Chromo-fluorogenic detection of nerve-agent mimics using triggered cyclization reactions in push-pull dyes

Article abstract of DOI:10.1002/asia.201000058

A family of azo and stilbene derivatives (1-9) are synthesized, and their chromo-fluorogenic behavior in the presence of nerve-agent simulants, diethylchlorophosphate (DCP), diisopropylfluorophosphate (DFP), and diethylcyanophosphate (DCNP) in acetonitrile and mixed solution of water/acetonitrile (3:1 v/v) buffered at pH 5.6 with MES, is investigated. The prepared compounds contain 2-(2-N,N-dimethylaminophenyl) ethanol or 2-[(2-N,N-dimethylamino)phenoxy]ethanol reactive groups, which are part of the conjugated π-system of the dyes and are able to give acylation reactions with phosphonate substrates followed by a rapid intramolecular N-alkylation. The nerve-agent mimic-triggered cyclization reaction transforms a dimethylamino group into a quaternary ammonium, inducing a change of the electronic properties of the delocalized systems that results in a hypsochromic shift of the absorption band of the dyes. Similar reactivity studies are also carried out with other "non-toxic" organophosphorus compounds, but no changes in the UV/Vis spectra were observed. The emission behaviour of the reagents in acetonitrile and water-acetonitrile 3:1 v/v mixtures is also studied in the presence of nerve-agent simulants and other organophosphorous derivatives. The reactivity between 1-9 and DCP, DCNP, or DFP in buffered water-acetonitrile 3:1 v/v solutions under pseudo first-order kinetic conditions, using an excess of the corresponding simulant, are studied in order to determine the rate constants (k) and the half-life times (t_1/2=ln2/k) for the reaction. The detection limits in water/acetonitrile 3:1 v/v are also determined for 1-9 and DCP, DCNP, and DFP. Finally, the chromogenic detection of nerve agent simulants both in solution and in gas phase are tested using silica gel containing adsorbed compounds 1, 2, 3, 4, or 5 with fine results.

Full text of DOI:10.1002/asia.201000058

DOI: 10.1002/asia.201000058
Chromo-Fluorogenic Detection of Nerve-Agent Mimics Using Triggered
Cyclization Reactions in Push–Pull Dyes
Ana M. Costero,*[a, b] Margarita Parra,[a, b] Salvador Gil,[a, b] Raffll Gotor,[a, b, d]
Pedro M. E. Mancini,[a, b] Ramón Martínez-MµÇez,*[a, c, d] FØlix Sancenón,[a, c, d] and
Santiago Royo[c, d]
Abstract: A family of azo and stilbene
derivatives (1–9) are synthesized, and
their chromo-fluorogenic behavior in
the presence of nerve-agent simulants,
diethylchlorophosphate (DCP), diiso-
propylfluorophosphate (DFP), and di-
ethylcyanophosphate (DCNP) in aceto-
nitrile and mixed solution of water/ace-
tonitrile (3:1 v/v) buffered at pH 5.6
with MES, is investigated. The pre-
pared compounds contain 2-(2-N,N-di-
methylaminophenyl)ethanol or 2-[(2-
N,N-dimethylamino)phenoxy]ethanol
reactive groups, which are part of the
conjugated p-system of the dyes and
are able to give acylation reactions
with phosphonate substrates followed
by a rapid intramolecular N-alkylation.
The nerve-agent mimic-triggered cycli-
zation reaction transforms a dimethyla-
mino group into a quaternary ammoni-
um, inducing a change of the electronic
properties of the delocalized systems
that results in a hypsochromic shift of
the absorption band of the dyes. Simi-
lar reactivity studies are also carried
out with other “non-toxic” organophos-
phorus compounds, but no changes in
the UV/Vis spectra were observed. The
emission behaviour of the reagents in
acetonitrile and water–acetonitrile 3:1
v/v mixtures is also studied in the pres-
ence of nerve-agent simulants and
other organophosphorous derivatives.
The reactivity between 1–9 and DCP,
DCNP, or DFP in buffered water–ace-
tonitrile 3:1 v/v solutions under pseudo
first-order kinetic conditions, using an
excess of the corresponding simulant,
are studied in order to determine the
rate constants (k) and the half-life
times (t1/2 =ln2/k) for the reaction. The
detection limits in water/acetonitrile
3:1 v/v are also determined for 1–9 and
DCP, DCNP, and DFP. Finally, the
chromogenic detection of nerve agent
simulants both in solution and in gas
phase are tested using silica gel con-
taining adsorbed compounds 1, 2, 3, 4,
or 5 with fine results.
Keywords: acylation · cyclization ·
nerve agents · phosphorus · recep-
tors
[a] Prof. Dr. A. M. Costero, Dr. M. Parra, Dr. S. Gil, R. Gotor,
Introduction
Prof. Dr. P. M. E. Mancini, Prof. Dr. R. Martꢀnez-MꢁÇez,
Dr. F. Sancenꢂn
Instituto de Reconocimiento Molecular y Desarrollo Tecnolꢂgico
(IDM)
Centro mixto Universidad Politꢃcnica de Valencia - Universidad de
Valencia
Valencia (Spain)
Fax : (+34)963543831
E-mail: Ana.Costero@uv.es
The current increase in international concern in relation to
criminal terrorist attacks using chemical warfare (CW)
agents has brought about increasing interest in the develop-
ment of reliable detection techniques of these lethal chemi-
cals. A typical classification of chemical warfare agents in-
cludes nerve agents, asphyxiant/blood agents, vesicant
agents, choking/pulmonary agents, lachrymatory agents, in-
capacitating agents, and cytotoxic proteins.[1,2] Among them,
nerve agents are especially dangerous species, and poisoning
may occur through inhalation or consumption of contami-
nated liquids or foods. The effects of nerve agents are
caused by their ability to inhibit the action of acetylcholines-
terase.[3]
[b] Prof. Dr. A. M. Costero, Dr. M. Parra, Dr. S. Gil, R. Gotor,
Prof. Dr. P. M. E. Mancini
Departamento de Quꢀmica Orgꢁnica
Facultad de Quꢀmicas, Universidad de Valencia
Doctor Moliner 50, 46100 Burjassot, Valencia (Spain)
[c] Prof. Dr. R. Martꢀnez-MꢁÇez, Dr. F. Sancenꢂn, S. Royo
Departamento de Quꢀmica
Universidad Politꢃcnica de Valencia
Camino de Vera s/n, 46022 Valencia (Spain)
Chemically, nerve gases are highly toxic phosphoric acid
esters, which are structurally related to the larger family of
organophosphate compounds. Tabun (GA), sarin (GB), and
[d] R. Gotor, Prof. Dr. R. Martꢀnez-MꢁÇez, Dr. F. Sancenꢂn, S. Royo
CIBER de Bioingenierꢀa, Biomateriales y Nanomedicina (CIBER-
BBN)
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1573

FULL PAPERS
soman (GD) were developed during the Second World War,
whereas further research resulted in the discovery of V-
nerve agents. The ease of production and extreme toxicity
of organophosphorus-containing nerve agents underlines the
need to detect these chemicals. In fact, an intense research
effort has been directed to develop sensitive and selective
systems for the detection of these compounds. Current
methods for nerve-agents monitoring are mainly based on
the use of biosensors,[4] ion-mobility spectroscopy (IMS),[5]
electrochemistry,[6] microcantilevers,[7] photonic crystals,[8]
and optical-fiber arrays.[9] As an alternative to these instru-
mental methods, the development of easy-to-use fluorogenic
and chromogenic reagents has been gaining interest in
recent years.[10] For instance, paradigms involving PET-based
fluorescent probes,[11] assays using oximate-containing deriv-
atives[12] molecular imprinting polymers,[13] nanoparticles,[14]
carbon nanotubes,[15] porous silicon,[16] or displacement-like
procedures[17] have been recently reported. Most of these
paradigms rely on the changes in fluorescence properties,
whereas few examples are related to color modulations. For
instance, reported chromogenic examples include the
sodium perborate-mediated oxidation of the organophos-
phorus agent to a peracid, which was able to oxidize certain
aromatic amines to give colored derivatives.[18] Also, oxi-
mates and hydrazones have been used for the development
of chromogenic reagents for chemical warfare agents. When
these moieties were implemented into an organic scaffold
with absorption bands in the visible region, the reaction
with the electrophilic phosphorus centers of the simulants,
induced significant color changes.[12a,b,d] Finally, gold nano-
particles as signalling subunits coupled with an enzymatic
assay (based on the inhibition of the enzymatic activity of
the acetylcholinesterase) have also been reported.[14a,d]
Despite these interesting examples, the development of
selective chromogenic probes for the detection of these
deadly chemical species in vapors or in aqueous environ-
ments is still rare. Following our interest in the development
of new chromo-fluorogenic chemosensors[19,20] for target
chemical species, we report herein the design of colorimetric
probes for nerve-agent simulants for their detection in solu-
tion or in gas phase. The sensing scheme uses the reactivity
of the 2-(2-N,N-dimethylaminophenyl)ethanol or 2-[(2-N,N-
dimethylamino)phenoxy]ethanol fragments with phospho-
nate substrates and its coupling with a colorimetric event
following a chemodosimeter paradigm. We have already re-
ported a preliminary communication of this study recent-
ly.[21]
mediate II. Furthermore, it is known that II will suffer a
rapid intramolecular N-alkylation to afford III, a quaternary
ammonium salt. Following the scheme of the above-men-
tioned paradigm, we envisaged that the use of fragment I as
a donor group and its coupling with an acceptor (A) moiety
in certain chromophores could be a suitable procedure to
develop colorimetric probes for nerve-agent detection (see
Scheme 1). Thus, the overall conversion of the correspond-
ing tertiary amine IV to the quaternary ammonium V upon
reaction with certain organophosphorus (OP) substrates will
induce a change on the electronic donor properties of the
nitrogen atom resulting in a decrease of the push–pull char-
acter of the dye and color modulation. Among the different
possibilities, we have used here as reactive groups 2-2-(N,N-
dimethylamino)phenyl)ethanol or 2-[2-(N,N-dimethylami-
no)phenoxy]ethanol.
Scheme 1. Colorimetric sensing paradigm. The 2-(2-dimethylaminophen-
yl)ethanol group suffers cyclization reaction in the presence of nerve-
agent simulants. It acts as a donor system in push–pull chromophores.
