Synthesis and selective coronary vasodilatory activity of 3,4-dihydro- 2,2-bis(methoxymethyl)-2H-1-benzopyran-3-ol derivatives: Novel potassium channel openers

Article abstract of DOI:10.1021/jm960270l

A variety of compounds having a benzopyran such as levcromakalim generally exhibit potent antihypertensive activity. During extensive investigations aimed toward identifying K⁺ channel openers having selective coronary vasodilation without pote

Full text of DOI:10.1021/jm960270l

J . Med. Chem. 1996, 39, 3797-3805
3797
Syn th esis a n d Selective Cor on a r y Va sod ila tor y Activity of
3,4-Dih yd r o-2,2-bis(m eth oxym eth yl)-2H-1-ben zop yr a n -3-ol Der iva tives: Novel
P ota ssiu m Ch a n n el Op en er s
Hidetsura Cho,* Susumu Katoh, Shinsuke Sayama, Kengo Murakami, Hiroyuki Nakanishi, Yasuyuki Kajimoto,
Hiroshi Ueno, Hisashi Kawasaki, Kazuo Aisaka, and Itsuo Uchida*
J apan Tobacco Inc., Central Pharmaceutical Research Institute, 1-1, Murasaki-cho, Takatsuki, Osaka 569, J apan
Received April 8, 1996X
A variety of compounds having a benzopyran such as levcromakalim generally exhibit potent
antihypertensive activity. During extensive investigations aimed toward identifying K+ channel
openers having selective coronary vasodilation without potent hypotensive and tachycardiac
effects, we synthesized a series of 3,4-dihydro-2H-1-benzopyran-3-ol derivatives modified at
positions 2, 4, and 6 in the benzopyran ring. Initially, compounds having two methoxymethyl
groups at position 2 were found to show a selective effect on coronary blood flow (CoBF) relative
to mean arterial pressure (MAP) in anesthetized dogs. To find more potent vasodilators, various
benzopyran derivatives modified at position 4 were synthesized and structure-activity
relationships were examined by evaluation of the extent and duration of the increase in CoBF
in anesthetized dogs. As a result, compounds having a (1,6-dihydro-6-oxopyridazin-3-yl)amino
group at position 4, in addition to the two methoxymethyl groups at position 2, were found to
be more potent and to have an improved duration of action. Among these compounds, J TV-
506, (-)-(3S,4R)-6-cyano-3,4-dihydro-4-[(1,6-dihydro-1-methyl-6-oxopyridazin-3-yl)amino]-2,2-
bis(methoxymethyl)-2H-1-benzopyran-3-ol, exhibited good selectivity for its effect. Adminis-
tration of this compound (0.03 mg/kg, po) elicited an increase of CoBF without a change of
systemic blood pressure and heart rate (HR) in conscious dogs. Further evaluation was
performed with respect to (i) the selectivity of its action on the coronary artery versus the
aorta and (ii) its effects on MAP, HR, and electrocardiographic ST elevation. As a result, J TV-
506 was selected as a potent and selective coronary vasodilator with various pharmacological
features favoring clinical development.
In tr od u ction
discovery of more potent coronary vasodilators lacking
hypotensive and tachycardiac activity. We therefore
synthesized a series of 3,4-dihydro-2H-1-benzopyran-3-
ol derivatives with modified substituents at positions
2, 4, and 6 and investigated the structure-activity
relationships of these compounds by evaluation of their
effects on coronary arterial blood flow (CoBF) and the
mean arterial pressure (MAP) in anesthetized dogs. In
addition, an extensive pharmacological evaluation was
performed on compound 3, which was selected for
development.
Since the discovery of cromakalim, a potent antihy-
pertensive agent, a variety of related compounds pos-
sessing a benzopyran skeleton have been reported as
K+ channel openers.1 Among them the well-known
compounds include levcromakalim (the active enanti-
omer of cromakalim), bimakalim,2 and Y-27152 (Figure
1).3 These benzopyrans exert a hypotensive effect by
relaxing peripheral vascular smooth muscle via opening
the ATP-sensitive K+ channels in the cell membrane.
When peripheral vasodilators are used to treat ischemic
heart disease, the dosage is limited by hemodynamic
changes such as hypotension and tachycardia. In
clinical studies, cromakalim was found to decrease the
blood pressure, but it also caused reflex tachycardia.4
The contribution of KATP channels to the regulation of
blood pressure, coronary circulation, and myocardial
contraction is unclear. It was recently reported that the
myoprotective effect of K+ channel openers (e.g., BMS-
180448) on the ischemic heart was unrelated to the
antihypertensive effect.5 On the other hand, we hy-
pothesized that it might be possible to find KATP channel
openers selective for coronary vascular smooth muscle.
Therefore, we investigated coronary-selective K+ chan-
nel openers with minimal hypotensive effects for use as
anti-ischemic agents.
Ch em istr y
(A) Gen er a l Syn th etic Meth od s. Syn th esis of
Key In ter m ed ia tes 8 a n d 9 of th e 3,4-Dih yd r o-2H-
1-ben zop yr a n -3-ol Der iva tives. The key optically
pure intermediate 8 was synthesized according to
Scheme 1. Thus, cyclization of 5-cyano-2-hydroxyac-
etophenone7 with 1,3-dimethoxypropan-2-one8 in pyr-
rolidine-AcOH followed by reduction with NaBH4, de-
hydration with p-TsOH, and chiral epoxidation with
J acobsen’s reagent [(S,S)-Mn(III)-salen complex]9 and
NaOCl in the presence of pyridine N-oxide or 4-phe-
nylpyridine N-oxide afforded epoxide 8 in good yield and
having an ee of 95%. The optical purity of 8 was
determined by high-performance liquid chromatography
(HPLC), with the racemate being prepared by epoxida-
tion of compound 7 with m-chloroperbenzoic acid.
Treatment of compound 8 with an aqueous solution of
NH3 in ethanol gave amino alcohol 9. Similarly, the
synthesis of compounds substituted with a halogen atom
and a nitro group at position 6 was carried out using
During previous investigations, we found a potent
coronary vasodilator (compound 1, Figure 1) which had
a slow onset of antihypertensive effect.6 In the present
study, our investigations were directed toward the
X Abstract published in Advance ACS Abstracts, August 15, 1996.
S0022-2623(96)00270-1 CCC: $12.00 © 1996 American Chemical Society

3798 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19
Cho et al.
F igu r e 1. Representative K+ channel openers and typical compounds 1-4.
Sch em e 1a
a
Reagents: (a) MeOCH2COCH2OMe/pyrrolidine-AcOH/toluene/reflux/1 h; (b) NaBH4/MeOH/0 °C/1.5 h; (c) p-TsOH/toluene/reflux/1 h;
(d) NaOCl/CH2Cl2/pyridine N-oxide/0 °C/7 h; (e) aq NH3/EtOH/rt/1 day; (f) method i, primary amine/NaH, 60 °C, 2 h, or t-BuOK, 0-5 °C,
1 h/anhyd DMF, method ii, heterocyclic secondary amine/NaH, 50 °C, or K2CO3, 80 °C, 2.5 h/DMF, method iii, phenol, or thiophenol/
pyridine/EtOH/reflux/8.5 h, or Na2CO3/DMF; (g) method iv, imidate/MeOH/50-70 °C/1 day, method v, thiourea/WSC-HCl/DMF/rt/6 h,
method vi, isocyanate/EtOH/80-90 °C/18 h, method vii, acyl chloride/Et3N/CH2Cl2/rt/18 h.
5-bromo-2-hydroxyacetophenone and 5-nitro-2-hydroxy-
acetophenone as the respective starting materials in-
stead of 5-cyano-2-hydroxyacetophenone.7
quired to construct the spiro-benzopyran skeleton;
namely, 2,2-bis(tert-butoxymethyl)-6-cyano-2H-1-ben-
zopyran was successively treated with trifluoroacetic
acid and chloromethyl methyl ether in diisopropylamine
to yield the corresponding spiro-benzopyran, which was
converted via three steps to compound 14 (Experimental
Section). In an attempt to investigate the stereochem-
istry at position 2 of compounds 10, 12, and 13,
stereoisomers of each compound were isolated, but the
stereochemistry could not be determined.11
Mod ifica tion s a t P osition 2 of th e Ben zop yr a n
Sk eleton . Employing essentially the same process
shown in Scheme 1, compounds 10-13 were synthesized
via five steps using 2H-benzopyran-4-ones derived from
5-cyano-2-hydroxyacetophenone and the following com-
mercially available ketones: 1-methoxypropan-2-one,
1,3-diethoxypropan-2-one, 1-phenoxypropan-2-one, 1,1-
dimethoxypropan-2-one, pentan-2-one, and cyclohex-
anone instead of 1,3-dimethoxypropan-2-one, respec-
tively10 (Table 1 and Supporting Information). In the
case of compound 14, additional procedures were re-
Mod ifica tion s a t P osition 4 of th e Ben zop yr a n
Sk eleton . Compounds having modifications at position
4 of the benzopyran skeleton were prepared by a variety
of methods.

