Pyridopyrimidine based cannabinoid-1 receptor inverse agonists: Synthesis and biological evaluation

Article abstract of DOI:10.1016/j.bmcl.2009.03.005

The synthesis, SAR and binding affinities are described for cannabinoid-1 receptor (CB1R) specific inverse agonists based on pyridopyrimidine and heterotricyclic scaffolds. Food intake and pharmacokinetic evaluation of several of these compounds indicate

Full text of DOI:10.1016/j.bmcl.2009.03.005

Bioorganic & Medicinal Chemistry Letters 19 (2009) 2591–2594
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Pyridopyrimidine based cannabinoid-1 receptor inverse agonists: Synthesis
and biological evaluation
a
a
a
John S. Debenham a, , Christina B. Madsen-Duggan , Junying Wang , Xinchun Tong ,
Julie Lao b, Tung M. Fong b, Marie-Therese Schaeffer b, Jing Chen Xiao b, Cathy C. R.-R. Huang b,
Chun-Pyn Shen b, D. Sloan Stribling c, Lauren P. Shearman c, Alison M. Strack c, D. Euan MacIntyre c,
Jeffrey J. Hale a, Thomas F. Walsh a
*
a Department of Medicinal Chemistry, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
b Department of Metabolic Disorders, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
c Department of Pharmacology, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis, SAR and binding affinities are described for cannabinoid-1 receptor (CB1R) specific inverse
agonists based on pyridopyrimidine and heterotricyclic scaffolds. Food intake and pharmacokinetic eval-
uation of several of these compounds indicate that they are effective orally active modulators of CB1R.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 3 January 2009
Revised 3 March 2009
Accepted 4 March 2009
Available online 9 March 2009
Keywords:
Cannabinoid
CB1
Inverse agonist
Pyridopyrimidine
Obesity
The incidence of clinically severe obesity continues to increase
globally. In the United States 5% of the population is considered
morbidly obese.1 The estimated cost to the United States for all
obesity related issues in 2000 was a staggering $117 billion ($61
billion direct and $56 billion indirect).2 Obese patients respond
well to surgical interventions that modify the gastrointestinal tract
limiting food/nutritional intake.1 Unfortunately, in a study of
Medicare beneficiaries undergoing bariatric surgical procedures,
one out of 50 patients die within the first 30 days post surgery.3
Clearly, more conservative approaches for treatment are needed.
Inverse agonists of the cannabinoid-1 receptor (CB1R)4 have
been shown to be effective in reducing food intake with concomi-
tant weight loss in both human5 and animal6 studies. In our previ-
ous reports,7 we disclosed the SAR and lead optimization of a
screening hit containing a pyridine core arrayed by three hydro-
phobic domains. This was modified to 1 which effected reductions
in body weight (BW) gain and suppressed food intake (FI) in diet
induced obese (DIO) rats at 10 mg/kg (48% FI suppression and
ꢀ8 g BW change vs +7 g vehicle).
2.8 This compound showed similar binding affinity to 1 but was
markedly more brain penetrant in rats (4 h brain/plasma 2.7 vs
0.61). Cannabinoid-1 receptors are primarily located in the CNS5
therefore 2 had similar in vivo efficacy as 1 at one third of the dose
(Fig. 1). Additionally, the acute efficacy of 2 was on par with that of
MK-0364/taranabant which has been tested extensively in rodents
and humans (Fig. 1). MK-0364 dosed in rats at 3 mg/kg leads to a
49% FI suppression and ꢀ10 g BW change versus +10 g vehicle.9
Since 2 had low clearance in several of our safety assessment spe-
cies (rats and dogs, but not monkeys),8 we wanted to further opti-
mize drug candidates by maintaining in vivo efficacy while
decreasing half-life. Given that the heterobicyclic core of 2 showed
better efficacy at suppressing food intake relative to the monocy-
clic pyridine core of 1, we opted to pursue modifications to the
naphthyridinone core. Herein we describe the SAR and synthetic
efforts utilizing the generalized pyridopyrimidine core 3.10
The construction of the pyrido[2,3-d]pyrimidine core system
has been reviewed.11 Since CB1 inverse agonists often contain
three hydrophobic domains arrayed around a more polar core4
we envisioned a hydrophobic domain in the R1 position. In our
SAR efforts, amidines were engaged to position the hydrophobic
group. Addition of t-butylcarbamidine to the appropriately substi-
tuted ethyl 2-chloronicotinate in the presence of DBU at 135 °C
afforded the pyridopyrimidinone 5 directly (Scheme 1).
