6440
L. R. Roberts et al. / Bioorg. Med. Chem. Lett. 18 (2008) 6437–6440
Table 2
with a further increase in potency. Single enantiomer 19 had the
best overall in vitro pharmacology profile.
Physicochemical, pharmacological and ADME properties of 14 and 19.
Both 14 and 19 were selective over the other
a subtypes, the
14
19
hERG channel and a wide ligand panel of receptors, enzymes and
ion channels although we did see some weak CYP inhibition (Table
2). Interestingly, compound 14 had a binding Ki of 83 nM whereas
19 was much more potent at 5 nM, but the pharmacological rele-
vance for the difference in binding activity is not well understood.
In rat experiments, the free plasma/cerebral spinal fluid (CSF) ratio
after iv infusion to steady state was 1:1 for both compounds. This
indicated that both compounds had excellent BBB penetration.12
Compound 14 had moderate clearance in the dog to give a human
PK predicted clearance in the range 4–11 ml/min/kg with a low
volume of distribution (consistent with an essentially neutral com-
pound) and bioavailability of around 65%.
a1a Ki
LogD7.4
HLM, Cli (
DLM, Cli (
83 nM
2.6
30
5 nM
2.6
l
l
l/min/mg)
l/min/mg)
24
35
82a
hERG activity
>10
lM
>10 lM
Cerep/BioprintTM panel (170 assays
>50ꢀ selective against all
>50ꢀ
across receptor, enzyme and ion targets
channel targets)
selective
against all
targets
CYP2C9, 2C19, 2D6, 3A4 inhibition
Dog PK (IV)
2C9 and 3A4 < 35% at
10 M 2C19 IC50 5.7
2D6 IC50 6.6
<50%
inhibition at
10 lM
Cl 25 ml/min/
kg Vd 3 L/kg
T1/2 1.5 h
1:1
l
lM
lM
Cl 14 ml/min/kg Vd 0.9 L/
kg T1/2 0.9 h
In summary, 2-substituted imidazole a1A partial agonists with
methylene spaced groups at the 4-position of the indane gave
Rat free plasma/CSF
1:1
excellent selectivity over a1B, a1D and a2A. Emax can be modulated
by placement of a halogen at the 5-position. Compounds 14 and 19
were identified as having the best balance of pharmacological
properties. Keeping the polar surface area of the compounds low
resulted in no P-gp efflux as predicted from the MDCK assay with
good CNS penetration. This work also demonstrated the use of
ethers and heterocycles as bioisosteric replacements of sulfona-
mides. The in vivo efficacy of 14 in models of SUI and selectivity
over CV endpoints will be reported separately.3
Acknowledgements
We thank Alison Bridgeland for screening data; Debbie Lover-
ing, Edward Pegden, Katherine England, Rachel Osbourne and He-
len Mason for compound synthesis. We also thank Peter Bungay
for ADME assessment of all compounds.
Figure 1. In-silico prediction of conformation of compounds
methoxy analogue (c).
5 (a), 6 (b) and
The key difference is the preferred out-of-plane orientation of the
pendent methylene sulfone in Figure 1a (5) and methoxymethyl
substituent in Figure 1b (6) which seems to bring in selectivity
compared to the planar methoxy in Figure 1c.
Variation in the size, type and position of the ether such as com-
pounds 7 and 8, tended to be detrimental to potency and/or HLM
stability driven by higher LogD. The only amines showing any
activity had low pKas, courtesy of adjacent fluorines such as 9
and 10.11
Placing small halogens on the aromatic ring, e.g., 5-F 11 and 5-
Cl 14 analogs, showed good potency with lower Emax values. On
balance, 14 had the better in vitro profile of the two. Fluorine in
the other positions either had a big drop-off in potency or in-
creased the Emax significantly (12 and 13).
Benzylic heterocycles were investigated as they also have the
propensity to act as strong hydrogen bond acceptors. Initial success
came with the benzylic N-linked pyrazole 15 which had good po-
tency, selectivity and low Emax. Other N- or C-linked heterocycles
had reduced potency. The triazole 16 with a slightly higher TPSA
of 59 Å2, had a resultant asymmetry in the MDCK assay. In this in-
stance, other factors such as hydrogen bond basicity of the exposed
nitrogen on the triazole may make it more susceptible to P-gp ef-
flux. The oxadiazole 17 was interesting as it had a low Emax but
showed compromised potency and was highly susceptible to
microsomal oxidation. The addition of a fluoro group to the pyra-
zole 18 increased potency but raised the Emax. By adding a further
fluorine to the 5-postion of the indane the Emax was lowered to 58%
References and notes
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J. Bioorg. Med. Chem. Lett. 2008, 18, 2930.
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in preparation.
4. Madin-Darby canine kidney (MDCK) cell line expressing the P-glycoprotein
transporter (P-gp). Flux across cells was measured at 10 lM substrate
concentrations. Figures quoted correspond to the flux rates (Papp ꢀ 10ꢁ6 cm-1
)
for apical to basolateral (AB) and basolateral to apical (BA) directions. See
reference: Mahar Doan, K. M.; Humphreys, J. E.; Webster, L. O.; Wring, S. A.;
Shampine, L. J.; Serabjit-Singh, C. J.; Adkison, K. K.; Polli, J. W. J. Pharm. Exper.
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8. X-ray structure of the diastereomer of 14 confirmed the absolute
stereochemistry as S so by inference, 14 was proposed to be R.
9. Human a1A (clone 54), a1B (SNB0000700, clone 11) and a1D (SNB0000706,
clone 23) were expressed in Chinese Hamster Ovary cells. Receptor activation
was determined via calcium mobilisation through the Gq pathway using
calcium-sensitive fluorescent dye (Molecular Devices, Part No. R8033),
measured by
concentration–response curves were calculated, with Emax calculated as
percent relative to 10 M phenylephrine response.
a Fluorescent Light Imaging Plate Reader (FLIPr). 11-point
a
l
10. a Abraham, M. H.; Duce, P. P.; Prior, D. V.; Barratt, D. G.; Morris, J. J.; Taylor, P. J.
J. J. Chem. Soc., Perkin Trans. 2 1989, 1355; b Abraham, M. H.; Grellier, P. L.;
Prior, D. V.; Morris, J. J.; Taylor, P. J. J. Chem. Soc., Perkin Trans. 2 1990, 521.
11. For a recent report on the effect of fluorines on nitrogen pKa, see: Morgenthaler,
M.; Schweizer, E.; Hoffmann-Roder, A.; Benini, F.; Martin, R. E.; Jaeschke, G.;
Wagner, B.; Fischer, H.; Bendels, S.; Zimmerli, D.; Schneider, J.; Diederich, F.;
Kansy, M.; Muller, K. ChemMedChem 2007, 2, 1100.
12. Hitchcock, S. A.; Pennington, L. D. J. Med. Chem. 2006, 49, 1.