Synthesis and evaluation of (2-phenethyl-2H-1,2,3-triazol-4-yl)(phenyl)methanones as Kv1.5 channel blockers for the treatment of atrial fibrillation

Article abstract of DOI:10.1016/j.bmcl.2006.06.001

A series of novel (2-phenethyl-2H-1,2,3-triazol-4-yl)(phenyl)methanones were prepared and examined for utility as Kv1.5 channel blockers for the treatment of atrial fibrillation.

Full text of DOI:10.1016/j.bmcl.2006.06.001

Bioorganic & Medicinal Chemistry Letters 16 (2006) 4629–4632
Synthesis and evaluation of (2-phenethyl-2H-1,2,3-
triazol-4-yl)(phenyl)methanones as Kv1.5 channel blockers for the
treatment of atrial fibrillation
Benjamin E. Blass,* Keith Coburn, Wenlin Lee, Neil Fairweather, Andrew Fluxe,
Shengde Wu, John M. Janusz, Michael Murawsky, Gina M. Fadayel, Bin Fang,
Michelle Hare, Jim Ridgeway, Ron White, Chris Jackson, Laurent Djandjighian,
Richard Hedges, Fred C. Wireko and Amanda L. Ritter
Procter & Gamble Pharmaceuticals, Health Care Research Center, 8700 Mason Montgomery Road, Mason, OH 45040, USA
Received 1 May 2006; revised 31 May 2006; accepted 1 June 2006
Available online 21 June 2006
Abstract—A series of novel (2-phenethyl-2H-1,2,3-triazol-4-yl)(phenyl)methanones were prepared and examined for utility as Kv1.5
channel blockers for the treatment of atrial fibrillation.
Ó 2006 Elsevier Ltd. All rights reserved.
Atrial fibrillation (AF), a common cardiac arrhythmia
that afflicts 2–3 million Americans, is associated with
an increased risk of thromboembolism, stroke, and a
two fold increase in mortality.1 Available treatments
are limited to implantable atrial defibrillators and class
III anti-arrhythmic agents, such as dofetilide.2 Class
III anti-arrhythmic agents increase myocardial refracto-
riness by blocking ion channels responsible for repolar-
ization, resulting in prolongation of the action potential
duration (APD). These drugs, however, act on ion chan-
nels (e.g., IKr) that are found in both the atria and ven-
tricles. Blockade of potassium ion channels in the
ventricles (e.g., hERG) leads to a prolongation of the
QT interval and an increased propensity for life-threat-
ening ventricular arrhythmias (torsade de pointes). As
part of our ongoing efforts to develop an effective ther-
apy for AF, we have been exploring the utility of
Kv1.5 blockade. This channel and its associated current
(IKur) are found only in the atrial chambers of the
heart, suggesting that selective blockade of this channel
would provide relief from AF, without the associated
risk of ion channel blockade in the ventricle.3
Herein, we wish to report the development of a series of
functionalized 1,2,3-triazoles as blockers of the Kv1.5
channel. Members of this class of compounds have been
identified as adenosine antagonists, oxalic acid antago-
nists, metalloprotease inhibitors, antibacterials, b-lacta-
mase inhibitors, antivirals, and anticonvulsants.4 We
have recently found that this scaffold also has utility in
the blockade of the Kv1.5 channel. Specifically, 2,4-di-
substituted-1,2,3-triazoles (1) have been prepared and
examined for their ability to block the Kv1.5 channel
and increase the atrial effective refractory period
(AERP) for the treatment of atrial fibrillation. The ini-
tial rationale for the design of this class of compounds
was the Icagen benchmark ICA-32 (Fig. 1), a selective
Kv1.5 blocker (IC50 = 132 nM) (Scheme 1).
A series of analogs was readily prepared in a two-step
process from the appropriate phenyl-ketoacetylene (2).
O
MeO
O
N
N
N
N
ICA-32
Kv1.5 IC50 = 137 nM
S
1
O
Me
R
Keywords: Atrial fibrillation; Kv1.5 ion channel; 1,2,3-Triazole.
*
Me
Corresponding author. Tel.: +1 513 622 3797; fax: +1 513 622
4396; e-mail: bblass2@fuse.net
Figure 1. ICA-32 and a proposed 1,2,3-triazole lead structure.
