New nitrilotriacetic acid and ethylenediaminetetraacetic acid nitro derivatives for the synthesis of bifunctional and trifunctional chelating agents

Article abstract of DOI:10.1080/00397910500189718

Dehydration of serine derivatives into didehydroamino acids and subsequent conjugate addition of nitromethane led to novel nitro derivatives of nitrilotriacetic acid and ethylenediaminetetraacetic acid. Straightforward transformations of these compounds a

Full text of DOI:10.1080/00397910500189718

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New Nitrilotriacetic Acid and
Ethylenediaminetetraacetic
Acid Nitro Derivatives for the
Synthesis of Bifunctional and
Trifunctional Chelating Agents
Stéphane Meunier a , Pierre Cristau a & Frédéric
Taran a
a Service de Marquage Moléculaire et de Chimie
Bio‐Organique, DBJC/DSV CEA Saclay, Gif sur Yvette
Cedex, France
Published online: 18 Aug 2006.
To cite this article: Stéphane Meunier , Pierre Cristau & Frédéric Taran (2005):
New Nitrilotriacetic Acid and Ethylenediaminetetraacetic Acid Nitro Derivatives
for the Synthesis of Bifunctional and Trifunctional Chelating Agents, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:18, 2415-2425
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Synthetic Communicationsw, 35: 2415–2425, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500189718
New Nitrilotriacetic Acid and
Ethylenediaminetetraacetic Acid Nitro
Derivatives for the Synthesis of Bifunctional
and Trifunctional Chelating Agents
´
Stephane Meunier, Pierre Cristau, and Frederic Taran
Service de Marquage Moleculaire et de Chimie Bio-Organique,
´ ´
´
DBJC/DSV CEA Saclay, Gif sur Yvette Cedex, France
Abstract: Dehydration of serine derivatives into didehydroamino acids and subsequent
conjugate addition of nitromethane led to novel nitro derivatives of nitrilotriacetic acid
and ethylenediaminetetraacetic acid. Straightforward transformations of these
compounds allowed the synthesis of bifunctional and trifunctional metal-chelating
agents via an Henry reaction.
Keywords: Chelates, Henry reaction, lanthanides, ligands, polyaminocarboxylates
INTRODUCTION
Polyaminocarboxylate chelates have the ability to form stable metal
complexes with many metal ions such as nickel, copper, indium, technetium,
and iron, in different oxidation states. Therefore, the development of
bifunctional chelating agents that can be attached to macro(bio)molecules
offers useful tools such as (1) probes of proteins structure,[1] (2) probes for
molecular recognition,[2] (3) contrast agents for magnetic resonance,[3] (4)
in vivo tumor imaging reagents,[4] and (5) radioimmunotherapy agents.[5]
The purpose of designing trifunctional chelating agents is to combine
these properties to achieve more complex and targeted applications.
Received in the U.K. January 11, 2005
´ ´
´
Address correspondence to Frederic Taran, Service de Marquage Moleculaire et
de Chimie Bio-Organique, DBJC/DSV CEA Saclay, 91191 Gif sur Yvette Cedex,
France. Fax: þ33 (0)3 69 08 79 91; E-mail: frederic.taran@cea.fr
2415

