Urea based CCR3 antagonists employing a tetrahydro-1,3-oxazin-2-one spacer

Article abstract of DOI:10.1016/j.bmcl.2008.11.002

Conformational restriction of open chain analogs with a more polar tetrahydro-1,3-oxazin-2-one spacer led to the identification of potent urea-based CCR3 antagonists that exhibited excellent selectivity over binding to CYP2D6. The in vitro binding and eos

Full text of DOI:10.1016/j.bmcl.2008.11.002

Bioorganic & Medicinal Chemistry Letters 19 (2009) 96–99
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Urea based CCR3 antagonists employing a tetrahydro-1,3-oxazin-2-one spacer
*
T. G. Murali Dhar , Guchen Yang, Paul Davies, Mary F. Malley, Jack Z. Gougoutas, Dauh-Rurng Wu,
Joel C. Barrish, Percy H. Carter
Bristol-Myers Squibb Company, Research and Development, Princeton, NJ 08543-4000, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Conformational restriction of open chain analogs with a more polar tetrahydro-1,3-oxazin-2-one spacer
led to the identification of potent urea-based CCR3 antagonists that exhibited excellent selectivity over
binding to CYP2D6. The in vitro binding and eosinophil shape change data are presented. Compound
19b exhibited similar selectivity and potency to our development candidate BMS-639623.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 1 October 2008
Revised 30 October 2008
Accepted 3 November 2008
Available online 6 November 2008
Keywords:
CCR3
Chemokine
Urea
CYP2D6
Tetrahydro-13-oxazin-2-one
Accumulation of pulmonary eosinophils is one of the hallmarks
of allergic asthma,1 and the number of eosinophils is often corre-
lated with disease severity.1,2 Although the pathophysiological role
of the eosinophil remains enigmatic, studies in both humans3 and
mice4 have suggested that this leukocyte likely participates in
remodeling of the asthmatic airway. CC Chemokine Receptor 3
(CCR3) serves as the primary chemokine receptor5 on eosinophils
and, together with its ligands, mediates both the migration and
activation of eosinophils.6 Several independent studies with
CCR3-deficient mice have confirmed the central role of CCR3 in
governing eosinophilia in murine models of asthma.7 Moreover,
human genetic studies have suggested that the primary CCR3
ligand (eotaxin-1) plays a role in human asthma.8 Given these
results, numerous researchers have pursued the discovery and
development of selective CCR3 antagonists for the treatment of
allergic asthma.9
Colleagues in our laboratories recently described the discovery
of DPC168 (A, Fig. 1) as a picomolar antagonist of CCR3 with phar-
macokinetics suitable for clinical development.10 Subsequent to
this, we described our efforts to improve the selectivity of this ser-
ies of urea-based CCR3 antagonists relative to inhibition of the 2D6
isoform of human cytochrome P-450 (CYP2D6) by reducing the
lipophilicity of the central ring (see piperidine B, Fig. 1)11 or by
replacing the central ring with an acyclic chain substituted with
polar groups (C and D, Fig. 1).12 These latter studies led to the iden-
tification of BMS-639623 (C, Fig. 1) as a backup candidate for clin-
ical development in asthma. We reasoned that combining the
structural features inherent in the central linking moieties of A–
D in the form of tetrahydro-1,3-oxazin-2-ones (hereafter ‘oxazolid-
inones’; see E, Fig. 1) should provide an alternative series of urea-
based CCR3 antagonists with improved selectivity over CYP2D6
inhibition. In this Letter, we describe the synthesis, in vitro binding
and functional profiles of this new oxazolidinone-linked series of
CCR3 antagonists.
We envisioned that oxazolidinones of type E (Fig. 1) can be syn-
thesized from the known13 ethyl ester 3a. However, attempted
hydrolysis of 3a under mild conditions did not yield the desired
acid 4 (Scheme 1), presumably due to the base-lability of 3a.14 In
order to avoid base-mediated decomposition, the tert-butyl ester
3b was prepared in a fashion analogous to literature protocol,
starting with t-Bu acrylate (Scheme 1). The relative stereochemis-
try of the vinyl and ester moieties in 3b was assigned based on the
literature precedent,13 and was not unambiguously confirmed
(vide infra). Deprotection of the tert-butyl ester provided the race-
mic acid 4 in high yield. However, Curtius rearrangement pro-
ceeded in poor yield, presumably due to the basic conditions and
high temperature employed during the reaction.15 Ozonolysis of
the double bond, followed by reductive workup, afforded the alde-
hyde, which was subjected to reductive amination with known
amines (6, 7a, 7b)10,16 to provide the amino-oxazolidinones 8. Car-
bamate deprotection, followed by coupling of the nascent amine
with known phenyl carbamates (9, 10)10,12 afforded the original
target compounds 11–13.
Because of the apparent base sensitivity of oxazolidinone 4—
presumably due to the labile hydrogen atom alpha to the acid moi-
ety—we decided to quarternize this carbon atom by incorporating
a methyl group, with the aim of increasing the yield during the
* Corresponding author. Tel.: +1 609 252 4158; fax: +1 609 252 7410.
E-mail address: murali.dhar@bms.com (T.G.M. Dhar).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.11.002

