A convenient biomimetic synthesis of optically active putative neurotoxic metabolites of MDMA ("ecstasy") from R-(-)- and S-(+)-N-methyl- α-methyldopamine precursors

Article abstract of DOI:10.1039/c2ob25245g

(±)-3,4-Methylenedioxymethamphetamine (MDMA, also known as "ecstasy") is a psychoactive drug with selective neurotoxic potential toward brain serotonin (5-HT) neurons. One hypothesis holds that MDMA neurotoxicity may at least partially be a consequence of its metabolism. In most species (including primates), O-demethylenated MDMA metabolites such as N-methyl-α-methyldopamine (HHMA) have been postulated to serve as precursors for toxic thioether conjugates. As yet, chirality of MDMA was not considered in previously reported in vivo studies because HHMA was used as the racemate. Since the stereochemistry of this chiral drug needs to be considered, the total synthesis of enantiomerically pure precursors, R-(-)-HHMA and S-(+)-HHMA, was envisioned with the ultimate goal to prepare substantial amounts of optically active thioether conjugates. Recently, we reported the first total synthesis of the R-enantiomer. In this paper, a novel synthesis of the S-enantiomer is described, in 45% overall yield (six steps) and 99% ee, using commercially available l-Boc-alanine (99% ee) as the chiral source. Having at our disposal suitable amounts of R-(-)-HHMA and S-(+)-HHMA precursors, a straightforward one-pot electrochemical procedure has been further developed for the synthesis of several catechol-thioether conjugates in acceptable yields (40-53%) and high degree of purity (99%), with complete diastereoselectivity. The availability of these newly synthesized optically active catechol-thioether conjugates is crucial for ongoing future in vivo studies about their role in MDMA neurotoxicity.

Full text of DOI:10.1039/c2ob25245g

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PAPER
A convenient biomimetic synthesis of optically active putative neurotoxic
metabolites of MDMA (“ecstasy”) from R-(−)- and S-(+)-N-methyl-
α-methyldopamine precursors†
Claire-Marie Martinez, Anne Neudörffer and Martine Largeron*
Received 2nd February 2012, Accepted 8th March 2012
DOI: 10.1039/c2ob25245g
( )-3,4-Methylenedioxymethamphetamine (MDMA, also known as “ecstasy”) is a psychoactive drug
with selective neurotoxic potential toward brain serotonin (5-HT) neurons. One hypothesis holds that
MDMA neurotoxicity may at least partially be a consequence of its metabolism. In most species
(including primates), O-demethylenated MDMA metabolites such as N-methyl-α-methyldopamine
(HHMA) have been postulated to serve as precursors for toxic thioether conjugates. As yet, chirality of
MDMAwas not considered in previously reported in vivo studies because HHMAwas used as the
racemate. Since the stereochemistry of this chiral drug needs to be considered, the total synthesis of
enantiomerically pure precursors, R-(−)-HHMA and S-(+)-HHMA, was envisioned with the ultimate goal
to prepare substantial amounts of optically active thioether conjugates. Recently, we reported the first total
synthesis of the R-enantiomer. In this paper, a novel synthesis of the S-enantiomer is described, in 45%
overall yield (six steps) and 99% ee, using commercially available L-Boc-alanine (99% ee) as the chiral
source. Having at our disposal suitable amounts of R-(−)-HHMA and S-(+)-HHMA precursors, a
straightforward one-pot electrochemical procedure has been further developed for the synthesis of several
catechol–thioether conjugates in acceptable yields (40–53%) and high degree of purity (99%), with
complete diastereoselectivity. The availability of these newly synthesized optically active catechol–
thioether conjugates is crucial for ongoing future in vivo studies about their role in MDMA neurotoxicity.
peripherally administered MDMA.3 In particular, O-demethyle-
nated MDMA metabolites such as N-methyl-α-methyldopamine
Introduction
( )-3,4-Methylenedioxymethamphetamine (MDMA, also known
as “ecstasy”) is a psychoactive drug with selective neurotoxic
potential toward brain serotonin (5-HT) neurons.1 Despite inten-
sive research, the precise mechanism by which MDMA selec-
tively damages brain 5-HT neurons in most species (including
primates) remains unknown.2 One hypothesis holds that MDMA
neurotoxicity may at least partially be a consequence of its
metabolism (Scheme 1), because direct injection of the drug into
specific brain area (especially cortex, hippocampus and striatum)
of the rat fails to reproduce the 5-HT neurotoxic effects of
(HHMA) or α-methyldopamine (HHA), have been postulated to
serve as precursors for toxic catechol–thioether conjugates.4
Recently, the catechol–thioether conjugate of HHMA, 5-(N-acet-
ylcystein-S-yl)-N-methyl-α-methyldopamine (5-NAC-HHMA)
has been strongly implicated in MDMA neurotoxicity,5 but
efforts to replicate these findings have been unsuccessful.6 So,
the specific neurotoxicity profile of thioether conjugates of
HHMA is controversial and remains to be well established.
As yet, chirality of MDMA was not considered in previously
reported in vivo studies, because HHMA, the precursor of cate-
chol–thioether conjugates, was used as the racemate. However,
both MDMA enantiomers show different pharmacological and
pharmacokinetic profiles.7 Enantioselective metabolism is the
most likely explanation for the enantioselective pharmacokinetics
of MDMA and was observed for the cytochrome P450-mediated
phase I metabolism into HHMA (Scheme 1),8 for the catechol-
O-methyltransferase (COMT)-catalyzed methylation of HHMA
to HMMA9 and for HHMA sulfation,10 with a preference for the
S-enantiomers. In contrast, recent findings have indicated that
O-glucuronidation of HMMA in vivo11 as well as HMMA sulfa-
tion10 are not expected to be enantioselective.
UMR 8638 CNRS-Université Paris Descartes, Synthèse et Structure de
Molécules d’Intérêt Pharmacologique, Faculté des Sciences
Pharmaceutiques et Biologiques, 4 avenue de l’Observatoire, 75270
Paris cedex 06, France. E-mail: martine.largeron@parisdescartes.fr;
Fax: +33144073588; Tel: +33153739646
†Electronic supplementary information (ESI) available: 1H and 13C
NMR spectra of S-(+)-HHMA 7 and its synthetic intermediates 1–6,
together with optically active catechol-thioether conjugates 8–15;
analytical HPLC chromatograms of S-(+)-HHMA 7 and of optically
active catechol-thioether conjugates 8–15. See DOI: 10.1039/
c2ob25245g
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Scheme 1 Stereochemistry of the hepatic metabolism of MDMA in humans including the postulated conjugate formation. Only, O-demethylenation
leading to R-(−)-HHMA and S-(+)-HHMA is presented.
