A diverse and versatile regiospecific synthesis of tetrasubstituted alkylsulfanylimidazoles as p38α mitogen-activated protein kinase inhibitors

Article abstract of DOI:10.3390/molecules23010221

An alternative strategy for the synthesis of 1-aryl- and 1-alkyl-2-methylsulfanyl-4-(4-fluorophenyl)-5-(pyridin-4-yl)imidazoles as potential p38α mitogen-activated protein kinase inhibitors is reported. The regioselective N-substitution of the imidazole ring was achieved by treatment of α-aminoketones with different aryl or alkyl isothiocyanates. In contrast to previously published synthesis routes starting from 2-amino-4-methylpyridine, the presented route is characterized by a higher flexibility and a lower number of steps. This strategy was also applied to access 1-alkyl-2-methylsulfanyl-5-(4-fluorophenyl)-4-(pyridin-4-yl)imidazoles in six steps starting from 2-chloro-4-methylpyridine.

Full text of DOI:10.3390/molecules23010221

molecules
Article
A Diverse and Versatile Regiospecific Synthesis of
Tetrasubstituted Alkylsulfanylimidazoles as p38α
Mitogen-Activated Protein Kinase Inhibitors
Francesco Ansideri 1, Stanislav Andreev 1, Annette Kuhn 1, Wolfgang Albrecht 2,
Stefan A. Laufer 1 and Pierre Koch 1,
*
ID
1
Institute of Pharmaceutical Sciences, Department of Medicinal and Pharmaceutical Chemistry, Eberhard
Karls Universität Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany;
francesco.ansideri@uni-tuebingen.de (F.A.); stanislav.andreev@uni-tuebingen.de (S.A.);
annette.kuhn@uni-tuebingen.de (A.K.); stefan.laufer@uni-tuebingen.de (S.A.L.)
Teva-Ratiopharm, Graf-Arco-Str. 3, 89079 Ulm, Germany; wolfgang.albrecht@ratiopharm.de
Correspondence: pierre.koch@uni-tuebingen.de; Tel.: +49-7071-29-74579
2
*
Received: 12 December 2017; Accepted: 17 January 2018; Published: 20 January 2018
Abstract: An alternative strategy for the synthesis of 1-aryl- and 1-alkyl-2-methylsulfanyl-4-(4-
fluorophenyl)-5-(pyridin-4-yl)imidazoles as potential p38
is reported. The regioselective N-substitution of the imidazole ring was achieved by treatment of
-aminoketones with different aryl or alkyl isothiocyanates. In contrast to previously published
α mitogen-activated protein kinase inhibitors
α
synthesis routes starting from 2-amino-4-methylpyridine, the presented route is characterized
by a higher flexibility and a lower number of steps. This strategy was also applied to
access 1-alkyl-2-methylsulfanyl-5-(4-fluorophenyl)-4-(pyridin-4-yl)imidazoles in six steps starting
from 2-chloro-4-methylpyridine.
Keywords: regiospecific synthesis; tetrasubstituted imidazoles; p38α MAP kinase
1. Introduction
The p38
role in signal transduction pathways, modulating the cellular response to external stress stimuli like
infection, heat or osmotic shock, UV light, and inflammatory cytokines [ ]. Through phosphorylation
α mitogen-activated protein (MAP) kinase is a serine/threonine kinase, which plays a
1
of multiple downstream targets, this kinase triggers a wide range of cellular processes mostly resulting
in the stimulation of the inflammatory reaction (e.g., release of pro-inflammatory cytokines like
tumor necrosis factor-
The function of the p38
chronical inflammatory conditions like rheumatoid arthritis, Crohn’s disease, psoriasis, and chronic
asthma [ ]. Additionally, several studies suggested that the p38 MAP kinase may also play a role
as a major character in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease,
Parkinson’s disease and multiple sclerosis [ ]. Due to this well-documented physiopathological
MAP kinase has been widely pursued in many medicinal chemistry
α
, interleukin-1
β, and interleukin-6 and induction of COX-2 transcription) [1,2].
α
MAP kinase has therefore been regarded as crucial in those cytokine-driven
3,4
α
5–8
role, inhibition of the p38
α
programs [9,10].
Pyridinylimidazoles represent a privileged scaffold in the field of kinase inhibition, especially
concerning the targeting of the p38 MAP kinase, as very recently reviewed by some of us [11].
In particular, tetrasubstituted pyridinylimidazoles like compounds 3a 4a and 4b 12 15] represent
adenosine triphosphate (ATP)-competitive inhibitors of p38 MAP kinase, which might be considered
α
2,
,
[
–
α
as open analogues of the imidazolthiazolidine-based early lead compound SKF86002 (
1) from
SmithKline & French [16] (Figure 1).
Molecules 2018, 23, 221; doi:10.3390/molecules23010221
www.mdpi.com/journal/molecules

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F
F
F
CH3
N
N
S
CH3
CH3
N
N
N
N
F
F
S
S
N
CH3
N
N
N
N
O
CH3
CH3
N
N
HN
O
S
S
O
CH3
HN
CH3
HN
CH3
CH3
N
N
1
2
3a
4a
4b
IC50 = 729 nMa
IC50 = 190 nMa
OCH3
IC50 = 48 nMb
IC50 = 40 nMc
IC50 = 70 nMc
Figure 1. Early lead compound SKF86002 (1) and 1,2,4,5-tetrasubstituted imidazoles
2
,
3a
,
4a and 4b as
a
p38
α
MAP kinase inhibitors. unpublished data from our research group; compounds tested in assay
conditions described by Goettert et al. [17]; b data taken from [14]; c data taken from [15].
Figure 2 shows the well-described binding mode of tetrasubstituted pyridinylimidazoles like
compounds 3a 4a and 4b within the ATP cleft of the p38 MAP kinase. Worth to mention
2
,
,
α
are the occupation of two hydrophobic pockets named hydrophobic region (HR) I and HR II as
well as the formation of a hydrogen bond with the conserved Lys53 side chain. Tetrasubstituted
pyridinylimidazoles were initially reported to display a lower inhibitory activity in comparison
to the analogous trisubstituted derivatives lacking the substituent on the imidazole-N1 atom [18].
Nevertheless, it was observed that by inserting opportune substituents at this position, a high
potency could still be maintained, probably thanks to additional interactions. Furthermore, some
tetrasubstituted pyridinylimidazoles showed a markedly reduced inhibition of the CYP450 enzymes,
considered one of the major drawbacks of their trisubstituted counterparts [13].
Figure 2. Binding mode of tetrasubstituted imidazoles bearing an acylamino or alkylamino group at
the pyridine-C2 position. Figure modified from ref. [19].
Due to the binding mode of this class of inhibitors, a compulsory structural requisite is that the
substituted imidazole-N atom is the one adjacent to the pyridine ring. Substitution on the imidazole-N
atom proximal to the 4-fluorophenyl ring would instead prevent the formation of the hydrogen bond
with Lys53 and has been reported to cause a tremendous drop in inhibitory activity [20]. For this
reason, in order to preserve their binding affinity to the p38α MAP kinase, these inhibitors need to be
accessed through a regiospecific synthetic route.

Molecules 2018, 23, 221
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The first synthetic route toward tetrasubstituted 2-alkylsulfanylimidazoles was reported in
2002 and 2003 (Scheme 1) [21 22] and was subsequently employed in several studies on kinase
inhibitors [13 15 23 25]. This route, comprising eleven steps, starts from 2-amino-4-methylpyridine (
which was first protected as an acetamide and successively oxidized to a carboxylic acid. Ethanone
was then obtained by coupling with 4-fluorophenylacetonitrile followed by hydrolysis-decarboxylation
reaction of the resulting cyanoketone , causing the simultaneous cleavage of the N-acetyl protecting
group. After repeating the protection step, ethanone 10 was converted into the α-oximinoketone 11
,
–
,
–
5)
9
8
,
and then cyclized with an opportunely substituted 1,3,5-trialkyltriazinane to regioselectively
afford imidazole-N-oxides 12. Intermediates 12 were then transformed into the corresponding
imidazole-2-thiones 13 and then methylated on the exocyclic sulphur. Finally, the amino group
of compounds 14 was deprotected and then coupled with different carboxylic acids to produce
final compounds 3. From intermediates 15 it is also possible to obtain alkylamino derivatives 4 by
nucleophilic substitution reaction with alkyl halides [13].
Scheme 1. Synthetic pathway toward 1,2,4,5-tetrasubstituted imidazol◦es
3 and 4. Reagents and
conditions: (i) Ac2O, DMAP, reflux temperature; (ii) KMnO4, H2O, 50–90 C; (iii) CDI, DMF, t-BuOK,
◦
120 C; (iv) HBr, reflux temperature; (v) Ac2O, DMAP, reflux temperature; (vi) isoamyl nitrite, MeONa,
MeOH, rt; (vii) EtOH, reflux temperature; (viii) 2,2,4,4-tetramethylcyclobutane-1,3-dithione, DCM, rt;
(ix) iodomethane, Na2CO3, EtOH, rt; (x) 10% HCl(aq), reflux temperature; (xi) R2-COCl, NEt3, THF,
◦
◦
0 C or R2-COOH, CDI, N-methylpyrrolidinone, rt, then 120 C; (xii) R3-Br, NaH, DMF, rt.
This reported route noticeably entails a large number of steps and the preparation of intermediate
10 is particularly inconvenient due to the repeated introduction and cleavage of the N-acetyl