Novel Potassium Channel Openers
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19 3799
Ta ble 1. Extent and Duration of the Increase of Coronary
Blood Flow in Anesthesized Dogsa
T1/2
ED50 (min)
no.
R2
R3
W
X
Y
1
2
Me
CH2OMe
Me
CH2OMe CN N-CN 3-pyridyl 14
Me CN N-CN 3-pyridyl 17
CH2OEt CN N-CN 3-pyridyl >30
CN N-CN 3-pyridyl 1.3
4.8
2.8
2.4
10 CH2OMe
11 CH2OEt
12 CH2OC6H5 Me
13 CH2CH2Me Me
CN N-CN 3-pyridyl >30
CN N-CN 3-pyridyl 20
CN N-CN 3-pyridyl >30
1.0
14
CH2OCH2OCH2
42 CH2OMe
43 CH2OMe
44 CH2OMe
45 CH2OMe
46 CH2OMe
49 CH2OMe
50 CH2OMe
CH2OMe CN N-CN Me
CH2OMe CN N-CN C6H5
6.0
5.4
1.9
0.8
CH2OMe CN N-CN NHC6H5 >30
CH2OMe CN
CH2OMe CN
CH2OMe Br
O
O
NHC6H5 >30
3-pyridyl 14
0.6
1.0
1.0
N-CN 3-pyridyl 20
CH2OMe NO2 N-CN 3-pyridyl 4.4
F igu r e 2. Compounds having modifications at position 4 of
the benzopyran skeleton.
The racemate was prepared by nucleophilic addition of
3-amino-1-methyl-1,6-dihydropyridazin-6-one to the ra-
cemic epoxide.12 Compound 16 was synthesized by
successive chemical transformations via compounds 8,
15, and 17 (Figure 2 and Experimental Section).
T1/2
Treatment of compound 3 with Lawesson’s reagent
furnished thiocarbonyl derivative 18. Since the coro-
nary vasodilatory activity of compound 3 was very
potent, modifications on the nitrogen atom (N-1) of this
compound were carried out (Table 1). Treatment of 1613
with alkyl halides, allyl halides, or benzyl halides in the
presence of potassium carbonate in DMF yielded a
series of compounds (20-36), and the Michael addition
reaction of 16 with methyl acrylate provided compound
25.
no.
W
X
Y
Z
ED50
(min)
3
16
18
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
40
47
48
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
Br
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
O
Me
H
Me
Et
i-Pr
Bz
O
O
S
0.58
6.2
24
0.57
1.3
28
3.2
2.6
0.6
5.2
5.5
1.0
1.5
2.9
2.3
1.5
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
CH2COOMe
CH2CHdCH2
CH2CH2COOMe
C7H15
CH2COOH
CH2CH2NO2
C6H4-p-NO2
CH2CH2OMe
CH2CH2SMe
CH2-cyclopropyl
CH2CH2F
CH2CN
17
1.2
2.3
13
>30
1.6
>30
4.1
3.3
1.5
1.8
5.0
6.4
1.5
6.4
2.3
1.1
Meth od ii: Compounds 37 and 39 were obtained by
nucleophilic cleavage of epoxide 8 with the heterocyclic
secondary amines in the presence of NaH in DMF
(Figure 2). Compounds 38, 64, and 65 were obtained
by reaction of compound 8 with the amines in the
presence of potassium carbonate. A nucleophilic sub-
stitution of the nitrogen atom at position 1 (not the
amino group at position 3) in 3-amino-1,6-dihydropy-
ridazin-6-one to epoxide 8 gave compound 39 without
the formation of compound 16.
4.9
1.6
1.8
10.5
4.1
3.1
3.2
3.8
2.6
3.5
10.0
CH2CF3
n-Pr
Me
Me
Me
NH
NH
NO2
a
Meth od iii: In the presence of pyridine or sodium
carbonate, nucleophilic substitution of heterocyclic com-
pounds with OH or SH group to epoxide 8 gave
compounds 40, 41, and thioether derivatives, respec-
tively (Supporting Information).
After intracoronary administration, the ED50 was calculated
as follows: ED50 is the dose (µg) of a compound causing a 50%
increase of coronary blood flow relative to the flow increase caused
by injection of 1 µg of nifedipine (100%); n ) 2.
Meth od i: Compounds were obtained by nucleophilic
cleavage of optically active epoxide 8 with primary
amines, hydrazine, or hydroxylamine derivatives (Sup-
porting Information). For example, epoxide 8 was
treated with 3-amino-1-methyl-1,6-dihydropyridazin-6-
one12 in the presence of NaH or t-BuOK in anhydrous
DMF to give compound 3 in 70-80% yield (99.5% ee).
The optical purity of compound 3 was determined by
comparison with the racemate using HPLC analysis.
Meth od iv: Amidine derivatives 2, 42, and 54 were
obtained by the reaction of amino alcohol 8 with the
imidates in methanol (Table 1).
Meth od v: Guanidine derivatives 44 and 55 were
obtained by the reaction of compound 9 with the
thioureas in the presence of 1-[3-(dimethylamino)pro-
pyl]-3-ethylcarbodiimide hydrochloride (WSC/HCl) in
DMF.

3800 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19
Cho et al.
hypotensive activity were directed to modification of the
substituents at position 4 while maintaining the meth-
oxymethyl groups at position 2. As shown in Table 1,
amidines 42 and 43 exhibited more potent coronary
vasodilation than compound 2, but the duration of action
was shorter. Guanidine 44 and urea 45 did not increase
CoBF even after the injection of 30 µg. Various com-
pounds substituted with heterocyclic, phenolic, or
thiophenolic groups at position 4 were synthesized
(Figure 2 and Supporting Information), but, with the
exception of compounds, these did not cause any in-
crease in CoBF after injection at a dose of 30 µg.
Compound 3 having the (1,6-dihydro-6-oxopyridazin-
3-yl)amino group elicited an extremely potent increase
of CoBF (ED50 ) 0.58 µg, T1/2 ) 3.2 min) (Table 1).12,14
Following this result, derivatives of compound 3 (com-
pounds 20-36) were synthesized, which possessed a
lower alkyl group or a lower alkyl substituted by an
electron-withdrawing group at the N-1 atom of the 1,6-
dihydro-6-oxopyridazin-3-yl ring. Among these com-
pounds, 20, 21, 28, 32, 33, 36, and 48 had potent activity
(ED50 ) 0.57-1.8 µg) and a relatively long duration of
action (T1/2 > 3.2 min). Compound 18 with a thioxo
group instead of an oxo group on the dihydropyridazine
skeleton was 40-fold less active than compound 3, while
compound 40 with a (1,6-dihydro-6-oxopyridazin-3-yl)-
oxy group at position 4 of the benzopyran ring main-
tained activity. Compound 19 with a (3-methyl-4-oxo-
3,4-dihydrophthalazin-1-yl)amino residue did not increase
CoBF at all (Figure 2). Position 6 was modified to
obtain halogen derivatives 47 and 49 as well as nitro
derivatives 48 and 50. As shown in Table 1, the bromo
atom of 47 and 49 proved to be less effective in
increasing CoBF than the cyano group.
F igu r e 3. ORTEP drawings of (a) compound 3 (1/2H2O) and
(b) compound 51.
Meth od vi: Urea derivatives 45 and 56 were obtained
by the reaction of compound 9 with the isocyanates in
ethanol.
Meth od vii: Amide derivatives 46 and 57 were
obtained by acylation of compound 9 with the acyl
chloride in triethylamine/methylene chloride.
