Y. Xiong et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1870–1873
1873
0.5
0.4
0.3
0.2
0.1
0.0
**
80
70
60
50
40
30
20
10
0
7
6
5
4
3
2
1
0
**
**
VEH 0.1 0.3
Delta power
1
VEH 0.1
0.3
1
VEH 0.1
0.3
1
NREM bout duration
NREM bout number
Figure 3. Rat sleep study of compound 35. Data represent the sum total of sleep measures recorded 5 h after compound administration. It induces a statistically significant
increase in delta power (left figure), and a dose-dependent statistically significant increase in sleep consolidation, as indicated by the concomitant decrease in NREM bout
number (middle figure) and increase in NREM bout duration (right figure). ⁄P <0.05; ⁄⁄P <0.01 versus vehicle treated controls.
brain to plasma ratio of 1.32 at 0.3 mg/kg (Table 2). Compound 35
was thus 10 times more potent than the initial starting point 1 in
the DOI reversal assay. Further assessment of pharmacokinetics in
rat revealed this improvement was most likely the result of the
good oral bioavailability of 35 (47%), which had a much higher
exposure level than 1 (AUC 440 h ng/mL) (Table 2). Interestingly,
this greater bioavailability was observed despite a lack of improve-
ment in microsomal stability compared to 1 (T1/2 for 35 = 16 min in
rat liver microsomes). Given the excellent efficacy of 35 in the
in vivo DIO reversal assay, the imidazo[1,2-a]pyridine 8-acid core
was further examined to introduce substitutions to both the imid-
azole and pyridine ring portions (Table 3). Of note is 38, substi-
tuted with a nitrile group at the 3-position, it was the most
highly 5-HT2A selective compound among all the 5,6-fused bicyclic
heterocycles prepared. However, none of these substituted analogs
were more potent in the in vivo DIO reversal assay than 35.9 As a
result 35 was further evaluated in a sleep study at doses of 0.1,
0.3 and 1 mg/kg PO (Fig. 3). In this study, compound was adminis-
tered orally 6 h after lights on in the middle of the rat’s inactive
period (subjective night). Both delta power, a measure of deep
sleep, and sleep consolidation were analyzed. 35 significantly in-
creased delta power 1 h after dosing at 0.1 mg/kg compared to
vehicle treated controls, and the effect lasted 3–4 h following dos-
ing. In addition, 35 significantly and dose-dependently increased
sleep consolidation, as indicated by the decrease in non-rapid
eye movement (NREM) bout number and increase in NREM bout
duration.
a satisfactory margin (approximately 175-fold) between this calcu-
lated free fraction concentration and the IC50 from the hERG study
for this compound. However, we decided that further evaluation
would be prudent at this stage and so a cardiovascular assessment
in a telemeterized dog model was conducted, wherein no adverse
effects were observed on hemodynamic or ECG measures at doses
up to 30 mg/kg.
The identification of 35 with potent in vivo antagonist activity
demonstrated that improved exposure could be achieved with a
phenethylpiperazine linker if appropriate acid group cores were
identified and this compound was selected for further development.
References and notes
1. Abrams, J. K.; Johnson, P. L.; Hay-Schmidt, A. Neuroscience 2005, 133, 983.
2. Hoyer, D.; Clarke, D. E.; Fozard, J. R.; Hartig, P. R.; Martin, G. R.; Mylecharane, E.
J.; Saxena, P. R.; Humphery, P. P. Pharmacol. Rev. 1994, 46, 157.
3. Leysen, J. E. Curr. Drug Targets CNS Neuro Disord. 2004, 3, 11.
4. (a) Borbély, A. A.; Trachsel, L.; Tobler, I. Eur. J. Pharmacol. 1988, 156, 275–278;
(b) Monti, J. M.; Jantos, H. Eur. J. Pharmacol. 2006, 553, 163.
5. Teegarden, B. R.; Al Shamma, H.; Xiong, Y. Curr. Top. Med. Chem. 2008, 8, 969.
6. Xiong, Y.; Ullman, U.; Choi, J.; Cherrier, M.; Strah-Pleynet, S.; Decaire, M.; Dosa,
P. I.; Feichtinger, K.; Teegarden, B. R.; Frazer, J. M.; Yoon, W. H.; Shan, Y.;
Whelan, K.; Hauser, E. K.; Grottick, A. J.; Semple, G.; Al-Shamma, H. J. Med.
Chem. 2010, 53, 5696.