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protecting group. An additional drawback of the reported route is the flexibility of application.
As reported from the authors, this route is indeed not suitable for the introduction of aryl or heteroaryl
moieties at the imidazole-N1 position [22]. Moreover, the functionalization of the pyridine-C2 position
by nucleophilic substitution reaction of 2-aminopyridine derivatives 15 and alkyl halides represents a
limitation when introducing alkyl groups featuring a stereocenter adjacent to the amino moiety. The use
of chiral alkyl halides can indeed result in inversion of configuration or racemization, thus hampering
the stereoselective synthesis of some derivatives (e.g., compound 4a, wherein the hypothetical use of
the corresponding benzyl halide would favor an SN1 mechanism with the consequent loss of chirality).
For this reason, preparation of derivatives 4a and 4b could only be achieved by converting the 2-amino
group into a fluorine atom and introducing the chiral amine by nucleophilic aromatic substitution, as
reported in 2008 [12].
In 2011, Selig et al. published an alternative synthetic route to tetrasubstituted imidazoles
(Scheme 2) [18]. This route is overall similar to the previously reported one and only differs in the
replacement of the amino group of intermediate with a fluorine, allowing the realization of the
following steps without the necessity of the protecting group. The amino group was then reintroduced
at the penultimate step, before its functionalization with different acyl derivatives yielding compounds 3
Nevertheless, because of the replacement of the amino group only after the preparation of ethanone
3
9
.
9
,
this route does not bypass the issues relative to the installation and cleavage of the N-acetyl protecting
group and encompasses the same number of steps as the one presented in Scheme 1.
Scheme 2. Synthetic pathway toward 1,2,4,5-tetrasubstituted imidazoles
3
. Reagents and conditions:
◦
(i) NaNO2, 70% HF-pyridine;
temperature; (iv) 2,2,4,4-tetramethylcyclobutane-1,3-dithione, DCM, rt; (v) iodomethane, K2CO3,
−
15 to
−
10 C, then rt; (ii) NaNO2, glacial AcOH, rt; (iii) EtOH, reflux
MeOH, rt; (vi) NH3, reactor; (vii) R2-COOH, CDI, N-methylpyrrolidinone, rt, then 120 C.
◦
2. Results and Discussion
2.1. Chemistry
Our retrosynthetically-planned synthetic strategy towards 1,2,4,5-tetrasubstituted imidazoles 3 and
4
is depicted in Scheme 3. In contrast to the aforementioned routes, we sought to introduce the whole
alkyl- or acylamino group at the pyridine-C2 position starting from 2-chloropyridine derivatives 21 since
the higher stability of the 2-halopyridine moiety avoids the need for protection/deprotection steps
However, in contrast to the route reported by Selig et al., chlorine was preferred over fluorine, as it
can be displaced through both nucleophilic aromatic substitution reaction and Buchwald-Hartwig
arylamination/amidation. Moreover, this choice would allow the introduction of chiral amines
having the stereocenter adjacent to the amino group without leading to racemization or inversion
of configuration, as the reaction mechanism does not involve the chiral center. Key passage
.
of the synthesis is then the cyclization reaction of
α-aminoketone 23 and alkyl/aryl-substituted

Molecules 2018, 23, 221
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isothiocyanates 24, allowing the regioselective introduction of the imidazole-N-substituent, followed
by methylation of resulting intermediates 22. Finally, a suitable precursor for the preparation of
α
-aminoketone 23 could be represented by ethanone derivative 25, which in turn can arise from the
commercially available 2-chloroisonicotinic acid (26).
Scheme 3. Retrosynthetic strategy for the preparation of 1,2,4,5-tetrasubstituted imidazoles 3 and 4.
The initial step of our alternative route consisted in the preparation of the 1-(2-chloropyridin-4-yl)
-2-(4-fluorophenyl)ethan-1-one (25). This compound represents the 2-chloropyridine-substituted
analogue of derivative
tetrasubstituted pyridinylimidazoles (Schemes 1 and 2). As already mentioned, the preparation of
ethanone constituted one of the major bottlenecks of both previously reported routes and as a
9, a common intermediate of both published synthetic pathways toward
9
consequence, the new synthetic strategy would benefit from a more efficient method to achieve its
analogue 25. Several attempts were carried out in order to yield compound 25, which are displayed in
Scheme 4.
Despite their similarity, it was not possible to prepare compound 25 in an analogous
fashion as ethanone
9, namely by condensation of the 2-chloroisonicotinic acid with
4-fluorophenylacetonitrile followed by hydrolysis of the resulting cyanoketone. A convenient
method for the synthesis of ketones is generally represented by the addition of Grignard reagents
to Weinreb amides. Unfortunately, Grignard reaction of 4-fluorobenzyl magnesium chloride with
2-chloro-N-methoxy-N-methylisonicotinamide (27) afforded ethanone 25 in a non-satisfactory yield
of 49%. A reason for the reduced yield is probably a well-described E2 elimination reaction starting
with the extraction of a proton from the N-methoxy group and resulting in the formation of the
corresponding N-methylamide and formaldehyde [26]. In order to avoid this undesired side reaction
a previously described approach was followed [27], consisting in the use of a modified Weinreb
amide wherein the methoxy group was replaced by a tert-butoxy moiety. Such group has no H
atoms adjacent to the oxygen atom and is therefore not prone to deprotonation by the Grignard
reagent. N-(tert-butoxy)-2-chloro-N-methylisonicotinamide (29) could be prepared in good yield
via a two-step procedure starting from the corresponding carboxylic acid 26. In detail, coupling
of 26 with N-methylhydroxylamine afforded the corresponding hydroxamic acid 28, which was
then converted into the Weinreb amide 29 by acid-catalyzed esterification with tert-butyl acetate.
The use of amide 29 in the Grignard reaction with 4-fluorobenzyl magnesium chloride permitted a
significantly increased yield of up to 81%, with an overall yield of 62% over 3 steps for the preparation of
intermediate 25. It is worth mentioning that the ethanone derivative 25 could also be prepared by direct
Grignard reaction of 2-chloroisonicotinic acid (26) with 4-fluorobenzyl magnesium chloride, adapting
a procedure previously reported by Reeves et al. [28]. The latter method allows the preparation of key
intermediate 25 in a single step and consists in reacting the carboxylic acid with two equivalents of
organomagnesium reactant in order to achieve nucleophilic addition on the carboxylate derivative. This

Molecules 2018, 23, 221
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approach afforded derivative 25 in a low yield (35%) and the formation of 1,2-bis(4-fluorophenyl)ethane
as a by-product was observed.
Scheme 4. Diverse strategies for the synthesis of ethanone derivative 25. Reagents and conditions:
(i) SOCl2, reflux temperature; (ii) N,O-dimethylhydroxylamine hydrochloride, NEt3, DCM, rt;
(iii) 4-fluorobenzyl magnesium chloride, dry THF,
hydrochloride, NEt3, dry DCM, rt; (v) t-BuOAc, 70% HClO4(aq), 1,4-dioxane, 60 C, sealed vial.
−
10 ◦C, then rt; (iv) N-methylhydroxylamine
◦
After obtaining a convenient method for the preparation of ethanone intermediate 25
for its conversion into -aminoketone 23 was pursued. As shown in Scheme 5, reduction of the
-ketoxime 30 did not succeed in producing the desired -aminoketone 23 starting from ethanone 25.
, a strategy
α
α
α
Such transformation was instead successfully achieved through a three-step procedure involving a
base-mediated Neber rearrangement of an O-tosyl-oxime derivative (Scheme 6). In detail, ethanone 25
was first reacted in a nucleophilic addition with hydroxylamine and the resulting oxime 31
was tosylated. Following the tosylation protocol of Lantos and coworkers for a related ketoxime [29],
a significantly slower conversion was observed, accompanied by the formation of by-products, which
deteriorated under increased thermal conditions. Carrying out the reaction at room temperature
afforded a sufficiently clean tosylation, yet requiring a high excess of p-toluenesulfonylchloride to
compensate for the resultant low conversion rate. Intermediate 32 was then reacted in a Neber
rearrangement with potassium ethoxide, affording an aziridine derivative, which was immediately
hydrolyzed in acidic conditions, yielding α-aminoketone 23 as a hydrochloride salt.
Scheme 5. Attemped short strategy for the preparation of α-aminoketone 23. Reagents and conditions:
(i) NaNO2, glacial AcOH, rt; (ii) Pd/C 10%, H2, isopropanolic HCl, rt.
Construction of the imidazole ring was performed by reaction of the α-aminoketone 23 and
alkyl or aryl isothiocyanates 24 in a single two-step procedure. First, the nucleophilic addition
of the amino group to the isothiocyanate took place using triethylamine as both base and solvent.
The cyclization was then promoted by evaporating the triethylamine and by heating the reaction
mixture in glacial acetic acid, succeeding in the regioselective preparation of N-alkyl and -aryl
substituted imidazole-2-thiones 22 in moderate yields. Tetrasubstituted imidazole derivatives 21
were then easily accessible through nucleophilic substitution of compounds 22 with iodomethane in
the presence of a base. The last step of our alternative route consisted in the introduction of the alkyl-
or acylamino functions at the pyridine-C2 position. In case of aliphatic amines this was obtained by

Molecules 2018, 23, 221
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nucleophilic aromatic substitution of synthones 21 with large excess of amine in solvent-free conditions.
Amide moieties could instead be introduced starting from the same derivative via palladium-catalyzed
Buchwald-Hartwig reaction.
Scheme 6. Optimized synthesis of tetrasubstituted imidazoles
3 and 4. Reagents and conditions:
(i) hydroxylamine hydrochloride, NaOH(aq), MeOH, rt; (ii) tosyl chloride, pyridine, rt; (iii) (a) EtOK,
EtOH(abs), 0 ◦C, then rt; (b) conc. HCl(aq), 50 ◦C; (iv) (a) NEt3, 50 ◦C; (b) glacial AcOH, 80 ◦C;
◦
(v) iodomethane, t-BuONa, MeOH, 50 C; (vi) 3-(4-methoxyphenyl)propanamide, Pd2(dba)3, XantPhos,
◦
◦
Cs2CO3, DMF, 100 C; (vii) (S)-phenylethan-1-amine, 180 C, sealed tube.
As already mentioned, derivatization of the imidazole-N atom adjacent to the 4-fluorophenyl ring
is detrimental for inhibitory activity on the p38α MAPK, as the introduced alkyl or aryl substituent
prevents the formation of a hydrogen bond interaction with the Lys53 of the enzyme. Nevertheless,
in order to broaden the applicability of our alternative synthetic pathway, we tested its suitability for the
regioselective synthesis of 1,2,4,5-tetrasubstituted pyridinylimidazoles bearing the substituent on the
imidazole-N atom distal from the pyridine ring (Scheme 7). In this series, derivatives 38 and 39, bearing
a methyl group on the imidazole-N atom, were prepared as an example to prove the applicability
of the presented synthetic route. In order to invert the substitution pattern on the imidazole ring,
the cyclization step clearly needs to be performed starting from α-aminoketone 36, a regioisomer of
compound 23. This derivative could be obtained via a previously described procedure consisting in
the condensation of 2-chloro-4-picoline (33) with ethyl 4-fluorobenzoate followed by
of the ethanone intermediate 34 and reduction of the resulting -ketoxime 34. Differently from the
attempt depicted in Scheme 4, the -ketoxime 34, presenting the opposite arrangement of the two
aryl substituents, could be smoothly reduced affording aminoketone 35 in very good yields. Starting
from the -aminoketone 35, the cyclization-methylation steps were carried out in an analogous fashion
as the ones described in Scheme 6. Finally, using the same conditions as for compounds 3 and 4
α-nitrosylation
α
α
α
,
compounds 38 and 39 could be obtained by Buchwald-Hartwig amidation and by nucleophilic aromatic
substitution, respectively.

