Non-covalent thrombin inhibitors featuring P3-heterocycles with P1-monocyclic arginine surrogates

Article abstract of DOI:10.1016/S0960-894X(02)00129-4

Investigations on P₂-P₃-heterocyclic dipeptide surrogates directed towards identification of an orally bioavailable thrombin inhibitor led us to pursue novel classes of achiral, non-covalent P₁-arginine derivatives. The design, synthesis, and biological activity of inhibitors NC1-NC30 that feature three classes of monocyclic P₁-arginine surrogates will be disclosed: (1) (hetero)aromatic amidines, amines and hydroxyamidines, (2) 2-aminopyrazines, and (3) 2-aminopyrimidines and 2-aminotetrahydropyrimidines.

Full text of DOI:10.1016/S0960-894X(02)00129-4

Bioorganic & Medicinal Chemistry Letters 12 (2002) 1203–1208
Non-Covalent Thrombin Inhibitors Featuring P3-Heterocycles
with P1-Monocyclic Arginine Surrogates
John E. Reiner, Daniel V. Siev, Gian-Luca Araldi, Jingrong Jean Cui, Jonathan Z. Ho,
Komandla Malla Reddy, Lala Mamedova, Phong H. Vu, Kuen-Shan S. Lee,
Nathaniel K. Minami, Tony S. Gibson, Susanne M. Anderson, Annette E. Bradbury,
Thomas G. Nolan and J. Edward Semple*
Department of Medicinal Chemistry, Corvas International, Inc., 3030 Science Park Road, San Diego, CA 92121, USA
Received 17 December 2001; accepted 1 February 2002
Abstract—Investigations on P2–P3-heterocyclic dipeptide surrogates directed towards identification of an orally bioavailable
thrombin inhibitor led us to pursue novel classes of achiral, non-covalent P1-arginine derivatives. The design, synthesis, and bio-
logical activity of inhibitors NC1–NC30 that feature three classes of monocyclic P1-arginine surrogates will be disclosed: (1)
(hetero)aromatic amidines, amines and hydroxyamidines, (2) 2-aminopyrazines, and (3) 2-aminopyrimidines and 2-aminotetrahy-
dropyrimidines. # 2002 Elsevier Science Ltd. All rights reserved.
Thrombosis, or excessive blood clotting, is a significant
factor in cardiovascular and related diseases, accounting
for nearly half of US and European deaths annually.
Although thrombus formation normally occurs in blood
vessels to repair minor internal injuries, major vessel
injury or other pathophysiological conditions can cause
the thrombus to become very large. Acute myocardial
infarction (MI, heart attack), unstable angina (serious
chest pain preceding MI), ischemic stroke, deep vein
thrombosis (DVT), pulmonary embolism and dis-
seminated intravascular coagulation (DIC) all result
from such aberrant thrombosis.1
Figure 1. Design of P3-heterocyclic thrombin inhibitors NC1–NC30.
*Corresponding author. Tel.: +1-858-455-9800x1140; fax: +1-858-455-5169; e-mail: ed_semple@corvas.com
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00129-4

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J. E. Reiner et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1203–1208
Thrombin (fIIa), a multifunctional serine protease with
trypsin-like specificity, plays a central role in thrombosis
and hemostasis by regulating the blood coagulation
cascade and platelet activation processes. Serving as the
terminal enzyme of the cascade, thrombin cleaves the
zymogen fibrinogen to fibrin, which ultimately combines
with platelets and other components to form a blood clot.2
Limited efficacy and side effects of established antithrom-
botics including heparin, warfarin and aspirin have
provided the impetus for development of alternate drug
classes.3 Thrombin, along with procoagulant congeners
factor Xa (fXa) and prothrombinase (PTase), are deemed
as top targets for therapeutic intervention and continue
to attract enormous attention in the pharmaceutical
industry.4 In this letter, we disclose the design, synthesis,
and biological profiles of novel non-covalent P3-hetero-
cyclic thrombin inhibitors NC1–NC30 that feature three
different classes of P1-monocyclic arginine mimics.5
mol binding energy) was expected a priori to result in
decreased inhibitor potency, which necessitated the
identification of alternate active–site interactions so as
to restore the desired activity levels.12
As summarized in Figure 1, our strategy was to explore
the S3 specificity pocket of thrombin with tethered,
optimally substituted P4-aromatics (increase potency,
selectivity) and to survey S1 with diverse P1-monocyclic
arginine surrogates13 while maintaining the P3-hetero-
cycle (intrinsic potency via b-sheet H-bond with Gly216
plus interaction at 60’s loop of S2). Ideally, our rigid P1-
arginine surrogates would encompass a range of basicity
(pKa ꢀ3–14), participate in hydrogen bonding and/or
salt bridge interactions with Asp189, and benefit from
hydrophobic interactions at the S1 binding pocket.