Upon reaction with the nerve-agent simulants, the donor ability of the
amine group is reduced, resulting in a weakening of the push–pull charac-
ter of the dye and color modulation.
Even though a similar reaction (acylation and intramolec-
ular N-alkylation) had been previously used in fluorogenic
nerve-agent sensing, this paradigm has been barely used for
the chromogenic signaling of nerve agents.[21]
Synthesis, Characterization, and Spectroscopic Properties
Chromoreagent 1 (see Scheme 2) was prepared by the reac-
tion of 2-(2-dimethylaminophenyl)ethanol (11) with the di-
azonium salt of 4-nitroaniline using the well-documented
procedures for the preparation of azo dyes.[22] The starting
compound 11 was synthesized following a previously de-
scribed method.[23] First, 2-nitrotoluene was transformed
into 2-(2-nitrophenyl)ethanol. Then, a reductive amination
in the presence of formaldehyde gave rise to 2-(2-dimethyla-
minophenyl)ethanol, (11).[24] Chromoreagents 2 and 3 were
prepared by the reaction of ethyl 2-(2-dimethylaminophe-
noxy)acetate (13) with the diazonium salts of 4-nitroaniline
(for 2) and 4-aminobenzonitrile (for 3). The starting com-
Results and Discussion
Design of the Colorimetric Probes
The colorimetric recognition and signalling of the nerve-
agent mimics is based on the use of suitable properties of
fragment I. This moiety contains a nucleophile, the hydroxyl
functional group, which has been reported to give acylation
reactions with phosphonate substrates to form the inter-
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Chromo-Fluorogenic Detection of Nerve-Agent Mimics
ceptor character at the other
end of the molecular frame-
work. 1–3 shows adsorption
bands in the visible region,
whereas the stilbene derivatives
4–9 absorb in the 260–380 nm
range. The influence of the dif-
ferent electronic properties of
the stilbene family (derivatives
4–9) on the absorption band of
the chromophores is evident
from the data in Table 1, and it
agrees with the expectation that
changes in the acceptor charac-
ter of the appended groups
(pyridinium>NO2 >CN~an-
thraquinone>OCH3) in the p-
system will result in a hypso-
chromic shift of the absorption
band (labs 5>4>6=7>8/9).
This effect is also observed for
compounds 2 and 3; the stronger the acceptor character
(NO2 >CN), the larger the wavelength of the absorption
band.
Scheme 2. Chromoreagents 1–10.
pound 13 was prepared from 2-nitrophenol, which was first
transformed into 2-(N,N-dimethylamino)phenol by reaction
with formaldehyde, followed by catalytic reduction with hy-
drogen.
The stilbene derivatives 4–9 were synthesized by using a
Wittig reaction from 2-(4-formyl-(2-dimethylaminophenyl)-
ethanol (16) and the corresponding phosphonium salts, or
by coupling with 1,4-dimethylpyridinium iodide for chro-
moreagent 5. Compound 16 was not commercially available,
and its synthesis was performed from 4-nitro-3-methylben-
zoic acid (17) by two alternative pathways (see Scheme 3).
In the first route, 4-nitro-3-methylbenzoic acid was convert-
ed into methyl ester (18), which was condensed with formal-
dehyde to afford compound 19. Reductive amination of 19
transforms the nitro group into the corresponding dimethy-
lamino moiety. The last step was the transformation of the
methoxycarbonyl group into the formyl group. This last re-
action cannot be carried out in one single step. It was ach-
ieved by the reduction of 20 with LiAlH4 and further con-
trolled oxidation to the aldehyde 16.
The second pathway followed for the synthesis of 16 start-
ed with the conversion of 17 into the corresponding methoxy-
methylamide 22. The transformation of 22 into 24 was ach-
ieved following the same reaction route for the conversion
of 18 to 20. Finally, 24 was reduced with DIBAL to afford
16. Even though the first procedure involves one more step,
the overall yields were similar for both synthetic routes. Fi-
nally, compound 10 was prepared from 5-methoxy-2-nitroto-
luene following the same procedure described for the syn-
thesis of 11.
Reactivity with Nerve-Agent Simulants
First, the reactivity of the prepared chromoreagents was
tested with diethylchlorophosphate (DCP), diisopropylfluor-
ophosphate (DFP), and diethylcyanophosphate (DCNP) in
acetonitrile (see Scheme 4). Arising from the high toxicity
of nerve agents, sarin, soman, and tabun, the related com-
pounds DFP, DCP, and DCNP have been typically used as
models for the design of indicators and sensing systems, as
they have similar reactivity but lack the efficacy of typical
nerve agents. Preliminary studies were carried out with com-
pound 1 (1ꢅ10À5 moldmÀ3), which displays an intense ab-
sorption band at 410 nm in acetonitrile, typical of azo-dye
derivatives. The addition of DCP, DFP, or DCNP to acetoni-
trile solutions of 1 resulted in a clear hypsochromic shift of
the absorption band and color modulation from yellow to
colorless. The observed results are consistent with the intra-
molecular cyclization process shown in Scheme 1 and the re-
duction of the donor character of the N,N-dimethylamino
moiety in the chromophore. In this preliminary step, it was
also confirmed that 1 was not able to react with other orga-
nophosphorus derivatives, such as OP1–OP4 (see
Scheme 4). A similar reactivity of 1 with DCP, DFP, and
DCNP in mixed water–acetonitrile solutions was also found.
Motivated by these favorable features observed for deriv-
ative 1, similar studies of reactivity were carried out with de-
rivatives 2–9 (1ꢅ10À5 moldmÀ3) in water–acetonitrile (3:1
v/v) solutions buffered at pH 5.6 with MES (1ꢅ
10À1 moldmÀ3). Mixtures containing a larger percentage of
water could not be used in this work because of the poor
solubility of some of the reagents. Furthermore, derivative
10 was prepared and used as the model compound. Com-
1–3 are azo dyes, 4–7 can be classified as donor–acceptor
stilbenes, whereas 8 and 9 are described as donor–donor stil-
benes. The spectroscopic characteristics of all compounds
are shown in Table 1. 1–9 display a relatively intense absorp-
tion band in the 300–400 nm range. Based on their electron-
ic properties, compounds 1–9 are chromophores, containing
a donor dimethyl amino moiety and a group of variable ac-
Chem. Asian J. 2010, 5, 1573 – 1585
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A. M. Costero, R. Martinez-MꢁÇez et al.
FULL PAPERS
pounds 8 and 9 were separated
in the synthetic process and
were perfectly identified by
using 1H NMR, however, be-
cause of their photo-instability,
after a short time at room tem-
perature, both samples (in solid
state or solution) became iden-
tical; that is, a mixture of both
isomers.[25] Therefore, studies in
the presence of the reagents for
8 and 9 were carried out in sol-
utions containing a mixture of
both compounds 8/9.
As observed for compound 1,
the reagents 2–9 also show hyp-
sochromic shifts of the absorp-
tion band upon addition of an
excess of the nerve-agent simu-
lants DCP, DFP, and DCNP in
mixed water–acetonitrile (3:1 v/
v) solutions buffered at pH 5.6
with MES. For 1–5, a bleaching
of the yellow or pale yellow sol-
utions could be observed with
the naked eye. Figure 1 shows a
photograph with the color
changes observed for
3 (1ꢅ
10À5 moldmÀ3) in water/acetoni-
trile (3:1 v/v, MES 1ꢅ
10À1 moldmÀ3) upon addition of
an excess of nerve-agent
mimics DCP, DFP, and DCNP.
Moreover, Figure 2 shows the
UV/Vis spectrum of chromore-
agent 3 (1ꢅ10À5 moldmÀ3) in
Scheme 3. a) HCHO, PhOÀ, DMSO, 60–708C, 1 h; b) H2, Pd-C, 37% HCHO; c) 4-nitroaniline, NaNO2, H+;
d) HCHO, H2, Pd-C; e) BrCH2COOCH2CH3, Cs2CO3, ACN; f) 4-aminobenzonitrile, NaNO2, H+; g) MeOH/
H+, 5 h; h) LiAlH4, Et2O, 30 min; i) MnO2, Et2O, 2.5 h; j) CBr4, Et3N, CH3NH2OCH3Cl, Ph3P, DCM, 2.5 h;
k) DIBAL, THF, 45 min.
water/acetonitrile (3:1 v/v, MES
1ꢅ10À1 moldmÀ3) after the ad-
dition of DCP.
Data in Table 1 shows that
the hypsochromic shift of the
Table 1. UV absorptions of pure ligands 1–10 (1ꢅ10À5 moldmÀ3
) in
water/acetonitrile (3:1 v/v, MES 1ꢅ10À1 moldmÀ3) and in the presence of
DCP.
absorption band in the presence of nerve-agent simulants
for ligands 1–3 (Dl of 125, 114, and 98 nm) was larger than
that for other prepared reagents (Dl of 19, 53, 44, 5, and
<5 nm for 4, 5, 6, 7, and 8/9, respectively). In general, the
Receptor
Receptor+DCP
abs
abs
l
[nm]
loge [mÀ1 cmÀ1
]
l
[nm]
loge [mÀ1 cmÀ1
]
max
max
1[a]
407
428
412
366
378
309
310
268
267
3.9
4.1
4.1
4.3
4.2
4.3
4.1
4.3
4.0
282
314
314
347
325
265
305
266
4.0
4.4
4.3
4.5
4.5
4.3
4.2
4.5
–
2[c]
3[b]
4[c]
5[c]
6[b]
7[c]
8/9[a,d]
10[a]
[e]
–
[a] 10 equivalents of DCP were used. [b] 200 equivalents of DCP were
used. [c] 700 equivalents of DCP were used. [d] Arising from the photo-
conversion between 8 and 9, the studies were carried out in mixtures of
both compounds 8/9. [e] Very low shifts of the absorption band (lower
than 3 nm) were observed in the presence of the DCP simulant.
Scheme 4. Chemical structure of different organophosphorus derivatives.