HHMA, which is a major metabolite in humans,12 is the pre-
cursor of thioether conjugates. Because HHMA exists as a pair
of enantiomers (Scheme 1), its thioether conjugates exist as a
mixture of diastereoisomers as they possess several chiral
centers: that of HHMA present in the alkylamino side chain
(carbon atom α to the amine function), together with those
present in the thiol moieties. Because MDMA enantiomers have
different pharmacological properties, one would also predict that
the thioether conjugates of the HHMA enantiomers similarly
display distinct neurotoxicity profiles. The preparation of such
diastereoisomers requires the tedious synthesis of enantiomeri-
cally pure precursors R-(−)-HHMA and S-(+)-HHMA. To over-
come this limitation, analytical and semipreparative
methodologies for the diastereoisomeric separation of HHMA
thioether conjugates have been recently reported, but this separ-
ation method only furnished small quantities of both
diastereoisomers.13
inducer of chirality, the preparation of R-(−)-HHMA was
achieved through seven steps, in 30% overall yield and 99.5%
enantiomeric excess (ee).14
In this paper, we describe the first total synthesis of S-
(+)-HHMA in 45% overall yield (six steps) and 99% ee, using
commercially available L-Boc-alanine (99% ee) as the chiral
source. To the best of our knowledge, the only synthesis of enan-
tiomerically enriched S-(+)-HHMA (80% ee), performed
through resolution of N-methyl-α-methyldopamine with diben-
zoyl-L-(−)-tartaric acid, is known.15 Having at our disposal large
amounts of R-(−)-HHMA and S-(+)-HHMA precursors, we have
further prepared several optically active catechol–thioether
mono- and bis-conjugates, following the straightforward one-pot
procedure we have recently developed starting from ( )-HHMA
racemate,16 using anodic oxidation as a mimic of P450-mediated
enzymatic oxidation.
This prompted us to realize the total synthesis of enantiomeri-
cally pure precursors, R-(−)-HHMA and S-(+)-HHMA, with the
ultimate goal to prepare large amounts of optically active
thioether conjugates and to further determine if these conjugates
play a role in MDMA neurotoxicity. Recently, we reported the
first total synthesis of R-(−)-HHMA. Using L-DOPA as the
Results and discussion
Synthesis of S-(+)-HHMA
Inexpensive N-protected amino-acids are attractive starting
materials for the preparation of optically active arylalkylamines.
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Scheme 2 Synthetic procedure for the total synthesis of S-(+)-HHMA 7.
This is the reason why we chose L-Boc-alanine, commercially
available with high optical purity (99%), as the chiral source. At
the outset, our synthetic strategy for the preparation of S-
(+)-HHMA (Scheme 2) involved the common synthesis of the
Weinreb amide 1 that was achieved in 98% yield, followed by
condensation with lithiated 4-bromoveratrol for producing the
arylketone intermediate 2. Although it was reported that close
Weinreb amides coupled with lithiated bromobenzene derivatives
in good to high yields,17 in our case the yield of arylketone 2 did
not exceed 15%. We also attempted to employ the very attractive
Merck procedure which afforded large quantities of α-Boc-
amino ketones from α-Boc-amino Weinreb amides through a
pre-deprotonation protocol using a stoichiometric amount of a
simple aryl Grignard reagent.18 However, when applied to the
Weinreb amide 1, the expected arylketone 2 was synthesized in
moderate yield (51%). Finally, treatment of the Weinreb amide 1
with 3 equivalents of the Grignard reagent (3,4-dimethoxyphe-
nylmagnesium bromide)19 allowed us to markedly improve the
yield in arylketone 2 which reached 73%.
Different methods could be then utilized to reduce the aryl-
ketone 2 into the corresponding methylene derivative 5 including
catalytic hydrogenation,20 Clemensen reduction,21 reduction
with hydride reagents such as lithium aluminum hydride
(LiAlH4) in combination with strong Lewis acids,22 or use of
triethylsilane in trifluoroacetic acid or in BF3·Et2O.23 Unfortu-
nately, most of these reduction methods necessitate the use of
strongly acidic reagents which can lead to undesired side reac-
tions such as Boc protecting group cleavage. So, we focused on
the reduction system using sodium cyanoborohydride in the pres-
ence of zinc iodide (NaBH3CN–ZnI2) in dichloroethane, earlier
reported to reduce arylketones into arylalkanes with a high
degree of selectivity.24 However, under these experimental con-
ditions, only the corresponding alcohol 3 was isolated in 36%
yield. Since sterically hindered ketones are often resistant to
reduction even under forcing conditions,25 we envisioned an
indirect method via the intermediacy of a tosylhydrazone deriva-
tive 4.26 Accordingly, the arylketone 2 was transformed into the
corresponding tosylhydrazone 4 in almost quantitative yield
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(91%), in refluxing chloroform in the presence of p-toluenesulfo-
nylhydrazine (p-TSH). As can be seen below, the choice of
chloroform as the solvent was crucial for a perfect control of
enantioselectivity. Further, reduction using the NaBH3CN–ZnI2
system failed to produce arylalkane 5 because tosylhydrazone 4
decomposed under these experimental conditions. Finally, repla-
cing ZnI2 with ZnCl2 allowed the reduction of the tosylhydra-
zone 4 to the expected arylalkane 5 in high yield (90%). Upon
optimization, we found that a combination of 1 mmol of tosylhy-
drazone with 8 mmol of NaBH3CN and 4 mmol of ZnCl2 in
refluxing methanol gave the best results. Reduction of Boc group
was accomplished using LiAlH4 in dichloroethane, leading to
S-(+)-MMMA 6 in 73% yield, with high optical purity (99%), as
determined by HPLC analysis of the Mosher amide. The latter
could be easily compared with the Mosher amide previously
obtained from enantiomerically pure R-(−)-HHMA, previously
prepared in our laboratory.14 Finally, complete demethylation of
S-(+)-MMMA 6 using hydrobromic acid heated at reflux,
afforded S-(+)-HHMA 7 in 96% yield. As earlier observed, no
racemisation occurred in the course of the deprotection step.14
Finally, using L-Boc-alanine (99% ee) as the chiral source, the
preparation of S-(+)-HHMA 7 was achieved through six steps, in
45% overall yield and 99% ee.
solvents, the ee increased to 97% in tetrahydrofuran, while no
detectable racemisation was found in chloroform as the ee was
equivalent to that of the starting L-Boc-alanine (99%).
Synthesis of optically active catechol–thioether mono-conjugates
8–11
In the racemic series, the most utilized method for synthesizing a
thioether mono-conjugate involves the oxidation of ( )-HHMA
with mushroom tyrosinase in the presence of a thiol.4f,h,5a,28 The
reaction proceeds via the formation of the o-quinone intermedi-
ate, followed by a 1,6-Michael addition reaction of thiol.