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Scheme 7. Synthesis of tetrasubstituted imidazoles 38 and 39
Reagents and conditions: (i) Pd/C 10%, H2, isopropanolic HCl, rt; (ii) (a) NEt3, 60 C; (b) glacial AcOH,
.
a Procedure reported by Laufer et al. [30].
◦
◦
◦
80 C; (iii) iodomethane, t-BuONa, MeOH, 50 C; (iv) 3-(4-methoxyphenyl)propanamide, Pd2(dba)3,
◦
◦
XantPhos, Cs2CO3, DMF, 100 C; (v) (S)-1-phenylethan-1-amine, 180 C, sealed tube.
2.2. Biological Evaluation and SAR Insights
Compounds 3b–c, 4c, 38 and 39 were tested in an enzyme-linked immunosorbent assay (ELISA)
in order to evaluate their capability to inhibit the p38α MAP kinase and the results were compared
to the ones of compounds 3a and 4a , which were previously tested in the same assay [17]
–
b
(Table 1). Although the scant number of evaluated compounds does not allow an exhaustive analysis
of structure-activity relationships, tetrasubstituted pyridinylimidazoles were confirmed as potent
inhibitors of the p38α MAP kinase, reaching IC50 values down to the low double-digit nanomolar
range (compound 3b). As expected, substitution of the N atom adjacent to the 4-fluorophenyl ring
(compounds 38 and 39) was detrimental for the inhibitory activity, due to the suppression of the
hydrogen bond with the Lys53. When comparing the two compound series 3a–c and 4a–c it appears
evident that substitution of the imidazole-N atom with a phenyl ring (compounds 3c and 4c) has
a negative effect on the inhibitory activity, even reaching an IC50 value in the micromolar range in
case of compound 4c. This can be either due to unfavorable interactions with the phosphate/sugar
pocket or to a sterical hindrance with the 2-alkylamino- or 2-acylaminopyridine moiety, which does
not allow a correct positioning of the molecule in the binding pocket of the enzyme. Finally, whereas
the acylamino substituent appears to be overall preferable to the alkylamino group at the pyridine-C2
position, no clear indication could be obtained regarding the superiority of either the methyl or the
methoxyethyl substituent at the imidazole-N atom.

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Table 1. Biological activity of tetrasubstituted pyridinylimidazoles 3a–c, 4a–c, 38, and 39.
IC50 (µM)
Cpd.
3a
R1
R2
Mean ± SEM a
0.048 ± 0.010 b
0.020 ± 0.004
0.413 ± 0.072
0.040 ± 0.010 c
3b
3c
4a
4b
4c
0.070 ± 0.030 c
1.51 ± 0.15
IC50 (µM)
Cpd.
38
R1
R2
Mean ± SEM a
2.70 ± 0.02
39
3.19 ± 0.78
a
n = 3; b data taken from ref. [14]; c data taken from ref. [15], n = 4.
To sum up, the herein reported route represents a valid alternative for the synthesis of
tetrasubstituted pyridinylimidazoles, a class of molecules counting several examples in the field
of kinase inhibition due to the capability of reaching high inhibitory potency together with reduced
interaction with the CYP450 enzymes. This route comprises a lower number of synthetic steps in
comparison with previously reported strategies along with an increased versatility. Both aliphatic and
aromatic moieties can be introduced at the imidazole-N1 atom without modifying the synthetic path.
Furthermore, the range of possible substituents is extremely broad thanks to both the commercial
availability of diversely substituted isothiocyanates and to reported procedures describing facile
preparation methods for these intermediates [31–33]. The presence of a Cl atom at the pyridine-C2
position eliminates the necessity of protection/deprotection steps and permits the functionalization
with both amines and amides in the last step of the route. Furthermore, chiral amines featuring

Molecules 2018, 23, 221
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the stereocenter in the
or racemization.
α
-position can be introduced without the risk of inversion of configuration
The introduction of an aromatic ring on the imidazole-N atom, constituting one of the advantages
of the presented route with respect to published ones, did not emerge as a beneficial substitution to
increase the inhibitory activity on the p38α MAP kinase; likewise, functionalization of the imidazole-N
atom distal to the pyridine ring results in a significantly reduced potency on the same target.
Nevertheless, since pyridinylimidazoles represent a privileged scaffold in the realm of kinase inhibition,
these synthetic improvements can still result helpful in the targeting of different kinases having
dissimilar structural features compared to the p38α MAP kinase.
3. Materials and Methods
3.1. General Information
All reagents and solvents were of commercial quality and utilized without further purification.
Thin layer chromatography (TLC) reaction controls were performed for all reactions using fluorescent
silica gel 60 F254 plates (Merck, Darmstadt, Germany) and visualized under natural light and UV
illumination at 254 and 366 nm. The purity of all tested compounds are >95% as determined via
reverse phase high performance liquid chromatography (HPLC) on a 1100 Series HPLC system
(Agilent, Santa Clara, CA, USA) equipped with a UV diode array detector (detection at 218 nm,
254 nm and 280 nm). The chromatographic separation was performed on a XBridge
™
C18 column
L and the
◦
(150 mm × 4.6 mm, 5
µm) at 24 C oven temperature. The injection volume was 10
µ
flow was 1.5 mL/min using the following gradient: 0.01 M KH2PO4, pH 2.3 (solvent A), MeOH
(solvent B), 45% B to 85% B in 10 min; 85% B for 6 min; stop time 16 min. Column chromatography
was performed on Davisil LC60A 20–45 µm silica from Grace Davison (Columbia, MD, USA) and
Geduran Si60 63–200 µm silica from Merck for the pre-column using an PuriFlash 430 automated
flash chromatography system (Interchim, Montluçon, France). Nuclear magnetic resonance (NMR)
spectra were measured at 300/75 MHz on an Avance III HD NMR spectrometer (Bruker, Billerica,
MA, USA) at the Organic Chemistry Institute, Eberhard Karls Universität Tübingen. Chemical shifts
are reported in parts per million (ppm) relative to tetramethylsilane. All spectra were calibrated
against the (residual proton) peak of the deuterated solvent used. Mass spectra were performed
on an Expression S electrospray ionization mass spectrometer (ESI-MS, Advion, Ithaca, NY, USA)
with TLC interface in the Institute of Pharmaceutical Sciences, Eberhard Karls Universität Tübingen.
High-resolution mass spectra (HRMS) were measured on a Bruker maXis 4G ESI time of flight mass
spectrometer (ESI-TOF-MS) in the positive mode in the Organic Chemistry Institute, Eberhard Karls
Universität Tübingen.
3.2. Experimental Procedures
3.2.1. General Procedure for the Preparation of Imidazole-2-Thione Derivatives 22a–c and 36 (General
Procedure A)
In a pressure vial the corresponding alkyl or aryl isothiocyanate 24 (3–5 equiv.) was dissolved
in NEt3 (2 mL) and then the appr◦opriate
α-aminoketone derivative 35 or 23 (1 equiv.) was added.
The closed vial was heated at 50 C and stirred until the starting compound resulted completely
consumed as detected by HPLC analysis (1.5–4 h). The NEt3 was then evaporated at reduced pressure
and the residue was taken up in glacial AcOH and stirred at 80 ◦C for 2 to 16 h. After concentrating
the mixture at reduced pressure, a NaHCO3 saturated solution was added until reaching pH
≈
8 and
the aqueous layer was then extracted with EtOAc. The combined organic layers were then washed
with NaCl saturated solution, dried over anhydrous Na2SO4, and concentrated at reduced pressure.
The residue was finally purified by flash column chromatography.

