A Convenient Synthesis for HBED-CC-tris(tert -butyl ester)

Article abstract of DOI:10.1055/s-0036-1591950

HBED-CC is a bifunctional complexing agent that, at ambient temperature, tightly chelates the trivalent radiometal ⁶⁸ Ga (T _1/2 = 68 min). This complexing agent has attracted a lot of interest in tumor imaging applications. Depending on the chemical structure, different HBED-CC variants may be employed as radiolabeling precursor for the synthesis of desired radiopharmaceuticals. In this context, HBED-CC-tris(tert-butyl ester) is the only known monovalent variant of HBED-CC which is used for the synthesis of non-symmetric HBED-CC-based radiopharmaceuticals. Commercial HBED-CC-tris(tert -butyl ester) is very expensive, with limited availability. Nevertheless, no synthetic procedure for this useful product has been reported to date. This work introduces a convenient and comparatively cost-efficient method for the preparation of HBED-CC-tris(tert -butyl ester).

Full text of DOI:10.1055/s-0036-1591950

SYNLETT
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©
Georg Thieme Verlag Stuttgart · New York
2018, 29, A–E
letter
A
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Synlett
A. Makarem et al.
Letter
A Convenient Synthesis for HBED-CC-tris(tert-butyl ester)
Ata Makarem*
Moritz Konrad
Christos Liolios
Klaus Kopka
German Cancer Research Center (DKFZ) Heidelberg,
Division of Radiopharmaceutical Chemistry, INF 280,
6
9120 Heidelberg, Germany
a.makarem@dkfz.de
Received: 28.01.2017
Accepted after revision: 11.02.2018
Published online: 07.03.2018
HO C
2
t-BuO2C
t-BuO2C
HO C
2
OH
DOI: 10.1055/s-0036-1591950; Art ID: st-2018-d0056-l
OH
N
N
N
N
Abstract HBED-CC is a bifunctional complexing agent that, at ambi-
OH
68
OH
CO2H
ent temperature, tightly chelates the trivalent radiometal Ga (T1/2 = 68
min). This complexing agent has attracted a lot of interest in tumor im-
aging applications. Depending on the chemical structure, different
HBED-CC variants may be employed as radiolabeling precursor for the
synthesis of desired radiopharmaceuticals. In this context, HBED-CC-
tris(tert-butyl ester) is the only known monovalent variant of HBED-CC
which is used for the synthesis of non-symmetric HBED-CC-based radio-
pharmaceuticals. Commercial HBED-CC-tris(tert-butyl ester) is very
expensive, with limited availability. Nevertheless, no synthetic proce-
dure for this useful product has been reported to date. This work intro-
duces a convenient and comparatively cost-efficient method for the
preparation of HBED-CC-tris(tert-butyl ester).
2
CO t-Bu
O
CO2H
NH
HBED-CC-tris(t-Bu ester)
O
O
=
modified bioactive molecule
O
O
N
N
O
O
Key words HBED-CC, bifunctional chelator, hexadentate ligand, syn-
thesis, radiotracer
O
2
HO C
HN
Radiopharmaceuticals are essential for cancer diagnosis
1–3
as well as therapy in nuclear medicine. To date, a variety
of radiopharmaceuticals with different structures and
Scheme 1 Preparation of monovalent radiopharmaceuticals, starting
with HBED-CC-tris(tert-butyl ester)
4,5
functional groups have been introduced. Among them,
radiometal-based radiopharmaceuticals bearing the com-
plexing agent N,N′-bis[2-hydroxy-5-(carboxyethyl)ben-
zyl]ethylenediamine-N,N′-diacetic acid (HBED-CC) have
been drawing the attention of many research groups over
for highly sensitive and specific diagnosis of cancer (i.e.,
6
8
Ga[Ga]DKFZ-11, prostate cancer diagnosis) and other dis-
eases. Hence, syntheses of HBED-CC variants and their cor-
responding radiometal-based radiopharmaceuticals have
6–13
the past decade.
HBED-CC is a bifunctional hexadentate
15–20
ligand with an N O donor set that forms strong complexes
been developed in recent years.
In this context, HBED-
2
4
with gallium, in particular in this context, its radioactive
CC-tris(tert-butyl ester)21 is the only known monovalent
variant of HBED-CC. This compound is employed as a pre-
cursor for synthesis of HBED-CC-based radiopharmaceuti-
cals with non-symmetric structures (Scheme 1).15 In gener-
al, preparation of HBED-CC-based radiopharmaceuticals
from the HBED-CC-tris(tert-butyl ester) precursor is divid-
ed into two main steps, namely bioconjugation and subse-
14
isotopes, such as the positron emitter gallium-68. There-
68
fore, Ga-labelled HBED-CC-based radiopharmaceuticals
have become popular in recent years for noninvasive imag-
ing by means of positron-emission-tomography/computer
tomography (PET/CT) due to their particular nuclear physi-
cal and at the same time pharmacokinetic characteristics
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

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A. Makarem et al.
