Synthesis of 4-maleimidobutyric acid and related maleimides

Article abstract of DOI:10.1055/s-2008-1032016

Maleimidoalkanoic acids and their activated derivatives, such as their N-hydroxysuccinimide esters, are important, though expensive, linkers for the conjugation of biomolecules. During our synthesis of UCS1025A, we have developed a chromatography-free preparation of 4-maleimidobutyric acid on a one-mole scale. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1032016

1316
PRACTICAL SYNTHETIC PROCEDURES
Synthesis of 4-Maleimidobutyric Acid and Related Maleimides
S
ynthesis of 4-M
e
aleimidobu
n
tyric
A
cid
a
n
a
d Relate
d
M
t
a
leim
a
ides Marcia de Figueiredo,a Philipp Oczipka,a Roland Fröhlich,b Mathias Christmann*a
a
Institute of Organic Chemistry, RWTH Aachen, Landoltweg 1, 52074 Aachen, Germany
Institute of Organic Chemistry, University of Münster, Corrensstraße 40, 48149 Münster, Germany
Fax +49(241)8092127; E-mail: christmann@oc.rwth-aachen.de
b
PSP
Received 12 September 2007
No121
Abstract: Maleimidoalkanoic acids and their activated derivatives, such as their N-hydroxysuccinimide esters, are important, though ex-
pensive, linkers for the conjugation of biomolecules. During our synthesis of UCS1025A, we have developed a chromatography-free prep-
aration of 4-maleimidobutyric acid on a one-mole scale.
Key words: imides, condensations, maleic anhydride, aminobutanoic acid, cross-linking reagents
peptide
O
O
O
O
O
O
AcOH, reflux, 90 min
peptide
S
( )n
( )n
( )n
HO
NH2
O
+
HO
N
N
N
R
H
R
then aqueous workup
and recrystallization
1
3
O
O
O
2
6 examples, 52–68% yield
0.1–1 mol scale
peptide conjugate
Scheme 1
O
O
Introduction
H
O
H
N
MeO2C
N
In the mid-1970s Rich et al. introduced peptides with an
N-maleoylamino terminus as an alkylating trap for sulfa-
nyl groups.1 Since that time many groups have exploited
the orthogonal reactivity of maleimidoalkanoic acids 3 for
the cross-linking of peptides and other biomolecules.2
Rich’s initial synthesis involved a two-step procedure;
formation and isolation of the amide 4 was followed by
separate cyclization (Scheme 2). Accordingly, heating of
4 with two equivalents of triethylamine in an aromatic sol-
vent afforded the desired products.
5
O
OH
O
O
H
UCS1025A
Scheme 3 Methyl 4-maleimidobutyrate (5) in the total synthesis of
UCS1025A
Scope and Limitations
O
O
In this context, we now wish to report the large-scale syn-
thesis of maleimidoalkanoic acids 3. Before we describe
our refinements, we would like to briefly discuss the orig-
inal procedures on which they are based. Although the
Rich protocol1 is still in use, it is known that this reaction
can be carried out as a one-step procedure by heating of
the starting materials in acetic acid. Thus column chroma-
tography affords sufficiently pure maleimidoalkanoic ac-
ids in 41–53% yield.7 On a larger scale, chromatographic
separation of >50% side products did not seem an attrac-
tive venture to us. Therefore, we decided to first minimize
the formation of side products, and then try to increase the
purity of the desired product by extraction and finally re-
crystallization of the crude product. Toward this end, the
reaction between 1 and 2 in acetic acid was monitored pe-
riodically by NMR spectroscopy. After 90 minutes at re-
flux, increased addition of acetic acid to the Michael
2 equiv Et3N
toluene, heat
AcOH
( )n
HO
N
3
1 + 2
H
4
HO2C
Scheme 2 Rich’s synthesis of maleimidoalkanoic acids
More recently, Danishefsky3 and Hoye4 identified methyl
4-maleimidobutyrate (5) as a starting material for the
pyrrolizidine fragment of the telomerase inhibitor
UCS1025A (Scheme 3).5 Our group has developed a scal-
able enantioselective synthesis of the pyrrolizidine scaf-
fold using the direct cyclization of maleimidobutyric acid
3b (Scheme 1).6
SYNTHESIS 2008, No. 8, pp 1316–1318
Advanced online publication: 10.01.2008
DOI: 10.1055/s-2008-1032016; Art ID: E19307SS
x
x
.
x
x
.2
0
0
7
© Georg Thieme Verlag Stuttgart · New York