2416
S. Meunier, P. Cristau, and F. Taran
Biotinylated-EDTA–based trifunctional agents have been used for the prep-
aration of radiolabeled antibodies that can be easily removed from blood
with the aim to decrease side effects of radiotherapies.[6] As a second
example, functionalization of phospholipids using a biotinylated-NTA–
based trifunctional agent allows the organization of streptavidin and poly-
histidine-tagged proteins around tubular structures offering valuable tools to
structural biology.[7]
Although nitrilotriacetic acid (NTA)–based bifunctional chelating agents
are usually synthesized from protected L-Lysine by alkylation with bromo-
acetic acid,[8] the most common method for attaching ethylenediaminetetra-
acetic acid (EDTA) to macromolecules involves the reaction of EDTA
dianhydride with an amine residue on the target molecule. However, in this
latter case, the stability constant of the resulting carboxamide-derivatized
metal chelate can be lower than that of the parent EDTA. One solution to
circumvent this difficulty is to design an EDTA derivative bearing an
additional reactive function dedicated to the attachment to the target
molecule. Several EDTA–based bifunctional chelating agents have been
described, corresponding either to the modification of the ethylenediamino
fragment or to the modification at the methylene carbon of one carboxymethyl
arm; among them are EDTA derivatives bearing a carboxylic acid,[9] a bro-
moacetate,[10] an amine,[11] or an isothiocyanobenzyl reactive moiety.[12]
Herein is reported the synthesis, starting from serine, of two nitro deriva-
tives of NTA and EDTA, compounds 1 and 2, which are modified on one
carboxymethyl arm (Figure 1). These molecules are key intermediates for
the straightforward synthesis of bifunctional and trifunctional chelating agents.
RESULTS AND DISCUSSION
As outlined in Scheme 1, the NTA derivative 3 was built by double N-alkylation
of serine tert-butyl ester using tert-butyl bromoacetate at the reflux of aceto-
nitrile. Under similar conditions, but in the presence of 1.2 equivalent of tert-
butyl bromoacetate, the product of mono N-alkylation 4 was obtained in a
67% yield. This compound was further N-alkylated using N, N-bis[(tert-butoxy-
calbonyl)methyl]-2-bromoethylamine[13] to afford the EDTA derivative 5. It
should be underlined that tert-butyl esters were chosen as protective groups
Figure 1. Structure of key compounds 1 and 2.

Synthesis of Bifunctional and Trifunctional Chelating Agents
2417
Scheme 1. (a) BrCH2CO2t-Bu (4 equiv), DIPEA (6 equiv), CH3CN, reflux, 20 h
(70%); (b) BrCH2CO2t-Bu (1.2 equiv), DIPEA (4 equiv), CH3CN, reflux, 4 h
(67%); (c) Br(CH2)2N(CH2CO2t-Bu)2 (3 equiv), DIPEA (5 equiv), CH3CN, reflux,
20 h (87%).
for the carboxylate moieties because of the ease of deprotection in the presence
of TFA, and to avoid the lactonization that was observed when serine was
submitted to N-alkylation with methyl bromoacetate.
The nitro derivatives 1 and 2 were obtained by a two-step reaction from the
primary alcohols 3 and 5, as shown in Scheme 2. The use of Mitsunobu reagents,
tris(n-butyl)phosphine and diethyl azodicarboxylate, allowed the smooth conver-
sion of the serine derivatives 3 and 5 into the didehydroamino acids 6 and 7,
presumably through a-deprotonation.[14] NMR analysis of the crude
mixtures obtained after evaporation of the solvent under reduced pressure
demonstrated that these reactions proceed very cleanly and in excellent
yield; however, the didehydroaminoacids 6 and 7 could not be purified
because of their instability on silica gel. Michael additions of nitromethane
to 6 and 7 in the presence of fluoride ions afforded the nitro derivatives 1
and 2 in 50% and 64% yields. The addition of nitromethane on several
protected
dehydroalanines
(phthalimido,
benzyloxycarbonylamino,
acetamido) has been already extensively studied.[15] In the case of 6 and 7,
despite a reduced reactivity resulting from the absence of electron-
Scheme 2. (a) (n-Bu)3P (1.5 equiv), DEAD (1.5 equiv), Et2O, from 2108C to rt, 3 h;
.
(b) n-Bu4NF 3H2O (6 equiv), CH3NO2, 508C, 20 h (1 50%, 2 64%).