Letter
quent radiolabeling. Initially, the HBED-CC triester precur-
sor binds a modified bioactive molecule (e.g., a peptide, in-
hibitor). In the next step, the tert-butyl groups have to be
removed to yield the complete set of coordinating sites
ready for radiolabeling with radiogallium, which results in
group of this gives product 1.23 This product is converted
into aldehyde 2 through ortho-formylation.24 Then, alde-
hyde 2 is transformed into amine 5 by reductive amination
25
in the 2,2,2-trifluoroethanol (pK 12.4) solution. This sol-
a
vent adjusts the pH to 5–6, which is ideal for reduction of
22
26
very strong complexes.
the imine intermediate. Use of other common protic sol-
However, commercial HBED-CC-tris(tert-butyl ester) is
very expensive and has limited availability. To our knowl-
edge, no synthetic method and characterization data for
this compound have yet been reported. Therefore, there is a
need to find a suitable and efficient method to prepare this
very useful complexing agent. The current work presents a
new and convenient synthetic procedure for HBED-CC-
tris(tert-butyl ester), together with full structural charac-
terization of this product and its intermediates (Scheme 2).
As illustrated in Scheme 2, the synthetic pathway starts
with 4-hydroxyhydrocinnamic acid as the first commercial-
ly available reactant. Esterification of the carboxylic acid
vents, such as methanol, for this reaction causes incomplete
reaction and increases the number of by-products. Subse-
quently, removal of the tert-butyl dicarbonate (Boc) group
provides salt 6. This salt is then used for the reductive ami-
nation of 8 to provide amine 10. Intermediate 8 is prepared
from ester 7 through ortho-formylation.24 Finally, com-
pound 10 is alkylated, followed by hydrolysis to yield
HBED-CC-tris(tert-butyl ester) as the final product (Scheme
2).
In conclusion, we have developed a convenient and cost-
efficient procedure for the synthesis of HBED-CC-tris(tert-
butyl ester).2
7,28
All the commercially available chemicals
OH
OH
PFA
MgCl2
Et3N
PFA
MgCl2
Et3N
OH
1) CDI
THF, inert gas
40 °C, 2 h
MeOH
H2SO4 (cat.)
reflux, 2 h
MeCN
reflux, 1 h
MeCN
reflux, 1 h
2
) t-BuOH
DBU
quantitative yield
reflux, 48 h
0%
CO2Me
CO2t-Bu
CO2H
95%
6
80%
1
7
3
OH
O
OH
OH
OH
O
OH
NaBH4
TFE
HCl
H2N
NHBoc
NHBoc dioxane
NH2
NHBoc
N
H
H
N
H
H
N
+
CH2Cl2
r.t., 1 h
0 °C to r.t.
inert gas
r.t., 15 min
2
HCl
1
h
89%
CO2t-Bu
CO2Me
CO2Me
CO2Me
CO2Me
quantitative yield
quantitative yield
2
4
5
6
8
CO2t-Bu
1) Br
CO2t-Bu
2
CO t-Bu
CO2t-Bu
Na2CO3
MeCN
reflux, 3.5 h
CO2t-Bu
MeOH
Et3N
NaBH4
TFE
OH
OH
H
N
OH
N
N
N
H
N
H
N
0 °C to r.t.
inert gas
OH
r.t., 1 h
OH
2) MeOH/H O
OH
2
NaOH (aq)
r.t., 1 h
t-BuO2C
1
h
MeO2C
MeO2C
quantitative yield
HO2C
9
quantitative yield
10
Via:
HBED-CC-tris(tert-butyl ester)
CO2t-Bu
overall yield: 28%
Boc = tert-butyloxycarbonyl
PFA = paraformaldehyde
CDI = 1,1'-carbonyldiimidazol
DBU = 1,8-diazabicyclo[5.4.0]undec-7-en
TFE = 2,2,2-trifluoroethanol
CO2t-Bu
OH
N
N
OH
t-BuO2C
MeO2C
Scheme 2 Synthesis of HBED-CC-tris(tert-butyl ester)
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Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

C
Synlett
A. Makarem et al.
Letter
used in our synthetic protocol are relatively low-priced.
Furthermore, most reaction steps are short and easy to per-
form, and also involve simple, fast and cost-efficient purifi-
cation methods.
