Potent, orally active inhibitors of lipoprotein-associated phospholipase A2: 1-(biphenylmethylamidoalkyl)-pyrimidones

Article abstract of DOI:10.1016/S0960-894X(01)00678-3

A series of 1-(biphenylmethylamidoalkyl)-pyrimidones has been designed as nanomolar inhibitors of recombinant lipoprotein-associated phospholipase A₂ with high potency in whole human plasma. 5-(Pyrazolylmethyl) derivative 16 and 5-(methoxypyrimidinylmethyl) derivative 27 demonstrated excellent pharmacodynamic profiles which correlated well with their pharmacokinetic effects.

Full text of DOI:10.1016/S0960-894X(01)00678-3

Bioorganic & Medicinal Chemistry Letters 12 (2002) 51–55
Potent, Orally Active Inhibitors of Lipoprotein-Associated
Phospholipase A2: 1-(Biphenylmethylamidoalkyl)-pyrimidones
Helen F. Boyd, Stephen C. M. Fell, Deirdre M. B. Hickey, Robert J. Ife, Colin A. Leach,
Colin H. Macphee, Kevin J. Milliner, Ivan L. Pinto, D. Anthony Rawlings,
Stephen A. Smith,* Ian G. Stansfield, Steven J. Stanway, Colin J. Theobald
and Caroline M. Whittaker
GlaxoSmithKline, Medicines Research Centre, Gunnell’s Wood Road, Stevenage SG1 2NY, UK
Received 20 July 2001; revised 5 October 2001; accepted 11 October 2001
Abstract—A series of 1-(biphenylmethylamidoalkyl)-pyrimidones has been designed as nanomolar inhibitors of recombinant lipo-
protein-associated phospholipase A2 with high potency in whole human plasma. 5-(Pyrazolylmethyl) derivative 16 and 5-
(methoxypyrimidinylmethyl) derivative 27 demonstrated excellent pharmacodynamic profiles which correlated well with their
pharmacokinetic effects. # 2001 Elsevier Science Ltd. All rights reserved.
The regulation of plasma lipid levels, particularly LDL
cholesterol, represents the focus of current therapy for
atherosclerosis. Whilst the statins have achieved both
medical and commercial success in this role,1 they are
only particularly effective in about 30% of patients.
With the aim of treating many more of the at risk
population, we have focussed our attention on treating
the inflammatory nature of the disease2 and, in parti-
cular, targeted the enzyme lipoprotein-associated phos-
pholipase A2 (Lp-PLA2). This enzyme has been shown
to release pro-inflammatory mediators from oxidatively
modified phosphatidylcholines.3 Furthermore, a strong
positive correlation has been shown between Lp-PLA2
levels and coronary events in asymptomatic hypercho-
lesterolemic males, suggesting that Lp-PLA2 is a new
independent marker of coronary heart disease.4 We
therefore wished to identify potent, orally effective inhi-
bitors of this enzyme in order to assess its role in the
atherosclerotic disease process.
In two recent reports,5,6 we described the identification
of a series of 1-((amidolinked)-alkyl)-pyrimidones 1 and
a related series of 1-(arylpiperazinylamidoalkyl)-pyrim-
idones 2 as inhibitors of Lp-PLA2 which showed
activity in the Watanabe hereditable hyperlipidaemic
rabbit (WHHL rabbit). In the belief that additional
enhancements in oral performance could be achieved
through further modification of the pyrimidone N-1
substituent, we investigated the replacement of this
group with a series of biarylmethyl amides and now
*Corresponding author. Fax: +44-1438-763620; e-mail: stephen_l_smith@gsk.com
0960-894X/02/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00678-3

