Chiral analysis of chloro intermediates of methylamphetamine by one-dimensional and multidimentional NMR and GC/MS

Article abstract of DOI:10.1021/ac300503g

Impurity profiling and classification of abused drugs using chiral analytical techniques is of particular interest and importance because of the additional information obtained from this approach. When these methods are applied to the synthesis of illicitly used substances, they can supply valuable information about the conditions/chemicals used in the synthesis. We have applied GC and NMR methods to the study of intermediates found in methylamphetamine manufacture with the aim of linking the intermediates to the ephedrine/pseudoephedrine starting materials. Therefore, determination of the stereochemical makeup within samples of forensic interest is important giving further specific information to the analyst. This study investigates the stereochemical course of the Emde synthesis of methylamphetamine with particular focus on intermediate formation via the chlorination of ephedrine and pseudoephedrine enantiomers. The configurations of these chloro-phenethylamines were determined by 1D and 2D NMR analysis, and thereafter, the GC/MS analysis was carried out. We have shown here that chlorination of the ephedrine/pseudoephedrine compounds occurs via inversion (S_N2) and retention (S_Ni) of configuration around the α carbon and mixture of diastereoisomers (chloroephedrine and chloropseudoephedrine) were formed, with the ratio of the resulting compounds dependent on the precursors used. The preparation and analytical properties of these intermediate standards provide data for laboratories interested in the stereochemical analysis of methylamphetamine intermediates such as forensic/law enforcement, and illustrate the value of using a combination of analytical methodology.

Full text of DOI:10.1021/ac300503g

Article
pubs.acs.org/ac
Chiral Analysis of Chloro Intermediates of Methylamphetamine by
One-Dimensional and Multidimentional NMR and GC/MS
Justyna M. Płotka,*,† Calum Morrison,‡ David Adam,§ and Marek Biziuk†
†Department of Analytical Chemistry, Chemical Faculty, Gdan
Poland
́ ́
sk University of Technology, Narutowicza 11/12, 80-233 Gdansk,
‡School of Science, Faculty of Science and Technology, University of the West of Scotland, Paisley PA1 2BE, Scotland, U.K.
§School of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K.
S
* Supporting Information
ABSTRACT: Impurity profiling and classification of abused drugs
using chiral analytical techniques is of particular interest and
importance because of the additional information obtained from
this approach. When these methods are applied to the synthesis of
illicitly used substances, they can supply valuable information about
the conditions/chemicals used in the synthesis. We have applied
GC and NMR methods to the study of intermediates found in
methylamphetamine manufacture with the aim of linking the
intermediates to the ephedrine/pseudoephedrine starting materials.
Therefore, determination of the stereochemical makeup within
samples of forensic interest is important giving further specific
information to the analyst. This study investigates the stereo-
chemical course of the Emde synthesis of methylamphetamine with
particular focus on intermediate formation via the chlorination of ephedrine and pseudoephedrine enantiomers. The
configurations of these chloro-phenethylamines were determined by 1D and 2D NMR analysis, and thereafter, the GC/MS
analysis was carried out. We have shown here that chlorination of the ephedrine/pseudoephedrine compounds occurs via
inversion (SN2) and retention (SNi) of configuration around the α carbon and mixture of diastereoisomers (chloroephedrine and
chloropseudoephedrine) were formed, with the ratio of the resulting compounds dependent on the precursors used. The
preparation and analytical properties of these intermediate standards provide data for laboratories interested in the
stereochemical analysis of methylamphetamine intermediates such as forensic/law enforcement, and illustrate the value of using a
combination of analytical methodology.
psychoactive drug is a loosely defined grouping of drugs
that affect perception, mood, cognition, behavior, or
the United States, southeast Asia, Australia, and New Zealand.
Several countries report few but mostly industrial-sized
operations, particularly in east Asia and parts of North America,
existing for criminal profit.4,5 This is because methylamphet-
amine has low production costs, easily obtained precursor
chemicals, and a simple production process.5
The problems associated with MAM abuse are well reported
not only in the media but also in the scientific literature.6
Therefore, many national and international organizations such as
the U.S. Drug Enforcement Agency7 and The United Nations
Office of Drugs5 are concerned with these substances. Indeed,
the stereochemical determination of MAM is a requirement in
the U.S. since federal sentencing guidelines8 carry a greater
penalty for seizures containing >80% of the (+)-S enantiomer.
