2-Aminothiazoles with Improved Pharmacotherapeutic Properties for Treatment of Prion Disease

Article abstract of DOI:10.1002/cmdc.201300007

Recently, we described the aminothiazole lead (4-biphenyl-4-ylthiazol-2-yl)-(6-methylpyridin-2-yl)-amine (1), which exhibits many desirable properties, including excellent stability in liver microsomes, oral bioavailability of ～40%, and high exposure in the brains of mice. Despite its good pharmacokinetic properties, compound 1 exhibited only modest potency in mouse neuroblastoma cells overexpressing the disease-causing prion protein PrP^Sc. Accordingly, we sought to identify analogues of 1 with improved antiprion potency in ScN2a-cl3 cells while retaining similar or superior properties. Herein we report the discovery of improved lead compounds such as (6-methylpyridin-2-yl)-[4-(4-pyridin-3-yl-phenyl)thiazol-2-yl]amine and cyclopropanecarboxylic acid (4-biphenylthiazol-2-yl)amide, which exhibit brain exposure/EC₅₀ ratios at least tenfold greater than that of compound 1.

Full text of DOI:10.1002/cmdc.201300007

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DOI: 10.1002/cmdc.201300007
2-Aminothiazoles with Improved Pharmacotherapeutic
Properties for Treatment of Prion Disease
Zhe Li,[a, b] B. Michael Silber,[a, b, c] Satish Rao,[a, b] Joel R. Gever,[a, b] Clifford Bryant,[a, d]
Alejandra Gallardo-Godoy,[a, d] Elena Dolghih,[e] Kartika Widjaja,[a] Manuel Elepano,[a]
Matthew P. Jacobson,[e] Stanley B. Prusiner,*[a, b] and Adam R. Renslo[a, d]
Recently, we described the aminothiazole lead (4-biphenyl-4-
ylthiazol-2-yl)-(6-methylpyridin-2-yl)-amine (1), which exhibits
many desirable properties, including excellent stability in liver
microsomes, oral bioavailability of ~40%, and high exposure in
the brains of mice. Despite its good pharmacokinetic proper-
ties, compound 1 exhibited only modest potency in mouse
neuroblastoma cells overexpressing the disease-causing prion
protein PrPSc. Accordingly, we sought to identify analogues of
1 with improved antiprion potency in ScN2a-cl3 cells while re-
taining similar or superior properties. Herein we report the dis-
covery of improved lead compounds such as (6-methylpyridin-
2-yl)-[4-(4-pyridin-3-yl-phenyl)thiazol-2-yl]amine and cyclopro-
panecarboxylic acid (4-biphenylthiazol-2-yl)amide, which exhib-
it brain exposure/EC50 ratios at least tenfold greater than that
of compound 1.
Introduction
A rapidly expanding body of evidence indicates that prions
cause many different neurodegenerative disorders including
Alzheimer’s, Parkinson’s, and Creutzfeldt-Jakob (CJD) diseases,
as well as the frontotemporal dementias and some forms of
amyotrophic lateral sclerosis (ALS).[1,2] The human prion diseas-
es caused by the aberrantly folded prion protein (PrP) include
kuru, CJD, fatal insomnia, and Gerstmann–Strꢀussler–Scheinker
disease.[2,3] Bovine spongiform encephalopathy (BSE), or “mad
cow” disease, is the most well-known among the animal PrP
diseases that also encompass scrapie of sheep and goats,
feline spongiform encephalopathy, and chronic wasting dis-
ease of deer and elk. The unique characteristic common to all
of these disorders, whether sporadic, dominantly inherited, or
acquired by infection, is the aberrant refolding of cellular PrP
(PrPC) into a disease-causing isoform (PrPSc).[4–6] The exact
mechanism by which a-helix-rich PrPC is transformed into b-
sheet-rich PrPSc is unknown, but auxiliary proteins such as
chaperones seem likely to participate in the replication pro-
cess, as is the case for yeast prions.[7,8] Oligomers of PrPSc are
thought to be cytotoxic and responsible for neuronal dysfunc-
tion.[9–12] Prion diseases are invariably fatal, and no effective
treatment for these devastating disorders is currently available.
Attempts to decrease levels of PrPSc by inhibiting its produc-
tion and/or increasing its clearance would seem to be among
the viable therapeutic approaches for prion diseases. Moreover,
lowering levels of glycosyl phosphatidylinositol-anchored PrPC
on the surface of neurons may represent a useful complemen-
tary therapy.[13] Several research groups have screened for an-
tiprion compounds; typically, scrapie-infected murine neuro-
blastoma cells (ScN2a) have been used. Both biologics (anti-
bodies) and small organic molecules with antiprion activity
have been identified by assays based on PrPSc levels in ScN2a
cells. Among known antiprion small molecules are Congo
red,[14] acridines,[15] diphenyloxazoles and diphenylthiazoles,[16]
pyrazolones,[17] 2-aminopyridines,[18] statins, and indole-3-glyox-
ylamides.[19]
[a] Prof. Dr. Z. Li, Prof. Dr. B. M. Silber, Prof. Dr. S. Rao, Prof. Dr. J. R. Gever,
C. Bryant, Dr. A. Gallardo-Godoy, K. Widjaja, M. Elepano,
Prof. Dr. S. B. Prusiner, Prof. Dr. A. R. Renslo
Institute for Neurodegenerative Disease
University of California, San Francisco, San Francisco, CA 94143 (USA)
E-mail: stanley@ind.ucsf.edu
[b] Prof. Dr. Z. Li, Prof. Dr. B. M. Silber, Prof. Dr. S. Rao, Prof. Dr. J. R. Gever,
Prof. Dr. S. B. Prusiner
Department of Neurology
University of California, San Francisco, San Francisco, CA 94143 (USA)
We previously reported on the identification of several
classes of antiprion compounds including 2-aminothiazoles
(AMT).[20] Subsequent structure–activity relationship (SAR) stud-
ies of the AMT series led to the discovery of several blood–
brain barrier (BBB)-penetrant AMT lead compounds.[21] From
lead optimization studies in which ~30 early leads were pro-
filed in PK studies, the AMT lead 1 (Figure 1) and a related ana-
logue were selected as possessing optimal pharmacokinetic
(PK) properties for evaluation in animal models of prion dis-
ease. For example, compound 1 was found to achieve sus-
tained brain exposure in mice on oral dosing (%F~40), with
[c] Prof. Dr. B. M. Silber
Department of Bioengineering and Therapeutic Sciences
University of California, San Francisco, San Francisco, CA 94143 (USA)
Current address: ELMEDTECH, San Francisco, CA 94123 (USA)
[d] C. Bryant, Dr. A. Gallardo-Godoy, Prof. Dr. A. R. Renslo
Department of Pharmaceutical Chemistry and
Small Molecule Discovery Center
University of California, San Francisco, San Francisco, CA 94143 (USA)
[e] Dr. E. Dolghih, Prof. Dr. M. P. Jacobson
Department of Pharmaceutical Chemistry
University of California, San Francisco, San Francisco, CA 94143 (USA)
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system. In parallel, we sought to explore substituents that
would alter the pKa of the pyridine C ring, favoring nonplanar
B–C ring conformers via steric or protonation effects.
The synthesis of the desired AMTs was accomplished by
using Hantzsch-type condensation reactions of bromomethyl
ketones with thioureas (Schemes 1–3). The key aminothiazole
intermediate 2 was formed by Hantzsch reaction of 2-bromo-
1-(4-bromophenyl)ethanone with thiourea 5, which is derived
from 2-amino-6-methylpyridine 4.[21] Bromide 2 could be con-
verted into pinacol borate 3 via palladium-catalyzed Suzuki–
Miyaura reaction (Scheme 1). Both aryl bromide 2 and pinacol
borate ester 3 proved to be versatile intermediates for subse-
Figure 1. Structure of lead compound 1 and conformational analysis of neu-
tral (top) and protonated (bottom) forms of 1 by density functional theory.
brain area under the curve (AUC) values for both bound and
unbound drug well in excess of the EC50 values for
the compound.[22]
Despite its promising PK properties, 1 exhibited
only moderate potency (EC50 =1.29 mm) in ScN2a-cl3
cells and was challenging to formulate at the relative-
ly high doses that were predicted to be required to
reach therapeutic brain levels. Accordingly, we
sought to identify close analogues of 1 that might
exhibit substantially improved potency in ScN2a-cl3
cells while retaining the favorable PK and metabolic
properties of 1. With decreased dosing requirements,
we expected to mitigate the formulation issues en-
countered with 1, while also minimizing the potential
for drug-associated toxicities during the necessarily
chronic dosing regimens required in animal models
of prion disease. Herein we report the discovery of
new 2-AMT analogues that exhibit substantially (up
to ~20-fold) improved antiprion potency, while re-
taining or improving upon the PK properties of 1.
Scheme 1. Synthesis of key synthetic intermediates 2 and 3 used in subsequent coupling
reactions to prepare 12–21 and 25–33. Reagents and conditions: a) BzSCN, acetone,
reflux, 1–3 h; b) NaOH, MeOH, reflux, 30 min; c) bromoacetophenone, EtOH, reflux, 3 h;
d) bis(pinacolato)diboron, Pd(dppf)2Cl2, AcOK, 1,4-dioxane, 808C, overnight; e) for com-
pounds 12–21 from 2: ArB(OH)2, 1,4-dioxane, K3PO4, Pd2(dba)3, tricyclohexylphosphine,
microwave (1508C), 30 min; f) for compounds 25–33 from 3: ArBr, Pd(dppf)2Cl2, K2CO3,
1,4-dioxane/H2O (5:1), 808C, overnight.
Table 1. Antiprion potency for AMT analogues.