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3.2.2. General Procedure for the Preparation of 2-Methylsulfanylimidazole Derivatives 21a–c and 37
(General Procedure B)
In a pressure vial the appropriate imidazole-2-thione derivative (22a–c or 36, 1 equiv.) was
suspended in MeOH (4–10 mL) and after that t-BuONa (1.2 equiv.) was added. After cooling the
mixture at 0 ◦C, iodomethane (5 equiv.) was added and the tightly closed vial was heated to 50 ◦C
and stirred for 45 min to 2 h. After removing the solvent at reduced pressure H2O was added and the
aqueous phase was extracted with DCM. The combined organic layers were then washed with NaCl
saturated solution, dried over anhydrous Na2SO4, and concentrated at reduced pressure. The residue
was finally purified by flash column chromatography or directly used for the following step.
3.2.3. General Procedure for the Preparation of Amides 3a–c and 38 (General Procedure C)
Under argon atmosphere the corresponding imidazole derivative 21a–c or 37 (1 equiv.),
3-(4-methoxyphenyl)propanamide (1.5 equiv.), Pd2(dba)3 (0.05 equiv.), XantPhos (0.1 equiv.), and
Cs2CO3 (3 equiv.) were suspended in dry DMF and after that the reaction mixture was heated at
100 ◦C and stirred overnight (18 h). The reaction mixture was poured in H2O and the aqueous phase
was extracted with EtOAc. The combined organic layers were then washed with NaCl saturated
solution, dried over anhydrous Na2SO4, and concentrated at reduced pressure. The residue was finally
purified by flash column chromatography.
3.2.4. General Procedure for the Preparation of Amines 4a–c and 39 (General Procedure D)
In a pressure vial, the corresponding imidazole derivative 21a
–
c
or 37◦(1 equiv.) was suspended in
(S)-1-phenylethan-1-amine (1.5 mL) and the closed vial was stirred at 180 C for 18–40 h. The reaction
mixture was poured in H2O and the aqueous phase was extracted with EtOAc. The combined
organic layers were then washed with NaCl saturated solution, dried over anhydrous Na2SO4, and
concentrated at reduced pressure. The residue was finally purified by flash column chromatography.
3.2.5. Detailed Procedures for the Preparation of Synthesized Compounds
2-Chloro-N-methoxy-N-methylisonicotinamide (27). 2-Chloroisonicotinic acid (26, 21.0 g, 133.3 mmol) was
suspended in SOCl2 (60 mL) and the mixture was stirred at reflux temperature for 5 h. After removing
the excess of solvent, the residue was taken up in dry DCM and added dropwise to an ice-cooled
previously prepared suspension of N,O-dimethylhydroxylamine hydrochloride (15.6 g, 160 mmol) and
NEt3 (45.0 mL, 320 mmol) in dry DCM (50 mL). After completion of the addition the mixture was let
heating at rt and stirred overnight. After evaporating the solvent at reduced pressure H2O was added
and the aqueous phase was extracted with DCM. The combined organic layers were then washed with
NaCl saturated solution, dried over anhydrous Na2SO4, and concentrated at reduced pressure giving
26.0 g of product as a light brown solid, which was directly used for the following step without further
purification (97% yield); 1H-NMR (300 MHz, CDCl3)
1H), 7.54 (s, 1H), 8.45 (d, J = 5.1 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
149.8, 151.6, 166.0; ESI-MS: (m/z) 201.1 [M + H]+; HPLC: tr = 2.051 min.
δ
3.35 (s, 3H), 3.53 (s, 3H), 7.43 (dd, J = 5.0, 1.2 Hz,
32.9, 61.5, 120.7, 122.8, 144.5,
δ
2-Chloro-N-hydroxy-N-methylisonicotinamide (28). 2-Chloroisonicotinic acid (26, 5.0 g, 31.7 mmol) was
suspended in SOCl2 (25 mL) and the mixture was stirred at reflux temperature for 6 h. After removing
the excess of solvent, the residue was taken up in dry DCM and added dropwise to an ice-cooled
previously prepared suspension of N-methylhydroxylamine hydrochloride (3.2 g, 38.0 mmol) and
NEt3 (9.7 mL, 76.1 mmol) in dry DCM (15 mL). After completion of the addition the mixture was
let heating at rt and stirred overnight. After evaporating the solvent at reduced pressure H2O was
added and the aqueous phase was extracted with EtOAc. The combined organic layers were then
washed with NaCl saturated solution, dried over anhydrous Na2SO4, and concentrated at reduced
pressure giving 5.6 g of product as a white-pink solid, which was directly used for the following step
without further purification (95% yield); 1H-NMR (300 MHz, DMSO-d6)
δ 3.27 (s, 3H), 7.53 (dd, J = 5.0,

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1.2 Hz, 1H), 7.61 (dd, J = 1.2, 0.5 Hz, 1H), 8.49 (dd, J = 5.0, 0.5 Hz, 1H), 10.40 (br. s, 1H); 13C-NMR
(
75 MHz, DMSO-d6) δ
36.9, 122.1, 123.1, 146.5, 150.50, 150.56, 165.7; ESI-MS: (m/z) 187.2 [M + H]+,
185.1 [M − H]−; HPLC: tr = 1.568 min.
N-(tert-butoxy)-2-chloro-N-methylisonicotinamide (29). In a pressure vial 2-chloro-N-hydroxy-N-
methylisonicotinamide (27, 500 mg, 2.68 mmol) was suspended in dry 1,4-dioxane (5 mL) and t-BuOAc
(20 mL). After adding 70% HClO4(aq) (27 mg, 0.27 mmol) the vial was tightly closed and the mixture
◦
was stirred at 60 C for 48 h. After cooling down, the mixture was poured in a K2CO3 saturated
solution and the aqueous phase was extracted with EtOAc. The combined organic layers were then
dried over anhydrous Na2SO4 and the solvent was evaporated at reduced pressure giving 402 mg of
the desired compound, which was used for the following step without further purification; 1H-NMR
(300 MHz, CDCl3)
δ 1.10 (s, 9H), 3.43 (s, 3H), 7.48 (dd, J = 5.1, 1.2 Hz, 1H), 7.60 (br. s, 1H), 8.43 (dd,
J = 5.0, 0.5 Hz, 1H); ESI-MS: (m/z) 243.1 [M + H]+; HPLC: tr = 4.733 min.
1-(2-Chloropyridin-4-yl)-2-(4-fluorophenyl)ethan-1-one (25). The title compound could be obtained
alternatively through the following three procedures:
(1) Under argon atmosphere Mg turnings (1.2 g, 50.0 mmol) were suspended in dry THF
(120 mL) and after that 4-fluorobenzyl chloride (6.0 g, 41.5 mmol) was added in one portion.
After the reaction was initiated, the mixture warmed up and was stirred until it cooled down to
rt. The residual Mg was let decanting and the supernatant was added dropwise to a solution of
2-chloro-N-methoxy-N-methylisonicotinamide (27, 3.2 g, 16.0 mmol) in dry THF (35 mL) under
argon atmosphere. The mixture was then stirred for 2 h at a temperature of 30–35 ◦C. The reaction
was quenched with NH4Cl saturated solution (100 mL) and stirred overnight at rt. The two
formed phases were separated and the aqueous phase was then further extracted by EtOAc.
The combined organic layers were then washed with NaCl saturated solution, dried over anhydrous
Na2SO4, and concentrated at reduced pressure. Finally, the residue was purified by flash column
chromatography (SiO2, petroleum ether 40/60: EtOAc 4:1) giving 1.96 g of pure product as a yellow
oil, which solidifies after cooling (49% yield).
(2) Under argon atmosphere Mg turnings (1.22 g, 50.1 mmol) were suspended in dry THF
(15 mL) and then 4-fluorobenzyl chloride (1.07 g, 7.4 mmol) was added in one portion. When the
mixture started to become warm it was immediately cooled with an ice bath and then stirred
for 2 h. After letting the residual Mg decanting, the supernatant was added dropwise to a
solution of N-(tert-butoxy)-2-chloro-N-methylisonicotinamide (29, 900 mg, 3.7 mmol) in dry THF
(10 mL), previously cooled at
−
10 ◦C. After completion of the addition the mixture was let slowly
heating at rt and stirred for 3 h. NH4Cl saturated solution (80 mL) was added and the two
formed phases were separated. The aqueous phase was then further extracted 3 times with EtOAc.
The combined organic layers were then washed with NaCl saturated solution, dried over anhydrous
Na2SO4, and concentrated at reduced pressure. Finally, the residue was purified by flash column
chromatography (SiO2, n-hexane: EtOAc gradient elution from 4:1 to 3:2) giving 747 mg of pure
product as a yellow oil, which solidifies after cooling (81% yield).
(3) Under argon atmosphere Mg turnings (6.94 g, 285.6 mmol) were suspended in dry THF
(
35 mL). After that 4-fluorobenzyl chloride (13.6 g, 92.5 mmol◦) was added in portions: after adding
1 mL and starting the reaction, the mixture was cooled at 0 C with an ice bath and the addition
continued by 0.5 mL/min at the same temperature. After the addition was competed the mixture
was let stirring until warming up to rt. After letting the Mg decanting the supernatant was added
slowly dropwise to a suspension of 2-chloroisonicotinic acid (26, 6.0 g, 38.1 mmol) in dry THF (24 mL),
previously cooled at
−
30 ◦C. During the addition the temperature was maintained between
−
25 and
−30 ◦C. After complete addition the mixture was let heating to rt and stirred overnight. The mixture
was poured on NH4Cl saturated solution (100 mL). The aqueous phase was extracted twice with
EtOAc and the combined organic layers were dried over anhydrous Na2SO4, and concentrated at
reduced pressure. Finally, the residue was purified by flash column chromatography (SiO2, petroleum

