Synthesis and capillary electrophoretic analysis of enantiomerically enriched reference standards of MDMA and its main metabolites

Article abstract of DOI:10.1016/S0968-0896(01)00367-4

Enantiomerically-enriched (S)-3,4-methylenedioxymethamphetamine (MDMA) and its main metabolites (S)-4-hydroxy-3-methoxymethamphetamine (HMMA) and (S)-3,4-dihydroxymethamphetamine (HHMA) were prepared or unequivocal identification of the differential enantioselective metabolism of these compounds as well as for its application in the analysis of biological samples. Capillary electrophoresis with cyclodextrin derivatives and a chemical correlation of (S)-MDMA, (S)-HMMA and (S)-HHMA has been performed to assign the absolute stereochemistry of major isomers in analytical standards enriched with such enantiomers. Copyright

Full text of DOI:10.1016/S0968-0896(01)00367-4

Bioorganic & Medicinal Chemistry 10 (2002) 1085–1092
Synthesis and Capillary Electrophoretic Analysis of
Enantiomerically Enriched Reference Standards of
MDMA and its Main Metabolites
Nieves Pizarro,a Rafael de la Torre,a Magı Farre,a Jordi Segura,a
Amadeu Llebariab and Jesus Joglarb,*
a
´
`
Pharmacology Research Unit, Institut Municipal d’Investigacio Medica (IMIM), Doctor Aiguader 80, E-08003 Barcelona, Spain
bDepartment of Biological Organic Chemistry, IIQAB-CSIC, Jordi Girona 18-26, E-08034 Barcelona, Spain
Received 9February 2001; accepted 15 October 2001
Abstract—Enantiomerically-enriched (S)-3,4-methylenedioxymethamphetamine (MDMA) and its main metabolites (S)-4-hydroxy-
3-methoxymethamphetamine (HMMA) and (S)-3,4-dihydroxymethamphetamine (HHMA) were prepared for unequivocal identi-
fication of the differential enantioselective metabolism of these compounds as well as for its application in the analysis of biological
samples. Capillary electrophoresis with cyclodextrin derivatives and a chemical correlation of (S)-MDMA, (S)-HMMA and (S)-
HHMA has been performed to assign the absolute stereochemistry of major isomers in analytical standards enriched with such
enantiomers. # 2002 Elsevier Science Ltd. All rights reserved.
Introduction
shown that capillary electrophoresis (CE) using (2-
hydroxypropyl)-b-cyclodextrin as enantioselective selec-
tor provided an efficient baseline separation of these
enantiomers.3 However, unequivocal identification of
elution order of enantiomers is indispensable to char-
acterize the results obtained from the analysis of biolo-
gical samples. Although two syntheses of (S)-MDMA
are already described in the literature,4 preparation of
the enantiomers of HMMA and HHMA has not been
performed. Accordingly, a study was conducted to
undertake the synthesis of standards of MDMA,
HMMA and HHMA enriched in its S enantiomer. The
synthetic chemistry leading to these standards and the
chemical correlation used for enantiomer identification
in the CE peaks are here reported.
3,4-Methylenedioxymethamphetamine(MDMA,‘ecstasy’)
is an illicit drug frequently misused by the youth, and
potentially associated with acute and long-term effects.
MDMA is available as its racemate (R,S)-MDMA but
different pharmacological properties for each enantio-
mer have been reported. Acute effects of MDMA that
ultimately may be the cause of death1 are related to
sympathetic hyperactivity in the neural and cardiovas-
cular systems. Neurotoxicity and some psychomimetic
properties are related to the (S)-isomer.2 Body disposi-
tion of MDMA is also subjected to selective enantiomeric
metabolism. Well characterized metabolites of MDMA
include 3,4-methylenedioxyamphetamine (MDA), 4-
hydroxy-3-methoxymethamphetamine (HMMA) and 4-
hydroxy-3-methoxyamphetamine (HMA). 3,4-Dihy-
droxyamphetamine (HHA) and 3,4-dihydroxymeth-
amphetamine (HHMA) are metabolic intermediates.
Analysis of the enantiomeric ratio of major MDMA
metabolites in human samples is desirable given the
pharmacological relevance of the enantioselectivity of
MDMA, HHMA and HMMA. We have recently
Results and Discussion
Synthesis of (S)-HHMA was originally planned as pre-
viously described5 using the key intermediate (S)-(3,4-
dibenzyloxyphenyl)-2-propanamine
1 and expecting
transformation of 1 into HHMA by N-monomethylation
followed by hydrogenolytic debenzylation. Racemic 1
was prepared from commercially available 3,4-dibenzy-
loxybenzaldehyde upon condensation with nitroethane
followed by reduction with lithium aluminium hydride
*Corresponding author. Tel:+34-93-4006115; fax: +34-93-2045904;
e-mail: joglar@iiqab.csic.es
0968-0896/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(01)00367-4

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N. Pizarro et al. / Bioorg. Med. Chem. 10 (2002) 1085–1092
.
Scheme 1. Synthesis of enantiomerically enriched (S)-HHMA HCl. a: 1) CH3CO2NH4; 2) LiAlH4; b: resolution; c: ClCO2Et; d: 1) LiAlH4; 2) HCl;
e: H2, Pd-C, MeOH.
(see Scheme 1). Reaction of amine 1 with an equimolar
amount of dibenzoyl-d-(+)-tartaric acid gave rise to a
crystalline diastereomeric salt that after a single crystal-
lization step with methanol resulted in a compound with
an [a]2D0 +65.8 (c 0.84, methanol). The optical rotation
sign of this compound was opposed to that reported by
Pratesi et al. ([a]2D0 À62.9( c 0.78, methanol)].5 This
result, however, was confirmed by treating the salt with
1 N NaOH giving rise to a recovered amine 1 with an
[a]2D0 À6.4 (c 1.8, chloroform) that also had an optical
rotation sign opposed to that reported in the literature
for 1 [a]2D0 +12.6 (c 3.7, chloroform)].5
and cesium carbonate in anhydrous N,N-dimethyl-
formamide.