(13) Eder, M.; Knackmuss, S.; Le Gall, F.; Reusch, U.; Rybin, V.; Little,
M.; Haberkorn, U.; Mier, W.; Eisenhut, M. Eur. J. Nucl. Med. Mol.
Imaging 2010, 37, 1397.
(
14) (a) Zöller, M.; Schuhmacher, J.; Reed, J.; Maier-Borst, W.;
Matzku, S. J. Nucl. Med. 1992, 33, 1366. (b) Schuhmacher, J.;
Klivenyi, G.; Hull, W. E.; Matys, R.; Hauser, H.; Kalthoff, H.;
Schmiegel, W. H.; Maier-Borst, W.; Matzku, S. Nucl. Med. Biol.
Funding Information
1992, 19, 809.
(
15) Trencsényi, G.; Dénes, N.; Nagy, G.; Kis, A.; Vida, A.; Farkas, F.;
Szabó, J. P.; Kovács, T.; Berényi, E.; Garai, I.; Bai, P.; Hunyadi, J.;
Kertész, I. J. Pharm. Biomed. Anal. 2017, 139, 54.
This work was partly funded by a grant of the German Cancer Aid
(
Deutsche Krebshilfe), project number 70112043.
D
e
ustch
e
Krebeshfli
7(
0
1
1
2
0
4
3)
(16) Kung, H. F.; Wu, Z.; Choi, S. R.; Ploessl, K.; Zha, Z. PCT Int. Appl
WO 2017007790, 2017.
Acknowledgment
(
17) Zha, Z.; Song, J.; Choi, S. R.; Wu, Z.; Ploessl, K.; Smith, M.; Kung,
H. Bioconjugate Chem. 2016, 27, 1314.
The authors gratefully acknowledge Mrs. Jana Schmidt (technical as-
sistant), together with Dr. Karel Klika and colleagues of the NMR ser-
vice at the German Cancer Research Center (DKFZ) Heidelberg.
(18) Liolios, C.; Schäfer, M.; Haberkorn, U.; Eder, M.; Kopka, K. Bio-
conjug ate Chem. 2016, 27, 737.
(
(
(
19) Eder, M.; Schäfer, M.; Bauder-Wüst, U.; Hull, W. E.; Wängler, C.;
Mier, W.; Haberkorn, U.; Eisenhut, M. Bioconjug ate Chem. 2012,
23, 688.
20) Eder, M.; Wängler, B.; Knackmuss, S.; LeGall, F.; Little, M.;
Haberkorn, U.; Mier, W.; Eisenhut, M. Eur. J. Nucl. Med. Mol.
Imaging 2008, 35, 1878.
21) Commercially known as EBED-CC-tris(tBu)ester; chemical
name: 3-(3-{[(2-{[5-(2-tert-butoxycarbonyl-ethyl)-2-hydroxy-
benzyl]-tert-butoxycarbonylmethyl-amino}-ethyl)-tert-butoxy-
carbonylmethyl-amino]-methyl}-4-hydroxy-phenyl)-propionic
acid.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1591950.
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ortioIgnfrm oaitn
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p
ortioIgnfrm oaitn
References and Notes
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(
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(
(
(
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29, 1463.
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Aggarwal, R.; Ryan, C. J.; Carroll, P. R.; Small, E. J.; Evans, M. J.
J. Nucl. Med. 2017, 58, 81. (b) Hope, T. A.; Aggarwal, R.; Chee, B.;
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(26) Baxter, E. W.; Reitz, A. B. Org. React. 2002, 18, 1.
(27) Preparation of the known compounds are described in the Sup-
porting Information.
(
28) Synthesis of Methyl 3-{3-[({2-[(tert- Butoxycarbonyl)amino]
ethyl}imino)methyl]-4-hydroxyphenyl}propanoate (4)
To a solution of methyl 3-(3-formyl-4-hydroxyphenyl)propa-
noate (2) (3.00 g, 14.41 mmol, 1.0 equiv) in anhydrous dichloro-
methane (10 mL) was added tert-butyl (2-aminoethyl)carba-
mate (3) (2.54 g, 15.85 mmol, 1.1 equiv). The mixture was
stirred at room temperature for 1 h, and then diluted with
dichloromethane (40 mL). The reaction mixture was then
washed with aq. sodium bisulfite (0.5 M, 50 mL). The product
residue in the aqueous phase was recovered by washing four
times with dichloromethane. Then, the combined organic
phases were dried over sodium sulfate, filtered and the solvent
(c) Fendler, W. P.; Eiber, M.; Beheshti, M.; Bomanji, J.; Ceci, F.;
Cho, S.; Giesel, F.; Haberkorn, U.; Hope, T. A.; Kopka, K.; Krause,
B. J.; Mottaghy, F. M.; Schöder, H.; Sunderland, J.; Wan, S.;
Wester, H. J.; Fanti, S.; Herrmann, K. Eur. J. Nucl. Med. Mol.