There are various routes to the synthesis of MAM, and they are
illustrated in Figure 1. However, the most popular MAM
A
consciousness. This is a result of changes in the functioning of
the central nervous system.1 The pharmacological classification
and effects of psychoactive substances can be divided as follows:2
neuroleptics, depressants, hallucinogens, and stimulants.
Stimulants are drugs that speed up the mind and body. Their
effects resemble those of the body’s natural hormones,
adrenaline. But unlike natural hormones, stimulants can cause
serious harm to the body.3 Because stimulants bring about
subjective changes in consciousness and mood that the user may
find advantageous such as increased alertness or euphoria, many
stimulants are abused and used excessively, despite the health
risks or negative consequences. Recently, one of the most
popular and widely abused within this class is methylamphet-
amine (MAM).
As is reported in the EMCDDA4 (European Monitoring
Centre for Drugs and Drug Addiction) and in the 2011 World
Drug Report,5 MAM is used to some extent in all European
countries (notably the Czech Republic, the Republic of Moldova,
and Slovakia), and is a huge problem worldwide particularly in
Received: March 2, 2012
Accepted: June 4, 2012
Published: June 4, 2012
© 2012 American Chemical Society
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Figure 1. Common methods used to the manufacture of methylamphetamine.
synthetic routes (Birch, Nagai, and Emde method) employ
ephedrine or pseudoephedrine as a precursor.5,9
Impurity analysis for drug profiling has been used to enable the
identification of the synthetic route for MAM manufacture from
ephedrines. For example, route-specific impurities can be
detected by HPLC and GC/MS.15 Chiral analysis of seized
MAM may also be useful, for example, whether the enantiomeric
composition of intermediate suggests that the starting materials
were extracted from pharmaceutical product (single enan-
tiomers), the plant ephedra (mixture of enantiomers), or
perhaps illicit ephedrine synthesized by fermentation pro-
cesses.15 The stereospecific separation of MAM can be
approached using a variety of analytical techniques. The most
commonly used are chromatography techniques: GC, LC,
HPLC, and CE. There have been several reports that use of
chiral stationary phases such as cyclodextrins and chiral
derivatizating reagents greatly facilitates these methods.16 For
example, LeBelle et al.17 investigated the chiral identyfication and
determination of ephedrine, pseudoephedrine, methamphet-
amine, and metecatinone by both GC/MS after derivatization
with (R)-(+)-methoxy-(α)-(trifluoromethyl)phenylacetic acid
and nuclear magnetic resonance using a chiral solvating agent.
GC/MS was shown to be capable of measuring the enantiomeric
ratios of mixtures of these compounds. This study also shows
that the analysis of compounds by NMR is also potentially useful
for drug profiling. NMR spectroscopy has enormous potential
for investigating conformations and configurations in organic
Because the enantiomeric ratio of MAM is closely related with
the optical activity of precursors and reagents used for the
synthesis, this knowledge can provide useful information
concerning the origins and synthetic methods used for illicit
manufacture.10 This information can be utilized for regulation of
the precursors, investigation of the manufacturing sources, and
resultant prevention of abuse. To obtain this information,
analytical techniques which offer a high degree of enantior-
esolution are required.