Arginine mimics investigated are collected in Figure 2 in
order of decreasing basicity and are identified by the
indicated acronyms (see SAR, Table 1). The calculated
pKa values14 for several prototypical P1 arginine surro-
gates are listed and range from highly basic cyclic gua-
nidines (THAmPyrim, THMeAmPyrim, calcd pKa
ꢀ14) through the weakly basic aminopyrazine
(AmPyraz, calcd pKa ꢀ2.7). The targets NC1–NC30 are
comprised by three novel sub-classes of P1-arginine
mimics: (1) (hetero)aromatic amidines, amines and
hydroxyamidines, (2) 2-aminopyrazines, and (3) 2-ami-
nopyrimidines and 2-aminotetrahydropyrimidines. Sev-
eral potent, selective, and orally bioavailable thrombin
inhibitors resulted from this exercise.
Our investigations on covalent thrombin6 and fXa7
inhibitors incorporating P3-pyridones, -benzazepinones,
-lactams and related heterocyclic P2–P3 dipeptide sur-
rogates resulted in the identification of several potent,
selective and orally bioavailable inhibitors. Evolution of
these scaffolds coupled with a desire to overcome the
limitations imposed by the P1-argininal functionality
(high basicity of the guanidine moiety impacting OBA/
PK profiles, chiral lability, scale-up issues) led us to
pursue novel classes of non-covalent thrombin inhibi-
tors.8 SAR and modeling considerations from the pro-
totypical P3-pyridone–P1-argininals CVS 2139, CVS
2359, and CVS 2361 (Fig. 1)9 along with reference inhi-
bitors L374,08710 and L375,37811 (Table 1) suggested
the novel, achiral heterocyclic targets NC1–NC30.
Deletion of the covalent aldehyde handle (ꢀ5–6 kcal/
Synthetic routes to the P1-arylamidine precursors
4-amidinobenzylamine, 2-fluoro-4-amidinobenzylamine,
2-azidomethyl-5-cyanothiophene 3, 2-hydroxyamidino-
thiophene-5-methylamine and 2-amidinothiophene-5-
methylamine were recently disclosed.8 Preparation of
2-chloro-4-amidinobenzylamine paralleled the route to
the 2-fluoro-analogue. Scheme 1 summarizes our routes
to the (hetero)aromatic P1-precursors 2, 4, 5a–c, and
6a,b.15 Using classical aromatic substitution protocols,
p-tolunitrile was elaborated over five steps to the sub-
stituted benzyl bromide 1, which in turn led to the pro-
tected amidine precursor 2 after four additional steps.
Azide 38 was converted to the protected silyl ether 4 in
three steps. Three commercially available 2-aminopyri-
midines underwent nucleophilic aromatic substitution
with cyanide under thermal conditions. The resultant
4-cyanopyrimidines were treated with Boc2O/DMAP
and then hydrogenated to provide the bis-N-Boc-pro-
tected amines 5a–c in satisfactory overall yields. Further
hydrogenation of 5a,b in the presence of stoichiometric
HCl effected smooth reduction of the heteroaromatic
ring and produced the corresponding cyclic guanidines
(tetrahydropyrimidines) 6a,b in very high yield.