However, this enzymatic procedure is not adapted for routine
synthesis because it is too expensive and not suitable for yielding
substantial amounts of catechol–thioether mono-conjugates. For
a long time, electrochemical oxidation has proved to be an
efficient tool for the generation of highly electrophilic o-quinone
species, which can be further scavenged by diverse nucleophilic
entities.29 In particular, unstable o-quinone species have been
electrogenerated from catecholamines such as dopamine,30 nor-
epinephrine,31 or N-acetyldopamine32 and then scavenged by
thiol residues to afford the corresponding catechol–thioether
adducts.
The tosylhydrazone synthesis constituted the critical step for
the enantioselectivity of the overall synthetic procedure, because
of the occurrence of a keto–enol displacement at the origin of
racemisation. Indeed, heating arylketone 2 in refluxing protic sol-
vents such as methanol, in the presence of hydrazine, favored the
keto–enol displacement and then the racemisation of the stereo-
center.27 This was confirmed by using ethanol, another protic
solvent which possesses a higher boiling point. Then, the ee dra-
matically failed to 84% (Fig. 1). Conversely, using aprotic
Recently, we reported a straightforward one-pot electrochemi-
cal synthesis of catechol–thioether mono-conjugates of
( )-HHMA, which proved to be especially attractive for routine
synthesis because of acceptable yields, high degree of purity and
environmentally friendly conditions.16a This methodology was
found to be much more efficient than the enzymatic procedure
for producing a thioether mono-conjugate of ( )-2,4,5-trihy-
droxy-methamphetamine.33 So, we decided to adapt our electro-
chemical procedure to the synthesis of optically active thioether
Fig. 1 HPLC chromatograms for the analytical resolution of Mosher amide diastereoisomers prepared from S-(+)-MMMA 6. Tosylhydrazone inter-
mediate 4 was prepared in different refluxing solvents: (a) ethanol; (b) methanol; (c) tetrahydrofuran; (d) chloroform. Conditions of HPLC: column
Kromasil C18, 250 × 4.6 mm–5 μm; eluent (H2O + 1‰ TFA)/MeCN 55/45; flow rate, 0.4 mL min−1
.
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Scheme 3 Multi-step one-pot electrosynthesis of optically active cate-
chol–thioether bis-conjugates 12–15.
Table 1 One-pot synthesis of optically active catechol–thioether
mono- and bis-conjugates 8–15a
Series
RSH
Product
Yieldb (%)
Mono-conjugates
S-(+)-
S-(+)-
R-(−)-
R-(−)-
Bis-conjugates
S-(+)-
S-(+)-
R-(−)-
R-(−)-
NAC
Glutathione
NAC
8
9
10
11
51
48
52
48
Glutathione
NAC
Glutathione
NAC
12
13
14
15
46c
40
53
Glutathione
40c
a Reagents and conditions: R-(−)-HHMA or S-(+)-HHMA = 1 mM;
RSH = 2 mM (mono-conjugate) and RSH = 5 mM (bis-conjugate); 0.2
M HCl; 10 °C; Pt anode (E = +1.0 V vs. Ag/AgCl); 30 min. b Yields
refer to isolated products (after semi-preparative reversed-phase HPLC,
degree of purity: 99%). NAC: N-acetylcysteine. c Mono-conjugate was
also recovered (5–17%).
Fig. 2 Spectrophotometric changes accompanying the electrosynthesis
of optically active catechol–thioether mono-conjugate 8. (Spectra a–e):
electrochemical oxidation of S-(+)-HHMA (1 mM), at a platinum anode
(E = +1.0 V versus Ag/AgCl), in deaerated 0.2 M HCl aqueous solution;
(a) 0 (before electrolysis), (b) 0.5, (c) 1.0, (d) 1.5, (e) 2.0 mol of elec-
trons, (Spectrum f): after addition of 2 equiv of N-acetylcysteine to the
two electron-oxidized solution. Cell thickness is 0.1 cm.
due to the formation of the catechol–thioether mono-conjugate,
which was identified by the change in the UV absorption spec-
trum (Fig. 2, spectrum f), showing new absorption maxima
around 256 and 285 nm. Treatment of the electrolysis solution
afforded, after semipreparative reversed-phase HPLC (see the
Experimental section), optically active catechol–thioether mono-
conjugates 8–11 (Scheme 3) in yields ranging from 48 to 52%
(Table 1).
mono-conjugates starting from S-(+)-HHMA and R-(−)-HHMA
precursors. The anodic oxidation of S-(+)-HHMA or R-
(−)-HHMA was realized through controlled potential electroly-
sis, under acidic conditions, in the absence of the thiol substrate
because the thioether conjugate was also electroactive at the
applied potential.
When the controlled potential of the platinum anode was fixed
at +1.0 V versus Ag/AgCl, which is at a potential for which
S-(+)-HHMA (or R-(−)-HHMA) could be oxidized to the
o-quinone species, a coulometric value of 2.0 0.1 was found
for the number (n) of electrons involved in the oxidation of one
molecule of S-(+)-HHMA (or R-(−)-HHMA) into the transient
o-quinone species. The latter was rather stable in aqueous 0.2 M
HCl, as shown by monitoring the UV absorption spectrum in the
course of the electrolysis (Fig. 2). After the application of the
potential, a decrease in the UV absorption band shown by S-
(+)-HHMA (or R-(−)-HHMA) at 280 nm (ε = 2190 dm3 mol−1
cm−1) was observed, while a new band at 391 nm developed.
Spectral changes showed two isosbestic points at 268 and
290 nm, indicating that a simple equilibrium between two
species was shifted (Fig. 2, spectra a–e). Subsequent addition of
2 equiv of thiol such as N-acetylcysteine (NAC) or glutathione
resulted in the immediate discoloration of the yellow solution,
Synthesis of optically active catechol–thioether bis-conjugates
12–15
For the synthesis of optically active catechol–thioether bis-conju-
gates 12–15, we used our multi-step one-pot electrochemical
procedure first reported for the preparation of thioether bis-conju-
gates of ( )-HHMA.16b The undeniable benefits of this method,
which uses R-(−)-HHMA or S-(+)-HHMA as the starting
material without the need to isolate the optically active thioether
mono-conjugate intermediate, include atom economy, as well as
economies of time, resource management, and waste generation
(Scheme 3).