Imaging 2017, 44, 1014.
(
7) (a) McCarthy, M.; Langton, T.; Kumar, D.; Campbell, A. Eur.
J. Nucl. Med. Mol. Imaging 2017, 44, 1455. (b) Baranski, A. C.;
Schäfer, M.; Bauder-Wüst, U.; Wacker, A.; Schmidt, J.; Liolios, C.;
Mier, W.; Haberkorn, U.; Eisenhut, M.; Kopka, K.; Eder, M. Bio-
conjugate Chem. 2017, 28, 2485.
(
8) Pyka, T.; Weirich, G.; Einspieler, I.; Maurer, T.; Theisen, J.;
Hatzichristodoulou, G.; Schwamborn, K.; Schwaiger, M.; Eiber,
M. J. Nucl. Med. 2016, 57, 367.
was removed under reduced pressure to give product 4 as an
1
orange oil (quantitative yield). H NMR (400.13 MHz, CDCl ,
3
(
9) Rauscher, I.; Maurer, T.; Beer, A. J.; Graner, F.-P.; Haller, B.;
Weirich, G.; Doherty, A.; Gschwend, J. E.; Schwaiger, M.; Eiber,
M. J. Nucl. Med. 2016, 57, 1713.
3
2
2
5 °C): δ = 8.32 (s, 1 H, CCHN), 7.15 (dd, JH–H = 8.4 Hz, 4JH–H
=
4
.2 Hz, 1 H, CHCHCCH), 7.09 (d, J
= 2.2 Hz, 1 H, CCHC), 6.90
H–H
3
(
d, JH–H = 8.4 Hz, 1 H, CHCHCCH), 4.72 (br s, 1 H, NH), 3.70 (t,
JH–H = 5.7 Hz, 2 H, CH CH NHBoc), 3.66 (s, 3 H, OCH ), 3.45 (m,
H, CH CH NHBoc), 2.90 (t, JH–H = 7.7 Hz, 2 H, CH CH CO ),
(
(
(
10) Haberkorn, U.; Eder, M.; Kopka, K.; Babich, J. W.; Eisenhut, M.
3
2
2
3
Clin. Cancer Res. 2016, 22, 9.
3
2
2
2
3
2
2
2
2
11) Verburg, F. A.; Krohn, T.; Heinzel, A.; Mottaghy, F. M.; Behrendt,
F. F. Eur. J. Nucl. Med. Mol. Imaging 2015, 42, 1622.
12) Afshar-Oromieh, A.; Zechmann, C. M.; Malcher, A.; Eder, M.;
Eisenhut, M.; Linhart, H. G.; Holland-Letz, T.; Hadaschik, B. A.;
Giesel, F. L.; Debus, J. J.; Haberkorn, U. Eur. J. Nucl. Med. Mol.
Imaging 2014, 41, 11.
.60 (t,
J
= 7.7 Hz, 2 H, CH CH CO ), 1.43 (s, 9 H, C(CH ) )
H–H
1
2 2 2 3 3
1
3
ppm. C{ H} NMR (100.61 MHz, CDCl , 25 °C): δ = 173.40
3
Boc
(
(
1
5
3
CO CH ), 166.59 (COH), 159.57 (CCHN), 155.98 ( CO ), 132.65
2
3
2
CHCHCCH), 131.10 (CHCHCCH), 130.81 (CCHC), 118.60 (CCHN),
Boc
17.24 (CHCHCCH), 79.71 ( CO CCH ), 59.57 (CH CH NHBoc),
2 3 2 2
1.78 (CO CH ), 41.37 (CH CH NHBoc), 36.00 (CH CH CO ),
2
3
2
2
2
2
2
0.07 (CH CH CO ), 28.51 (C(CH ) ). HRMS (ESI+, CH2-
2
2
2
3 3
©
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A. Makarem et al.