2418
S. Meunier, P. Cristau, and F. Taran
withdrawing groups on the amino site of the didehydroaminoacid moiety,
smooth additions occurred in the presence of an excess of nitromethane.
As shown in Scheme 3, the nitro derivatives 1 and 2 are readily reduced
by ammonium formate in the presence of palladium on activated carbon to
afford the bifunctional chelating agents 8 and 9 in good yields. At this stage
the carboxylic acids are quantitatively deprotected by the treatment of 8 or
9 in pure trifluoroacetic acid at room temperature for 6 h. Although the
protocols are not emphasized in this report, these bifunctional polyamino-
carboxylate chelates can be conjugated to proteins using, for instance, a
commercially available bis-N-hydroxysuccinimide linker.
To illustrate the preparation of trifunctional chelating agents starting from
the nitro derivatives 1 or 2, the synthesis of such a molecule was investigated
(Scheme 4). In the course of our research project a trifunctional molecule was
needed that would contain (1) an EDTA moiety to chelate iron, (2) a
histamine-like fragment to be recognized by an antihistamine monoclonal
antibody, and (3) a Bolton–Hunter fragment allowing the introduction of
radioisotopes (compound 13, Scheme 4). In a first step the EDTA derivative
2 was condensed on benzyl 6-oxohexanoate via an Henry reaction. Among
the different sets of conditions or catalysts reported to promote the nitroaldol
reaction,[16] the use of neutral alumina,[17] and the n-Bu4NF/triethylamine/
tert-butyldimethylchlorosilane reagent system were found unacceptably
slow or inefficient in that case.[18] However, the adduct 10 was obtained
with an excellent yield using one equivalent of n-Bu4NF in THF after 6 h at
room temperature. The use of a catalytic amount of n-Bu4NF led to a slow
reaction and a moderate yield (for 0.2 equiv, yield was 63% after 2 days at
room temperature). The b-nitroalcohol 10 was then converted to the nitro
compound 11 by a two-step, one-pot reaction, corresponding to the dehy-
dration of 10 by the use of tris(n-butyl)phosphine and diethyl azodicarboxy-
late. This led to the intermediate nitroalkene and its subsequent reduction in
the presence of sodium borohydride.
Hydrogenolysis of the benzyl ester on compound 11 in the presence of
palladium on activated carbon under an atmospheric pressure of hydrogen
Scheme 3. (a) Pd/C (50 wt.%), HCO2NH4 (40 equiv), MeOH, rt, 1 h (1 75%, 2 80%).

Synthesis of Bifunctional and Trifunctional Chelating Agents
2419
.
Scheme 4. (a) HCO(CH2)4CO2Bn (1.5 equiv), n-Bu4NF 3H2O (1 equiv), THF, rt,
6 h (95%); (b) (n-Bu)3P (2 equiv), DEAD (2 equiv), CH2Cl2, 08C, 1 h, then dilution
with EtOH, NaBH4 (6 equiv), 08C, 1 h (49%); (c) Pd/C (10 wt.%), H2 (1 atm.),
MeOH, rt, 1 h (96%); (d) NHS (1.1 equiv), DCC (1.1 equiv), CH2Cl2, rt, 4 h, then hist-
amine (1.3 equiv), DMF, rt, 1.5 h (91%); (e) Pd/C (10 wt.%), HCO2NH4 (40 equiv),
MeOH, rt, 6 h (77%); (f) Bolton–Hunter reagent (1.2 equiv), TEA (3 equiv),
CH2Cl2, rt, 20 h (57%); (g) TFA, rt, 6 h (95%).
was carried out quantitatively without reducing the nitro group. Activation
of the obtained carboxylic acid as an N-hydroxysuccinimidyl ester and
subsequent coupling with histamine led to 12 in high yield (Scheme 4).
Then, the nitro group was reduced using ammonium formate and palladium
on activated carbon, and the corresponding amine was coupled with the
Bolton–Hunter reagent. Finally, quantitative removal of the tert-butyl ester
protective groups by treatment with trifluoroacetic acid at room temperature
led to the trifunctional chelating agent 13.
In conclusion, the synthesis of new nitro derivatives of NTA and EDTA
have been reported. These compounds are versatile building blocks for the
preparation of bi- or trifunctional chelating agents, taking advantage of the
nitro moiety reactivity. This was illustrated by the preparation of a bifunc-
tional metal-chelating agent via the reduction of the nitro group and the
design of a trifunctional metal-chelating agents via the coupling with an
aldehyde using a Henry reaction.
EXPERIMENTAL
Analytical thin-layer chromatography (TLC) was performed using 0.25-mm
silica gel–coated MERCK 60 F254 plates. Visualization of the chromatogram
was by UV absorbance and ethanolic phosphomolybdic acid. Flash chromato-
graphy was performed using compressed air with the indicated solvent system
and silica gel 60 (MERCK, 230–400 mesh). 1H NMR (300MHz) and 13C NMR
(75MHz) spectra were recorded on a BRUKER AC 300 spectrometer.
Chemical shifts are reported in parts per million (ppm) on the d scale from
an internal standard. Mass spectra (MS) by chemical ionisation in ammonia