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.06.001

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B. E. Blass et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4629–4632
O
O
O
O
2
N
N
Na2CO3, DMA
TMSN3, DMA
110 oC
N
NH
R
R
R
Cl
N
N
3
1
O
Scheme 1. Synthesis of 2,4-substituted-1,2,3-triazoles.
Thus, treatment of acetylene (2) with TMS azide in
dimethylacetamide at 110 °C established the 1,2,3-tria-
zole core (3) via a 2 + 3 cycloaddition reaction. Alkyl-
ation with 4-methoxyphenethyl chloride in the
presence of sodium carbonate and dimethyl acetamide
provided the desired products (1, see Table 1).5
Since alkylation of the 1,2,3-triazole intermediate 3
could potentially occur at any of the three nitrogens,
an independent synthesis of the 1,2,3-triazole core struc-
ture that did not require alkylation of the triazole was
also examined (Scheme 2). Thus, conversion of 4-meth-
oxyphenethyl alcohol to the azide with triphenyl phos-
Table 1. Representative examples of the synthesis of (2-phenethyl-2H-
1,2,3-triazol-4-yl)(phenyl)methanones and their blockade of Kv1.5
O
O
N
N
R
N
phine,
diphenyl
phosphoryl
azide,
and
1
diisopropylazodicarboxylate, followed by cycloaddition
with acetylene 4, provided 5, an isomer of the previously
described material.6 The 1,4-orientation of this isomer
was later confirmed by single crystal X-ray
crystallography.7
Entry
R
% Yield % Yield % blockade
step 1
step 2
Kv1.5 @ 1 lM
1a
1b
1c
1d
1e
1f
2-Cl
51
79
38
47
43
68
94
33
16
53
33
57
18
52
22
87
17
22
84
85
86
88
90
97
99
0
4-OCH3
4-Cl
4-Et
While the synthesis of this alternative isomer does ex-
clude the possibility that the Kv1.5 active compounds
are 1,4-disubstituted triazoles, it still leaves open the
two other possible isomers. Single crystal X-ray struc-
tures of several analogs from the alkylation series were
obtained, all of which displayed the substituents about
3,4-Di-Cl
3,4-Di-CH3
4-i-Pr
1g
1h
1i
4-NMe2
2-OMe-4-NMe2 83
N
O
N
N
1) Ph2P(O)N3, DIAD, PPh3, THF
OH
2) DMA,100 oC
O
O
O
5
4
Scheme 2. Synthesis of 1,4-disubstituted triazole and associated X-ray structure.
Cl
Cl
O
O
N
N
N
N
O
N
N
O
Figure 2. Selected X-ray structures of Kv1.5 blockers.

B. E. Blass et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4629–4632
4631
5. Typical Experimental Procedure: Step 1: 1,2,3-triazole ring
formation: 1,2,3-triazole: 1-(3,4-dimethylphenyl) prop-2-
yn-1-one (1.0 g, 6.3 mmol) was dissolved in 63 ml DMA
and trimethylsilyl azide (0.874 ml, 7.59 mmol, 1.2 equiv)
was added. The reaction mixture was then heated to 110 °C
and monitored for loss of the alkyne. When the starting
alkyne was consumed, the reaction mixture was cooled to
room temperature and the solvent was removed under
reduced pressure. The residual material was then purified via
normal phase chromatography with a hexane and ethyl
acetate gradient to yield 865 mg (68%) of the desired product.
Step 2: Alkylation of the 1,2,3-triaozles: (3,4-dimethylphe-
nyl)(2H-1,2,3-triazol-4-yl)methanone (1.0 g, 4.97 mmol) and
sodium carbonate (1.05 g, 0.99 mmol, 2.0 equiv) were
dissolved in 50 ml of DMA and stirred briefly. 4-Methoxy-
phenethylchloride (0.86 g, 763 lL, 5.47 mmol, 5.07 mmol,
1.02 equiv) was added and the reaction mixture was stirred at
room temperature while monitoring for loss of the starting
materials. When the reaction was complete, the solvent was
removed under reduced pressure, and the residual material
was purified by chromatography with a hexane and ethyl
acetate gradient to yield 869 mg (52%) of the desired product.