52
H. F. Boyd et al. / Bioorg. Med. Chem. Lett. 12 (2002) 51–55
report the result of these studies alongside the effect
of introducing some novel 5 substituents into the
pyrimidone ring.
We initially investigated the biphenyl moiety and the
effect of substitution of this group in the pyrimidone
acetamide and butyramide series (Tables 1 and 2,
respectively). Although secondary amides were initially
prepared, they proved particularly insoluble and as a
result, we quickly moved to the corresponding N-methyl
derivatives. For similar solubility issues, much of the
SAR was developed in the 5-(1-methylpyrazol-4-yl)me-
thyl and 5-(2-methoxypyrimidin-5-yl)methyl series. Pre-
liminary work indicated the 4-biaryl substitution
pattern to be preferred over either 3- or 2-substitu-
tion (cf. 10 vs 12 and 13). Substitution of the 4-
biphenyl moiety proved advantageous (e.g., 16 vs 14)
with 4-substitution being somewhat favoured over the
2- or 3-substituted derivatives (cf. 16 with 20 and 21). A
lipophilic 4-substituent proved optimal for potency
against rhLp-PLA2 with the more bulky bromo and
trifluoromethyl groups the most potent. More polar
electron withdrawing or strongly donating groups were
less well tolerated (see 16, 18, 19 and 22–25).
The synthesis of inhibitors 10–13, 26–29 and 34–38
started from substituted pyrimidines 3 and used meth-
ods similar to those previously reported (Scheme 1).5,6
The related 2-trifluoromethyl derivative 43 was pre-
pared via aldehyde 8 which was itself prepared in three
steps from pyrimidone ester 7 (Scheme 2).7 Knoevenagel
reaction, esterification and reduction gave the propionic
ester 9 which was converted through to acid 4 as before.
The corresponding 1-methylpyrazol-4-yl derivatives 14–
25 and 30–33 were prepared in a similar fashion from
1-methylpyrazole-4-carboxaldehyde.8 Biarylmethylami-
nes 6 were prepared via reductive amination of the cor-
responding aldehydes 5 (R=Me) or by reduction of 5
followed by Mitsonobu reaction with phthalimide and
deprotection (R=H). Subsequent carbodiimide coupl-
ing proceeded smoothly. All compounds in Tables 1–3
were evaluated using recombinant human Lp-PLA2
(rhLp-PLA2). In order to include non-specific binding
effects in plasma, compounds were assessed against the
plasma enzyme in both whole human and WHHL rab-
bit plasma.5 Good activity in rabbit and human plasma
was required before compounds were evaluated in vivo
in WHHL rabbits.9
In contrast to our previous work with long-chain
amides at the pyrimidone N-1 position,5 activity in the
related butyramide series proved somewhat disappoint-
ing (Table 2). In this series, no additional advantage was
seen on increasing the size of the 4-substituent from
fluoro to chloro and although secondary amides showed
Scheme 1. Reagents and conditions: (i) (a) NaOMe, MeOH or (b) amine, CH2Cl2; (ii) for elaboration to acid 4, see ref 6; (iii) for R=H: (a) NaBH4,
EtOH; (b) phthalimide, DEAD, PPh3, THF; (c) NH2NH2, EtOH; for R=Me (a) MeNH2, 4 A molecular sieves, CH2Cl2; (b) NaBH4, EtOH; (iv)
EDC, HOBT, CH2Cl2 or DMF; for subsequent transformations within Ar (Ar=2-oxo-pyrimidin-5-yl and derivatives), see ref 6.
Scheme 2. Reagents and conditions: (i) (a) (COCl)2, CH2Cl2; (b) H2, Pd/C, iPr2NEt, EtOH; (c) iBu2AlH, THF; (ii) (a) CH2(CO2H)2, piperidine,
pyridine; (b) EtOH, H2SO4; (c) H2, Pd/C, EtOH.

