Synthesis of a methacrylic monomer containing an L-lysine-based dendron

Article abstract of DOI:10.1007/s11167-005-0437-2

Procedures were developed for preparing a polylysine dendron of second generation, containing terminal Boc-protected amino groups and a free focal amino group; from this substance, a previously unknown methacrylic monomer linked to the L-lysine-based dendron was prepared.

Full text of DOI:10.1007/s11167-005-0437-2

Russian Journal of Applied Chemistry, Vol. 78, No. 6, 2005, pp. 1003 1007. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005,
pp. 1024 1028.
Original Russian Text Copyright
2005 by Khimich, Tennikova.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
Synthesis of a Methacrylic Monomer
Containing an L-Lysine-Based Dendron
G. N. Khimich and T. B. Tennikova
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received July 26, 2004; in final form, January 2005
Abstract Procedures were developed for preparing a polylysine dendron of second generation, containing
terminal Boc-protected amino groups and a free focal amino group; from this substance, a previously unknown
methacrylic monomer linked to the L-lysine-based dendron was prepared.
Much attention is given today to development of
hybrid materials combining dendritic and linear struc-
tural fragments [1]. The use of dendritic monomers as
building blocks along with linear monomers substan-
tially extends the possibilities of macromolecular de-
sign; it has led to preparation of polymers of unusual
architecture [2]. By using various structural elements
forming a polymeric framework, it is possible not
only to modify the physical properties of polymers,
but also to impart additional functions to the polymer
skeleton, such as complexing power, response to cer-
tain physical actions, and possibilities of further trans-
formations. Introduction of dendrimers combining
a high functionality with a compact molecular struc-
ture opens wide prospects for application of such
materials in biology, medicine, and medical diagnos-
tics [3 7].
Published data on synthesis of dendritic polymers
and copolymers containing monomeric units with
dendritic poly-L-lysine fragments are lacking. There
are three fundamentally different routes to such sub-
stances: (1) synthesis of a linear polymer, followed by
addition of separately prepared dendrons to the chain
(convergent route); (2) synthesis of a polymer with
active substituents, followed by stepwise build-up of
a dendron at the polymer chain (divergent route); and
(3) synthesis of macromonomers, i.e., dendrons con-
taining a polymerizable functional group at the focal
point, followed by polymerization [1, 15]. Use of
such macromonomers containing terminal function-
al groups capable of further chemical transforma-
tions under relatively mild conditions may be promis-
ing for preparation of new polymeric materials and
macroporous polymeric sorbents [16].
The goal of this study was to develop a procedure
for preparing a methacrylic monomer containing a frag-
ment of a poly-L-lysine dendron of second generation.
Dendrimers prepared from natural amino acids
by peptide synthesis [8 10] contain on the periphery
a controllable amount of reactive functional groups.
The interest in polymers containing branched poly-
lysine [11, 12] is due to the possibility of preparing
new amphiphilic materials to be used in molecular
biology. Dendrimers derived from L-lysine and block
copolymers containing dendritic poly-L-lysine exhibit
a high compacting power toward DNA [13, 14].
EXPERIMENTAL
We used the following chemicals: L-lysine hydro-
chloride (Reanal, Hungary), di-tert-butyl pyrocarbo-
nate, dicyclohexylcarbodiimide (DCC), N-hydroxy-
benzotriazole (HOBT) (all Sigma Aldrich, Germany),
methacryloyl chloride, and thionyl chloride (both
Reakhim, Russia).
Two types of denritic-linear polymers containing
poly-L-lysine fragments are known: dumbbell-like
compounds prepared by reactions of bifunctional line-
ar compounds (low-molecular-weight or polymeric)
with dendritic fragments [12] and compounds in which
