A straightforward route to obtain 13C1-labeled clenbuterol

Article abstract of DOI:10.1016/j.tet.2011.05.118

Singly-labeled ¹³C₁-clenbuterol has been synthesized employing a straightforward pathway starting from easily available acetanilide. The critical step was the Friedel-Crafts acylation of this compound with marked acetyl chloride, bei

Full text of DOI:10.1016/j.tet.2011.05.118

Tetrahedron 67 (2011) 5577e5581
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
13
A straightforward route to obtain C1-labeled clenbuterol
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Ana Gonzalez-Antuna , Ivan Lavandera , Pablo Rodríguez-Gonzalez , Julio Rodríguez ,
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b,
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Jose Ignacio García Alonso , Vicente Gotor
Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, C/Julian Clavería 8, 33006 Oviedo, Spain
Departamento de Química Organica e Inorganica, Instituto Universitario de Biotecnología de Asturias, Universidad de Oviedo, C/Julian Clavería 8, 33006 Oviedo, Spain
Innovative Solutions in Chemistry S.L., Edificio Científico-Tecnologico, Campus de ‘El Cristo’, Oviedo 33006, Spain
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a r t i c l e i n f o
a b s t r a c t
Singly-labeled 13C1-clenbuterol has been synthesized employing a straightforward pathway starting from
easily available acetanilide. The critical step was the FriedeleCrafts acylation of this compound with
marked acetyl chloride, being the first example of the use of this methodology applied to the synthesis of
a clenbuterol derivative. Subsequent chemical reactions afforded the desired product with good yields.
Ó 2011 Elsevier Ltd. All rights reserved.
Article history:
Received 2 May 2011
Received in revised form 25 May 2011
Accepted 29 May 2011
Available online 2 June 2011
Keywords:
b
-Agonists
Clenbuterol
Minimal labeling
FriedeleCrafts reaction
13C-Labeling
1. Introduction
Clenbuterol (1, Fig. 1a), as a member of the b2-agonists family,
has extensively been (and is still) prescribed as bronchodilatator in
asthmatic patients.1 In fact, this compound is licensed in the EU for
therapeutic use in food producing species and approved by the US
Food and Drug Administration (FDA) for use in horses.2 Its ther-
apeutical role to combat skeletal muscle atrophy secondary to
disuse, injury and denervation has intensively been investigated
and is not completely clear its relevance in this point.3
The main problem of this type of compounds is that they are
illegally employed because of their anabolic effects on skeletal
muscle and their lipolytic effect, on the one hand, by sportsmen for
doping purposes, and on in the other hand, by farmers to feed cattle
due to financial profit reasons. This has raised public health concern
and highlights the relevance for developing efficient analytical
methods to detect clenbuterol and similar growth promoting sub-
stances in low levels.4 For this reason, identification and quantifi-
cation of these compounds is difficult and requires reliable
methodologies. Immunological,5 electrochemical,5 spectrophoto-
metric,6 and mass spectrometric approaches have been described
but those based on chromatography coupled to mass spectrometric
detection, such as GCeMS7 or LCeMS8 provide an easier
Fig. 1. (a) Clenbuterol. (b) 13C1-Labeled DMS-clenbuterol derivative and two of the
characteristic breaks in its MS spectrum. The symbol * refers to the enriched 13C
position in the molecule.