Results and Discussion
Chemistry
Compound 1 contains four aromatic and heteroaro-
matic rings (Figure 1) joined directly by sp2-hybridized
carbon or nitrogen atoms, producing a highly conju-
gated structure. Density functional theory (DFT)-
based quantum mechanical calculations suggest that
this molecule adopts a largely planar conformation at
neutral pH, with only the terminal ring of the biaryl
system slightly out of plane in the lowest-energy con-
formation. At more acidic pH, the aminopyridine
C ring is protonated, and as a result, 1 adopts a con-
formation in which the B and C rings are no longer
coplanar (Figure 1). Earlier SAR studies provided com-
pelling evidence that a coplanar conformation of the
A–B ring system is required for antiprion effects in
cells.[21] The DFT analysis of 1, however, suggested
that the terminal biaryl A ring system may have less
rigid requirements with regard to coplanarity. Accord-
ingly, we sought to explore diverse heteroaryl and
heterocyclic substitutions at this terminal ring, includ-
ing the introduction of ortho substituents that would
intentionally favor a nonplanar conformation of this
Compd
R
X
EC50 [nm][a]
n[b]
1
phenyl
CH3
CH3
CH3
CH3
CH3
CH3
CH3
1290ꢀ122
87ꢀ43
85
3
3
3
5
12
13
14
15
16
17
pyridin-4-yl
pyridin-4-yl N-oxide
2-methypyridin-4-yl
pyridin-3-yl
pyridin-3-yl N-oxide
2-methylpyridin-3-yl
559ꢀ120
400ꢀ61
68ꢀ13
203ꢀ10
618ꢀ54
3
3
18
CH3
89ꢀ35
3
3
19
CH3
2133ꢀ226
20
21
22
23
24
N-methylpiperazinyl
morpholino
phenyl
CH3
CH3
840ꢀ132
51ꢀ7
3
3
3
3
5
CH3OCH2CH2O–
(CH3)2N–
N-methylpiperazinyl
>10000
phenyl
phenyl
699ꢀ87
1183ꢀ206
[a] Antiprion potency in ScN2a-cl3 cells determined by ELISA; data represent average
values ꢀSEM, which is the standard deviation divided by the square root of n.
[b] Number of repetitions.
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carbonyl) could serve as viable surrogates for the pyr-
idine C ring of 1. Among the amide C groups exam-
ined, cyclopropylamides were deemed of greatest in-
terest due to their good potency and the expectation
of superior hydrolytic/proteolytic stability relative to
acetamides, which were also active. We therefore
sought means to access cyclopropylamide C group
analogues of 1 with diverse A ring substitutions.
Hence, Hantzsch reaction of 9 with thiourea afforded
an AMT intermediate that was then treated with cy-
clopropylcarbonyl chloride to afford the aryl bromide
10 (Scheme 3). We found that bromide 10 and the
corresponding pinacol borate ester 11 readily partici-
pated in Buchwald–Hartwig or Suzuki–Miyaura reac-
tions, affording analogues 39–47 (Table 3).
Table 2. Antiprion potency for AMT analogues with terminal 4-pyridyl or 3-pyridyl
rings.
Compd
R1
R2
EC50 [nm][a]
n[b]
12
15
25
H
–
–
–
H
CH3O
87ꢀ43
68ꢀ13
3
5
3
140ꢀ23
26
27
CH3OCH2CH2O-
–
–
153ꢀ36
137ꢀ13
3
3
CH3OCH2CH2O–
28
29
iPrO–
–
–
2840ꢀ22
3
3
Structure–activity relationships
iPrO–
5860ꢀ327
All EC50 values were determined in ScN2a-cl3 cells as
described previously,[21] and mean EC50 values from
three or more separate determinations are reported
in the tables, along with standard error of the mean
(SEM) values. To confirm that lowering of PrPSc levels
was due to drug-like action and not from the com-
pound affecting the viability of ScN2a-cl3 cells, each
compound was evaluated for its effects on cell viabil-
30
31
(CH3)2N–
–
–
123ꢀ35
69ꢀ21
3
3
(CH3)2N–
32
33
N-methylpiperazinyl
–
–
759ꢀ374
96ꢀ31
3
4
N-methylpiperazinyl
[a] Antiprion potency in ScN2a-cl3 cells determined by ELISA; data represent average
values ꢀSEM, which is the standard deviation divided by the square root of n.
[b] Number of repetitions.
quent Suzuki–Miyaura or Buchwald–Hartwig coupling reac-
tions, yielding the desired biaryl A ring analogues 12–21
(Table 1) and 25–33 (Table 2).
To alter B–C ring diaxial conformational preferences, we
sought to introduce amine substituents neighboring the nitro-
gen atom on the pyridine C ring of AMT analogues. The com-
mercially available aminopyridine 6 was converted in two
steps into thiourea 7 using the standard procedure. The inter-
mediate 7 was next employed in a Hantzsch reaction to afford
the key intermediate 8. As expected, fluoropyridine 8 readily
participated in SNAr reaction with various amines or alkoxides
to afford the desired analogues 22–24 (Table 1, Scheme 2).
More dramatic alteration of the C ring moiety was explored
with commercial and synthetic analogues of 1. Although the
majority of such analogues were devoid of useful antiprion ac-
tivity, we did find that small alkyl amides (acetyl, cyclopropyl-
Scheme 3. Synthesis of intermediates 10 and 11 used in subsequent cou-
pling reactions to afford analogues 39–47. Reagents and conditions: a) thio-
urea, EtOH, RT, 18 h; b) cyclopropanecarbonyl chloride, (iPr)2EtN, CH2Cl2, RT,
24 h; c) bis(pinacolato)diboron, Pd(dppf)2Cl2, KOAc, 1,4-dioxane, 808C, 3 h;
d) for compounds 39–41 from 10: ArB(OH)2, 1,4-dioxane, K3PO4, Pd2(dba)3,
tricyclohexylphosphine, microwave (1508C), 30 min; e) for compounds 42–
47 from 11: ArBr, Pd(dppf)2Cl2, K2CO3, 1,4-dioxane/H2O (5:1), 808C, over-
night.
ity by using the fluorescent probe calcein-AM.[21] As with the
AMT analogues described in our earlier communications, the
new AMTs reported herein do not affect the viability of ScN2a-
cl3 cells at relevant concentrations (LC50 >10 mm for all ana-
logues reported herein).
Our SAR studies began with the premise that the pyridyl
C ring and distal ring of the biaryl A ring system would be
most tolerant of modification and offered the best opportunity
for identifying more potent analogues. This conjecture was in-
formed by our best understanding of SAR for the AMT class
and the results of the DFT-based conformational analysis, as
described above. In fact, seemingly minor structural changes
such as replacement of the terminal phenyl ring with pyridyl
Scheme 2. Synthesis of key synthetic intermediate 8 used in subsequent
SNAr reactions to prepare analogues 22–24. Reagents and conditions:
a) BzNCS, acetone, reflux, 3 h; b) NaOH, MeOH, reflux, 3 h; c) 1-([1,1’-biphen-
yl]-4-yl)-2-bromoethanone, NaHCO3, CH3CN, reflux, 6 h; d) ROH and Na or
R1R2NH, 120–1308C, 4–12 h.
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AMT series led us to analogues such as 1, which
bears a methyl group proximal to the pyridine ring
nitrogen atom. It is possible that the excellent meta-
bolic stability and prolonged half-life of 1 derives in
part from the presence of flanking substituents on
either side of the pyridine C ring nitrogen.[22] In the
current study, we sought to retain flanking substitu-
ents while exploring amines or ethers in place of the
methyl substituent in 1. New analogues such as 22–
24 alter the basicity of the pyridine ring while intro-
ducing greater steric bulk. Evaluation of 22–24 in
ScN2a-cl3 cells revealed that pKa appears relatively
unimportant with respect to antiprion activity. Hence,
weak base 1 (pKa ~5.6) is nearly equipotent to the in-
creasingly basic analogues 23 and 24 (Table 1). Fur-
thermore, the observation that analogue 24 retains
activity suggests that reasonable steric bulk can be
accommodated at the position proximal to the pyri-
dine nitrogen atom (i.e., substituent X, Table 1). The
methoxyethoxy ether analogue 22, in contrast, was
found to be inactive, suggesting an unfavorable en-
tropic and/or steric effect arising from the larger
cone angle of the acyclic ether substituent in 22 as
compared with the cyclic piperazine ring in 24.
With compounds 12 and 15 representing im-
proved leads, we next explored the introduction of
ether or amine substituents on the terminal pyridine
ring (Table 2). A relatively small para-methoxy sub-
stituent as in 25 had little effect on potency, so more
sterically demanding side chains were explored. In
fact, a methoxyethoxy ether was well tolerated at
either the meta or para positions (analogues 26 and
27). Branched side chains were less well tolerated,
however, with isopropyl ethers 28 and 29 somewhat
less potent than 1 and much less potent than the
parent pyridine analogues 12 and 15. As with the
C ring modifications discussed above, modifying ba-
Table 3. Antiprion potency for AMT analogues with amide C groups.
Compd
R1
R2
EC50 [nm][a]
n[b]
34
35
36
37
38
39
40
41
phenyl
phenyl
phenyl
phenyl
phenyl
pyridin-4-yl
2-methylpyridin-3-yl
4-(CH3)2N-pyridin-3-yl
cPr
CH3
CH3OCH2–
iPr
phenyl
cPr
248ꢀ67
119 ꢀ10
4
3
3
3
3
3
3
3
1588ꢀ295
>10000
>10000
173ꢀ16
cPr
cPr
>10000
109ꢀ12
42
43
44
cPr
cPr
cPr
>10000
>10000
1315ꢀ233
3
3
4
45
46
cPr
cPr
682ꢀ100
118ꢀ11
3
3
47
cPr
70ꢀ23
4
[a] Antiprion potency in ScN2a-cl3 cells determined by ELISA; data represent average
values ꢀSEM, which is the standard deviation divided by the square root of n.
[b] Number of repetitions.
was not only tolerated but produced analogues (12 and 15)
with >10-fold greater potency than 1 in ScN2a-cl3 cells
(Table 1). The corresponding pyridine N-oxides 13 and 16 were
less potent than the reduced forms, but still more potent than
1.