Scheme 2 outlines general approaches to the advanced
heteroaromatic intermediates 8, 10, and 12. Curtius
rearrangement of commercial 5-methyl-2-pyrazinecar-
boxylic acid followed by radical bromination afforded 7.
Azide displacement of 7 and reduction delivered pro-
tected pyrazine 8. Thiazole 9 was obtained from bromo-
pyruvate and thioacetamide components via a four-step
Figure 2. Acronyms and calculated pKa values for representative rigi-
dified P1-arginine surrogates.

Table 1. In vitro and in vivo activity of non-covalent P3-heterocyclic–P1-arginine surrogate-type thrombin inhibitors NC1–NC30
Compd
P4
P3
P1
ꢁKi Values (nM)a
Dog PK dosed @ 1 mg/kg
Ki FIIa
Ki FXa
Ki Trypn
AUC (mg* min/mL)
Cmax (mg/mL)
t1/2 (min)
Reference compounds:
CVS 2139
CVS2359
(2F)BnSO2
(2F)BnSO2
Pdn
Pdn(6Me)
Pdn(6Me)
Pdn(6Me)
Pdn[4aza](6Me)
Arg-al
Arg-al
Arg-al
AmMePyr
AmMePyr
0.56
0.14
0.10
0.68
1.0
192.0
674.0
1810
Inactive
Inactive
20.8
12.4
16.6
Inactive
Inactive
198
2.0
50
CVS2361
L374,087
L375,378
(2CO2Me,5F)BnSO2
BnSO2
3PhEtAm
160Æ28
275Æ17
0.79Æ0.12
0.90Æ0.05
107Æ7
199Æ11
New non-covalent targets:
NC1
NC2
NC3
NC4
(3OMe)PhSO2
Pdn
Pdn
Pdn
Pdn
AmdnBnAm
2ClAmdnBnAm
3-FAmdnBnAm
2-OMeAmdn
BnAm
5.3
20.8
6.0
152.7
Inactive
248.6
18.7
76.5
31.3
11.9
9.9Æ4.5
1.3Æ0.5
0.14Æ0.05
No test
Not absorbed
0.4Æ0.01
53Æ6
(3OMe)PhSO2
(3OMe)PhSO2
(3OMe)PhSO2
1.6
76.8
62Æ25
NC5
NC6
NC7
NC8
(3OMe)PhSO2
BnSO2
BnSO2
BnSO2
BnSO2
PhEtAm
PhEtAm
PhEtAm
PhEtAm
BnSO2
PhEtAm
Pdn
Pdn(6Me)
Pdn(6Me)
Pdn(6Me)
Pdn(6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn(6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn(6Me)
AmdnThzl
5.9
0.37
3.6
178.6
Inactive
Inactive
96.4
>168
No test
No test
AmdnBnAm
3-FAmdnBnAm
AmdnTpn
AmThzl
AmdnBnAm
AmdnTpn
49.3
Inactive
13.6
>168
Not absorbed
0.4Æ0.01
0.10
136.0
0.57
0.12
30.8
13.2
157.9
276.2
9.8
1.1Æ0.5
2.3Æ1.0
9.2Æ2.0
ND
ND
NC9
>338
No test
0.6Æ0.01
NC10
NC11
NC12
NC13
NC14
NC15
NC16
NC17
NC18
NC19
NC20
NC21
NC22
NC23
NC24
NC25
NC26
NC27
NC28
NC29
NC30
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
19.7
4.4
No test
0.29Æ0.04
OHAmdnTpn
OHAmdnTpn-TBDMS
AmPyraz
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
38Æ26
No test
176Æ29
293Æ36
69Æ10
104Æ50
55Æ10
43Æ7
0.70Æ0.08
2.01Æ0.13
0.88Æ0.07
0.83Æ0.15
0.81Æ0.18
0.24Æ0.02
1.57Æ0.26
1.95Æ0.16
0.6Æ0.1
157Æ4
84Æ10.6
43Æ5
AmPyraz
AmPyraz
AmPyraz
AmPyraz
Me2AmPyrim
AmPyrim
AmPyrim
MeAmPyrim
MeAmPyrim
MeAmPyrim
MeAmPyrim
MeAmPyrim
THAmPyrim
THAmPyrim
THMeAmPyrim
THMeAmPyrim
Ph(2,2-diF)EtAm
(4Cl)Ph(2,2-cycloBu)EtAm
(4F)Ph(2,2-diF)EtAm
BnSO2
5.5