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ether 40/60:EtOAc gradient elution from 3:1 to 1:1) giving 3.37 g of pure compound as a yellow
1
oil, which solidifies after cooling (35% yield); H-NMR (300 MHz, CDCl3)
δ 4.24 (s, 2H), 6.99–7.10
(
m, 2H), 7.15–7.23 (m, 2H), 7.67 (dd, J = 5.1, 1.5 Hz, 1H), 7.79 (dd, J = 1.4, 0.7 Hz, 1H), 8.56 (dd, J = 5.1,
0.5 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
δ 44.9, 115.9 (d, J = 21.6 Hz), 120.2, 122.7, 128.4 (d, J = 3.3 Hz),
131.1 (d, J = 8.3 Hz), 145.2, 151.0, 153.0, 162.2 (d, J = 246.6 Hz); ESI-MS: (m/z) 249.9 [M + H]+; HPLC:
tr = 5.555 min.
1-(2-Chloropyridin-4-yl)-2-(4-fluorophenyl)-2-(hydroxyimino)ethan-1-one (30). Ethanone derivative 25
(1.96 g, 7.85 mmol) was dissolved in glacial AcOH (15 mL) and after that NaNO2 (1.67 g, 24.2 mmol),
previously dissolved in H2O (7 mL), was added dropwise and the reaction mixture was stirred
overnight at rt. Afterwards 50 mL H2O were added and the voluminous precipitate formed was
filtered off and washed with H2O. The residue was then suspended in H2O and the suspension was
extracted with EtOAc. The combined organic layers were dried over anhydrous Na2SO4 and the
solvent was then removed at reduced pressure, affording 1.8 g of the desired product, which was
used for the following step without further purification (82% yield); 1H-NMR (300 MHz, DMSO-d6)
7.23–7.37 (m, 2H), 7.51–7.62 (m, 2H), 7.73 (dd, J = 5.0, 1.4 Hz, 1H), 7.89 (dd, J = 1.2, 0.7 Hz, 1H), 8.58
(dd, J = 5.0, 0.7 Hz, 1H), 13.14 (s, 1H); 13C-NMR (75 MHz, DMSO-d6)
115.3 (d, J = 21.6 Hz), 122.8,
δ
δ
124.3, 125.6 (d, J = 3.9 Hz), 132.5 (d, J = 8.3 Hz), 149.2, 150.5, 150.6, 154.3, 162.8 (d, J = 246.6 Hz), 190.4;
ESI-MS: (m/z) 276.9 [M − H]−; HPLC: tr = 7.405 min.
1-(2-Chloropyridin-4-yl)-2-(4-fluorophenyl)ethan-1-one oxime (31). Hydroxylamine hydrochloride (1.52 g
,
21.93 mmol) was dissolved in H2O (3.5 mL) and then 20% NaOH(aq) (0.7 mL) and a solution of ethanone
derivative 25 (3.65 g, 14.62 mmol) in MeOH (17.5 mL) were added. The reaction mixture was stirred at
rt for 48 h while a precipitate formed. Saturated NH4Cl solution (50 mL) was added and the precipitate
was filtered off, rinsed with H2O and dried in vacuo over P2O5 affording 3.71 g of the desired product
as an off-white solid, which was used for the following step without further purification (96% yield).
Extraction with EtOAc represents an alternative work-up procedure giving similar yields; 1H-NMR
(300 MHz, DMSO-d6)
δ
4.16 (s, 2H), 7.12–7.02 (m, 2H), 7.28–7.20 (m, 2H), 7.64 (dd, J = 5.2, 1.5 Hz, 1H),
29.0, 115.4
7.71–7.68 (m, 1H), 8.37 (d, J = 5.2 Hz, 1H), 12.27 (s, 1H); 13C-NMR (75 MHz, DMSO-d6)
δ
(
d, J = 21.3 Hz), 119.7, 120.5, 130.2 (d, J = 8.0 Hz), 132.5 (d, J = 3.1 Hz), 146.5, 150.2, 151.0, 152.7, 160.9
(d, J = 242.4 Hz); ESI-MS: 265.0 [M + H]+, 263.0 [M − H]−; HPLC: tr = 6.934 min.
1-(2-Chloropyridin-4-yl)-2-(4-fluorophenyl)ethan-1-one O-tosyl oxime (32). A solution of ketoxime 31 (1.20 g
,
4.53 mmol) and p-toluenesulfonyl chloride (3.46 g, 18.14 mmol) in dry pyridine (6 mL) was stirred
at rt under N2 atmosphere for 50 h. The mixture was poured into a NaCl saturated solution (30
mL) and extracted three times with EtOAc. The combined organic layers were then washed 3 times
with a NaCl saturated solution, dried over anhydrous Na2SO4 and concentrated at reduced pressure.
Finally, the residue was purified by flash column chromatography (SiO2, petroleum ether 40/60:EtOAc
2:3) giving 1.68 g of the desired product as a yellow oil (88% yield); 1H-NMR (300 MHz, CDCl3)
2.48 (s, 3H), 4.12 (s, 2H), 6.89–7.06 (m, 4H), 7.33 (dd, J = 5.2, 1.5 Hz, 1H), 7.39 (d, J = 8.2 Hz, 2H),
7.42–7.46 (m, 1H), 7.89 (d, J = 8.3 Hz, 2H), 8.39 (d, J = 5.2 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
δ
δ
21.8, 32.6, 116.1 (d, J = 21.6 Hz), 120.0, 122.1, 128.8 (d, J = 3.3 Hz), 129.0, 129.9 (d, J = 7.7 Hz), 129.9,
131.9, 143.4, 145.9, 150.3, 152.4, 162.5 (d, J = 246.6 Hz), 161.5; ESI-MS: (m/z) 473.2 [M + Na + MeOH]+;
HPLC: tr = 9.342 min.
2-Amino-1-(2-chloropyridin-4-yl)-2-(4-fluorophenyl)ethan-1-one hydrochloride (23). In a three-necks
round bottom flask under argon atmosphere K chunks (175 mg, 4.4 mmol) were added
portionswise to EtOH(abs) (20 mL). After complete dissolution the mixture was cooled at 0 ◦C and
1-(2-chloropyridin-4-yl)-2-(4-fluorophenyl)ethan-1-one O-tosyl oxime (31, 1.70 g, 4.0 mmol), previously
dissolved in EtOH(abs) (50 mL) was added slowly dropwise. The mixture was then stirred at 0 ◦C for
3 h and after that dry Et2O (250 mL) was added and the mixture was stirred for 30 min at rt. The white
precipitate formed was removed by filtration and the filtrate was concentrated at reduced pressure.

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The residue was taken up in conc. HCl(aq) and the mixture was stirred at 60 ◦C for 2 h. The residual
solvent was removed at reduced pressure and the residue was treated with a mixture of THF:Et2O
1:2. The white precipitate obtained was filtered off and dried affording 725 mg of the desired product,
which was used for the following step without further purification (60% yield); ESI-MS: (m/z) 264.9
[M + H]+, 263.0 [M − H]−; HPLC: tr = 2.329 min.
5-(2-Chloropyridin-4-yl)-4-(4-fluorophenyl)-1-(2-methoxyethyl)-1,3-dihydro-2H-imidazole-2-thione
The title compound was prepared following general procedure A starting from compound 23
500 mg, 1.65 mmol) and 2-methoxyethyl isothiocyanate (24a, 965 mg, 8.25 mmol); The residue was
(22a).
(
treated with Et2O obtaining a precipitate, which was filtered off and dried. The filtrate was then
concentrated at reduced pressure and the residue was purified by flash column chromatography (SiO2,
n-hexane:EtOAc gradient elution from 7:3 to 1:1). 293 mg of the desired product were obtained in
total (49% yield); 1H-NMR (300 MHz, DMSO-d6)
δ 3.06 (s, 3H), 3.52–3.60 (m, 2H), 3.99–4.14 (m, 2H),
7.08–7.32 (m, 4H), 7.42 (d, J = 4.6 Hz, 1H), 7.64 (s, 1H), 8.49 (d, J = 4.9 Hz, 1H), 13.07 (br. s, 1H); ESI-MS:
(m/z) 364.2 [M + H]+, 362.2 [M − H]−; HPLC: tr = 5.321 min.
5-(2-Chloropyridin-4-yl)-4-(4-fluorophenyl)-1-methyl-1,3-dihydro-2H-imidazole-2-thione (22b). The title
compound was prepared following general procedure A starting from compound 23 (400 mg,
1.32 mmol) and methyl isothiocyanate (24b, 643 mg, 6.62 mmol); After the addition of NaHCO3
saturated solution, a precipitate was formed, which was filtered off and purified twice by flash column
chromatography (SiO2, DCM:EtOH gradient elution from 100:0 to 97:03) and (SiO2, DCM:EtOH 99:01).
The obtained solid was treated with a mixture of Et2O:n-hexane 1:2 and the yellow precipitate obtained
1
was then filtered off and dried, affording 255 mg of the desired compound (60% yield); H-NMR
(
300 MHz, DMSO-d6)
δ
3.43 (s, 3H), 7.16–7.25 (m, 2H), 7.26–7.35 (m, 2H), 7.42 (dd, J = 5.1, 1.3 Hz,
32.1, 115.9
1H), 7.6 (s, 1H), 8.49 (d, J = 5.0 Hz, 1H), 13.01 (br. s, 1H); 13C-NMR (75 MHz, DMSO-d6)
δ
(
d, J = 22.1 Hz), 123.1, 123.9 (d, J = 2.8 Hz), 124.3, 125.1, 125.6, 129.7 (d, J = 8.3 Hz), 139.9, 150.7, 151.0,
161.9 (d, J = 246.6 Hz), 162.7; ESI-MS: (m/z) 318.3 [M − H]−; HPLC: tr = 4.389 min.
5-(2-Chloropyridin-4-yl)-4-(4-fluorophenyl)-1-phenyl-1,3-dihydro-2H-imidazole-2-thione (22c). The title
compound was prepared following general procedure A starting from compound 23 (400 mg,
1.32 mmol) and phenyl isothiocyanate (24c, 535 mg, 3.96 mmol); The residue was purified by flash
column chromatography (SiO2, DCM:EtOH gradient elution from 100:0 to 98:02). The solid obtained
was treated with a mixture of Et2O:n-hexane 1:2 and the white precipitate formed was then filtered
off and dried, affording 260 mg of the desired compound (51% yield);1H-NMR (300 MHz, CDCl3)
δ
6.69 (d, J = 4.7 Hz, 1H), 6.81 (s, 1H), 6.89–7.03 (m, 2H), 7.11–7.21 (m, 2H), 7.21–7.30 (m, 2H), 7.32–7.46
−
(m, 3H), 8.11 (d, J = 5.2 Hz, 1H), 12.63 (br. s, 1H); ESI-MS: (m/z) 380.5 [M
−
H] ; HPLC: tr = 5.867 min.
2-Chloro-4-(4-(4-fluorophenyl)-1-(2-methoxyethyl)-2-(methylthio)-1H-imidazol-5-yl)pyridine (21a). The title
compound was prepared following general procedure B starting from compound 22a 263 mg
(
,
0.72 mmol), t-BuONa (83 mg, 0.86 mmol), and iodomethane (511 mg, 3.6 mmol) obtaining 270 mg of
the desired product, which was used for the following step without further purification (99% yield);
1H-NMR (300 MHz, CDCl3)
δ
2.73 (s, 3H), 3.25 (s, 3H), 3.55 (t, J = 5.5 Hz, 2H), 4.00 (t, J = 5.5 Hz, 2H),
6.87–6.98 (m, 2H), 7.21 (dd, J = 5.1, 1.4 Hz, 1H), 7.33–7.41 (m, 2H), 7.42 (dd, J = 1.3, 0.6 Hz, 1H), 8.40 (dd,
J = 5.1, 0.6 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
16.0, 44.4, 58.9, 70.5, 115.3 (d, J = 21.6 Hz), 124.1, 125.7,
δ
126.3, 128.9 (d, J = 8.3 Hz), 129.5 (d, J = 3.3 Hz), 139.5, 141.9, 145.4, 150.1, 152.1, 162.0 (d, J = 246.6 Hz);
ESI-MS: (m/z) 378.3 [M + H]+; HPLC: tr = 7.524 min.
2-Chloro-4-(4-(4-fluorophenyl)-1-methyl-2-(methylthio)-1H-imidazol-5-yl)pyridine (21b). The title compound
was prepared following general procedure B starting from compound 22b (225 mg, 0.70 mmol),
t-BuONa (81 mg, 0.84 mmol), and iodomethane (497 mg, 3.5 mmol). The crude product was purified by
flash column chromatography (SiO2, DCM:EtOH gradient elution from 100:0 to 99:01) giving 189 mg of
the desired compound (80% yield); 1H-NMR (300 MHz, CDCl3)
2H), 7.13 (dd, J = 5.1, 1.4 Hz, 1H), 7.34–7.45 (m, 2H), 8.42 (d, J = 5.1 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
δ 2.73 (s, 3H), 3.49 (s, 3H), 6.90–7.02 (m,