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Chromo-Fluorogenic Detection of Nerve-Agent Mimics
Furthermore, to assess the
mechanism involved in the ob-
served chromogenic response,
the corresponding ammonium
salts (V in Scheme 1) for some
compounds were prepared fol-
Figure 1. Color changes observed for 1 (left) and 3 (right) (1ꢅ10À5 moldmÀ3) in water/acetonitrile (3:1 v/v,
MES 1ꢅ10À1 moldmÀ3) upon addition of nerve-agent mimics DCP, DFP, and DCNP. In each photograph from
left to right; reactand, reactand +DCP, reactand +DFP, and reactand +DCNP.
lowing
a
different synthetic
route, which involves the reac-
tion of the corresponding chro-
moreagent with p-toluenesul-
fonyl chloride in the presence
of sodium carbonate in acetonitrile. This gave the corre-
sponding tosylated derivative, which suffered a spontaneous
cyclization that resulted in the formation of the correspond-
ing cyclic compounds 25 and 26 when using 1 and 4, respec-
tively (Scheme 5). This transformation was easily detected
Figure 2. Absorption spectra of chromoreagent 3 (1ꢅ10À5 moldmÀ3) in
water/acetonitrile (3:1 v/v, MES 1ꢅ10À1 moldmÀ3) and 3 after the addi-
tion of an excess of DCP.
Scheme 5. Chemical structure of cyclized derivatives 25 and 26.
1
hypsochromic shifts upon addition of the nerve-agent
mimics are in agreement with the expectation that transfor-
mation of the donor amine into the corresponding quaterna-
ry ammonium in push–pull systems will produce a blue-shift
of the absorption band because of a modulation of the
dipole moments of the ground and excited states, and there-
fore, a change in the relative energy of HOMO and LUMO.
In general, the trend observed in the hypsochromic shift
when changing from amine to ammonium for the stilbene
derivatives in the presence of simulants agrees with the ac-
ceptor strength. This is for instance clear when comparing
the Dl of 53 nm for 4 (having a strong electron-acceptor
NO2 group) with the Dl of <5 nm for 8/9, which includes a
donor-OCH3 moiety. It was also observed that for a certain
dye, the absorption spectra after reaction with the three sim-
ulants DCP, DFP, and DCNP, were very similar, corroborat-
ing the fact that the same reaction takes place in all cases.
in the H NMR spectra of the final products. For example,
in the case of 25, one triplet centered at 4.36 ppm, indicative
of a methylene subunit located near the quaternary ammo-
nium, (Figure 3) is shown. Also, a significant long-range
1H–13C coupling between this signal and the 13C signals cor-
responding to the methyls (54 ppm) and to the aromatic
carbon (149 ppm) attached to the N,N-dimethylanilinium
fragment, points toward the unambiguous formation of the
cyclized product. Moreover, UV/Vis data confirmed that the
The apparent anomalous shift observed for 7 and DCNP
abs
max
(l =265 nm) may be caused by the formation of the cya-
nohydrin derivatives as consequence of the reaction of the
evolved cyanide with the carbonyl groups in the ligand.
Similar reactivity studies were also carried out with 2–9
and other “nontoxic” organophosphorus compounds (see
Scheme 4, OP1–OP4), but no changes in the UV/Vis spectra
were observed, indicating that the reactivity with the nerve-
agent mimics is selective.
Figure 3. 1H NMR (aliphatic zone) of ligand 1 and its corresponding
cyclic compound 25.
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A. M. Costero, R. Martinez-MꢁÇez et al.
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products obtained by tosylation displayed the same spectro-
scopic characteristics as the products obtained from the re-
action of the corresponding chromoreagent with the nerve-
agent simulants.
The UV/Vis spectrum of compounds 1–9 are character-
ized by the presence of intense absorption bands centered in
the 300–430 nm range. The emission behavior of reagents 1–
9 in acetonitrile and water–acetonitrile (3:1 v/v) mixtures
(1ꢅ10À5 moldmÀ3) was also studied (see Table 2 for data in
the presence of nerve-agent simulants. In contrast, the addi-
tion of DCP, DFP, and DCNP to 8/9 resulted in an enhance-
ment of the emission. This result is displayed in Figure 4,
which shows the emission spectra (lexc =280 nm) of 8/9 and
8/9 in the presence of 4 equivalents of DCP in water/aceto-
nitrile (3:1 v/v); a remarkable 3.5-fold enhancement of the
emission intensity was observed.
Table 2. Fluorescence properties of reagents 4–10 (1ꢅ10À5 moldmÀ3) in
acetonitrile and after the reaction with 100 equiv of DCP.
Reagent
Reagent+DCP
Enhancement
Ireagent+DCP/Ireagent
abs
em
max
em
l
[nm]
l
[nm]
l [nm]
max
max
4
5
6
7
381
404
270
317
304
580
627
570
453
430
576
415
590
509
390
1.25
5.40
0.68
3.33
0.03
8/9[a]
[a] Arising from the photoconversion between 8 and 9, the studies were
carried out in mixtures of both compounds 8/9.
Figure 4. Emission spectra (lexc =280 nm) of 8/9 and 8/9 (10À5 moldmÀ3
)
acetonitrile). Chromogenic reagents 1–3 are poorly fluores-
cent, and no remarkable emission modulations were found
in the presence of nerve-gas simulants. Therefore, the stud-
ies detailed below were only performed with the stilbene-de-
rivatives 4–9. The photophysics of donor–acceptor stilbenes
(similar to 4–7) and donor–donor stilbenes (similar to 8 and
9) have been widely studied in the literature. In general, the
spectroscopic behavior of such dyes is often determined by
an intramolecular charge-transfer process upon optical exci-
tation and the presence of different emitting states involving
planar geometry and double-bond twist- and single-bond
twist states.[26] As expected for this class of dye compounds,
4–9 show characteristics broad and structureless emission
bands with a large Stokes shift. The addition of OP1–OP4
to 4–9 resulted in negligible changes in the emission-intensi-
ty profiles of the reagents. In contrast, the addition of the
nerve-agent simulants DCP, DFP, and DCNP, induced
changes in the fluorescence behavior (see Table 2 for data
with DCP). The changes in fluorescence intensity upon reac-
tion with DCP, comprise fluorescence enhancement (for 4,
5, and 7) and fluorescence quenching (for 6 and 8/9). The
fluorescence-quenching factors are relatively low for 6 and
large for 8/9, whereas fluorescence-enhancement factors
range from small (for 4) to medium (for 5 and 7). In all
cases, the presence of the simulant DCP induced the disap-
pearance of the fluorescence band of the reactand, and the
growth of a new emission band that is either red- or blue-
shifted depending on the receptor used.
in the presence of DCP (4 eq.) in water/acetonitrile (3:1 v/v, MES 1ꢅ
10À1 moldmÀ3).
The design using the formation of azo and stilbene dyes,
shown in Scheme 2, in relation to the sensing response ob-
served for compounds 1–9 is evident when one compares
the performance of these derivatives with the model com-
pound 10, for which no remarkable changes in the UV/Vis
(Dl of <5 nm) nor in the emission spectra were observed
upon the addition of the nerve-agent simulants.
To ascertain that the chromogenic and fluorogenic re-
sponse observed was caused by a nucleophilic addition–in-
tramolecular cyclization mechanism and not by a protona-
tion of the nitrogen atom of the N,N-dimethylaniline
moiety, control experiments were carried out. Thus, the ad-
dition of HCl at typical simulant concentrations to water–
acetonitrile (3:1 v/v) solutions (MES, pH 5.6) of reagents 1–
9 induced negligible changes in the UV/Vis and fluorescence
profiles of the products. This experiment disables the possi-
bility that the response observed was solely caused by the
partial hydrolysis of DCP.
Kinetic and Detection-Limit Studies
To achieve a better understanding of the reaction, the reac-
tivity between 1–9 and DCP, DCNP, or DFP in buffered
water–acetonitrile (3:1 v/v) solutions under pseudo first-
order kinetic conditions, using an excess of the correspond-
ing simulant, was studied. By monitoring the changes in the
Similar emission studies were carried out for receptors 4–
9 (1ꢅ10À5 moldmÀ3) in water–acetonitrile (3:1 v/v, MES 1ꢅ
10À1 moldmÀ3) solutions. In this medium, 4, 5, and 7 were
not fluorescent, whereas 6 and mixtures of 8/9 were still
emissive. The addition of OP1–OP4 on 6 or 8/9 resulted in
negligible changes in the fluorescence. Furthermore, the
fluorescence behavior of 6 showed no significant changes in
absorbance intensity and by plotting lnACHTNUTGRNEUNG[(A0-A)/A] versus
time (in which, A0 is the final absorbance and A is the ab-
sorbance at a given time), allowed us the determination of
the rate constants (k) and the half-life times (t1/2 =ln2/k) for
the reaction of the nerve-gas simulants with reagents 1–9.
1578
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ꢄ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1573 – 1585

Chromo-Fluorogenic Detection of Nerve-Agent Mimics
Figure 5. Absorption changes at 410 nm upon reaction of 1 with DCP (left) and at 360 nm and upon reaction of 4 with DFP (right). The inset in both
cases shows the first-order kinetic plot.
Figure 5 shows the absorbance changes at the UV/Vis band
maximum for dyes 1 and 4 with DCP and DFP, respectively.
In all cases, the reaction is relatively quick, and complete
UV/Vis changes are observed after a few seconds. It has
been suggested, in fluorogenic systems using similar cycliza-
tion paradigms, that the reaction of the alcohol with the
phosphate derivatives to form the phosphate-ester inter-
mediate is slow relative to the intramolecular cyclization.
However, for a given nerve-agent mimic, the rate constants
are quite different depending on the reactand used, suggest-
ing that cyclization could also possibly play some role in the
overall rate constant of the reaction process.
Table 3 also includes the detection limits observed for the
detection of these chemicals determined from changes in
the UV/Vis spectra (for 1–6) and from changes in the emis-
sion (for 8/9) in aqueous water–acetonitrile (3:1 v/v) mix-
tures. The lower detection limits (DLs) have been observed
for the chromogenic reactand 1 (DLs of 1ꢅ10À4 moldmÀ3
for DCP and DCNP) and especially for the fluorogenic re-
actand 8/9 (DL of 1ꢅ10À5 moldmÀ3 for DCP).
Sensing in Mixed Aqueous Environments and in Gas Phase
Motivated by the favorable chromogenic and fluorogenic
sensing features shown by the compounds studied, we took
a step forward towards the potential use of these ligands for
in-situ sensing and rapid-screening applications. With this
idea in mind, we simply adsorbed compound 1, 2, 3, 4, or 5
on silica gel (resulting in modified yellow/orange solids con-
taining the probes), and tested their chromogenic ability to
nerve-agent simulants both in solution and in gas phase.