Finally, reduction with lithium aluminium hydride and
subsequent hydrochloride formation yielded (S)-(+)-
20
.
MDMA HCl with an optical rotation of [a]D +15.2 (c
0.79, H2O). Analysis of this compound by CE gave a
77% ee, confirming that the synthesised (S)-N-methyl-1-
[(S)-HHMA]
(3,4-dihydroxyphenyl)-2-aminopropane
had the expected S configuration.
On the other hand, synthesis of (S)-HMMA (see
Scheme 3) was accomplished following an asymmetric
synthesis described for similar compounds.6 Condensa-
tion of the commercially available 4-benzyloxy-3-meth-
oxybenzaldehyde with nitroethane, followed by
reduction with iron metal in aqueous HCl resulted in
ketone 6.7 Reductive amination of 6 with (S)-a-methyl-
benzylamine and sodium cyanoborohydride gave rise to
amine 7 as a 67:33 mixture of diastereomers. Methyl-
ation of amine 7 with iodomethane and sodium car-
bonate provided the corresponding N-methylamine as a
mixture of two diastereomers. They were partially
Resolution of 1 with dibenzoyl-l-(À)-tartaric acid was
assessed. Products with specific sign and rotation values
consistent with those obtained for resolution of 1 with
dibenzoyl-d-(+)-tartaric acid5 were recovered. More-
over, repeated re-crystallization of the salt formed from
1 with dibenzoyl-l-(À)-tartaric acid resulted in a very
slight enrichment after three steps. For this reason,
synthesis of HHMA with the enantioenriched amine 1
was continued. Thus, (S)-(3,4-dibenzyloxyphenyl)-2-
propanamine was converted to the corresponding car-
bamate 2 by reaction with ethyl chloroformate. Reduc-
tion with lithium aluminium hydride and subsequent
treatment with an ethereal solution of hydrogen chlo-
ride resulted in N-methylamine 3 as its hydrochloride
salt. Hydrogenation with a catalytic amount of palla-
.
dium on charcoal yielded (S)-HHMA HCl with an 80%
.
ee. A sample of racemic HHMA HCl was also prepared
from racemic 1-(3,4-dibenzyloxyphenyl)-2-propanamine
1 following the same synthetic scheme.
A chemical correlation with (S)-MDMA4 was per-
formed in order to determine the stereochemistry of
.
(S)-HHMA HCl. (S)-MDMA was prepared from a
common intermediate to the previously synthesized
(S)-HHMA (Scheme 2). Thus, hydrogenation of (S)-N-
ethoxycarbonyl-1-(3,4-dibenzyloxyphenyl)-2-aminopro-
pane 2 with a catalytic amount of Pd/C resulted in
(S)-N-ethoxycarbonyl-1-(3,4-dihydroxyphenyl)-2-ami-
nopropane 4. The corresponding (S)-N-ethoxycarbonyl-
.
Scheme 2. Chemical correlation of (S)-HHMA HCl with (S)-
.
MDMA HCl. a: 1) LiAlH4, 2) HCl; b: H2, Pd-C, MeOH; c: BrCH2Cl,
CsCO3.
1-(3,4-methylenedioxyphenyl)-2-aminopropane 5 was
obtained after treatment with bromochloromethane

N. Pizarro et al. / Bioorg. Med. Chem. 10 (2002) 1085–1092
1087
.
Scheme 3. Synthesis of enantiomerically enriched (S)-HMMA HCl. a: 1) CH3CO2NH4; 2) Fe, HCl-H2O; b: (S)-a-methylbenzylamine, Na BH4 CN;
c: 1) CH3L, Na2CO3; 2) chromatography separation; d: 1) HCl; 2) H2, Pd-C, MeOH.
Conclusion
separated by flash column chromatography yielding a
fraction enriched in the (S,S)-isomer 8. After hydro-
chloride formation, hydrogenolysis provided the corre-
sponding (S)-HMMA hydrochloride with a 72% ee as
determined by CE analysis.
This is the first report describing the synthesis and che-
mical correlation of enantioenriched (S)-MDMA, (S)-
HHMA and (S)-HMMA. Although these methods
would probably allow the preparation of higher enan-
tiomerically pure compounds, it was considered this
unnecessary for the current objectives of the present
study, and irrelevant from an analytical point of view.
The availability of the newly synthesized enantiomeric
enriched metabolites of MDMA are crucial for ongoing
an future studies on in vivo differential metabolism of
MDMA enantiomers and their role in the neurotoxicity
and other pharmacological effects of MDMA in
humans.
.
The stereochemistry of synthetic (S)-HMMA HCl was
confirmed by correlation with HHMA and MDMA.
Thus, reaction of (S)-N-methyl-1-(3,4-dihydroxyphenyl)-
.
2-aminopropane hydrochloride [(S)-HHMA HCl] with
an ethereal solution of diazomethane provided the enri-
ched (S)-isomer of N-methyl-1-(3,4-dimethoxyphenyl)-2-
.
aminopropane hydrochloride [(S)-MMMA HCl] 9 (see
Scheme 4) and the same reaction was performed with
.
synthetic (S)-HMMA HCl. Comparison of the results
obtained from enantioselective capillary electrophoresis
.
analysis of MMMA HCl 9 from both sources confirmed
that both compounds had the same configuration (see
Fig. 1).
Experimental
General methods
To determine the elution order of the enantiomers of the
synthesised compounds and the enantiomeric excess for
(S)-MDMA, (S)-HHMA and (S)-HMMA, CE analysis
was performed following the method developed by
our group.3 Thus, for each analyte, separate analysis
was performed for the racemic mixture and the syn-
thesized enantioenriched material. In all cases, (S)-
enantiomers eluted after the (R)-enantiomers (see Fig.