Molecules 2018, 23, 221
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δ
15.8, 32.0, 115.4 (d, J = 21.6 Hz), 123.4, 124.8, 126.1, 129.1 (d, J = 7.7 Hz), 129.5 (d, J = 3.3 Hz), 139.8,
141.6, 146.1, 150.4, 152.4, 162.2 (d, J = 246.6 Hz); ESI-MS: (m/z) 334.3 [M + H]+; HPLC: tr = 6.695 min.
2-Chloro-4-(4-(4-fluorophenyl)-2-(methylthio)-1-phenyl-1H-imidazol-5-yl)pyridine (21c). The title compound
was prepared following general procedure B starting from compound 22c (219 mg, 0.57 mmol),
t-BuONa (55 mg, 0.57 mmol), and iodomethane (404 mg, 2.85 mmol). After adding H2O a precipitate
was formed, which was filtered off and dried, giving 185 mg of the desired product that was used
for the following step without further purification (82% yield); 1H-NMR (300 MHz, CDCl3)
3H), 6.82 (d, J = 4.7 Hz, 1H), 6.93 (s, 1H), 6.96–7.09 (m, 2H), 7.11–7.25 (m, 2H), 7.37–7.58 (m, 5H), 8.15
(d, J = 4.9 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
15.1, 115.5 (d, J = 21.6 Hz), 122.6, 124.2, 126.2, 127.6,
δ 2.68 (s,
δ
129.5 (d, J = 3.3 Hz), 129.6, 129.7, 135.1, 140.8 (d, J = 7.7 Hz), 147.6, 149.6, 151.7, 162.4 (d, J = 247.1 Hz);
ESI-MS: (m/z) 396.6 [M + H]+; HPLC: tr = 9.718 min.
N-(4-(4-(4-Fluorophenyl)-1-(2-methoxyethyl)-2-(methylthio)-1H-imidazol-5-yl)pyridin-2-yl)-3-(4-
methoxyphenyl)propanamide (3a) [14]. The title compound was prepared according to general
procedure C starting from imidazole 21a (100 mg, 0.26 mmol), 3-(4-methoxyphenyl)propanamide
(
(
72 mg, 0.40 mmol), Pd2(dba)3 (12 mg, 0.013 mmol), XantPhos (15 mg, 0.026 mmol), and Cs2CO3
254 mg, 0.78 mmol). The residue was purified twice by flash column chromatography (SiO2,
DCM:EtOH gradient elution from 100:0 to 95:05) and (SiO2, DCM:EtOH gradient elution from 100:0
1
to 97:03) giving 50 mg of the desired product (37% yield); H-NMR (300 MHz, CDCl3)
δ 2.64–2.77
(m, 5H), 3.00 (t, J = 7.6 Hz, 2H), 3.24 (s, 3H), 3.51 (t, J = 6.0 Hz, 2H), 3.79 (s, 3H), 4.10 (t, J = 6.0 Hz,
2H), 6.79–6.88 (m, 2H), 6.88–6.99 (m, 3H), 7.11–7.20 (m, 2H), 7.36–7.47 (m, 2H), 8.16 (br. s, 1H), 8.24
−
(
d, J = 5.1 Hz, 1H), 8.29 (s, 1H); ESI-MS: (m/z) 521.5 [M + H]+, 543.4 [M + Na]+, 519.5 [M
−
H] ; HPLC:
tr = 8.476 min.
N-(4-(4-(4-Fluorophenyl)-1-methyl-2-(methylthio)-1H-imidazol-5-yl)pyridin-2-yl)-3-(4-methoxyphenyl)-
propanamide (3b). The title compound was prepared according to general procedure C starting from
imidazole 21b (70 mg, 0.21 mmol), 3-(4-methoxyphenyl)propanamide (75 mg, 0.41 mmol), Pd2(dba)3
(10 mg, 0.01 mmol), XantPhos (12 mg, 0.021 mmol), and Cs2CO3 (205 mg, 0.63 mmol). The residue was
purified twice by flash column chromatography (SiO2, DCM:EtOH gradient elution from 99:01 to
95:05) and (SiO2, n-hexane:EtOAc gradient elution from 4:1 to 1:1) giving 44 mg of the desired product
(45% yield); 1H-NMR (300 MHz, CDCl3)
(s, 3H), 6.84 (d, J = 8.6 Hz, 2H), 6.88–7.00 (m, 3H), 7.14 (d, J = 8.6 Hz, 2H), 7.36–7.50 (m, 2H), 8.21 (d, J =
5.1 Hz, 1H), 8.27 (s, 1H), 8.36 (br. s, 1H); 13C-NMR (75 MHz, CDCl3)
16.1, 30.3, 32.1, 39.6, 55.3, 114.0,
δ 2.62–2.81 (m, 5H), 3.00 (t, J = 7.5 Hz, 2H), 3.54 (s, 3H), 3.79
δ
114.6, 115.3 (d, J = 21.6 Hz), 121.1, 127.6, 129.1 (d, J = 7.7 Hz), 129.3, 130.0 (d, J = 3.3 Hz), 132.3, 139.3,
141.1, 145.3, 148.1, 151.9, 158.2, 162.1 (d, J = 246.6 Hz), 171.0; ESI-TOF-HRMS: (m/z) [M + H]+ calcd. for
C26H25FN4O2S 477.1755, found 477.1762; HPLC: tr = 8.855 min.
N-(4-(4-(4-Fluorophenyl)-2-(methylthio)-1-phenyl-1H-imidazol-5-yl)pyridin-2-yl)-3-(4-methoxyphenyl)-
propanamide (3c). The title compound was prepared according to general procedure C starting from
imidazole 21c (70 mg, 0.18 mmol), 3-(4-methoxyphenyl)propanamide (64 mg, 0.36 mmol), Pd2(dba)3
(8 mg, 0.009 mmol), XantPhos (10 mg, 0.018 mmol), and Cs2CO3 (173 mg, 0.53 mmol). The residue
was purified twice by flash column chromatography (SiO2, DCM:EtOH gradient elution from 99:01
to 95:05) and (SiO2, n-hexane:EtOAc gradient elution from 4:1 to 1:1) giving 24 mg of the desired
product (25% yield); 1H-NMR (300 MHz, DMSO-d6)
6.77–6.90 (m, 3H), 7.05–7.22 (m, 4H), 7.25–7.36 (m, 2H), 7.39–7.60 (m, 5H), 7.93 (s, 1H), 8.16 (dd, J = 5.1,
0.7 Hz, 1H), 10.44 (s, 1H); 13C-NMR (75 MHz, CDCl3)
15.3, 30.3, 39.7, 55.2, 113.9, 114.5, 115.3 (d,
δ 2.54–2.68 (m, 5H), 2.70–2.84 (m, 2H), 3.71 (s, 3H),
δ
J = 21.6 Hz), 120.5, 127.9, 129.1, 129.2, 129.4, 129.5 (d, J = 7.7 Hz), 129.8 (d, J = 2.8 Hz), 132.3, 135.4,
140.0, 140.8, 146.8, 147.2, 151.4, 158.1, 162.2 (d, J = 246.6 Hz), 170.4; ESI-TOF-HRMS: (m/z) [M + H]+
calcd. for C31H27FN4O2S 539.1911, found 539.1915; HPLC: tr = 10.160 min.
(S)-4-(4-(4-Fluorophenyl)-1-(2-methoxyethyl)-2-(methylthio)-1H-imidazol-5-yl)-N-(1-phenylethyl)pyridin-2-
amine (4a) [15]. The title compound was prepared according to general procedure D starting from