Thus, in the first test, the colored silica support containing
the probe was prepared by adsorption of
a
(1ꢅ
10À5 moldmÀ3) solution of the corresponding probe in water/
acetonitrile (3:1 v/v) buffered at pH 5.6 (MES 1ꢅ
10À1 moldmÀ3). These samples were put in contact with an
acetonitrile solution containing DCP (CDCP =1.0ꢅ
10À3 moldmÀ3), and a very rapid bleaching was observed
over a few seconds. An additional assay was related to the
possible detection of vapors of the simulants. For this pur-
pose, an ambient vapor containing a low amount of DCP
(5 ppm) was prepared. At the same time, the orange/yellow-
colored silica was placed on a column, and the air contain-
ing the simulant was passed through. As the silica comes in
contact with the air sample, it becomes colorless (see
Table 3. Detection limits and kinetic data.
Chromoreagent
1
2
3
4
Simulant
DFP
1.0
DCP
0.1
DCNP
0.1
DFP
10
DCP
4.5
DCNP
8.1
DFP
7
DCP
1.8
DCNP
4.1
DFP
10
DCP
7.0
DCNP
6.0
Detection limit ꢅ103
[moldmÀ3
]
0.20
3.5
0.13
5.3
0.061
11.4
0.38
1.8
0.22
3.1
5.11
0.1
0.86
0.8
0.52
1.3
1.35
0.5
0.57
1.2
0.28
2.5
173.2
0.004
Chromoreagent
5
6
7
8/9
Simulant
DFP
8.0
DCP
7.0
DCNP
7.0
DFP
1.0
DCP
2.0
DCNP
1.0
DFP
10
DCP
7.0
DCNP
11
DFP
0.04
DCP
0.01
DCNP
0.04
Detection limit ꢅ103
[moldmÀ3
]
0.86
0.80
0.15
4.5
0.46
1.5
693.1
<0.001
14.4
0.048
346.5
0.002
0.69
1
0.23
3
1.64
0.42
31.5
0.022
18.2
0.038
77
0.005
Chem. Asian J. 2010, 5, 1573 – 1585
ꢄ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1579

A. M. Costero, R. Martinez-MꢁÇez et al.
FULL PAPERS
tra were recorded in the positive ion mode on a VG-AutoSpec mass spec-
trometer. UV/Vis spectra were recorded using a 1 cm path length quartz
cuvette. All measurements were carried out at 293 K (thermostated).
Fluorescence spectra were carried out in a Varian Cary Eclipse fluorime-
ter.
Figure 6 for ligand 1). Similar bleaching responses were ob-
served when the simulants DFP and DCNP were used,
whereas the modified silica remained yellow-orange in the
2-(2-N,N-dimethylaminophenyl)ethanol (11): 2-Nitrotoluene (9.2 g,
67.2 mmol), sodium phenoxide (0.06 g, 0.52 mmol), and para-formalde-
hyde (0.9 g, 25 mmol, 95%) in DMSO (20 mL) were heated under stir-
ring at 60–708C for 1 h. The cold reaction mixture was poured into water
(20 mL) and extracted with ethyl ether. The combined organic phases
were washed (with aq. NaCl), dried (using Mg SO4), evaporated, and the
residue was distilled (Kugelrohr, 1608C, 0.2 mmHg) to give 2-(2-nitro-
phenyl)ethanol
(4.3 g,
37%).
2-(2-Nitrophenyl)ethanol
(3.30 g,
19.7 mmol), formaldehyde (4.83 mL, 32.3 mmol, 37%), ethanol (200 mL,
99%), and Pd/C (480 mg, 10%) were placed under an H2 atmosphere
until the uptake of hydrogen ceased. After filtration through celite, the
solvent was evaporated, and the residue was dissolved in chloroform, and
extracted with an aqueous solution of HCl (1n, 2ꢅ50 mL). The aqueous
phase was basified with a saturated solution of Na2CO3 and extracted
with chloroform. After drying (using MgSO4), the solvent was evaporated
to give 2-(2-(N,N-dimethylamino)phenyl)ethanol (2.85 g, 84%) as a light
yellow oil. IR (neat): n˜ =3367, 3059, 3020, 2937, 2860, 2826, 2785, 1597,
Figure 6. Left: a glass tube with silica gel containing adsorbed 1. Right:
silica gel containing 1 after passing through the tube (1000 mL) of air
containing DCP (5 ppm).
presence of vapors of the OP1–OP4 derivatives. This simple
test suggests that this or similar chromogenic systems based
on the reactivity of group I in Scheme 1 might prove useful
for the development of easy-to-use chromogenic alarm
assays, and studies relating to real applications are being
performed in our laboratory.
1492, 1451, 1046, 945, 768, 749 cmÀ1 1H NMR (400 MHz, CDCl3): d=
;
7.3–7.0 (m, 4H), 5.3 (br. s, 1H), 3.85 (t, J=11.6 Hz, 2H), 3.01 (t, J=
11.6 Hz, 2H), 2.70 ppm (s, 6H); 13C{1H} NMR (100 MHz, CDCl3): d=
152.1, 136.0, 131.1, 127.6, 124.9, 120.0, 64.2, 44.9, 36.0 ppm; HRMS (EI):
m/z (%) calcd for C10H15NO: 165.1154 [M]+; found: 165.1153.
2-((E)-5-(2-(4-nitrophenyl)diazenyl)-2-dimethylaminophenyl)ethanol (1):
4-Nitroaniline (0.836 g, 6.05 mmol), concentrated sulfuric acid (1.25 mL,
23 mmol), and water (8 mL) were stirred and slightly heated until the 4-
nitroaniline was completely dissolved, and then placed in an ice bath (0–
58C) for 10 min before a solution of NaNO2 (0.418 g, 6.05 mmol) in
water (4 mL) was added dropwise. After stirring for an additional
10 mins at 0–58C, a solution of 11 (1.0 g, 6.05 mmol), concentrated HCl
(1.3 mL, 15.1 mmol), and water (4 mL) was added dropwise during
15 min. The resulting orange solution was stirred for 15 min in an ice
bath, and 15 min at room temperature, then was neutralized with
Na2CO3 and extracted with CH2Cl2. The dried (using MgSO4) organic
phases were evaporated to give a dark oil that was dissolved in ethyl ace-
tate. Upon addition of hexane, a red dark precipitate appeared, identified
as 1 (1.2 g, 63%). M.p.: 98–1008C; IR (neat): n˜ =2948, 2873, 1591, 1517,
Conclusions
In summary, a family of new reagents for the chromo-fluoro-
genic detection of nerve-agent simulants has been prepared.
These chromoreagents display an intramolecular cyclization
reaction coupled with a color change upon interaction with
certain nerve-agent simulants. The sensing paradigm relies
on the use of 2-(2-(N,N-dimethylamino)phenyl)ethanol or 2-
(2-(N,N-dimethylamino)phenoxy)ethanol reactive sites that
are also part of the conjugated p-system in azo and stilbene-
dye scaffolds. Furthermore, the synthesis is easy and the ap-
proach is highly modular, bearing in mind that a number of
acceptor groups could be anchored to the I donor moieties.
In all cases, the reaction of the reactants with the nerve-
agent mimics is quick, and complete UV/Vis changes are ob-
served after a few seconds. These reagents react only with
DCP, DFP, and DCNP that show close chemical structures
to sarin, soman, and tabun, whereas they remain silent in
the presence of other organophosphorus derivatives, such as,
OP-1–4. Finally, the fact that the probe retains its signaling
abilities upon adsorption on silica and displays color modu-
lations to nerve-agent simulants in both vapors and mixed
aqueous solution, are additional issues of interest.
1345, 1099, 1039, 858, 827 cmÀ1 1H NMR (400 MHz, CDCl3): d=8.36 (d,
;
J=9.0 Hz, 2H), 7.98 (d, J=9.0 Hz, 2H), 7.85 (d, J=8.1 Hz, 1H), 7.81 (s,
1H), 7.26 (d, J=8.1 Hz, 1H), 3.95 (t, J=5.8 Hz, 2H), 3.10 (t, J=5.8 Hz,
2H), 2.83 ppm (s, 6H); 13C{1H} NMR (100 MHz, CDCl3): d=156.7, 155.9,
148.8, 148.4, 135.4, 125.4, 124.7, 123.9, 123.2, 119.9, 63.8, 44.6, 35.8 ppm;
HRMS (EI): m/z (%) calcd for C16H18N4O3: 314.1379 [M]+; found:
314.1371.
2-(N,N-dimethylamino)phenol (12): 2-Nitrophenol (2.68 g, 19.3 mmol),
formaldehyde (3.54 mL, 42.46 mmol, 36%), and Pd/C (480 mg, 10%)
were dissolved in absolute ethanol (43 mL), and placed under an H2 at-
mosphere until uptake of hydrogen ceased. After filtration through
celite, the solvent was evaporated, and the product was purified by subli-
mation at 1558C to give 2-(N,N-dimethylamino)phenol (1.81 g, 69%) as a
white solid. 1H NMR (300 MHz, CDCl3): d=7.08 (dd, J=7.8 Hz, 1.5 Hz,
1H), 6.96 (dt, J=7.7 Hz, 1.5 Hz, 1H), 6.84 (dd, J=8.07 Hz, 1.49 Hz, 1H),
6.77 (dt, J=7.55 Hz, 1.55 Hz, 1H), 6.56 (s, 1H), 2.62 ppm (s, 6H);
13C{1H} NMR (75 MHz, CDCl3): d=151.9, 141.0, 126.4, 121.1, 120.5,
114.6, 45.5 ppm.