PRACTICAL SYNTHETIC PROCEDURES
4-Maleimidobutyric Acid and Related Maleimides
1317
Melting points were determined with a Büchi 510 apparatus and are
uncorrected. 1H and 13C NMR spectra were recorded on a Varian In-
ova 400 and a Varian Unity 500 instrument. 1H NMR are reported
relative to residual CHCl3 (for CDCl3) d = 7.26 or TMS. 13C NMR
are reported for CDCl3 relative to the central line of the triplet at
d = 77.0. IR spectra were recorded neat on a Perkin-Elmer PE 1759
FT instrument. LR-MS were recorded on a Varian MAT 212 S in-
strument using EI ionization (EI, 70 eV). Elemental analyses were
performed by the Microanalytical Laboratory of the Institute of Or-
ganic Chemistry.
acceptor was observed. We therefore stopped the reaction
at this point and evaporated the solvent in vacuo. Polar
impurities were easily removed by partitioning between
ethyl acetate and water. After some experimentation, we
found that the crude product could be recrystallized from
fairly concentrated ethyl acetate solutions to give the crys-
talline products in acceptable to good yields (Table 1).
This material is sufficiently pure for most reactions. How-
ever, if higher purity (>99%) is required, the maleimidoal-
kanoic acids can be purified by Kugelrohr distillation. The
maleimidoalkanoic acids proved surprisingly robust to-
ward heat as little decomposition was detected even after
extended heating.
3-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)propanoic Acid (3a);
Typical Procedure
A suspension of maleic anhydride (9.95 g, 102 mmol) and b-alanine
(9.18 g, 103 mmol) in AcOH (75 mL) was heated to reflux (bath
temperature: 170 °C) for 90 min. The soln was cooled to r.t. and the
solvent was evaporated in vacuo. Residual AcOH was removed by
azeotroping with toluene (2 × 50 mL). The combined organic ex-
tracts were dried (MgSO4) and evaporated in vacuo. The crude res-
idue was recrystallized (EtOAc, 50 mL, 7 °C) to give 3a (9.83 g,
57%) as colorless prisms (mp 108–109 °C). Alternatively, the purity
can be upgraded by Kugelrohr distillation (170 °C, 0.1 mbar); Rf =
0.52 (EtOAc).
Table 1 Synthesis of Maleimidoalkanoic Acids 3a–f
O
O
O
O
AcOH
heat
( )n
( )n
HO
NH2
O
HO
N
+
R
R
1
3
O
O
2
IR (KBr): 3454, 1706, 1413, 834, 772 cm–1.
1H NMR (500 MHz, CDCl3): d = 6.72 (s, 2 H), 3.83 (t, J = 7.2 Hz,
2 H), 2.70 (t, J = 7.2 Hz, 2 H).
13C NMR (125 MHz, CDCl3): d = 176.4, 170.3 (2 ×), 134.2 (2 ×),
33.2, 32.5.
Entry
Product
3a
n
1
2
3
4
2
4
R
H
H
H
H
Yielda (%)
1
2
3
4
5
6
57
52
60
57
68
66
3b
3c
MS (EI): m/z (%) = 169 (M+, 4), 151 (34), 123 (100), 110 (81), 82
(40), 70 (18), 54 (29).
3d
Anal. Calcd for C7H7NO4: C, 49.71; H, 4.17; N, 8.28. Found: C,
49.76; H, 4.26; N, 8.30.
3e
Me
Me
3f
4-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)butanoic Acid (3b)
A 2-L-round bottom flask equipped with a heating mantle and a re-
flux condenser was charged with maleic anhydride (100 g, 1.02
mol) and 4-aminobutanoic acid (106 g, 1.03 mol). AcOH (750 mL)
a Yield of isolated products.
Gratifyingly, 3a afforded crystals suitable for X-ray crys- was added and the mixture was heated to reflux for 90 min. The soln
tallography and its structure is shown in Figure 1.8
was cooled to r.t. and the solvent was evaporated in vacuo. Residual
AcOH was removed by azeotroping with toluene. The residue was
dissolved in H2O (1 L) and extracted with EtOAc (3 × 1 L). The
combined organic extracts were dried (MgSO4) and evaporated in
vacuo. The crude residue was recrystallized (EtOAc). The mother
liquor was concentrated and the crystallization was repeated (3 ×) to
give 3b (97 g, 52%) as a colorless solid; mp 93–94 °C; Rf = 0.55
(EtOAc).
IR (KBr): 1702, 1453, 1413, 1225, 910, 834, 695 cm–1.
1H NMR (500 MHz, CDCl3): d = 6.71 (s, 2 H), 3.60 (t, J = 6.9 Hz,
2 H), 2.37 (t, J = 7.4 Hz, 2 H), 1.96–1.89 (m, 2 H).
13C NMR (125 MHz, CDCl3): d = 178.3, 170.8 (2 ×), 134.1 (2 ×),
36.9, 31.1, 23.5.
MS (EI): m/z (%) = 183 (M+, 13), 165 (52), 137 (28), 124 (30), 123
(18), 110 (100), 99 (27), 82 (38), 54 (19).
Anal. Calcd for C8H9NO4: C, 52.49; H, 4.96; N, 7.65. Found: C,
52.32; H, 5.02; N, 7.53.
5-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)pentanoic Acid (3c)
Figure 1 Crystal structure of 3-maleimidopropionic acid (3a)
Colorless solid; mp 84–85 °C; Rf = 0.55 (EtOAc).
IR (KBr): 1704, 1457, 1408, 1320, 1220, 831, 695 cm–1.
1H NMR (500 MHz, CDCl3): d = 6.69 (s, 2 H), 3.53 (t, J = 6.8 Hz,
2 H), 2.37 (t, J = 7.1 Hz, 2 H), 1.69–1.55 (m, 4 H).
In summary, we have developed a reliable protocol for the
preparation of maleimidoalkanoic acids, which is amen-
able to large-scale synthesis due to its operational sim-
plicity and the absence of chromatographic separations.
Synthesis 2008, No. 8, 1316–1318 © Thieme Stuttgart · New York