1).
Reactions sensitive to moisture were carried out under
Ar atmosphere. Commercial grade reagents were used
directly without further purification (unless otherwise
indicated). Solvents were dried by standard methods
and distilled before use. Purification of products by
column chromatography was performed on Merck silica
gel 60. TLC was carried out on precoated silica gel
Merck 60 F254 (0.25 mm) sheets. IR spectra were recor-
.
Scheme 4. Chemical correlation of (S)-HHMA HCl and (S)-HMMA HCl with (S)-MDMA HCl. a: CH2N2-Et2O.
.
.

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N. Pizarro et al. / Bioorg. Med. Chem. 10 (2002) 1085–1092
Figure 1. Capillary electropherograms for racemic and enantioenriched samples of HHMA, HMMA, MDMA and MMMA. (A) Top: (R,S)-
HHMA; bottom: enriched (S)-HHMA; (B) top: (R,S)-HMMA, bottom: enriched (S)-HMMA; (C) top: (R,S)-MDMA; bottom: enriched (S)-
MDMA; and (D) top: (R,S)-MMMA, middle: enriched (S)-MMMA from (S)-HMMA, bottom: enriched (S)-MMMA from (S)-HHMA.
ded on a Michelson Bomem MB-120 with Fourier
1
methylsiloxane
capillary
column
(12 mÂ0.2 mm
transform instrument and are reported in cmÀ1. H and
I.D.Â0.3 mm film thickness) (HP, Ultra-2) was
employed, with helium as the carrier gas at a flow rate
of 1.2 mL/min. The oven was maintained at 100 ꢀC for
1 min and two cycles were programmed, from 100–
200 ꢀC at 10 ꢀC/min followed by 200–280 ꢀC at 30 ꢀC/
min (total run time 13.67 min). Samples were injected in
the split mode. Insert liners packed with silanized glass-
wool were used. Injector and interface were set at
280 ꢀC. The mass spectrometer was operated by electron
impact ionisation (E.I., 70 eV) and in the scan mode
(working range 100–550 amu).
13C NMR spectra were obtained in CDCl3 Solutions
(unless otherwise indicated) on a Varian Gemini XL200
and a Varian Unity 300 spectrometers, operating at 200
and 300 MHz for 1H and 50 and 75 MHz for 13C,
respectiviely. Chemical shifts are reported in delta (d)
units, parts per million (ppm) downfield from (CH3)4Si,
or in ppm relative to the singlet at 7.26 ppm of CDCl3
1
for H and in ppm relative to the centre line of a triplet
1
at 77.0 ppm of CDCl3 for 13C. H NMR: splitting pat-
tern abbreviations include the following: s, singlet; bs,
broad singlet; d, doublet; t, triplet; q, quartet; m, multi-
plet. 13C NMR: multiplicities were determined by
DEPT experiments using standard pulse sequences. In
case of a mixture of diastereomers, abbreviations ‘min’
and ‘maj’ refer to signals of the minor and major dia-
stereomer, respectively; when no specification is men-
tioned, it either has not been possible to assign the
signal to any diastereomer or belongs to both of them.
Trifluoroacyl derivatives of each enriched forms were
analysed by GC–MS for assessing the purity of all syn-
thesized standards. Methanolic solutions of every race-
mic and enriched form were allowed to react with an
appropriate amount of N-methyl-bis(trifluoroace-
tamide) (MBTFA) at 70 ꢀC for 45 min, and the corre-
sponding N-TFA and/or O-TFA derivatives were
obtained.
A 341 Perkin-Elmer polarimeter was used for optical
rotatory measures. A gas chromatograph (HP 6890 ser-
ies GC system, Hewlett-Packard, Palo Alto, CA, USA)
equipped with a quadrupole mass spectrometer (HP
5973 mass selective detector) and an autosampler (5683
series injector) was used. A cross-linked 5% phenyl-
A capillary electrophoresis system (3DCE, Hewlett-
Packard) equipped with a diode-array detector was
employed for the enantiomeric separation. Separation
was performed in an untreated fused-silica capillary of
48.5 cm total length (40 cm effective length) and a stan-

N. Pizarro et al. / Bioorg. Med. Chem. 10 (2002) 1085–1092
1089
dard 50 mm optical path length cell. A constant voltage
of 30 kV was applied and the cartridge temperature was
maintained at 15 ꢀC. The diode-array detector was set to
monitor the signal at 204 nm. (2-Hydroxypropyl-b-
cyclodextrin (Hewlett-Packard CE grade 97+%. Part #
8501-0133) in 50 mM H3PO4 (pH=2.5) at a concentra-
tion of 50 mM as running buffer was used for the
enantioselective separation of the enantiomers, with
50 mM H3PO4 for 1.5 min and running buffer for 1 min
as preconditioning conditions before each experiment.
Injection of the sample was performed by applying
external pressure of 50 mbar for 2 s.
(A of an ABX syst., J=8.2, 13.4 Hz, 1H), 2.61 (B of an
ABX syst., J=5.0, 13.4 Hz, 1H), 3.01–3.12 (X of an ABX
syst., m, 1H), 5.15 (s, 2H), 5.17 (s, 2H), 6.68–6.90 (m,
3H), 7.28–7.47 (m, 10H). 13C NMR (75 MHz; CDCl3,
d): 23.4, 46.0, 48.4, 71.2, 71.4, 115.1, 116.4, 122.1, 127.2,
127.3, 127.6, 127.7, 128.4, 133.1, 137.2, 137.4, 147.4,
148.6.
(S)-1-(3,4-Dibenzyloxyphenyl)-2-aminopropane.5 10 g of
racemic 1-(3,4-dibenzyloxyphenyl)-2-aminopropane was
placed in a 500 mL round bottom flask containing
250 mL of boiling methanol, and 10 g of dibenzoyl-l-
(À)-tartaric acid was added. Once the solution reached
the room temperature, it was stored in the refrigerator
for about one week until the crystals precipitated.
