Tri- and tetravalent photoactivable cross-linking agents

Article abstract of DOI:10.1055/s-0031-1290444

A modular synthesis of photoactivable cross-linking agents is described, using an aromatic core, di- or triethyleneglycol spacers and photoaffinity labeling synthons that feature either perfluorophenyl azide or aryl(trifluoromethyl)diazirine motifs. Symmetrical and nonsymmetrical trivalent structures were obtained from phloroglucinol and dopamine, respectively. Symmetrical tetravalent structures resulted from the coupling of two dopamine derivatives with oxalyl chloride. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0031-1290444

PAPER
▌2249
paper
Tri- and Tetravalent Photoactivable Cross-Linking Agents
Multivalent Cross-Linkers
Alexandre Welle, François Billard, Jacqueline Marchand-Brynaert*
Université catholique de Louvain, Institute of Condensed matter and Nanosciences – IMCN / MOST, Bâtiment Lavoisier, place Louis Pasteur
L4.01.02, 1348 Louvain-la-Neuve, Belgium
Fax +32(10)474168; E-mail: jacqueline.marchand@uclouvain.be
Received: 28.02.2012; Accepted after revision: 08.05.2012
ity labeling of proteins with aryl azide or diazirine-based
Abstract: A modular synthesis of photoactivable cross-linking
linkers.9
agents is described, using an aromatic core, di- or triethyleneglycol
spacers and photoaffinity labeling synthons that feature either per-
fluorophenyl azide or aryl(trifluoromethyl)diazirine motifs. Sym-
metrical and nonsymmetrical trivalent structures were obtained
from phloroglucinol and dopamine, respectively. Symmetrical tet-
ravalent structures resulted from the coupling of two dopamine de-
rivatives with oxalyl chloride.
spacer
spacer
spacer
spacer
R
R
R
O
O
O
O
R
spacer
= PEG
O
R
NHCO
,
= OH, NH2, SH, N3, CO2H,
O2S
N
O
Key words: ethers, amides, arenes, protecting groups, coupling
O2C
O2C
Figure 2 Thermoreactive cross-linkers used for the synthesis of hy-
drogels in the literature
Aryl azides and diazirines are well-known precursors of
nitrenes and carbenes respectively. Upon photolysis, dini-
trogen is liberated and the highly unstable species formed
in situ react with neighboring molecules in a variety of
nonselective reactions depending on their singlet or triplet
nature.1 Perfluorophenyl azides form less reactive nitrene
intermediates that are able to cleanly insert into C–H
bonds in moderate to good yields.2 Similarly, aryl(trifluo-
romethyl)diazirines generate more stable carbenes, i.e.
less prone to rearrangement, giving high yields of inser-
tion reactions under UV irradiation at wavelengths that do
not damage biomacromolecules.3 Therefore, the photo-
sensitive reagents 1 and 2 (Figure 1) are commonly used
in biology4 and chemistry.5
Polyvalent cross-linking agents are less abundant in the
literature, and most of their applications deal with hydro-
gels.10 Hydrogels are highly hydrated cross-linked poly-
mer networks considered as promising biomaterials for
regenerative medicine. The synthesis of polyethylene gly-
col (PEG)-based hydrogels, the gold standard in this field,
makes use of tetravalent linkers derived from pentaeryth-
ritol as the core and PEG-arms terminated with different
functions (hydroxy, amine, thiol, azide, carboxy, vinyl
sulfone, maleimide, acrylate, alkyne), as shown in Figure
2.11 To our knowledge, photoactivable moieties have not
been considered as yet for the construction of polyvalent
linkers. Only two divalent photoactivable reagents, name-
ly 1,3-bis[3-(trifluoromethyl)diazirin-3-yl]benzene12a and
2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone12b
were recently disclosed for cross-linking PEGs and gas
separation membranes, respectively.
F
F
F3C
O
O
O
O
O
O
N3
N
N
N
N
F
F
In this paper, we report the synthesis of original tri- and
tetravalent photoactivable cross-linking agents based on
the perfluorophenyl azide and aryl(trifluoromethyl)di-
azirine motifs. Our strategy relies on the preparation of an
aromatic core decorated with three or four spacer-arms,
followed by coupling of the photosensitive reagents at the
extremity of the spacer-arms in the last synthetic step
(Figure 3).
O
O
1
2
Figure 1 Photosensitive reagents
Divalent cross-linking agents are usual tools in molecular
biology for the preparation of biomacromolecular conju-
gates,6 and in material sciences for the surface grafting of
molecules of interest.7 Many α,ω-heterofunctionalized
linkers are now commercially available; the chemistry be-
hind these tools are peptide coupling, Michael addition,
reductive amination, various ‘click’ methods, and photo-
activation.8 In the latter case, heterobifunctional cross-
linkers containing a thermoreactive and a photoreactive
function are used; this is well illustrated by the photoaffin-
= OEG
spacer
spacer
spacer
spacer
hν
hν
hν
core
hν
= UV-sensitive motifs
aromatic derivative
=
core
spacer
spacer
hν
hν
hν
hν
core
core
spacer
spacer
SYNTHESIS 2012, 44, 2249–2254
Advanced online publication: 18.06.2012
DOI: 10.1055/s-0031-1290444; Art ID: SS-2012-Z0203-OP
© Georg Thieme Verlag Stuttgart · New York
Figure 3 General structures of tri- and tetravalent photoreactive
cross-linkers obtained via a modular synthesis using an aromatic core
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X