For the synthesis of catechol–thioether bis-conjugate 12, for
example, the first experimental step consisted of the generation
of the o-quinone species and consecutive addition of 2 equiv of
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Since the stereochemistry of MDMA needed to be considered,
we recently accomplished the first total synthesis of R-
(−)-HHMA enantiomer.14 However, the synthesis of optically
pure S-enantiomer was also required for comparison. This is the
reason why we have developed an efficient and stereocontrolled
route for the total synthesis of S-(+)-HHMA through six steps, in
45% overall yield and 99% ee, using L-Boc-alanine (99% ee) as
the inducer of chirality. Having at our disposal suitable amounts
of both enantiomers, we have further used anodic oxidation as a
mimic of P450 enzymatic oxidation for the synthesis of several
optically pure catechol–thioether mono- and bis-conjugates. To
the best of our knowledge, no optically active catechol–thioether
metabolites of MDMA have never been prepared as yet. Then,
using S-(+)-HHMA and R-(−)-HHMA as the starting materials,
the straightforward one-pot electrochemical procedure we have
developed allows the synthesis of diastereomerically pure conju-
gates 8–15, in acceptable yields (40–53%) and high degree of
purity (99%), under environmentally friendly conditions. The
availability of these newly synthesized optically active thioether
conjugates is crucial for ongoing future in vivo studies about
their exact role in the neurotoxic effects of MDMA.
Fig. 3 Spectrophotometric changes accompanying the multi-step one-
pot electrosynthesis of S-(+)-catechol–thioether bis-conjugate 12. (Spec-
trum f): after addition of 3 equiv of N-acetylcysteine to the two electron-
oxidized solution of S-(+)-HHMA (1 mM), at a platinum anode (E =
+1.0 V versus Ag/AgCl), in deaerated 0.2 M HCl aqueous solution;
(Spectra g–j): spectra recorded after the consumption of additional
3.5 mol of electrons: (g) 1.0, (h) 2.0, (i) 3.0, ( j) 3.5 (end of the process).
Cell thickness is 0.1 cm.
NAC, under the aforementioned experimental conditions. After
the electrolysis solution became colorless, catechol–thioether
mono-conjugate 8 was not isolated but a third equiv of NAC was
added. In a second step, the resulting solution was oxidized
again at +1.0 V versus Ag/AgCl, which is at a potential for
which 8 could be oxidized to the corresponding o-quinone–
thioether species. Then, the solution became pale yellow, while a
new band at 274 nm, with a shoulder around 305 nm (Fig. 3,
spectrum j), developed at the expense of both UV absorption
bands at 256 and 285 nm (Fig. 3, spectrum f). At the end of the
electrolysis, a coulometric value of 3.5 was found for n and the
recorded spectrum j corresponded to that of optically active cate-
chol–thioether bis-conjugate 12, as corroborated after recording
the UV absorption of the isolated product. To maintain a redu-
cing medium during work-up, two additional equiv of NAC
were then added. Finally, treatment of the electrolysis solution
afforded, after semi-preparative reversed-phase HPLC (see the
Experimental section), the catechol–thioether bis-conjugate 12 in
46% yield.
Experimental section
All reagents and solvents (HPLC grade) were commercial pro-
ducts of the highest available purity and were used as supplied.
Analytical thin-layer chromatography was carried out on silica
gel Macherey-Nagel Polygram SIL G/UV 254 (0.25 mm).
Column chromatography was performed on Macherey-Nagel Si
60 M silica gel (40–63 μm).
HPLC was carried out using a Waters system consisting of a
600E multi-solvent delivery system, a Rheodyne-type loop injec-
tor, and a 2487 dual-channels UV-visible detector set at 254 and
278 nm. A mixture of two solvents A and B constituted the
mobile phase. Solvent A was prepared by adding 1‰ concen-
trated trifluoroacetic acid (TFA) to deionized water. Solvent B
was prepared by adding 0.5‰ TFA to a 1 : 1 (v/v) mixture of
methanol and deionized water. Semipreparative reversed-phase
HPLC was performed using a 250 × 20 mm, 5 μm Kromasil
C18 column and a 2 mL loop injector, whereas for the analytical
reversed-phase HPLC, a 250 × 4.6 mm, 5 μm Kromasil C18
column, together with a 50 μL loop injector, were used.
The same one-pot procedure allowed the isolation of cate-
chol–-thioether bis-conjugate 13–15 in yields ranging from 40 to
53% (Table 1). As expected, the electrochemical procedure pro-
ceeded with complete diastereoselectivity (see the ESI†).
Melting points were measured on a Köfler apparatus. Optical
rotations were measured at 25 °C using a Perkin-Elmer 341
polarimeter. [α]D values are given in 10−1 deg cm2 g−1
.
UV absorption spectra were recorded on a Varian Cary 100
spectrophotometer. IR absorption spectra were recorded on a
Shimadzu FT IRAffinity-1 spectrometer equipped with PIKE
Gladi-Diam ATR.
Conclusions
For years, the potential role of metabolites in MDMA neurotoxi-
city has been a topic of interest. Recently, 5-NAC-HHMA has
been strongly suspected to be involved in MDMA neurotoxici-
ty,5a but efforts to replicate these findings have been unsuccess-
ful.6 The reasons for this discrepancy is not clear, but it is
important to note that 5-NAC-HHMA used in these studies was
prepared through different methods yielding a different ratio of
5-NAC-HHMA diastereoisomers.13 This raised the question of
the chirality of MDMA which was not considered in previously
reported in vivo studies, because HHMA, the precursor of 5-
NAC-HHMA metabolite, was used as the racemic mixture.
1H NMR and 13C NMR spectra were performed on a Brucker
AC-300 spectrometer operating at 300 and 75 MHz, respectively.
Chemical shifts are expressed as δ units (part per million)
downfield from TMS (tetramethylsilane). The measurements
were carried out using the standard pulse sequences. The carbon
type (methyl, methylene, methine, or quaternary) was deter-
1
mined by DEPT experiments. H and 13C NMR spectra of all
compounds are included in the ESI† as a proof of their identity.
Low-resolution mass spectra (LRMS) were recorded on a
Waters ZQ 2000 operating in positive ion mode. High-resolution
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mass spectra (HRMS) were recorded on a LTQ-Orbitrap spec-
trometer operating in positive or negative ion mode.
50.5, 56.0, 56.1, 79.6, 110.2, 110.6, 123.4, 127.1, 149.2, 153.8,
155.2, 197.9; HRMS (ESI) m/z calcd for [M + Na]+ 332.1474;
found, 332.1476.
Controlled-potential electrolyses were carried out in a cylindri-
cal three-electrode divided cell (9 cm diameter), using a Voltalab
32 electrochemical analyser (Radiometer, Copenhagen). In the
main compartment, a cylindrical platinum grid (area = 47 cm2)
served as the anode (working electrode). A platinum sheet was
placed in the concentric cathodic compartment (counter-elec-
trode), which was separated from the main compartment with a
glass frit. The reference electrode was an Ag–AgCl electrode, to
which all potentials quoted are referred.