2-(2-Dimethylaminophenoxy)acetate (13): A mixture of 2-(N,N-dimethy-
lamino)phenol (12) (1.81 g, 13.2 mmol), ethyl bromoacetate (1.50 mL,
13.2 mmol, 98%), and caesium carbonate (12.9 g, 39.6 mmol) in acetoni-
trile (100 mL) was refluxed overnight. The volatile materials were re-
moved by concentration on a rotary evaporator, and the residue was par-
titioned between water (100 mL) and EtOAc (100 mL). The organic
layer was separated, and the aqueous layer was extracted with EtOAc
(2ꢅ100 mL). The combined organic extracts were dried over anhydrous
magnesium sulfate, filtered, and concentrated to give the title compound
Experimental Section
General Procedures and Materials
THF was distilled from Na/benzophenone under Ar prior to use. All
other reagents were commercially available, and were used without pu-
rification. Silica gel 60 F254 (Merck) plates were used for TLC. 1H and
13C NMR spectra were recorded with the deuterated solvent as the lock
and residual solvent as the internal reference. High-resolution mass spec-
1580
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ꢄ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1573 – 1585

Chromo-Fluorogenic Detection of Nerve-Agent Mimics
(2.54 g, 86%) as a brown oil. 1H NMR (300 MHz, CDCl3): d=6.96–6.76
(m, 3H), 6.74–6.64 (m, 1H), 4.62 (s, 1H), 4.17 (q, J=7.1 Hz, 2H), 2.76 (s,
6H), 1.21 ppm (t, J=7.1 Hz, 3H); 13C{1H} NMR (75 MHz, CDCl3): d=
169.6, 150.8, 143.3, 122.6, 122.5, 118.9, 113.5, 65.9, 61.6, 43.6, 14.5 ppm.
with MgSO4, filtered, and evaporated. The product was purified by
column chromatography with aluminum oxide using dichloromethane as
solvent to give the final compound (0.044 g, 79%) as an orange powder.
1H NMR (300 MHz, CDCl3): d=8.41 (d, J=8.7 Hz, 2H), 8.04 (d, J=
8.7 Hz, 2H), 7.69 (dd, J=8.5 Hz, 2.2 Hz, 1H), 7.58 (d, J=2.1 Hz, 1H),
7.10 (d, J=8.5 Hz, 1H), 4.21 (t, J=4.42 Hz, 2H), 3.99 (t, J=4.42 Hz,
2H), 3.02 ppm (s, 6H); 13C{1H} NMR (75 MHz, CDCl3): d=155.3, 151.6,
148.0, 147.6, 133.5, 123.4, 123.1, 119.1, 117.7, 113.4, 106.1, 72.0, 61.5,
43.5 ppm; HRMS (EI): m/z (%) calcd for C17H19N4O2: 311.1508 [M+1]+;
found: 311.1511.
Ethyl 2-[(E)-5-(2-(4-nitrophenyl)diazenyl)-2-(dimethylamino)phenoxy]-
acetate (14): 4-Nitroaniline (0.182 g, 1.29 mmol), concentrated sulfuric
acid (0.5 mL, 9.2 mmol), and water (10 mL) were stirred and slightly
heated until the 4-nitroaniline was completely dissolved, then, the mix-
ture was placed in an ice bath (0–58C) for 10 min before a solution of
NaNO2 (0.089 g, 1.29 mmol) in water (5 mL) was added dropwise. After
stirring for an additional 10 min at 0–58C, a solution of the ethyl 2-(2-di-
methylaminophenoxy)acetate (13) (0.287 g, 1.29 mmol) in ethanol was
added dropwise during 30 min. The resulting orange solution was stirred
for 30 min in an ice bath, and 30 min at room temperature, and was neu-
tralized with potassium acetate. The precipitate was filtered, and the
aqueous phase was extracted with CH2Cl2. The precipitated and extracted
product was purified by column chromatography with silica gel using
hexane/ethyl acetate (9/1, v/v) as solvent. The final product (0.28 g, 58%)
Methyl 3-methyl-4-nitrobenzoate (18): Sulfuric acid (0.3 mL) was added
to a solution of 3-methyl-4-nitrobenzoic acid (5 g, 27.6 mmol) in metha-
nol (12 mL). The mixture was refluxed for 5 h, and then the methanol
was evaporated. The reaction mixture was poured into water (25 mL)
and extracted with ethyl ether. The combined organic phases were
washed with NaHCO3 and aqueous solution of NaCl. After drying (using
MgSO4), the solvent was evaporated to give methyl 3-methyl-4-nitroben-
zoate (18) (4.8 g, 87%) as a pale yellow solid. 1H NMR (400 MHz,
CDCl3): d=8.03–7.97 (m, 3H), 3.97 (s, 3H), 2.63 ppm (s, 3H);
13C{1H} NMR (100 MHz, CDCl3): d=165.3, 151.9, 134.0, 133.7, 133.5,
128.0, 124.6, 52.7, 20.0 ppm.
1
was obtained as a dark red powder. H NMR (300 MHz, CDCl3): d=8.28
(d, J=8.91 Hz, 2H), 7.88 (d, J=8.91 Hz, 2H), 7.61 (dd, J=8.5 Hz,
2.1 Hz, 1H), 7.33 (d, J=2.1 Hz, 1H), 6.93 (s, 1H), 4.70 (s, 2H), 4.23 (q,
J=6.7 Hz, 2H), 2.99 (s, 3H), 1.26 ppm (t, J=6.7 Hz, 3H); 13C{1H} NMR
(75 MHz, CDCl3): d=168.8, 156.6, 150.0, 148.31, 148.0, 147.4, 147.3,
125.1, 124.1, 123.3, 117.3, 103.9, 65.9, 61.9, 43.3, 14.6 ppm.
Methyl 3-(2-hydroxyethyl)-4-nitrobenzoate (19): Methyl 3-methyl-4-nitro-
benzoate (18) (4.0 g, 30.3 mmol), sodium phenoxide (0.026 g, 0.22 mmol),
and para-formaldehyde (0.42 g, 12 mmol, 95%) in DMSO (10 mL) were
heated under stirring at 60–708C for 1 h. The cold reaction mixture was
poured into water (20 mL) and extracted with ethyl ether. The combined
organic phases were washed (with aq. NaCl), dried (using MgSO4),
evaporated, and the residue was purified by flash chromatography
(EtOAc/hexane, 1:2) to afford methyl 3-(2-hydroxyethyl)-4-nitrobenzoate
(19) (0.9 g, 24%) and the recovered starting material (3.02 g, 75%).
1H NMR (400 MHz, CDCl3): d=8.10 (s, 1H), 8.01 (d, J=8.5 Hz, 1H),
7.90 (d, J=8.5 Hz, 1H), 3.85 (s, 3H), 3.84 (t, J=6.4 Hz, 2H), 3.17 ppm (t,
J=6.4 Hz, 2H); 13C{1H} NMR (100 MHz, CDCl3): d=165.3, 152.5, 134.0,
133.9, 133.6, 128.6, 124.7, 62.3, 52.8, 35.7 ppm.
2-[(E)-5-(2-(4-nitrophenyl)diazenyl)-2-dimethylaminophenoxy]ethanol
(2): To a solution of ester 14 (0.05 g, 0.1344 mmol) in dry THF (20 mL),
LiAlH4 (0.27 mmol) was slowly added in portions at 08C. The reaction
mixture was stirred at 08C for an additional 1 h. Then, the reaction was
warmed to room temperature, stirred for 1 h more, and then, water
(1 mL) was carefully added. The mixture was stirred for 2 h, the precipi-
tate was filtered off, and washed with THF (40 mL). The combined or-
ganic solutions were dried with MgSO4, filtered, and evaporated. The
final product was purified by column chromatography with aluminum
oxide using dichloromethane as solvent to give the title compound
(0.042 g, 95%) as a dark red powder. 1H NMR (300 MHz, CDCl3): d=
8.41 (d, J=9.13 Hz, 2H), 8.04 (d, J=9.13 Hz, 2H), 7.69 (dd, J=8.5 Hz,
2.2 Hz, 1H), 7.58 (d, J=2.1 Hz, 1H), 7.10 (d, J=8.5 Hz, 1H), 4.21 (t, J=
5.12 Hz, 2H), 3.99 (t, J=5.12 Hz, 2H), 3.02 ppm (s, 6H); 13C{1H} NMR
(75 MHz, CDCl3): d=156.5, 151.5, 148.6, 147.2, 140.0, 125.1, 123.5, 123.0,
118.0, 106.2, 77.8, 77.6, 77.4, 77.0, 72.1, 61.4, 43.9 ppm; HRMS (TOF):
m/z (%) calcd for C16H19N4O4: 331.1406 [M+1]+; found: 331.1396.
Methyl 4-dimethylamino-3-(2-hydroxyethyl)benzoate (20): Methyl 3-(2-
hydroxyethyl)-4-nitrobenzoate (19) (1.0 g, 4.4 mmol), formaldehyde
(1.1 mL, 7.4 mmol, 37%), ethanol (54 mL, 99%), and Pd/C (110 mg,
10%) were placed under an H2 atmosphere until the uptake of hydrogen
ceased. After filtration through celite, the solvent was evaporated, and
the residue was dissolved in chloroform, and was extracted with aqueous
solution of HCl (1n, 2ꢅ50 mL). The aqueous phase was basified with a
saturated solution of Na2CO3 and was extracted with chloroform. After
washing (with aq. NaCl), and drying (using MgSO4), the solvent was
evaporated to give methyl 4-dimethylamino-3-(2-hydroxyethyl)benzoate
(20) (0.95 g, 89%) as a light yellow oil. 1H NMR (400 MHz, CDCl3): d=
7.79 (d, J=8.4 Hz, 1H), 7.77 (s, 1H), 7.01 (d, J=8.4 Hz, 1H), 4.10 (brs,
1H), 3.80 (s, 3H), 3.79 (t, J=5.9 Hz, 2H), 2.94 (t, J=5.9 Hz, 2H),
2.66 ppm (s, 6H).
Ethyl 2-[(E)-5-(2-(4-cyanophenyl)diazenyl)-2-(dimethylamino)phenoxy]-
ACHTUNGTRENNUNGacetate (15): 4-Aminobenzonitrile (0.230 g, 1.91 mmol, 98%), concentrat-
ed sulfuric acid (0.5 mL, 9.2 mmol), and water (10 mL) were stirred and
slightly heated until the 4-aminobenzonitrile was completely dissolved.