Removal of the difluorophenoxy ring of 1 and annulation of a
new ring to the core structure ultimately led to naphthyridinone
* Corresponding author. Tel.: +1 732 594 5497; fax: +1 732 594 2210.
E-mail address: john_debenham@merck.com (J.S. Debenham).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.03.005

2592
J. S. Debenham et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2591–2594
O
Cl
Cl
Cl
Cl
X
N
Cl
Cl
NH O
CN
NH
a
CN
O
N
+
H2N R1
N
6
Cl
N
R1
N
7
N
N
O
Cl
Cl
Cl
Cl
8a X= NH2
8b X= OH
8c X= Cl
1
2
Cl
b
R2
N
F
c
CB1R IC50 3.7 nM
CB1R IC50 7.5 nM
F
d
O
See Table 2 for R1 and R2
O
R2
N
N
N
R1
NC
N
H
X
Y
9
O
Cl
N
N
Cl
Cl
e
N
O
N
R1
O
N
O
N
Cl
CF3
N
N
N
8b
+
MK-0364 (taranabant) CB1R IC50 0.3 nM
3
N
N
N
N
Figure 1. Early Merck leads, MK-0364 and core structure 3.
11
10
Cl
Cl
Scheme 2. Reagents and conditions: (a) DBU, DMF, 130 °C, 50–66%; (b) MeSO3H,
H2O, 110 °C, 95%; (c) POCl3, toluene, 108 °C, 81%; (d) for amine nucleophiles, excess
amine, THF, rt-40 °C or for 35 4-fluorophenylboronic acid, Pd(PPh3)4, Na2CO3, DME,
H2O, EtOH, microwave heating 120 °C, 30%; (e) 3-(chloromethyl)-1,2,4-oxadiazole,
Cs2CO3, DMF, rt, 58% 11, 6% 10.
Cl
Cl
Cl
O
O
N
OEt
NH
N
Cl
N
4
5
Cl
Cl
Cl
Cl
Cl
a
Scheme 1. Reagents and conditions: (a) tert-butylcarbamidine hydrochloride, DBU,
DMF, 138 °C, 50%.
CN
Cl
X
12a X= CN
b
12b X= C(O)NH2
N
N
NH2
6
Cl
Cl
Alternatively, amidine addition to the 2-chloronicotinonitrile 6
affords the 4-aminopyridopyrimidine analog 8a which can then
be hydrolyzed to the pyridopyrimidinone 8b with methanesulfonic
acid in high yield (Scheme 2). As the 3-ethylcarboxylate group for
the starting material in Scheme 1 was prepared from hydrolysis of
the 3-cyano group, analogs could be prepared more expeditiously
and with greater diversity (both 4-amino and 4-hydroxy variants)
utilizing the general route depicted in Scheme 2. After hydrolysis of
the amino group, treatment of the resultant pyridopyrimidinone
with POCl3 in toluene produced a very reactive 4-chloro derivative
8c that was ready for nucleophilic displacement or Suzuki cross
coupling reactions. Exposure of 8c to an excess of the necessary
amine in THF produced a variety N-substituted analogs in excellent
yield. The effects of N- and O-substitution of the 3- and 4-positions,
respectively, were also examined. Alkylations were carried out by
treating the pyridopyrimidinone 8b to Cs2CO3 and the appropriate
alkylation agent as exemplified with the chloromethyl oxadiazole
(Scheme 2).