Perturbation of the pyridine–phenyl dihedral angle with
ortho substituents (in 14 and 17) was also tolerated, in contrast
to the detrimental effects we observed for similar perturbation
of the A–B ring dihedral.[21] Heterocycles other than pyridine
could also be introduced at the terminal position, including
pyrazole (18), piperazine (20), and morpholine (21). The isoxa-
zole analogue 19 was the only heteroaromatic analogue inferi-
or to 1, although this effect may be less related to the isoxa-
zole ring than to the presence of two methyl groups in posi-
tions that must severely limit the number of energetically rea-
sonable conformations available to this analogue.
sicity through A ring substitutions had a negligible effect on
potency: the dimethylaminopyridines 30 and 31 were essen-
tially equipotent to their parent pyridine analogues. Introduc-
tion of an N-methylpiperazine side chain was better tolerated
at the para position (33) than in the meta position (32). In
summary, the introduction of amine or ether side chains in the
terminal pyridyl A ring produced several new analogues that
retained the good potency of 12 and 15. With altered basici-
ties and polar surface areas, the in vivo behavior of these new
AMT analogues was of considerable interest.
A parallel SAR effort was directed at exploring more diverse
substituents in place of the pyridyl C ring in 1. Various aliphatic
and aromatic substituents were examined with little success.
However, small aliphatic amides proved to be perfectly viable
C groups, with acetamide 35 and cyclopropylamide 34 proving
to be ten- and fivefold more potent than 1, respectively. Steric
requirements are strict in this series, however, as the marginal-
ly larger methoxyacetamide 36 was notably less potent than
34 or 35, whereas isopropylamide 37 and benzamide 38 were
without measurable antiprion activity (Table 3).
In our earlier SAR studies of the C ring, we had noted that
distal ring substitutions, including fusion to a second ring
system (e.g., quinoline for pyridine), produced more potent an-
alogues.[21] However, optimization of brain exposure for the
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The SAR of amide-type C groups was distinct from that of
the original AMT series, where aromatic C rings as large as
quinoline were not only tolerated but exhibited enhanced po-
tency.[21] We soon found that other SAR trends also failed to
translate between the original pyridyl C ring series and the
new amide C group series. Hence, a reinvestigation of “opti-
mal” biaryl A rings was undertaken in the context of a cyclo-
propyl C group (Table 3). While a terminal pyridine ring was
well tolerated in both contexts (compare 12 and 39), an ortho-
methyl substituent was not permitted in the cyclopropylamide
series (analogues 40, 42, and 43). Moving to the meta and
para positions, we found that para substitution (46 and 47)
was better tolerated than meta substitution (44 and 45). Over-
all, SAR in the cyclopropylamide C group series suggests more
stringent steric requirements about the biaryl A ring. Another
interpretation of this SAR is that cyclopropylamide analogues
require a more nearly coplanar biaryl A ring system for effec-
tive binding. Overall, it appears that AMT analogues bind
slightly differently depending on the nature of the C ring
group.
dized form of 15) achieved overall exposure similar to 15, but
was predominantly distributed in plasma rather than brain.
The same was true of 27, the pyridin-3-yl analogue bearing
a methoxyethoxy side chain. Despite having poorer brain pen-
etration than 1, analogues 16 and 27 nevertheless exhibited
improved brain AUC/EC50 ratios relative to 1 (Table 4).
Given the exceptional in vivo profile of pyridin-3-yl analogue
15, it was surprising to find that regioisomeric analogue 12 ex-
hibited much inferior brain exposure and an only slightly im-
proved AUC/EC50 ratio over that of 1. Related pyridin-4-yl ana-
logues such as 26 and 32 were similarly disappointing in vivo,
with AUC/EC50 ratios only similar to 1. The N-methylpiperazine
analogue 32 exhibited the best brain/plasma AUC ratio (>3)
of the AMT analogues studied, but its modest potency pro-
duced a brain AUC/EC50 ratio slightly inferior to 1. Of the pyri-
dine C ring analogues examined in mice, pyridin-3-yl analogue
15 emerged as the clear winner. Hence, an increase in brain
AUC/EC50 ratio from 7.6 to 160 was realized by the introduction
of a single nitrogen atom (compare 1 and 15).
We also examined the in vivo PK properties of AMT ana-
logues bearing cyclopropylamide C groups, beginning with the
progenitor of this series, compound 34. This analogue exhibit-
ed the highest brain exposure of all the AMT analogues exam-
ined, producing an excellent brain AUC/EC50 ratio of 75. Disap-
pointingly, however, none of the other cyclopropylamide ana-
logues evaluated demonstrated anywhere near the brain expo-
sure observed with 34. Indeed, cyclopropylamide analogues
45, 46, and 47 exhibited very poor exposure in both brain and
plasma, resulting in brain AUC/EC50 ratios that were inferior to
1. Possibly the poor metabolic stability of the N-methylpipera-
zine analogues 45 and 47 is partly to blame for their poor per-
formance. It is interesting to compare the congeneric pairs 34/
1 and 32/45, which differ only in the nature of the C group/
ring. With regard to brain AUC levels, the cyclopropylamide in
34 is superior to the pyridine in 1, whereas in the case of 32
and 45, pyridine is favored over cyclopropylamide. Such find-
ings highlight the necessarily empirical nature of lead optimi-
zation and the difficulty in predicting in vivo exposure levels,
even among closely related structural analogues.
In vivo pharmacokinetics
In vivo evaluation of the new AMT analogues was conducted
throughout the course of the optimization described above.
Here we summarize our findings and evaluate specific physio-
chemical properties that appear to impact the brain exposure
of AMT analogues in mice. Following an oral dose of
10 mgkgꢁ1, compound 1 achieved a brain AUC value of 9.78ꢀ
2.07 mmh, a brain/plasma AUC ratio >1, and a brain AUC/EC50
ratio of 7.6 (Table 4). These values represented a benchmark at
the outset of the current study. Specifically, we sought to im-
prove the brain AUC/EC50 ratio in new analogues, with the
long-term aim of achieving animal efficacy at the lowest possi-
ble daily dose. Gratifyingly, the highly potent pyridin-3-yl ana-
logue 15 was found to have a brain AUC value similar to that
of 1, resulting in a dramatically improved brain AUC/EC50 ratio
of 160 (as compared with 7.6 for 1). The N-oxide 16 (the oxi-
In an attempt to better understand which physio-
chemical properties most influence the brain expo-
sure of AMT analogues, we correlated experimental
PK parameters for the compounds in Table 4 with
readily calculated properties such as molecular
weight, clogP, and total polar surface area (TPSA).
These properties have been proposed[23] as potential
predictors of permeability across the BBB. We exclud-
ed from this analysis 32, 45, and 47, as these ana-
logues appear to have a metabolic liability associat-
ed with the N-methylpiperazine ring and are there-
fore not representative of the AMT class in general
(Table 4). Correlation coefficients (r2 values) were de-
termined with the software package Vortex (Dotmat-
ics, Ltd.) and are presented in Table 5. With regard to
measured brain AUC values, clogP was very poorly
correlated (r2 =0.13), whereas molecular weight (r2 =
0.54) and TPSA (r2 =0.60) were better predictors. Of
Table 4. In vivo PK parameters and microsome stability for selected AMT analogues
following a single 10 mgkgꢁ1 oral dose in mice.
[b]
Compd
Cmax [mm]
Brain
AUC [mmh]
t1/2 [min][a]
AUC/EC50
Brain
Brain
Plasma
1
2.45ꢀ0.74
0.50ꢀ0.05
2.46ꢀ0.85
0.33ꢀ0.16
1.17ꢀ0.19
0.97ꢀ0.22
0.90ꢀ0.24
4.34ꢀ0.53
0.25ꢀ0.11
0.15ꢀ0.01
0.06ꢀ0.03
9.78ꢀ2.07
1.68ꢀ0.10
10.90ꢀ1.75
1.04ꢀ0.13
5.22ꢀ0.10
3.27ꢀ0.44
3.85ꢀ0.52
18.60ꢀ3.75
1.29ꢀ0.02
0.32ꢀ0.00
0.19ꢀ0.08
6.99ꢀ0.73
ND[c]
>60
>60
>60
ND[c]
6.8
>60
>60
>60
4.4
7.6
19
160
6.8
6.9
24
19
75
1.9
2.7
2.7
12
15
26
32
27
16
34
45
46
47
15.60ꢀ0.06
ND[c]
1.57ꢀ0.15
6.75ꢀ0.45
11.50ꢀ0.71
12.70ꢀ1.11
0.76ꢀ0.01
0.26ꢀ0.01
0.38ꢀ0.19
55
2.5
[a] Stability to mouse liver microsomes. [b] Ratio of brain AUC [mmh] to EC50 [mm].
[c] Not determined.
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Epik, and two protonation states were generated: neutral and with
+1 charge. Each of the states, initially in planar configuration, was
then subjected to geometry optimization in Jaguar[25] using
DFT[26,27] with B3LYP functional and 6-31G** basis set. The DIIS con-
vergence scheme and default convergence criteria were used:
maximum iteration number of 48 and energy change of 5ꢂ
10ꢁ5 hartrees. The calculated properties provided in Table 5 were
calculated with Vortex software (Dotmatics, Ltd.).
Table 5. Correlation of selected calculated properties with experimentally
determined PK parameters, expressed as correlation coefficients (r2
values).
Mr [Da]
clogP[a]
TPSA[a]
Brain AUC
Plasma AUC
Total AUC
Brain/plasma AUC ratio
0.54
0.43
0.70
0.21
0.13
0.10
0.10
0.00
0.60
0.27
0.60
0.32
Compound characterization and purity: Reagents and solvents
were purchased from Aldrich Chemical, Acros Organics, Alfa Aesar,
AK Scientific, or TCI America and used as received unless otherwise
indicated. Compounds 34–38 were obtained from commercial
sources. Air- and/or moisture-sensitive reactions were carried out
under an argon atmosphere in oven-dried glassware using anhy-
drous solvents from commercial suppliers. Air- and/or moisture-
sensitive reagents were transferred via syringe or cannula and in-
troduced into reaction vessels through rubber septa. Solvent re-
moval was accomplished with a rotary evaporator at ~10–50 torr.