Molecules 2018, 23, 221
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compound 21a (100 mg, 0.26 mmol). The reaction was stopped after 24 h. The residue was then
purified twice by flash column chromatography (SiO2, DCM:EtOH gradient elution from 100:0
to 95:05) and (SiO2, DCM:EtOH gradient elution from 99:01 to 97:03) giving 50 mg of the desired
1
product (41% yield); H-NMR (300 MHz, DMSO-d6)
δ 1.42 (d, J = 6.8 Hz, 3H), 2.63 (s, 3H), 3.06 (s,
3H), 3.22–3.32 (m, 2H, partially overlapping with H2O signal), 3.78–3.95 (m, 2H), 4.90–5.09 (m, 1H),
6.35–6.52 (m, 2H), 7.01–7.13 (m, 2H), 7.13–7.24 (m, 2H), 7.24–7.46 (m, 6H), 8.03 (d, J = 5.1 Hz, 1H);
ESI-MS: (m/z) 463.5 [M + H]+, 461.5 [M − H]−; HPLC: tr = 6.398 min.
(S)-4-(4-(4-Fluorophenyl)-1-methyl-2-(methylthio)-1H-imidazol-5-yl)-N-(1-phenylethyl)pyridin-2-amine
(4b) [15]. The title compound was prepared according to general procedure D starting from compound
21b (35 mg, 0.105 mmol). The reaction was stopped after 32 h although not completed. The residue
was then purified by preparative TLC (SiO2, DCM:EtOH 95:05) and by flash column chromatography
(SiO2, n-hexane:EtOAc gradient elution from 7:3 to 1:1) giving 17 mg of the desired product (39%
yield); 1H-NMR (300 MHz, CDCl3)
δ 1.54 (d, J = 6.7 Hz, 3H), 2.64 (s, 3H), 3.08 (s, 3H), 4.47–4.69 (m, 1H),
5.51 (br. s, 1H), 6.05 (s, 1H), 6.42 (d, J = 4.7 Hz, 1 H), 6.76–6.95 (m, 2H), 7.14–7.53 (m, 7H, overlapping
−
with the solvent peak), 8.05 (d, J = 5.1 Hz, 1 H); ESI-MS: (m/z) 419.3 [M + H]+, 417.2 [M
tr = 7.063 min.
−
H] ; HPLC:
(S)-4-(4-(4-Fluorophenyl)-2-(methylthio)-1-phenyl-1H-imidazol-5-yl)-N-(1-phenylethyl)pyridin-2-amine (4c).
The title compound was prepared according to general procedure D starting from compound 21b
(42 mg, 0.106 mmol). The reaction was stopped after 26 h. The residue was purified by flash column
chromatography (SiO2, n-hexane:EtOAc gradient elution from 9:1 to 1:1) giving 42 mg of the desired
product (82% yield); 1H-NMR (300 MHz, CDCl3)
δ 1.41 (d, J = 6.8 Hz, 3H), 2.63 (s, 3H), 4.16–4.34 (m,
1H), 5.18–5.36 (m, 1H), 5.90 (s, 1H), 6.21 (dd, J = 5.3, 1.2 Hz, 1H), 6.86–6.98 (m, 2H), 7.00–7.10 (m, 2H),
7.11–7.31 (m, 5H, overlapping with the solvent peak), 7.31–7.41 (m, 3H), 7.41–7.51 (m, 2H), 7.83 (d,
J = 5.2 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
δ 15.3, 24.4, 52.2, 107.4, 114.1, 115.2 (d, J = 21.6 Hz), 125.6,
127.1, 127.6, 128.4, 128.7, 128.9, 129.2 (d, J = 7.7 Hz), 129.3, 129.9 (d, J = 3.3 Hz), 135.5, 139.2, 139.8, 144.0,
146.0, 147.4, 157.8, 162.0 (d, J = 246.0 Hz); ESI-TOF-HRMS: (m/z) [M + H]+ calcd. for C29H25FN4S
481.1857, found 481.1865; HPLC: tr = 9.148 min.
2-Amino-2-(2-chloropyridin-4-yl)-1-(4-fluorophenyl)ethan-1-one hydrochloride (35) [13,30]. Oxime 34 [13,30]
(500 mg, 1.8 mmol) and 10% Pd on charcoal (100 mg, 0.095 mmol) were placed in a Schlenk reaction
tube, which was then evacuated and filled with a H2 atmosphere. Isopropanolic HCl (10 mL) was then
added and the mixture was vigorously stirred at rt under a constant supply of H2 for 1 h. The solvent
was evaporated at reduced pressure and then MeOH was added. The Pd catalyst was removed by
filtration and the filtrate was concentrated at reduced pressure. Finally, the residue was treated with
EtOAc and the white solid obtained was filtered off and dried, affording 520 mg of the desired product,
which were used for the following step without further purification (92% yield); ESI-MS: (m/z) 264.9
[M + H]+, 262.9 [M − H]−; HPLC: tr = 2.486 min.
4-(2-Chloropyridin-4-yl)-5-(4-fluorophenyl)-1-methyl-1,3-dihydro-2H-imidazole-2-thione (36). The title
compound was prepared following general procedure A starting from compound 35 (550 mg,
1.82 mmol) and methyl isothiocyanate (24b, 665 mg, 9.1 mmol); the residue was then purified by
flash column chromatography (SiO2, DCM:EtOH gradient elution from 100:0 to 95:05) obtaining
1
267 mg of the desired product (46% yield); H-NMR (300 MHz, DMSO-d6)
δ 3.27 (s, 3H), 7.03 (dd,
J = 5.3, 1.6 Hz, 1H), 7.32 (d, J = 1.1 Hz, 1H), 7.37–7.48 (m, 2H), 7.51–7.63 (m, 2H), 8.22 (d, J = 5.3 Hz,
1H), 13.09 (br. s, 1H); ESI-MS: (m/z) 318.0 [M − H]−; HPLC: tr = 5.864 min.
2-Chloro-4-(5-(4-fluorophenyl)-1-methyl-2-(methylthio)-1H-imidazol-4-yl)pyridine (37). The title compound
was prepared following general procedure B starting from compound 36 (267 mg, 0.83 mmol), t-BuONa
(96.1 mg, 1.0 mmol), and iodomethane (639 mg, 4.15 mmol) obtaining 255 mg of the desired product,
which was used for the following step without further purification (92% yield); 1H-NMR (300 MHz,
CDCl3)
δ 2.65 (s, 3H), 3.28 (s, 3H), 7.03 (d, J = 5.0 Hz, 1H), 7.08–7.31 (m, 4H), 7.44 (s, 1H), 8.02 (d,

Molecules 2018, 23, 221
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J = 5.2 Hz, 1H); 13C-NMR (75 MHz, CDCl3)
δ
15.6, 31.3, 116.7 (d, J = 21.6 Hz), 118.7, 120.4, 125.6 (d,
J = 3.3 Hz), 132.3 (d, J = 8.3 Hz), 132.5, 134.3, 144.7, 144.9, 149.2, 151.7, 163.3 (d, J = 251.0 Hz); ESI-MS:
(m/z) 334.0 [M + H]+; HPLC: tr = 8.065 min.
N-(4-(5-(4-Fluorophenyl)-1-methyl-2-(methylthio)-1H-imidazol-4-yl)pyridin-2-yl)-3-(4-methoxyphenyl)-
propanamide (38). The title compound was prepared according to general procedure C starting from
imidazole 37 (90 mg, 0.27 mmol), 3-(4-methoxyphenyl)propanamide (73 mg, 0.41 mmol), Pd2(dba)3
(12 mg, 0.013 mmol), XantPhos (16 mg, 0.027 mmol), and Cs2CO3 (264 mg, 0.81 mmol). The residue
was purified by flash column chromatography (SiO2, DCM:EtOH gradient elution from 100:0 to 95:05)
affording 82 mg of the desired product (64% yield); 1H-NMR (300 MHz, CDCl3)
2H), 2.76 (s, 3H), 2.94 (t, J = 7.6 Hz, 2H), 3.37 (s, 3H), 3.78 (s, 3H), 6.82 (d, J = 8.6 Hz, 2H), 7.05–7.15 (m,
3H), 7.18–7.27 (m, 2H), 7.29–7.38 (m, 2H), 8.00 (d, J = 5.4 Hz, 1H), 8.21–8.42 (m, 2H); 13C-NMR (75 MHz
CDCl3) 15.7, 30.3, 31.3, 39.6, 55.2, 110.8, 113.9, 116.5 (d, J = 21.6 Hz), 116.8, 125.9 (d, J = 3.3 Hz),
δ 2.59 (t, J = 7.7 Hz,
,
δ
129.3, 132.2, 132.4 (d, J = 8.3 Hz), 132.6, 135.7, 144.4, 144.5, 146.9, 151.5, 158.0, 163.3 (d, J = 246.6 Hz),
170.4; ESI-TOF-HRMS: (m/z) [M + H]+ calcd. for C26H25FN4O2S 477.1755, found 477.1763; HPLC:
tr = 7.745 min.
(S)-4-(5-(4-Fluorophenyl)-1-methyl-2-(methylthio)-1H-imidazol-4-yl)-N-(1-phenylethyl)pyridin-2-amine (39).
The title compound was prepared according to general procedure D starting from compound 21a
(55 mg, 0.16 mmol). The reaction was stopped after 40 h although not fully completed. The residue
was then purified by flash column chromatography (SiO2, n-hexane:EtOAc gradient elution from
4:1 to 1:1) obtaining 39 mg of the desired product (58% yield); 1H-NMR (300 MHz, CDCl3)
δ 1.39 (d,
J = 6.8 Hz, 3H), 2.60 (s, 3H), 3.22 (s, 3H), 4.37–4.50 (m, 1 H), 4.91 (d, J = 6.4 Hz, 1H), 6.30 (s, 1H), 6.57
(dd, J = 5.5, 1.4 Hz, 1H), 6.98–7.31 (m, 9H overlapping with the solvent peak), 7.80 (d, J = 5.4 Hz, 1H);
13C-NMR (75 MHz, CDCl3)
δ 15.8, 24.2, 31.2, 51.7, 103.4, 110.9, 116.3 (d, J = 21.6 Hz), 125.8, 126.3 (d,
J = 3.9 Hz), 126.8, 128.4, 131.3, 132.4 (d, J = 8.3 Hz), 136.1, 143.1, 143.8, 144.6, 147.6, 158.0, 163.0 (d,
J = 249.9 Hz); ESI-TOF-HRMS: (m/z) [M + H]+ calcd. for C24H23FN4S 419.1700, found 419.1706; HPLC:
tr = 6.899 min.
Acknowledgments: The authors acknowledge Lars Kuckuck for contribution in the synthesis of compounds
3a and 4a. In addition, Jens Strobach, Katharina Bauer, and Mark Kudolo are gratefully acknowledged for the
biological assay of synthesized compounds. This study was supported by the Federal Ministry of Education and
Research (BMBF) within the BioPharma—Neuroallianz consortium.
Author Contributions: F.A., S.A., A.K., W.A., S.A.L. and P.K. conceived and designed the experiments; F.A., S.A.
and A.K. performed syntheses; F.A., W.A., S.A.L. and P.K. analyzed the data; F.A., S.A and P.K. wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
2.
3.
Cuenda, A.; Rousseau, S. p38 MAP-kinases pathway regulation, function and role in human diseases.
Biochim. Biophys. Acta 2007, 1773, 1358–1375. [CrossRef] [PubMed]
Zarubin, T.; Han, J.H. Activation and signaling of the p38 MAP kinase pathway. Cell Res. 2005, 15, 11–18.
[CrossRef] [PubMed]
Kaminska, B. MAPK signalling pathways as molecular targets for anti-inflammatory therapy—From
molecular mechanisms to therapeutic benefits. Biochim. Biophys. Acta 2005, 1754, 253–262. [CrossRef]
[PubMed]
4.
5.
6.
7.
Kumar, S.; Boehm, J.; Lee, J.C. p38 MAP kinases: Key signalling molecules as therapeutic targets for
inflammatory diseases. Nat. Rev. Drug Discov. 2003, 2, 717–726. [CrossRef] [PubMed]
Correa, S.A.; Eales, K.L. The Role of p38 MAPK and Its Substrates in Neuronal Plasticity and
Neurodegenerative Disease. J. Signal Transduct. 2012, 2012, 649079. [CrossRef] [PubMed]
Krementsov, D.N.; Thornton, T.M.; Teuscher, C.; Rincon, M. The emerging role of p38 mitogen-activated
protein kinase in multiple sclerosis and its models. Mol. Cell. Biol. 2013, 33, 3728–3734. [CrossRef] [PubMed]
Munoz, L.; Ammit, A.J. Targeting p38 MAPK pathway for the treatment of Alzheimer’s disease.
Neuropharmacology 2010, 58, 561–568. [CrossRef] [PubMed]