(S)-tert-Butyl-1-hydroxy-1-(3,4-dimethoxy)phenylpropan-2-
ylcarbamate (3)
Zinc iodide (239 mg, 0.75 mmol, 1.5 equiv) and NaBH3CN
(236 mg, 3.75 mmol, 7.5 equiv) were added to a solution of
arylketone 2 (154 mg, 0.5 mmol) in dry dichloroethane
(2.5 mL). The resulting mixture was stirred at room temperature
for 4 h, and filtered through Celite®. The white solid was then
washed with 100 mL of dichloromethane, and the combined
filtrates were evaporated to dryness. Column chromatography
(dichloromethane–methanol–triethylamine 89 : 10 : 1) afforded
alcohol 3 as a colorless oil (57 mg, 0.18 mmol) in 36% yield
(mixture of diastereoisomers). UV λmax (MeOH)/nm 279 (ε/dm3
mol−1 cm−1 2495), 300sh; IR (neat) 3356, 2974, 2934, 1682,
1514, 1452, 1365, 1254, 1232, 1157, 1140, 1024 cm−1; Major
(R)-N-Methyl-α-methyldopamine hydrobromide, [R-(−)-
HHMA, HBr] was synthesized in seven steps from commercially
available L-DOPA, using our previously reported procedure.14
(S)-tert-Butyl 1-[(methoxy-methyl)amino]-1-oxopropan-2-
ylcarbamate (1)
N,O-Dimethylhydroxylamine hydrochloride (1.06 g, 10.9 mmol,
1.03 equiv) and N-methylmorpholine (1.2 mL, 10.9 mmol, 1.03
equiv) were added to a solution of L-Boc-alanine (2 g,
10.6 mmol) in CH2Cl2 (17 mL) at −10 °C, followed by addition
of small portions of 1-(3-dimethylaminopropyl)-3-ethylcarbodii-
mide hydrochloride (EDCI·HCl) (2.08 g, 10.9 mmol, 1.03
equiv). After stirring at the same temperature for 1.5 h, the reac-
tion was quenched with ice cold 1 M HCl (6.4 mL). The organic
phase was separated and the aqueous phase was extracted with
CH2Cl2 (10 mL). The combined organic phases (27 mL) were
washed with saturated aqueous NaHCO3 (6 mL). The saturated
aqueous NaHCO3 phase was back extracted with CH2Cl2
(10 mL). The combined CH2Cl2 phases were then dried over
MgSO4. Filtration and evaporation of the solvent under reduced
pressure afforded Weinreb amide 1 as a white solid (2.4 g,
10.33 mmol) in 98% yield. mp 150–152 °C; [α]2D5 − 25.6 (c
1
diastereoisomer: H NMR (CDCl3) δ 0.96 (d, 3H), 1.44 (s, 9H),
3.51 (broad s, 1H), 3.85 (s, 3H), 3.86 (s, 3H), 3.94 (m, 1H), 4.77
(m, 2H), 6.82 (m, 2H), 6.88 (m, 1H); 13C NMR (CDCl3) δ 14.8,
28.3, 51.9, 55.8, 55.9, 76.3, 79.7, 109.4, 110.7, 118.5, 133.5,
148.2, 148.7, 156.3; LRMS (ES+) m/z 334 [M + Na]+.
(S)-Methyl-N′-[1-(3,4-dimethoxyphenyl)-(2-tert-
butoxycarbonylamino)propylidene] benzenesulfonylhydrazide (4)
To a solution of arylketone 2 (562 mg, 1.82 mmol) in chloro-
form (4.0 mL) were added 406 mg of para-toluenesulfonylhy-
drazine (2.18 mmol, 1.2 equiv). The resulting solution was
heated to reflux for 6 h, and stirred at room temperature during
the night. After evaporation of the solvent under reduced
pressure, the resulting yellow solid was purified by column
chromatography (petroleum ether–ethyl acetate 65 : 35) leading
to tosylhydrazone 4 as a white solid (790 mg, 1.65 mmol) in
91% yield. mp 96–98 °C; [α]2D5 −4.85 (c 0.04, MeOH); 1H
NMR (CDCl3) δ 1.20 (d, J = 6.9 Hz, 3H), 1.45 (s, 9H), 2.45 (s,
3H), 3.84 (s, 3H), 3.91 (s, 3H), 4.54 (m, 1H), 5.38 (d, 1H), 6.65
(s, 1H), 6.77 (d, J = 8.0 Hz, 1H), 6.93 (d, J = 8.0 Hz, 1H), 7.32
(d, J = 8.1 Hz, 2H), 7.58 (s, 1H), 7.79 (d, J = 8.1 Hz, 2H); 13C
NMR (CDCl3) δ 20.0, 21.6, 28.4, 50.9, 56.0 (×2), 79.4, 109.9,
111.6, 120.4, 122.4, 128.0, 129.6, 135.0, 144.2, 149.7, 150.4,
155.0, 157.1; HRMS (ESI) m/z calcd for [M + Na]+ 500.1831;
found, 500.1835.
1
0.04, MeOH); H NMR (CDCl3) δ 1.32 (d, J = 6.9 Hz, 3H),
1.44 (s, 9H), 3.22 (s, 3H), 3.78 (s, 3H), 4.69 (m, 1H), 5.29 (m,
1H); 13C NMR (CDCl3) δ 18.6, 28.4, 32.1, 46.5, 61.6, 79.5,
155.2, 173.6. HRMS (ESI) m/z calcd for [M + Na]+ 255.1321;
found, 255.1321.
(S)-tert-Butyl-1-oxo-1-(3,4-dimethoxy)phenylpropan-2-
ylcarbamate (2)
To a solution of Weinreb amide 1 (0.75 g, 3.21 mmol) in dry
THF (33 mL) at 0 °C was added dropwise a 0.5 M solution of
3,4-dimethoxyphenylmagnesium bromide in THF (19.5 mL,
9.63 mmol, 3 equiv). The mixture was stirred at 0 °C for 1 h,
allowed to warm to room temperature and stirred for 20 h. Then,
the reaction mixture was quenched with 1 M HCl (39 mL) and
extracted with ethyl acetate (3 × 50 mL). The combined organic
phases were washed with a saturated NaCl aqueous solution
(30 mL), dried over MgSO4 and filtered off, and the solvent was
evaporated under reduced pressure. Column chromatography
(toluene–acetone 95 : 5), afforded arylketone 2 in 73% yield
(0.72 g, 2.33 mmol) as a white solid. mp 88–90 °C; [α]2D5 − 13.3
(S)-tert-Butyl-1-(3,4-dimethoxy)phenylpropan-2-ylcarbamate (5)
Zinc chloride (681 mg, 5 mmol, 4 equiv) and NaBH3CN
(628 mg, 10 mmol, 8 equiv) were added to a solution of tosyl-
hydrazone 4 (595 mg, 1.25 mmol) in methanol (10 mL). The
reaction mixture was heated to reflux for 6 h, and stirred at 56 °C
during the night. After addition of 20 mL of 0.1 M NaOH, the
resulting mixture was extracted with diethyl ether (3 × 80 mL).