2420
S. Meunier, P. Cristau, and F. Taran
(CI/NH3) were recorded on a quadripolar FINNIGAN-MAT 4600 spectrometer
and by electrospray on an ESI/TOF MARINER spectrometer.
tert-Butyl-2-di(tert-butyloxycarbonylmethyl)amino-3-
hydroxypropanoate (3)
To a suspension of serine tert-butyl ester hydrochloride (600 mg, 3.04 mmol)
in acetonitrile (25 mL), di-iso-propylethylamine (3.17 mL, 18.23 mmol) and
tert-butyl bromoacetate (1.79 mL, 12.15 mmol) were added. The mixture was
heated under reflux for 20 h. After cooling at room temperature and evapor-
ation of the solvent under reduced pressure, the residue was purified by
column chromatography (silica gel, hexane–EtOAc 8 : 2) to afford 3
1
(826 mg, 70%). H NMR (300 MHz, CDCl3) d: 1.42 (s, 27H), 3.38–3.55
(m, 6H), 3.67–3.78 (m, 1H), 4.28 (d, J ¼ 10.3 Hz, 1H). MS (CI, NH3): m/z
390 [M þ 1].
tert-Butyl-2-(tert-butyloxycarbonylmethylamino)-3-
hydroxypropanoate (4)
To a suspension of serine tert-butyl ester hydrochloride (3.58 g, 18.14 mmol)
in acetonitrile (150 mL), di-iso-propylethylamine (11.42 mL, 72.55 mmol) and
tert-butyl bromoacetate (3.21 mL, 21.76 mmol) were added. The mixture was
heated under reflux for 4 h. After cooling at room temperature and evaporation
of the solvent under reduced pressure, the residue was purified by column
chromatography (silica gel, hexane–EtOAc 5 : 5) to afford 4 (3.33 g, 67%).
1H NMR (300 MHz, CDCl3) d: 1.46 (s, 9H), 1.50 (s, 9H), 3.25 (dd
ABX-system, J ¼ 4.3 and 6.1 Hz, 1H), 3.27 and 3.39 (2d AB-system,
J ¼ 17.1 Hz, 2H), 3.60 (dd ABX-system, J ¼ 6.1 and 11.0 Hz, 1H), 3.72 (dd
ABX-system, J ¼ 4.3 and 11.0 Hz, 1H). 13C NMR (300 MHz, CDCl3) d:
27.8, 49.5, 62.3, 62.6, 81.3, 81.6, 171.2, 171.3. MS (CI, NH3): m/z 276
[M þ 1].
tert-Butyl-2-tert-butyloxycarbonylmethyl[2-di(tert-
butyloxycarbonylmethyl)aminoethyl]amino-3-hydroxypropanoate (5)
To a solution of 4 (300 mg, 1.09 mmol) in acetonitrile (10 mL) di-iso-propyl-
ethylamine (0.87 mL, 5.45 mmol) and N,N-bis[(tert-butoxycalbonyl)methyl]-
2-bromoethylamine (1.15 g, 3.27 mmol)[13] were added. The mixture was
heated under reflux for 20 h. After cooling at room temperature and evapor-
ation of the solvent under reduced pressure, the residue was purified by
column chromatography (silica gel, hexane–EtOAc 7 : 3) to afford 5 (520 g,
1
87%). H NMR (300 MHz, CDCl3) d: 1.43 (s, 36H), 2.74–2.98 (m, 4H),