(B) Absolu te Str u ctu r e. By analogy to the work of
J acobsen,9 the optically active epoxide 8 should have
the 3S,4R-stereochemistry as shown in Scheme 1. In
order to confirm the stereochemistry of a series of
benzopyran derivatives, X-ray crystallographic analysis
of compound 3 was carried out. It revealed that two
molecules of compound 3 and one molecule of water
were arranged in a unit cell and that the relative
configuration of the two substituents at positions 3 and
4 was trans (Figure 3a, the ORTEP drawings). To
determine the absolute stereochemistry, compound 3
was quantitatively converted to heavy atom-containing
compound 51 by benzoylation with p-bromobenzoyl
chloride, and X-ray crystallographic analysis gave the
absolute structure depicted in Figure 3b. Since no
epimerization could occur through benzoylation, com-
pound 3 was determined to have the expected 3S,4R-
configuration.
Further pharmacological evaluation of these potent
coronary vasodilators to select compounds for possible
clinical development was carried out by detailed exami-
nation of the selectivity of their effect on CoBF relative
to that on MAP. In order to confirm the importance of
the methoxymethyl groups at benzopyran position 2 for
coronary selectivity, compound 3 was compared to
compound 415 (the corresponding dimethyl benzopyran)
and levcromakalim (Figure 1). As shown in Figures 4
and 5, compound 3 revealed selectivity in comparison
to compound 4 and also levcromakalim, as compound 2
did to compound 1. Since compound 37, which is a
levcromakalim analog with two methoxymethyl groups
at position 2 instead of dimethyl groups, caused a very
weak increase of CoBF (ED50 > 30 µg, Figures 1 and
2), the potent and coronary-selective vasodilatory activ-
ity of compound 3 was due to the combination of two
methoxymethyl groups at position 2 crucial for selectiv-
ity and a (1,6-dihydro-6-oxopyridazin-3-yl)amino group
at position 4 that increased the potency. Next, a
comparison was performed of compound 3 and the fairly
potent coronary vasodilators 20, 21, 32, and 48, which
caused a more prolonged increase of CoBF than 3
(Figure 5). Compound 32 was found to have almost the
same selectivity as 3, but compounds 20, 21, and 48
showed less selectivity.
Resu lts a n d Discu ssion
During the course of synthetic modification of com-
pound 1, it was found that compounds 2 and 10, with
respectively one or two methoxymethyl groups intro-
duced at position 2, selectively increased CoBF and
decreased hypotensive effects in anesthetized dogs
(Table 1, Figures 4 and 5, and Experimental Section for
the pharmacological evaluation). In order to examine
the effect of substitutions at position 2, we synthesized
compounds 11-14 with other alkoxy or alkyl groups at
this position.11 Evaluation of the increase of CoBF
produced by these derivatives demonstrated that sub-
stitution of groups other than the methoxymethyl group
led to a weaker effect (Supporting Information), sug-
gesting that bulk (2 vs 11, 2 vs 14, and 10 vs 12),
flexibility of the methoxymethyl group (2 vs 14), and
the existence of an oxygen atom (10 vs 13) in the group
at position 2 might influence the extent and duration
of the increase in CoBF. Thus, subsequent efforts to
obtain more potent coronary vasodilators with minimal
Compound 3 was selected as the candidate for devel-
opment because it was obtained as fine crystals, while
compound 32 was amorphous. Oral administration of
compound 3 (0.03 mg/kg, po) elicited an increase of
CoBF without apparent changes of the systemic blood

Novel Potassium Channel Openers
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19 3801
Ta ble 2. Vasorelaxant Effect on KCl-Induced Contraction of
Porcine Coronary Artery and Rat Aortaa
IC50 (µM)
compound 3 levcromakalim nicorandil nifedipine
coronary
artery (a)
0.11
0.36
3.2
0.0036
aorta (b)
0.3
0.29
0.81
13
4.06
0.0036
1.0
ratio (b/a)
2.73
a
KCl-induced established contraction was taken as 100%. The
mean IC50 (50% relaxation vs KCl-induced contraction) was
determined from the concentration-relaxation curves.
F igu r e 4. Effects of coronary vasodilators on coronary blood
flow (CoBF) and mean arterial pressure (MAP) in anesthetized
dogs. Each compound was administered intravenously.
F igu r e 6. Effect of glibenclamide (Glib: 0.3, 1, and 3 mM)
on compound 3-, levcromakalim-, nicorandil-, or nifedipine-
induced relaxation of rat aorta precontracted with phenyle-
phrine (1 mM). Glib or DMSO was added to the bath 20 min
before the addition of phenylephrine. Each point represents
the mean ( SEM derived from five experiments. Inset: The
corresponding Schild plots for Glib yield a slope of 1.31 and
1.12 and pA2 values of 6.85 and 7.25 for 3- and levcromakalim-
induced relaxation, respectively.
cium antagonist) but not to that of nicorandil.16 These
results demonstrated that the coronary selectivity of
compound 3 with bis(methoxymethyl) groups at position
2 was superior to that of benzopyran compounds with
dimethyl groups at position 2 and to that of typical
calcium antagonists. As for the mechanism of action,
compound 3 was proved to be a K+ channel opener
because glibenclamide (0.3, 1, and 3 µM), a selective
blocker of KATP channels,17 antagonized compound
3-induced relaxation of isolated rat aorta precontracted
with phenylephrine (1 µM) (Figure 6), and compound 3
caused slight or no relaxation in arteries contracted by
60 or 80 mM KCl. In an experimental angina model,
intraduodenal administration of compound 3 inhibited
the electrocardiographic ST elevation induced by intra-
coronary administration of methacholine to anesthetized
rats without any apparent changes of heart rate and
systemic blood pressure (Figure 7). This result suggests
that compound 3 may be useful in the therapy of angina
pectoris, especially variant angina pectoris. Further
pharmacological results will be reported in due course.
In conclusion, a novel K+ channel opener, compound
3 (J TV-506), appears to show promise as a potent and
selective coronary vasodilator, and a clinical trial is now
under way.18
F igu r e 5. Correlation between the CoBF increase and MAP
decrease after intravenous administration of various vasodi-
lators. Abbreviations are as for Figure 4.
pressure and heart rate in conscious dogs (data not
shown). The coronary artery selectivity of compound 3
was also compared to that of other vasodilators using
isolated arteries. As shown in Table 2, the selectivity
(coronary artery versus aorta) of compound 3 was
superior to that of levcromakalim and nifedipine (cal-

3802 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19
Cho et al.
(40.87 g, 346 mmol), acetic acid (8.5 mL, 148 mmol), and
pyrrolidine (10 mL, 120 mmol). Then the solution was refluxed
for 1 h using a Dean-Stark apparatus. After cooling, the
mixture was treated with activated charcoal (20 g) and filtered.
The filtrate was washed successively with 1 N hydrochloric
acid, 2 N sodium hydroxide, and brine. Then it was dried and
evaporated under reduced pressure to give crystals, which
were recrystallized from ethanol to yield 39.75 g (61%) of
compound 5: 1H NMR (CDCl3/ppm) δ 2.95 (2H, s), 3.35 (6H,
s), 3.55 (2H, d, J ) 10.3 Hz), 3.60 (2H, d, J ) 10.3 Hz), 7.07
(1H, d, J ) 8.6 Hz), 7.68 (1H, dd, J ) 8.6, 2.2 Hz), 8.14 (1H,
d, J ) 2.2 Hz). Anal. (C14H15NO4) C, H, N.
Using the reaction mentioned above, 6-bromo-3,4-dihydro-
2,2-bis(methoxymethyl)-2H-1-benzopyran-4-one and 3,4-dihy-
dro-2,2-bis(methoxymethyl)-6-nitro-2H-1-benzopyran-4-one were
also synthesized (Supporting Information).
Syn t h esis of 6-Cya n o-3,4-d ih yd r o-2,2-b is(m et h oxy-
m eth yl)-2H-1-ben zop yr a n -4-ol (6). To a stirred solution of
compound 5 (12.1 g, 46.4 mmol) in methanol (150 mL) was
added sodium borohydride (1.96 g, 51.8 mmol) at 0 °C. After
1.5 h, the reaction was quenched with water and the mixture
extracted with ethyl acetate. The organic layer was washed
with brine, dried, and evaporated to yield compound 6 (11.5
g, 95%): IR (neat) 3444, 2224; 1H NMR (CDCl3) 2.12 (1H, dd,
J ) 14.5, 5.3 Hz), 2.33 (1H, d, J ) 14.5, 5.6 Hz), 3.36 (3H, s),
3.41 (3H, s), 3.40-3.70 (4H, m), 4.77 (1H, m), 6.92 (1H, d, J )
8.6 Hz), 7.44 (1H, dd, J ) 8.6, 2.1 Hz), 7.72 (1H, d, J ) 2.1
Hz). Anal. (C14H17NO4) C, H, N.