5.9
96Æ22
35Æ3
281.0
461.9
357.1
85.2
103.2
196.8
323.8
140.8
1.0
112Æ7
139Æ22
248Æ39
74Æ12
BnSO2
PhEtAm
BnSO2
Benzodioxan-SO2
PhEtAm
Pdn(6Me)
390Æ75
801Æ141
97Æ6
Pdn[4aza](6Me)
Pdn(6Me)
Pdn(6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn[4aza](6Me)
Pdn(6Me)
Pdn[4aza](6Me)
Pdn(6Me)
Pdn[4aza](6Me)
Not absorbed
1.2Æ0.2
387Æ90
240Æ75
2,3-Dihydro-benzofuran-5-EtAm
Ph(2,2-diF)EtAm
BnSO2
Poor absorption
No test
Not absorbed @ 0.6 mg/kg
Not absorbed @ 0.4 mg/kg
No test
PhEtAm
BnSO2
PhEtAm
1.9
1.1
3.2
No test
aInhibition constants (Ki) of compounds 1a–w are derived from the corresponding IC50 values necessary to inhibit human thrombin (FIIa), factor Xa (FXa) and trypsin cleavage of the chromogenic
substrates described in ref 8 by 50%. Reported values for each compound are from a single IC50 determination that confirmed the initial range values.

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J. E. Reiner et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1203–1208
process and was further functionalized to the P1-amine
10 in three additional steps. The regioisomeric thiazole
11 was secured in three steps from commercial
5-methylthiazole. Subjection of intermediate 11 to a five-
step sequence provided the requisite thiazole methylamine
12 in good overall yield.
P3-pyrazinone intermediate 18 was prepared by two
complimentary multistep routes using modifications of
literature protocols.11a,b
The final coupling and elaboration reactions between
14, 16, and 18 and the various P1-arginine precursors
are outlined in Scheme 4. Coupling reactions generally
employed EDC, HOBt or HOAt with added Et3N or
NMM bases at ambient temperature in dry acetonitrile,
THF, or DMF solvents or mixtures thereof. In cases
where such couplings afforded P1-nitrile intermediates,
further reaction with hydroxylamine installed the
appropriate hydroxyamidine functionality. Optional
final deprotections were effected by either TFA-cleavage
Construction of the advanced P4-sulfonamido-/aralkyl-
amino–P3-heterocyclic–P2-acetic acid intermediates 14,
16 and 18 is summarized in Scheme 3. Multigram
quantities of P3-pyridone intermediates 14 and 16
were secured via modification of our recent methods.6f,9
Scheme 1. (Hetero)aromatic P1-arginine mimic precursors. Reagents
and conditions: (a) HNO3, À10 ꢂC, 30%; (b) Pd/C, H2 (1 atm), EtOH,
95%; (c) ꢂHNO2, 0–100 ꢂC, 48%; (d) NaH, MeI, DMF, 95%; (e) NBS,
.
CCl4, 80 C, 48%; (f) NaN3, DMF, rt, 20 h, 90%; (g) HONH2 HCl,
NMM, MeOH, rt to reflux, 55%; (h) MeI, Cs2CO3, DMF, 20 h, 72%;
.