Synthesis of Bifunctional and Trifunctional Chelating Agents
2421
3.30–3.55 (m, 8H), 3.65–3.80 (m, 1H). 13C NMR (300 MHz, CDCl3) d: 27.7,
27.8, 27.9, 52.0, 53.2, 53.7, 55.9, 59.7, 67.2, 80.7, 81.1, 81.2, 170.2, 170.4,
172.1. MS (CI, NH3): m/z 547 [M þ 1].
Typical Procedure for the Synthesis of tert-Butyl-2-di(tert-
butyloxycarbonylmethyl)amino-4-nitrobutanoate (1)
and tert-Butyl-2-tert-butyloxycarbonylmethyl[2-di(tert-
butyloxycarbonylmethyl)aminoethyl]amino-4-nitrobutanoate (2)
To a solution of 5 (150 mg, 0.27 mmol) in diethyl ether (6 mL) under argon
and at 2108C, tris(nbutyl)phosphine (100 mL, 0.41 mmol) and diethyl azodi-
carboxylate (65 mL, 0.41 mmol) were added. The mixture was stirred for 3 h,
while the temperature was allowed to reach 208C. After evaporation of the
solvent under reduced pressure, the crude material was diluted with nitro-
methane (8 mL), and tributylammonium fluoride trihydrate (520 mg,
1.65 mmol) was added. The mixture was stirred at room temperature for 1 h,
and at 508C overnight. After cooling at room temperature and evaporation
of the solvent under reduced pressure, the residue was purified by column
chromatography (silica gel, hexane–EtOAc 8 : 2) to afford 2 (103 mg, 64%).
1H NMR (300 MHz, CDCl3) d: 1.41 (s, 27H), 1.43 (s, 9H), 2.08–2.40
(m, 2H), 2.67–2.93 (m, 4H), 3.21 (d AB-system, J ¼ 17.1 Hz, 1H), 3.33
(d AB-system, J ¼ 17.1 Hz, 1H), 3.37 (d AB-system, J ¼ 17.7 Hz, 2H),
3.45 (d AB-system, J ¼ 17.7 Hz, 2H), 3.62 (dd ABX-system, J ¼ 4.3 and
11.6 Hz, 1H), 4.60–4.88 (m, 2H). 13C NMR (300 MHz, CDCl3) d: 27.7,
27.8, 28.0, 50.6, 51.2, 53.8, 55.6, 60.5, 72.1, 80.7, 80.8, 81.5, 170.3, 170.6.
HRMS: m/z calcd.: 590.3652; found: 590.3657 [M þ 1]. Analytical data for
1
compound 1: H NMR (300 MHz, CDCl3) d: 1.42 (s, 18H), 1.45 (s, 9H),
2.10–2.45 (m, 2H), 3.34 (d AB-system, J ¼ 17.1 Hz, 2H), 3.37 (d AB-
system, J ¼ 17.1 Hz, 2H), 3.47 (dd ABX-system, J ¼ 4.3 and 11.6 Hz, 1H),
4.68–4.90 (m, 2H). 13C NMR (300 MHz, CDCl3) d: 27.3, 27.8, 27.9, 54.0,
61.9, 71.9, 80.9, 81.8, 169.9, 170.4. HRMS: m/z calcd.: 433.2550; found:
433.2547 [M þ 1].
Typical Procedure for the Synthesis of tert-Butyl-4-amino-2-di(tert-
butyloxycarbonylmethyl)aminobutanoate (8) and tert-Butyl-
4-amino-2-tert-butyloxycarbonylmethyl[2-di(tert-
butyloxycarbonylmethyl)aminoethyl]aminobutanoate (9)
To a solution of 2 (100 mg, 0.17 mmol) in methanol (3 mL), palladium on
activated carbon (20 mg) and ammonium formate (428 mg, 40 eq) were
added in four portions every hour. The catalyst was filtered and washed
with methanol. The filtrate was evaporated under reduced pressure. The
residue was diluted with methylene chloride and washed with a saturated