Letter
Cl /MeOH): m/z calcd for C18H27N O : 351.1914; found:
dichloromethane. The combined organic phase was dried over
sodium sulfate, filtered and the solvent was removed under
2
2
5
3
51.1914. HRMS (ESI-, CH Cl /MeOH): m/z calcd for
2 2
C18H25N O : 349.1769; found: 349.1769.
reduced pressure to give product 9 as orange solid in quantita-
2
5
1
Synthesis of Methyl 3-{3-[({2-[(tert-Butoxycarbonyl)amino]
ethyl}amino)methyl]-4-hydroxyphenyl}propanoate (5)
A solution of compound 4 (4.90 g, 14.00 mmol, 1.0 equiv) in
tive yield. Mp 77–79 °C. H NMR (400.13 MHz, CDCl , 25 °C): δ =
3
3
4
8.35 (s, 1 H, CCHN), 7.15 (dd, JH–H = 8.4 Hz, JH–H = 2.2 Hz, 1 H,
2.2 Hz, 1 H, CCHC-
(CH ) CO Me), 6.98 (dd, JH–H = 8.2 Hz, JH–H = 2.1 Hz, 1 H,
CHCHC-(CH ) CO Me), 7.08 (d, 4J
=
2
2
2
H–H
3
4
2,2,2-trifluoroethanol (60 mL) was cooled in an ice-bath.
2
2
2
3
Sodium borohydride (1.32 g, 35 mmol, 2.5 equiv) was added in
portions and then the reaction mixture was allowed to warm to
room temperature. After being stirred under an inert atmo-
sphere at room temperature for one hour, the reaction was
quenched with water (50 mL). The product was extracted with
dichloromethane and the organic layer was dried over sodium
sulfate and filtered. By removal of the solvent under reduced
pressure compound 5 was obtained as a colorless oil in quanti-
tative yield. This product was almost pure and used in the next
CHCHC-(CH ) CO t-Bu), 6.88 (d, JH–H = 8.4 Hz, 1 H, CHCHC-
2 2 2
4
(CH ) CO Me), 6.81 (d, J
= 2.1 Hz, 1 H, CCHC-(CH ) CO t-Bu),
2 2 2
= 8.2 Hz, 1 H, CHCHC-(CH ) CO t-Bu), 3.98 (s, 2 H,
2
2
2
3
H–H
6.74 (d, J
H–H
2 2 2
Bn
3
CH ), 3.75 (t, JH–H = 5.3 Hz, 2 H, CH CH NH), 3.65 (s, 3 H,
= 5.3 Hz, 2 H, CH CH NH), 2.83 (m, 4 H,
CH CH CO Me and CH CH CO t-Bu), 2.56 (t, JH–H = 7.8 Hz, 2 H,
= 7.6 Hz, 2 H, CH CH CO t-Bu), 1.40
(s, 9 H, C(CH ) ). C{ H} NMR (100.61 MHz, CDCl , 25 °C): δ =
2
2
2
OCH ), 3.00 (t, 3J
3
H–H
2 2
3
2
2
2
2
2
2
3
CH CH CO Me), 2.50 (t, J
2
2
2
H–H
2
2
2
1
3
1
3
3
3
173.58 (CO CH ), 172.28 (CO t-Bu), 166.76 (CCHN), 159.31
2
3
2
step without further purification. However, for spectroscopic
(C(OH)CCH(imine)), 156.53 (C(OH)CCH2), 132.82 (CHCHC-
(CH ) CO Me), 131.17 (C-(CH ) CO Me and C-(CH ) CO t-Bu),
1
characterization it was purified through HPLC.
H
NMR
2
2
2
2
2
2
2
2
2
3
(
2
400.13 MHz, CDCl , 25 °C): δ = 6.98 (dd, JH–H = 8.2 Hz, 4J
=
131.15 (CCHC-(CH ) CO Me), 128.60 (CCHC-(CH ) CO t-Bu),
3
H–H
2 2 2 2 2 2
4
.2 Hz, 1 H, CHCHCCH), 6.81 (d, J
= 2.2 Hz, 1 H, CCHC), 6.74
128.45 (CHCHC-(CH ) CO t-Bu), 122.17 (CCH NH), 118.4
2 2 2 2
H–H
3
(
d, JH–H = 8.4 Hz, 1 H, CHCHCCH), 4.75 (br s, 1 H, CH NHCH ),
(CCHN), 117.24 (CHCHC-(CH ) -CO t-Bu), 116.51 (CHCHC-
2
2
2 2 2
3
.97 (s, 2 H, CCH NH), 3.66 (s, 3 H, OCH ), 3.28 (m, 2 H,
(CH ) CO Me), 80.52 (CO CCH ), 59.31 (CH CH NH), 52.53
2 2 2 2 3 2 2
2
3
3
Bn
CH NHBoc), 2.83 (t, JH–H = 7.7 Hz, 2 H, CH CH CO ), 2.78 (t,
( CH ), 51.67 (CO CH ), 48.60 (CH CH NH), 37.33 (CH CH CO t-
2
2
3
2
2
2 2 3 2 2 2 2 2
3
JH–H = 5.7 Hz, 2 H, CH CH NHBoc), 2.56 (t, JH–H = 7.7 Hz, 2 H,
Bu), 36.18 (CH CH CO Me), 30.22 (CH CH CO Me), 30.19
2 2 2 2 2 2
2
2
13
1
CH CH CO ), 1.44 (s, 9 H, C(CH ) ). C{ H} NMR (100.61 MHz,
CDCl , 25 °C): δ = 173.62 (CO CH ), 156.51 ( CO ), 156.33
(CH CH CO t-Bu), 28.18 (C(CH ) ). HRMS (ESI+, CH Cl /MeOH):
2
2
2
3
3
2 2 2 3 3 2 2
Boc
m/z calcd for C27H37N O : 485.2646; found: 485.2649;
2 6
3
2
3
2
(
1
COH), 131.16 (CHCHCCH), 128.63 (CCHC), 128.47 (CHCHCCH),
C27H36N NaO : 507.2471; found: 507.2474. HRMS (ESI-, CH -
2
6
2
Boc
22.27 (CCH NH), 116.52 (CHCHCCH), 79.78 ( CO CCH ), 52.48
Cl /MeOH): m/z calcd for C27H35N O : 483.2501; found:
2
2
3
2
2
6
(
CCH NH), 51.70 (CO CH ), 48.55 (CH CH NHBoc), 40.16
483.2500.