Microwave irradiation was carried out with a CEM Intellivent Ex-
plorer system. Automated silica gel column chromatography was
carried out with a Biotage SP1 system and silica gel cartridges
from Biotage. Analytical TLC plates from EM Science (silica gel
[a] Calculated in Vortex using “XlogP” and “TPSA_NOPS” predictors.
course, brain AUC values clearly depend on other PK parame-
ters such as oral bioavailability, metabolism, and clearance,
which will vary unpredictably between analogues. Given this,
the brain/plasma AUC ratio might be regarded as a more
direct measure of BBB penetration. Unfortunately, none of the
calculated properties showed a compelling correlation with
brain/plasma AUC ratio, although TPSA was again best (r2 =
0.00, 0.21, and 0.32, for clogP, Mr, and TPSA, respectively). This
poor correlation may reflect the inability of crude measures
such as TPSA and clogP to explain active efflux by the drug
transporter P-glycoprotein, which plays an important role in
small-molecule permeability across the BBB.[24]
1
60 F254) were used for TLC analyses. H NMR spectra were recorded
with a Varian INOVA-400 400 MHz spectrometer for compounds 1,
12–21, 25, and 39–43, or a Bruker Avance III plus 400 MHz for
compounds 22–24, 26–33, and 44–47. Chemical shifts (d) are re-
ported in ppm relative to tetramethylsilane (TMS) as an internal
standard. Coupling constants (J) are reported in hertz (Hz). Charac-
terization data are reported as follows: chemical shift, multiplicity
(s=singlet, d=doublet, t=triplet, q=quartet, br=broad, m=
multiplet), coupling constants, number of protons, mass-to-charge
ratio.
Conclusions
In this study, we sought to improve the potency of new AMT
leads while maintaining the favorable in vivo PK profile of our
previous best lead compound 1. The majority of the new ana-
logues described herein showed improved potency over that
of 1, and several exhibited EC50 values <100 nm in ScN2a-cl3
cells (Tables 1–3). Of ten new AMT leads evaluated in single-
dose mouse PK studies, half (12, 15, 16, 27, and 34) demon-
strated brain AUC/EC50 ratios that were substantially improved
over 1. Compounds 15 and 34 appear to be particularly prom-
ising leads, with respective brain AUC/EC50 ratios of 160 and 75
following a single oral dose of 10 mgkgꢁ1. These analogues
would therefore be predicted to achieve therapeutic brain con-
centrations at oral doses much lower than might be required
for 1, thus satisfying the original objectives of our study. The
evaluation of 15 and 34 in animal models of prion disease will
be of significant interest.
All analogues submitted for testing were judged to be of 95%
purity or higher based on analytical LC–MS analysis. For com-
pounds 1, 12–21, 25, and 39–43, LC–MS analyses were performed
on a Waters Micromass ZQ/Waters 2795 Separation Module/Waters
2996 Photodiode Array Detector system controlled by MassLynx
4.0 software. Separations were carried out on an XTerra MS C18
5 mm, 4.6ꢂ50 mm column at ambient temperature using a mobile
phase of H2O/CH3CN containing 0.05% trifluoroacetic acid. Gradi-
ent elution was employed wherein the CH3CN/H2O ratio was in-
creased linearly from 5 to 95% CH3CN over 2.5 min, maintained at
95% CH3CN for 1.5 min, then decreased to 5% CH3CN over
0.5 min, and maintained at 5% CH3CN for 0.5 min. Compound
purity was determined by integrating peak areas of the liquid chro-
matogram, monitored at l 254 nm.
LC–MS analyses for compounds 22–24, 26–33, and 44–47 were
performed on an Agilent LC–MSD 1200 Series, a quadrupole mass
spectrometer equipped with a Welchrom XB-C18 column (50ꢂ
4.6 mm, 5 mm) at ambient temperature using a mobile phase of
H2O/CH3CN containing 0.05% trifluoroacetic acid at a flow rate of
1.5 mLminꢁ1. Gradient elution was used wherein the CH3CN/H2O
ratio was increased linearly from 5 to 95% CH3CN over 2.5 min,
maintained at 95% CH3CN for 1.5 min, then decreased to 5%
CH3CN over 0.5 min, and maintained at 5% CH3CN for 0.5 min.
Compound purity was determined by integrating peak areas of the
liquid chromatogram, monitored at l 254 nm.
Experimental Section
EC50 and LC50 assays: The methods employed to evaluate the ef-
fects of compounds on PrPSc levels and cell viability were analo-
gous to previously published protocols.[21]
Microsome stability and in vivo PK studies: Procedures and anal-
ysis for the microsome stability and PK studies were performed as
previously reported.[22] All animal studies were approved by the In-
stitutional Animal Care and Use Committee at the University of Cal-
ifornia San Francisco.
General procedure A for preparing aminothiazole analogues
from thioureas: An ethanolic solution (~10 mL) of the desired thi-
ourea (1 mmol) and the requisite bromoacetophenone (1 mmol)
was heated at reflux for 3–5 h, or until the reaction was judged
Computational methods: The structure of compound 1 was pre-
pared and minimized in the Ligprep module of Schrçdinger Soft-
ware Suite 2010.[25] Nitrogen pKa values were predicted by using
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complete (LC–MS). The reaction mixture was then poured into ice-
water (20 mL) and stirred for another 30 min. A solution of aque-
ous 1n Na2CO3 was then added to produce a solution of pH~8.
The aminothiazole product typically precipitated from this solution
and was collected by filtration and washed with H2O. Crude amino-
thiazoles were purified by column chromatography on silica gel
(~40–80% EtOAc/hexanes) or by using reversed-phase HPLC. Rele-
vant fractions were collected and concentrated to afford the de-
sired product.
were washed with brine and H2O, dried over Na2SO4, and concen-
trated to intermediate 7 as a yellow solid (1.7 g, 56% yield);
1H NMR (400 MHz, CDCl3): d=6.62 (1H, dd, J=2.0, 8.0 Hz), 6.76
(1H, dd, J=1.2, 8.0 Hz), 7.73–7.76 (1H, m), 10.21 ppm (1H, brs);
MS (ESI) m/z 172 [M+H]+.
4-([1,1’-Biphenyl]-4-yl)-N-(6-fluoropyridin-2-yl)thiazol-2-amine
(8): A mixture of intermediate 7 (1.7 g, 10.0 mmol), 1-([1,1’-biphen-
yl]-4-yl)-2-bromoethanone (2.78 g, 10.0 mmol) and NaHCO3 (1.0 g,
12 mmol) in CH3CN (25 mL) was stirred at 808C for 6 h. The reac-
tion mixture was concentrated to give a brown residue, which was
suspended in CH2Cl2 (50 mL). The suspension was filtered, and the
filtrate was concentrated to afford intermediate 8 as a yellow solid
(4-Biphenyl-4-ylthiazol-2-yl)-(6-methylpyridin-2-yl)amine (1): (6-
Methylpyridin-2-yl)thiourea[21] was treated with commercially avail-
able 1-biphenyl-4-yl-2-bromoethanone, according to general proce-
dure A to afford the title compound as an off-white powder in
1
(1.4 g, 40% yield); H NMR (400 MHz, CDCl3): d=6.43 (1H, dd, J=
1
85% yield; mp: 218–2228C; H NMR (400 MHz, [D6]DMSO): d=2.47
2.4, 8.0 Hz), 6.50 (1H, dd, J=1.2, 8.0 Hz), 7.12 (1H, s), 7.35 (1H, t,
J=7.2 Hz), 7.45 (2H, t, J=8.0 Hz), 7.51 (1H, q, J=8.0 Hz), 7.60–7.64
(4H, m), 7.94 (2H, d, J=8.0 Hz), 9.79 ppm (1H, brs); MS (ESI) m/z
348 [M+H]+.
(s, 3H), 6.79 (d, J=7.14 Hz, 1H), 6.90 (d, J=8.24 Hz, 1H), 7.32–7.40
(m, 1H), 7.42–7.51 (m, 3H), 7.55–7.63 (m, 1H), 7.67–7.76 (m, 4H),
7.96–8.02 (m, 2H), 11.35 ppm (s, 1H); 13C NMR (100 MHz,
[D6]DMSO): d=23.4, 106.2, 107.5, 114.9, 126.1, 126.4, 126.8, 127.0,
127.4, 128.9, 128.9, 129.1, 134.0, 138.1, 138.9, 139.7, 148.1, 151.1,
155.1, 159.7 ppm; MS (ESI) m/z 344 [M+H]+.
Cyclopropanecarboxylic acid [4-(4-bromophenyl)thiazol-2-yl]a-
mide (10): A mixture of commercially available 2-bromo-1-(4-bro-
mophenyl)ethanone (9, 1 mmol) and 1.0 equiv of thiourea
(1 mmol) in EtOH (~10 mL) was stirred overnight, or until the reac-
tion was judged complete (LC–MS). The reaction mixture was
evaporated and dissolved in EtOAc, the organic layer was washed
with aqueous NaHCO3. The organic layer was separated, dried over
MgSO4, filtered, and concentrated to afford 4-(4-bromophenyl)thia-
zol-2-ylamine in 95% yield. This material was used without further
purification. 1H NMR (400 MHz, [D6]DMSO): d=7.08 (s, 3H), 7.51–
7.57 (m, 2H), 7.70–7.77 ppm (m, 2H); MS (ESI) m/z 256 [M+H]+.
[4-(4-Bromophenyl)thiazol-2-yl]-(6-methylpyridin-2-yl)amine (2):
An ethanolic solution of (6-methylpyridin-2-yl)thiourea (5,
1 mmol)[21] and commercially available 2-bromo-1-(4-bromopheny-
l)ethanone (1 mmol, 1:1 equiv) was reacted according to general
procedure A. The crude product was purified by column chroma-
tography on silica gel (40!100% EtOAc/hexanes), and relevant
fractions were collected and concentrated to afford the aryl bro-
mide 2 as a white powder in 80% yield. 1H NMR (400 MHz,
[D6]DMSO): d=2.47 (s, 3H), 6.79 (d, J=7.33 Hz, 1H), 6.88 (d, J=
8.24 Hz, 1H), 7.56–7.64 (m, 3H), 7.82–7.89 (m, 2H), 7.49 (s, 1H),
11.35 ppm (s, 1H); MS (ESI) m/z 347 [M+H]+.