Crystals were filtered, washed with cool methanol and
dried achieving a total amount of 9.48 g. The crystals
were dissolved in 50 mL of dichloromethane and treated
with 15 mL of 1 N NaOH aqueous solution. The organic
layer was decanted and the aqueous layer extracted with
dichloromethane (3Â5 mL). The combined organic
phases were dried over anhydrous Na2SO4 to obtain the
free amine. After two repetitions of these steps 3.90 g of
salt with an [a]2D0 À59.5 (c 0.82, methanol) were obtained
[literature:5 [a]D20 À59.3 (c 0.84, methanol) for the salt of
the dibenzoyl-d-(+)-tartaric acid]. After treatment with
base, it yielded 1.44 g of (S)-1-(3,4-dibenzyloxyphenyl)-
2-aminopropane with an [a]2D0 +10.89( c 3.35, chloro-
form) [literature:5 [a]2D0 +15.1 (c 3.4, chloroform)].
Synthesis of enantiomerically enriched (S)-N-methyl-1-
(3,4-dihydroxyphenyl)-2-aminopropane [(S)-3,4-dihydroxy
methamphetamine, (S)-HHMA]
1-(3,4-Dibenzyloxyphenyl)-2-nitropropene. This com-
pound was synthesized following the method described
by Glennon et al.8 3,4-Dibenzyloxybenzaldehyde (10 g,
30.77 mmol), nitroethane (150 mL) and ammonium ace-
tate (2.47 g, 30.77 mmol) were dissolved in a 250 mL
round bottom flask and the mixture heated at reflux for
17 h. Nitroethane was then removed with a Buchi rotary
evaporator and the solid residue was taken up in
250 mL of ethyl acetate and then washed with water
(2Â40 mL) and brine (40 mL). The organic layer was
dried over anhydrous MgSO4 and filtered. The solvent
was removed and 1-(3,4-dibenzyloxyphenyl)-2-nitro-
propene as a yellow powder (11.08 g, 29.55 mmol, 96%
yield) was obtained. IR (neat, nmax cmÀ1): 1600, 1523,
(S)-N-Ethoxycarbonyl-1-(3,4-dibenzyloxyphenyl)-2-ami-
nopropane (2). Carbamate 2 was synthesized as descri-
bed by Yousif et al.9 Again, 10 mL of anhydrous THF,
1.24 g (3.57 mmol) of (S)-1-(3,4-dibenzyloxyphenyl)-2-
aminopropane, 1.1 mL (7.14 mmol, 2 equiv) of triethy-
lamine and 6.74 mg (0.06 mmol, 0.01 equiv) of 4-(dim-
ethylamino)pyridine (DMAP) were placed in an ice
cooled 100 mL round bottom flask under an argon
atmosphere and continuous stirring. A solution of ethyl
chloroformate (0.66 mL, 6.95 mmol, 2 equiv) in 10 mL
of anhydrous THF was slowly added, and the mixture
left at room temperature for 6 h. The residue was dis-
solved in diethyl ether (60 mL) and washed with 20 mL
of water. Ether was decanted and the aqueous phase
extracted with diethyl ether (2Â25 mL). The combined
organic extracts were washed with water (10 mL), HCl
1 N (20 mL) and saturated NaCl (10 mL), dried over
anhydrous Na2SO4, and evaporated to obtain 1.22 g
(2.90 mmol, 81%) of (S)-N-ethoxycarbonyl-1-(3,4-
dibenzyloxyphenyl)-2-aminopropane 2 as a white solid.
1H NMR (300 MHz; CDCl3): d 1.03 (d, 3H), 1.24 (t,
3H), 2.57 (A of an ABX syst., J=7.2, 13.5 Hz, 1H), 2.75
(B of an ABX syst., J=5.4, 13.5 Hz, 1H), 3.80–3.96 (X
of an ABX syst., m, 1H), 4.10 (q, 2H), 5.14 (s, 2H), 5.16
(s, 2H), 6.67–6.88 (m, 3H), 7.28–7.47 (m, 10H). 13C
NMR (75 MHz; CDCl3): d 14.6, 20.0, 42.2, 47.7, 60.5,
71.2, 71.3, 115.0, 116.5, 122.4, 127.2, 127.3, 127.6, 127.7,
128.4, 131.3, 137.2, 137.4, 147.6, 148.6, 155.8.
1
1510, 1454, 1317, 1269, 1236, 1141, 1022, 860, 696. H
NMR (300 MHz; CDCl3, d): 2.31 (s, 3H), 5.22 (s, 2H),
5.24 (s, 2H), 6.96–7.01 (m, 3H), 7.32–7.49 (m, 10H),
7.98 (s, 1H). 13C NMR (75 MHz; CDCl3, d): 13.9, 70.8,
71.3, 114.1, 116.6, 124.8, 125.2, 127.0, 127.1, 127.9,
128.0, 128.5, 128.6, 133.6, 136.5, 136.7, 145.9, 148.4,
150.6.
1-(3,4-Dibenzyloxyphenyl)-2-aminopropane. According
to a method previously described,8,9 100 mL of anhy-
drous tetrahydrofurane (THF) and LiAlH4 (2.5 g,
62.5 mmol) were introduced into a three-neck round
bottom flask, previously evacuated (equipped with a
thermometer, a dropping funnel with pressure-equalisa-
tion arm, and a septum) under an argon atmosphere
and with continuous stirring, placed in an ice bath.