It is reported that MAM synthesized by Emde contains the
following byproduct: ephedrine, chloroephedrine, cis- and trans-
1,2-dimethyl-3-phenylaziridine, and two unidentified impur-
ities.11,12 The stereochemical relationship of (S)-(+)-MAM to
its initial precursor (1R,2S)-(−)-ephedrine or (1S,2S)-(+)-pseu-
doephedrine is achieved by detection of (1S,2S)-(+)-chlorop-
seudoephedrine or cis-1,2-dimethyl-3-phenylaziridine, and
(1R,2S)-(−)-chloroephedrine or trans-1,2-dimethyl-3-phenyl-
aziridine, respectively (Figure S1).11 Thus, knowledge about
the chiral profile of MAM synthesized by Emde is important and
may be a useful tool for both evidential and intelligence
purposes.13 Therefore, as previously described, to prevent the
production of clandestine MAM, it is important to monitor,
control, and evaluate the precursors of seized MAM.14
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Scheme 1. Synthesis of the Chloro Intermediates of Methylamphetamine
compounds as well as for quantitative analysis which has been
shown by Matsumoto et al.14 1D and 2D hetero- and
homonuclear NMR experiments enable complete assignment
and structural information, and therefore can be useful when
applied to chiral profiling of MAM and its derivatives.15
To create comprehensive characterization of MAM synthe-
sized by the Emde in terms of impurity and chirality profile,
which will provide a link between starting materials and the illicit
MAM synthesized by the clandestine chemist, reference
substances such as ephedrine derivatives and chloro-intermedi-
ates of MAM are required. Presently, pure enantiomers of
ephedrine/pseudoephedrine are commercially available, but the
four enantiomers of chloro intermediates are not available,
meaning that the preparation of these compounds is required,
and thereafter, separation into single enantiomers and
purification is necessary.
analysis was obtained from Acros Organic. Helium and nitrogen
(oxygen free) were supplied by BOC. Four chloroephedrine
derivatives were synthesized by the first step of Emde with
slightly modifications (outlined in Scheme 1).
Synthesis (Scheme 1). Chloro analogues of ephedrine were
synthesized by the method of B. J. Ko et al.11 Analysis was in
agreement with published data for IR20 and melting point.21 The
details are described in the Supporting Information (SI).
Recrystallization Procedure. Recrystallization procedure22
is described in the SI.
IR Analysis. The IR spectra were obtained on a Perkin-Elmer
FT IR spectrometer. Spectra of chloro analogues of ephedrine/
pseudoephedrine have been recorded in the region 4000−400
cm−1. The range (100−0% T) was correct.
Derivatization Procedure. Derivatization procedure was
carried out as described in the SI.
Therefore, the purpose of this study was to investigate the
stereochemical course of part I of the Emde method involving the
synthesis chloroephedrine/chloropseudoephedrine via chlorina-
tion of ephedrine/pseudoephedrine. It is an extension of the
work presented by Allen et al.18 where products and
intermediates of Emde synthesis for MAM were evaluated via
1H NMR. In our research the configuration of the all of possible
enantiomers of chloroephedrine and chloropseudoephedrine
was determined by 1D and 2D NMR and thereafter by GC/MS.
This research was presented at the EUROanalysis 2011 (16th
European Conference on Analytical Chemistry: Challenges in
Modern Analytical Chemistry) in Belgrade.19
NMR Spectroscopy. Resonance spectra were recorded on a
Bruker DPX 400 and Avance 400 NMR. Crystals of
chloroephedrine in 1 mL of CDCl3 containing 1% of TMS
solution were dissolved. The solution was transferred to an NMR
tube, and the spectra were recorded under conventional
conditions.
Chromatography. Analysis was performed on a Hewlett-
Packard 6890 GC and 5973 mass selective detector. Separation
was achieved with a nonpolar capillary column (TR-5MS, 30 m ×
0.25 mm i.d., 0.25 μm, Thermo Scientific, U.K.) with helium as
the carrier gas at a constant flow rate of 1.8 mL/min. The oven
temperature program started at 70 °C for 2 min, was increased to
250 °C at a rate of 10 °C/min, and then held at 300 °C for 2 min.
A 1 μL aliquot of the derivatized sample was injected in the
splitless mode with a purge time of 3 min. The injector and the
GC interface temperatures were maintained at 200 and 250 °C,
respectively. Mass spectra were obtained in the full scan mode
over the range 40−500 m/z.
EXPERIMENTAL SECTION
■
Materials and Chemicals. (1S,2R)-(+)-Ephedrine HCl,
(1R,2S)-(−)-ephedrine HCl, (1S,2S)-(+)-pseudoephedrine,
(1R,2R)-(−)-pseudoephedrine, (S)-(+)-methylamphetamine
HCl, (R)-(−)-deoxyephedrine, thionyl chloride, and trifluoro-
acetic anhydride were purchased from Sigma-Aldrich. Acetone,
chloroform, diethyl ether anhydrous, methanol, and ethyl acetate
were obtained from Fisher Scientific. Ethyl acetate was dried over
type 5A molecular sieve from Sigma-Aldrich prior to use.