Cl
Cl
d
Cl
N
NH
N
c
N
O
O
N
N
N
OEt
R
Cl 13
Cl
14a R= OEt
14b R= NEt2
e-f
Scheme 3. Reagents and conditions: (a) NH4OH, dioxane, 100 °C, 95%; (b) H2SO4,
100 °C; (c) ClCOCO2Et, toluene, then POCl3, 100 °C, 40%; (d) isopropylamine, THF, rt,
88%; (e) KOH, THF, H2O, rt; (f) diethylamine, HOBT, EDAC, DIPEA, dimethylacet-
amide, 40 °C, 22%.
Cl
NH
N
O
N
In order to evaluate the effect of amides at the 2-position of the
pyridopyrimidine system, 6 was converted to the substituted 2-
aminonicotinamide as shown in Scheme 3. Acylation and cycliza-
tion with ethyl 2-chloro-2-oxoacetate followed by in situ chlorina-
tion with POCl3 provided 13 that was elaborated to the i-propyl
amino 14a. Saponification of the ester allowed for amide formation
as indicated to afford 14b.
The chlorine at the 4-position of 8c provided an opportunity for
elaboration of the bicyclic scaffold into a tricyclic core. The fusion
of the third ring at this site was readily achieved in two steps
(Scheme 4). Exposure of 8c to excess hydrazine provided hydrazide
15. This, in turn, was cyclized with either carbonyldiimidazole at
room temperature or trimethylorthoformate in refluxing toluene
forming the fused triazolone12 16 or triazole 17, respectively
(Scheme 4).
Cl
NH2
N
HN
N
N
N
a
b
16
Cl
Cl
Cl
N
N
N
15
N
Cl
N
N
17
Scheme 4. Reagents and conditions: (a) CDI, THF, CH2Cl2, 89%; (b) triethylortho-
formate, NMP, 130 °C, 48%.
boronic acids on the final step of the synthesis, thereby facilitating
the rapid assembly of analogs (Scheme 5). The pyridone ring of 19
was prepared by treating chloroacetophenone with dimethylform-
amide dimethylacetal to yield a vinylogous amide which was re-
acted with cyanoacetamide under basic conditions to generate
In order to more fully explore the effects of aryl substitution on
the newly formed heterotricyclic core, a Suzuki strategy was em-
ployed in which triazolone 21 could be reacted with a variety of

J. S. Debenham et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2591–2594
2593
increasing the bulk of R1 from methyl to i-propyl and then to t-bu-
tyl provided the most active compounds, showing over 300-fold
improvement to 6–7.4 nM for 30 and 5, respectively. Further elab-
oration of R1 to 4-chlorophenyl did not yield any additional
improvement in binding activity. It is of note that there was only
a small difference in potency where R2 was either amino or hydro-
xy (or its tautomer). The spread was only 1–5-fold, being most pro-
nounced (fivefold) for the t-butyl pair 30 and 31 where X2 was
hydrogen.