implementation for a routine basis. The accuracy and precision in
the results is an important handicap due to matrix effects and the
required time-consuming sample preparation steps. Isotope Di-
lution Mass Spectrometry (IDMS)9 is regarded as an absolute
measurement method directly traceable to the International Sys-
tem of units as it provides results with the highest metrological
quality. Most of the procedures use deuterated10 compounds as
internal standards, however, labeling with 1 mass unit (‘minimal
labeling’) with 13C is more efficient to avoid differences in the
physicochemical properties between the unlabeled and labeled
compounds.11
The EU regulations require the confirmation of the presence of
clenbuterol by gas chromatographyemass spectrometry. When
a full scan spectrum is recorded, a minimum of four ions shall be
present with a relative intensity of ꢀ10% of the base peak.12 In the
analysis of clenbuterol by GCeMS, several reagents have been
employed to derivatize it into a volatile and thermally stable
* Corresponding author. Tel./fax: þ34 985 103448; e-mail address: vgs@uniovi.es
(V. Gotor).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.05.118

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5578
molecule. Among them, chloro(chloromethyl)dimethylsilane13
produces a dimethylsilamorpholine (DMS) derivative with five
t
ions [i.e., 331 (MꢁCH3) and 289 (Mꢁ Bu) m/z, Fig.1b] with a relative
intensity of ꢀ10% of the base peak that confirms the presence of
clenbuterol.14
Due to this, it was envisaged the synthesis of a singly-labeled
clenbuterol analogue at the carbon linked to the hydroxyl group,
since both breaks will contain the isotopic label and therefore will
be suitable for IDMS quantification. There are few routes described
to obtain clenbuterol,15 labeled analogues, such as D9- and D3-
clenbuterol,16 or a radiolabeled monotritiated derivative.17 In these
protocols, the starting material was usually 4-aminoacetophenone
or similar compounds, that obviously cannot be employed as pre-
cursors of our target molecule since we need to introduce the mark
at the carbonyl position. In our case, due to its easy accessibility,
aniline (2) or acetanilide (3) was chosen as the starting material,
and therefore the key-step to introduce the labeled carbon was the
employment of a FriedeleCrafts acylation protocol.
Scheme 1. Synthesis of compound 5 starting from 4.
conditions (Table S2, Supporting data). Thus, we started employing
an excess of NCS with p-toluenesulfonic acid (p-TsOH) at different
temperatures, but in all cases a mixture of different compounds
was obtained. When employing a lower excess of both NCS and
acid, the desired product was isolated with 25% yield after flash
chromatography. Finally, we followed a procedure using NCS in HCl
2 N at 45 ꢂC.15b Under these conditions, hydrochloride 6$HCl was
obtained as a precipitate in the reaction medium, and therefore
a simple filtration afforded the desired product with 75% yield.
When repeating this sequence starting from 3 and using CH313COCl,
labeled compound 6a$HCl was achieved with similar yields
(Scheme 2).
2. Results and discussion
FriedeleCrafts acylation18 provides a useful methodology to
achieve aromatic ketones. The usual way to perform it makes use of
Lewis acids such as AlCl3. While with ortho- and para-directing
groups like alkyl, alkoxy, or halogen present in the benzene moiety,
the p-acylated product is usually obtained with high yields, when
highly deactivating or amino groups are present at the molecule,
this reaction is more difficult to achieve. In fact, there are only few
examples employing aniline or acetanilide as substrates in order to
obtain the corresponding acetophenone derivatives. Thus, ZrO2 and
acetyl chloride at 60 ꢂC,19 aluminum metal powder20 or zinc21 with
acetyl chloride under microwave conditions, and Ga(OTf)3 with
acetic anhydride at 50 ꢂC22 have been used to perform this specific
transformation. Unfortunately, in our hands most of these pro-
cedures did not work although several conditions were tried (see
Supporting data).
Due to this, we decided to achieve this transformation under the
more usual conditions with AlCl3 or FeCl3 (Table S1, Supporting
data). When aniline was used as substrate with acetyl chloride or
acetic anhydride as acylating agent, N-acylation was always ach-
ieved, therefore we tried this reaction with acetanilide directly.
Microwave or thermal conditions were employed with AlCl3 and
acetyl chloride23 in dichloromethane, but no or very low conver-
sion (8%) was observed. The use of FeCl3 as catalyst was not efficient
as well. Finally, we were glad to obtain a good conversion of 70% of
3 into 4 when 3.2 equiv of AlCl3 and 2 equiv of acetyl chloride were
employed in 1,2-dichloroethane at 60 ꢂC for 24 h. When this re-
action was repeated employing marked CH313COCl to obtain 4a, the
reaction yield was comparable.
Scheme 2. Obtaining of derivative 6a$HCl from acetanilide 3.