F igu r e 7. Effect of compound 3 on mean blood pressure
(MBP), heart rate (HR), and S wave elevation of the ECG (lead
II) induced by intracoronary administration of methacholine.
Each value represents the mean ( SEM for six animals.
Compound 3 was administered at time 0. S wave elevation
occurred 30-60 s after methacholine administration. *p <
0.05 vs the control (c) by Dunnett’s multiple comparison test.
The compounds 6-bromo-3,4-dihydro-2,2-bis(methoxymethyl)-
2H-1-benzopyran-4-ol and 3,4-dihydro-2,2-bis(methoxymethyl)-
6-nitro-2H-1-benzopyran-4-ol were obtained in a similar man-
ner.
Syn th esis of 6-Cya n o-2,2-bis(m eth oxym eth yl)-2H-1-
ben zop yr a n (7). To a stirred solution of compound 6 (6.5 g,
24.7 mmol) in toluene (60 mL) was added p-toluenesulfonic
acid (0.6 g, 3.15 mmol), and the solution was refluxed for 1 h
with a Dean-Stark apparatus. After cooling the reaction was
quenched with water and the mixture extracted with ethyl
acetate. The organic layer was washed with an aqueous
solution of sodium bicarbonate and brine, dried, and evapo-
Exp er im en ta l Section
Gen er a l Meth od s (Ch em istr y). Melting points were
determined with a Yanagimoto (Yanako) micromelting point
apparatus (HK-10D) and are uncorrected. 1H NMR spectra
(ppm, δ) were recorded using a J EOL J NMA 300 (300 MHz)
spectrometer with tetramethylsilane as the internal standard.
IR spectra (cm-1) were obtained with a Perkin Elmer FT 1650
infrared spectrometer, and UV spectra were obtained with a
Hitachi U-3000 spectrophotometer. Mass spectra (FAB+) were
recorded with a Finnigan TSQ 700 instrument. [R]D values
were obtained at 25 °C with a Perkin Elmer 241 polarimeter.
HPLC was performed with a Shimazu LC-6A instrument, and
thin-layer chromatography (TLC) was carried out on Merck
silica gel plates (60F-254). Column chromatography was
performed with Merck silica gel (70-230 mesh) using activated
charcoal (or Shirasagi-A, Takeda Pharmaceutical Co.). After
extraction, the extract was dried over anhydrous magnesium
sulfate.
1
rated to yield compound 7 (4.91 g, 82%): IR (KBr) 2221; H
NMR (CDCl3) 3.39 (6H, s), 3.55 (2H, d, J ) 10.2 Hz), 3.60 (2H,
d, J ) 10.2 Hz), 5.76 (1H, d, J ) 10.1 Hz), 6.49 (1H, d, J )
10.1 Hz), 6.87 (1H, d, J ) 8.4 Hz), 7.25 (1H, d, J ) 2.0 Hz),
7.39 (1H, dd, J ) 8.4, 2.0 Hz). Anal. (C14H15NO3) C, H, N.
The same procedure also gave 6-bromo-2,2-bis(methoxym-
ethyl)-2H-1-benzopyran and 2,2-bis(methoxymethyl)-6-nitro-
2H-1-benzopyran.
Syn th esis of (-)-(3S,4S)-6-Cyan o-3,4-dih ydr o-3,4-epoxy-
2,2-bis(m eth oxym eth yl)-2H-1-ben zop yr a n (8). To a solu-
tion of compound 7 (14.72 g, 60 mmol) in methylene chloride
(75 mL) were added (S,S)-mangane(III)-salen complex9 (1.91
g, 3.0 mmol) and pyridine N-oxide (2.85 g, 30.0 mmol). Then
a cooled solution of 0.05 M sodium dihydrogen phosphate
(NaH2PO4) (150 mL) and fresh 0.6 M sodium hypochlorite
solution (NaOCl) (375 mL, 225 mmol) were added to the
mixture at 0 °C. Vigorous stirring was continued for 7 h at 0
°C, after which methylene chloride (100 mL) and Celite were
added, and the mixture was filtered through a filter covered
with Celite. The organic layer of the filtrate was separated
from the aqueous layer, dried, and evaporated to leave a
residue, which was purified by silica gel column chromatog-
raphy (the residue was dissolved in toluene and developed with
ethyl acetate:n-hexane ) 1:4) to yield compound 8 [13.32 g,
85%, 95.1% ee; DAICEL Chemical Industries Ltd., HPLC
Chiralcel OD column; n-hexane:ethanol ) 19:1; flow rate, 0.5
mL/min; 8 was eluted as the earlier fraction than its enanti-
Syn th eses of Com p ou n d s 5-9. (i) Mod ified P r ep a r a -
tion of 1,3-Dim eth oxyp r op a n -2-on e. To a stirred solution
of 1,3-dimethoxypropan-2-ol (216 g, 1.80 mol) in methylene
chloride (800 mL) were successively added 2,2,6,6-tetramethyl-
1-piperidinyloxy, free radical (TEMPO; 3.25 g, 0.02 mol),
sodium bromide (10.75 g, 0.1 mol), and sodium bicarbonate
(17.5 g, 0.2 mol) at 0 °C. To the mixture, 1.63 L of sodium
hypochloride (NaOCl; Wako Ltd.; available chlorine min 5%)
was added dropwise over 2 h at 0 °C. After 10 min, brine was
added and the organic layer was separated. The aqueous layer
was extracted with methylene chloride, and the organic layer
was combined with the above solution, which was washed with
potassium iodide (6.8 g, 0.04 mol) dissolved in a saturated
aqueous solution of potassium hydrogen sulfate (KHSO4).
Then it was successively washed with a saturated aqueous
solution of sodium thiosulfate (Na2S2O3‚5H2O), dried, and
evaporated to leave a residue. Distillation of the oily com-
pound gave 1,3-dimethoxypropan-2-one (152.179 g, 72%): bp
56 °C/1 × 103 Pa.
1
omer (k′ ) 2.31, R ) 1.19)]: IR (film) 2222; H NMR (CDCl3)
3.27 (3H, s), 3.48 (3H, s), 3.57 (1H, d, J ) 10.3 Hz), 3.70 (1H,
d, J ) 10.3 Hz), 3.71 (1H, s), 3.82 (1H, d, J ) 4.4 Hz), 3.94
(1H, d, J ) 4.4 Hz), 6.91 (1H, d, J ) 8.5 Hz), 7.53 (1H, dd, J
) 8.5, 2.0 Hz), 7.65 (1H, d, J ) 2.0 Hz); [R]D ) -18.4° (c )
1.22, MeOH). Anal. (C14H15NO4) C, H, N.
(ii) Syn th esis of 6-Cya n o-3,4-d ih yd r o-2,2-bis(m eth oxy-
m eth yl)-2H-1-ben zop yr a n -4-on e (5). To a stirred solution
of 5-cyano-2-hydroxyacetophenone (40.18 g, 248 mmol)7 in
toluene (320 mL) were added 1,3-dimethoxypropan-2-one8
In addition, (+)-(3R,4R)-6-cyano-3,4-dihydro-3,4-epoxy-2,2-
bis(methoxymethyl)-2H-1-benzopyran was obtained with (R,R)-
mangane(III)-salen complex by the procedure described above.
In addition, the racemate was obtained from compound 7 and

Novel Potassium Channel Openers
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19 3803
m-chloroperbenzoic acid under the usual reaction conditions.
6-Bromo-3,4-epoxy-3,4-dihydro-2,2-bis(methoxymethyl)-2H-1-
benzopyran and 3,4-epoxy-3,4-dihydro-2,2-bis(methoxymethyl)-
6-nitro-2H-1-benzopyran were also obtained as mentioned
above.
(iii) P r ep a r a tion of Com p ou n d 36. To a stirred solution
of compound 16 (60 mg, 0.16 mmol) in dimethylformamide
(DMF) (1 mL) were added 1-bromopropane (0.017 mL, 0.19
mmol) and potassium carbonate (45 mg). The reaction mixture
was heated for 3 h at 70 °C with stirring, after which the
reaction was quenched with water and extracted with ethyl
acetate. The organic layer was washed with brine, dried, and
evaporated to leave a residue, which was purified by SiO2
column chromatography (methanol:chloroform ) 1:24) to yield
compound 36 (33 mg, 50%).