Deuterated chloroform containing 1% (v/v) TMS for NMR
RESULTS AND DISCUSSION
■
For the experiment described here, four stereoisomers of
ephedrine as starting materials were used to manufacture
chloroephedrine derivatives by chlorination with thionyl
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chloride. The two chiral centers in these phenethylamines give
rise to four stereoisomers. By convention the enantiomers with
opposite stereochemistry around the chiral centers (1R,2S and
1S,2R) are designated chloroephedrine, while chloropseudoe-
phedrine exhibits the same stereochemistry around the chiral
carbons (1R,2R and 1S,2S).
Three mechanisms for the reaction of alcohols with thionyl
chloride are proposed.18 Typically, the reaction of alcohols with
thionyl chloride proceeds via an internal nucleophilic sub-
stitution (SNi, Figure S-2a). The corresponding alkyl chlorides
are produced. This method is known as Darzan’s process and
involves a two step reaction. First, thionyl chloride reacts with the
alcohol to form an alkyl chloro sulfite, actually forming an
intimate ion pair. Then, the concerted loss of a sulfur dioxide
molecule has taken place, and thereafter, its replacement by the
chlorides which was attached to the sulfite group. SNi results in
final products which retain configuration of starting materials.18
A second possible mechanism is another two-step reaction.
The first step is attack of the oxygen upon the sulfur of thionyl
chloride, which results in displacement of chloride ion. Then,
chloride ion attacks the carbon in bimolecular nucleophilic
substitution (SN2) fashion, resulting in cleavage of the C−O
bond with inversion of configuration (Figure S-2b).18
Another possible route to the synthesis of chloroephedrine
derivatives is a neighboring group mechanism, in which two
successive SN2 reactions (each with inversion of configuration)
take place and the final stereochemistry is retained. First,
inversion takes place when nitrogen attacks and forces out the
leaving group, staying in its own position in molecule. The
second inversion occurs after attacking of chloride.18
Therefore, four different stereoisomers could be expected
during experiment. To differentiate the structure of chloro
intermediates of MAM manufactured by first step of Emde, 1D
and 2 D NMR have been used. To confirm these results, GC/MS
was carried out.
Melting Point and IR Studies. After each synthesis the
melting point was measured and compared favorably with
literature values (Table S-1).18 Completion of the reaction has
also been followed by the IR spectroscopy. IR spectra confirm the
conversion from ephedrine and pseudoephedrine enantiomers
into chloride derivatives of these precursors. The resulting
products do not contain hydroxyl groups but contain the
characteristic peak originating from the chlorine which indicates
that the reaction had occurred (Figure S-3).
Figure 2. 1H NMR spectra of chloro analogue synthesized from
(1R,2S)-(−)-ephedrine.
atoms (Figure 3). The region from 127 to 137 ppm has been
assigned to the carbon resonance of aromatic region, which is
overlapped, with the carbon resonances (Cm, Cp, Co, Ci) of the
aromatic region (C unit). The signals at 14 and 30.5 have been
assigned to the methyl groups (C-3, CH3-TS). The signals at 61
and 63 have been assigned to the methine carbon (C-2, C-1).
The chloro analogues obtained from pseudoephedrine are not
single enantiomers, and can be deduced from the more
complicated 13C NMR and 13C NMR DEPT spectra. The 13C
DEPT NMR revealed 4 methyl, 10 methine, and 2 quaternary
carbon signals for 16 carbon atoms. It can be concluded that two
chloro analogues of ephedrine are present in the sample.
The results of the assignment of 13C NMR and 13C NMR
DEPT spectra of 2a, 2b, 2c, and 2d at room temperature are
summarized in Table 1.