The next step was the
a-bromination of 6$HCl to obtain de-
rivative 7 employing the typical conditions with Br2 in CH2Cl2. The
same transformation was previously reported in chloroform.27 This
reaction was very dependent concerning the bromine equivalents
and the addition procedure. Thus, it was found that the best con-
ditions were observed when adding at the beginning 0.6 equiv of
Br2 and later several portions of 0.2 equiv of bromine until the a,a-
dibrominated derivative 8 was detected by TLC. At this point, we
were able to isolate compound 7 with a yield of 71%, as previously
shown in chloroform (Scheme 3).27 Again, this reaction afforded
a comparable yield when marked substrate 6a$HCl was used as
substrate.
Scheme 3. Bromination of derivative 6$HCl to afford 7 and 8.
Once compound 4 was achieved with good yield, the next step
was to find the suitable reaction conditions to hydrolyze the acet-
amido into the corresponding amine affording 5, since the follow-
ing chlorination step would need the free amino group to activate
positions 3 and 5 in order to achieve derivative 6. Among the dif-
ferent methodologies to obtain aniline derivatives from their
acetylated counterparts,24 we chose the basic hydrolysis employing
NaOH 3 N in MeOH at 50 ꢂC (Scheme 1). Thus, after 20 h the desired
compound was obtained as the only product with good yield. In
a subsequent experiment, the two first reactions were done with-
out purification of 4, synthesizing 5 from 3 with a combined yield of
40% after flash chromatography.
The next step is the chlorination of the phenyl ring at positions 3
and 5. Among all methods described in the bibliography to perform
this transformation, it can be highlighted the use of NaOCl,15a,25
chlorine,26 and N-chlorosuccinimide (NCS). Due to its easy han-
dling, we chose this last reagent trying to find the optima
To synthesize labeled clenbuterol 1a from intermediate 7a, two
different approaches can be done (Scheme 4). This is: (a) reduction
of the ketone into the corresponding bromohydrin 9a and sub-
sequent SN2 reaction with tert-butylamine; or (b) nucleophilic
substitution with BuNH2 to afford ketone 10a and subsequent re-
duction of this intermediate.
Firstly, pathway ‘a’ (Scheme 4) was tried employing substrate 7.
Thus, reduction with NaBH4 in EtOH at 0 ꢂC quantitatively afforded
the desired alcohol 9 with traces of epoxide 11, but this should not
be a problem since the SN2 reaction over both substrates should
afford clenbuterol. Surprisingly, when this substitution reaction
was done with tBuNH2 in different solvents and temperatures
(Table S3, Supporting data), the reaction proceeded forming one
product, although by 1H NMR and MS it was discovered that this
compound was not 1 but its regioisomer 12 (Scheme 5). This fact
can be explained taking into account the formation of epoxide 11 as
t

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A. Gonzalez-Antuna et al. / Tetrahedron 67 (2011) 5577e5581
5579
conditions with good yields. This is the first time where a Frie-
deleCrafts protocol has been applied to the synthesis of a clenbu-
terol derivative. Special mention must be done in the formation of
the regioisomer of clenbuterol when the substitution reaction oc-
curs over the epoxide and not over the bromohydrin, being a nice
example of how although epoxides and halohydrins are considered
as similar chemical functionalities, they can offer different features
that can be exploited chemoselectively.29
4. Experimental section
4.1. General
All employed reagents were purchased from commercial sour-
ces. Reagents and solvents were of the highest quality available.
4-Acetamidoacetophenone was purchased from SigmaeAldrich (St.
Louis, MO, USA). Labeled compound 13C1-acetyl chloride (99%
nominal enrichment) was obtained from SigmaeAldrich (St. Louis,
MO, USA) in pure liquid form. Aluminum chloride, N-chlor-
osuccinimide, bromine, tert-butylamine, sodium borohydride and
sodium hydroxide of pure grade were commercially supplied by
SigmaeAldrich. All solvents (hexane, methanol, dichloroethane,
dichloromethane and chloroform) were obtained from Merck.