4-(4-Bromophenyl)thiazol-2-ylamine (2.61 mmol) was treated with
cyclopropanecarbonyl chloride (2 equiv, 5.33 mmol) and DIPEA
(4 equiv, 10.4 mmol) in CH2Cl2 (40 mL). The reaction mixture was
stirred at room temperature overnight or until the reaction was
judged complete (LC–MS). The reaction mixture was washed with
1n HCl (40 mL), and the organic layer was separated, washed with
aqueous NaHCO3 and brine. The organic layer was separated, dried
over MgSO4, filtered, and the solvent evaporated. The resulting
solid was further washed with Et2O and dried to afford 10 in 35%
yield; 1H NMR (400 MHz, [D6]DMSO): d=0.87–0.96 (m, 4H), 1.93–
2.01 (m, 1H), 7.59–7.68 (m, 3H), 7.81–7.88 (m, 2H); LCMS (ESI) m/z
324 [M+H]+.
N-(6-Methylpyridin-2-yl)-4-[4-(4,4,5,5-tetramethyl-1,3,2-dioxabor-
olan-2-yl)phenyl]thiazol-2-amine (3):
A modification of the
Miyaura borylation procedure[28] was employed. A solution of 2
(5.0 g, 14.5 mmol), bis(pinacolato)diboron (4.8 g, 18.8 mmol), Pd-
(dppf)2Cl2 (1.2 mg, 1.5 mmol), and KOAc (4.3 g, 43.3 mmol) in 1,4-
dioxane (100 mL) was heated at 808C under N2 overnight. The re-
action mixture was loaded directly onto a rotary evaporator to
remove most of the solvents under vacuum. H2O (200 mL) was
added to the resulting residue, which was then extracted with
CH2Cl2 (3ꢂ60 mL). The combined organic layers were dried over
Na2SO4, filtered, and evaporated to give the crude product as
a brown residue. This material was purified by silica gel column
chromatography using EtOAc/hexane to afford compound 3 as
a yellow solid (2.7 g, 64%); 1H NMR (400 MHz, CDCl3): d=1.35
(12H, s), 2.54 (3H, s), 6.33–6.35 (1H, m), 6.66–6.68 (1H, m), 7.11
(1H, s), 7.29–7.33 (1H, m), 7.81–7.83 (2H, m), 7.89–7.91 (2H, m),
9.72 ppm (1H, s).
N-{4-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]thia-
zol-2-yl}cyclopropanecarboxamide (11): A modification of the
Miyaura borylation procedure[28] was employed. A solution of 10
(500 mg, 1.55 mmol), bis(pinacolato)diboron (510 mg, 2.01 mmol),
Pd(dppf)2Cl2 (120 mg, 0.15 mmol), and KOAc (460 mg, 4.65 mmol)
in 1,4-dioxane (8.0 mL) was heated at 808C under N2 overnight.
The reaction mixture was placed onto a rotary evaporator to
remove most of the solvents under vacuum. H2O (20 mL) was
added to the resulting residue, which was extracted with CH2Cl2
(3ꢂ30 mL). The combined organic layers were dried over Na2SO4,
filtered, and evaporated to give the crude product as a brown resi-
due, which was purified by silica gel column chromatography
using EtOAc/petroleum ether (1:20) to afford 11 as an off-white
1-(6-Fluoropyridin-2-yl)thiourea (7): To a solution of benzoyl iso-
thiocyanate (3.2 g, 19.6 mmol) in acetone (30 mL) was added 6-flu-
oropyridin-2-amine (6, 2.0 g, 17.9 mmol) in acetone (15 mL) drop-
wise, and then the reaction mixture was heated at reflux for 3 h.
The reaction mixture was poured on to crushed ice, filtered, and
washed with H2O to afford N-[(6-fluoropyridin-2-yl)carbamothioyl]-
benzamide as a yellow solid (4.9 g, 91% crude yield). LCMS (ESI)
m/z 276 [M+H]+.
1
solid (460 mg, 80% yield); H NMR (400 MHz, CDCl3): d=0.72–0.77
(2H, m), 1.06–1.11 (2H, m), 1.25 (1H, m), 1.36 (12H, s), 7.18 (1H, s),
7.80–7.86 (4H, m), 10.30 ppm (1H, brs).
To a solution of N-[(6-fluoropyridin-2-yl)carbamothioyl]benzamide
as a yellow solid (4.9 g, 17.9 mmol) in THF (72 mL) was added 2n
NaOH (18 mL), the reaction mixture was then heated at reflux for
3 h. The reaction mixture was then diluted with H2O (60 mL) and
extracted with CH2Cl2 (3ꢂ60 mL). The combined organic layers
General procedure B for preparing aminothiazole analogues
from intermediate 2: Coupling conditions described by Fu and
colleagues[29] were employed. A 10-mL microwave reaction vial was
charged with
2 (0.42 mmol), the appropriate boronic acid
(2.0 equiv), tricyclohexylphosphine (0.04 mmol), and tris(dibenzyli-
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deneacetone)dipalladium (0.016 mmol) dissolved in degassed 1,4-
dioxane (0.8 mL). A degassed 1.26m solution of K3PO4 (0.92 mmol)
was then added along with a stir bar. The reaction tube was
capped, and the contents were further degassed for 1 min by bub-
bling argon through the solution. The reaction was then subjected
to microwave irradiation at 1508C for 30 min. After cooling, the
crude reaction mixture was subjected to one of three workup pro-
cedures: In workup A, the precipitated product was collected;
washed with H2O, CH3OH, and Et2O, and then subjected to prepa-
rative HPLC purification. In workup B (for products that did not
precipitate), the reaction mixture was partitioned between EtOAc
and aqueous NaHCO3, and the organic layer separated, dried, and
solvent removed under vacuum to afford crude product, which
was purified by automated silica gel column chromatography
using EtOAc/hexane. In workup C, the precipitated product was fil-
tered, re-dissolved in ~2 mL DMSO, filtered through a 0.02 mm
Whatman Anatop filter, and gently swirled on an orbital stirrer with
70 mg Quadrapure MPA resin overnight to remove palladium; the
resin was then removed by filtration and the product was precipi-
tated from ice water to afford the product.
(6-Methylpyridin-2-yl)-[4-(4-pyridin-4-yl-phenyl)thiazol-2-yl]a-
mine (12): Intermediate 2 was treated with pyridin-4-ylboranediol
according to general procedure B and workup C to afford the title
compound (13 mg) in 9% yield; mp: 238–2428C; 1H NMR
(400 MHz, [D6]DMSO): d=2.48 (s, 3H), 6.80 (d, J=7.51 Hz, 1H), 6.90
(d, J=8.06 Hz, 1H), 7.59 (t, J=8.0 Hz, 1H), 7.57 (s, 1H), 7.76 (d, J=
8.0 Hz, 2H), 7.87–7.92 (m, J=8.24 Hz, 2H), 8.03–8.09 (m, J=
8.42 Hz, 2H), 8.64 (d, J=5.86 Hz, 2H), 11.38 ppm (s, 1H); MS (ESI)
m/z 345 [M+H]+.
4-(4-{2-[(6-Methylpyridin-2-yl)amino]thiazol-4-yl}phenyl)pyridine
1-oxide (13): Pinacoboronate intermediate 3 was treated with 4-
bromopyridine 1-oxide according to general procedure C to afford
the title compound as a yellow solid (100 mg) in 36% yield;
1H NMR (400 MHz, [D6]DMSO): d=2.42 (3H, s), 6.79–6.80 (1H, m),
6.88–6.90 (1H, m), 7.56–7.62 (2H, m), 7.83–7.88 (4H, m), 8.02–8.04
(2H, m), 8.29–8.28 (2H, m), 11.38 ppm (1H, s); LCMS (ESI) m/z 361.1
[M+H]+.
(6-Methylpyridin-2-yl)-{4-[4-(3-methylpyridin-4-yl)phenyl]thiazol-
2-yl}amine trifluoroacetate salt (14): Intermediate 2 was treated
with commercially available 3-picoline-4-boronic acid according to
general procedure B and workup A to afford the title compound
(20 mg) in 29% yield. 1H NMR (400 MHz, [D6]DMSO): d=2.44 (s,
3H), 2.48 (s, 3H), 6.81 (d, J=7.33 Hz, 1H), 6.92 (d, J=8.06 Hz, 1H),
7.57–7.65 (m, 4H), 7.81 (d, J=5.68 Hz, 1H), 8.06–8.12 (m, 2H), 8.74
(d, J=5.86 Hz, 1H), 8.81 ppm (s, 1H); MS (ESI) m/z 359 [M+H]+.
General procedure C for preparing aminothiazole analogues
from intermediate 3: A solution of pinacol boronate 3 (300 mg,
0.76 mmol), the appropriate aryl bromide (1.3 equiv), Pd(dppf)2Cl2
(62 mg, 0.08 mmol, 10 mol%), and K2CO3 (316 mg, 2.29 mmol) in
1,4-dioxane (25 mL) and H2O (5 mL) was heated at 808C under N2
overnight. The reaction mixture was loaded directly onto a rotary
evaporator to remove most of the solvents under vacuum. H2O
(10 mL) was added to the resulting residue, which was then ex-
tracted with CH2Cl2 (3ꢂ20 mL). The combined organic layers were
dried over Na2SO4, filtered, and evaporated to give the crude prod-
uct, which was then purified by preparative HPLC to afford the
product.