CN
O
Br
CN
O
a-b
O
c
N
N
H
H
Cl
Cl
Cl
20
18
19
NH
NH
N
N
Br
Ar
O
O
N
N
j
d-i
N
N
N
N
21
22
After optimization of R1, we turned out attention to the further
examination of R2 and substitution of the 3-position nitrogen with
R3 (Table 2). In our examples, the elaboration of R2 led to highly po-
tent compounds (<10 nM CB1R). The carbon linked 4-fluorophenyl
35 was the most potent at 0.6 nM. The dimethylamino 41, and hy-
droxyl fluorinated alkyl 42 were about 12-fold less active at about
9 nM CB1R. Piperazine 36, diethyl 37, t-butyl 38, and i-propylami-
no 39 all had similar potencies of 2–4 nM. O-linked derivatives at
R2 were also acceptable with oxadiazole 10 having an IC50 of
1 nM. In contrast, the N-linked oxadiazole 11 was 80-fold less ac-
Cl
Cl
Scheme 5. Reagents and conditions: (a) (CH3)2NCH(OCH3)2, DMF, 90 °C, 89%; (b) 2-
cyanoacetamide, DMF, NaOCH3, 95 °C, 51%; (c) NBS, dioxane, MeOH, rt, 88%; (d)
POCl3, toluene, 90 °C, 82%; (e) tert-butylcarbamidine hydrochloride, DBU, DMA,
microwave heating 135 °C, 58%; (f) MeSO3H, H2O, 110 °C, 92%; (g) POCl3, toluene,
110 °C, 90%; (h) hydrazine hydrate, THF, rt; (i) CDI, CH2Cl2, rt, 85%; (j) ArB(OH)2,
Pd(PPh3)4, Na2CO3, DME, H2O, EtOH, microwave heating, 120 °C, 9–37%.
19. Bromination with NBS provided 20 in 88% yield on a 100 g
scale. The remaining steps were similar to that described above.
Finally, the effect of replacement of aryl chlorides with cyano
groups (Scheme 6) was explored as these groups can be helpful
in reducing the log D values, potentially improving physicochemi-
cal properties such as solubility. Two palladium catalyzed methods
were utilized (Scheme 6). While the substrates were not identical,
we found that treatment with Zn(CN)2, Pd2(dba)3, dppf in slightly
aqueous DMF13 (conditions a) to be more robust and suitable for
scale up.
Binding affinities were determined using a standard protocol
and all compounds tested were found to be functional inverse ago-
nists of CB1R.14 In optimization to find an appropriate hydrophobic
domain R1 (Table 1), we found the methyl analogs 26 and 27 least
active at 2500 and 1500 nM CB1R, respectively. Not surprisingly,
Table 2
Binding affinity of compounds at the human CB1R and CB2R expressed as IC50 (nM)
Cl
Cl
R2
N
O
N
R3
R1
N
N
N
R1
N
Cl
Cl
Compound R2
R3
R1
CB1R:
CB2R
35
36
37
38
39
14b
40
41
42
10
4-F–Ph
–NPiperazine
–NEt2
–NHt-Bu
–NHi-Pr
–NHi-Pr
–OMe
—
—
—
—
—
—
—
—
—
—
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
0.63:9833
1.9:1800
2.2:2700
2.7:>2000
4.1:>2000
a or b
X1
Xn=CN
Xn=Br
NH
N
CONEt2 150:12,000
O
23 X1=CN, X2=H, X3=Cl 85%a
24 X1=Cl, X2=CN, X3=Cl 64%b
25 X1=Cl, X2=H, X3=CN 78%b
t-Bu
t-Bu
t-Bu
i-Pr
7.5:8400
8.5:1800
9.5:>2000
1.1:6300
N
–NMe2
–NHCH2CF2CH2OH
–OCH2(1,2,4-
oxadiazol-3yl)
—
N
N
X2
X3
11
–CH2(1,2,4-
i-Pr
82: 9800
Scheme 6. Reagents and conditions: (a) Zn(CN)2, Pd2(dba)3, dppf, DMF/H2O 99:1,
110 °C; (b) Pd(PPh3)4, 18-crown-6, dioxane, KCN, 90 °C.