The organic phase was then dried over MgSO4 and filtered off,
and the solvent was evaporated under reduced pressure. The
resulting oil was purified by column chromatography (petroleum
ether–ethyl acetate 65 : 35) to afford compound 5 as a white
1
(c 0.04, MeOH); H NMR (CDCl3) δ 1.41 (d, J = 7.0 Hz, 3H),
1.46 (s, 9H), 3.95 (s, 3H), 3.96 (s, 3H), 5.27 (m, 1H), 5.59
(d, 1H), 6.92 (d, J = 7.0 Hz, 1H), 7.53 (s, J = 1.9 Hz, 1H), 7.64
(dd, J = 7.0 and 1.9 Hz, 1H); 13C NMR (CDCl3) δ 20.3, 28.4,
This journal is © The Royal Society of Chemistry 2012
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solid in 90% yield (333 mg, 1.13 mmol). mp 98–100 °C; [α]D25
+
colorless. The reaction mixture was immediately frozen at
−80 °C and then freeze-dried. The residue was subdivided in
fractions of about 25 mg. Each fraction was dissolved in 2 mL of
water, and then purified by semipreparative reversed-phase
HPLC, using a mixture of solvent A–solvent B 80 : 20 as the
eluent (flow rate: 14 mL min−1). Fractions containing (S)-5-
NAC-HHMA 8 were collected, immediately frozen at −80 °C,
and then freeze-dried. Compound 8 was isolated as a white solid
(44 mg, 0.13 mmol), in 51% yield. Its degree of purity (99.5%)
was determined by analytical HPLC (eluent: solvent A–MeCN
93 : 7 – flow rate: 0.8 mL min−1); UV λmax (aqueous 0.2 M
6.5° (c 0.04, methanol); 1H NMR (CDCl3) δ 1.08 (d, J = 6.6 Hz,
3H), 1.43 (s, 9H), 2.59 (m, J = 13.4 Hz, 1H), 2.79 (m, J = 13.4
Hz, 1H), 3.86 and 3.87 (2 s, 7H), 4.40 (broad s, 1H), 6.71 (m,
2H), 6.79 (d, J = 8.6 Hz, 1H); 13C NMR (CDCl3) δ 20.1, 28.4,
42.5, 47.4, 55.7, 55.8, 79.0, 111.0, 112.5, 121.5, 130.8, 147.5,
148.7, 155.2; HRMS (ESI) m/z calcd for [M + Na]+ 318.1681;
found, 318.1678.
(S)-3,4-Dimethoxymethamphetamine (S)-MMMA (6)
1
HCl)/nm 255 (ε/dm3 mol−1 cm−1 2640), 292 (1980); H NMR
LiAlH4 solution in THF (2.4 M, 1.02 mL) was added dropwise
to a solution of compound 5 (480 mg, 1.625 mmol) in dry
dichloroethane (20 mL) at 0 °C. The resulting solution was
heated to reflux for 1.5 h, quenched successively with 0.55 mL
of water, 0.55 mL of 5 M NaOH and 1.55 mL of water, stirred
for 45 min and filtered through Celite®. The white solid was
then washed with 100 mL of dichloromethane, and the combined
filtrates were evaporated to dryness. After purification by column
(D2O) δ 1.11 (d, J = 6.5 Hz, 3H), 1.78 (s, 3H), 2.55 (s, 3H),
2.60 (m, 1H), 2.78 (m, 1H), 3.04 (m, 1H), 3.28 (m, 2H), 4.23
(m, 1H), 6.65 (s, 1H), 6.75 (s, 1H). 13C NMR (D2O) δ 14.7,
21.5, 29.8, 34.5, 37.8, 52.7, 56.2, 117.2, 119.4, 126.2, 128.1,
143.9, 144.3, 173.8, 174.1. HRMS (ESI) m/z calcd for [M + H]+
343.1322; found, 343.1322.
(S)-5-(Glutathion-S-yl)-N-methyl-α-methyl-dopamine (9)
chromatography
(dichloromethane–methanol–triethylamine
87 : 10 : 3), (S)-MMMA 6 was obtained as a colorless oil in 73%
yield (249 mg, 1.19 mmol). [α]2D5 + 12.2° (c 0.04, MeOH); note
[α]2D5 was found to be −12.4° for the R enantiomer when
measured under the same experimental conditions; UV λmax
(MeOH)/nm 280 (ε/dm3 mol−1 cm−1 2600), 285sh; 1H NMR
(CDCl3) δ 1.08 (d, J = 6.2 Hz, 3H), 1.69 (broad s, 1H), 2.40 (s,
3H), 2.63 (m, 2H), 2.77 (m, 1H), 3.87 (s, 3H), 3.88 (s, 3H), 6.74
(m, 2H), 6.82 (d, J = 8,7 Hz, 1H); 13C NMR (CDCl3) δ 19.6,
33.9, 43.1, 55.8 (×2), 56.4, 111.1, 112.3, 121.1, 131.9, 147.4,
148.7. HRMS (ESI) m/z calcd for [M + H]+ 210.1494; found,
210.1496.
General procedure A, replacing N-acetylcysteine with glutathione
(157 mg, 0.50 mmol) afforded after semipreparative reversed-
phase (eluent: solvent A–solvent B 69 : 31 – flow rate: 3 mL
min−1), (S)-5-Glu-HHMA
9 as a white solid (58 mg,
0.12 mmol), in 48% yield. Its degree of purity (99.5%) was
determined by analytical HPLC (eluent: solvent A–MeCN 93 : 7
– flow rate: 1 mL min−1). UV λmax (aqueous 0.2 M HCl)/nm
1
256 (ε/dm3 mol−1 cm−1 2630), 292 (1820); H NMR (D2O) δ
1.09 (d, J = 6.5 Hz, 3H), 2.02 (m, 2H), 2.36 (t, J = 7.5 Hz, 2H),
2.54 (s, 3H), 2.61 (m, 1H), 2.76 (m, 1H), 3.04 (m, 1H), 3.24 (m,
2H), 3.69 (s, 2H), 3.90 (m, 1H), 4.27 (m, 1H), 6.63 (s, 1H), 6.73
(s, 1H).13C NMR (D2O) δ 14.7, 25.3, 29.8, 30.7, 34.7, 37.8,
40.9, 52.1, 53.0, 56.2, 117.0, 119.3, 126.0, 128.2, 143.9, 144.4,
171.5, 172.3, 172.7, 174.0. HRMS (ESI) m/z calcd for [M + H]+
487.1857; found, 487.1858.
