ACS Medicinal Chemistry Letters
Letter
limited success in the first two areas. Ultimately, it was
exploration of replacements for the 2,3-dihydrobenzo[b][1,4]-
dioxine-6-carboxy group on the 4-amino piperidine that proved
most productive.
ASSOCIATED CONTENT
* Supporting Information
Experimental details for the preparation and characterization of
8, 15, 20−22, and 26−28 and methods for in vitro profiling.
This material is available free of charge via the Internet at
■
S
Structure−activity relationships in the 4-aminopiperidine
region of 15 were rapidly explored using parallel synthesis
methods employing amine 20 (Scheme 3). Amine 20 was
prepared from (2R,4R)-1-tert-butyl 2-methyl 4-aminopiper-
idine-1,2-dicarboxylate 10. Protection of the 4-amino group as
the carbobenzoxy derivative and hydrolysis of the ester afforded
17. Activation of the acid, coupling to 1,2-diaminobenzene
(13), and cyclization were carried out in an analogous manner
as described in Scheme 2. Reductive removal of the
carbobenzoxy protecting group gave 20. Amine 20 was coupled
with a diverse set of carboxylic acids and isocyanates in high
yields using standard conditions. Although potency gains were
difficult to achieve in the amide series, the urea exploration
proved to be more productive. Following preparation of a small
set of alkyl, cyclic alkyl, and aryl ureas, phenyl urea 21 was
identified as an attractive lead for further investigation (Table
2). Further studies to optimize the potency of 21 provided the
following general trends: (1) ortho substitution was not
tolerated; (2) both meta (27) and para (23−26) substitution
generally increased potency, with para being preferred (26 vs
27); (3) replacement of phenyl with pyridyl diminished
potency (28), as did additional heteroaromatic replacements;
and (4) methylation of either of the urea nitrogen's produced
inactive compounds.
Profiling of several ureas both in vitro and in vivo revealed
that p-cyano urea 26 comprised the best overall combination of
properties.26 The physical properties and in vitro and in vivo
pharmacokinetic data for 26 are summarized in Table 3. In
vitro microsomal assays predicted 26 to have high clearance in
rat and low clearance in dog and human, with free fractions in
rat, dog, and human plasma of 10−14%. Additionally, 26 did
not inhibit any of the major cytochrome P450 isoforms, nor did
it form covalent adducts when incubated with glutathione,
either with or without metabolic activation. It is negative in
Ames and micronucleus assays used to assess genotoxicity risk.
The aqueous solubility of the dihydrochloride salt is poor;
however, solubility in simulated gastric fluid is high.
Permeability is moderate in Caco-2 cells with asymmetry,
indicating that 26 is a p-glycoprotein substrate. In vivo
pharmacokinetic studies in rat27 and dog28 demonstrated that
the in vivo clearances correlated well with in vitro microsomal
data, and volumes of distribution were moderate, with oral
bioavailabilities of 33 and 68%, in rat and dog, respectively.
Together, on the basis of the preclinical in vitro and in vivo
pharmacokinetic data, 26 was predicted to have low plasma
clearance (1.03 mL/min/kg), moderate volume of distribution
(2.7 L/kg), a half-life of 30 h, and an oral bioavailability of 55%
in humans.
AUTHOR INFORMATION
Corresponding Author
Notes
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The authors declare no competing financial interest.
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identified possessing excellent potency and physical properties
that translate to an attractive predicted human pharmacokinetic
profile. On the basis of these data, 26 was advanced to in vivo
tumor growth inhibition studies, preclinical safety studies, and
ultimately to human clinical trials. These results will be
reported in separate disclosures.
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dx.doi.org/10.1021/ml2002423 | ACS Med. Chem. Lett. 2012, 3, 106−111