The mixture was placed in an ice bath (0–58C) for 10 min, and then, a so-
lution of NaNO2 (0.132 g, 1.91 mmol) in water (5 mL) was added drop-
wise. After stirring for an additional 10 min at 0–58C, a solution of ethyl
2-(2-dimethylaminophenoxy)acetate (13) (0.425 g, 1.91 mmol) in ethanol
(20 mL) was added dropwise during 30 min. The resulting red solution
was stirred for 30 min in an ice bath, and another 30 min at room temper-
ature. Then, the resulting solution was neutralized with potassium ace-
tate. The mixture was extracted with CH2Cl2. The product was purified
by column chromatography with silica gel using hexane/ethyl acetate (8/
2, v/v) as eluent. The final pure product (0.19 g, 27%) was isolated as an
orange powder. 1H NMR (300 MHz, CDCl3): d=7.81 (d, J=8.78 Hz,
2H), 7.68 (d, J=8.78 Hz, 2H), 7.57 (dd, J=8.5 Hz, 2.1 Hz, 1H), 7.30 (d,
J=2.1 Hz, 1H), 6.88 (d, J=8.5 Hz, 1H), 4.66 (t, J=6.9 Hz, 2H), 4.21 (q,
J=7.1 Hz, 2H), 2.95 (s, 6H), 1.23 ppm (t, J=7.1 Hz, 3H); 13C{1H} NMR
(75 MHz, CDCl3): d=168.8, 155.3, 150.0, 147.2, 146.9, 133.5, 123.7, 123.3,
119.2, 117.2, 113.1, 104.0, 65.9, 61.8, 43.2, 14.6 ppm.
2-(2-Dimethylamino-5-(hydroxymethyl)phenyl)ethanol (21): Methyl 4-di-
methylamino-3-(2-hydroxyethyl)benzoate (20) (0.41 g, 1.84 mmol) in
ethyl ether (2 mL) was added dropwise to a solution of lithium aluminum
hydride (0.07 g, 1.8 mmol) in ethyl ether (5 mL). The mixture was stirred
for 30 min, and then aqueous solution of ethyl ether and water was
added. The solution was extracted with ethyl acetate. The combined or-
ganic phases were washed (with aq. NaCl), dried (using MgSO4), evapo-
rated, and the residue was purified by flash chromatography (EtOAc/
hexane, 1:2) to give 2-(2-dimethylamino-5-(hydroxymethyl)phenyl)etha-
nol (21) (0.34 g, 81%). 1H NMR (400 MHz, CDCl3): d=7.11–7.05 (m,
3H), 4.49 (s, 2H), 3.71 (t, J=5.5 Hz, 2H), 2.88 (t, J=5.5 Hz, 2H),
2.58 ppm (s, 6H); 13C{1H} NMR (100 MHz, CDCl3): d=151.4, 137.9,
136.2, 130.2, 129.9, 126.3, 120.1, 64.5, 64.2, 45.0, 36.1 ppm.
2-[(E)-5-(2-(4-cyanophenyl)diazenyl)-2-dimethylaminophenoxy]ethanol
(3): To a solution of ester 15 (0.064 g, 0.182 mmol) in dry THF (20 mL),
LiAlH4 (2m) in THF (155 mL, 0.31 mmol) was slowly added at 08C. The
reaction was then stirred at 08C for 1 h, warmed to room temperature,
stirred for another hour, and then water (1 mL) was carefully added. The
mixture was stirred for 2 h, and the precipitate was filtered off, and
washed with THF (40 mL). The combined organic solutions were dried
N-Methoxy-N,3-dimethyl-4-nitrobenzamide (22): 3-Methyl-4-nitrobenzoic
acid (17) (9.05 g, 50 mmol), tetrabromomethane (16.6 g, 50 mmol), trie-
thylamine (7.0 mL, 50 mmol), and N,O-dimethylhydroxylamine hydro-
chloride (5.63 g, 55 mmol), were stirred in dry dichloromethane (75 mL)
under argon atmosphere. Then, a solution of triphenylphosphine (50 mL,
1m) in dichloromethane was added within 5 min, and the reaction was al-
lowed to run for 2.5 h. Hexane was added, and the precipitate was fil-
Chem. Asian J. 2010, 5, 1573 – 1585
ꢄ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1581

A. M. Costero, R. Martinez-MꢁÇez et al.
FULL PAPERS
tered. The organic solvents were washed once with Na2CO3 (10%) and
NaHCO3 (10%). Aqueous layers were extracted, and the combined or-
ganic layers were dried (with MgSO4), evaporated, and purified by flash
chromatography (EtOAc/hexane, 15:85) to give N-methoxy-N,3-dimeth-
NaHSO3. The aqueous layer was extracted with EtOAc, and the organic
layers were dried (using MgSO4), and evaporated. The reddish oil was
purified by flash chromatography (EtOAc/hexane, 30:70) to afford (E)-2-
(2-dimethylamino-5-(4-nitrostyryl)phenyl)ethanol (4) (53 mg, 68%) as a
red solid. 1H NMR (300 MHz, CDCl3): d=8.13 (dt, J=8.8 and 1.9 Hz,
2H), 7.53 (dt, J=8.8 and 1.9 Hz, 2H), 7.34 (dd, J=8.3 and 2.1 Hz, 1H),
7.28 (d, J=2.1 Hz, 1H), 7.14 (d, J=16.3 Hz, H-8, 2H), 7.12 (d, J=8.0, H-
11, 1H), 6.98 (d, J=16.3 Hz, H-7, 1H), 3.82 (t, J=6.0 Hz, 2H), 2.96 (t,
J=5.6 Hz, 2H), 2.67 ppm (s, 6H); 13C{1H} NMR (75 MHz, CDCl3): d=
145.6, 143.0, 135.3, 131.7, 131.6, 128.7, 125.7, 125.5, 124.5, 123.1, 119.3,
63.3, 43.8, 35.2 ppm; HRMS (EI): m/z (%) calcd for C11H15NO2: 312.1470
[M]+; found: 312.1474.
1
yl-4-nitrobenzamide (22) (6.93 g, 62%). H NMR (300 MHz, CDCl3): d=
7.89 (d, J=7.2 Hz, 2H), 7.54 (s, 1H), 7.52 (d, J=7.2 Hz, 1H), 3,47 (s,
3H), 3,30 (s, 3H), 2,53 ppm (s, 3H); 13C{1H} NMR (75 MHz, CDCl3): d=
168.2, 150.3, 138.8, 133.8, 132.9, 126.9, 124.7, 61.7, 33.6, 20.7 ppm; HRMS
(EI): m/z (%) calcd for C10H12N2O4: 224,0797 [M]+; found: 224,0805.
3-(2-Hydroxyethyl)-N-methoxy-N-methyl-4-nitrobenzamide (23): N-me-
thoxy-N,3-dimethyl-4-nitrobenzamide (22) (2.44 g, 10.9 mmol), sodium
phenoxide (0.010 g, 0.09 mmol), and para-formaldehyde (0.13 g, 4 mmol,
95%) in DMSO (30 mL) were heated under stirring at 60–708C for 1 h.
The cold reaction mixture was poured into water (30 mL) and extracted
with ethyl acetate. The combined organic phases were washed (with aq.
NaCl), dried (using MgSO4), evaporated, and the residue was purified by
flash chromatography (EtOAc:hexane, 70:30 to 80:20) to afford 3-(2-hy-
droxyethyl)-N-methoxy-N-methyl-4-nitrobenzamide (23) (1.05 g, 41%) as
a yellow oil. 1H NMR (300 MHz, CDCl3): d=7.85 (d, J=7.2, 2H), 7.65
(s, 1H), 7.59 (d, J=7.20 Hz, 1H), 3.88 (t, J=6.8 Hz, 2H), 3.49 (s, 3H),
3.29 (s, 3H), 3.10 (t, J=7.2 Hz, 2H), 1.81 ppm (bs, 1H); 13C{1H} NMR
(75 MHz, CDCl3): d=168.2, 151.0, 138.6, 134.2, 133.0, 127.6, 124.8, 62.8,
61.8, 36.3, 33.7 ppm; HRMS (EI): m/z (%) calcd for C11H14N2O5:
254.0910 [M]+; found: 254.0903.
(E)-4-(4-dimethylamino-3-(2-hydroxyethyl)styryl)-1-methylpyridinium
iodide (5): 4-dimethylamino-3-(2-hydroxyethyl)benzaldehyde (16)
(30 mg, 0.16 mmol) and 1,4-dimethylpyridinium iodide (43 mg,
0.19 mmol) in methanol (20 mL) were stirred until complete dissolution,
and then, fresh distilled triethylamine (0.25 mL, 0.19 mmol) was added.
The mixture was refluxed for 24 h, and then the reaction mixture was al-
lowed to cool. Toluene (2 mL) was added, and the methanol was evapo-
rated. The residue was diluted again with dichloromethane and dried
(with MgSO4.). After evaporating the solvents, Al2O3 flash chromatogra-
phy (MeOH/EtOAc, 20:80 to 40:60) afforded (E)-4-(4-dimethylamino-3-
(2-hydroxyethyl)styryl)-1-methylpyridinium iodide (5) (mg, 58%) as
1
orange-ish solid. H NMR (400 MHz, [D4]MeOH): d=8.73 (d, J=6.6 Hz,
1H), 8.66 (d, J=6.8 Hz, 2H), 8.11 (d, J=6.9 Hz, 2H), 7.91 (d, J=6.4 Hz,
1H), 7.88 (d, J=16.3 Hz, 1H), 7.64 (d, J=2.1 Hz, 1H), 7.58 (dd, J=8.4
and 2.2 Hz, 1H), 7.31 (d, J=16.2 Hz, 1H), 7.19 (d, J=8.4 Hz, 1H), 4.29
(s, 3H), 3.85 (t, J=7.1 Hz, 2H), 3.00 (t, J=7.0 Hz, 2H), 2.76 ppm (s,
6H); 13C{1H} NMR (100 MHz, [D4]MeOH): d=157.1, 145.8, 143.1, 135.1,
131.9, 131.2, 129.6, 128.9, 124.6, 121.8, 120.8, 63.3, 47.6, 45.0, 35.7,
21.9 ppm; HRMS (EI): m/z (%) calcd for C11H15NO2: 283.1815 [M]+;
found: 283.1810.
4-Dimethylamino-3-(2-hydroxyethyl)-N-methoxy-N-methylbenzamide
(24): 3-(2-Hydroxyethyl)-N-methoxy-N-methyl-4-nitrobenzamide (23)
(2.19 g, 8.61 mmol), formaldehyde (2.2 mL, 15.1 mmol, 37%), ethanol
(220 mL, 99%), and Pd/C (200 mg, 10%) were placed under an H2 at-
mosphere (pressure of 3.5 bar) until the uptake of hydrogen ceased.