A solution of 11.08 g (29.55 mmol) of 1-(3,4-dibenzy-
loxyphenyl)-2-nitropropene in 75 mL of anhydrous
THF was transferred to the dropping funnel via can-
nula. Its addition over the LiAlH4 suspension was
slowly and carefully performed so that the temperature
did not exceed 15 ꢀC. Once the addition was complete,
the funnel was changed to a condenser and the resulting
mixture was refluxed and stirred for 4 h and cooled to
room temperature followed by an ice bath. LiAlH4
excess was removed by careful dropwise addition of water
and then treated with anhydrous Na2SO4. After filtration,
the solution was concentrated and dried yielding 1-(3,4-
dibenzyloxyphenyl)-2-aminopropane 1, 7.1 g (19.97 mmol,
71% yield) as a pale yellow powder. 1H NMR
(300 MHz; CDCl3, d): 1.07 (d, 3H), 1.20 (bs, 2H), 2.38
(S)-N-Methyl-1-(3,4-dibenzyloxyphenyl)-2-aminopropane
hydrochloride (3). This reaction has been previously
described.9 In this case, 11 g of LiAlH4 (2.86 mmol, 3
equiv) and 6 mL of anhydrous THF were added in a

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N. Pizarro et al. / Bioorg. Med. Chem. 10 (2002) 1085–1092
three-neck round bottom flask, previously evacuated
and filled with argon (equipped with a thermometer, a
dropping funnel with pressure-equalization arm, and a
septum) and placed on an ice bath. A solution of car-
bamate 2 (0.4 g, 0.95 mmol) in 18 mL of anhydrous
THF was slowly added through the dropping funnel
controlling to keep the temperature below 15 ꢀC. When
the addition was done, the funnel was exchanged by a
condenser and the resulting mixture was refluxed and
stirred for 18 h, obtaining a grey suspension. The
LiAlH4 excess was destroyed by addition of water (drop
by drop) and then of anhydrous Na2SO4. The resulting
solid was filtered, washed with diethyl ether (2Â25 mL)
giving rise to a colorless solution. This solution was
concentrated and dried under vacuum yielding an oil
that was purified by column chromatography (silica gel)
using dichloromethane/methanol (1500 mL, 9:1, v/v). A
total of 264.1 mg (0.73 mmol, 78% yield) of colorless oil
475 mg (2.18 mmol, 54% overall yield) of racemic
N-methyl - 1 - (3,4 - dihydroxyphenyl) - 2 - aminopropane
.
hydrochloride (HHMA HCl) were obtained starting
from 880 mg (2.76 mmol) of 3,4-dibenzyloxybenzald-
ehyde.
Synthesis of enantiomerically enriched (S)-(3,4-methyl-
enedioxyphenyl)-2-aminopropane hydrochloride [(S)-3,4-
methylenedioxymethamphetamine, (S)-MDMA]
(S)-N-Ethoxycarbonyl-1-(3,4-methylenedioxyphenyl)-2-
aminopropane (5).10 In a round bottom flask were dis-
solved 373 mg (0.89mmol) of ( S)-N-ethoxycarbonyl-1-
(3,4-dibenzyloxyphenyl)-2-aminopropane 2 in 8 mL of
methanol. A catalytic amount of Palladium 10 wt. % on
carbon powder was added and hydrogenation was per-
formed as usual. After the workup were obtained
202 mg (0.84 mmol, 95% yield) of (S)-N-ethoxy-
1
was obtained. H NMR (CDCl3, 300 MHz): d 1.03 (d,
carbonyl-1-(3,4-dihydroxyphenyl)-2-aminopropane
4
3H), 2.35 (s, 3H), 2.55 (A of an AB syst., J=2.4 Hz,
1H), 2.58 (B of an AB syst., J=2.1 Hz, 1H), 2.64–2.75
(m, 1H), 5.15 (s, 2H), 5.18 (s, 2H), 6.70–6.90 (m. 3H),
7.28–7.49(m, 10H). 13C NMR (CDCl3, 75 MHz): d
19.5, 33.9, 42.9, 56.2, 71.1, 71.3, 115.0, 116.3, 122.0,
127.1, 127.2, 127.5, 127.6, 128.3, 132.7, 137.2, 137.3,
147.4, 148.5. Finally, HCl 3 N in anhydrous diethyl
ether was added (dropwise) to the oil dissolved in 5 mL of
anhydrous diethyl ether. A pale yellow solid precipitate
was filtered and dried yielding (S)-N-methyl-1-(3,4-diben-
zyloxyphenyl)-2-aminopropane hydrochloride (278.5 mg,
0.70 mmol, 74% yield from 2) that was used without
further characterization.
that was used without further purification. This crude
product was dissolved in a 50 mL round bottom flask in
3 mL of anhydrous dimethylformamide. To this solu-
tion was added 100 mL (1.34 mmol, 1.6 equiv) of
BrCH2Cl and 0.44 g (1.34 mmol, 1.6 equiv) of CsCO3
and the mixture was stirred for 2 h. After that time, the
solution was filtered through a Celite1 pad and taken to
dryness under vacuum. The residue was then dissolved
in 200 mL of ethyl acetate and washed with water
(2Â25 mL) and brine (25 mL). The organic layer was
dried over anhydrous MgSO4, filtered and the solvent
was removed giving a solid that was dried under
vacuum. This product was purified by column chroma-
tography (silica gel) using hexane/ethyl acetate (starting
with hexane and increasing ethyl acetate concentration
in 5% every 100 mL, 1200 mL of total volume). Finally,
213.2 mg (0.85 mmol, 95% yield) of (S)-N-ethoxy-
carbonyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane
(S)-N-Methyl-1-(3,4-dihydroxyphenyl)-2-aminopropane
8,9
.
hydrochloride, (S)-HHMA HCl.
In a 10 mL round
bottom flask were placed 115 mg of (S)-N-methyl-1-
(3,4-dibenzyloxyphenyl)-2-aminopropane hydrochloride
dissolved in 2 mL of anhydrous methanol and a cataly-
tic amount of palladium (10 wt% on carbon powder)
and the flask was capped with a septum. By means of a
three-way stopcock connected to a hydrogen containing
ballon, a water aspirator, and the flask, three cycles of
vacuum/hydrogen filling were done. The flask was then
left under hydrogen atmosphere and stirred for 4 h.