Melting points were taken on samples in open capillary tubes
and are uncorrected. IR spectra were recorded on an Infrared
Fourier Transform spectrophotometer using KBr or NaCl pellets.
Flash chromatography was performed using silica gel 60
(230e400 mesh). 1H and 13C NMR spectra were measured on DPX-
300 (1H, 300.13 MHz and 13C, 75.5 MHz). Chemical shifts are given
Scheme 4. Pathways to obtain labeled clenbuterol 1a from derivative 7a.
in delta (d) values, the coupling constants (J) in hertz (Hz), and
tetramethylsilane was used as the internal standard. ESIþ or EIþ
was used to record mass spectra (MS) and high-resolution mass
spectra (HRMS). Microwave employed was purchased from CEM
Corporation, Mathews, N.C., USA.
13
4.1.1. C1-40-Acetamidoacetophenone (4a). To a solution of acet-
anilide (0.8 mmol, 108 mg) in 1,2-dichloroethane (2 mL), AlCl3
(2.55 mmol, 341 mg) and 13C1-acetyl chloride (1.6 mmol, 117
mL)
Scheme 5. Formation of derivative 12 through epoxide 11.
were added under nitrogen atmosphere. The resulting mixture was
stirred and heated at 60 ꢂC during 24 h. The progress of the reaction
was followed by TLC (60% ethyl acetate/hexane), and it was stopped
when the starting material had been totally consumed. After
cooling at room temperature, the crude was firstly extracted with
dichloromethane (5ꢃ10 mL). The aqueous phase was treated with
NaOH pellets until pH 5e6 was reached, and then it was extracted
with dichloromethane (2ꢃ10 mL). The organic layers were com-
bined, washed with brine (2ꢃ10 mL), and dried over anhydrous
Na2SO4, filtered, and concentrated under reduced pressure to afford
a crude that was purified by flash chromatography using mixtures
of ethyl acetate/hexanes as eluent, affording 4a with 70% isolated
intermediate of this process catalyzed by the amine. The synthesis
of similar derivatives through the corresponding epoxides has al-
ready been described.28
Due to this, we chose pathway ‘b’ (Scheme 4) to obtain clen-
buterol. Thus, reaction of 7 with tert-butylamine in CHCl3 at 50 ꢂ
C
afforded derivative 10 after 24 h. Due to its low stability, the re-
duction process was performed in situ, after evaporation of the
solvent and the remaining tBuNH2, using NaBH4 in MeOH or LiAlH4
in THF at room temperature, but in both cases the final product
could not be isolated. However, when the reduction with NaBH4
was kept at pH 7, the final product could be obtained as chlorhy-
drate with a combined yield of 25% for both processes. When these
reactions were done over labeled 7a, 13C1-clenbuterol 1a$HCl was
achieved with comparable yield.
yield. Solid; mp 165e169 ꢂC; IR (NaCl)
n
744, 896, 1179, 1265, 1422,
2.33
1601, 1642, 2306, 2987, 3055; 1H NMR (300 MHz, MeOD-d4)
d
(s, 3H, Ha), 2.74 (d, 3H, H2, 2JCH 5.7 Hz), 7.88 (d, 2H, Hm, 3JHH 8.5 Hz),
8.13 (dd, 2H, Ho, 3JHH 8.3, 3JCH 3.3 Hz); 13C NMR (75 MHz, MeOD-d4)
d
22.6 (Ca), 25.0 (d, C2, 1JCC 42.4 Hz), 118.6 (d, Cm, 3JCC 3.8 Hz), 129.3
2
3. Conclusions
(d, Co, JCC 2.8 Hz), 132.2 (d, Ci, 1JCC 53.2 Hz), 142.1 (Cp), 170.5 (Cc),
198.0 (C1); MS [EIþ, m/z (%)] 179 (6), 178 (32), 163 (10), 136 (20), 121
(100); HRMS (ESIþ) calcd for 13CC9H11NNaO2 [(MþNa)þ] 201.0715,
found 201.0715.