COSY and HSQCED Studies. In Figures 4 and S-4, the
COSY spectra for 2a, 2b, 2c, and 2d are given. The proton
spectrum is plotted along each axis. The COSY spectrum shows a
distinct set of spots on a diagonal, with each spot corresponding
to the same peak on each coordinate axis. Lines have been drawn
to identify the correlations. From the COSY spectrum of 2a we
can see that the protons of the methyl group (c) correlate with
the methine proton (d). We can also see the correlation between
methine proton (d) and another methine proton (b). The
methyl group of the amine moiety (e) does not show off-diagonal
peaks. COSY spectra for 2c and 2d are more complicated.
Although the same correlation of corresponding protons can be
seen, it also shows that each proton signal is doubled indicating
the presence of two stereoisomers of chloroephedrine.
1H NMR Studies. NMR analysis was used to probe the
conformations of the chloroephedrine derivatives (2a, 2b, 2c,
2d) in solution. In spectra obtained for 2a and 2b there were six
proton signals (described in SI). Considering these signals, the
following structure (Figure 2) of sample analyzed can be
deduced.
The spectra obtained for 2c and 2d show a different situation.
Each proton signal is doubled which means that two stereo-
isomers are present in the sample. The signals of appropriate
compounds are described in SI.
1H−13C HSQC NMR spectra were obtained to determine the
direct carbon−proton bonds. The proton spectrum is plotted
along the x axis, while the carbon spectrum is plotted on the y
axis. Application of a 1H−13C HSQC pulse sequence allows the
user to overcome the broad overlapping peaks in a one-
dimensional proton spectra by dispersing the signals into the
second 13C dimension. 1H−13C HSQC NMR spectra are given in
Figure 5. Lines have been drawn, and each hydrogen and carbon
has been marked in order to facilitate the identification of
correlations.
In the spectrum obtained for 2a and 2b the correlations
between C1−H6, C2−H10, C3−H7,8,9, CH3-Ts-H12,13,14,
Co,Cp,Cm-H1,2,3,4,5 are clearly observed. From the spectrum
obtained for 2c and 2d, it can be seen that in the sample two
stereoisomers of chloroephedrine are present. From a compar-
ison of all the NMR data it can be concluded that samples 2a and
2b are single stereoisomers of chloroephedrine; product 2c
13C NMR and DEPT Studies. For structure elucidation of the
chloroephedrine derivatives, a series of NMR experiments
including COSY, NOESY, DEPT were carried out. In the case
of 2a, 2b compounds, there was the appearance of eight carbons
in the 13C NMR by DEPT experiments (Table 1). The spectra
showed two methyl group proton signals, five methine signals,
and additional one quaternary carbon signal coming from the
aromatic ring. The 13C DEPT NMR revealed two methyl, five
methine, and one quaternary carbon signals for eight carbon
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Table 1. 13C NMR and DEPT NMR
13C NMR
DEPT
2c
2a
2b
2c
2d
2a
2b
2d
C-1
C-2
C-3
CH3-Ts
Ci
62.8742
61.0642
13.9854
30.4291
136.9013
129.2722
129.6382
127.7558
62.8653
61.0646
13.9829
30.4186
136.8974
129.2734
129.6422
127.7554
62.6623; 62.8305
60.8687; 61.0269
10.3556; 13.9821
30.4684; 31.0392
136.3145; 136.9113
128.8705; 129.2668
128.9950; 129.6301
127.4584; 127.7645
62.6659; 62.8395
60.8677; 61.0368
10.3713; 13.9829
30.4583; 31.0481
136.3163; 136.9189
128.8715; 1292679
128.9975; 129.6313
127.4585; 127.7643
CH
CH
CH3
CH3
CH
CH
CH
C
CH
CH
CH3
CH3
CH
CH
CH
C
CH; CH
CH; CH
CH3; CH3
CH3; CH3
CH; CH
CH; CH
CH; CH
C; C
CH; CH
CH; CH
CH3; CH3
CH3; CH3
CH; CH
CH; CH
CH; CH
C; C
Cp
Co
Cm
After analysis of 1D SELNOESY spectra obtained for 2a and
2b, it may be deduced that conversion of 1a/1b to the chloro
analogues occurred with inversion of configuration around the α
atom to give one enantiomer, (1S,2S)-(+)-chloropseudoephe-
drine/(1R,2R)-(−)-chloropseudoephedrine, respectively, which
is in accordance with an SN2 mechanism. To confirm these
results, GC/MS analysis was carried out.