Syn th esis of (3S,4R)-6-Cya n o-3,4-d ih yd r o-4-[(1,6-d ih y-
d r o-1-m e t h yl-6-t h ioxo-3-p yr id a zin yl)a m in o]-2,2-b is-
(m eth oxym eth yl)-2H-1-ben zop yr a n -3-ol (18). To a stirred
solution of 3-amino-1-methyl-1,6-dihydropyridazin-6-one (500
mg, 4 mmol) in pyridine (5 mL) was added Lawesson’s reagent
(970 mg, 2.4 mmol), and the mixture was refluxed for 5 h. After
concentration, the residue was purified by silica gel column
chromatography (chloroform:methanol ) 100:1) to give 3-amino-
1-methyl-1,6-dihydropyridazine-6-thione (218 mg). Cleavage
of epoxide 8 with this compound yielded compound 18 via the
same synthetic procedure. Spectral data for compounds 15-
36, 47, and 48 are available as Supporting Information.
Syn th esis of (3S,4R)-4-Am in o-6-cya n o-3,4-d ih yd r o-2,2-
bis(m eth oxym eth yl)-2H-1-ben zopyr an -3-ol (9). To a stirred
solution of compound 8 (3.88 g, 14.9 mmol) in ethanol (64 mL)
was added an aqueous solution of 28% ammonium hydroxide
(64 mL) at room temperature, and stirring was continued for
24 h at the same temperature. After evaporation, the residue
was purified by silica gel column chromatography to give
compound 9 (4.00 g, 96.5%): IR (KBr) 2220; 1H NMR (CDCl3)
3.33 (3H, s), 3.48 (3H, s), 3.60-3.90 (6H, m), 6.91 (1H, d, J )
8.5 Hz), 7.43 (1H, dd, J ) 8.5, 1.9 Hz), 7.92 (1H, d, J ) 1.9
Hz). Anal. (C14H18N2O4) C, H, N.
Syn th esis of (-)-(3S,4R)-6-Cya n o-3,4-d ih yd r o-4-[(1,6-
d ih yd r o-1-m et h yl-6-oxo-3-p yr id a zin yl)a m in o]-2,2-b is-
(m eth oxym eth yl)-2H-1-ben zop yr a n -3-ol (3). To a stirred
solution of compound 8 (4.18 g, 16 mmol) [dried by azeotropic
distillation with anhydrous toluene (20 mL)] in anhydrous
N,N-dimethylformamide (40 mL) was added 3-amino-1-methyl-
1,6-dihydropyridazin-6-one12 (1.92 g, 48 mmol) under an argon
atmosphere. Then sodium hydride (60% dispersed in mineral
oil; 1.92 g, 48 mmol) was added, and stirring was continued
at 60 °C for 2 h, after which the reaction mixture was poured
into ice water (200 mL) and extracted three times with
chloroform (100 mL). The organic layer was washed with brine
(5 mL), dried, and evaporated to leave a residue (15 g), which
was purified by silica gel column chromatography [silica gel
100 g, ethyl acetate:ethanol ) 9:1 (v/v)] to yield crystals (5.07
g). The crystals were dissolved in ethyl acetate, and the
insoluble solid was filtered off. The filtrate was concentrated
to give compound 3, which was recrystallized from ethyl
acetate (10 mL) to yield colorless crystals of this compound 3
(2.89 g, 47%, 99.5% ee) [HPLC column, Shinwakakou Ltd. ES-
OVM, 4.6 × 150 mm; solvent, 20 mM K2HPO4 (pH 6.0);
acetonitrile ) 97:3; flow rate, 1 mL/min at 25 °C; 3 was eluted
as the later fraction (k′ ) 2.52, R ) 1.75) than its enantiomer].
Alternatively compound 3 was prepared by the following
procedure. To a stirred solution of compound 8 (1.0 g, 3.83
mmol) and 3-amino-1-methyl-1,6-dihydropyridazin-6-one12 (528
mg, 4.21 mmol) in anhydrous N,N-dimethylformamide (17 mL)
was added potassium tert-butoxide (1.29 g, 11.5 mmol). After
stirring for 1 h at 0-5 °C, 6 N sulfuric acid (1.91 mL) was
added (pH 6-7). Concentration of the reaction mixture at 60
°C reduced pressure gave a residue to which chloroform and
1 N hydrochloric acid (50 mL each) were added. The organic
layer was separated, washed with saturated sodium bicarbon-
ate solution (50 mL) and brine (50 mL), dried, and evaporated
to leave a solid that was dissolved in methanol. The solution
was treated with activated charcoal (500 mg), filtered, and
concentrated to yield pale yellow crystals of compound 3 (545
mg, 80%), which were purified by recrystallization from ethyl
acetate or silica gel column chromatography [colorless crystals,
prisms; mp 159.5-161.5 °C (AcOEt) or mp (160.0-161.0 °C
(EtOH:H2O ) 1:2)]: [R]D ) -126.6° (c ) 0.99, MeOH); IR (KBr)
2221, 1655, 1572; UV λmax (MeOH) 205.6 (ꢀ ) 31 000), 245.6
(ꢀ ) 32 000), 350.0 nm (ꢀ ) 1800); 1H NMR (CD3OD) 3.32 (3H,
s), 3.38 (3H, s), 3.59 (3H, s), 3.64-3.85 (4H, m), 4.16 (1H, d, J
) 9 Hz), 4.36 (1H, d, J ) 9 Hz), 5.09 (1H, t, J ) 9 Hz), 6.80-
7.00 (3H, m), 7.46 (1H, dd, J ) 9, 1 Hz), 7.65 (1H, dd, J ) 9,
1 Hz); MS m/z 387 (M + H)+. Anal. (C19H22N4O5‚1/2H2O) C,
H, N.
Syn th eses of Com p ou n d s 10-14. All of the compounds
shown in Table 1 were synthesized by the same procedure as
that used for compound 2 (Supporting Information).
Syn th esis of N′-Cya n o-N-[tr a n s-6-cya n o-3,4-d ih yd r o-
3-h yd r oxy-2H-1-ben zop yr a n -2-sp ir o-5′-(1′,3′-d ioxa cyclo-
h exyl)-4-yl]-3-p yr id in eca r boxa m id in e (14). 6-Cyano-2,2-
bis(tert-butoxymethyl)-2H-1-benzopyran (5.2 g; 19% yield over
three steps) was obtained by cyclization of 5-cyano-2-hydroxy-
acetophenone (13.3 g, 82.6 mmol) and 1,3-di-tert-butoxypropan-
2-one (19.9 g, 98.5 mmol), reduction with NaBH4 in methanol,
mesylation with methanesulfonylchloride, and dehydration
with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). To a stirred
solution of 6-cyano-2,2-bis(tert-butoxymethyl)-2H-1-benzopy-
ran (4.8 g, 14.6 mmol) in methylene chloride (30 mL) was
added trifluoroacetic acid (20 mL, 260 mmol) at 0 °C. After
stirring for 5 h at 0 °C, the reaction mixture was concentrated
under reduced pressure. Then the residue was dissolved in
an aqueous solution of sodium bicarbonate, and the solution
was extracted with ethyl acetate. The organic layer was
washed with brine, dried, and evaporated to leave 6-cyano-
2,2-bis(hydroxymethyl)-2H-1-benzopyran (2.7 g, 85%): 1H
NMR (DMSO-d6) 3.40-3.60 (4H, m), 4.98 (1H, d, J ) 5.9 Hz),
5.00 (1H, d, J ) 5.9 Hz), 5.79 (1H, d, J ) 10.1 Hz), 6.57 (1H,
d, J ) 10.1 Hz), 6.85 (1H, d, J ) 8.1 Hz), 7.50-7.60 (2H, m).
MS m/z 218 (M + H)+.
To a stirred solution of 6-cyano-2,2-bis(hydroxymethyl)-2H-
1-benzopyran (1.0 g, 4.6 mmol) in methylene chloride (9 mL)
were added diisopropylamine (3 mL, 22.9 mmol) and chlorom-
ethyl methyl ether (1.2 mL, 15.8 mmol) at 0 °C. Stirring was
continued for 3 h at room temperature and then for another 3
h at 40 °C. The reaction mixture was concentrated to leave a
residue, which was dissolved in 10% citric acid. The resulting
solution was extracted with ethyl acetate. The organic layer
was then washed with sodium bicarbonate solution and brine,
dried, and evaporated to leave an oily compound. This was
dissolved in benzene, and boron trifluoride etherate (1.4 mL,
11.4 mmol) was added at room temperature. After 2 h, the
reaction mixture was poured into ice water, and the solution
was extracted with methylene chloride. The organic layer was
washed with sodium bicarbonate solution and brine, dried, and
evaporated to leave a residue, which was triturated with
methanol to give 6-cyanospiro[2H-1-benzopyran-2,5′-1′,3′-di-
oxacyclohexane] (0.74 g, 70%): 1H NMR (CDCl3) 3.83 (2H, d,
Compounds 47 and 48 were also obtained by the above
procedure.