Recent analytical findings11 have demonstrated the utility of
labeled compounds with a minimum number of 13C-atoms to de-
velop new methodologies based on IDMS for the analysis of organic
compounds. Thus, we strongly believe that demand of further
single 13C-enriched compounds will significantly increase in the
near future. Herein, we have described the first synthesis of the
singly-labeled 13C1-clenbuterol derivative. The crucial step was the
FriedeleCrafts reaction with marked acetyl chloride over acetani-
lide, and the following reactions were done under typical
13
13
4.1.2. C1-40-Aminoacetophenone (5a). To a solution of C1-40-
acetamidoacetophenone (5.75 mmol, 1019.2 mg) in methanol
(10 mL), NaOH 3 N (45 mmol, 15 mL) was added under stirring. The
mixture was heated at 50 ꢂC for 20 h. The progress of the reaction
was followed by TLC (60% ethyl acetate/hexane). After cooling at
room temperature, the solvent was removed by evaporation under

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A. Gonzalez-Antuna et al. / Tetrahedron 67 (2011) 5577e5581
5580
reduced pressure. The crude material was extracted with
dichloromethane (3ꢃ20 mL), the organic layers were combined,
dried over anhydrous Na2SO4, filtered, and concentrated under
reduced pressure. The residue was subjected to flash chromatog-
raphy (silica gel) using ethyl acetate/hexane mixtures as eluent,
chloroform (5ꢃ2 mL). The organic layers were combined, dried over
anhydrous Na2SO4, filtered, and concentrated under reduced pres-
sure. The solid was diluted in 3 mL of anhydrous chloroforme and
HCl/diethylether was added dropwise to afford the chlorhydrate.
Some drops of diethylether were added to improve the pre-
cipitation. The resulting solid was filtered, washed with diethylether
(2ꢃ3 mL), and dried under reduced pressure obtaining 10a$HCl. Due
to its instability, we subsequently proceeded with the reduction.
affording 5a in 61% isolated yield. Solid, mp 103e107 ꢂC; IR (NaCl)
n
740, 896, 1266, 1422, 1596, 2306, 2987, 3055, 3405; 1H NMR
2
(300 MHz, CDCl3)
d
2.50 (d, 3H, H2, JCH 5.8 Hz), 6.64 (d, 2H, Hm, 3JHH
3
3
8.6 Hz), 7.80 (dd, 2H, Ho, JHH, 8.4 JCH 3.5 Hz); 13C NMR (75 MHz,
13
CDCl3)
d
26.4 (d, C2, 1JCC 42.3 Hz), 114.1 (d, Cm, 3JCC 3.9 Hz), 128.3 (d,
4.1.6. C1-1-(40-Amino-30,50-dichlorophenyl)-2-(tert-butylamine)
Ci, 1JCC 55.8 Hz), 131.1 (d, Co, JCC 2.6 Hz), 151.4 (Cp), 196.8 (C1); MS
[EIþ, m/z (%)] 137 (4), 136 (48), 121 (100), 92 (42); HRMS calcd for
13CC7H9NNaO [(MþNa)þ] 159.0615, found 159.0609.
ethanol$HCl or 13C1-clenbuterol$HCl (1a$HCl). To a solution of
10a$HCl (0.25 mmol, 80 mg) in water (1.5 mL) and methanol
(2 mL), NaOH 1 N was added until pH 7, and afterwards a NaBH4
solution in water (0.05 mmol, 2 mg of NaBH4 in 0.5 mL of water)
was added in portions. The mixture was stirred at room tempera-
ture and after 1 h, the mixture was basified with NaOH 2 N until pH
10. The progress of the reaction was followed by TLC (50%
dichloromethane/methanol) until the starting material was totally
consumed. Methanol was removed by evaporation at reduced
pressure. The aqueous phase was extracted with dichloromethane
(3ꢃ10 mL). The organic layers were combined, dried over anhy-
drous Na2SO4, filtered, and concentrated under reduced pressure.
The solid was dissolved with dichloromethane (1 mL) and drops of
HCl/diethylether (pH 3e4) were added to afford the chlorhydrate.