2250
A. Welle et al.
PAPER
In the first approach, trihydroxybenzene was considered yield. After N-carbamate deprotection with trifluoroacetic
as the core; in a second approach, dopamine was used to acid and coupling to the activated esters 1 and 2 in the
construct the trivalent target molecules, and also the tetra- presence of a large excess of triethylamine, we recovered
valent target molecules by linking two dopamine units. In the target molecules 11, 12 and 13, 14 in 37%, 35% and
both cases, the spacer-arms were short α-amino-ω-hy- 19%, 34% yields, respectively (Scheme 1).
droxy-OEGs (oligoethylene glycols); the O-terminus
With a view to increasing the yields of the first step (fixa-
could be used for fixation onto the aromatic core
tion of the spacer-arms on the aromatic core), we consid-
(Williamson etherification or Mitsunobu coupling), and
ered dopamine as starting material. Indeed, the ortho
relationship of the two hydroxy groups should enhance
their nucleophilic character compared to the all-meta-sub-
the N-terminus for grafting the photosensitive moieties
(Figure 4).
stituted phloroglucinol. N-(tert-Butyloxycarbonyl)-pro-
tected dopamine 1516 was successively treated with
cesium carbonate in methanol, and then with tosylate 4 or
6 in hot N,N-dimethylformamide (Scheme 2). The diether
derivatives 16 and 17 were isolated in 67% and 52%
yields, respectively. The Mitsunobu reaction (using the al-
cohols 3 or 5) did not significantly increase the yields, and
was abandoned because the separation of triphenylphos-
phine oxide (byproduct of the reaction) was arduous. As
above, the next steps were trifluoroacetic acid deprotec-
tion of all carbamate groups and the coupling of the acti-
vated ester 1 or 2 to furnish the target compounds 20, 21
and 22, 23 in 36%, 36% and 25%, 37% yields, respective-
ly (Scheme 2).
O
O
X
BocHN
X
BocHN
O
3, X = OH
4, X = OTs
5, X = OH
6, X = OTs
Figure 4 Spacer-arms
The molecule 1 was synthesized in three steps from meth-
yl pentafluorobenzoate in 84% overall yield by using stan-
dard reactions5a (see Supporting Information). Several
protocols in the literature were adapted for the preparation
of 2 from trifluoromethyl 4-tolyl ketone,13 in six steps in
13% overall yield (see Supporting Information).
The spacer-arms 3, 4 and 5, 6 were obtained from com-
mercially available precursors, i.e. 2-(2-hydroxyeth-
oxy)ethylamine and 2-[2-(2-hydroxyethoxy)eth-oxy]eth-
anol, respectively, using well-established chemistry14 (see
Supporting Information).
We envisioned a possible rapid access to tetravalent pho-
toactivable cross-linkers via the ‘dimerization’ of dopa-
mine intermediates 18, 19; this would require simply
manipulation with orthogonal N-protecting groups. Thus,
N-(benzyloxycarbonyl)-protected dopamine 2417 was O-
alkylated as before, giving 25 and 26 (Scheme 3), and the
benzyloxycarbonyl group was selectively removed by hy-
The alkylation of phloroglucinol (1,3,5-trihydroxyben-
zene) was realized using Williamson’s etherification con-
ditions inspired by the literature.15
The preformed tricesium salt of phloroglucinol was react- drogenolysis. Reaction of the resulting amines 27 and 28
ed with tosylate 4 in N,N-dimethylformamide at 60 °C to with oxalyl chloride and triethylamine gave the ‘dimers’
furnish compound 7 in 40% yield after chromatography 29 and 30 in moderate yields.
(separation of mono- and disubstituted phloroglucinols).
