:
(
7) Coleman, A. L.; Robin, A. L.; Pollack, I. P. Apraclonidine
Hydrochloride. Ophthalm. Clinics N. Am. 1989, 2, 97-108.
1
H NMR (DMSO) 2.10 (s, 3H), 3.59 (s, 4H), 4.53 (s, 2H), 6.83
(
1
6
d, J ) 8.6 Hz, 1H), 6.90 (d, J ) 8.6 Hz, 1H), 8.07 (br s, 2H),
(8) Innemee, H. C.; de J onge, A.; van Meel, J . C. A.; Timmermans,
0.15 (vbr s, 1H), 10.42 (s, 1H); 13C NMR (DMSO) 11.8, 42.6,
6.6, 111.3, 121.7, 122.7, 126.8, 128.5, 143.4, 158.9, 165.3.
P. B. M. W. M.; van Zwieten, P. A. The Effect of Selective R
and R -Adrenoceptor Stimulation on Intraocular Pressure in the
Conscious Rabbit. Naunyn-Schmiedeberg’s Arch. Pharmacol.
981, 316, 294-298.
9) Butler, P.; Mannschreck, M.; Lin, S.; Hwang, I.; Alvarado, J .
Clinical Experience with the Long-Term Use of 1% Apracloni-
dine” Arch. Ophthalmol. 1995, 113, 293-296.
(10) Munk, S. A.; Wiese, A.; Thompson, C. D.; Macdonald, T.
Oxidation Potential And Allergic Response Of R Agonists. Assoc.
1
-
2
2
-[(5-Met h ylb en z-1-ox-4-a zin -6-yl)im in o]im id a zolin e
1
(
AGN 193080, 3). To a slurry of 14, the free base (0.41 g,
(
1
2
.68 mmol), in anhydrous THF (200 mL) under argon in a
-neck round-bottom flask equipped with a reflux condenser
“
was added borane-dimethyl sulfide complex (3.76 mL, 7.57
mmol). The mixture was warmed at reflux until starting
material was no longer observed via TLC (24 h). The reaction
mixture was cooled to room temperature, and the reaction was
carefully quenched by the dropwise addition of methanol. The
resulting mixture was then warmed at reflux for an additional
2
Res. Vision Ophthalmol. Annual Meeting, Ft. Lauderdale, FL,
Apr. 21-26, 1996; Abstract No. 3839. Full details of that study
have been submitted for publication.
(
11) Sanner, M. A.; Higgins, T. J . Chemical Basis for Immune
Mediated Idiosyncratic Drug Hypersensitivty. In Annual Reports
in Medicinal Chemistry; Bristol, J ., Ed.; Acadamic Press: San
Diego, 1991; Vol. 26, pp 181-190.
(12) For an early study by the Smith Kline group, see: Young, R.
C.; Mitchell, R. C.; Brown, T. H.; Ganellin, C. R.; Griffiths, R.;
J ones, M.; Rana, K. K.; Saunders, D.; Smith, I. R.; Sore, N. E.;
Wilks, T. J . Development of a New Physicochemical Model for
Brain Penetration and its Application to the Design of Centrally
5
min. The crude reaction mixture was concentrated in vacuo
and purified by flash chromatography using 30% methanol
saturated with NH
) in chloroform to give pure 3 (0.31 g) as
a hydrochloride salt in 68% yield. The HCl salt was derived
from acid present in the CHCl . The compound proved to be
a hard foam: H NMR (DMSO) 1.91 (s, 3H), 3.34 (m, 2H), 3.57
(
3
3
1
(
s, 4H), 4.07 (m, 2H), 5.51 (s, 1H), 6.37 (d, J ) 8.4 Hz, 1H),
Acting H
2
Receptor Histamine Antagonists. J . Med. Chem. 1988,
6
1
1
.58 (d, J ) 8.4 Hz, 1H), 8.30 (vbr s, 3H); 13C NMR (DMSO)
3
1, 656-671.