2
2
3
2
2
(
CH NHBoc), 36.20 (CH CH CO ), 30.24 (CH CH CO ), 28.50
Synthesis of tert-Butyl 3-(4-hydroxy-3-{[(2-{[2-hydroxy-5-
(3-methoxy-3-oxopropyl)ben-
2
2
2
2
2
2
2
(C(CH ) ). HRMS (ESI+, CH Cl /MeOH): m/z calcd for C18H29N O :
3 3 2 2 2 5
3
53.2071; found: 353.2071. HRMS (ESI-, CH Cl /MeOH): m/z
zyl]amino}ethyl)amino]methyl} phenyl)propanoate (10)
A solution of compound 9 (2.33 g, 4.80 mmol, 1.0 equiv) in
2,2,2-trifluoroethanol (50 mL) was cooled in an ice-bath.
Sodium borohydride (0.45 g, 12 mmol, 2.5 equiv) was added in
portions to this solution, and then the reaction mixture was
allowed to warm to room temperature. After being stirred
under inert gas atmosphere at room temperature for one hour,
the reaction was quenched with water (50 mL). The product
was extracted with dichloromethane and the organic layer was
dried over sodium sulfate and filtered. By removal of the solvent
2
2
calcd for C18H27N O : 351.1925; found: 351.1925.
2
5
Synthesis of [Methyl 3-(3-{[(2- Aminoethyl)amino]methyl}-
-hydroxyphenyl)propanoate] Dihydrochloride (6)
4
Compound 5 (4.90 g, 13.90 mmol) was dissolved in 4 M HCl in
dioxane (20 mL). After being stirred at room temperature for 15
min, diethyl ether (40 mL) was added and the reaction mixture
stirred for another 5 min. The white precipitate was filtered,
washed with diethyl ether and dried under vacuum to give salt
6
1
(4.04 g, 12.37 mmol, 89%). Mp 190–191 °C.