7. Venkatesan, A. M.; Agarwal, A.; Abe, T.; Ushirogochi, H.; Yamamura, I.; Ado, M.;
Tsuyoshi, T.; Dos Santos, O.; Gu, Y.; Sum, F.; Li, Z.; Francisco, G.; Lin, Y.-I.;
Petersen, P. I.; Yang, Y.; Kumagai, T.; Weiss, W. J.; Shlaes, D. M.; Knox, J. R.;
Mansour, T. S. J. Med. Chem. 2006, 49, 4623.
8. Xiong, Y.; Feichtinger, K.; Ren,
A S.; Ullman, B. Imidazo[1,2-a]pyridine
derivatives as modulators of the 5-HT2A serotonin receptor useful for the
treatment of disorders related thereto. PCT/US2008/009740, WO2009023253,
2009.
As a result of its excellent activity in the DOI reversal assay and
good CNS penetration, 35 was further profiled. Selectivity screen-
ing against a panel of 70 human GPCRs, ion channels and trans-
porters (CEREP) showed it had no binding of >50% of control at
9. Synthesis of 35: To a mixture of 2-aminonicotinic acid (0.69 g, 5.00 mmol) in
CH3CN (20 mL) was added bromoacetaldehyde dimethyl acetal (0.59 mL,
5.00 mmol). The resulting slurry was heated to 150 °C under microwave
irradiation for 2 h. The resulting precipitate was filtered off and washed with
CH3CN and hexane to afford H-imidazo[1,2-a]pyridine-8-carboxylic acid
(0.924 g) as a grey solid. Exact mass calculated calcd for C8H6N2O2: 162.04;
Found: LC–MS m/z = 163.1(M+H+). 1H NMR (400 MHz, DMSO-d6) d ppm 7.58–
7.69 (m, 1H), 8.15 (d, J = 2.27 Hz, 1H), 8.50 (dd, J = 7.45, 1.14 Hz, 1H), 8.56 (d,
J = 2.02 Hz, 1H), 9.20 (dd, J = 6.69, 1.14 Hz, 1H). To a solution of H-imidazo[1,2-
10
lM, on any target tested including dopamine receptors D1-5,
a1-adrenergic and
a
2-adrenergic receptors. CYP inhibition assays
using human liver microsomes revealed 35 was not an inhibitor
of any major CYP isoforms (1A2, 2C9, 2C19, 2D6 and 3A4; IC50
>40
sponse assay, 35 inhibited hERG channel function with an IC50 of
1.9 M. From these data, we calculated that there likely still re-
lM). However, in the patch clamp in a full concentration-re-
a]pyridine-8-carboxylic
difluorophenethyl)piperazine dihydrochloride (45.0 mg, 150
triethylamine (210 l, 1504
propylphosphonic acid anhydride solution (50 wt % in ethyl acetate, 183
acid
(36.6 mg,
226
l
mol),
1-(2,4-
mol), and
l
l
lmol) in DMF (0.75 mL) was added 1-
l
lL,
mained a significant margin between the hERG inhibition and
the plasma concentration required for efficacy. The latter was esti-
mated as 11 ng/mL based on the 45 min time point (close to the
Tmax) at the fully efficacious dose of 0.3 mg/kg in rat. This concen-
tration equated to approximately 33 nM. With the plasma protein
binding in human measured at 67.4%, this would give a free frac-
tion of ꢀ11 nM in vivo. Hence we adjudged there would likely be
0.301 mmol). The mixture was stirred for 2 h, quenched with water and
purified by HPLC to give 35 (33.0 mg) as a white solid. Exact mass calculated for
C
20H20F2N4O: 370.16; Found: LC–MS m/z = 371.4 (M+H+). 1H NMR (400 MHz,
chloroform-d6) d ppm 2.45–2.53 (m, 2H), 2.57–2.64 (m, 2H), 2.64–2.71 (m, 2H),
2.74–2.84 (m, 2H), 3.29–3.43 (m, 2H), 3.85–3.98 (m, 2H), 6.69–6.92 (m, 3H),
7.10–7.21 (m, 1H), 7.23–7.28 (m, 1H), 7.64 (d, J = 1.26 Hz, 1H), 7.69 (d,
J = 1.26 Hz, 1H), 8.18 (dd, J = 6.82, 1.26 Hz, 1H).
10. Cheng, Y. C.; Preusoff, W. H. Biochem. Pharmacol. 1973, 23, 3099.