oxadiazol-3yl)
Table 1
Table 3
Binding affinity of compounds at the human CB1R and CB2R expressed as IC50 (nM)
Binding affinity of compounds at the human CB1R and CB2R expressed as IC50 (nM)
Cl
R2
NH
N
N
Ar
O
N
N
N
R1
N
N
X2
Cl
X2
X3
R1
R2
X2
CB1R:CB2R
Compound
Ar
X2
X3
CB1R:CB2R
Compound
16
43
23
24
25
44
45
46
47
48
4-Cl-Ph
3-Cl-Ph
4-CN-Ph
4-Cl-Ph
4-Cl-Ph
4-MeO-Ph
4-CF3-Ph
4-Ac-Ph
4-NMe2-Ph
4-CN-3-Pyr
H
H
H
CN
H
H
H
H
H
Cl
Cl
Cl
Cl
CN
Cl
Cl
Cl
Cl
Cl
1.9:3800
34:2700
5.9:18,000
1.0:19,000
3.2:2400
3.0:891
1.1:9200
10:5800
28:770
26
27
28
29
30
5
31
32
33
34
Me
Me
OH
NH2
OH
NH2
OH
OH
NH2
NH2
OH
H
H
H
H
H
Cl
H
Cl
H
H
2500:>2000
1500:1100
130:7300
190:>2000
7.4:8600
6.0:5500
40:4900
11:5200
59:>2000
16:>2000
i-Pr
i-Pr
t-Bu
t-Bu
t-Bu
t-Bu
4-Cl-Ph
4-Cl-Ph
H
100:18,000
NH2

2594
J. S. Debenham et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2591–2594
Table 4
oral bioavailability and less brain penetration, yet only afforded a
small decrease in response. Cyano analog 23 has the shortest
half-life in the rat. In higher species, 23 also had a much shorter
half-life than 2 along with an unfortunate drop in bioavailability.
In summary, we have shown that both the heterobicyclic pyr-
ido[2,3-d]pyrimidine and heterotricyclic pyrido[3,2-e][1,2,4]triaz-
olo[4,3-c]pyrimidin-3(2H)-one core structures (typified by 42 and
16) can lead to potent and specific CB1R inverse agonists that are
effective in modulating feeding behavior to suppress both FI and
BW gain. Importantly, tricyclic 16 achieved similar in vivo efficacy
to 2 at 3 mg/kg oral dosing, but with a reduced half-life. Further
SAR studies and pharmacological evaluation of related heterobicy-
clic systems will be reported in due course.
Rat overnight (18 h) body weight change (g) and food intakea
Compound
D
BW vehicle
D
BW
Food intake
suppression (%)
(control)
compound
5
42
16
23
25
2
+5
+4
+5
+5
+6
+12
+1
21
39
50
36
25
68
ꢀ4
ꢀ9
ꢀ5
ꢀ2
ꢀ4
a
BW = body weight. All rats were dosed at 3 mg/kg. All p values were <0.05.
Table 5
Pharmacokinetic profiles (Monkey = Rhesus macaque)
References and notes
Compound (animal)
F (%)
T1/2 (h)
Clp (mL/min/kg)
Rat brain/plasma
0.25 h, 4 h
1. Buchwald, H.; Avidor, Y.; Braunwald, E.; Jensen, M. D.; Pories, W.; Fahrbach, K.;
Schoelles, K. J. Am. Med. Assoc. 2004, 292, 1724.
16 (rat)
23 (rat)
23 (dog)
23 (monkey)
2 (rat)
33
53
2.1
9.7
93
5.6
3.5
7.4
9.9
>8
12
4.0
24
5.3
12
0.14, 0.59
NA
NA
NA
0.9, 2.7
2. U.S. Department of Health and Human Services. The Surgeon General’s call to
action to prevent and decrease overweight and obesity. [Rockville, MD]: U.S.
Department of Health and Human Services, Public Health Service, Office of the
Surgeon General; [2001]. Available from: US GPO, Washington.
3. The rates of 30-day, 90-day and 1 year mortality were 2.0%, 2.8%, and 4.6%,
respectively: Flum, D. R.; Salem, L.; Dellinger, E. P.; Cheadle, A.; Chan, L. J. Am.
Med. Assoc. 2005, 294, 1903.
4. For a leading review of reported compounds see: Jagerovic, N.; Fernandez-
Fernandes, C.; Goya, P. Curr. Top. Med. Chem. 2008, 8, 205.