(i) Ph3P, THF, H2O, rt, 20 h, 73%; (j) H2NOH HCl, NMM, MeOH,
rt, 65%; (k) TBDMSCl, Et3N, CH2Cl2, ꢀquant; (l) 1,3-propane-
dithiol, Et3N, MeOH, rt, 18 h, 21%; (m) CuCN, DMF, reflux, 18–20
h, 64% quant; (n) Boc2O, DMAP, THF, rt, 2 h, 60–77%; (o) H2, Pd/
C, HCl (cat.), EtOH, 40–50 psi, 16 h, 43–93%; (p) H2, Pd/C, 1 N HCl,
EtOH, THF, 20 psi, 16 h, 94% ꢀquant.
Scheme 3. Assembly of P2–P3 heterocyclic acetic acids. Reagents and
conditions: (a) LiN(TMS)2, THF, BrCH2CO2Et, 0 ꢂC to rt; (b) H2, Pd/
C, 16 h; (c) R4SO2Cl, CH3CN, collidine, 0 ꢂC to rt; (d) LiOH, MeOH,
H2O, 0 ꢂC to rt, ꢀ70–85% over four steps; (e) BrCH2CO2t-Bu,
K2CO3, DMF, 75%; (f) LiOH, EtOH, ꢀquant; (g) DPPA, Et3N,
dioxane, reflux; BnOH, reflux, 78%; (h) H2, Pd/C, EtOH, 82%;
(i) R4SO2Cl, NMM or collidine, 60–90%; (j) TFA, CH2Cl2, 0 ꢂC to rt,
95% quant; (k) TMSCN, MeCHO, Et3N, CH2Cl2, rt, 18 h, 87%;
(l) (COCl)2, o-DCB, 100 ꢂC, 18 h, 82%; (m) for R=Et: 1.
Ar(CH2)2NH2, solvent; 2. LiOH, THF, H2O; 3. H2, Pd/C, 65–87% for
3 steps; (n) for R=Bn: 1. Ar(CH2)2NH2, dioxane; 2. Pd(OH)2/C,
NH4O2CH, ꢀ60–80% over two steps; (o) diethyl oxalate, Et3N,
EtOH, 50 ꢂC, 91%; (p) amino-2-propanol, EtOH, rt to reflux, 97%;
(q) RuCl3, H2O, NaBrO3, 62%; (r) (CF3CO)2O, 80 ꢂC; (s) POBr3,
reflux; NH4OH, ꢀ76% for 2 steps; (t) Ar(CH2)2NH2, dioxane, Et3N,
65–100 ꢂC, 12–48 h; or toluene, reflux, ꢀ12 h; 90–94%; (u) LiOH,
H2O, THF or EtOH, rt, 12–40 h, 60–88% over 2 steps.
Scheme 2. Synthesis of heteroaromatic P1-arginine mimics. Reagents
and conditions: (a) DPPA, Et3N, dioxane, 100 ꢂC; t-BuOH, 25 h,
70%; (b) NBS, (PhCO2)2, CCl4, NaHCO3, reflux, 54%; (c) NaN3,
DMF, rt, 5 h, 98%; (d) H2, Pd/C, 1 atm, MeOH, 98%; (e) Et3N,
CH3CN, rt –90 ꢂC, 1 h; (f) CSA (cat.), toluene, reflux, Dean–Stark,
-H2O, 12 h, 88% for two steps; (g) NH4OH, MeOH, rt, 16 h, 89%;
(h) SOCl2, NMM, DMF, 0 ꢂC rt, 5 h, 56%; (i) NBS, CCl4, 80 ꢂC, 39%;
(j) NaN3, DMF, rt, 20 h; (k) Ph3P, THF, H2O, rt, 20 h, 80%; (l) n-
Scheme 4. Coupling and elaboration to targets NC1–NC30. Reagents
and conditions: (a) couple protected P1-amine precursors 2, 4, 5a–c,
6a,b, 8, 10, and 12: EDC, HOBt or HOAt, Et3N or NM M , CHCN,
THF, or DMF; rt, 12–15 h, 27%–quant; (b) for nitrile intermediates:
.