(6-Methylpyridin-2-yl)-[4-(4-pyridin-3-yl-phenyl)thiazol-2-yl]a-
mine (15): Intermediate 2 was treated with pyridin-3-ylboranediol
according to general procedure B and was further treated accord-
ing to workup C to afford the title compound (52 mg) in 37%
yield; mp: 176–1788C; 1H NMR (400 MHz, [D6]DMSO): d=2.48 (s,
3H) 6.81 (d, J=7.14 Hz, 1H) 6.91 (d, J=8.24 Hz, 1H) 7.52–7.67 (m,
2H) 7.79 (dd, J=8.15, 5.22 Hz, 1H) 7.89 (d, J=8.61 Hz, 2H) 8.08 (d,
J=8.42 Hz, 2H) 8.50 (d, J=7.69 Hz, 1H) 8.72 (d, J=4.94 Hz, 1H)
9.12 (brs, 1H) 1.37 ppm (brs, 1H); 13C NMR (100 MHz, [D6]DMSO):
d=23.4, 106.7, 107.5, 115.0, 123.9, 126.3, 127.1, 133.9, 134.6, 135.1,
135.8, 138.2, 147.4, 147.9 148.4, 151.1, 155.2, 159.7 ppm; MS (ESI)
m/z 345 [M+H]+.
General procedure D for preparing aminothiazole analogues
from intermediate 10: A 10 mL microwave reaction vial was
charged with 10 (0.23 mmol), the appropriate boronic acid
(0.46 mmol,
2.0 equiv),
tris(dibenzylideneacetone)dipalladium
(0.008 mmol), and tricyclohexylphosphine (0.02 mmol) dissolved in
degassed 1,4-dioxane (0.8 mL). A degassed 1.26m solution of
K3PO4 (0.518 mmol) was then added along with a stir bar. The reac-
tion tube was capped, and the contents were further degassed for
1 min by bubbling argon through the solution. The reaction was
then subjected to microwave irradiation at 1508C for 30 min. After
cooling, reaction products were isolated by one of the following
workups: In workup A, the precipitated product was washed with
H2O, MeOH, and Et2O, then subjected to preparative HPLC purifica-
tion. In workup B (for products that did not precipitate), the reac-
tion mixture was partitioned between EtOAc and aqueous
NaHCO3; the organic layer was separated and dried, and the sol-
vent was removed under vacuum to afford crude product that was
purified on silica gel column chromatography using EtOAc/hexane.
3-(4-{2-[(6-Methylpyridin-2-yl)amino]thiazol-4-yl}phenyl)pyridine
1-oxide (16): Pinacoboronate intermediate 3 was treated with 3-
bromopyridine 1-oxide according to general procedure C to afford
1
the title compound as a yellow solid (42 mg) in 23% yield; H NMR
(400 MHz, [D6]DMSO): d=2.50 (3H, s), 6.80–6.81 (1H, m), 6.89–6.91
(1H, m), 7.49–7.61 (3H, m), 7.63 (1H, s), 7.71–7.73 (2H, m), 8.03–
8.05 (2H, m), 8.21–8.23 (1H, m), 8.64 (1H, s), 11.38 ppm (1H, s); MS
(ESI) m/z 361.1 [M+H]+.
(6-Methylpyridin-2-yl)-{4-[4-(2-methylpyridin-3-yl)phenyl]thiazol-
2-yl}amine trifluoroacetate salt (17): Intermediate 2 was treated
with commercially available 2-methyl-3-(4,4,5,5-tetramethyl-
[1,3,2]dioxaborolan-2-yl)pyridine according to general procedure B
and workup B. Automated silica gel chromatography followed by
preparative HPLC purification afforded the title compound (44 mg)
General procedure E for preparing aminothiazole analogues
from intermediate 11: A solution of pinacol boronate 11 (200 mg,
0.54 mmol), the appropriate aryl bromide (1.2 equiv), Pd(dppf)2Cl2
(44 mg, 0.054 mmol, 10 mol%), and K2CO3 (224 mg, 1.62 mmol) in
1,4-dioxane (25 mL) and H2O (5 mL) was heated at 808C under N2
overnight. The reaction mixture was loaded directly onto a rotary
evaporator to remove most of the solvents under vacuum. H2O
(10 mL) was added to the resulting residue, which was extracted
with CH2Cl2 (3ꢂ20 mL). The combined organic layers were dried
over Na2SO4, filtered, and evaporated to give the crude product,
which was then purified by preparative HPLC to afford the final
product.
1
in 64% yield; mp: 174–1768C; H NMR (400 MHz, [D6]DMSO): d=
2.45 (s, 3H), 2.68 (s, 3H), 6.81 (d, J=7.3 Hz, 1H), 6.92 (d, J=8.2 Hz,
1H), 7.49–7.72 (m, 4H), 7.89 (d, J=5.7 Hz, 1H), 8.08 (d, J=7.3 Hz,
2H), 8.36 (d, J=7.9 Hz, 1H), 8.79 (d, J=5.5 Hz, 1H), 11.37 ppm (brs,
1H); MS (ESI) m/z 359 [M+H]+.
{4-[4-(2-Methyl-2H-pyrazol-3-yl)phenyl]thiazol-2-yl}-(6-methyl-
pyridin-2-yl)amine (18): Intermediate 2 (50 mg, 0.145 mmol) was
treated with commercially available (1-methyl-1H-pyrazol-5-yl)bora-
nediol (36.5 mg, 0.290 mmol) according to general procedure B,
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1
except that catalyst loading was increased (0.21 mmol tricyclohexyl
phosphine, 0.087 mmol palladium catalyst) and with microwave ir-
radiation at 1508C for 1 h. Workup B afforded in the title com-
as a yellow solid (49 mg, 21% yield); H NMR (400 MHz, CDCl3): d=
3.48 (3H, s), 3.83–3.85 (2H, m), 4.69–4.71 (2H, m), 6.23 (1H, d, J=
8.0 Hz), 6.38 (1H, d, J=8.0 Hz), 7.05 (1H, s), 7.26–7.35 (1H, m),
7.37–7.47 (3H, m), 7.62–7.65 (4H, m), 7.92–7.94 (2H, m), 8.77 ppm
(1H, s); MS (ESI) m/z 404 [M+H]+.
1
pound (32 mg) in 62% yield. H NMR (400 MHz, CDCl3): d=2.54 (s,
3H), 3.87 (s, 3H), 6.31 (d, J=1.83 Hz, 1H), 6.35 (d, J=8.24 Hz, 1H),
6.68 (d, J=7.33 Hz, 1H), 7.10 (s, 1H), 7.30 (t, J=7.78 Hz, 1H), 7.42
(d, J=8.42 Hz, 2H), 7.51 (d, J=1.83 Hz, 1H), 7.96 (d, J=8.24 Hz,
2H), 9.79 ppm (s, 1H); MS (ESI) m/z 348 [M+H]+.
N2-(4-([1,1’-Biphenyl]-4-yl)thiazol-2-yl)-N6,N6-dimethylpyridine-
2,6-diamine (23): To a 200 mL reaction vessel, intermediate 24
(450 mg, 1.3 mmol) and aqueous NH(CH3)2 (100 mL, 33%) were
added. The vessel was then sealed and heated at 1308C overnight.
After cooling to room temperature, the reaction mixture was ex-
tracted with EtOAc (3ꢂ100 mL). The combined organic layers were
washed with brine, then dried over Na2SO4, and concentrated to
give a brown residue, which was purified by preparative HPLC to
{4-[4-(3,5-Dimethylisoxazol-4-yl)phenyl]thiazol-2-yl}-(6-methyl-
pyridin-2-yl)amine (19): Intermediate 2 (50 mg, 0.145 mmol) was
treated with commercially available (3, 5-dimethyl-1,2-oxazol-4-yl)-
boranediol (29.7 mg, 0.211 mmol) according to general procedure
B and workup B. The material was further purified by preparative
HPLC purification, which afforded the title compound as a trifluor-
1
afford the product 23 as a gray solid (54 mg, 11% yield); H NMR
1
(400 MHz, CDCl3): d=3.20 (6H, s), 5.93 (1H, d, J=8.0 Hz), 6.02 (1H,
d, J=8.0 Hz), 7.02 (1H, s), 7.30–7.36 (2H, m), 7.43–7.47 (2H, m),
7.63–7.65 (4H, m), 7.92–7.95 (2H, m), 8.52 ppm (1H, s); MS (ESI) m/
z 373 [M+H]+.
oacetate salt (43 mg) in 62% yield. H NMR (400 MHz, CDCl3): d=
2.32 (s, 3H), 2.46 (s, 3H), 2.62 (s, 3H), 6.96 (t, J=3.66 Hz, 2H), 7.31
(d, J=7.69 Hz, 1H), 7.38–7.43 (m, 2H), 7.70 (t, J=7.87 Hz, 1H),
7.84–7.90 ppm (m, 2H); MS (ESI) m/z 363 [M+H]+.
4-([1,1’-Biphenyl]-4-yl)-N-(6-(4-methylpiperazin-1-yl)pyridin-2-
yl)thiazol-2-amine (24): A vial was charged with intermediate 8
(130 mg, 0.4 mmol) and N-methylpiperazine (5 mL), then sealed
and heated at 1208C for 4 h. After cooling to room temperature,
the reaction mixture was poured slowly to ice water (30 mL); the
resulting light-brown precipitates were collected by filtration. Fur-
ther purification by preparative HPLC gave 24 as a white solid
(69 mg, 37% yield); 1H NMR (400 MHz, CDCl3): d=2.37 (3H, s),
2.56–2.58 (4H, m), 3.69–3.72 (4H, m), 6.07–6.09 (1H, m), 6.19–6.21
(1H, m), 7.02 (1H, s), 7.33–7.46 (4H, m), 7.63–7.65 (4H, m), 7.91–
7.93 (2H, m), 8.26–8.32 ppm (1H, s); MS (ESI) m/z 428.1 [M+H]+.
{4-[4-(4-Methylpiperazin-1-yl)phenyl]thiazol-2-yl}-(6-methylpyri-
din-2-yl)amine (20): Intermediate 2 (500 mg, 1.45 mmol), N-methyl
piperazine (311 mg, 0.345 mL, 3.11 mmol), sodium tert-butoxide
(350 mg,
3.60 mmol),
tris(dibenzylideneacetone)dipalladium
(63 mg, 0.068 mmol) and (ꢁ)-BINAP (63 mg, 0.1 mmol) were dis-
solved in dry N,N-dimethylformamide that had been degassed by
bubbling with argon for 2 min. The tube was further degassed for
1 min and then subjected to microwave irradiation (1408C for 1 h).