H. F. Boyd et al. / Bioorg. Med. Chem. Lett. 12 (2002) 51–55
53
better activity in whole human plasma than their ter-
tiary counterparts (see 31 and 32, 37 and 38), activity
was reduced when compared with the best acetamide
derivatives (cf. 16 with all compounds in Table 2).
With these results in hand, we decided to concentrate
our efforts on the pyrimidone acetamide series and,
conscious of the rather lipophilic nature of these mole-
cules, we targeted the 4-chlorobiphenyl derivatives as a
Table 1. Acetamides: biaryl variation
No.a
X
RN
Ar
% Inhibition in plasma
IC50 (nM)
Human (10 nM)
8
Human (100 nM)
Rabbit (100 nM)
10
11
12
13
4-Ph
4-Ph
3-Ph
2-Ph
H
Me
H
Pyrimidin-5-yl
Pyrimidin-5-yl
Pyrimidin-5-yl
Pyrimidin-5-yl
4
8
50
66
42
41
24
194
23
NTb
18
NT
H
14
15
16
17
18
19
20
21
22
23
24
25
4-Ph
4-(4-F-Ph)
Me
Me
Me
H
Me
Me
Me
Me
Me
Me
Me
Me
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
5
2.7
1
4
9
44
55
50
53
69
40
35
44
23
42
12
78
88
83
4-(4-Cl-Ph)
4-(4-Cl-Ph)
4-(4-Br-Ph)
4-(4-CF3-Ph)
4-(3-Cl-Ph)
4-(2-Cl-Ph)
4-(4-Me-Ph)
4-(4-MeO-Ph)
4-(4-NC-Ph)
4-(4-MeO2S-Ph)
43
28
53
70
13
18
43
13
43
8
1.6
0.5
0.7
1.6
1.6
0.9
17
2.6
5
96
65
70
64
26
27
28
29
4-(4-F-Ph)
4-(4-Cl-Ph)
4-(4-Cl-Ph)
4-(4-CF3-Ph)
Me
Me
H
2-MeO-pyrimidin-5-yl
2-MeO-pyrimidin-5-yl
2-MeO-pyrimidin-5-yl
2-MeO-pyrimidin-5-yl
0.6
0.2
0.5
0.2
37
51
42
75
84
93
90
97
51
65
52
78
Me
aAll new compounds gave satisfactory analytical/spectral data.10
bNot tested.
Table 2. Biaryl butyramides
No.a
Y
RN
Ar
% Inhibition in plasma
IC50 (nM)
Human (10 nM)
Human (100 nM)
Rabbit (100 nM)
30
31
32
33
H
F
F
Cl
H
H
Me
Me
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
1-Me-pyrazol-4-yl
5
4
8
5
6
19
8
28
69
36
36
18
33
25
15
8
34
35
36
37
38
H
F
F
Cl
Cl
H
H
Me
H
2-MeO-pyrimidin-5-yl
2-MeO-pyrimidin-5-yl
2-MeO-pyrimidin-5-yl
2-MeO-pyrimidin-5-yl
2-MeO-pyrimidin-5-yl
4
3
15
4
4
27
12
29
3
55
83
52
81
46
22
36
34
31
20
Me
5
aAll new compounds gave satisfactory analytical/spectral data.10

54
H. F. Boyd et al. / Bioorg. Med. Chem. Lett. 12 (2002) 51–55
Table 3. Effect of pyrimidone 5-substituent variation
No.a
R5
% Inhibition in plasma
Human (10 nM)
IC50 (nM)
Rabbit (100 nM)
16
27
39
40
41
42
43
44
45
1-Me-pyrazol-4-yl
5-(2-MeO-pyrimidin-5-yl)
2-Morpholinylpyrimidin-5-yl
2-Me2N-pyrimidin-5-yl
1
0.2
1
0.8
1.7
0.2
5
1
0.5
43
51
48
41
59
64
14
48
33
55
65
48
47
76
55
16
63
43
2-(4-Me-piperazin-1-yl)pyrimidin-5-yl
2-(Piperazin-1-yl)pyrimidin-5-yl
2-CF3-pyrimidin-5-yl
2-Oxo-1H-pyrimidin-5-yl
1-Et-2-oxo-pyrimidin-5-yl
aAll new compounds gave satisfactory analytical/spectral data.10
Figure 1. Inhibition of plasma Lp-PLA2 in the WHHL rabbit @ 10
mg/kg (n=2) po.
Figure 2. Correlation of pharmacodynamic and pharmacokinetic
effects in the WHHL rabbit @ 10 mg/kg (n=2) po.
compromise between potency and lipophilicity/mole-
cular weight (16 vs 18 and 19) or reduced potential for
metabolic liability (16 vs 22). We then investigated the
effect of varying the pyrimidone 5-substituent in these
biphenyl derivatives and showed that high potency
could be achieved with a wide variety of pyrimidine
substituents (Table 3).
In conclusion, we have shown that compounds of high
potency against rhLp-PLA2 may be obtained by replac-
ing the long lipophilic chain present in our pre-
viously described orally active inhibitors5 with a
series of 4-biphenylacetamide derivatives. Compounds
16 and 27 show excellent activity in vivo and possess
enhanced physicochemical properties over our pre-
viously described orally active leads (in particular a
reduced clogP). These compounds should be of con-
siderable value in our evaluation of the role of Lp-PLA2
in atherosclerosis.
Based on these encouraging results, all compounds from
Table 3 (with the exception of trifluoromethyl derivative
43) were evaluated in WHHL rabbits at 10 mg/kg po.9
From this study, compounds 16 and 27 proved of most
interest, displaying prolonged inhibition (> 8 h) (Fig. 1)
with an excellent correlation of pharmacodynamic effect
with pharmacokinetic effect (Fig. 2). Furthermore, the
inhibition profiles of 16 and 27 (clogP11 5.5 and 5.9
respectively) match or better the best previously repor-
ted in the WHHL rabbit (compound 1, Ra=C18H35,
Rb=H, n=3, clogP 9.2).5 These very promising results
alongside a much greater activity in human rather than
in rabbit plasma would suggest that compounds 16 and
27 have the potential for potent inhibition of Lp-PLA2
in man.
References and Notes
1. Farnier, M.; Davignon, J. Am. J. Cardiol. 1998, 82, 3J, and
references therein.
2. Macphee, C. H. Curr. Opin. Pharmacol. 2001, 1, 121.
3. Also known as PAF acetyl hydrolase, this enzyme has
much broader substrate specificity than this name implies. See:
Tew, D. G.; Southan, C.; Rice, S. Q. J.; Lawrence, M. P.;
Haodong, L.; Boyd, H. F.; Moores, K.; Gloger, I. S.; Mac-
phee, C. H. Atheroscler. Thromb. Vasc. Biol. 1996, 16, 591.