NH2OH HCl, NMM, MeOH, rt to reflux, 31–80%; (c) optional
ꢂ
ꢂ
.
BuLi, THF, À78 C, 30 min; DMF, À78 C to rt; (m) HONH2 HCl,
NMM, MeOH, rt, 22 h, 91% over two steps; (n) CDI, CH2Cl2, rt, 1 h,
92%; (o) NBS, CCl4, 80 ꢂC, 48%; (p) NaN3, DMF, rt, 20 h, 90%; (q)
3
.
HONH2 HCl, NMM, MeOH, rt, 55%; (r) n-PrI, Cs2CO3, DMF,
deprotection of P1-group: for NC1–11: Zn, HOAc, H2O, RP-HPLC,
20–70%; for NC14–26: TFA, CH2Cl2, 0 ꢂC to rt, RP-HPLC, 33–90%.
50 ꢂC, 20 h, 42%; (s) Ph3P, THF, H2O, rt, 20 h, 73%.

J. E. Reiner et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1203–1208
1207
or Zn–HOAc reduction and were followed by RP-HPLC
purification to deliver the targets NC1–NC30.
efficacy appears to be governed by a number of factors
including choice of P4-hydrophobe, P3-heterocycle and
especially the P1-arginine mimic. Arginine surrogates
with calculated pKa’s ꢀ2.7–7.4 appear to confer the
best OBA, however optimal inhibitor potency results
from incorporation of the more highly basic functions.
The in vitro and in vivo biological activity for targets
NC1–NC30 along with the standards CVS 2139, CVS
2359, CVS 2361 (F ꢀ37–70%, absolute oral bioavail-
ability in dogs),9 L374,08710 and L375,37811 is sum-
marized in Table 1 [Pdn(6Me)=6-methylpyridone and
Pdn[4aza](6Me)=6-methylpyrazinone]. In vivo phar-
macokinetic (PK) data from cassette oral dosing studies
in fasted dogs at 1 mg/kg is included for reference com-
pounds and for several new targets. L374,087 and
L375,378 demonstrated impressive PK profiles in dogs
when dosed po at 1 mg/kg due to the presence of the
well-engineered P1-AmMePyr moiety (efficacious in
FeCl3 thrombosis model, F ꢀ44–91%).10,11 Moderate
to excellent levels of thrombin inhibition were observed
in vitro, with Ki’s=0.1–141 nMfor our top candidates.
All new targets were selective against the thrombolytic
enzymes plasmin, tissue plasminogen activator (tPA)
and urokinase plasminogen activator (uPA) as well as
activated protein C (PCa). Most new targets demon-
strated moderate to excellent levels of selectivity against
the digestive enzyme trypsin (trypn).
In conclusion, a structure-based design strategy, which
hybridized the prototypical P3-pyridone P1-argininals
CVS 2139, CVS 2359 and CVS 2361 with L374,087 and
L375,378, was employed to generate a novel family of
non-covalent thrombin inhibitors NC1–NC30 featuring
P3-heterocyclic P1-monocyclic arginine surrogates. Our
series probed the S3 specificity pocket with eight P4-
residues and the S1 pocket with 15 rigid arginine surro-
gates of varying size, shape and basicity, while main-
taining the intrinsically potent P3-pyridone and
pyrazinone pharmacophores at the S2 pocket. Potent,
selective and orally bioavailable thrombin inhibitors
were identified which serve as attractive leads for further
SAR/PK development. Numerous active-site interac-
tions and optimal physical properties (net pKa, log P)
are deemed as critical factors for conferring high
potency, specificity, and useful PK properties in this
class of inhibitors.