5. Després, J.-P.; Golay, A.; Sjöström, L. New Engl. J. Med. 2005, 353, 2121.
6. Cota, D.; Marsicano, G.; Tschöp, M.; Grübler, Y.; Flachskamm, C.; Schubert, M.;
Auer, D.; Yassouridis, A.; Thöne-Reinecke, C.; Ortmann, S.; Tomassoni, F.;
Cervino, C.; Nisoli, E.; Linthorst, A. C. E.; Pasquali, R.; Lutz, B.; Stalla, G. K.;
Pagotto, U. J. Clin. Invest. 2003, 112, 423.
7. (a) Meurer, L. C.; Finke, P. E.; Mills, S. G.; Walsh, T. F.; Toupence, R. B.;
Debenham, J. S.; Wang, J.; Tong, X.; Fong, T. M.; Lao, J.; Schaeffer, M.-T.; Chen, J.;
Shen, C.-P.; Stribling, D. S.; Shearman, L. P.; Strack, A. M.; MacIntyre, D. E.; Van
der Ploeg, L. H. T.; Goulet, M. T. Bioorg. Med. Chem. Lett. 2005, 15, 645. and 1755;
(b) Madsen-Duggan, C.; Debenham, J. S.; Walsh, T. F.; Toupence, R. B.; Huang, S.
X.; Wang, J.; Tong, X.; Lao, J.; Fong, T. M.; Schaeffer, M.-T.; Xiao, J. C.; Shen, C.-P.;
Stribling, D. S.; Shearman, L. P.; Strack, A. M.; Van der Ploeg, L. H. T.; Goulet, M.
T. Bioorg. Med. Chem. Lett. 2007, 17, 2031.
8. Debenham, J. S.; Madsen-Duggan, C. B.; Walsh, T. F.; Wang, J.; Tong, X.; Doss, G.
A.; Lao, J.; Fong, T. M.; Schaeffer, M.-T.; Xiao, J. C.; Huang, C. R.-R. C.; Shen, C.-P.;
Feng, Y.; Marsh, D. J.; Stribling, D. S.; Shearman, L. P.; Strack, A. M.; MacIntyre,
D. E.; Van der Ploeg, L. H. T.; Goulet, M. T. Bioorg. Med. Chem. Lett. 2006, 16, 681.
9. Fong, T. M.; Guan, X.-M.; Marsh, D. J.; Shen, C.-P.; Stribling, D. S.; Rosko, K. M.;
Lao, J.; Yu, H.; Feng, Y.; Xiao, J. C.; Van der Ploeg, L. H. T.; Goulet, M. T.;
Hagmann, W. K.; Lin, L. S.; Lanza, T. J., Jr.; Jewell, J. P.; Liu, P.; Shah, S. K.; Qi, H.;
Tong, X.; Wang, J.; Xu, S. S.; Francis, B.; Strack, A. M.; MacIntyre, D. E.;
Shearman, L. P. J. Pharm. Exp. Ther. 2007, 321, 1013.
tive. Increasing the hydrophilicity of R1 by installation of diethyl-
amide 14b showed a 37-fold drop in binding affinity relative to
39 demonstrating the preference for more hydrophobic groups at
this position.
Annulation of the triazolone ring between the 3- and 4-posi-
tions was also very well tolerated in the binding assay (Table 3).
4-Substituted phenyl groups were critical for good activity at
CB1R: 4-chloro 16, 4-OMe 44, 4-CF3 45 were all very attractive at
1–3 nM CB1R. When the 4-chloro was moved to the 3-position
(43), an 18-fold drop in potency to 34 nM was observed. Exchange
of chloro with the cyano group resulted in little difference in bind-
ing affinity for the cyano analogs 23, 24, and 25. 4-Acetyl 46 at 10
nM was also reasonably well tolerated compared to 4-chloro 16. As
the aryl group (Ar) became substantially more polar we saw a 17-
fold drop in activity to 100 nM CB1R for 4-cyano-pyridine 48. Of
note was the des-oxy variant 17 (Scheme 4), where loss of the oxy-
gen only resulted in a fourfold drop in activity (8.0 nM CB1R:3400
CB2R).