Data from Table 1: Entry 1 (1H NMR, 300 MHz, CD3OD): d
3.22 (t, 2H, J = 6.8 Hz), 3.76 (s, 3H), 4.69 (t, 2H, J = 7.0 Hz),
6.80 (d, 2H, J = 6.6 Hz), 7.01 (d, 2H, J = 6.7 Hz), 7.40 (m,
2H), 7.51 (m, 2H), 8.18 (s, 1H). (M+H+) 342. Entry 2 (1H
NMR, 300 MHz, CD3OD): d 3.26 (t, 2H, J = 6.9 Hz), 3.75 (s,
3H), 3.91 (s, 3H), 4.78 (t, 2H, J = 6.9 Hz), 6.83 (d, 2H,
J = 6.6 Hz), 7.0 (d, 2H, J = 7.0 Hz), 7.06 (d, 2H, J = 8.6 Hz),
8.08 (d, 2H, J = 8.9 Hz), 8.17 (s, 1H). (M+H+) 338. Entry 3
(1H NMR, 300 MHz, CD3OD): d 3.27 (t, 2H, J = 6.8 Hz),
3.76 (s, 3H), 4.80 (t, 2H, J = 6.8 Hz), 6.85 (d, 2H, J = 6.6 Hz),
7.06 (d, 2H, J = 8.6 Hz), 7.50 (d, 2H, J = 6.7 Hz), 8.06 (d, 2H,
J = 6.7 Hz), 8.24 (s, 1H). (M+H+) 342. Entry 4 (1H NMR,
300 MHz, CD3OD): d 1.29 (t, 3H, J = 7.2 Hz), 2.73, (q, 2H,
J = 6.9 Hz), 3.24 (t, 2H, J = 6.5 Hz), 3.72 (s, 3H), 4.75 (t, 2H,
J = 6.9 Hz), 6.81 (d, 2H, J = 8.5 Hz), 7.03 (d, 2H,
J = 8.5 Hz), 7.31 (d, 2H, J = 8.2 Hz), 7.98 (d, 2H, 8.3 Hz),
8.19 (s, 1H). (M+H+) 336. Entry 5 (1H NMR, 300 MHz,
CD3OD): d 3.29 (t, 2H, J = 6.8 Hz), 3.77 (s, 3H), 4.83 (t, 2H,
J = 7.0 Hz), 6.86 (d, 2H, J = 6.5 Hz), 7.08 (d, 2H,
J = 6.7 Hz), 7.68 (d, 1H, J = 8.4 Hz), 8.03 (dd, 1H, J = 1.9,
8.37 Hz), 8.29 (s, 1H), 8.32 (d, 1H, J = 2.0 Hz). (M+H+) 376.
Entry 6 (1H NMR, 300 MHz, CD3OD): d 2.36 (s, 3H), 2.39,
(s, 3H), 3.27 (t, 2H, J = 6.6 Hz), 3.77 (s, 3H), 4.78 (t, 2H,
J = 6.9 Hz), 6.84 (d, 2H, J = 9.7 Hz), 7.07 (d, 2H,
J = 8.4 Hz), 7.27 (d, 1H, J = 8.1 Hz), 7.83 (d, 1H, 8.3 Hz),
7.90 (s, 1H), 8.20 (s, 1H). (M+H+) 336. Entry 7 (1H NMR,
300 MHz, CD3OD): d 1.38 (d, 6H, J = 7.4 Hz), 3.07 (m, 1H,
J = 7.2 Hz), 3.31 (t, 2H, J = 6.3 Hz), 3.81 (s, 3H), 4.82 (t, 2H,
J = 6.5 Hz), 6.91 (d, 2H, J = 8.7 Hz), 7.12 (d, 2H,
J = 8.1 Hz), 7.41 (d, 2H, J = 8.1 Hz), 8.04 (d, 2H, 7.9 Hz),
8.26 (s, 1H). (M+H+) 350. Entry 8 (1H NMR, 300 MHz,
CD3OD): d 3.13 (s, 3H), 3.27 (t, 2H, J = 6.6 Hz), 3.77 (s, 3H),
4.78 (t, 2H, J = 6.9 Hz), 6.74 (d, 2H, J = 9.3 Hz), 6.85 (d, 2H,
J = 8.7 Hz), 7.06 (d, 2H, J = 8.7 Hz), 8.02 (d, 2H, 9.3 Hz),
8.10 (s, 1H). (M+H+) 351. Entry 9 (1H NMR, 300 MHz,
CD3OD): d 3.11 (s, 6H), 3.26 (t, 2H, J = 6.8 Hz), 3.76 (s, 3H),
3.79 (s, 3H), 4.70 (t, 2H, J = 7.0 Hz), 6.30 (s, 1H), 6.33 (d, 2H,
J = 6.5 Hz), 6.82 (d, 2H, J = 6.6 Hz), 7.05 (d, 1H,
J = 6.7 Hz), 7.45 (d, 1H, J = 8.8 Hz) 7.97 (s, 1H). (M+H+)
381.