The crude residue was diluted with EtOAc and extracted twice
with saturated aqueous NaHCO3. The combined organic layers
were dried with brine and MgSO4, filtered, and evaporated. The
crude residue was purified using automated silica gel chromatog-
raphy (CH2Cl2/CH3OH, 9:1). The product thus obtained was taken
up in 8 mL 1:1 CH3OH/CH2Cl2, and 1m HCl in Et2O was added until
a precipitate formed. The hydrochloride salt was filtered to afford
{4-[4-(6-Methoxypyridin-3-yl)phenyl]thiazol-2-yl}-(6-methylpyri-
din-2-yl)amine (25): 4-(4-Bromophenyl)-N-(6-methylpyridin-2-yl)-
1,3-thiazol-2-amine 2 (50 mg, 0.145 mmol) was treated with (6-me-
thoxypyridin-3-yl)boranediol (33.2 mg, 0.217 mmol) according to
general procedure B and workup C to afford the title compound
(16 mg) in 29% yield; mp: 217–2228C; 1H NMR (400 MHz,
[D6]DMSO): d=2.48 (s, 3H), 3.91 (s, 3H), 6.79 (dd, J=0.55, 7.33 Hz,
1H), 6.87–6.95 (m, 2H), 7.48 (s, 1H), 7.57–7.63 (m, 1H), 7.70–7.76
(m, J=8.06 Hz, 2H), 7.96–8.02 (m, J=7.87 Hz, 2H), 8.07 (ddd, J=
0.82, 2.61, 8.65 Hz, 1H), 8.48–8.60 (m, 1H), 11.35 ppm (s, 1H); MS
(ESI) m/z 375 [M+H]+.
1
the title compound (34 mg) in 5% yield. H NMR (400 MHz, D2O):
d=2.46 (s, 3H), 2.98 (s, 3H), 3.05 (m, 2H), 3.18–3.29 (m, 2H), 3.65
(d, J=12.27 Hz, 2H), 3.80 (d, J=13.37 Hz, 2H), 6.82 (d, J=8.42 Hz,
2H), 6.90 (d, J=8.79 Hz, 1H), 7.04–7.13 (m, 2H), 7.33 (d, J=8.24 Hz,
2H), 8.01 ppm (t, J=8.15 Hz, 1H); MS (ESI) m/z 366 [M+H]+.
(6-Methylpyridin-2-yl)-[4-(4-morpholin-4-yl-phenyl)thiazol-2-yl]a-
mine (21): Intermediate 2 (200 mg, 0.580 mmol) and morpholine
(126 mg, 0.126 mL, 1.45 mmol), were reacted according to the pro-
cedure described above for 6-methyl-N-{4-[4-(4-methylpiperazin-1-
yl)phenyl]-1,3-thiazol-2-yl}pyridin-2-amine (20). The crude reaction
residue was purified by automated silica gel chromatography (1:1
hexanes/EtOAc). Half of this material was further purified by prepa-
rative HPLC to afford the trifluoroacetate salt (2.9 mg) in 2.1%
4-{4-[2-(2-Methoxyethoxy)pyridin-4-yl]phenyl}-N-(6-methylpyri-
din-2-yl)thiazol-2-amine (26): Intermediate 3 was treated with 4-
bromo-2-(2-methoxyethoxy)pyridine according to general proce-
dure C to afford the title compound as a yellow solid (74 mg) in
1
35% yield; H NMR (400 MHz, [D6]DMSO): d=2.56 (3H, s), 3.47 (3H,
s), 3.77–3.80 (2H, m), 4.52–4.54 (2H, m), 6.52–6.54 (1H, m), 6.72–
6.73 (1H, m), 6.07–6.10 (2H, m), 7.10–7.13 (1H, m), 7.40–7.44 (1H,
m), 7.64–7.66 (2H, m), 7.96–7.98 (2H, m), 8.17–8.18 (1H, m),
8.19 ppm (1H, s); MS (ESI) m/z 419.1 [M+H]+.
1
yield. H NMR (400 MHz, CDCl3): d=2.60 (s, 3H) 3.22–3.29 (m, 4H),
3.85–3.91 (m, 4H), 6.70 (s, 1H), 6.93 (d, J=7.51 Hz, 1H), 6.96–7.02
(m, 2H), 7.20 (brs, 1H), 7.63–7.68 (m, 1H), 7.68–7.72 ppm (m, 2H);
MS (ESI) m/z 353 [M+H]+.
4-{4-[6-(2-Methoxyethoxy)pyridin-3-yl]phenyl}-N-(6-methylpyri-
din-2-yl)thiazol-2-amine (27): Intermediate 3 was treated with 5-
bromo-2-(2-methoxyethoxy)pyridine according to general proce-
dure C to afford the title compound as a yellow solid (123 mg) in
4-([1,1’-Biphenyl]-4-yl)-N-(6-(2-methoxyethoxy)pyridin-2-yl)thia-
zol-2-amine (22): To a reaction vial loaded with 2-methoxyethan-1-
ol (10 mL), Na0 (106 mg, 4.6 mmol) was added; the resulting mix-
ture was stirred at room temperature until a clear solution was ob-
tained. 2-Fluropyridine intermediate 8 (200 mg, 0.58 mmol) was
added to the reaction mixture, and the reaction was heated at
1258C for 14 h. After cooling to room temperature, the reaction
mixture was diluted with H2O (30 mL) and extracted with CH2Cl2
(3ꢂ50 mL). The combined organic layers were washed with brine,
then dried over Na2SO4, and concentrated to give a brown residue,
which was purified by preparative HPLC to afford the product 22
1
58% yield; H NMR (400 MHz, [D6]DMSO): d=2.48 (3H, s), 3.34 (3H,
s), 3.67–3.70 (2H,m), 4.42–4.44 (2H, m), 6.79–6.80 (1H, m), 6.89–
6.95 (2H, m), 7.49 (1H,s), 7.59–7.62 (1H,m), 7.72–7.74 (2H,m), 7.99–
8.00 (1H,m), 8.06–8.09 (1H, m), 8.08–8.09 (1H, m), 8.53 (1H, m),
11.37 ppm (1H, s); MS (ESI) m/z 419.1 [M+H]+.
4-[4-(2-Isopropoxypyridin-4-yl)phenyl]-N-(6-methylpyridin-2-
yl)thiazol-2-amine (28): Pinacoboronate intermediate 3 was treat-
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ed with 4-bromo-2-isopropoxypyridine according to general proce-
dure C to afford the title compound as a yellow solid (57 mg) in
28% yield; 1H NMR (400 MHz, [D6]DMSO): d=1.35–1.39 (6H, m),
2.55 (3H, s), 5.32–5.39 (1H, m), 6.37–6.39 (1H, m), 6.68–6.70 (1H,
m), 6.93 (1H, s), 7.07–7.12 (2H, m), 7.30–7.34 (1H, m), 7.63–7.65
(2H, m), 7.97–7.99 (2H, m), 8.18–8.19 (1H, m), 9.72 ppm (1H, s); MS
(ESI) m/z 403.1 [M+H]+.
commercially
available
2-methyl-3-(4,4,5,5-tetramethyl-
[1,3,2]dioxaborolan-2-yl)pyridine according to general procedure D.
The crude product was further purified via workup B to afford the
title compound in 50% yield; mp: 264–2668C; H NMR (400 MHz,
CDCl3): d=0.55–0.66 (m, 2H), 1.00–1.09 (m, 2H), 1.22–1.36 (m, 1H),
2.57 (s, 3H), 7.15–7.25 (m, 2H),11.66 (brs, 1H), 7.34–7.46 (m, 2H),
7.54 (dd, J=1.65, 7.69 Hz, 1H), 7.88–7.96 (m, 2H), 8.54 ppm (dd,
J=1.74, 4.85 Hz, 1H); MS (ESI) m/z 336 [M+H]+.
1
4-[4-(6-Isopropoxypyridin-3-yl)phenyl]-N-(6-methylpyridin-2-
yl)thiazol-2-amine (29): Intermediate 3 was treated with 5-bromo-
2-isopropoxypyridine according to general procedure C to afford
Cyclopropanecarboxylic acid {4-[4-(6-dimethylaminopyridin-3-
yl)phenyl]thiazol-2-yl}amide (41): Intermediate 10 was treated
with commercially available 6-(dimethylamino)pyridine-3-boronic
acid according to general procedure D except that the workup
was modified. The crude product was filtered on paper, re-dis-
solved in ~2 mL DMSO and filtered through a 0.02 mm Whatman
Anatop filter. The filtrate was swirled gently on an orbital stirrer
with 70 mg of Quadrapure MPA resin overnight. The resin was
then removed by filtration, and the product precipitated from ice
water to afford the title compound in 58% yield. 1H NMR
(400 MHz, [D6]DMSO): d=0.89–0.96 (m, 4H), 1.94–2.04 (m, 1H),
3.07 (s, 6H), 6.73 (d, J=8.97 Hz, 1H), 7.60 (s, 1H), 7.68 (d, J=
8.24 Hz, 2H), 7.88 (dd, J=2.56, 8.97 Hz, 1H), 7.93 (d, J=8.24 Hz,
2H), 8.49 (d, J=2.56 Hz, 1H), 12.53 ppm (s, 1H); MS (ESI) m/z 365
[M+H]+.
1
the title compound as a yellow solid (42 mg) in 21% yield; H NMR
(400 MHz, [D6]DMSO): d=1.35–1.39 (6H, m), 2.55 (3H, m), 5.32–
5.38 (1H,m), 6.60 =6.62 (1H, m), 6.74–6.77 (2H, m), 7.06 (1H, s),
7.46–7.50 (1H,m), 7.56–7.58 (2H, m), 7.80–7.81 (1H, m), 7.93–7.95
(2H, m), 8.37–8.42 ppm (2H, m); MS (ESI) m/z 403.1 [M+H]+.