Since similar treatment with tosylate 6 gave less than 10%
Finally, tert-butoxycarbonyl deprotection with trifluoro-
acetic acid and coupling to 1 or 2 led to the target mole-
yield of triether 8, another coupling method was used,
cules 33, 34 and 35, 36 in 31%, 41% and 37%, 38% yields,
namely the Mitsunobu reaction. Thus, the reaction of
respectively (Scheme 3). The strategy based on dopamine
phloroglucinol with alcohol 5, triphenylphosphine, and
as the aromatic core appears more practical and versatile
than that using phloroglucinol. For the first time, tri- and
diethyl azodicarboxylate in tetrahydrofuran gave 8 in 25%
OH
O
O
+
1. Cs2CO3, MeOH
–
NHBoc
NH3
3 CF3CO2
O
2. 4, DMF
O
TFA
O
n
n
or 5, Ph3P,
DEAD, THF
CH2Cl2
HO
OH
O
+
O
O
+
BocHN
H3N
O
O
NHBoc
O
O
NH3
n
n
n
n
9, n = 1 (100%)
10, n = 2 (100%)
7, n = 1 (40%)
8, n = 2 (25%)
O
F
F
F
O
F
O
R
N
O
1 or 2
R =
or
H
n
N
N3
Et3N (excess)
CH2Cl2
N
F3C
R
O
O
R
11, n = 1 (37%)
12, n = 2 (35%)
13, n = 1 (19%)
14, n = 2 (34%)
N
H
O
O
N
n
n
H
Scheme 1 Synthesis of the trivalent photoactivable molecules; first method
Synthesis 2012, 44, 2249–2254
© Georg Thieme Verlag Stuttgart · New York

PAPER
Multivalent Cross-Linkers
2251
O
+
O
O
+
HO
HO
NHBoc
H3N
1. Cs2CO3, MeOH
BocHN
BocHN
nO
nO
NH3
nO
nO
NHBoc TFA
CH2Cl2
O
+
2. 4 or 6, DMF
–
H3N
3 CF3CO2
15
16, n = 1 (67%)
17, n = 2 (52%)
18, n = 1 (100%)
19, n = 2 (100%)
O
F
F
O
R
N
H
O
F
H
N
R
O
n
1 or 2
or
R =
N
N
R
N
H
O
N3
Et3N (excess)
CH2Cl2
O
n
F3C
F
22, n = 1 (25%)
23, n = 2 (37%)
20, n = 1 (36%)
21, n = 2 (36%)
Scheme 2 Synthesis of the trivalent photoactivable molecules; second method
O
O
BocHN
BocHN
nO
nO
NHCbz
O
O
NH2
HO
HO
NHCbz
n
1. Cs2CO3,MeOH
H2, Pd/C
O
O
2. 4 or 6, DMF
EtOH–CH2Cl2
BocHN
BocHN
n
24
25, n = 1 (60%)
26, n = 2 (65%)
27, n = 1 (100%)
28, n = 2 (100%)
–
2 CF3CO2
O
O
O
H
H
BocHN
BocHN
H3N
nO
nO
N
TFA
1 or 2
(COCl)2
nO
nO
N
Et3N
CH2Cl2
CH2Cl2
O
Et3N (excess)
CH2Cl2
O
O
H3N
2
2
29, n = 1 (60%)
30, n = 2 (47%)
31, n = 1 (100%)
32, n = 2 (100%)
O
F
F
O
F
H
O
N
R =
or
O
O
O
R
R
N
H
O
O
H
N
n
N
N
nO
nO
N3
H
N
R
N
O
F3C
F
H
R
N
H
O
n
33, n = 1 (31%)
34, n = 2 (41%)
35, n = 1 (37%)
36, n = 2 (38%)
Scheme 3 Synthesis of tetravalent photoactivable molecules
tetravalent photoreactive cross-linkers could be obtained Infrared spectra were recorded with an FTIR-84005 spectrophotom-
eter operating in the ATR mode. 1H, 13C, and 19F NMR spectra were
recorded with Bruker Avance (300 and 500 MHz) spectrometers,
relative to the solvent signals. HRMS analyses were performed by
using the ESI method at the University of Oxford (UK). Analytical
thanks to a convergent strategy using mild conditions for
the introduction of the sensitive motifs (i.e., aryl azide and
diazirine) in the final step, and minimizing chromato-
graphic purifications.
grade solvents and commercially available reagents were used with-
out purification. Chromatography was carried out with Rocc silica
gel 40–63 μm or 60–200 μm.
In conclusion, the synthesis of 20–23 and 33–36 was
achieved with reasonable purification difficulties and ac-
ceptable overall yields, considering the size and function-
ality of the molecules, and the presence of light-sensitive
moieties inherently susceptible to lose dinitrogen under
smooth acidic conditions (or under heating). The final
cross-linkers could be stored for several months in dark
flasks, under an argon atmosphere, and at low temperature
(–18 °C). Application to the cross-linking of PEGs and
PEG block copolymers is currently under investigation in
the context of drug delivery systems.18
O-Alkylation of Aromatic Cores; General Procedure 1
A soln of phenol (1.5 mmol) and Cs2CO3 (diol: 537 mg, 1.65 mmol;
triol: 806 mg, 2.45 mmol) in degassed MeOH (10 mL) was stirred
under argon at 45 °C for 30 min and then evaporated to dryness in
vacuo. The residue was dissolved in DMF (30 mL) and the mixture
heated at 60 °C under argon. A soln of tosylate (diol: 3.15 mmol, 2.1
equiv; triol: 4.65 mmol, 3.1 equiv) in DMF (12 mL) was added
dropwise. The mixture was magnetically stirred at 60 °C overnight
and then evaporated to dryness under high vacuum. The residue was
taken up in CH2Cl2 (150 mL) and sat. NaHCO3 (30 mL). The de-
canted CH2Cl2 soln was washed with sat. NaHCO3 (2 × 30 mL),
then with brine (30 mL), dried (MgSO4), filtered, and evaporated in
vacuo.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 2249–2254

2252
A. Welle et al.
PAPER
Tri-tert-butyl [Benzene-1,3,5-triyltris(oxyethane-2,1-diyloxy-
ethane-2,1-diyl)]triscarbamate (7)
Following general procedure 1 using phloroglucinol (190 mg 1.5
mmol) and 4 (1.67 g 4.65 mmol) with purification by flash chroma-
tography (EtOAc–hexane, 70:30) gave 7 (412 mg, 40%) as a yel-
lowish oil.