H NMR
(
400.13 MHz, D O, 25 °C): δ = 7.24 (m, 2 H, CHCHCCH), 6.94 (d,
under reduced pressure white solid 10 was obtained in quanti-
2
3
Bn
1
JH–H = 9.0 Hz, 1 H, CHCHCCH), 4.31 (s, 2 H, CH ), 3.66 (s, 3 H,
tative yield. Mp 74–76 °C. H NMR (400.13 MHz, CDCl , 25 °C):
2
3
OCH ), 3.45 (m, 4 H, CH CH NH), 2.89 (t, 3JH–H = 7.3 Hz, 2 H,
CH CH CO ), 2.70 (t, JH–H = 7.3 Hz, 2 H, CH CH CO ). C{ H}
NMR (100.61 MHz, D O, 25 °C): δ = 176.50 (CO CH ), 153.48
δ = 6.98 (d, JH–H
3
=
8.2 Hz, 2 H, CHCHC-(CH ) CO Me and
3
2
2
2
2
2
3
13
1
CHCHC-(CH ) CO t-Bu), 6.80 (br s, 2 H, CCHC-(CH ) CO Me and
2
2
2
2
2
2
2
2
2
2
2
2
3
4
CCHC-(CH ) CO t-Bu), 6.73 (dd, J
= 8.2 Hz, J
= 2.2 Hz, 2 H,
2
2
3
2
2
2
H–H
H–H
(
COH), 132.68 (CHCHCCH), 131.49 (CCHC), 131.42 (CHCHCCH),
CHCHC-(CH ) CO Me and CHCHC-(CH ) CO t-Bu), 3.94 (s, 2 H,
2 2 2 2 2 2
Bn
1
16.80 (CCH N), 115.70 (CHCHCCH), 52.16 (CO CH ),47.42
CH ), 3.65 (s, 3 H, OCH ), 2.81 (m, 8 H, NH(CH ) NH, CH CH -
2 3 2 2 2 2
2
2
3
Bn
3
(
CH ), 43.48 (ArCH NHCH ), 35.45 (CH NH ), 35.40 (CH CH -
CO Me and CH CH CO t-Bu), 2.56 (t, J
= 7.5 Hz, 2 H, CH CH -
2
2
2
2
2
2
2
2
2
2
2
H–H 2 2
3
CO ), 29.25 (CH CH CO ) ppm. Anal. Calcd. (included 3.56%
CO Me), 2.50 (t, J
= 7.8 Hz, 2 H, CH CH CO t-Bu), 1.41 (s, 9 H,
2
2
2
2
2
H–H 2 2 2
13
1
water; hydroscopic salt) C: 46.30, H: 6.97, N: 8.31; found C:
6.46, H: 6.88, N: 8.13.
Synthesis of tert-Butyl 3-(4-Hydroxy-3-{[(2-{[2-hydroxy-5-
3-methoxy-3-oxopropyl)benzyl]amino}ethyl)imino]
C(CH ) ). C{ H} NMR (100.61 MHz, CDCl , 25 °C): δ = 173.60
3
3
3
4
(CO CH ), 172.56 (CO t-Bu), 156.38 (COH), 156.53 (COH), 131.49
2 3 2
(C-(CH ) CO Me), 131.20 (C-(CH ) CO t-Bu), 128.70 (CCHC-
2
2
2
2
2
2
(
(CH ) CO Me), 128.62 (CCHC-(CH ) CO t-Bu), 128.48 (CHCHC-
2 2 2 2 2 2
methyl}phenyl)propanoate (9)
(CH ) CO Me), 128.44 (CHCHC-(CH ) CO t-Bu), 122.22 (CCHC-
2 2 2 2 2 2
Dry triethylamine (1.51 g, 14.88 mmol, 3 equiv) was added to a
solution of compound 6 (1.77 g, 5.46 mmol, 1.1 equiv) in abso-
lute methanol (25 mL). To this mixture was added aldehyde 8
(CH ) CO Me), 122.06 (CCHC-(CH ) CO t-Bu), 116.46 (CHCHC-
2 2 2 2 2 2
(CH ) CO Me),
116.34
(CHCHC-(CH ) CO t-Bu),
80.37
2
2
2
2
2
2
Bn
(CO CCH ), 52.70 ( CH ), 51.68 (CO CH ), 47.97 (CH CH NH-
2
3
2
2
3
2
2
(1.24 g, 4.96 mmol, 1 equiv) and the reaction mixture was
ArCO Me), 47.93 (CH CH NH-ArCO t-Bu), 37.55 (CH CH CO t-
2 2 2 2 2 2 2
stirred for 1 h at room temperature. The reaction mixture was
diluted with dichloromethane (50 mL) and washed with sodium
bicarbonate solution (0.5 M, 50 mL). The product residue was
recovered from the aqueous phase by washing four times with
Bu), 36.16 (CH CH CO Me), 30.38 (CH CH CO t-Bu), 30.20
2 2 2 2 2 2
(CH CH CO Me), 28.18 (C(CH ) ). HRMS (ESI+, CH Cl /MeOH):
2
2
2
3
3
2
2
m/z calcd for C27H39N O : 487.2803; found: 487.2816. HRMS
2
6
(ESI-, CH Cl /MeOH): m/z calcd for C27H37N O : 485.2657;
2
2
2
6
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

E
Synlett
A. Makarem et al.
Letter
found: 485.2657.