4-{4-[2-(Dimethylamino)pyridin-4-yl]phenyl}-N-(6-methylpyridin-
2-yl)thiazol-2-amine (30): Intermediate 3 was treated with 4-
bromo-N,N-dimethylpyridin-2-amine according to general proce-
dure C to afford the title compound as a yellow solid (33 mg) in
1
17% yield; H NMR (400 MHz, [D6]DMSO): d=2.57 (3H, s), 3.16 (6H,
s), 6.50–6.52 (1H, m), 6.72–6.74 (2H, m), 6.80 (1H, m), 7.40–7.42
(1H, m), 7.42–7.44 (2H, m), 7.96–7.98 (2H, m), 8.22–8.24 (1H, m),
9.01 ppm (1H, s); MS (ESI) m/z 388.1 [M+H]+.
Cyclopropanecarboxylic acid {4-[4-(2-methyl-2H-pyrazol-3-yl)-
phenyl]thiazol-2-yl}amide (42): Intermediate 10 was treated with
commercially available 1-methyl-1H-pyrazole-5-boronic acid ac-
cording to general procedure D to afford the title compound in
4-{4-[6-(Dimethylamino)pyridin-3-yl]phenyl}-N-(6-methylpyridin-
2-yl)thiazol-2-amine (31): Intermediate 3 was treated with 5-
bromo-N,N-dimethylpyridin-2-amine according to general proce-
dure C to afford the title compound as a yellow solid (127 mg) in
1
95% yield; mp: 215–2178C; H NMR (400 MHz, CDCl3): d=0.68 (m,
1
43% yield; mp: 234–2368C; H NMR (400 MHz, [D6]DMSO): d=2.47
2H), 1.08 (m, 2H), 1.28–1.38 (m, 1H), 3.95 (s, 3H), 6.35 (s, 1H), 7.21
(s, 1H), 7.46–7.53 (d, J=7.33, 2H), 7.55 (s, 1H), 7.88–7.98 (d, J=
7.51, 2H), 11.02 ppm (brs, 1H); MS (ESI) m/z 325 [M+H]+.
(3H, s), 3.08 (6H, s), 6.73–6.75 (2H, m), 6.85–6.87 (1H, m), 7.39 (1H,
s), 7.55–7.59 (1H, m), 7.65–7.68 (2H, m), 7.88–7.90 (1H, m), 7.92–
7.96 (2H, m), 8.49 ppm (1H, s); MS (ESI) m/z 388.1 [M+H]+.
Cyclopropanecarboxylic acid {4-[4-(3,5-dimethylisoxazol-4-yl)-
phenyl]thiazol-2-yl}amide (43): Intermediate 10 was treated with
commercially available 3,5-dimethylisoxazole-4-boronic acid ac-
cording to general procedure D with purification on silica to afford
the title compound in 54% yield; mp: 222–2238C; 1H NMR
(400 MHz, CDCl3): d=0.59 (m, 2H), 0.98–1.08 (m, 2H), 1.22 ꢁ1.32
(m, 1H), 2.32 (s, 3H), 2.45 (s, 3H), 7.19 (s, 1H), 7.29–7.37 (m, 2H),
7.88–7.95 (m, 2H), 11.51 ppm (s, 1H); MS (ESI) m/z 340 [M+H]+.
4-{4-[2-(4-Methylpiperazin-1-yl)pyridin-4-yl]phenyl}-N-(6-methyl-
pyridin-2-yl)thiazol-2-amine (32): Intermediate 3 was treated with
1-(4-bromopyridin-2-yl)-4-methylpiperazine according to general
procedure C to afford the title compound as a yellow solid
1
(110 mg) in 49% yield; H NMR (400 MHz, [D6]DMSO): d=2.23 (3H,
s), 2.42–2.47 (4H, m), 2.50 (3H, s), 3.58 (4H, m), 6.75–6.76 (1H, m),
6.84–6.86 (1H, m), 6.99–7.01 (1H, m), 7.10 (1H, s), 7.49 (1H, s),
7.55–7.59 (1H, m), 7.82–7.84 (2H, m), 8.00–8.02 (2H, m), 8.16–8.18
(1H, m), 11.42 ppm (1H, s); MS (ESI) m/z 443.2 [M+H]+.
N-(4-{4-[2-(2-Methoxyethoxy)pyridin-4-yl]phenyl}thiazol-2-yl)cy-
clopropanecarboxamide (44): Pinacoboronate intermediate 11
was treated with 4-bromo-2-(2-methoxyethoxy)pyridine according
to general procedure E to afford the title compound as a white
4-{4-[6-(4-Methylpiperazin-1-yl)pyridin-3-yl]phenyl}-N-(6-methyl-
pyridin-2-yl)thiazol-2-amine (33): Intermediate 3 was treated with
1-(5-bromopyridin-2-yl)-4-methylpiperazine according to general
procedure C to afford the title compound as a yellow solid
1
solid (106 mg) in 43% yield; H NMR (400 MHz, [D6]DMSO): d=0.93
1
(4H, t), 1.99 (1H, m), 2.82 (3H, s), 3.68 (2H, t), 4.43 (2H, t), 7.18 (1H,
s), 7.37 (1H, d), 7.73 (1H, s), 7.87 (2H, d), 8.02 (2H, d), 8.21 (1H, d),
12.55 ppm (1H, s); MS (ESI) m/z 396 [M+H]+.
(128 mg) in 57% yield; H NMR (400 MHz, [D6]DMSO): d=2.23 (3H,
s), 2.31–2.33 (4H, m), 2.40 (3H,s), 3.52–3.57 (4H, m), 6.76–6.78 (1H,
m), 6.86–6.94 (2H, m), 7.42 (1H,s), 7.56–7.59 (1H, m), 7.67–7.69
(2H, m), 7.89–7.97 (3H, m), 8.50–8.52 (1H, m), 11.37 ppm (1H, s);
MS (ESI) m/z 443.2 [M+H]+.
N-(4-{4-[2-(4-Methylpiperazin-1-yl)pyridin-4-yl]phenyl}thiazol-2-
yl)cyclopropanecarboxamide (45): Pinacoboronate intermediate
11 was treated with 1-(4-bromopyridin-2-yl)-4-methylpiperazine ac-
cording to general procedure E to afford the title compound as
a white solid (27 mg) in 9% yield; 1H NMR (400 MHz, CDCl3): d=
0.86 (2H, m), 1.14 (2H, m), 1.50 (1H, m), 2.67 (4H, s), 3.72 (4H, s),
6.90 (2H, m), 7.18 (1H, s), 7.65 (2H, d), 7.90 (2H, d), 8.25 (1H, d),
10.21 ppm (1H, s); MS (ESI) m/z 420 [M+H]+.
Cyclopropanecarboxylic acid [4-(4-pyridin-4-yl-phenyl)thiazol-2-
yl]amide trifluoroacetate salt (39): Intermediate 10 was treated
with commercially available 4-pyridineboronic acid according to
general procedure D. The crude material was further purified via
workup A to afford the title compound in 12% yield; mp: 233–
1
2398C; H NMR (400 MHz, [D6]DMSO): d=0.88–0.98 (m, 4H), 1.95–
2.04 (m, 1H), 7.82–7.86 (s, 1H), 8.05–8.15 (m, 4H), 8.25 (d, J=
5.49 Hz, 2H), 8.87 ppm (d, J=5.49 Hz, 2H); MS (ESI) m/z 322 [M+
H]+.
N-(4-{4-[6-(2-Methoxyethoxy)pyridin-3-yl]phenyl}thiazol-2-yl)cy-
clopropanecarboxamide (46): Pinacoboronate intermediate 11
was treated with 5-bromo-2-(2-methoxyethoxy)pyridine according
to general procedure E to afford the title compound as a white
Cyclopropanecarboxylic acid {4-[4-(2-methylpyridin-3-yl)phe-
nyl]thiazol-2-yl}amide (40): Intermediate 10 was treated with
1
solid (28 mg) in 13% yield; H NMR (400 MHz, [D6]DMSO): d=0.92
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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[8] J. Shorter, S. Lindquist, EMBO J. 2008, 27, 2712–2724.
(4H, t), 1.99 (1H, m), 2.82 (3H, s), 3.68 (2H, t), 4.43 (2H, t), 6.93 (1H,
d), 7.74 (2H, d), 7.98 (2H, d), 8.52 (1H, d), 12.54 ppm (1H, s); MS
(ESI) m/z 396 [M+H]+.
[9] S. B. Prusiner, M. Scott, D. Foster, K.-M. Pan, D. Groth, C. Mirenda, M.
Torchia, S.-L. Yang, D. Serban, G. A. Carlson, P. C. Hoppe, D. Westaway,
S. J. DeArmond, Cell 1990, 63, 673–686.
N-(4-{4-[6-(4-Methylpiperazin-1-yl)pyridin-3-yl]pheyl}thiazol-2-
yl)cyclopropanecarboxamide (47): Pinacoboronate intermediate
11 was treated with 1-(5-bromopyridin-2-yl)-4-methylpiperazine ac-
cording to general procedure E to afford the title compound as
a white solid (17 mg) in 6% yield; 1H NMR (400 MHz, [D6]DMSO):
d=0.93 (4H, t), 1.99 (1H, m), 2.24 (3H, s), 2.45 (4H, m), 3.56 (4H,
m), 6.93 (1H, d), 7.61 (1H, s), 7.69 (2H, d), 7.92 (3H, m), 8.50 (1H,
d), 12.54 ppm (1H, s); MS (ESI) m/z 420 [M+H]+.
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Acknowledgements
This work was funded by grants from the National Institutes of
Health (AG021601, AG031220, AG002132, AG010770) as well as
by gifts from the Sherman Fairchild Foundation, the Lincy Foun-
dation, the Rainwater Charitable Foundation, and the Schott
Foundation for Public Education. The authors thank Mr. Phillip
Benner for the preparation, animal dosing, and sample collection
in PK studies; and Dr. Kurt Giles and the staff of the Hunter’s
Point animal facility for expert animal studies. M.P.J. is a consul-
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Keywords: 2-aminothiazoles
pharmacokinetic optimization · prion disease · structure–
activity relationships
·
neurological
agents
·
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Received: January 4, 2013
Published online on March 18, 2013
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ChemMedChem 2013, 8, 847 – 857 857