1.5, 40.2, 42.5, 63.9, 113.9, 114.8, 119.8, 126.6, 133.4, 142.4,
(
13) van de Waterbeemd, H.; Kansy, M. Hydrogen-Bonding Capacity
-1
58.9; IR (KBr) 1485, 1601, 1656, 2700-3600 cm ; mass calcd
O ) 232.1324, obsd ) 232.1311. Anal. (C12
O) C, H, N.
Deter m in a tion of p K
Sirius PCA-101 automatic titrator with expert system software
was used to determine the pK , log DC, and log P values of
and Brain Penetration. Chimia 1992, 46, 299-303.
for C12
ClN
H
16
N
4
H
17
-
(14) Maryanoff, C. A.; Stanzione, R. C.; Plampin, J . N.; Mills, J . E. A
Convenient Synthesis of Guanidines from Thioureas. J . Org.
Chem. 1986, 51, 1882-1884.
4
a
, log DC, a n d log P Va lu es. A
(
15) Gluchowski, C.; Wong, H. N.; Garst, M. E. A New Synthesis of
-Amino-2-Imidazoline Derivatives. 199th American Chemical
2
a
Society Meeting, Boston, MA, 1990; ORGN 16.
2
4
the agents from potentiometric titration data. In a typical
experiment, the instrument automatically added 0.15 M KCl
in water to a weighed sample and then added an accurately
measured amount of acid to dissolve the agent and reach a
predetermined starting pH. After the agent had dissolved, the
(
16) Munk, S. A.; Harcourt, D.; Arasasingham, P.; Gluchowski, C.;
Wong, H.; Burke, J .; Kharlamb, A.; Manlapaz, C.; Padillo, E.;
Williams, L.; Wheeler, L.; Garst, M. Analogs of UK 14,304:
2
Structural Features Responsible for R Adrenoceptor Activity.
BioMed. Chem. Lett. 1995, 5, 1745-1750.
(
17) Munk, S. A.; Gluchowski, C.; Dolby, L.; Wong, H.; Burke, J .;
solution was titrated to the predetermined final pH. The pK
a
Kharlamb, A.; Manlapaz, C.; Padillo, E.; Rodgers, D.; Ohta, B.;
values were calculated using the system software. The log P
value of the agent was determined by adding either octanol
or dodecane to the sample before titration. The log P values
was derived from the known relationship between the aqueous
2
Wheeler, L.; Garst, M. Analogs of UK 14,304 as R -Adrenoceptor
Agonists. Twist and Agent Polarity as Design Elements. BioMed.
Chem. Lett. 1994, 4, 459-462.
(18) Gluchowski, C. G. U.S. Patent 5 091 528, 1992; Chem. Abstr.
1993, 118, 234070.
pK
a a
and the pK determined in the presence of the partition
(
19) Bylund, D. B.; Blaxall, H. S.; Iverson, L. J .; Caron, M. G.;
solvent.
Lefkowitz, R. J .; Lomasney, J . W. Pharmacological Character-
2
istics of R -Adrenergic Receptors: Comparison of Pharmacologi-
Ack n ow led gm en t. We thank Professor J ohn G.
Topliss (Department of Medicinal Chemistry, The Uni-
versity of Michigan) for stimulating discussions regard-
ing these studies.
cally Defined Subtypes with Subtypes Identified by Molecular
Cloning. Mol. Pharmacol. 1992, 42, 1-5.
(20) See Hansch, C.; Leo, A. Exploring QSAR. Fundamentals and
Applications in Chemistry and Biology; American Chemical
Society: Washington, DC, 1995; and references cited therein.
(
21) Timmermans, P. B. M. W. M.; Brands, A.; van Zwieten, P. A.
Lipophilicity and Brain Disposition of Clonidine and Structurally
Related Imidazolidines. Naunyn-Schmeideberg’s Arch. Pharma-
col. 1977, 300, 217-226.
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1) Maze, M.; Tranquilli, W. Alpha-2 Adrenoceptor Agonists: Defin-
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81-605.
(
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(
2
3) Chacko, D. M.; Camras, C. B. The Potential of R -Adrenergic
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(
4) Makabe, R. Ophthalmologische Untersuchungen mit Dichloro-
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J M960359R