the triazole in a 2,4-orientation, verifying the structural
assignment of the active series (Fig. 2).8
Initial screening of this class of compounds was accom-
plished by whole-cell patch-clamp electrophysiology to
determine channel block in LTK cells expressing the
Kv1.5 channel.9 Results for some representative exam-
ples are shown in Table 1. From this data, one can con-
clude that substitution in the 4-position of the
acetophenone-derived portion of the scaffold is highly
favored. Increased lipophilicity is well tolerated (e.g.,
1g and 1h), but the difference between electron donating
and electron withdrawing is not substantial. Substitu-
tion in the 2-position of the same scaffold, however, ap-
pears to be detrimental to the desired activity. This is
especially clear in the comparison of entries 1h and 1i,
as the simple addition of a methoxy substituent in the
2-position eliminates all of the desired activity. Interest-
ingly, 1,4-regioisomer 5 showed no activity.
Of this set, entry 1f was selected for further progression
based on its selectivity for Kv1.5 over other channels.
The Kv1.5 blockade IC50 was 294 nM. Significantly de-
creased potency was observed at other related channels,
such as hERG channel (>50 lM), Kv1.3 channel
(10.1 lM), and the L-type calcium channel (26 lM). In
vivo efficacy was demonstrated after a 15 min infusion
of 30 mg/kg in an anesthetized pig model. An increase
of 12% in the atrial effective refractory period (AERP)
was observed, and the ventricular effective refractory
period (VERP) remained unchanged. Control experi-
ments showed no changes in AERP.
In summary, we have developed a new class of selective
Kv1.5 channel blockers, which demonstrate atrial selec-
tive prolongation of the effective refractory period in a
pig model of arrhythmic events.
References and notes
1. (a) Kannel, W. B.; Wolf, P. A.; Benjarmin, E. J.; Levy, D.
Am. J. Cardiol. 1998, 82, 2N; (b) Pratt, C. M.; Moye, L. A.
Am. J. Cardiol. 1990, 65, 20B; (c) Waldo, A. L.; Camm, A.
J.; Deruyther, H. Lancet 1996, 348, 7; (d) Tomasell, G.
Heart Drug 2001, 1, 183.
2. (a) Cross, P. E.; Arrowsmith, J. E.; Thomas, G. N.; Gwilt,
M.; Burges, R. A.; Higgins, A. J. Med. Chem. 1990, 33,
1151; (b) Lenz, T. L.; Hilleman, D. E. Pharmacotherapy
2000, 20(7), 776.
3. (a) Wang, Z.; Fermini, B.; Nattel, S. Circ. Res. 1993, 73,
1061; (b) Li, G. R.; Feng, J.; Wang, Z.; Fermini, B.; Nattel,
S. Circ. Res. 1996, 78, 907; (c) Purerfellner, H. Curr. Med.
Chem. CV & H Agents 2004, 2, 79.
4. Cappellacci, L.; Franchetti, P.; Grifantini, M.; Messini, L.;
Lucacchini, A.; Martini, C. XIIIth Int. Symp. Med. Chem.
1994, P13; Sankyo, K.K. JP07017861-A; Kohn, E.; Liotta,
L. A. WO9507695-A1; Adams, A. D.; Heck, J. V.
US5350746-A; Im, C.; Maiti, S. N.; Micetich, R. G.;
Daneshtalab, M.; Atchison, K.; Phillips, O. A. J. Antibiot.
1994, 47, 1030; Alvarez, R.; Velazquez, S.; San Felix, A.;
Aquaro, S.; Clercq, E. de; Perno, C. F. J. Med. Chem. 1994,
37, 4185; Palhagen, S.; Canger, R.; Henriksen, O.; van
Parys, J. A.; Riviere, M. E.; Karolchyk, M. A. Epilepsy Res.
2001, 43, 115.