After that time, the solution was filtered through
Celite1, washing the solid with previously degassed
anhydrous methanol. Finally, the solution was con-
centrated and dried to yield 58 mg (0.26 mmol, 92%
yield) of grey oil that was conserved under nitrogen
atmosphere and protected from the light until its use.
1H NMR (DMSO-d6, 200 MHz): d 1.01 (d, 3H), 2.34 (A
of an AB syst., J=12.4 Hz, 1H), 2.94 (B of an AB syst.,
J=13.0 Hz, 1H), 3.00–3.20 (m, 1H), 3.09(s, 3H), 6.38–
6.64 (m, 3H), 8.97 (bs, 2H). 13C NMR (DMSO-d6,
50 MHz): d 14.9, 29.5, 37.7, 55.5, 115.8, 116.6, 119.9,
127.3, 144.1, 145.2. GC–MS (N-TFA, O-TFA deriva-
tive); m/z 110, 154, 343.
1
5 were obtained. H NMR (CDCl3; 200 MHz): d 1.07
(d, 3H), 1.19(t, 3H), 2.55 (A of an ABX syst., J=11.2,
13.4 Hz, 1H), 2.73 (B of an ABX syst., J=5.8, 13.4 Hz,
1H), 3.71–3.96 (X of an ABX syst., 1H), 4.05 (q, 2H),
4.67 (bs, 1H), 5.88 (s, 2H), 6.53–6.76 (m. 3H).
(S)-3,4-Methylenedioxyphenyl-2-aminopropane
hydro-
chloride. To a previously evacuated 100 mL Schlenck
flask, and under argon atmosphere, containing 97 mg of
LiAlH4 (2.55 mmol, 3 equiv) in 5 mL of anhydrous THF,
were dropwise added 213 mg of (S)-N-ethoxycarbonyl-1-
(3,4-methylenedioxyphenyl)-2-aminopropane 5 in 10 mL
of anhydrous THF. The mixture was refluxed with stir-
ring for 2 h and then was cooled to room temperature
and worked-up as performed for compound 3 achieving
160.4 mg (0.83 mmol, 98% yield) of the white solid (S)-
1
MDMA. H NMR (CDCl3; 200 MHz): d 1.02 (d, 3H),
1.84 (bs, 1H), 2.36 (s, 3H), 2.46–2.75 (m, 3H), 5.89(s,
2H), 6.55–6.77 (m, 3H). This compound was then dis-
solved in anhydrous diethyl ether and HCl 3 N (in
anhydrous diethyl ether) was dropwise added, yield-
ing 180 mg (0.79mmol, 94% yield) of ( S)-3,4-
methylenedioxyphenyl-2-aminopropane hydrochloride,
Synthesis of racemic N-methyl-1-(3,4-dihydroxyphenyl)-2-
aminopropane (3,4-dihydroxymethamphetamine, HHMA).
Following the above-mentioned method for the enantio-
merically enriched (S)-N-methyl-1-(3,4-dihydroxyphenyl)-
.
(S)-MDMA HCl, as a white solid whose optical rota-
tion was [a]2D0 +15.16 (c 0.79, H2O). GC–MS (N-TFA
derivative); m/z 110, 135, 154, 162, 289.
.
2-aminopropane
hydrochloride
[(S)-HHMA HCl],

N. Pizarro et al. / Bioorg. Med. Chem. 10 (2002) 1085–1092
1091
Synthesis of enantiomerically enriched (S)-N-methyl-1-
(4-hydroxy-3-methoxyphenyl)-2-aminopropane [(S)-4-
hydroxy-3-methoxymethamphetamine, (S)-HMMA]
in 200 mL of CH2Cl2 and treated with 3N NaOH aqu-
eous solution until pH>12, decanted and extracted with
CH2Cl2 (2Â50 mL). The combined organic layer was
washed with water (2Â25 mL) and brine (25 mL). Dry-
ing with MgSO4 and concentration produced 4.25 g
(11.32 mmol, 59% yield) of N-(S)-(1-phenylethane)-
(R,S)-1-(4-benzyloxy-3-methoxyphenyl)-2-aminopro-
pane as a yellow oil. Attempts to separate the two dia-
1-(4-benzyloxy-3-methoxyphenyl)-2-nitropropene. This
compound was prepared as already described for 1-(3,4-
dibenzyloxyphenyl)-2-nitropropene. By reaction of 12.3 g
(50 mmol) of 4-benzyloxy-3-methoxybenzaldehyde were
obtained 14.22 g (47.5 mmol, 95%) of 1-(4-benzyloxy-3-
methoxyphenyl)-2-nitropropene. IR (neat, nmax cmÀ1):