After filtration through celite, the solvent was evaporated, and the resi-
due was dissolved again in ethyl acetate, dried (using MgSO4), and
evaporated. Flash chromatography purification (EtOAc/hexane, 90:10)
afforded 4-dimethylamino-3-(2-hydroxyethyl)-N-methoxy-N-methylben-
zamide (24) (1.75 g, 80%). 1H NMR (400 MHz, CDCl3): d=7.51 (dd, J=
8.3 and 2.1 Hz, 1H), 7.46 (d, J=2.0 Hz, 1H), 7.09 (d, J=8.3 Hz, 1H),
3.79 (t, J=5.8 Hz, 2H), 3.51 (d, J=3.0 Hz, 3H), 3.28 (s, 3H), 2.95 (t, J=
5.7 Hz, 2H), 2.67 ppm (s, 6H); 13C{1H} NMR (100 MHz, CDCl3): d=
169.5, 154.6, 135.3, 131.4, 130.0, 127.9, 119.3, 64.3, 61.0, 44.7, 36.0,
33.9 ppm; HRMS (EI): m/z (%) calcd for C13H20N2O3: 252.1476 [M]+;
found: 252.1474.
(E)-4-(4-dimethylamino-3-(2-hydroxyethyl)styryl)benzonitrile (6): 1-(Bro-
momethyl)-4-cyanobenzene (1.96 g, 10 mmol) was dissolved in dry tolu-
ene (25 mL), then, triphenylphosphine (2.62 g, 10 mmol) was added. The
mixture was refluxed for 15 h, and was cooled. A white precipitate was
filtered, washed with toluene, and crystallized with ethanol to afford (4-
cyanobenzyl)triphenylphosphonium bromide[27] (3.92 g, 85%). (4-Cyano-
benzyl)triphenylphosphonium bromide (329 mg, 0.72 mmol) in dry THF
(21 mL) was stirred at 08C under argon atmosphere, and then, a solution
of BuLi (0.47 mL, 0.75 mmol, 1.6m) was added dropwise. After 30 min, 4-
4-Dimethylamino-3-(2-hydroxyethyl)benzaldehyde (16): 2-(2-Dimethyla-
mino-5-(hydroxymethyl)phenyl)ethanol (21) (0.25 g, 1.28 mmol), manga-
nese dioxide (1.28 g, 14.7 mmol), previously activated in ethyl ether
(10 mL), was stirred at room temperature for 2.5 h. The mixture was fil-
tered and washed with chloroform and ethanol. The organic layers were
combined and evaporated to afford 4-dimethylamino-3-(2-hydroxyethyl)-
benzaldehyde (16) (0.22 g, 75%) as yellow oil. In an alternative proce-
dimethylamino-3-(2-hydroxyethyl)benzaldehyde
(16)
(111 mg,
0.57 mmol) in dry THF (0.6 mL) was added at À788C, and the reaction
was then allowed to slowly reach room temperature. 18 h later, the reac-
tion mixture was poured over a solution of NaHCO3 (10%). The aqueous
layer was extracted with EtOAc, and the organic layers were dried (using
MgSO4), and evaporated. The fluorescent oil was purified by flash chro-
matography (EtOAc:hexane, 40:60) to afford 4-(4-dimethylamino-3-(2-
hydroxyethyl)styryl)benzonitrile (119 mg, 71%) as a yellow solid, as a
diastereoisomeric mixture (E/Z, 1:0.7).
dure,
4-dimethylamino-3-(2-hydroxyethyl)-N-methoxy-N-methylbenza-
mide (24) (253.2 mg, 1 mmol) in dry THF (11 mL) was stirred under
argon atmosphere at À788C. Then, a solution of DIBAL (3 mL, 1m) was
added dropwise, and the mixture was allowed to react during 45 min. Re-
action is quenched with acetone (1 mL) and after 15 min, solution was
poured over water (2.5 mL). Mixture was extracted with EtOAc, and the
combined organic layers were dried (using MgSO4), and evaporated.
Flash chromatography purification (EtOAc/hexane, 90:10) afforded 4-di-
methylamino-3-(2-hydroxyethyl)benzaldehyde (16) (0.130 g, 67%) as
yellow oil. 1H NMR (300 MHz, CDCl3): d=9.81 (s, 1H), 7.62 (m, 3H),
7.11 (d, J=9.2 Hz, 1H), 3.81 (t, J=6.6 Hz, 2H), 3.42 (bs, 1H), 2.96 (t, J=
7.0 Hz, 2H), 2.72 ppm (s, 6H); 13C{1H} NMR (75 MHz, CDCl3): d=193.2,
160.5, 136.5, 134.0, 133.8, 131.9, 121.4, 65.5, 46.3, 37.5 ppm; HRMS (EI):
m/z (%) calcd for C11H16NO2: 194.1181 [M+1]+; found: 194.1178.
(E)-4-(4-dimethylamino-3-(2-hydroxyethyl)styryl)benzonitrile
(6):
1H NMR (300 MHz, CDCl3): d=7.46 (d, J=8.6 Hz, 2H), 7.29 (d, J=
8.3 Hz, 2H), 6.98 (bs, 2H), 6.93 (bs, 1H), 6.59 (d, J=12.2 Hz, 1H), 6.45
(d, J=12.2 Hz, 1H), 3.70 (t, J=5.4 Hz, 2H), 2.82 (t, J=5.7 Hz, 2H),
2.64 ppm (s, 6H); 13C{1H} NMR (100 MHz, CDCl3): d=141.2, 134.8,
131.5, 131.4, 131.4, 131.0, 130.9, 128.5, 127.1, 125.8, 125.4, 119.3, 118.9,
117.9, 109.5, 63.2, 44.1, 34.9 ppm; HRMS (EI): m/z (%) calcd for
C19H20N2O: 292.1570 [M]+; found: 292.1576.
(E)-2-(4-dimethylamino-3-(2-hydroxyethyl)styryl)anthracene-9,10-dione
(7): 2-(Bromomethyl)anthracene-9,10-dione (301 mg, 1 mmol) was dis-
solved in dry toluene (2.5 mL), then, triphenylphosphine (262 mg,
1 mmol) was added. The mixture was refluxed for 24 h, and then, the
mixture was cooled. A white precipitate was filtered, washed with tolu-
ene, and crystallized with ethanol to afford ((9,10-dioxo-9,10-dihydroan-
thracen-2-yl)methyl)triphenylphosphonium bromide[28] (459 mg, 82%).
(E)-2-(2-dimethylamino-5-(4-nitrostyryl)phenyl)ethanol (4): (4-Nitroben-
zyl)triphenylphosphonium bromide (149.5 mg, 0.31 mmol) in dry THF
(1 mL) was stirred at 08C under argon atmosphere, and then, a solution
of BuLi (0.20 mL, 0.3 mmol, 1.6m,) was added dropwise. After 15 min, a
solution of 4-dimethylamino-3-(2-hydroxyethyl)benzaldehyde (16)
(0.25 mL, 0.25 mmol, 1m) in dry THF was added at room temperature.
24 h later, the reaction mixture was poured over a saturated solution of
((9,10-Dioxo-9,10-dihydroanthracen-2-yl)methyl)triphenylphosphonium
bromide (177 mg, 0,31 mmol) in dry THF (10 mL) was stirred at À788C
under argon atmosphere, and then,
a solution of BuLi (0.20 mL,
1582
www.chemasianj.org
ꢄ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1573 – 1585

Chromo-Fluorogenic Detection of Nerve-Agent Mimics
0.33 mmol, 1.6m) was added dropwise. After 30 min, a solution of 4-di-
methylamino-3-(2-hydroxyethyl)benzaldehyde (16) (0.25 mL, 0.25 mmol,
1m) in dry THF was added at À788C, and then the reaction was allowed
to slowly reach room temperature. 24 h later, the reaction mixture was
poured over a saturated solution of NaHSO3. The aqueous layer was ex-
tracted with EtOAc, and the organic layers were dried (with MgSO4),
and evaporated. The fluorescent oil was purified by flash chromatogra-
phy (EtOAc/hexane, 30:70) to afford (E)-2-(4-dimethylamino-3-(2-hy-
droxyethyl)styryl)anthracene-9,10-dione (7) (40 mg, 40%) as an oil.
1H NMR (400 MHz, CDCl3): d=8.40 (d, J=1.6 Hz, 1H), 8.34–8.30 (m,
2H), 8.28 (d, J=8.1 Hz, 1H), 7.86 (dd, J=8.1 and 1.8 Hz, 1H), 7.82–7.78
(m, 2H), 7.44 (dd, J=8.3 and 2.1 Hz, 1H), 7.38 (d, J=2.0 Hz, 1H), 7.33
(d, J=16.3 Hz, 1H), 7.21 (d, J=8.2 Hz, 1H), 7.14 (d, J=16.3 Hz, 1H),
3.93–3.87 (m, 2H), 3.04 (t, J=5.6 Hz, 2H), 2.74 ppm (s, 6H);
13C{1H} NMR (100 MHz, CDCl3): d=183.3, 182.6, 168.9, 166.7, 152.8,
151.5, 151.5, 143.4, 136.4, 134.2, 133.9, 133.9, 133.7, 133.6, 132.9, 132.4,
132.0, 131.4, 129.8, 128.0, 127.2, 127.2, 126.5, 125.9, 124.6, 120.4, 64.4,
44.9, 36,4 ppm; HRMS (EI): m/z (%) calcd for C26H23NO3: 397.1674
[M]+; found: 397.1680.
1H), 6.67 (d, J=9.3 Hz, 1H), 3.79 (t, J=6.6 Hz, 2H), 3.76 (s, 3H),
3.04 ppm (t, J=6.6 Hz, 2H); 13C{1H} NMR (75 MHz, CDCl3): d=163.4,
142.6, 137.6, 128.1, 118.4, 112.9, 62.7, 56.2, 37.4 ppm.
2-(5-Methoxy-2-nitrophenyl)ethanol (1.05 g, 5.33 mmol), formaldehyde
(1.5 mL, 18.5 mmol, 37%), absolute ethanol (70 mL), and Pd/C (100 mg,
10%) were placed under an H2 atmosphere until the uptake of hydrogen
ceased. After filtration through celite, the solvent was evaporated, and
the residue was dissolved in chloroform, and extracted with an aqueous
solution of HCl (1n, 2ꢅ50 mL). The aqueous phase was basified with sa-
turated Na2CO3 and extracted with chloroform. After washing (with aq.