6. Experimental conditions: 1-(2-azidoethyl)-4-methoxy ben-
zene: 4-methoxyphenethyl alcohol (2.65 g, 17.4 mmol, 1.0
equiv) and triphenyl phosphine (4.57 g, 17.4 mmol, 1.0
equiv) were dissolved in 100 ml of dry THF under a nitrogen
atmosphere, the reaction mixture was stirred briefly, and then
diisopropylazodicarboxylate (3.87 g, 3.78 ml, 19.2 mmol, 1.1
equiv) was added. The reaction mixture was stirred for 5 min,

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B. E. Blass et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4629–4632
diphenylphosphoryl azide (5.27 g, 19.2 mmol, 1.1 equiv) was
ments, Foster City,CA). Ltk-cells overexpressing Kv1.5
channels were cultured for 24–72 h, induced to express
Kv1.5 channels by 24 h incubation with 2 lM dexameth-
asone prior to use for patch clamp studies. Small, spherical
cells approximately 10 lm in diameter were used for all
patch recordings. Electrodes were made from TW-150F
glass capillary tubes (World Precision Instruments, New
Haven, CT) and had resistances of 1.5–3.0 MX when filled
with internal solution containing: 110 mM KCl, 5 mM
K2ATP, 5 mM K4BAPTA, 1 mM MgCl2, and 10 mM
Hepes, adjusted to pH 7.2 with KOH. The external solution
contained: 130 mM NaCl, 4 mM KCl, 1.8 mM CaCl2,
1 mM MgCl2, 10 mM Hepes, and 10 mM glucose, adjusted
to pH 7.4 with NaOH. Series resistance was compensated
following rupture of the seal. Currents were sampled at
1 KHz and filtered at 500 Hz. Cells were pulsed (0.2 Hz) to
+60 mV for 1 s, from a holding potential of À70 mV. After
stable control currents were obtained, inhibitors were
perfused onto the cells at increasing concentrations until
maximal inhibition was obtained for a given concentration.
Whole-cell patch-data were analyzed using Clampfit 8.0 in
pCLAMP software (Axon Instruments). IC50 values for
compounds were determined by nonlinear regression anal-
ysis using GraphPad Prism software (San Diego,CA).
Single point screening determinations were determined by
comparing control current amplitudes at the end of the
depolarizing pulses to maximally inhibited current ampli-
tudes at inhibitor concentrations of 1 lM.
added, and the reaction mixture was stirred for an additional
24 h. The solvents were then removed under reduced
pressure, and the residual material was purified by chroma-
tography with 7:1 hexane/ethyl acetate (2.22 g, 72%). (1H
NMR, 300 MHz, CDCl3): d 2.85 (t, 2H, J = 6.6 Hz), 3.47 (t,
2H, J = 6.9 Hz), 3.78 (s, 3H), 6.86 (d, 2H, J = 8.3 Hz), 7.15 (d,
2H, J = 8.7 Hz). (M+H+) 178. (1-(4-Methoxyphenethyl)-
1H-1,2,3-triazol-4-yl)(3,4-dimethylphenyl)methanone:
4-
methoxyphenethyl azide (60 mg, 0.34 mmol) and 1-(3,4-
dimethylphenyl)prop-2-yn-1-one (53.5 mg, 0.34 mmol) were
dissolved in 1.0 ml of dimethylacetamide and the reaction
mixture was heated to 100 °C. After 48 h, the reaction
mixture was cooled, the solvent was removed under reduced
pressure, and the residue was purified by reverse phase HPLC
(0.5% TFA in acetonitrile/H2O) to yield 76 mg (67%) of a
colorless oil. (1H NMR, 300 MHz, CD3OD): d 2.37 (s, 3H),
2.40, (s, 3H), 3.20 (t, 2H, J = 6.1 Hz), 3.75 (s, 3H), 4.72 (t, 2H,
J = 6.4 Hz), 6.88 (d, 2H, J = 8.7 Hz), 7.09 (d, 2H,
J = 7.9 Hz), 7.30 (d, 1H, J = 8.4 Hz), 7.86 (d, 1H, 7.9 Hz),
7.88 (s, 1H), 8.29 (s, 1H). (M+H+) 336.
7. Cambridge Crystallographic Data Centre reference number
CCDC 609610.
8. Cambridge Crystallographic Data Centre reference num-
bers CCDC 608957 and CCDC 608958.
9. Whole-cell Kv1.5 current recordings were made at room
temperature via the gigaseal patch clamp technique using
Axopatch-1D and Axopatch 200B amplifiers (Axon Instru-