Then, 1 mL of diethylether was added and the product was left at
ꢁ20 ꢂC to allow the precipitation of the final product 1a$HCl (25%
yield from 7a). The resulting solid was filtered, washed with
diethylether (2ꢃ5 mL) and dried under reduced pressure. Solid, mp
2
13
4.1.3. C1-40-Amino-30,50-dichloroacetophenone$HCl (6a$HCl). N-
Chlorosuccinimide (3.14 mmol, 420 mg) was added into a solution
of 5a (1.26 mmol, 170 mg) in HCl 2 N (2 mL). The reaction was
heated at 50 ꢂC and stirred during 10 h. The progress of the reaction
was followed by TLC (60% ethyl acetate/hexane), until the starting
material was totally consumed. The formed solid was filtered,
washed with water at 0 ꢂC (2ꢃ20 mL), and dried under reduced
pressure to give the corresponding product in 75% isolated yield.
Solid, mp 163e168 ꢂC; IR (NaCl)
n 740, 896, 1266, 1422, 1610, 2307,
2
2987, 3055, 3399; 1H NMR (300 MHz, CDCl33)
d 2.50 (d, 3H, H2, JCH
5.9 Hz), 4.93 (s, 2H, NH), 7.82 (d, 2H, Ho, JCH 3.8 Hz); 13C NMR
(75 MHz, CDCl3) d
25.9 (d, C2, 1JCC 42.9 Hz), 118.7 (d, Cm, 3JCC 5.7 Hz),
127.5 (d, Ci, 1JCC 54.6 Hz), 128.5 (d, Co, 2JCC 3.0 Hz), 144.1 (Cp), 194.4
(C1); MS [EIþ, m/z (%)] 208 (8), 206 (30), 204 (48), 193 (16), 191 (64),
189 (100), 164(2), 162 (10), 160 (14), 124 (22); HRMS (ESIþ) calcd for
13CC7H7Cl2NNaO [(MþNa)þ] 226.983, found 226.9832.
decompose. IR (NaCl) n 740, 896, 1265, 1421, 1626, 2306, 2987, 3055,
t
3402; 1H NMR (300 MHz, MeOD-d4)
d 1.42 (s, 9H, Bu), 2.99e3.18
(m, 2H, H2), 4.81 (ddd, 1H, H1, 1JCH 157.6, 3JHH 13.1, 3JHH 3.2 Hz), 7.37
13
3
4.1.4. C1-40-Amino-2-bromo-30,50-dichloroacetophenone (7a). To
(d, 2H, Ho, JCH 4.2 Hz); 13C NMR (75 MHz, MeOD-d4)
d
26.4 (C4),
a solution of 6a$HCl (1.70 mmol, 350 mg) in dichloromethane
(8 mL), a bromine solution [(1.02 mmol, 52 mL) in dichloromethane
58.9 (d, C2, 1JCC 7.4 Hz), 70.2 (C1), 80.0 (C3), 121.3 (d, Cm, 3JCC 5.6 Hz),
127.5 (d, Co, 2JCC 3.4 Hz),133.1 (d, Ci, 1JCC 48.8 Hz), and 142.4 (Cp); MS
[ESIþ, m/z (%)] 282 (10), 280 (63), 278 (100), 262 (15), 260 (24), 206
(19), 204 (30); HRMS (ESIþ) calcd for 13CC11H18Cl2N2O [Mþ]
278.0902, found 278.0900.
(2 mL)] was added dropwise under strong agitation. The progress of
the reaction was followed by TLC every few minutes (60% hexane/
dichloromethane), and when no progress was observed, other
0.2 equiv of Br2 in 0.5 mL of CH2Cl2 was added until the formation
of 2,2-dibrominated derivative was detected by TLC. The reaction
was kept at room temperature and the total time was usually 2 h.