T. G. Murali Dhar et al. / Bioorg. Med. Chem. Lett. 19 (2009) 96–99
97
F
F
OH
N
N
Me
N
N
N
N
H
N
H
N
N
N
HN
HN
O
N
N
R1
A (DPC168)
C (BMS-639623)
O
O
N
O
N
O
R2N
F
F
H
N
N
HN
Ar
N
N
N
N
E
H
H
N
N
HN
N
HN
S
N
Ac
O
N
B
D
O
Figure 1. Previous members of the urea-based class of CCR3 antagonists provide precedent for the use of tetrahydro-1,3-oxazin-2-one as a spacer.
Curtius rearrangement sequence. Although structure–activity rela-
tionships (SAR) in the acyclic series of CCR3 antagonists suggested
that quarternizing the carbon atom adjacent to the urea nitrogen
could be tolerated by the receptor,17 it was of interest to see if this
trend would continue in the oxazolidinone series. The key methyl-
oxazolidinone precursor 14 was synthesized following the afore-
mentioned literature protocol,13 and its conversion to the target
compounds is outlined in Scheme 2. Hydrolysis of the tert-butyl es-
ter in 14 employing 6 N HCl provided the racemic acid 15 in good
yield. In order to establish the relative stereochemistry of the acid
and vinyl moieties, a single crystal X-ray analysis of 15 was
performed.18
The single crystal X-ray analysis of compound 15 revealed it to
be a mixture of cis and trans isomers.19 Since separation of diaste-
reomers of the acid-oxazolidinone 15 was difficult, it was carried
over to the next step without further purification. Curtius rear-
rangement of 15 led to the desired Boc-protected amine 16 in good
yield after recrystallization from ethyl ether. Reductive amination
with amines (6, 7c), followed by Boc deprotection and coupling
with phenyl carbamates ( 9, 10, 18a, 18b) led to oxazolidinones
19–23. Fortuitously, the cis- and trans-diastereomers could be eas-
ily separated via silica gel column chromatography at this stage.
The relative stereochemistry of the individual diastereomers was
not established.20
The binding and cellular functional data for selected com-
pounds is listed in Table 1. From these data, it is clear that (i) quart-
ernizing the carbon atom adjacent to the urea functionality did not
lead to significant changes in binding potency (compare com-
pounds 11 with 19a and 19b); (ii) the m-(methyltetrazolyl)phenyl
moiety is the favored tail-piece in terms of binding (for example,
compare the diasteromeric pairs 19a,b with 20a,b); (iii) the bind-
ing potency of the open chain amines 23a and 23b are similar to
that of the cyclic piperidine analogs 19a and 19b; (iv) in terms of
cellular shape change, one diastereomer is approximately an order
of magnitude more potent than the other diastereomer (compare
19a with 19b and 23a with 23b); and (iv) most of the compounds
show better selectivity over CYP2D6 compared to B (Fig. 1,
IC50 = 7200 nM), BMS-639623 (C, Fig. 1, Ki = 2600 nM) and excel-
lent selectivity compared to DPC168 (A, Fig. 1, IC50 = 30 nM). Com-
pound 19b appeared to be the best compound in the series, as it
exhibited comparable binding, functional and CYP2D6 potency to
clinical candidate BMS-639623 (C). The compound also exhibited
excellent selectivity over the hERG channel (IC50 = 15,700 nM in a
Ca2+-flux assay). However, like all of the compounds in this oxazo-
lidinone series, it was not stable when incubated in vitro with hu-
man liver microsomes, and so it was not advanced into detailed
in vivo evaluation.
CO2R
NHBoc
OR
CO2R
Me
NHBoc
Me
O
O
4 steps
a
OEt
O
O
O
4 steps
a
c
O
b
N
O
N
1 R = Et
O
c
O
b
N
O
N
2 R = t-Bu
( )-3a R = Et
( )-3b R = t-Bu
( )-4 R = H
( )-5
1
14 R = Et
15 R = H
16
R2N
R2N
O
R2N
R2N
O
H
N
H
9 or 10
e
6, 7a or 7b
d
NHBoc
N
Me
NHBoc
Me
O
Ar
H
N
H
9, 10, 18, or 19
e
6 or 17
d
N
O
O
Ar
O
N
O
N
O
O
N
O
N
( )-8
( )-11, 12, 13
17
19 to 23
H
F
PhO
O
N
N
R"
R'
H
N
H
F
NH
N
H
PhO
N
N
PhO
N
PhO
N
Et
N
N
N
tBu
NH
6 (R', R" = -(CH2)3- )
7a (R' = propyl, R" = H)
7b (R' = c-Pr, R" = H)
O
S
O
S
O
S
7c
18a
18b
9
10
Ac
Scheme 1. Reagents and conditions: (a) see Ref. 13; (b) 6 N HCl, dioxane, 50 °C,
30 min, 85%; (c) DPPA, t-BuOH, toluene, Et3N, 110 °C, 18 h, 9%; (d) i—O3, CH2Cl2,
À78 °C, DMS; ii—CH2Cl2, Na(OAC)3BH, 10–36% over two steps; (e) i—3 N HCl,
dioxane, 50 °C, 1 h, quantitative; ii—CH3CN, rt, 18 h, 70%.
Scheme 2. Reagents and conditions: (a) see Ref. 13; (b) 6 N HCl, dioxane, 50 °C,
30 min, 79%; (c) DPPA, t-BuOH, toluene, Et3N, 110 °C, 18 h, 46%; (d) i—O3, CH2Cl2,
À78 °C, DMS; ii—CH2Cl2, Na(OAc)3BH, 44–59% over two steps; (e) i—3 N HCl,
dioxane, 50 °C, 1 h, quantitative; ii—CH3CN, rt, 18 h.