(S)-N-Methyl-α-methyl-dopamine hydrobromide [S-(+)-HHMA,
HBr] (7)
A 48% aqueous solution of HBr (3.3 mL) (18.9 mmol) was
added to (S)-MMMA 6 (531 mg, 2.55 mmol). The resulting sol-
ution was heated to reflux for 2 h, under nitrogen. After evapor-
ation under reduced pressure, the brown oil was purified by
column chromatography (dichloromethane–MeOH 80 : 20)
affording (S)-HHMA, HBr 7 as a colorless oil (640 mg,
2.44 mmol) in 96% yield. [α]2D5 + 3.2° (c 0.04, MeOH); UV
λmax (aqueous 0.2 M HCl)/nm 280 (ε/dm3 mol−1 cm−1 2190);
1H NMR (CDCl3) δ 1.11 (d, J = 6.5 Hz, 3H), 2.53 (s, 3H), 2.62
(m, 1H), 2.75 (m, 1H), 3.30 (m, 1H), 6.57 (d, J = 8.1 Hz, 1H),
6.66 (s, 1H), 6.74 (d, J = 8.1 Hz, 1H); 13C NMR (CDCl3) δ
14.8, 29.9, 37.9, 56.4, 116.2, 116.9, 121.7, 128.1, 142.8, 143.9.
HRMS (ESI) m/z calcd for [M + H]+ 182.1181; found,
182.1180.
(R)-5-(N-Acetylcystein-S-yl)-N-methyl-α-methyl-dopamine (10)
General procedure A, replacing S-(+)-HHMA, HBr by R-
(−)-HHMA, HBr afforded, after semipreparative reversed-phase
HPLC (eluent: solvent A–solvent B 80 : 20 – flow rate: 14 mL
min−1), (R)-5-NAC-HHMA 10 as a white solid (44 mg,
0.13 mmol), in 52% yield. Its degree of purity (99%) was deter-
mined by analytical HPLC (eluent: solvent A–MeCN 93 : 7 –
flow rate: 0.8 mL min−1). UV λmax (aqueous 0.2 M HCl)/nm
1
255 (ε/dm3 mol−1 cm−1 2640), 292 (1980); H NMR (D2O) δ
1.12 (d, J = 6.5 Hz, 3H), 1.79 (s, 3H), 2.55 (s, 3H), 2.62 (m,
1H), 2.78 (m, 1H), 3.04 (m, 1H), 3.28 (m, 2H), 4.23 (m, 1H),
6.66 (s, 1H), 6.76 (s, 1H). 13C NMR (D2O) δ 14.7, 21.5, 29.8,
34.6, 37.9, 52.7, 56.2, 117.1, 119.4, 126.3, 128.1, 144.0, 144.4,
173.8, 174.2. HRMS (ESI) m/z calcd for [M + H]+ 343.1322;
found, 343.1321.
(S)-5-(N-Acetylcystein-S-yl)-N-methyl-α-methyl-dopamine (8)
General procedure A. A solution of S-(+)-HHMA, HBr 7
(65.5 mg, 0.25 mmol), in 0.2 M HCl (250 mL), was oxidized
under nitrogen at 10 °C at a platinum grid whose potential was
fixed at +1.0 V versus Ag/AgCl. After the consumption of 2
electrons per molecule, 2 equiv of N-acetylcysteine (83 mg,
0.50 mmol) were added to the pale yellow solution which turned
(R)-5-(Glutathion-S-yl)-N-methyl-α-methyl-dopamine (11)
General procedure A replacing S-(+)-HHMA, HBr by R-
(−)-HHMA, HBr and N-acetylcysteine by glutathione (157 mg,
0.5 mmol) afforded, after semipreparative reversed-phase HPLC
3746 | Org. Biomol. Chem., 2012, 10, 3739–3748
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(eluent: solvent A–solvent B 69 : 31 – flow rate: 3 mL min−1),
(R)-5-Glu-HHMA 11 as a pale pink solid (58 mg, 0.12 mmol),
in 48% yield. Its degree of purity (99%) was determined by
analytical HPLC (eluent: solvent A–MeCN 93 : 7 – flow rate:
1 mL min−1). UV λmax (aqueous 0.2 M HCl)/nm 256 (ε/dm3
– flow rate: 0.6 mL min−1). UV λmax (aqueous 0.2 M HCl)/nm
1
274 (ε/dm3 mol−1 cm−1 7200), 305sh; H NMR (D2O) δ 1.08
(d, 3H), 2.01 (m, 4H), 2.33 (m, 2H), 2.39 (m, 2H), 2.59 (s, 3H),
2.82 (m, 1H), 3.10 and 3.30 (m, 6H), 3.71 (s, 2H), 3.73 (s, 2H),
3.79 (m, 2H), 4.24 (m, 2H), 6.85 (s, 1H). 13C NMR (D2O) δ
14.7, 25.3, 25.4, 29.9, 30.8 (×2), 34.5, 34.9, 37.1, 40.9 (×2),
52.3 (×2), 52.6, 53.4, 56.2, 118.9, 120.9, 125.8, 131.9, 143.7,
146.8, 171.8 (×2), 172.1, 172.2, 172.7, 174.0 (×2), 174.1.
HRMS (ESI) m/z calcd for [M − H]− 790.2393; found,
790.2395.
1
mol−1 cm−1 2630), 292 (1820); H NMR (D2O) δ 1.10 (d, J =
6.5 Hz, 3H), 2.01 (m, 2H), 2.36 (t, J = 7.5 Hz, 2H), 2.54 (s, 3H),
2.61 (m, 1H), 2.76 (m, 1H), 3.06 (m, 1H), 3.24 (m, 2H), 3.69 (s,
2H), 3.82 (m, 1H), 4.26 (m, 1H), 6.64 (s, 1H), 6.73 (s, 1H).13C
NMR (D2O) δ 14.7, 25.5, 29.8, 30.9, 34.6, 37.8, 40.9, 52.6,
53.0, 56.2, 117.1, 119.2, 126.0, 128.2, 143.9, 144.4, 172.1,
172.3, 172.8, 174.2. HRMS (ESI) m/z calcd for [M + H]+
487.1857; found, 487.1857.