soln was filtered over Celite and concentrated under reduced pres-
sure. Under an inert atmosphere, the crude amine 27 or 28 was dis-
solved in anhyd CH2Cl2 (10 mL) and Et3N (122 μL, 0.88 mmol, 1.1
equiv). Oxalyl chloride (34 μL, 0.4 mmol, 0.5 equiv) was added
dropwise and the mixture was stirred for 72 h. H2O (5 mL) was add-
ed and the phases were separated. The aqueous phase was extracted
with CH2Cl2 (3 × 20 mL) and the combined organic phases were
washed with brine (5 mL), dried (Na2SO4), filtered, and concentrat-
ed under reduced pressure.
IR (film): 3382, 2925, 1693, 1596, 1454, 1365, 1251, 1166, 1122,
1070, 1024 cm–1.
1H NMR (300 MHz, CDCl3): δ = 1.43 (s, 27 H, CH3), 3.30–3.35 (m,
6 H, NHCH2), 3.58 (t, J = 4.9 Hz, 6 H, NCH2CH2O), 3.77 (t, J = 4.3
Hz, 6 H, OCH2CH2O), 4.05 (t, J = 4.3 Hz, 6 H, PhOCH2), 4.97 (br
s, 3 H, NH), 6.12 (s, 3 H, HAr).
13C NMR (75 MHz, CDCl3): δ = 28.5 (CH3), 40.4 (NHCH2), 67.5
(ArOCH2), 69.4 (OCH2CH2O), 70.5 (NCH2CH2O), 79.4 [C(CH3)3],
94.5 (CHAr), 156.1 (CO), 160.6 (CArO).
tert-Butyl 2-[2-(4-{2-[2-(3,4-Bis{2-[2-(tert-butoxycarbonylami-
no)ethoxy]ethoxy}phenethylamino)-2-oxoacetamido]ethyl}-2-
{2-[2-(tert-butoxycarbonylamino)ethoxy]ethoxy}phenoxy)eth-
oxy]ethylcarbamate (29)
Following the general procedure 2 using 25 (529 mg, 0.8 mmol)
with purification by flash chromatography (EtOAc–acetone, 90:10)
gave 29 (532 mg, 60%) as a white powder.
HRMS (ESI): m/z [M + Na]+ calcd for C33H57N3O12Na: 710.3840;
found: 710.3850.
IR (film): 3359, 2931, 1693, 1512, 1456, 1265, 1253, 1166, 1122,
1060 cm–1.
tert-Butyl 2-[2-(2-{2-[2-(tert-Butoxycarbonylamino)ethoxy]eth-
oxy}-4-[2-(tert-butoxycarbonylamino)ethyl]phenoxy)eth-
oxy]ethylcarbamate (16)
Following general procedure 1 using 15 (380 mg, 1.5 mmol) and 4
(1.13 g 3.15 mmol) with purification by flash chromatography
(EtOAc–hexane, 70:30) gave 16 (630 mg, 67%) as a yellowish oil.
1H NMR (300 MHz, CDCl3): δ = 1.42 (s, 36 H, CH3), 2.77 (t, J =
7.0 Hz, 4 H, ArCH2), 3.30–3.35 (br m, 8 H, NHCH2CH2), 3.50 (t,
J = 7.0 Hz, 4 H, ArCH2CH2), 3.61 (t, J = 4.7 Hz, 8 H,
NHCH2CH2O), 3.80–3.85 (m, 8 H, OCH2CH2O), 4.14 (2 t, J = 4.0
Hz, 8 H, ArOCH2CH2), 5.19 (br s, 4 H, NH), 6.71–6.76 (m, 4 H,
HAr), 6.84 (d, J = 8.0 Hz, 2 H, HAr).
13C NMR (75 MHz, CDCl3): δ = 28.6 (CH3), 35.1 (PhCH2), 40.6
(PhCH2CH2), 41.0 (NHCH2), 68.9 (PhOCH2), 69.0 (PhOCH2′),
69.6 (OCH2CH2O), 70.6 (NHCH2CH2O), 79.3 [C(CH3)3], 115.1
(CHAr), 115.3 (CHAr), 121.7 (CHAr), 131.7 (CArCH2), 147.8 (CArO),
149.1 (CArO), 156.2 (CO), 159.8 (CO).
HRMS (ESI): m/z [M + Na]+ calcd for C54H88N6O18Na: 1131.6053;
found: 1131.6121.
IR (film): 3371, 2933, 1681, 1504, 1365, 1249, 1168, 1051, 732
cm–1.