2422
S. Meunier, P. Cristau, and F. Taran
solution of sodium hydrogenocarbonate. The organic phase was dried over
magnesium sulfate and evaporated under reduced pressure to afford 9
1
(76 mg, 80%). H NMR (300 MHz, CDCl3) d: 1.30–1.50 (m, 36H), 1.80–
2.10 (m, 2H), 2.58–2.90 (m, 4H), 3.18–3.50 (m, 9H), 3.67–3.74 (m, 1H).
13C NMR (300 MHz, CDCl3) d: 25.6, 27.7, 27.8, 27.9, 49.7, 50.1, 55.0,
60.8, 81.4, 81.7, 82.0, 170.4, 172.0. MS (CI, NH3): m/z 560 [M þ 1]. Analyti-
cal data for compound 8: 1H NMR (300 MHz, CDCl3) d: 1.41 (bs, 27H), 1.90–
2.30 (m, 2H), 3.05–3.60 (m, 7H). 13C NMR (300 MHz, CDCl3) d: 25.0, 27.8,
27.9, 38.6, 53.7, 64.1, 81.9, 82.0, 169.6, 170.6. MS (CI, NH3): m/z 403
[M þ 1].
Procedure for the Synthesis of 10
To a solution of 2 (800mg, 1.36mmol) in THF (20 mL), benzyl 6-oxohexanoate
(400mg, 2.04mmol) and tributylammonium fluoride trihydrate (428mg,
1.36mmol) were added. The mixture was stirred for 6 h at room temperature.
After evaporation of the solvent under reduced pressure, the crude material
was diluted with methylenechloride and washed twice with water and once
with brine. The organic phase was dried over magnesium sulfate and evaporated
under reduced pressure. The residue was purified by column chromatography
(silica gel, hexane–EtOAc 8 : 2) to afford 10 (1.5g, 95%). 1H NMR
(300MHz, CDCl3) d: 0.90–1.80 (m, 40H), 1.92–2.50 (m, 6H), 2.55–2.95
(m, 4H), 3.00–3.78 (m, 7H), 3.80–4.25 (m, 1H), 4.85–5.35 (m, 3H), 7.20–
7.45 (m, 5H). 13C NMR (300MHz, CDCl3) d: 24.4, 25.0, 27.8, 27.9, 28.0,
29.3, 29.9, 31.4, 32.5, 33.9, 51.3, 52.0, 54.0, 55.0, 55.7, 60.8, 61.2, 65.9, 70.5,
71.4, 72.2, 80.9, 81.0, 81.6, 87.2, 88.2, 127.9, 128.3, 135.8, 170.5, 170.7,
173.1. MS (CI, NH3): m/z 810 [M þ 1]. MS (TOF): m/z 832 [M þ 23].
Procedure for the Synthesis of 11
To a solution of 10 (270 mg, 0.33 mmol) in methylene chloride (2 mL) were
added, under argon and at 2158C, tris(nbutyl)phosphine (165 mL,
0.66 mmol) and diethyl azodicarboxylate (105 mL, 0.66 mmol). The mixture
was stirred for 1 h at 08C, then cooled at 258C, diluted with ethanol
(7 mL), and sobium borohydride (75 mg, 1.99 mmol) was added. The
mixture was stirred for 1 h at 08C, and quenched by addition of water. The
solution was extracted twice with ethyl acetate, the organic phases were
dried over magnesium sulfate and the solvent was evaporated under reduced
pressure. The residue was purified by column chromatography (silica
1
gel, hexane–EtOAc 8 : 2) to afford 11 (126 mg, 49%). H NMR (300 MHz,
CDCl3) d: 1.23–2.25 (m, 44H), 2.22–2.43 (m, 4H), 2.67–2.98 (m, 4H),
3.12–3.60 (m, 7H), 4.82 (quint., J ¼ 7.2 Hz, 0.5H), 5.00–5.34 (m, 2.5H),
7.28–7.43 (sl, 5H). 13C NMR (300 MHz, CDCl3) d: 24.3, 25.0, 27.8, 27.9,