1632, 1594, 1515, 1500, 1463, 1422, 1387, 1314, 1268,
1241, 1170, 1145, 1037, 998, 990, 915, 850, 815, 749,
1
stereomers were not successful at this point. H NMR
(CDCl3; 300 MHz): d 0.95 (d, 3H, maj), 1.08 (d, 3H,
min), 1.28 (d, 3H, min), 1.33 (d, 3H, maj), 2.29(bs, 1H),
2.40–2.86 (m, 3H), 3.80 (s, 3H, min), 3.83 (s, 3H, maj),
3.84–3.97 (m, 1H), 5.13 (s, 2H, maj), 5.18 (s, 2H, min),
6.57–6.97 (m, 3H), 7.16–7.52 (m, 10H). 13C NMR
(CDCl3, 300 MHz): d 19.8, 21.0, 24.3, 24.7, 41.9, 43.5,
50.7, 52.0, 54.7, 55.3, 55.7, 55.8, 71.0, 104.8, 112.5,
112.9, 113.9, 114.0, 121.1, 121.2, 126.2, 126.5, 126.6,
126.8, 127.1, 127.2, 127.3, 127.6, 127.7, 128.2, 128.4,
132.2, 132.7, 137.2, 145.1, 145.7, 146.3, 146.4, 149.3,
149.5. GC–MS m/z 91, 105, 148, 228, 270, 360, 376.
1
697. H NMR (300 MHz; CDCl3): d 2.47 (s, 3H), 3.92
(s, 3H), 5.21 (s, 2H), 6.93–7.00 (m. 3H), 7.32–7.50 (m,
10H), 8.05 (s, 1H). 13C NMR (75 MHz; CDCl3): d 14.1,
56.0, 70.8, 113.4, 113.5, 123.8, 125.2, 127.1, 128.0, 128.6,
133.7, 136.3, 145.9, 149.5, 149.8. GC–MS m/z 91, 176,
242, 267, 299.
1-(4-benzyloxy-3-methoxyphenyl)-2-propanone 6.7
A
mixture of 11 g (37 mmol) of 1-(4-benzyloxy-3-methoxy-
phenyl)-2-nitropropene, 15 g (257 mmol, 7 equiv) of
iron, 60 mg (0.37 mmol, 0.01 equiv) of FeCl3 and 25 mL
of water were placed in a 250 mL round bottom flask.
The mixture was refluxed and stirred, and 6 mL of con-
centrated HCl were carefully added through the con-
denser. After 6 h, it was allowed to cool to room
temperature and 100 mL of benzene were added. The
resulting suspension was filtered off through a Celite1
pad and the solids were washed with benzene
(2Â50 mL). Then, the benzene layer was separated and
washed with diluted HCl (25 mL) and water (2Â25 mL),
dried over anhydrous MgSO4 and filtered. The solvent
was removed and the residue was dried under vacuum
and purified by column chromatography (silica gel)
using hexane/ethyl acetate (1:1, v/v) to give 9.5 g
(35.14 mmol, 95% yield) of 1-(4-benzyloxy-3-methoxy-
phenyl)-2-propanone as an orange oil. IR (neat, nmax
cmÀ1): 1708, 1591, 1514, 1463, 1454, 1419, 1261, 1228,
N-methyl-N-[(S)-(1-phenylethane)]-(S)-1-(4-benzyloxy-3-
methoxyphenyl)-2-aminopropane (8). 2.26 g (6.03 mmol) of
N-(S)-(1-phenylethane)-(R,S)-1-(4-benzyloxy-3-methoxy-
phenyl)-2-aminopropane were dissolved in 50 mL of
CH2Cl2 in a round bottom flask. To this solution 1.9g
(18 mmol, 3 equiv) of Na2CO3 and 760 mL (12.05 mmol,
2 equiv) of CH3I were also added. After 16 h of stirring
at room temperature, another 760 mL of CH3I were
added and mixture was then stirred for 48 h. The
resulting solution was washed with water (2Â25 mL)
and brine (25 mL), dried with MgSO4 and concentrated
to give 2.22 g (0.60 mmol, 94% yield) of a yellow solid
consisting in a 6:4 diastereomeric mixture of N-(S)-(1-
phenylethane)-(S,S)-1-(4-benzyloxy-3-methoxyphenyl)-
2-aminopropane and N-(S)-(1-phenylethane)-(R,S)-1-
(4-benzyloxy-3-methoxyphenyl)-2-aminopropane. Silica
gel column chromatography purification of this dia-
stereomeric mixture, eluting with hexane/ethyl acetate
(1:1, v/v) resulted in the obtention of different diaster-
eomeric ratio mixtures depending on the column frac-
tions collected, observing that the minor component of
the crude mixture was the first one in eluting from the
column. Four different fractions were obtained: fraction
1 (256 mg) contained a 30:70 (S,S)/(R,S) diastereoi-
1
1157, 1139, 1033, 1026, 738, 698. H NMR (300 MHz;