1H NMR (300 MHz, CDCl3): δ = 1.40 (s, 27 H, CH3), 2.69 (t, J =
6.8 Hz, 2 H, ArCH2), 3.25–3.35 (m, 6 H, NHCH2), 3.59 (t, J = 4.9
Hz, 4 H, NHCH2CH2O), 3.80 (t, J = 4.6 Hz, 4 H, OCH2CH2O), 4.12
(2 t, J = 4.6 Hz, 4 H, ArOCH2), 4.60 (br s, 1 H, NH), 5.20 (br s, 2 H,
NH), 6.68–6.74 (m, 2 H, HAr), 6.82 (d, J = 8 Hz, 1 H, HAr).
13C NMR (75 MHz, CDCl3): δ = 28.5 (CH3), 35.8 (ArCH2), 40.5
(NHCH2), 41.9 (ArCH2CH2), 68.8 (ArOCH2), 69.0 (ArOCH2), 69.6
(OCH2CH2O), 70.5 (NHCH2CH2), 79.2 [C(CH3)3], 115.0 (CHAr),
115.3 (CHAr), 121.7 (CHAr), 132.6 (CArCH2), 147.4 (CArO), 148.9
(CArO), 156.0 (CO), 156.1 (CO).
HRMS (ESI): m/z [M + Na]+ calcd for C31H53N3O10Na: 650.3629;
found: 650.3625.
Boc Deprotection; General Procedure 3
To a stirred soln of Boc-protected amine (1 mmol, 1 equiv) in
CH2Cl2 (5 mL) was added TFA (5 mL). The resulting soln was
stirred at r.t. for 2 h and concentrated under reduced pressure giving
the corresponding ammonium salt in quantitative yield, which was
used without further purification.
Peptidic Coupling; General Procedure 4
tert-Butyl 2-[2-(4-[2-(Benzyloxycarbonylamino)ethyl]-2-{2-[2-
(tert-butoxycarbonylamino)ethoxy]ethoxy}phenoxy)eth-
oxy]ethylcarbamate (25)
Following general procedure 1 using 24 (430 mg, 1.5 mmol) and 4
(1.13 g 3.15 mmol) with purification by flash chromatography
(EtOAc–hexane, 70:30) gave 25 (595 mg, 60%) as a yellowish oil.
To a stirred soln of deprotected polyamine (0.3 mmol, 1 equiv) in
CH2Cl2 (20 mL) and Et3N (5 mL, 36 mmol, 115 equiv) was added
activated ester (1.2 mmol, 4 equiv). The resulting soln was stirred
overnight and diluted with CH2Cl2 (50 mL). The organic phase was
washed with aq sat. NaHCO3 (2 × 5 mL) and brine (5 mL), dried
(Na2SO4), filtered, and concentrated under reduced pressure.
IR (film): 3350, 2929, 1685, 1504, 1263, 1164, 1051, 1002, 862,
732, 696 cm–1.
N,N′,N′′-[Benzene-1,3,5-triyltris(oxyethane-2,1-diyloxyethane-
2,1-diyl)]tris(4-azido-2,3,5,6-tetrafluorobenzamide) (11)
Following general procedures 3 and 4 using 7 (206 mg, 0.3 mmol)
and 1 (398 mg, 1.2 mmol) with purification by flash chromatogra-
phy (EtOAc–hexane, 70:30) gave 11 (115 mg, 37%) as a white
foam.
1H NMR (300 MHz, CDCl3): δ = 1.40 (s, 18 H, CH3), 2.74 (t, J =
6.7 Hz, 2 H, ArCH2), 3.30–3.35 (m, 4 H, NHCH2), 3.41 (t, J = 6.7
Hz, 2 H, ArCH2CH2), 3.55–3.60 (m, 4 H, NHCH2CH2), 3.80–3.85
(m, 4 H, OCH2CH2O), 4.10–4.15 (m, 4 H, OCH2CH2O), 4.83 (br s,
1 H, NH), 5.10 (s, 2 H, ArCH2O), 5.20 (br s, 2 H, NH), 6.68–6.74
(m, 2 H, HAr), 6.84 (d, J = 8 Hz, 1 H, HAr), 7.34 (s, 5 H, Cbz-HPh).
13C NMR (75 MHz, CDCl3): δ = 28.5 (CH3), 35.7 (ArCH2), 40.5
(NHCH2), 42.4 (ArCH2CH2), 66.7 (ArCH2O), 68.8 (OCH2CH2O),
69.0 (OCH2CH2O), 69.5 (OCH2CH2O), 70.5 (NHCH2CH2O), 79.2
[C(CH3)3], 115.0 (CHAr), 115.3 (CHAr), 121.7 (CHAr), 128.2 (2 C,
Cbz-CHPh), 128.6 (Cbz-CHPh), 132.3 (CArCH2), 136.7 [Cbz-CPh],
147.5 (CArO), 149.0 (CArO), 156.1 (CO), 156.4 (CO).
IR (film): 3307, 2931, 2121, 1650, 1485, 1267, 1170, 1126, 1070,
991, 819 cm–1.