Figure 3. Structure of chloro intermediates of methylamphetamine with
marked carbon atoms.
All the NMR data showed that in the sample synthesized from
c two stereoisomers are present. The first is the same as
determined in the sample synthesized from 1a, that is (1S,2S)-
(+)-chloropseudoephedrine. The second diastereoisomer was
determined as (1R,2S)-(−)-chloroephedrine, because we
observed (1) large NOE correlation between H-e and H-c,
large correlation between H-e and H-d, H-e proton close to
amine group; (2) strong NOE correlation between H-c and H-d,
large correlation between H-c and H-b, and large correlation
between H-c and H-e; (3) strong NOE correlation between H-b
and H-a, large correlation between H-b and H-d, and weak
correlation between H-b and H-e.
Analysis of 1D SELNOESY spectra showed that conversion of
1c/1d to the chloro analogues occurred with inversion and
retention of configuration around the α atom to give two
stereoisomers, (1R,2S)-(−)-chloroephedrine and (1S,2S)-
(+)-chloropseudoephedrine/(1S,2R)-(+)-chloroephedrine and
(1R,2R)-(−)-chloropseudoephedrine, respectively, in accord-
ance with SN2 and SNi mechanisms. To confirm these results, the
GC/MS analysis was carried out.
contains two stereoisomers of chloroephedrine, one of which is
identical to sample 2a; and product 2d contains two stereo-
isomers of chloroephedrine, one of which is identical to sample
2b.
SELNOESY Studies. To determine the mutual position/
distance of protons in space, 1D SELNOESY NMR spectra were
obtained by irradiating the anomeric proton signals H-e, H-c, H-
b (more details in SI).
The NMR data from 1D SELNOESY showed that the
compound synthesized from 1a was (1S,2S)-(+)-chloropseu-
doephedrine, because we observed (1) large NOE correlation
between H-e and H-c, large correlation between H-e and H-d,
and weak correlation between H-e and H-b, H-e proton close to
amine group; (2) strong NOE correlation between H-c and H-d,
large correlation between H-c and H-e, and H-b, and weak
correlation between H-c and H-a; (3) strong NOE correlation
between H-b and H-a, large correlation between H-b and H-c,
weak correlation between H-b and H-e, and any NOE correlation
between H-b and H-d.
GC-MS Analysis. GC/MS was carried out for qualitative
analysis of synthesized analysis. Standards of the precursors,
Figure 4. COSY NMR spectra obtained for (a) 2a and (b) 2d.
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Figure 5. HSQC NMR spectra of chloro analogue obtained from (a) 1a and (b) 1d.
MAM, and samples 2a, 2b, 2c, 2d were trifluoroacetylated and
analyzed individually. Retention times and mass-to-charge ratios
are presented in Table S-2. Chromatograms and mass spectra
obtained for 2a and 2d are shown in Figures 6 and 7.
ance with SN2 and SNi mechanisms (Figure 9). The ratio of these
diastereomers is different in comparison with literature values
(Allen et al.18); however, the synthesis reaction in our work was
carried out under different conditions (differences in the amount
of reagents used, temperatures, time of synthesis, type of
recrystallization) since a slight modification of synthesis in our
work has been made. Moreover, the GC/MS data shows that one
unidentified product was formed during synthesis (the mass
spectral base peak of m/z 121).
CONCLUSION
■
Four stereoisomers of ephedrine as precursors were used to
manufacture chloroephedrine derivatives by chlorination with
thionyl chloride. After each synthesis, melting point, weight, and
IR spectra were obtained. Melting point was compared with
literature values, and in each case, values were consistent. IR
spectra confirm the conversion from ephedrine into chloro-
derivatives. The resulting products lack hydroxyl groups but
contain the characteristic peak originating from the chlorine
which indicates that the reaction had occurred.
1D NMR analysis was used to probe the conformations of the
Figure 6. Chromatogram of analytes. Analytes are trifluoroacetylated
derivatives of (a) (1R,2S)-(−)-ephedrine, (b) (1R,2R)-(−)-pseudoe-
phedrine.