CHCHC-(CH ) CO t-Bu), 6.76 (m, 4 H, CCHC-(CH ) CO H, CCHC-
2
2
2
2
2
2
Synthesis of 3-(3-{[(2-{[5-(2-tert-Butoxycarbonylethyl)-2-
hydroxybenzyl]-tert-butoxycarbonylmethylamino}ethyl)-
tert-butoxycarbonylmethylamino]methyl}-4-hydroxyphe-
nyl)propionic Acid [HBED-CC-tris(tert-butyl ester)]
Compound 10 (1.10 g, 2.26 mmol, 1 equiv) and anhydrous
sodium carbonate (0.96 g, 9.06 mmol, 4 equiv) were suspended
in anhydrous acetonitrile (25 mL). To this mixture was added
tert-butyl 2-bromoacetate (0.93 g, 4.76 mmol, 2.1 equiv). The
reaction mixture stirred for 3.5 h under reflux conditions. It was
cooled to room temperature, filtered and the solvent was
removed under reduced pressure. Then the residue was dis-
solved in methanol (15 mL), followed by dilution with water (10
mL). To this mixture was added sodium hydroxide solution
(CH ) CO t-Bu, CHCHC-(CH ) CO H and CHCHC-(CH ) CO t-Bu),
2
2
2
2
2
2
2
2
2
3
Bn
3.68 (d, 4 H, CH ), 3.16 (d, 4 H, t-BuO CH N), 2.84 (t, JH–H
=
2
2
2
3
7.6 Hz, 2 H, CH CH CO H), 2.78 (t, JH–H = 7.8 Hz, 2 H, CH CH -
2
2
2
2
2
3
CO t-Bu), 2.66 (s br, 4 H, N(CH ) N), 2.61 (t, JH–H = 7.6 Hz, 2 H,
CH CH CO H), 2.46 (t, J
2
2 2
3
= 7.8 Hz, 2 H, CH CH CO t-Bu), 1.45
2
2
2
H–H 2 2 2
(d, 18 H, NCH CO C(CH ) ), 1.41 (s, 9 H, CH CH CO C(CH ) ).
2
2
3
3
2
2
2
3 3
13
1
C{ H} NMR (100.61 MHz, CDCl , 25 °C): δ = 176.93 (CO H),
3
2
172.72 (CH CH CO t-Bu), 170.30 ([NCH CO t-Bu]-ArCO H),
2
2
2
2
2
2
170.27 ([NCH CO t-Bu]-ArCO t-Bu), 155.94 (COH), 155.71
2
2
2
(COH), 131.52 (C-(CH ) CO H), 130.87 (C-(CH ) CO t-Bu),
2
2
2
2
2
2
129.44 (CCHC-(CH ) CO H), 129.16 (CCHC-(CH ) CO t-Bu),
2
2
2
2
2
2
129.11 (CHCHC-(CH ) CO H), 129.08 (CHCHC-(CH ) CO t-Bu),
2
2
2
2
2
2
121.71 (CCHC-(CH ) CO H), 121.47 (CCHC-(CH ) CO t-Bu),
2
2
2
2
2
2
(
4 M, 5 mL) slowly. After being stirred for 1 h, the reaction
mixture was cooled in an ice-bath and the pH was adjusted to
–6 with HCl (0.5 M, ca. 40 mL). The crude product was
116.63 (CHCHC-(CH ) CO H), 116.46 (CHCHC-(CH ) CO t-Bu),
2 2 2 2 2 2
82.38 ([NCH CO CCH ]-ArCO H), 82.30 ([NCH CO CCH ]-
2
2
3
2
2
2
3
Bn
5
ArCO t-Bu), 80.49 (-(CH ) CO CCH ), 58.13 ( C-ArCO H), 58.06
2 2 2 2 3 2
Bn
extracted with ethyl acetate and the organic phase was dried
over sodium sulfate, filtered, concentrated under reduced pres-
sure and purified by flash column chromatography (ethyl
acetate–hexane, 3:2) to give HBED-CC-tris(tert-butyl ester) as a
colorless solid (0.53 g, 0.76 mmol, 33.4%). Note: The overall
( C-ArCO t-Bu), 55.87 ([NCH CO ]-ArCO H), 55.69 ([NCH CO ]-
2 2 2 2 2 2
ArCO t-Bu), 50.32 (NCH CH N), 37.59 (CH CH CO t-Bu), 35.88
2
2
2
2
2
2
(CH CH CO H), 30.39 (CH CH CO t-Bu), 30.01 (CH CH CO H),
2
2
2
2
2
2
2
2
2
28.20 (C(CH )). HRMS (ESI+, MeOH): m/z calcd for C38H57N O10:
3
2
701.4008; found: 701.4027. HRMS (ESI–, MeOH): m/z calcd for
1
product yield was 28%. Mp 43–45 °C. H NMR (400.13 MHz,
C38H55N O10: 699.3862; found: 699.3861. Anal. Calcd. (%) C:
2
CDCl , 25 °C): δ = 7.00 (sept, 2 H, CHCHC-(CH ) CO H and
65.12, H: 8.05, N: 4.00; found C: 65.35, H: 7.95, N: 3.91.
3
2
2
2
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E