Syn th esis of (-)-(3S,4R)-6-Cya n o-3,4-d ih yd r o-4-[(1,6-
d ih yd r o-6-oxo-1-n -p r op yl-3-p yr id a zin yl)a m in o]-2,2-b is-
(m eth oxym eth yl)-2H-1-ben zop yr a n -3-ol (36). (i) P r ep a -
r a tion of (-)-(3S,4R)-4-[(6-Ch lor o-3-p yr id a zin yl)a m in o]-
6-cya n o-3,4-d ih yd r o-2,2-b is(m et h oxym et h yl)-2H -1-b en -
zop yr a n -3-ol (15). Treatment of epoxide 8 (1.05 g, 4.02 mmol)
with 3-amino-6-chloropyridazine (1.00 g, 7.68 mmol) instead
of 3-amino-1-methyl-1,6-dihydropyridazin-6-one yielded com-
pound 15 (1.56 g, 99%).
(ii) P r ep a r a tion of (-)-(3S,4R)-4-[(6-Acetyloxy)-3-p y-
r id a zin yl)a m in o]-6-cya n o-3,4-d ih yd r o-2,2-b is(m et h oxy-
m eth yl)-2H-1-ben zop yr a n -3-ol (17) a n d (-)-(3S,4R)-6-Cy-
a n o-3,4-d ih yd r o-2,2-bis(m eth oxym eth yl)-2H-1-ben zop y-
r a n -3-ol (16). To a stirred solution of compound 15 (750 mg,
1.92 mmol) in acetic acid (6 mL) was added potassium acetate
(380 mg, 3.87 mmol), and the mixture was refluxed for 5 h.
After cooling, the reaction mixture was filtered off. The filtrate
was concentrated under reduced pressure to give a residue,
which was purified by SiO2 chromatography (ethyl acetate:
ethanol ) 95:5) to yield compound 17 (180 mg, 23%) as the
first fraction and compound 16 (500 mg, 70%) as the second
fraction.

3804 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19
Cho et al.
J ) 11.8 Hz), 4.02 (2H, d, J ) 11.8 Hz), 4.85 (1H, d, J ) 6.2
Hz), 4.98 (1H, d, J ) 6.2 Hz), 5.76 (1H, d, J ) 10.0 Hz), 6.52
(1H, d, J ) 10.0 Hz), 6.99 (1H, d, J ) 8.5 Hz), 7.29 (1H, d, J
) 1.9 Hz), 7.44 (1H, dd, J ) 8.5, 1.9 Hz). Anal. (C13H11NO3)
C, H, N.
Successive reactions of compound 2 afforded compound 14
as a colorless powder: IR (KBr) 3428, 2226, 2182; 1H NMR
(DMSO-d6) 3.90-4.20 (5H, m), 4.68 (1H, d, J ) 6.0 Hz), 4.90-
5.10 (2H, m), 6.21 (1H, d, J ) 5.4 Hz), 7.12 (1H, d, J ) 8.6
Hz), 7.63 (1H, dd, J ) 7.9, 4.9 Hz), 7.70 (1H, d, J ) 8.6 Hz),
7.99 (1H, s), 8.12 (1H, d, J ) 7.9 Hz), 8.78 (1H, d, J ) 4.9 Hz),
8.86 (1H, s), 9.57 (1H, d, J ) 7.5 Hz); MS m/z 392 (M + H)+.
Anal. (C20H17N5O4) C, H, N.
date20 (3.00 g, 18.6 mmol) in methanol (5 mL) at room
temperature. Then stirring was continued at 50-70 °C for 1
day. After removal of the solvent, the residue was purified
by silica gel column chromatography (3% methanol in chloro-
form) to yield compound 2 as a colorless powder (2.21 g,
50.3%): IR (KBr) 3428, 2226, 2182; 1H NMR (DMSO-d6) 3.20
(3H, s), 3.32 (3H, s), 3.50-3.80 (4H, m), 4.19 (1H, dd, J ) 9.6,
5.8 Hz), 5.36 (1H, dd, J ) 9.6, 8.5 Hz), 6.30 (1H, d, J ) 5.8
Hz), 6.98 (1H, d, J ) 8.5 Hz), 7.60-7.70 (2H, m), 7.78 (1H, s),
8.28 (1H, d, J ) 8.0 Hz), 8.79 (1H, d, J ) 4.9 Hz), 8.99 (1H, s),
9.54 (1H, d, J ) 8.5 Hz); [R]D ) -139.6° (c ) 1.01, MeOH).
Anal. (C21H21N5O4) C, H, N.
Compounds 42, 43, 49, and 50 were obtained in a similar
manner.
Syn th esis of (-)-(3S,4R)-3-[(4-Br om oben zoyl)oxy]-3,4-
d ih yd r o-4-[(1,6-d ih yd r o-1-m et h yl-6-oxo-3-p yr id a zin yl)-
a m in o]-2,2-bis(m eth oxym eth yl)-2H-1-ben zop yr a n -6-ca r -
bon itr ile (51). p-Bromobenzoyl chloride (560 mg, 2.55 mmol)
was added to a stirred solution of compound 3 (250 mg, 0.647
mmol) in pyridine (5 mL), and the mixture was stirred at 80
°C for 2 h. The solvent was evaporated under reduced
pressure to leave a residue, which was diluted with chloroform.
The organic layer was washed with water, dried, and evapo-
rated to leave a residue, which was purified with silica gel
column chromatography (CHCl3:EtOH ) 97:3, v/v) to give
compound 51 (368 mg) quantitatively as a colorless crystalline
solid: mp 184.0-186.5 °C (EtOH:H2O ) 2:1); IR (KBr) 2222,
Syn th esis of (-)-(3S,4R)-N′′-Cya n o-N-[6-cya n o-3,4-d i-
h yd r o-3-h yd r oxy-2,2-bis(m eth oxym eth yl)-2H-1-ben zop y-
r a n -4-yl]-N′-p h en ylgu a n id in e (44). To a stirred solution of
compound 9 (253 mg, 0.91 mmol) and N-cyano-N′-phenylth-
iourea (230 mg, 1.18 mmol) in DMF (1.2 mL) was added 1-[3-
(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (226
mg, 1.18 mmol) at room temperature. Then stirring was
continued for 6 h at room temperature, after which the reaction
mixture was diluted with ethyl acetate and dilute hydrochloric
acid. The organic layer was separated, washed successively
with saturated sodium bicarbonate and brine, dried, and
evaporated to leave a residue, which was purified by silica gel
column chromatography (2% methanol in chloroform) to afford
compound 44 as a colorless powder (200 mg, 52%): IR (KBr)
2224, 2184, 1607, 1582; 1H NMR (DMSO-d6) 3.17 (3H, s), 3.30
(3H, s), 3.50-3.70 (4H, m), 4.17 (1H, dd, J ) 9.7, 6.0 Hz), 5.06
(1H, dd, J ) 9.7, 8.5 Hz), 6.00 (1H, brs), 6.95 (1H, d, J ) 8.5
Hz), 7.10-7.20 (1H, m), 7.30-7.40 (4H, m), 7.50-7.70 (3H,
m), 9.28 (1H, s); [R]D ) -43.1° (c ) 0.99, MeOH); MS m/ z )
422 (M + H)+. Anal. (C22H23N5O4) C, H, N.