1H NMR (300 MHz, CDCl3): δ = 3.65 (t, J = 4.9 Hz, 6 H, NHCH2),
3.72 (t, J = 4.9 Hz, 6 H, NHCH2CH2), 3.82 (t, J = 4.2 Hz, 6 H,
OCH2CH2O), 3.99 (t, J = 4.2 Hz, 6 H, OCH2CH2O), 5.94 (s, 3 H,
HAr), 6.65 (br s, 3 H, NH).
13C NMR (75 MHz, CDCl3): δ = 40.1 (NHCH2), 67.4 (PhOCH2),
69.47 (PhOCH2CH2), 69.54 (NHCH2CH2), 93.9 (CHAr), 111.4 (t,
J = 18.4 Hz, CArN3), 121.8 (CArCO), 140 (dd, J = 252, 18 Hz, CArF),
143.2 (dd, J = 263, 19 Hz, CArF), 157.8 (CO), 160.4 (CArO).
HRMS (ESI): m/z [M + Na]+ calcd for C34H51N3O10Na: 684.3472;
found : 684.3449.
19F NMR (282 MHz, CDCl3): δ = –141.7 (dd, J = 9.3, 21.1 Hz, 6 F),
–151.3 (dd, J = 9.7, 20.7 Hz, 6 F).
Dimerization; General Procedure 2
A soln of the Cbz-protected amine (0.8 mmol, 1 equiv) and Pd/C
(10% w/w, 85 mg, 0.08 mmol, 0.1 equiv) in EtOH (10 mL) was
placed under a H2 atmosphere (1 atm) and stirred overnight. The
Synthesis 2012, 44, 2249–2254
© Georg Thieme Verlag Stuttgart · New York

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Multivalent Cross-Linkers
2253
HRMS (ESI): m/z [M + Na]+ calcd for C39H30N12O9F12Na:
1061.1965; found: 1061.1935.
7.05 (d, J = 8.2 Hz, 2 H, HAr), 7.09 (d, J = 8.2 Hz, 2 H, HAr), 7.18
(d, J = 8.2 Hz, 2 H, HAr), 7.31–7.37 (m, 2 H, NH), 7.71–7.74 (m, 4
H, HAr), 7.76 (d, J = 8.5 Hz, 2 H, HAr).
N,N′,N′′-[Benzene-1,3,5-triyltris(oxyethane-2,1-diyloxyethane-
2,1-diyl)]tris{4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benz-
amide} (13)
Following general procedures 3 and 4 using 7 (206 mg, 0.3 mmol)
and 2 (392 mg, 1.2 mmol) with purification by flash chromatogra-
phy (EtOAc–hexane, 90:10) gave 13 (58 mg, 19%) as a white pow-
der.
13C NMR (75 MHz, CDCl3): δ = 28.5 (q, J = 40 Hz, CCF3), 35.2
(PhCH2), 40.0 (NHCH2), 41.5 (PhCH2CH2), 68.3 (OCH2CH2O),
68.4 (OCH2CH2O), 69.3 (OCH2CH2O), 69.4 (OCH2CH2O), 70.0
(NHCH2CH2), 70.1 (NHCH2CH2), 113.5 (CHAr), 114.0 (CHAr),
121.6 (CHAr), 122.0 (q, J = 243 Hz, CF3), 126.4 (CHAr), 126.7
(CHAr), 127.4 (CHAr), 127.7 (CHAr), 132.1, 132.2 and 132.4 (CArCO,
CArCH2), 135.6 (CHAr), 135.7 (CArC), 146.9 (CArO), 148.3 (CArO),
166.4 (CO), 166.5 (CO).
IR (film): 3340, 2952, 1612, 1548, 1342, 1230, 1153, 1070, 939
cm–1.
19F NMR (282 MHz, CDCl3): δ = –65.49 (s, 6 F), –65.51 (s, 3 F).
HRMS (ESI): m/z [M + Na]+ calcd for C43H38N9O7F9Na: 986.2648;
1H NMR (500 MHz, CDCl3): δ = 3.67 (t, J = 4.9 Hz, 6 H, NHCH2),
3.72 (t, J = 4.9 Hz, 6 H, NHCH2CH2), 3.82 (t, J = 4.3 Hz, 6 H,
OCH2CH2O), 4.01 (t, J = 4.3 Hz, 6 H, ArOCH2), 6.05 (s, 3 H, HAr),
6.80 (br s, 3 H, NH), 7.15 (d, J = 8.3 Hz, 6 H, HAr), 7.75 (d, J = 8.3
Hz, 6 H, HAr).
13C NMR (75 MHz, CDCl3): δ = 28.5 (q, J = 40 Hz, CCF3), 39.9
(NHCH2), 67.4 (ArOCH2), 69.5 (ArOCH2CH2), 69.9
(NHCH2CH2O), 94.5 (CHAr), 122.0 (q, J = 273 Hz, CF3), 126.5
(CHAr), 127.6 (CHAr), 132.3 (CArCO), 135.5 (CArC), 160.4 (CArO),
166.4 (CO).
found: 986.2653.