1
chloroephedrine derivatives in solution. The H, 13C, DEPT,
COSY, and HSQC NMR spectra illustrate that depending on the
precursor used it is possible to obtain a single enantiomer or a
mixture of enantiomers. One-dimentional SELNOESY NMR
data illustrate that conversion of ephedrine enantiomers to the
chloro analogues occurred with inversion of configuration
around the α atom to give one enantiomer, chloropseudoephe-
drine; however, the GC/MS result showed that mixture of
diastereomers (1% chloroephedrine and 99% chloropseudoe-
phedrine) is formed during this synthesis. Both NMR and GC/
MS results obtained for samples manufactured from pseudoe-
phedrines showed that conversion of pseudoephedrines to the
chloro analogues occurred with inversion and retention of
configuration around the α atom to give mixture of two: 20%
chloroephedrine and 80% chloropseudoephedrine. Therefore,
the ratio of the resulting compounds was dependent on
precursors used. Moreover, the GC/MS data demonstrated
that one impurity was formed during synthesis.
After analysis of GC/MS spectra, different conclusions than
from NMR analysis may be deduced because, as is shown in
Figure 6, all of the batches contained two diastereomers, while
NMR only shows two products obtained from pseudoephedrine
enantiomers. Therefore, the chlorination of ephedrine enan-
tiomers does not follow SN2 completely as was shown in NMR,
and in fact, a mixture of chloropseudoephedrine and
chloroephedrine was determined, implying a mixture of SN2
and SNi. Although the chlorination of pseudoephedrine
enantiomers also occurred in accordance with SN2 and SNi
mechanisms to give a mixture of chloroephedrine and
chloropseudoephedrine, the ratio of distereomers in 2a, 2b, 2c,
2d was dependent on precursors used for the synthesis. And so,
the conversion of 1a/1b to the chloro analogues occurred with
inversion and retention of configuration around the α atom to
give a mixture of 99% chloropseudoephedrine and 1%
chloroephedrine (Figure 8). Conversion of c/d to the chloro
analogues occurred also with inversion and retention of
configuration around the α atom to give mixture of 20%
chloroephedrine and 80% chloropseudoephedrine, in accord-
The use of NMR and GC/MS analysis allowed the
determination of conformations and configurations of manufac-
tured chloroephedrine derivatives, and important and commer-
cially unavailable chloro intermediates of methylamphetamine
synthesized by the Emde method.
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Figure 7. Mass spectra of compound determined in 2a-TFAA. (a) (1S,2S)-(+)-Chloropseudoephedrine-TFAA. (b) (1R,2R)-(−)-Chloropseudoephe-
drine-TFAA. (c) Unidentified-TFAA.
Figure 9. Reaction of (a) (1S,2S)-(+)-pseudoephedrine and (b)
(1R,2R)-(−)-pseudoephedrine with thionyl chloride.
Figure 8. Reaction of (a) (1R,2S)-(−)-ephedrine and (b) (1S,2R)-
(+)-ephedrine with thionyl chloride.
NMR spectroscopy is one of the most powerful non-
destructive analytical techniques that provides direct information
on the structure of compounds, but it is not as sensitive as the
GC/MS technique, as can been seen with detection of the 1%
diastereomeric impurity produced from ephedrine enantiomers
by GC/MS. Because 2D NMR is needed to fully elucidate the
stereoisomers, both techniques were necessary to determine
chiral composition of synthesized samples. The combination of
NMR and GC/MS should be considered as a suitable approach
for chiral analysis of other compounds and useful for various
fields which require accurate stereochemical data. The examples
here are secondary amines required for forensic purposes, but
can be equally applied to molecules of interest to pharmaceutical
and general analytical science.
ASSOCIATED CONTENT
* Supporting Information
■
S
Additional information as indicated in text. This material is
available free of charge via the Internet at http://pubs.acs.org.
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dx.doi.org/10.1021/ac300503g | Anal. Chem. 2012, 84, 5625−5632

Analytical Chemistry
Article
AUTHOR INFORMATION
Corresponding Author
*E-mail: plotkajustyna@gmail.com. Phone: +48 58 347-21-10.
Fax: +48 58 347-26-94.
■
Notes
The authors declare no competing financial interest.
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