The solvent was removed by evaporation at reduced pressure and
the residue was subjected to flash chromatography (silica gel) using
dichloromethane/hexane mixtures as eluent, affording 7a in 70%
Acknowledgements
Financial support from the Spanish Ministerio de Ciencia e
ꢀ
Innovacion (MICINN, Project CTQ2007-61126/PPQ and CTQ2009-
12814) is gratefully acknowledged. A.G.-A. acknowledges the
isolated yield. Solid, mp 153e158 ꢂC; IR (NaCl)
1265, 1421, 1488, 1583, 1619, 2306, 2987, 3054, 3394, 3492; 1H NMR
(300 MHz, MeOD-d4)
4.55 (d, 2H, H2, 2JCH 3.4 Hz), 7.92 (d, 2H, Ho,
3JCH 3.8 Hz); 13C NMR (75 MHz, MeOD-d4) 31.9 (d, C2, 1JCC 44.3 Hz),
n 739, 896, 1076,
ꢀ
ꢀ
Fundacion para el Fomento en Asturias de la Investigacion
Científica Aplicada y la Tecnología (FICYT) for her predoctoral grant.
Finally, I.L. and P.R.-G acknowledge MICINN for their research
contract under the Ramon y Cajal Program.
d
d
119.8 (d, Cm, 3JCC 6.0 Hz), 124.7 (d, Ci, 1JCC 59.2 Hz), 131.0 (d, Co, 2JCC
3.0 Hz), 148.0 (Cp), 190.8 (C1); MS [ESIþ, m/z (%)] 208 (MꢁBr, 9), 206
(MꢁBr, 29), 204 (MꢁBr, 46), 193 (14),;191 (64), 189 (100).
Supplementary data
As byproduct, 13C1-40-amino-2,2-dibromo-30,50-dichloroacetop-
henone 8a was also obtained. Solid, 1H NMR (300 MHz, CDCl3)
Supplementary data associated with this article can be found in
online version at doi:10.1016/j.tet.2011.05.118.
d
5.13 (s, 2H, NH2), 6.53 (d, 1H, H2, 2JCH 0.7 Hz), 7.98 (d, 2H, Ho, 3JCH
3.8 Hz). 13C NMR (75 MHz, CDCl3)
d
38.9 (d, C2, 1JCC 44.1 Hz), 118.6
References and notes
3
1
2
(d, Cm, JCC 6.2 Hz), 120.1 (d, Ci, JCC 62.6 Hz), 129.9 (d, Co, JCC
2.8 Hz), 145.2 (Cp), 182.8 (C1); HRMS (ESIþ) calcd for 13CC7H5Br2
Cl2NNaO [(MþNa)þ] 382.804, found 382.8044.
1. (a) Prather, I. D.; Brown, D. E.; North, P.; Wilson, J. R. Med. Sci. Sports Exercise
1995, 27, 1118e1121; (b) Elliott, C. T.; McCaughey, W. J.; Shortt, H. D. Food Addit.
Contam. 1993, 10, 231e244.
2. (a) Harkins, J. D.; Woods, W. E.; Lehner, A. F.; Fisher, M.; Tobin, T. J. Vet. Phar-
macol. Ther. 2001, 24, 7e14; (b) Harkins, J. D.; Robinson, N. E.; Woods, W. E.;
Lehner, A. F.; Smith, M. D.; Gates, R. S.; Fisher, M.; Tobin, T. J. Vet. Pharmacol.
Ther. 2000, 23, 251e260.
13
4.1.5. C1-1-(40-Amino-30,50-dichlorophenyl)-2-(tert-butylamino)
ethanone$HCl (10a$HCl). In a sealed tube 7a (0.52 mmol, 150 mg)
was dissolved in anhydrous chloroform (3 mL) and then tert-
3. Cockman, M. D.; Jones, M. B.; Prenger, M. C.; Sheldon, R. J. Muscle Nerve 2001,
24, 1647e1658.
butylamine (8.20 mmol, 860 mL) was added. The solutionwas heated
at 50 ꢂC with agitation for 24 h. After this time, the solution had an
intense orange color. After cooling to room temperature, the solvent
and the excess of tert-butylamine were removed by evaporation
under reduced pressure and the residue was extracted with
€
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