10. All yields provided are for unoptimized reactions.
11. Sako, M.. In Science of Synthesis; Yamamoto, Y., Ed.; Thieme, 2004; Vol. 16, pp
1155–1267.
Many of the compounds described herein were very active at
CB1R and were highly selective against CB2R (100–19,000-fold).
Several compounds were evaluated in vivo to determine their
anorexigenic effects in DIO rats (Table 4). All compounds were
dosed orally at 3 mg/kg and rats were monitored for 18 h to deter-
mine changes in body weight (BW) and ability to suppress food in-
take (FI) relative to vehicle control.8 Both bicyclic 5 and 42 were
active in suppressing food intake (21–39%, respectively) and reduc-
ing overnight BW relative to control. Tricyclic 16 was 3–5-fold
more potent than 5 and 42 at CB1R and showed the strongest re-
sponse with a 50% suppression of FI. Tricyclic 23 and 25 were also
effective at acute suppression of overnight FI (36–25%,
respectively).
12. Unoptimized
procedure for 16: 5-tert-Butyl-8-(2-chlorophenyl)-9-(4-
To 8c
chlorophenyl)pyrido[3,2-e][1,2,4]triazolo[4,3-c]pyrimidin-3(2H)-one.
where R1 = t-Bu (252 mg, 0.569 mmol) in THF (7 mL) was added hydrazine
hydrate (0.7 mL, 14.4 mmol). The reaction aged at rt for about 25 min and was
concentrated. The residue was diluted with EtOAc, washed with brine, dried
(Na2SO4), filtered and concentrated to afford 15 which was used without
further purification. To 15 (assumed 0.569 mmol) in CH2Cl2 (10 mL) was added
1,10-carbonyldiimidazole (420 mg, 2.59 mmol) and the reaction aged about
18 h at rt. The reaction was diluted with EtOAc, washed with brine and
concentrated. The residue was purified via flash chromatography, on silica gel,
gradient eluted with 0–10% EtOAc in CH2Cl2 affording 16 (235 mg, 89%). HPLC/
MS: 464.0 (M+1), 466.0 (M+3); Rt = 3.75 min (Waters C18 XTerra 3.5 lm
3.0 ꢁ 50 mm column with gradient 10:90–100 v/v CH3CN/H2O + v 0.05% TFA
over 3.75 min then hold at 100 CH3CN + v 0.05% TFA for 1.75 min; flow rate
1.0 mL/min, UV wavelength 254 nm). 1H NMR (500 MHz, CDCl3): d 10.27 (s, 1
H); 8.47 (s, 1 H); 7.45–7.42 (m, 1 H); 7.33–7.24 (m, 3 H); 7.22 (d, J = 8.35 Hz, 2
H); 7.13 (d, J = 8.35 Hz, 2 H); 1.68 (s, 9 H).
Pharmacokinetic properties for select compounds are shown in
Table 5. The potent in vivo action of previously reported 2 on the
modulation of feeding behavior is the result of extended drug
exposure over time, as reflected by its long half-life, and its favor-
able brain/plasma ratio. Tricyclic 16 shows a shorter half-life, less
13. Maligres, P.; Waters, M. S.; Fleitz, F.; Askin, D. Tetrahedron Lett. 1999, 40, 8193.
14. The reported binding results were an average of 2–8 independent
determinations (each done in replicate) which were normally within 50% of
the average value. For both the binding and functional assay conditions, see:
Felder, C. C.; Joyce, K. E.; Briley, E. M.; Mansouri, J.; Mackie, K.; Blond, O.; Lai, Y.;
Ma, A. L.; Mitchell, R. L. Mol. Pharmacol. 1995, 48, 443.