Syn th esis of N-[tr a n s-6-Cya n o-3,4-d ih yd r o-3-h yd r oxy-
2,2-b is(m et h oxym et h yl)-2H -1-b en zop yr a n -4-yl]-N′-p h e-
n ylu r ea (45). To a suspension of compound 9 (racemate) (500
mg, 1.80 mmol) in ethanol (2 mL) was added phenyl isocyanate
(0.32 mL, 2.92 mmol) at room temperature, and stirring was
continued overnight at 80-90 °C. After evaporation, the
residue was purified by silica gel column chromatography
(chloroform and then 4% methanol in chloroform) to give
compound 45 (697 mg), which was recrystallized from metha-
nol to yield this compound as colorless needles (359.5 mg,
50.3%): mp 186.7-187.7 °C; IR (KBr) 2225, 1677; 1H NMR
(DMSO-d6) 3.19 (3H, s), 3.23 (3H, s), 3.50-3.70 (4H, m), 4.01
(1H, dd, J ) 9.6, 5.7 Hz), 4.84 (1H, dd, J ) 9.6, 8.2 Hz), 5.74
(1H, d, J ) 5.7 Hz), 6.57 (1H, d, J ) 8.3 Hz), 6.90-7.00 (2H,
s), 7.20-7.30 (2H, m), 7.40-7.50 (2H, m), 7.54-7.65 (2H, m),
8.52 (1H, s). Anal. (C21H23N3O5) C, H, N.
1
1721, 1661, 1610; H NMR (CDCl3) 3.31 (3H, s), 3.37 (3H, s),
3.54 (3H, s), 3.69 (2H, s), 3.71 (1H, d, J ) 10.5 Hz), 3.78 (1H,
d, J ) 10.5 Hz), 4.76 (1H, d, J ) 8.5 Hz), 5.31 (1H, dd, J )
8.5, 7.8 Hz), 5.79 (1H, d, J ) 7.8 Hz), 6.72 (1H, d, J ) 9.7 Hz),
6.78 (1H, d, J ) 9.7 Hz), 7.03 (1H, d, J ) 8.6 Hz), 7.49 (1H, d,
J ) 8.7 Hz), 7.68 (2H, s), 7.79 (2H, d, J ) 8.7 Hz); [R]D ) -82.6°
(c ) 1.05, MeOH). Anal. (C26H25BrN4O6) C, H, N.
Syn th esis of (-)-(3S,4R)-4-(1H-3-Am in o-6-oxopyr idazin -
1-yl)-6-cya n o-3,4-d ih yd r o-2,2-bis(m eth oxym eth yl)-2H-1-
ben zop yr a n -3-ol (39). To a stirred solution of compound 8
(212 mg, 0.81 mmol) and 3-amino-1,6-dihydropyridazin-6-one
(178 mg, 1.60 mmol) in anhydrous N,N-dimethylformamide
(4 mL) was added 60% NaH (58 mg, 1.45 mmol) at 0 °C, and
stirring was continued at 50 °C for 36 h. Then the reaction
mixtures was poured into ice water and extracted with
chloroform. The organic layer was washed with brine, dried,
and evaporated to leave a residue, which was purified by silica
gel column chromatography (chloroform:methanol ) 30:1) to
give compound 39 (134 mg, 44%) as the sole product: colorless
crystals; mp 186-189 °C (CHCl3-n-hexane); IR (KBr) 3353,
1
2225, 1611, 1560; H NMR (DMSO-d6) 3.18 (3H, s), 3.34 (3H,
s), 3.53-3.73 (4H, m), 4.53-4.60 (1H, m), 5.75 (1H, d, J ) 6.0
Hz), 5.86 (2H, s), 6.08 (1H, brs), 6.84 (1H, d, J ) 10.0 Hz),
6.94-6.99 (3H, m), 7.56 (1H, dd, J ) 8.5, 1.5 Hz); MS m/z 373
(M + H)+; [R]D ) -51.5° (c ) 1.31, MeOH). Anal. (C18H20N4O5)
C, H, N.
Syn th esis of (-)-(3S,4R)-6-Cya n o-3,4-d ih yd r o-2,2-bis-
(m eth oxym eth yl)-4-(3-p yr id in eca r boxa m id o)-2H-1-ben -
zop yr a n -3-ol (46). To a stirred mixture of compound 9 (306.5
mg, 1.10 mmol) in methylene chloride (4 mL) and triethy-
lamine (0.4 mL, 2.88 mmol) was added nicotinoyl chloride
hydrochloride (236.3 mg, 1.33 mmol) at room temperature, and
stirring was continued overnight at the same temperature.
Then the reaction was quenched with water and the mixture
extracted with chloroform. The organic layer was washed with
brine, dried, and evaporated to leave a residue (408 mg), which
was purified by silica gel column chromatography to yield
compound 46 as a colorless powder (240.5 mg, 56.9%): IR
Compound 37 was also obtained by the above procedure.
Syn th esis of (-)-(3S,4R)-6-Cya n o-3,4-d ih yd r o-4-[(1,6-
d ih y d r o -1-m e t h y l-6-o x o -3-p y r id a zin y l)o x y ]-2,2-b is -
(m eth oxym eth yl)-2H-1-ben zop yr a n -3-ol (40). To a stirred
solution of compound 8 (280 mg 1.07 mmol) and 3-hydroxy-
1-methyl-1,6-dihydropyridazin-6-one19 (142 mg, 1.13 mmol) in
ethanol (2.8 mL) was added pyridine (0.13 mL), and the
solution was refluxed for 8.5 h with stirring. After cooling,
evaporation of the solvent gave a residue, which was purified
with silica gel column chromatography (methanol:chloroform
) 1:99) to provide compound 40 (228 mg, 55%): mp 137.7-
138.7 °C; IR (KBr) 2222, 1658, 1580; 1H NMR (DMSO-d6) 3.24
(3H, s), 3.28 (3H, s), 3.49 (1H, d, J ) 10.3 Hz), 3.55-3.65 (2H,
m), 3.58 (3H, s), 3.73 (1H, d, J ) 10.3 Hz), 4.20 (1H, dd, J )
6.0, 5.6 Hz), 5.05 (1H, d, J ) 6.0 Hz), 6.06 (1H, d, J ) 5.6 Hz),
7.02 (1H, d, J ) 9.8 Hz), 7.04 (1H, d, J ) 8.5 Hz), 7.25 (1H, d,
J ) 9.8 Hz), 7.69 (1H, dd, J ) 8.5, 1.8 Hz), 7.80 (1H, d, J )
1.8 Hz); MS m/z 388 (M + H)+; [R]D ) -112.6° (c ) 1.0, MeOH).
Anal. (C19H21N3O6) C, H, N.
1
(KBr) 2225, 1644; H NMR (CDCl3) 3.36 (3H, s), 3.42 (3H, s),
3.73 (1H, d, J ) 11.0 Hz), 3.74 (2H, s), 3.88 (1H, d, J ) 11.0
Hz), 4.25 (1H, d, J ) 8.7 Hz), 5.52 (1H, dd, J ) 8.7, 8.5 Hz),
6.90 (1H, d, J ) 8.5 Hz), 7.30 (1H, d, J ) 8.5 Hz), 7.35-7.50
(2H, m), 7.59 (1H, s), 8.17 (1H, J ) 8.0 Hz), 8.71 (1H, d, J )
4.9 Hz), 9.02 (1H, s); [R]D ) -46.0° (c ) 0.50, methanol). Anal.
(C20H21N3O5) C, H, N.
P h a r m a cologica l Stu d ies. (1) Effect on Cor on a r y
Blood F low . Mongrel dogs of both sexes were used. Under
sodium pentobarbital anesthesia (30 mg/kg + 2-5 mg/kg/h,
iv), the animals were ventilated with a positive pressure
respirator (20 mL/kg × 18/min) after endotracheal intubation.
Mea su r em en t of Cor on a r y Blood F low follow in g In -
tr a cor on a r y Ad m in istr a tion . Coronary blood flow was
Syn th esis of (-)-(3S,4R)-N′-Cya n o-N-[6-cya n o-3,4-d i-
h yd r o-3-h yd r oxy-2,2-bis(m eth oxym eth yl)-2H-1-ben zop y-
r a n -4-yl]-3-p yr id in eca r boxa m id in e (2). To a stirred solu-
tion of compound 9 (3.00 g, 10.8 mmol) in methanol (5 mL)
was added a solution of methyl N-cyano-3-pyridinecarboximi-

Novel Potassium Channel Openers
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 19 3805
(2) Bergmann, R.; Gericke, R. Synthesis and Antihypertensive
Activity of 4-(1,2-Dihydro-2-oxo-1-pyridyl)-2H-1-benzopyrans and
Related Compounds, New Potassium Channel Activators. J .