Molecules 2018, 23, 221
18 of 19
8.
9.
Lee, J.K.; Kim, N.J. Recent Advances in the Inhibition of p38 MAPK as a Potential Strategy for the Treatment
of Alzheimer’s Disease. Molecules 2017, 22, 1287. [CrossRef] [PubMed]
Bühler, S.; Laufer, S.A. p38 MAPK inhibitors: A patent review (2012–2013). Expert Opin. Ther. Pat. 2014, 24,
535–554. [CrossRef] [PubMed]
10. Fischer, S.; Koeberle, S.C.; Laufer, S.A. p38 alpha mitogen-activated protein kinase inhibitors, a patent review
(2005–2011). Expert Opin. Ther. Pat. 2011, 21, 1843–1866. [CrossRef] [PubMed]
11. Koch, P.; Ansideri, F. 2-Alkylsufanyl-4(5)-aryl-5(4)-heteroarylimidazoles: An Overview on Synthetic
Strategies and Biological Activity. Arch. Pharm. 2017, 350, e1700258. [CrossRef] [PubMed]
12. Laufer, S.A.; Hauser, D.R.J.; Liedtke, A.J. Regiospecific and highly flexible synthesis of 1,4,5-trisubstituted
2-sulfanylimidazoles from structurally diverse ethanone precursors. Synthesis 2008, 253–266. [CrossRef]
13. Laufer, S.A.; Wagner, G.K.; Kotschenreuther, D.A.; Albrecht, W. Novel substituted pyridinyl imidazoles as
potent anticytokine agents with low activity against hepatic cytochrome P450 enzymes. J. Med. Chem. 2003
,
46, 3230–3244. [CrossRef] [PubMed]
14. Ziegler, K.; Hauser, D.R.J.; Unger, A.; Albrecht, W.; Laufer, S.A. 2-Acylaminopyridin-4-ylimidazoles as p38
MAP Kinase Inhibitors: Design, Synthesis, and Biological and Metabolic Evaluations. ChemMedChem 2009, 4,
1939–1948. [CrossRef] [PubMed]
15. Laufer, S.A.; Hauser, D.R.; Domeyer, D.M.; Kinkel, K.; Liedtke, A.J. Design, synthesis, and biological
evaluation of novel Tri- and tetrasubstituted imidazoles as highly potent and specific ATP-mimetic inhibitors
of p38 MAP kinase: Focus on optimized interactions with the enzyme’s surface-exposed front region.
J. Med. Chem. 2008, 51, 4122–4149. [CrossRef] [PubMed]
16. Griswold, D.E.; Marshall, P.J.; Webb, E.F.; Godfrey, R.; Newton, J.; Dimartino, M.J.; Sarau, H.M.;
Gleason, J.G.; Poste, G.; Hanna, N. Sk+F-86002—A Structurally Novel Antiinflammatory Agent
That Inhibits Lipoxygenase-Mediated and Cyclooxygenase-Mediated Metabolism of Arachidonic-Acid.
Biochem. Pharmacol. 1987, 36, 3463–3470. [CrossRef]
17. Goettert, M.; Graeser, R.; Laufer, S.A. Optimization of a nonradioactive immunosorbent assay for p38alpha
mitogen-activated protein kinase activity. Anal. Biochem. 2010, 406, 233–234. [CrossRef] [PubMed]
18. Selig, R.; Schattel, V.; Goettert, M.; Schollmeyer, D.; Albrecht, W.; Laufer, S. Conformational effects on potency
of thioimidazoles and dihydrothiazolines. MedChemComm 2011, 2, 261–269. [CrossRef]
19. Koch, P.; Jahns, H.; Schattel, V.; Goettert, M.; Laufer, S. Pyridinylquinoxalines and pyridinylpyridopyrazines
as lead compounds for novel p38 alpha mitogen-activated protein kinase inhibitors. J. Med. Chem. 2010, 53,
1128–1137. [CrossRef] [PubMed]
20. Wagner, G.K.; Kotschenreuther, D.; Zimmermann, W.; Laufer, S.A. Identification of regioisomers in a series
of N-substituted pyridin-4-yl imidazole derivatives by regiospecific synthesis, GC/MS, and H-1 NMR.
J. Org. Chem. 2003, 68, 4527–4530. [CrossRef] [PubMed]
21. Laufer, S.; Kotschenreuther, D.; Merckle, P.; Tollmann, K.; Striegel, H.G. 2-thio-Substituted Imidazole
Derivatives and the Use Thereof in the Pharmaceutical Industry. U.S. Patents 10/467,064, 7 August 2007.
22. Laufer, S.; Wagner, G.; Kotschenreuther, D. Ones, thiones, and N-oxides: An exercise in imidazole chemistry.
Angew. Chem. Int. Ed. 2002, 41, 2290–2293. [CrossRef]
23. Laufer, S.; Hauser, D.; Stegmiller, T.; Bracht, C.; Ruff, K.; Schattel, V.; Albrecht, W.; Koch, P. Tri- and
tetrasubstituted imidazoles as p38 alpha mitogen-activated protein kinase inhibitors. Bioorg. Med. Chem. Lett.
2010, 20, 6671–6675. [CrossRef] [PubMed]
24. Muth, F.; El-Gokha, A.; Ansideri, F.; Eitel, M.; Döring, E.; Sievers-Engler, A.; Lange, A.; Boeckler, F.M.;
Lämmerhofer, M.; Koch, P.; et al. Tri- and Tetrasubstituted Pyridinylimidazoles as Covalent Inhibitors of
c-Jun N-Terminal Kinase. J. Med. Chem. 2017, 60, 594–607. [CrossRef] [PubMed]
25. Muth, F.; Günther, M.; Bauer, S.M.; Döring, E.; Fischer, S.; Maier, J.; Drückes, P.; Köppler, J.; Trappe, J.;
Rothbauer, U.; et al. Tetra-Substituted Pyridinylimidazoles As Dual Inhibitors of p38 alpha Mitogen-Activated
Protein Kinase and c-Jun N-Terminal Kinase 3 for Potential Treatment of Neurodegenerative Diseases.
J. Med. Chem. 2015, 58, 443–456. [CrossRef] [PubMed]
26. Graham, S.L.; Scholz, T.H. A New Mode of Reactivity of N-Methoxy-N-Methylamides with Strongly Basic
Reagents. Tetrahedron Lett. 1990, 31, 6269–6272. [CrossRef]
27. Labeeuw, O.; Phansavath, P.; Genet, J.P. Synthesis of modified Weinreb amides: N-tert-butoxy-N-methylamides
as effective acylating agents. Tetrahedron Lett. 2004, 45, 7107–7110. [CrossRef]

Molecules 2018, 23, 221
19 of 19
28. Reeves, J.T.; Tan, Z.L.; Reeves, D.C.; Song, J.H.J.; Han, Z.X.S.; Xu, Y.B.; Tang, W.J.; Yang, B.S.; Razavi, H.;
Harcken, C.; et al. Development of an Enantioselective Hydrogenation Route to (S)-1-(2-(Methylsulfonyl)
pyridin-4-yl)propan-1-amine. Org. Process Res. Dev. 2014, 18, 904–911. [CrossRef]
29. Lantos, I.; Gombatz, K.; Mcguire, M.; Pridgen, L.; Remich, J.; Shilcrat, S. Synthetic and Mechanistic Studies
on the Preparation of Pyridyl-Substituted Imidazothiazoles. J. Org. Chem. 1988, 53, 4223–4227. [CrossRef]
30. Laufer, S.A.; Liedtke, A.J. A concise and optimized four-step approach toward 2-(aryl-)alkylsulfanyl-,
4(5)-aryl-, 5(4)-heteroaryl-substituted imidazoles using alkyl- or arylalkyl thiocyanates. Tetrahedron Lett.
2006, 47, 7199–7203. [CrossRef]
31. Li, Z.Y.; Ma, H.Z.; Han, C.; Xi, H.T.; Meng, Q.; Chen, X.; Sun, X.Q. Synthesis of Isothiocyanates by Reaction
of Amines with Phenyl Chlorothionoformate via One-Pot or Two-Step Process. Synthesis 2013, 45, 1667–1674.
[CrossRef]
32. Sun, N.; Li, B.; Shao, J.P.; Mo, W.M.; Hu, B.X.; Shen, Z.L.; Hu, X.Q. A general and facile one-pot process of
isothiocyanates from amines under aqueous conditions. Beilstein J. Org. Chem. 2012, 8, 61–70. [CrossRef]
[PubMed]
33. Wong, R.; Dolman, S.J. Isothiocyanates from tosyl chloride mediated decomposition of in situ generated
dithiocarbamic acid salts. J. Org. Chem. 2007, 72, 3969–3971. [CrossRef] [PubMed]
Sample Availability: Samples of the compounds 38 and 39 are available from the authors.
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2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).