98
T. G. Murali Dhar et al. / Bioorg. Med. Chem. Lett. 19 (2009) 96–99
Table 1
Binding and shape change data for urea-based CCR3 antagonists employing a tetrahydro 1,3-oxazin-2-one spacer21,22
Compound
Structure
CCR3 binding (IC50, nM)
Shape change (IC50, nM)
CYP2D6 (IC50, nM)
A
B
C
See Figure 1
See Figure 1
See Figure 1
2
1.2
0.3
ND
ND
0.038
30
7400
Ki = 2600
F
N
O
N
N
H
H
N
11
12
13
0.23
ND
4300
N
N
N
O
O
N
F
N
O
N
N
H
H
N
2.1
2.2, 2.9
ND
N
N
N
O
O
N
F
N
O
9.2
ND
ND
NH NH
O
N
S
O
N
F
N
O
N
N
H
N
H
N
N
19a
19b
0.12
0.15
2.4, 6.3
0.13, 0.12
33,000
17,000
N
O
O
N
F
N
O
H
N
H
N
20a
20b
5.4
0.37
ND
3.4
ND
2100
N
O
S
O
N
F
N
O
H
N
H
N
N
O
21a
21b
13
1.1
ND
ND
ND
21,000
O
S
O
N
F
N
O
H
N
H
N
22a
22b
44
5.5
ND
ND
ND
40,000
N
O
S
O
N