H. F. Boyd et al. / Bioorg. Med. Chem. Lett. 12 (2002) 51–55
4. Packard, C. J.; O’Reilly, D. St. J.; Caslake, M. J.; McMa- 8. Finar, I. L.; Lord, G. H. J. Chem. Soc. 1957, 3314.
55
hon, A. D.; Ford, I.; Cooney, J.; Macphee, C. H.; Suckling,
K. E.; Krishna, M.; Wilkinson, F. E.; Rumley, A.; Lowe,
G. D. O. N. Engl. J. Med. 2000, 343, 1148.
5. Boyd, H. F.; Fell, S. C. M.; Flynn, S. T.; Hickey, D. M. B.;
Ife, R. J.; Leach, C. A.; Macphee, C. H.; Milliner, K. J.;
Moores, K. E.; Pinto, I. L.; Porter, R. A.; Rawlings, D. A.;
Smith, S. A.; Stansfield, I. G.; Tew, D. G.; Theobald, C. J.;
Whittaker, C. M. Bioorg. Med. Chem. Lett. 2000, 10, 2557,
and references therein.
6. Bloomer, J. C.; Boyd, H. F.; Hickey, D. M. B.; Ife, R. J.;
Leach, C. A.; Macphee, C. H.; Milliner, K. J.; Pinto, I. L.;
Rawlings, D. A.; Smith, S. A.; Stansfield, I. G.; Stanway, S. J.;
Taylor, M. A.; Theobald, C. J.; Whittaker, C. M. Bioorg.
Med. Chem. Lett. 2001, 11, 1925, and references therein.
7. Suto, M. J.; Gayo, L. M.; Palanki, M. S. S.; Ransome-Fong,
L. J. WO Patent 9838171, 1998; Chem. Abstr. 1998, 129, 216625.
9. The method of ref
5
was used. Compounds were
administered in a 9:1 mixture of polyethylene glycol 300/
Pharmasolve1. Additionally, blood levels of compound
were measured: serial blood samples were collected over 8
h post dose and compound concentration analysed by LC/
MS/MS.
10. Representative examples: Compound 16 (250 MHz) 1H
NMR (DMSO) d 2.95 and 3.08 (3H, 2Âs), 3.61 (2H, m), 3.86
(3H, m), 4.46–4.61 (6H, m), 6.74 and 6.80 (1H, 2Âs), 6.91–6.99
(2H, m), 7.21–7.49 (12H, m); MS (APCI+) found
(M+1)=602; C32H29ClFN5O2S requires 601. Compound 27
(250 MHz) 1H NMR (DMSO) d 2.87 and 2.95 (3H, 2Âs), 3.54
(2H, m), 3.88 (3H, s), 4.37–4.62 (4H, m), 4.9–5.0 (2H, m),
7.05–7.75 (13H, m), 8.49 (2H, bd); MS (APCI+) found
(M+1)=630; C33H29ClFN5O3S requires 629.
11. Daylight CIS, Mission Viejo, CA, USA version 4.71.