(R)-2,5-bis-(N-Acetylcystein-S-yl)-N-methyl-α-methyl-dopamine
(14)
General procedure B replacing S-(+)-HHMA, HBr 7 by R-
(−)-HHMA, HBr afforded, after semipreparative reversed-phase
HPLC (eluent: solvent A–solvent B 84 : 16 – flow rate: 11 mL
min−1), (R)-2,5-bis-NAC-HHMA 14 in 53% yield (white solid,
70 mg, 0.14 mmol). The degree of purity for compound 14
(99.5%) was determined by analytical HPLC (eluent: solvent A–
MeCN 92 : 8 – flow rate: 0.8 mL min−1). UV λmax (aqueous 0.2
M HCl)/nm 274 (ε/dm3 mol−1 cm−1 6390), 305sh; 1H NMR
(D2O) δ 1.08 (d, J = 6.5 Hz, 3H), 1.75 (s, 3H), 1.82 (s, 3H),
2.60 (s, 3H), 2.83 (m, 1H), 3.07 and 3.30 (m, 6H), 4.26 (m, 2H),
6.84 (s, 1H). 13C NMR (D2O) δ 14.9, 21.5 (×2), 30.0, 34.5,
34.7, 37.0, 52.5, 53.6, 56.2, 119.4, 121.0, 126.3, 131.6, 143.9,
146.6, 173.8 (×4). HRMS (ESI) m/z calcd for [M + H]+
504.1469; found, 504.1469.
(S)-2,5-bis-(N-Acetylcystein-S-yl)-N-methyl-α-methyl-dopamine
(12)
General procedure B. A solution of (S)-HHMA, HBr
(65.5 mg, 0.25 mmol) in 0.2 M hydrochloric acid (250 mL), was
oxidized under nitrogen, at 10 °C, at a platinum grid (E = +1.0
V versus Ag/AgCl). After the consumption of 2 electrons per
molecule, the electrolysis was stopped and 3 equiv of N-acetyl-
cysteine (125 mg, 0.75 mmol) were added. When the yellow
electrolysis solution became colorless, it was oxidized again at
+1.0 V versus Ag/AgCl. After exhaustive electrolysis (n = 5.5,
that is 2.0 for the first step and 3.5 for the second one), 2 equiv
of N-acetylcysteine (83 mg, 0.50 mmol) were added to the reac-
tion mixture, which was immediately frozen at −80 °C and then
freeze-dried. The residue was subdivided in fractions of about
25 mg. Each fraction was dissolved in 2 mL of water and then
purified by semipreparative reversed-phase HPLC, using a
mixture of solvent A–solvent B 84 : 16 as the eluent (flow rate:
11 mL min−1). Fractions containing (S)-2,5-bis-NAC-HHMA
(12) and (S)-5-NAC-HHMA (8) were collected individually,
immediately frozen at −80 °C and then freeze-dried. Compound
12 was isolated as the major product in 46% yield (white solid,
58 mg, 0.115 mmol), along with compound 8 as the minor one,
in 4.5% yield (4 mg, 0.012 mmol). The degree of purity for
compound 12 (99%) was determined by analytical HPLC
(eluent: solvent A–MeCN 92 : 8 – flow rate: 0.8 mL min−1). UV
λmax (aqueous 0.2 M HCl)/nm 274 (ε/dm3 mol−1 cm−1 6390),
(R)-2,5-bis-(Glutathion-S-yl)-N-methyl-α-methyl-dopamine (15)
General procedure B, replacing S-(+)-HHMA, HBr 7 by R-
(−)-HHMA and N-acetylcysteine with glutathione (392 mg,
1.25 mmol, overall quantity), afforded, after exhaustive electroly-
sis (n = 5.5, that is 2 for the first step and 3.5 for the second one)
and semipreparative reversed-phase HPLC (eluent: solvent A–
solvent B 74 : 26 – flow rate: 4 mL min−1), (R)-2,5-bis-Glu-
HHMA 15 as the major product in 40% yield (pale pink solid,
80 mg, 0.101 mmol), along with compound 11 as the minor one,
in 17% yield (0.043 mmol). The degree of purity for compound
15 (99.5%) was determined by analytical HPLC (eluent: solvent
A–MeCN 95 : 5 – flow rate: 0.6 mL min−1). UV λmax (aqueous
0.2 M HCl)/nm 274 (ε/dm3 mol−1 cm−1 7200), 305sh; 1H NMR
(D2O) δ 1.08 (d, 3H), 2.01 (m, 4H), 2.33 (m, 2H), 2.40 (m, 2H),
2.58 (s, 3H), 2.85 (m, 1H), 3.10 and 3.28 (m, 6H), 3.70 (s, 2H),
3.73 (s, 2H), 3.80 (m, 2H), 4.24 (m, 2H), 6.84 (s, 1H). 13C
NMR (D2O) δ 14.8, 25.4, 25.5, 30.0, 30.9 (×2), 34.6, 34.9, 36.9,
40.9 (×2), 52.4 (×2), 52.7, 53.4, 56.3, 119.1, 120.8, 126.0,
131.8, 143.8, 146.7, 171.9 (×2), 172.1, 172.3 (×2), 172.7, 174.0,
174.2. HRMS (ESI) m/z calcd for [M − H]− 790.2393; found
790.2386.
1
305sh; H NMR (D2O) δ 1.09 (d, J = 6.5 Hz, 3H), 1.77 (s, 3H),
1.81 (s, 3H), 2.61 (s, 3H), 2.82 (m, 1H), 3.07 and 3.25 (m, 6H),
4.30 (m, 2H), 6.86 (s, 1H). 13C NMR (D2O) δ 14.8, 21.5 (×2),
30.0, 34.4, 34.7, 37.0, 52.4, 53.3, 56.2, 119.3, 121.1, 126.1,
131.7, 143.8, 146.6, 173.6, 173.7, 173.8 (×2). HRMS (ESI) m/z
calcd for [M + H]+ 504.1469; found, 504.1469.
(S)-2,5-bis-(Glutathion-S-yl)-N-methyl-α-methyl-dopamine (13)
General procedure B, replacing N-acetylcysteine with glutathione
(392 mg, 1.25 mmol, overall quantity), afforded, after exhaustive
electrolysis (n = 4.5, that is 2 for the first step and 2.5 for the
second one) and semipreparative reversed-phase HPLC (eluent:
solvent A–solvent B 74 : 26 – flow rate: 4 mL min−1), (S)-2,5-
bis-Glu-HHMA 13 in 40% yield (white solid, 80 mg,
0.10 mmol). The degree of purity for compound 13 (99%) was
determined by analytical HPLC (eluent: solvent A–MeCN 95 : 5
Acknowledgements
This research was supported by the joint grants of the “Mission
Interministérielle de Lutte contre la Drogue et la Toxicomanie”
(MILDT) and the “Institut National de la Santé et de la
Recherche Médicale” (INSERM). (Appel à projets commun
This journal is © The Royal Society of Chemistry 2012
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