In general, in vitro potency decreased as a function of
the P1-arginine surrogate as follows: AmdnTpn
(pKa=10.3)>THAmPyrim
AmdnBnAm (pKa=9.4–10.2)>OHAmdnTpn (pKa=4.1)
>AmdnThzl (pKa=8.8)>AmPyraz (pKa=2.7)>
(pKa=14.0)ꢃ2/3-substd
Acknowledgements
We gratefully acknowledge L. Truong and P. W. Ber-
gum for in vitro pharmacological studies, and T. K.
Brunck and S. Y. Tamura for stimulating discussions
regarding antithrombotic inhibitor targets.
AmPyrim (pKa=3.9–4.7). In our series, oral PK rank-
ing was essentially opposite to the potency ranking
above, decreasing as a function of the P1-arginine sur-
rogate in the following order: AmPyrim (pKa=3.9–
4.7)>AmPyraz (pKa=2.7)>OHAmdnTpn (pKa=4.1)
ꢃ2/3-substd AmdnBnAm (pKa=9.4–10.2)> THAm-
Pyrim (pKa=14.0)>AmdnTpn (pKa=10.3). Targets of
greatest interest in terms of activity, selectivity, and/or
PK profiles include NC6, NC8, NC10, NC11 (sub-
nanomolar FIIa Ki’s); NC5, NC7, NC12, NC13, NC16–
18, and NC27–30 (high potency, excellent selectivity);
NC14–15, NC17, NC19–21, and NC24 (moderate
potency, excellent selectivity, good to excellent PK pro-
file). Notably, the P1-aminopyrimidine derivatives NC21
and NC24, albeit only moderately potent as thrombin
inhibitors, showed impressive PK profiles in terms of
conferring maximal AUC, Cmax and t1/2 values. Further
details of in vivo oral bioavailability and efficacy will be
reported elsewhere.
References and Notes
1. (a) Coleman, R. W.; Marder, V. J.; Salzman, E. W.; Hirsch,
J. In Hemostasis and Thrombosis, Basic Principles and Clinical
Practice, 3rd ed.; Colman, R. W., Hirsch, J., Marder, V. J.,
Salzman, E. W., Eds.; J. B. Lippincott: Philadelphia, 1994;
Chapters 1, 9, 57, and 80–86. (b) Vlasuk, G. P. Thromb. Hae-
mosta. 1993, 70, 212.
2. (a) Kaiser, B. Drugs Future 1998, 23, 423. (b) Vlasuk, G. P.
In New Therapeutic Agents in Thrombosis and Thrombolysis;
Sasahara, A. A, Loscalzo, J., Eds.; Marcel Dekker: New York,
1997; Chapter 15.
3. (a) Recent reviews: Coburn, C. A. Exp. Opin. Ther. Pat.
2001, 11, 721. (b) Vacca, J. P. Curr. Opin. Chem. Biol. 2000, 4,
394. (c) Fevig, J. M.; Wexler, R. R. Annu. Rep. Med. Chem.
1999, 34, 81.
Potency and selectivity in the NC1–NC30 series result
from key binding interactions at each of the S1–S3 spe-
cificity pockets in the thrombin active site, including b-
sheet (Gly216), hydrophobic, van der Waals and aro-
matic edge-to-face interactions (S3 pocket plus 60 loop
in S2 pocket, Fig. 1). Binding to thrombin occurs in a
canonical substrate-like mode, with the rigid P1-arginine
surrogates participating in salt bridge and/or water-
mediated hydrogen-bonding interactions with Asp189
at the S1 specificity pocket.6,12 Other putative inter-
actions of the P1 residue at S1 include van der Waals
interaction with Val213 and hydrogen bonds with
Gly219, Gly193 and Tyr228.4,10,11 OBA and overall PK
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˚
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14. pKa calculations were performed using ACD/ChemSketch
software, version 4.55, May 2000. Advanced Chemistry
Development, Inc., Toronto, Ontario, Canada.
15. All new compounds were characterized by full spectro-
scopic (NMR, IR, MS) data. Yields refer to spectroscopically
1
and chromatographically homogeneous (595% by H NMR,
HPLC, TLC) materials.