N1,N2-Bis(3,4-bis{2-[2-(4-azido-2,3,5,6-tetrafluorobenzami-
do)ethoxy]ethoxy}phenethyl)oxalamide (33)
Following general procedures 3 and 4 using 29 (333 mg, 0.3 mmol)
and 1 (398 mg, 1.2 mmol) with purification by flash chromatogra-
phy (EtOAc–hexane, 90:10) gave 33 (118 mg, 31%) as a white
powder.
IR (film): 2927, 2123, 1670, 1487, 1263, 1112, 813 cm–1.
19F NMR (282 MHz, CDCl3): δ = –65.5 Hz.
HRMS (ESI): m/z [M + Na]+ calcd for C45H42N9O9F9Na:
1H NMR (300 MHz, CDCl3): δ = 2.78 (t, J = 6.9 Hz, 4 H, PhCH2),
3.48–3.55 (m, 4 H, PhCH2CH2), 3.60–3.67 (m, 8 H, NHCH2), 3.76
(br s, 8 H, NCH2CH2), 3.84 (br s, 8 H, OCH2CH2O), 4.04 (br s, 8 H,
OCH2CH2O), 6.64–6.74 (m, 6 H, HAr), 7.26 (br s, 4 H, NH), 7.48 (t,
J = 6.3 Hz, 2 H, NH).
13C NMR (125 MHz, CDCl3): δ = 35.0 (PhCH2), 40.3 (NHCH2),
40.4 (NHCH2), 40.9 (PhCH2CH2), 68.6 (OCH2CH2O), 68.7
(OCH2CH2O), 69.8 (OCH2CH2O), 70.1 (NHCH2CH2O), 113.9
(CHAr), 114.2 (CHAr), 116.1 (CArN3), 118.8 (CArCO), 121.7 (CHAr),
132.0 (CArCH2), 140.4 (d, J = 270 Hz, CArF), 144.0 (d, J = 240 Hz,
CArF), 146.9 (CArO), 148.2 (CArO), 158.1 (CO), 159.8 (CO).
19F NMR (282 MHz, CDCl3): δ = –141.68 to –141.86 (m, 8 F),
–151.35 to –151.50 (m, 8 F).
HRMS (ESI): m/z [M + Na]+ calcd for C62H52N18O14F16Na:
1599.3553; found: 1599.3416.
1046.2859; found: 1046.2802.
N,N′-({4-[2-(4-Azido-2,3,5,6-tetrafluorobenzamido)ethyl]-1,2-
phenylene}bis(oxyethane-2,1-diyloxyethane-2,1-diyl))bis(4-azi-
do-2,3,5,6-tetrafluorobenzamide) (20)
Following general procedures 3 and 4 using 16 (188 mg, 0.3 mmol)
and 1 (398 mg, 1.2 mmol) with purification by flash chromatogra-
phy (EtOAc–hexane, 60:40) gave 20 (106 mg, 36%) as a white
powder.
IR (film): 3336, 2960, 2123, 1650, 1485, 1265, 1135, 993 cm–1.
1H NMR (500 MHz, acetone-d6): δ = 2.80 (m, 2 H, PhCH2), 3.55–
3.65 (m, 6 H, PhCH2CH2, NHCH2), 3.75 (m, 4 H, NHCH2CH2),
3.83 (m, 4 H, OCH2CH2O), 4.08–4.12 (m, 4 H, OCH2CH2O), 6.79
(d, J = 8 Hz, 1 H, HAr), 6.86 (d, J = 8 Hz, 1 H, HAr), 6.90 (s, 1 H,
HAr), 8.02 (br s, 3 H, NH).
13C NMR (125 MHz, acetone-d6): δ = 35.4 (PhCH2), 40.6 (NHCH2),
42.0 (PhCH2CH2), 69.4 (PhOCH2), 69.6 (OCH2CH2O), 70.1
(NHCH2CH2), 113.8 (br m, CArN3), 115.0 (CHAr), 115.5 (CHAr),
121.9 (br m, CArCO), 122.1 (CHAr), 133.1 (CArCH2), 141.05 (d, J =
243 Hz, CArF), 144.2 (d, J = 250 Hz, CArF), 147.9 (CArO), 149.4
(CArO), 157.7 (CO), 157.9 (CO).
19F NMR (282 MHz, acetone-d6): δ = –142.9 to –143.1 (m, 6 F),
–152.0 to –152.2 (m, 6 F).
HRMS (ESI): m/z [M + Na]+ calcd for C37H26F12N12O7Na:
1001.1754; found: 1001.1755.
N1,N2-Bis{3,4-bis[2-(2-{4-[3-(trifluoromethyl)-3H-diazirin-3-
yl]benzamido}ethoxy)ethoxy]phenethyl}oxalamide (35)
Following general procedures 3 and 4 using 29 (333 mg, 0.3 mmol)
and 2 (392 mg, 1.2 mmol) with purification by flash chromatogra-
phy (EtOAc–hexane, 60:40) gave 35 (173 mg, 37%) as a white
powder.