NaCl) and drying (using MgSO4), the solvent was evaporated and was
purified by flash chromatography (EtOAc/hexane, 50:50) to give 2-(2-di-
methylamino-5-methoxyphenyl)ethanol (10) (0.84 g, 43%) as
a light
yellow oil. 1H NMR (300 MHz, CDCl3): d=7.14 (d, J=8.7 Hz, 1H), 6.73
(m, 2H), 3.85 (t, J=5.5 Hz, 2H), 3.78 (s, 3H), 2.95 (t, J=5.5 Hz, 2H),
2.64 ppm (s, 6H); 13C{1H} NMR (75 MHz, CDCl3): d=156.8, 145.2, 138.0,
121.1, 116.8, 112.7, 64.2, 55.3, 45.3, 36.5 ppm.
Cyclic ammonium salt from 1 (25): To a stirred mixture of 1 (63 mg,
0.2 mmol) and K2CO3 (56 mg, 0.4 mmol) in acetonitrile (1 mL), tosyl
chloride (36 mg, 0.2 mmol) in acetonitrile (0.5 mL) was slowly added.
After stirring at room temperature for 6 h, toluene (5 mL) was added.
The formed precipitate was filtered to give 25 (as its tosylate salt)
(46 mg, 0.1 mmol) as a white solid. M.p.: >3508C; IR (neat): n˜ =3082,
2-(2-dimethylamino-5-(4-methoxystyryl)phenyl)ethanol (8,9): Phosphorus
tribromide (0.31 mL, 3.3 mmol) was added dropwise to a solution of (4-
methoxyphenyl)methanol (1.39 g, 10 mmol) in dry dichloromethane
(15 mL) at 08C, under argon atmosphere. 2 h later, the reaction mixture
was poured over a solution of NaHCO3 (15 mL, 1m) and was extracted
(with dichloromethane). The organic layers were dried (using MgSO4)
and evaporated to afford the oily residue (1.81 g, 90%). The bromide
(1.70 g, 8.5 mmol) was redissolved in dry toluene (22 mL), and then, tri-
phenylphosphine (2.21 mg, 8.5 mmol) was added. The mixture was re-
fluxed for 15 h, and was cooled. A white precipitate was filtered, washed
with toluene, and crystallized with ethanol/hexane to afford (4-methoxy-
benzyl)triphenylphosphonium bromide[29] (3.56 g, 91%). (4-Methoxyben-
zyl)triphenylphosphonium bromide (88 mg, 0.19 mmol) in dry THF
(4.5 mL) was stirred at À788C under argon atmosphere. Then, a solution
of BuLi (0.11 mL, 0.17 mmol, 1.6m) was added dropwise. After 30 min, a
solution of 4-dimethylamino-3-(2-hydroxyethyl)benzaldehyde (16)
(0.15 mL, 0.15 mmol, 1m) in dry THF was added at room temperature.
16 h later, the reaction mixture was poured over a saturated solution of
NaHSO3. The aqueous layer was extracted with EtOAc, and the organic
layers were dried (using MgSO4), and evaporated. The oil was purified
by flash chromatography (EtOAc/hexane, 30:70) to afford a mixture of
isomers, (E)-2-(2-dimethylamino-5-(4-methoxystyryl)phenyl)ethanol (8)
(29 mg, 63%) and (Z)-2-(2-dimethylamino-5-(4-methoxystyryl)phenyl)e-
thanol (9) (9 mg, 20%).
E Isomer (8): 1H NMR (400 MHz, CDCl3): d=7.36 (d, J=8.7 Hz, 2H),
7.28 (dd, J=8.3 Hz, 2.1 Hz, 1H), 7.21 (d, J=2.0 Hz, 1H), 7.10 (d, J=
8.3 Hz, 1H), 6.92 (d, J=16.3 Hz, 1H), 6.86 (d, 1H), 6.82 (d, J=8.8 Hz,
2H), 3.81 (t, J=5.4 Hz, 2H), 3.75 (s, 3H), 2.96 (t, 2H), 2.67 ppm (s, 6H);
13C{1H} NMR (101 MHz, CDCl3): d=158.2, 129.1, 129.1, 128.0, 126.8,
126.6, 124.8, 124.5, 119.2, 113.1, 112.6, 95.3, 63.4, 54.4, 44.1, 35.4 ppm;
HRMS (EI): m/z (%) calcd for C19H23NO2: 297.1729 [M]+; found:
297.1728.
Z Isomer (9): 1H NMR (400 MHz, CDCl3): d=7.21 (d, J=8.6 Hz, 2H),
7.13 (dd, J=8.2 and 2.0 Hz, 1H), 7.06 (d, J=2.0 Hz, 1H), 7.04 (d, J=
8.3 Hz, 1H), 6.77 (d, J=8.8 Hz, 2H), 6.49 (d, J=12.2 Hz, 1H), 6.41 (d,
J=12.2 Hz, 1H), 3.79 (s, 3H), 3.77 (t, J=5.5 Hz, 2H), 2.91–2.84 (m, 2H),
2.70 ppm (s, 6H); 13C{1H} NMR (100 MHz, CDCl3): d=158.7, 150.7,
135.8, 134.3, 131.7, 130.2, 130.1, 129.7, 129.4, 128.1, 119.7, 114.1, 113.6,
64.5, 55.2, 45.0, 36.1 ppm; HRMS (EI): m/z (%) calcd for C19H23NO2:
297.1729 [M]+; found: 297.1727.
2961, 1628, 1398, 1381, 1127, 1007, 831, 701, 664 cmÀ1
;
1H NMR
(400 MHz, CD3OD): d=8.46 (d, J=8.8 Hz, 2H), 8.15 (m, 4H), 8.02 (d,
J=8.7 Hz, 1H), 7.72 (d, J=7.8 Hz, 2H), 7.25 (d, J=7.8 Hz, 2H), 4.36 (t,
J=7.2 Hz, 2H), 3.65 (s, 6H), 3.59 ppm (t, J=7.2 Hz, 2H); 13C{1H} NMR
(100 MHz, CDCl3): d 155.2, 153.8, 149.0, 142.1, 140.4, 128.4, 125.6, 124.9,
124.6, 123.6, 120.3, 118.2, 68.5, 54.0, 26.6, 19.9 ppm; HRMS (EI): m/z (%)
calcd for C16H17N4O2: 297.1352 [M]+; found: 297.1355.
Cyclic ammonium salt from 4 (26): To a stirred mixture of 4 (31 mg,
0.1 mmol) and triethylamine (14 mL, 0.1 mmol) in acetonitrile (1 mL),
tosyl chloride (19 mg, 0.1 mmol) in acetonitrile (0.5 mL) was slowly
added. After stirring at room temperature for 6 h, toluene (5 mL) was
added. The formed precipitate was filtered to give 26 (as its tosylate
salt). 1H NMR (300 MHz, CD3OD): d=7.96 (d, J=8.7 Hz, 2H), 7.51 (m,
4H), 7.43 (d, J=8.7 Hz, 1H), 7.16 (d, J=8.1 Hz, 2H), 6.96 (d, J=8.1 Hz,
2H), 3.99 (t, J=7.2 Hz, 2H), 3.30 (s, 6H), 3.22 (t, J=7.2 Hz, 2H),
2.09 ppm (s, 3H); HRMS (EI): m/z (%) calcd for C18H19N2O2: 295.1441
[M]+; found: 295.1439.
General Procedure for Detection-limit Determinations
To the corresponding receptor (1ꢅ10À5 moldmÀ3) in water/acetonitrile
(3:1 v/v, 3 dm3) buffered with MES (1ꢅ10À1 moldmÀ3), increasing
amounts of the corresponding simulant solutions were added. UV spectra
were recorded in 1 cm path length quartz cells at 208C (thermostated).
Representation of absorbance at the appropriate wavelength versus con-
centration of the simulant allows the calculation of the detection limit.
Detection in Solid-phase Experiments
Reagents 1, 2, 3, 4, or 5 (25 mL, 1ꢅ10À5 moldmÀ3) in water/acetonitrile
(3:1 v/v, MES 1ꢅ10À1 moldmÀ3) were adsorbed on silica gel. The corre-
sponding solid material was put in contact with a freshly prepared solu-
tion of DCP (1.0ꢅ10À3 moldmÀ3) in acetonitrile. A clear decoloration
was observed. Similar bleaching responses were observed when the simu-
lants DFP and DCNP were used, whereas the modified silica remained
yellow-orange in the presence of vapors of the OP1–OP4 derivatives.
Moreover, as a control experiment, the same materials were treated with
a solution of pure acetonitrile without simulant. No color changes were
found.
2-(2-Dimethylamino-5-methoxyphenyl)ethanol
(10):
4-Methoxy-2-
methyl-1-nitrobenzene (2.99 g, 17.9 mmol), sodium phenoxide (0.030 g,
0.26 mmol), and para-formaldehyde (0.24 g, 8 mmol, 95%) in DMSO
(10 mL) were heated under stirring at 60–708C for 1 h. The cold reaction
mixture was poured into water (10 mL) and extracted with hexane. The
combined organic phases were washed (with aq. NaCl), dried (using
MgSO4), and evaporated to afford an orange oil, 2-(5-methoxy-2-nitro-
phenyl)ethanol (0.77 g, 39%), which was used without further purifica-
Detection of DCP Vapors
Following a similar procedure as above, reagents 1, 2, 3, 4, or 5 (25 mL,
1ꢅ10À5 moldmÀ3) in water/acetonitrile (3:1 v/v, MES 1ꢅ10À1 moldmÀ3
)
were adsorbed on silica gel. Air, containing a DCP (5 ppm), was pre-
pared. The orange/yellow-colored silica, containing the corresponding re-
agent, was placed on a column, and the air, containing the simulant, was
passed through. As the silica comes in contact with the air sample, it be-
tion. 1H NMR (300 MHz, CDCl3): d=7.90 (d, J=9.3 Hz, 1H), 6.75
ACTHNUTRGNE(UNG s,
Chem. Asian J. 2010, 5, 1573 – 1585
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A. M. Costero, R. Martinez-MꢁÇez et al.
FULL PAPERS
comes colorless. Similar bleaching responses were observed when the
simulants DFP and DCNP (5 ppm) were used, whereas the modified
silica remained yellow-orange in the presence of vapors of the OP1–OP4
derivatives.
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Acknowledgements
We thank the Spanish Government (projects MAT2009-14564-C04) and
the Generalitat Valencia (project PROMETEO/2009/016 and
ACOMP07/080) for support. S.R. is grateful to the Generalitat Valenci-
ana for the fellowship. SCSIE (Universidad de Valencia) is gratefully ac-
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