Med. Chem. 1990, 33, 492-504.
measured using an extracorporeal flow probe connected to an
electromagnetic flowmeter (Nihon Kohden MFV-2100). To
measure blood flow, the left coronary artery was cannulated
with a metal tube through the right common carotid artery
and autoperfused with blood from the right femoral artery,
and the flow probe was placed in the perfusion circuit. The
perfusion pressure and systemic blood pressure were measured
with pressure transducers (Millar, MPC-500). Then each
compound was dissolved in 30% DMF and diluted with saline,
and the solution was injected into the coronary artery.
Mea su r em en t of Cor on a r y Blood F low follow in g In -
tr a ven ou s Ad m in istr a tion . After thoracotomy at the left
fourth intercostal space, the left circumflex artery was exposed
and blood flow was measured with an intracorporeal flow probe
connected to an electromagnetic flowmeter (Nihon Kohden
MFV 2100). Systemic blood pressure was measured from the
right femoral artery with a pressure transducer. Both pa-
rameters were recorded continuously on a polygraph (NEC
San-ei 360). All compounds were dissolved in DMF and
diluted with saline below 10% of DMF, and the solutions were
administered into the cannulated femoral vein.
(3) Nakajima, T. Y-27152, A Long-Acting K+ Channel Opener with
Less Incidence of Tachycardia. Cardiovasc. Drug Rev. 1991, 9,
372-384.
(4) Lebel, M.; Grose, J . H.; Lacourciere, Y. Effect of Short-Term
Administration of Cromakalim on Renal Hemodynamics and
Eicosanoid Excretion in Essential Hypertension. Am. J . Hyper-
tens. 1991, 4, 740-744.
(5) Toombs, C. F.; Norman, N. R.; Groppi, V. E.; Lee, K. S.; Gadwood,
R. C.; Shebuski, R. J . Limitation of Myocardial Injury with the
Potassium Channel Opener Cromakalim and the Nonvasoactive
Analog U-89, 232: Vascular vs Cardiac Actions in Vitro and in
Vivo. J . Pharmacol. Exp. Ther. 1992, 263, 1261-1268. Atwal,
K. S.; Grover, G. J .; Ferrara, F. N.; Ahmed, S. Z.; Sleph, P. G.;
Dzwonczyk, S.; Normandin, D. E. Cardioselective Antiischemic
ATP-Sensitive Potassium Channel Openers. 2. Structure-
Activity Studies on Benzopyranylcyanoguanidines: Modification
of the Benzopyran Ring. J . Med. Chem. 1995, 38, 1966-1973.
(6) Katoh, S.; Sayama, S.; Shibata, S.; Yamaki, T.; Uchida, I. J P
5186458A (Appl. J P 91188374, April 26, 1991).
(2) Va sor ela xa n t Effect. The thoracic aorta was isolated
from exsanguinated rats, and coronary arteries were isolated
from porcine hearts obtained from an abattoir. Helical or open
ring strips were prepared, and the endothelium was removed
mechanically. Each preparation was suspended in an organ
bath containing 10 mL of Krebs-Henseleit solution at 37 °C
and aerated with a mixture of 95% O2 and 5% CO2. Changes
in tension were recorded under a resting load of 1 g using an
isometric force transducer (Nihon Kohden TB-612T). The
strips were contracted with 30 or 40 mM KCl and 1 µM
phenylephrine. All test compounds were dissolved in DMSO
and applied to the organ bath.
(7) Ellis, G. P.; Show, D. Benzopyrones. Part VIII. Mono- and Di-
tetrazol-5-yl-chromones. The Infrared Cyano-Absorption of
Some 4-Oxo-chromencarbonitriles. J . Chem. Soc., Perkin Trans.
I 1972, 779-783.
(8) Petrusova, M.; Mihalov, V.; Kocis, P.; Fedoronko, M. Preparation
and Identification of Aldolization Products of 1,3-Dimethoxy-2-
propanone. Chem. Papers 1985, 39, 763-768.
(9) Lee, N. H.; Muci, A. R.; J acobsen, E. N. Enantiomerically Pure
Epoxychromans via Asymmetric Catalysis. Tetrahedron Lett.
1991, 32, 5055-5058. Zang, W.; J acobsen, E. N. Asymmetric
Olefin Epoxidation with Sodium Hypochlorite Catalyzed by
Easily Prepared Chiral Mn(III) Salen Complexes. J . Org. Chem.
1991, 56, 2296-2298.
(3) An tia n gin a l Effect. The antianginal effect was inves-
tigated in Sprague-Dawley rats under pentobarbital anes-
thesia as the inhibition of ST segment (T wave) elevation
induced by intracoronary administration of methacholine (5
µg). Systemic blood pressure was measured with a pressure
transducer in a femoral artery, and heart rate was measured
with a heart rate counter. Standard limb lead II of the
electrocardiogram was recorded on an ECG recorder. A poly-
(ethylene) tube was inserted into the coronary ostium through
the right carotid artery to a point near the aortic valve in order
to allow administration of methacholine into the coronary
arteries. Rats showing S wave elevation of over 0.15 mV were
used for this experiment. Compound 3 was dissolved in
distilled water and administered intraduodenally.
(10) Katoh, S.; Cho, H.; Sayama, S.; Kajimoto, Y.; Shibata, S.;
Mizushima, J .; Yamaki, T.; Uchida, I. WO 9502589.
(11) Compounds 10, 12, and 13 were two diastereomers at position
2 which were separated on a silica gel plate. The ED50 values
of the less polar diastereomers are shown in Table 1. The more
polar diastereomers of compounds 10 and 12 were inactive even
after injection at
a dose of 30 µg, while the more polar
diastereomer of compound 13 exhibited the same potency and
duration of action as the less polar one.
(12) Gericke, R.; Harting, J .; Lues, I.; Schittenhelm, C. 3-Methyl-
2H-1-benzopyran, Potassium Channel Activators. J . Med. Chem.
1991, 34, 3074-3085.
(13) Horie, T.; Kinjo, K.; Ueda, T. Studies on Pyridazine Derivatives
I. Synthesis and Antimicrobial Activity of 6-Substituted 3-Ami-
nopyridazine and its Sulfonamido Derivatives. Chem. Pharm.
Bull. 1962, 10, 580-591.
Ack n ow led gm en t. The authors wish to thank Mr.
Eiji Inagaki for the X-ray crystallographic analysis and
Mr. Ichiro Yamashita for his cooperation in the synthe-
sis of compounds. We also thank Mr. Yukiya Hirata,
Mr. Hisato Miyai, Mr. Atsunori Kanada, and Miss
Ayumi Irie for the pharmacological evaluations and Dr.
Tokuo Yamaki for his helpful advice on the pharmaco-
logical studies.
(14) In order to examine the structure-activity relationships of the
optically active compound and the racemate, the racemic com-
pound of 3 was prepared as mentioned before and found to have
an ED50 of 1.5 µg and a T1/2 of 1.8 min. Furthermore, compound
(3R,4S)-3, the optically active isomer of (3S,4R)-3, was synthe-
sized using the (R,R)-J acobsen reagent9 and shown to have one-
thirtieth of the activity of compound 3 itself.
(15) Baumgarth, M.; Bergmann, R.; Gericke, R.; Harting, J .; Lues,
I. J P 4300880A.
(16) It is speculated that nitric oxide released from nicorandil potently
relaxes coronary arteries.
(17) Wilson, C. Inhibition by Sulphonylureas of Vasorelaxation
Induced by K+ Channel Activators in vitro. J . Autonomic
Pharmacol. 1989, 9, 71-78.
(18) Cho, H.; Sayama, S.; Katoh, S.; Aisaka, K.; Uchida, I. WO
9513272.
(19) Rubinstein, H.; Skarbek, J . E.; Fener, H. Reactions of 3-Car-
boxyacryloyl-hydrazines and the Formation of Maleimides,
Isomaleimides, and Pyridazinones. J . Org. Chem. 1971, 36,
3372-3376.
(20) Izawa, T.; Kashiwabara, T.; Nakajima, S.; Ogawa, N. EP
0388528A.
Su p p or tin g In for m a tion Ava ila ble: IR spectra, 1H NMR
spectra, mass spectra, [R]D values, and elementary analysis
data for compounds 10-13, 15-67, 6-bromo derivatives, and
6-nitro derivatives and crystallographic data and table of
positional parameters, bond distances, and bond angles for
compounds 3 and 51 (55 pages). Ordering information is given
on any current masthead page.
Refer en ces
(1) Robertson, D. W.; Steinberg, M. I. Potassium Channel Modula-
tors: Scientific Applications and Therapeutic Promise. J . Med.
Chem. 1990, 33, 1529-1541.
J M960270L