IR (film): 2921, 1735, 1365, 1352, 1228, 1217, 939 cm–1.
1H NMR (300 MHz, CDCl3): δ = 2.77 (t, J = 7.0 Hz, 4 H, PhCH2),
3.49–3.55 (br m, 4 H, PhCH2CH2), 3.60 (m, 8 H, NHCH2), 3.68 (m,
8 H, NHCH2CH2), 3.78 (m, 8 H, OCH2CH2O), 4.02 (m, 8 H,
OCH2CH2O), 6.65–6.75 (6 H, HAr), 7.08 (d, J = 6.8 Hz, 4 H, HAr),
7.11 (d, J = 7.4 Hz, 4 H, HAr), 7.35–7.40 (br m, 4 H, NH), 7.45–7.50
(br m, 2 H, NH), 7.75 (d, J = 8.5 Hz, 4 H, HAr), 7.79 (d, J = 8.5 Hz,
4 H, HAr).
13C NMR (125 MHz, CDCl3): δ = 28.5 (q, J = 40.2 Hz, CCF3), 35.0
(PhCH2), 40.1 (NHCH2), 41.0 (PhCH2CH2), 68.4 (OCH2CH2O),
68.5 (OCH2CH2O), 69.4 (2 peaks) (OCH2CH2O), 70.2 (2 peaks)
(NHCH2CH2), 113.7 (CHAr), 113.9 (CHAr), 121.6 (CHAr), 122.0 (q,
J = 270 Hz, CF3), 126.4 (CHAr), 127.7 (CHAr), 131.6 (CArCH2),
132.1 (CArCO), 135.7 (CArC), 147.1 (CArO), 148.4 (CArO), 159.8
(CO), 166.5 (CO).
N,N′-[4-(2-{4-[3-(Trifluoromethyl)-3H-diazirin-3-yl]benzami-
do}ethyl)-1,2-phenylene]bis(oxyethane-2,1-diyloxyethane-2,1-
diyl)]bis{4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzamide}
(22)
Following general procedures 3 and 4 using 16 (188 mg, 0.3mmol)
and 2 (392 mg, 1.2 mmol) with purification by flash chromatogra-
phy (EtOAc–hexane, 90:10) gave 22 (72 mg, 25%) as a white pow-
der.
IR (film): 3332, 2939, 1641, 1546, 1510, 1342, 1309, 12228, 1186,
1151, 1051, 939 cm–1.
1H NMR (500 MHz, CDCl3): δ = 2.84 (t, J = 7.1 Hz, 2 H, PhCH2),
3.55–3.61 (m, 4 H, NHCH2), 3.62–70 (m, 6 H, PhCH2CH2,
NHCH2CH2), 3.73–3.78 (m, 4 H, OCH2CH2O), 3.98–4.01 (m, 4 H,
OCH2CH2O), 6.50 (t, J = 5.7 Hz, 1 H, NH), 6.73 (br s, 3 H, HAr),
19F NMR (282 Hz, CDCl3): δ = –65.47 (s, 12 F).
HRMS (ESI): m/z [M + Na]+ calcd for C70H68N14O14F12Na:
1579.4746; found: 1579.4602.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 2249–2254

2254
A. Welle et al.
PAPER
(11) Phelps, E. A.; Enemchukwu, N. O.; Fiore, V. F.; Sy, J. C.;
Murthy, N.; Sulchek, T. A.; Barker, T. H.; García, A. J. Adv.
Mater. (Weinheim, Ger.) 2012, 24, 64.
(12) (a) Blencowe, A.; Blencowe, C.; Cosstick, K.; Hayes, W.
React. Funct. Polym. 2008, 68, 868. (b) Du, N.; Dal-Cin, M.
M.; Pinnau, I.; Nicalek, A.; Robertson, G. P.; Guiver, M. D.
Macromol. Rapid. Commun. 2011, 32, 631.
Acknowledgment
This work was generously supported by the Fonds pour la Re-
cherche Scientifique (F.R.S.-FNRS) of Belgium and the Walloon
Government (Belgium) through the research programs EMULFIVE,
RAPARRAY and TARGETUM.
(13) (a) Brunner, J.; Senn, H.; Richards, F. M. J. Biol. Chem.
1980, 255, 3313. (b) Nassal, M. Liebigs Ann. Chem. 1983,
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W. G. Tetrahedron 2005, 61, 11244.
(14) (a) Rerat, V.; Dive, G.; Cordi, A. A.; Tucker, G. C.; Bareille,
R.; Amédée, J.; Bordenave, L.; Marchand-Brynaert, J.
J. Med. Chem. 2009, 52, 7029. (b) Moreau, J.; Marchand-
Brynaert, J. Eur. J. Org. Chem. 2011, 1641.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis. Included
are protocols for the synthesis of 1 to 6, 10, 12, 14, 15, 17, 21, 23,
24, 26, 30, 34, 36, and 13C NMR spectra.SupngIopif
omitratSnuIppfogmnirrti
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Synthesis 2012, 44, 2249–2254
© Georg Thieme Verlag Stuttgart · New York