650
L. C. Meurer et al. / Bioorg. Med. Chem. Lett. 15 (2005) 645–651
did not further improve binding (IC50 = 1.5 and
1.8 nM). In the hope of improving solubility, the 2-benz-
yloxy group was also replaced with two alkoxy moieties
as shown in Table 2. Interestingly, the smaller n-butyl
group (17a–c) gave only moderately diminished results
and the isosteric cyclohexylmethyl showed comparable
or better results than the benzyl compound (17b,d, and
4b; IC50 = 17, 3.4, and 7 nM). This implied that the
receptor interaction in this area was simply binding to
a lipophilic pocket without a direct aromatic interaction.
reduction in food intake at any of the doses as seen with
1. However, by 18 h post-dosing, the 10 mg/kg dose
afforded a cumulative, but non-significant (p > 0.05),
22% food intake reduction and a dose-dependent weight
loss of 1 g compared to an 8 g gain for vehicle treated
animals (p < 0.05). These results suggested that the slow
CNS exposure, as evident from the B/P ratio experi-
ment, prevented an immediate food intake effect. A simi-
lar feeding study with the slightly less potent 16c
afforded a cumulative 16% reduction in food intake at
10 mg/kg (p > 0.05), but did not give a net weight loss
(5 g gain vs an 11 g gain for vehicle). The results with
Removal of the 2-benzyloxy moiety was studied in the
2-chloro (19a–d, Table 3) and des-chloro-3-amido
(20a–d, Table 3) series and resulted in overall decreased
affinity. The 3-propyl and 3-hexyl amides 19b,c, and 20b
were moderately active (IC50 = 52, 58, and 65 nM,
respectively); however, the N-piperidinyl amides 19d
and 20d and the isosteric cyclohexyl amide 20c
(IC50 = 400, 480, and 210 nM, respectively) were sur-
prisingly inactive compared to 1 and the benzyloxy
derivatives discussed above. The secondary amides 19a
and 20a were also comparatively inactive.
16c were consistent with its poorer PK profile (AUCnom
=
5.2 lM h kg/mg; Clp = 5.8 mL/min/kg, Vdss = 0.4 L/kg;
t1/2 = 2.5 h), lower oral absorption (F = 12%), and
slower brain penetration (B/P ratio = 0.01–0.06 at
0.25–4 h).
5. Conclusions
The finding that both the 2- and 3-amido pyridine ana-
logs were only moderately potent hCB1 receptor inverse
agonists was disappointing based on the similarity to the
Sanofi compound 1. This might be a result of the addi-
tional ring atom slightly changing the relative orienta-
tion of the three pyridine substituents relative to the
proposed nitrogen interaction, and/or the pyridine nitro-
gen did not have an equivalently effective receptor inter-
action as the pyrazole nitrogen due to electronic
differences, and/or the effect of the neighboring methyl
of 1. However, the excellent binding affinity of the
six-membered ring 3-cyano-2-(3,4-difluorobenzyloxy)
pyridine derivative 10d and the equivalent 3-(N-propyl-
carboxamido) derivative 16c demonstrated the possibili-
ty that the amide moiety of the five-membered pyrazole
1 could be split into a lipophilic portion and a polar
functionality. This finding might allow more flexibility
in selection of derivatives in the future with enhanced
PK and CNS exposure profiles and improved physical
and off-target properties than could be achieved with a
single amide functionality. Further SAR studies will be
published elsewhere in the near future.
The poor binding of the 3-amido compounds led to the
investigation of the 2-amido series where somewhat
more encouraging results were obtained (Table 4). The
N-piperidinyl amide 29g analogous to 1 was found to
be modestly active (IC50 = 56 nM). The corresponding
cyclohexyl derivative 29e, as well as the cyclopentyl
29d and cycloheptyl 29f, were about the same, as were
the noncyclic n-hexyl 29b and 4-heptyl 29c and the benz-
yl amide 29i. The secondary piperidine amide 29a and
aniline derivative 29h had very weak binding. Although
these amides were not particularly potent, their overall
functional data appeared to indicate the desired inverse
agonist activity at high concentrations (data not shown).
There are several possible reasons for the relatively poor
binding of these 2- and 3-amido pyridine derivatives
compared to 1. The divergent affinity might be related
to the ring size giving a slightly different relative orienta-
tion of the three pyridine substituents, and/or the basic-
ity difference of the nitrogen, and/or possibly the effect
of a lack of a neighboring methyl, which would force
the amide moiety of 1 to be perpendicular to the pyraz-
ole ring, although in the 3-carboxamide series the neigh-
boring chloro in 19d did not have an effect compared to
20d.
References and notes
1. For general reviews of cannabinoid receptor ligands and
potential therapeutic applications, see: (a) Di Carlo, G.;
Izzo, A. A. Expert Opin. Invest. Drugs 2003, 12, 39; (b)
Pertwee, R. G. Expert Opin. Invest. Drugs 2000, 9, 1553;
(c) Xiang, J.-N.; Lee, J. C. Ann. Rep. Med. Chem. 1999, 34,
199.
2. (a) Trillou, C. R.; Delgorge, C.; Menet, C.; Arnone, M.;
Soubrie, P. Int. J. Obesity 2004, 28, 640; (b) Zimmer, A.;
Zimmer, A. M.; Hohmann, A. G.; Herkenham, M.;
Bonner, T. I. Proc. Natl. Acad. Sci. U.S.A. 1999, 96,
5780.
3. Barth, F.; Rinaldi-Carmona, M. Curr. Med. Chem. 1999,
6, 745.
4. Rinaldi-Carmona, M.; Barth, F.; Heaulme, M.; Shire, D.;
Calandra, B.; Congy, C.; Martinez, S.; Maruani, J.;
Neliat, G.; Caput, D.; Ferrarra, P.; Soubrie, P.; Breliere,
J. C.; Le Fur, G. FEBS Lett. 1994, 350, 240.
4. In vivo studies
Based on their favorable hCB1 binding and functional
assay results, 10d and 16c were selected for further in
vivo evaluation. Preliminary pharmacokinetic (PK)
studies in male Sprague–Dawley rats (1 mg/kg i.v.,
2 mg/kg p.o.) with 10d indicated good i.v. pharmacoki-
netic properties (AUCnom = 9.3 lM h kg/mg; Clp = 3.6
mL/min/kg; Vdss = 0.8 L/kg; t1/2 = 3.6 h) and moderate
oral absorption (F = 27%), but slow brain penetration
and a low brain-to-plasma ratio (B/P ratio = 0.03–0.26
at 0.25–4 h).23 In a food intake and body weight loss
study using diet-induced obese rats fed ad libitum, 10d
at 1, 3, and 10 mg/kg p.o. did not show an immediate