CDCl3): d 2.15 (s, 3H), 3.63 (s, 2H), 3.89(s, 3H), 5.15 (s,
2H), 6.74–6.87 (m. 3H), 7.28–7.56 (m, 10H). 13C NMR
(75 MHz; CDCl3) d 29.1, 50.6, 55.9, 71.0, 112,8, 114.1,
121.5, 127.2, 127.8, 128.3, 128.5, 137.1, 147.2, 149.7,
206.8. GC–MS m/z: 43, 91, 137, 227, 270.
1
somers ratio (determined by 300 MHz H NMR) [a]D20
N-(S)-(1-phenylethane)-(R,S)-1-(4-benzyloxy-3-methoxy-
phenyl)-2-aminopropane (7).11 In a 500 mL round bot-
tom flask was dissolved 5.2 g (19.2 mmol) of 1-(4-
benzyloxy-3-methoxyphenyl)-2-propanone in 50 mL of
methanol and 10.1 mL (76.9mmol, 4 equiv) of 1-( S)-
phenyletanamine. To this solution were also added 1.3 g
(21.1 mmol, 1.1 equiv) of NaBH4CN in 2 mL of diethyl
ether/HCl. The resulting orange mixture was stirred at
room temperature for 28 h, and after that time, con-
centrated HCl was added dropwise until pH<2 was
achieved and the solution was then concentrated to
dryness. The resulting mixture was dissolved with water
(150 mL) and ethyl acetate (250 mL) and the organic
layer was decanted. The aqueous layer was extracted
with ethyl acetate (2Â250 mL) and the combined
organic layer was dried over MgSO4 and concentrated
to give 6.74 g of a dark orange oil which was redissolved
À93.13 (c 0.99, chloroform), fraction 2 [991 mg, 50:50
(S,S)/(R,S) ratio], fraction 3 (404 mg, 80:20 (S,S)/(R,S)
ratio), and fraction 4 (390 mg, 92:8 (S,S)/(R,S) ratio
[a]D20 +77.36 (c 0.98, chloroform]. IR (neat, nmax cmÀ1):
3060, 3029, 2967, 2933, 2869, 2848, 2748, 1588, 1513, 1492,
1463, 1451, 1417, 1368, 1262, 1224, 1156, 1139, 1025, 734,
699. 1H NMR (CDCl3, 300 MHz): d Major isomer: 0.92
(d, 3H), 1.35 (d, 3H), 2.28 (A of an ABX syst., 1H con-
taining a s, 3H), 2.91 (B of an ABX syst., J=4.5, 12.9
Hz, 1H), 2.97–3.11 (X of an ABX syst., 1H), 3.71 (q,
1H), 3.79(s, 3H), 5.12 (s, 2H), 6.48–6.80 (m, 3H), 7.15–
7.50 (m, 10H). Minor isomer, 0.87 (d, 3H), 1.33 (d, 3H),
2.28 (s, 3H), 2.38 (A of an ABX syst., J=8.4, 13.2 Hz,
1H), 2.76 (B of an ABX syst., J=5.7, 13.2 Hz, 1H),
2.85–2.97 (X of an ABX syst., 1H), 3.62 (q, 1H), 3.80 (s,
3H), 5.15 (s, 2H), 6.48–6.80 (m, 3H), 7.15–7.50 (m,
10H). 13C NMR (CDCl3, 300 MHz): d Major isomer:

1092
N. Pizarro et al. / Bioorg. Med. Chem. 10 (2002) 1085–1092
15.7, 22.0, 32.3, 37.0, 55.7, 55.8, 62.2, 71.0, 112.5, 113.8,
120.9, 126.6, 127.1, 127.2, 127.6, 128.3, 128.4, 134.3,
137.3, 146.0, 146.3, 149.2. Minor isomer: 12.5, 22.1, 31.7,
40.6, 55.7, 56.0, 62.0, 71.1, 112.8, 113.7, 121.0, 126.4,
126.7, 127.2, 127.6, 128.1, 128.2, 128.4, 134.2, 137.4,
146.1, 146.1, 149.1. GC–MS m/z 91, 107, 136, 227, 262.
porator and the resulting residue dried under vacuum
1
yielding a solid in almost quantitative yield. H NMR
(CD3OD; 300 MHz): d 1.96 (d, 3H), 2.53 (s, 3H), 2.60–
2.73 (m, 1H), 2.85–3.01 (m, 2H), 3.85 (bs, 2H), 3.90 (s,
6H), 6.87–7.08 (m, 3H). 13C NMR (CD3OD, 75 MHz):
d 19.0, 33.6, 43.4, 56.4, 56.5, 57.7, 113.1, 114.1, 122.6,
133.2, 149.1, 150.5. In all cases, GC–MS (N-TFA deri-
vative); m/z 110, 151, 178, 305.
N-methyl-N-(S)-2-(4-hydroxy-3-methoxyphenyl)-1-methyl-
.
propanamine hydrochloride, (S)-HMMA HCl. In a pres-
sure resistant glass reactor, were dissolved 150 mg
(0.38 mmol) of N-methyl-N-(S)-(1-phenylethane)-(S)-1-
(4 - benzyloxy - 3 - methoxyphenyl) - 2 - aminopropane 8
[(S,S)/(R,S) 80:20 ratio] in diethyl ether and treated with
a solution of HCl/diethyl ether. The white solid that
precipitated was taken to dryness and redissolved in
8 mL of previously degassed methanol, and to this
solution was added a catalytic amount of Pd/C.
Hydrogenation was performed at 3 bar pressure with
continuous stirring at room temperature for 24 h. After
filtration through Celite1 of the residue and concentra-
tion were obtained 82 mg (0.35 mmol, 92%) of N-methyl-
N-(S)-2-(4-hydroxy-3-methoxyphenyl)-1-methylpropa-
namine hydrochloride as a white solid. 1H NMR
(CD3OD; 300 MHz): d 1.41 (d, 3H), 2.87 (A of an ABX
syst., 1H containing a s, 3H), 3.21 (B of an ABX syst.,
J=4.1, 13.4 Hz, 1H), 3.53–3.70 (X of an ABX syst.,
1H), 4.03 (s, 3H), 5.10 (bs, 4 H), 6.81–7.09(m, 3H). 13C
NMR (CD3OD, 75 MHz): d 15.8, 31.0, 39.9, 56.4, 57.9,
113.8, 116.4, 122.9, 128.1, 146.9, 149.2. GC–MS (N-
TFA, O-TFA derivative); m/z 110, 154, 260, 387.
Acknowledgements
This investigation was supported by: FIS 98/0181,
CIRIT 95-SGR-00432, CIRIT 99-SGR-00187, ISC-III
98/4344, and PNSD (Spain). We thank Marta Pulido
for editorial assistance.
References and Notes
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Synthesis of N-1-(3,4-dimethoxyphenyl)-2-aminopropane
hydrochloride (3,4-dimethoxymethamphetamine hydro-
.
chloride, MMMA HCl) and enantiomerically enriched
(S)-N-1-(3,4-dimethoxyphenyl)-2-aminopropane hydro
chloride [(S)-3,4-dimethoxymethamphetamine hydro
.
chloride, (S)-MMMA HCl]
9. Yousif, M.; Fitzgerald, R. L.; Narasimhachari, N.; Rose-
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General procedure. To an Erlenmeyer flask containing
the corresponding substrate dissolved in methanol was
slowly added an excess of an ethereal solution of CH2N2
and the resulting solution was left to stand overnight.
Then, the excess of reagent was evaporated by passing a
stream of argon, the solvent removed on a rotaeva-
11. Borch, R. F.; Berstein, M. D.; Durst, H. D. J. Am. Chem.
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