1318
R. M. de Figueiredo et al.
PRACTICAL SYNTHETIC PROCEDURES
13C NMR (125 MHz, CDCl3): d = 179.1, 170.8 (2 ×), 134.0 (2 ×),
37.3, 33.3, 27.8, 21.7.
MS (EI): m/z (%) = 225 (M+, 21), 207 (38), 123 (100), 111 (29), 96
(15), 68 (10), 56 (10).
MS (EI): m/z (%) = 197 (M+, 10), 179 (36), 151 (29), 116 (15), 110
(100), 98 (17), 82 (37), 54 (18).
Anal. Calcd for C11H15NO4: C, 58.66; H, 6.71; N, 6.22. Found: C,
58.72; H, 6.54; N, 6.18.
Anal. Calcd for C9H11NO4: C, 54.82; H, 5.62; N, 7.10. Found: C,
54.58; H, 5.81; N, 7.01.
Acknowledgment
6-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoic Acid (3d)
Colorless solid; mp 78 °C; Rf = 0.60 (EtOAc).
IR (KBr): 1700, 1446, 1409, 944, 837, 695 cm–1.
1H NMR (400 MHz, CDCl3): d = 6.69 (s, 2 H), 3.51 (t, J = 7.2 Hz,
2 H), 2.34 (t, J = 7.4 Hz, 2 H), 1.71–1.55 (m, 4 H), 1.38–1.28 (m, 2
We thank the Fonds der Chemischen Industrie for a Liebig Fel-
lowship (M.C.), the Deutsche Forschungsgemeinschaft for funding
(SPP1179 Organokatalyse) and Prof. Dieter Enders for his encour-
agement and support.
H).
References
13C NMR (100 MHz, CDCl3): d = 179.2, 170.7 (2 ×), 134.0 (2 ×),
37.6, 33.8, 28.2, 26.2, 24.1.
MS (EI): m/z (%) = 211 (M+, 10), 193 (34), 175 (16), 111 (23), 110
(100), 98 (21), 82 (26), 54 (14).
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Anal. Calcd for C10H13NO4: C, 56.87; H, 6.20; N, 6.63. Found: C,
56.91; H, 6.20; N, 6.60.
4-(3-Methyl-2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)butanoic
Acid (3e)
Recrystallization (pentane–EtOAc, 3:1, 4 °C, 12 h then 25 °C, 48 h)
gave a colorless solid; mp 61–64 °C; Rf = 0.54 (EtOAc).
IR (KBr): 1709, 1446, 1288, 1215, 926, 871, 750, 713 cm–1.
1H NMR (500 MHz, CDCl3): d = 6.32 (q, J = 1.8 Hz, 1 H), 3.55 (t,
J = 6.7 Hz, 2 H), 2.35 (t, J = 7.3 Hz, 2 H), 2.06 (d, J = 2.1 Hz, 3 H),
1.90 (quint, J = 7.0 Hz, 2 H).
13C NMR (125 MHz, CDCl3): d = 178.6, 171.8, 170.9, 145.7, 127.2,
36.9, 31.1, 23.6, 10.9.
MS (EI): m/z (%) = 197 (M+, 30), 179 (53), 151 (25), 138 (59), 137
(33), 124 (100).
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(8) CCDC 651593 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK, fax: +44(1223)336033, E-mail:
deposit@ccdc.cam.ac.uk.
Anal. Calcd for C9H11NO4: C, 54.82; H, 5.62; N, 7.10. Found: C,
54.74; H, 5.61; N, 7.01.
6-(3-Methyl-2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoic
Acid (3f)
Recrystallization (pentane–EtOAc, 3:1, –18 °C) gave a colorless
solid; mp 60 °C; Rf = 0.65 (EtOAc).
IR (KBr): 1710, 1440, 1407, 917, 872 cm–1.
1H NMR (400 MHz, CDCl3): d = 6.28 (s, 1 H), 3.47 (t, J = 7.1 Hz,
2 H), 2.33 (t, J = 7.4 Hz, 2 H), 2.06 (s, 3 H), 1.68–1.49 (m, 4 H),
1.36–1.27 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 179.4, 171.8, 170.9, 145.4, 127.2,
37.7, 33.8, 28.3, 26.2, 24.2, 11.1.
Synthesis 2008, No. 8, 1316–1318 © Thieme Stuttgart · New York