T. G. Murali Dhar et al. / Bioorg. Med. Chem. Lett. 19 (2009) 96–99
99
Table 1 (continued)
Compound
Structure
CCR3 binding (IC50, nM)
Shape change (IC50, nM)
CYP2D6 (IC50, nM)
F
N
O
N
N
H
N
H
N
N
23a
23b
0.18
0.47
4.4
>3, >10
5900
14,000
N
O
O
N
ND, not determined.
In conclusion, a series of urea-based CCR3 antagonists with a
tetrahydro-1,3-oxazin-2-one linker have been identified. Quartern-
izing the carbon atom adjacent to the urea functionality of the tet-
rahydro-1,3-oxazin-2-one core was critical to obtaining good
yields during the Curtius rearrangement reaction en route to the fi-
nal products. Of the compounds shown, the potency and selectivity
of analog 19b was similar to that of our development candidate
BMS-639623. We will report our additional efforts towards gener-
ating potent, selective, and bioavailable CCR3 antagonists in subse-
quent manuscripts.
Yeleswaram, S.; Graden, D. M.; Solomon, K. A.; Newton, R. C.; Trainor, G. L.;
Decicco, C. P.; Ko, S. S. J. Med. Chem. 2005, 48, 2194.
11. Pruitt, J. R.; Batt, D. G.; Wacker, D. A.; Bostrom, L. L.; Booker, S. K.; McLaughlin,
E.; Houghton, G. C.; Varnes, J. G.; Christ, D. D.; Covington, M.; Das, A. M.; Davies,
P.; Graden, D.; Kariv, I.; Orlovsky, Y.; Stowell, N. C.; Vaddi, K. G.; Wadman, E. A.;
Welch, P. A.; Yeleswaram, S.; Solomon, K. A.; Newton, R. C.; Decicco, C. P.;
Carter, P. H.; Ko, S. S. Bioorg. Med. Chem. Lett. 2007, 17, 2992.
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Delucca, G. V.; Wacker, D. S.; Watson, P. S.; Welch, P. K.; Wadman, E. S.; Davies,
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13. Kurihara, T.; Matsubara, Y.; Harusawa, S.; Yoneda, R. J. Chem. Soc. Perkin Trans. 1
1991, 3177.
14. The major peak by LC/MS corresponded to the arecoline derivative. There is
precedent for a similar type of reaction occurring in DMSO/DBU at 120 °C. See:
Matsubara, Y.; Yoneda, R.; Harusawa, S.; Kurihara, T. Chem. Pharm. Bull. 1988,
36, 1597.
Acknowledgments
The authors thank our colleagues John V. Duncia, Joseph B. San-
tella, Soo S. Ko and George V. DeLucca for providing intermediates
6, 7a, 7b, 9, 10, 17, 18a, and 18b.
15. The putative arecoline derivative was again observed by LC/MS as a major
product.
16. Gardner, D. S.; Santella, J. B., III; Tebben, A. J.; Batt, D. G.; Ko, S. S.; Traeger, S. C.;
Welch, P. K.; Wadman, E. A.; Davies, P.; Carter, P.; Duncia, J. V. Bioorg. Med.
Chem. Lett. 2008, 18, 586.
References and notes
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2004, 305, 1776.
18. Crystallographic data (excluding structure factors) for 15 have been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication Nos. CCDC 703990 and 703991. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk).
19. The authors in Ref. 13 observe that the threo aldol product undergoes
cyclization to the trans-oxazolidinone within 10 min, whereas the mesylate
of the erythro isomer gives the cis-oxazolidinone when kept at room
temperature for 3 days. When we subjected the diasteromeric mixture of
the aldol products to the cyclization conditions reported in Ref. 13 and
5. For leading references on chemokines and their receptors, see: Sallusto, F.;
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Rothenberg, M. C. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 16418.
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stirred the reaction mixture for 18 h at room temperature,
cis–trans-oxazolidinone isomers (15) was obtained
a
mixture of
along with
erythromesylate in a ratio of ꢀ1:1.5.
20. Chiral HPLC analysis (Chiracel OD, 250 Â 4.6 mm 10 u, CO2/MeOH, 70:30)
of 19a indicated the presence of a set of enantiomers, in a 1:1 ratio, as
expected.
21. For a description of the human CCR3 binding assay please see Ref. 12, and
references cited therein.
22. For a description of the eosinophil shape change assay please see: Sabroe, I.;
Hartnell, A.; Jopling, L. A.; Bel, S.; Ponath, P. D.; Pease, J. E.; Collins, P. D.;
Williams, T. J. J. Immunol. 1999, 162, 2946.
9. De Lucca, G. V. Curr. Opin. Drug Discov. Dev.. 2006, 9, 516.
10. De Lucca, G. V.; Kim, U.-T.; Vargo, B. J.; Duncia, J. V.; Santella, J. B., III; Gardner,
D. S.; Zheng, C.; Liauw, A.; Wang, Z.; Emmett, G.; Wacker, D. A.; Welch, P. K.;
Covington, M.; Stowell, N. C.; Wadman, E. A.; Das, A. M.; Davies, P.;