Synthesis of Bifunctional and Trifunctional Chelating Agents
2423
28.3, 33.1, 33.3, 33.4, 33.8, 34.1, 50.1, 52.0, 52.2, 52.5, 53.5, 53.9, 55.7, 55.8,
60.6, 61.7, 65.8, 80.6, 81.5, 84.4, 85.3, 127.9, 128.3, 135.8, 170.3, 170.7,
170.8, 170.9, 173.0. MS (TOF): m/z 794 [M þ 1].
Procedure for the Synthesis of 12
To a solution of 11 (112 mg, 0.14 mmol) in methanol (3 mL) was added
palladium on activated carbon (10 mg). The mixture was stirred for 1 h
under hydrogen (1 atm). The catalyst was filtered and washed with
methanol. The filtrate was evaporated under reduced pressure to afford the
1
corresponding benzyl-deprotected carboxylic acid (96 mg, 96%). H NMR
(300 MHz, CDCl3) d: 1.20–2.15 (m, 44H), 2.22–2.42 (m, 4H), 2.62–3.05
(m, 4H), 3.18–3.80 (m, 7H), 4.80–4.92 (m, 0.5H), 4.98–5.12 (m, 0.5H).
MS (TOF): m/z 704 [M þ 1]. To the solution of this compound in
methylene chloride (2 mL), N-hydroxysuccinimide (18 mg, 0.15 mmol) and
dicyclocarbodiimide (31 mg, 0.15 mmol) were added. The mixture was
stirred for 4 h and filtered. The filtrate was evaporated under reduced
pressure. The residue obtained was diluted with DMF (2 mL), and histamine
(20 mg, 0.17 mmol) was added. The mixture was stirred for 1.5 h, and then
the solvent was evaporated under reduced pressure. The residue was
purified by column chromatography (silica gel, methylene chloride–
1
methanol 9 : 1) to afford 12 (99 mg, 91%). H NMR (300 MHz, CDCl3) d:
1.12–1.30 (m, 4H), 1.40 (sl, 36H), 1.45–2.02 (m, 5H), 2.10 (t, J ¼ 7.3 Hz,
2H), 2.20–2.35 (m, 1H), 2.62–2.92 (m, 6H), 3.10–3.50 (m, 9H), 4.77
(quint., J ¼ 6.7 Hz, 0.5H), 4.93–5.08 (m, 0.5H), 6.68 (t, J ¼ 6.5 Hz, 1H),
6.76 (s, 1H), 7.54 (s, 1H). MS (TOF): m/z 797 [M þ 1].
Procedure for the Synthesis of 13
To a solution of 12 (83 mg, 0.10 mmol) in methanol (3 mL) were added
palladium on activated carbon (20 mg) and ammonium formate (264 mg, 40
eq) in four portions every 90 min. The catalyst was filtered and washed with
methanol. The filtrate was evaporated under reduced pressure. The residue
was diluted with methylene chloride and washed with a saturated solution
of sodium hydrogenocarbonate. The organic phase was dried over
magnesium sulfate and evaporated under reduced pressure to afford the
expected amine (62 mg, 77%) as the product of the nitro function reduction.
1H NMR (300 MHz, CDCl3) d: 1.00–1.93 (m, 46H), 2.11 (t, J ¼ 7.3 Hz),
2.58–2.90 (m, 6H), 3.00–3.80 (m, 10H), 6.74 (s, 1H), 7.45 (s, 1H). MS
(TOF): m/z 767 [M þ 1]. To the solution of the previous compound in
methylene chloride (2 mL), triethylamine (35 mL, 0.24 mmol) and the
Bolton–Hunter reagent (26 mg, 0.10 mmol) were added. The mixture was
stirred for 20 h, and then diluted with methylene chloride and washed with

2424
S. Meunier, P. Cristau, and F. Taran
a saturated solution of sodium hydrogenocarbonate. The organic phase was
dried over magnesium sulfate and evaporated under reduced pressure. The
residue was purified by column chromatography (silica gel, methylene
chloride–methanol 9 : 1) to afford the expected coupling adduct (42 mg,
57%). 1H NMR (300 MHz, CDCl3) d: 1.25–1.90 (m, 46H), 2.03
(t, J ¼ 7.3 Hz, 2H), 2.42–2.60 (m, 2H), 2.62–3.00 (m, 8H), 3.12–3.92
(m, 10H), 6.68–6.82 (m, 3H), 7.02 (d, J ¼ 6.7, 1H), 7.04 (d, J ¼ 8.5, 1H),
7.53 (s, 1H). MS (TOF): m/z 937 [M þ 23]. The solution of the previous
compound in trifluoroacetic acid (3 mL) was stirred for 6 h. Diethyl ether
was added, and the precipitate was filtered, washed with diethyl ether, and
1
dried under vacuum to afford 13-(tris-trifluoroacetate salt) (40 mg, 95%). H
NMR (300 MHz, CDCl3) d: 1.20–2.00 (m, 10H), 2.02–2.15 (m, 2H), 2.38–
2.52 (m, 2H), 2.70–3.20 (m, 8H), 2.35–2.70 (m, 4H), 3.80–4.48 (m, 6H),
6.62 (d, J ¼ 7.9 Hz, 2H), 6.97 (d, J ¼ 7.9 Hz, 1H), 6.99 (d, J ¼ 7.9 Hz, 1H),
7.28 (s, 1H), 8.75 (s, 1H). MS (TOF): m/z 691 [M þ 1].
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