one end of a polymer chain is linked to the focal
point of a dendron [11, 12].
Methylene chloride, ethyl acetate, and chloroform
were dried over P2O5 and then distilled (bp 40, 77,
and 62 C, respectively). Tetrahydrofuran and diethyl
ether were refluxed over alkali and then distilled
(bp 65 and 35 C, respectively). Acetone was refluxed
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1004
KHIMICH, TENNIKOVA
over anhydrous K2CO3, distilled (bp 56 C), and stored
over molecular sieves. Thionyl chloride was distilled
(bp 79 C). Other solvents and solid chemicals were
used without additional purification.
The H and 13C NMR spectra were recorded on
Bruker AC 300 (300 MHz) and Bruker DRX 500
CH3OLys(LysBoc2)2 III. To a solution of 3.244 g
(0.014 mol) of L-lysine methyl ester dihydrochloride
in 20 ml of DMF, we added 4.6 ml (0.033 mol) of
triethylamine to obtain mixture A. To a solution of
10.5 g (0.042 mol) of di(tert-butoxycarbonylamino)-L-
lysine in 40 ml of DMF, we added 3.97 g (0.033 mol)
of HOBT and 6.84 g (0.033 mol) of DCC. After stand-
ing for 40 min, the solution of the activated ester
was filtered through a glass frit and added to mix-
ture A. The mixture was stirred for a day, and the pre-
cipitate was separated. The filtrate was evaporated
in a vacuum to 1/3 of the initial volume. The result-
ing solution was diluted with 100 ml of ethyl acetate
and washed successively with saturated NaCl solu-
tion (40 ml), 2% NaHSO4 solution (2 20 ml), 5%
NaHCO3 solution (2 20 ml), and H2O (2 20 ml).
The organic layer was dried over Na2SO4 and evap-
orated; the yellow oily residue was purified by prepar-
ative adsorption chromatography on a column packed
with silica gel (40 60 m). The major fraction was
additionally purified by repeated chromatography on
a similar column. A mixture of chloroform with meth-
anol (ratio from 10 : 1 to 5 : 1) was used as eluent.
A white crystalline substance was obtained; yield
9.84 g (86%).
1H NMR spectrum (DMSO-d6), , ppm: 1.10
1.75 m (54H; t-C4H_9, CH2), 2.88 m (4H, CH_2), 2.95
3.1 m (2H), 3.61 m (3H, OCH_3), 3.80 m (1H, CH),
3.91 m (1H, CH), 4.20 m (1H, CH), 6.66 d (1H, NH),
6.71 m (3H, NH), 7.71 t (1H, NH), 8.05 t (1H, NH).
13C NMR spectrum (DMSO-d6), , ppm: 22.51,
22.72, 22.83, 24.48, 25.37, 28.22, 28.31, 28.61, 29.24,
29.26, 30.58, 31.64, 31.83, 33.38, 38.15, 39.72, 40.83,
47.55, 51.75, 54.03, 54.37, 77.34, 77.94, 155.28 (CO),
156.59 (CO), 171.95 (CO), 172.41 (CO), 172.53 (CO).
1
(500 MHz) spectrometers in DMSO-d6 or acetone-d6.
MALDI-TOF mass spectra were taken on a Bruker
IV device. Samples were ionized with an N2 laser
from a matrix of 2,4-dihydroxybenzoic acid.
The IR spectra were recorded on a Bruker IFS 88
spectrophotometer.
L-Lysine methyl ester dihydrochloride I. Thionyl
chloride (8 ml) was added dropwise with stirring to
60 ml of methanol cooled to 5 C with an ice salt
mixture, after which L-lysine hydrochloride (9.13 g,
0.005 mol) was added in portions with cooling. The
mixture was stirred for 40 min at room temperature
and then refluxed for 80 min. After cooling, the mix-
ture was left overnight. The precipitate was filtered off
and washed with diethyl ether (1 : 1). The precipitate
was dried in air and then in a desiccator over NaOH.
Yield 10.17 g (87.2%); white crystals.
1H NMR spectrum (DMSO-d6), , ppm: 1.39 m
(2H, CH2), 1.59 m (2H, CH2), 1.83 m (2H, CH2),
2.74 m (2H, CH2), 3.75 s (3H, OCH3), 3.96 t (1H,
CH), 8.16 br.s (NH+3), 8.72 (NH3+).
Di (tert-butoxycarbonylamino)-L-lysine II. To
a solution of 3.2 g (0.08 mol) of NaOH in 30 ml of
H2O, we added with stirring L-lysine hydrochloride
(7.306 g, 0.04 mol) and then sodium hydrocarbonate
(1.68 g, 0.02 mol). A solution of 18.2 g (0.088 mol)
of tert-butyl pyrocarbonate in 40 ml of ethanol was
added dropwise with stirring to the solution of the ami-
no acid, cooled with ice and water. The mixture was
stirred for a day at room temperature, after which
50 ml of H2O was added to dissolve the precipitate.
Excess tert-butyl pyrocarbonate was extracted with
petroleum ether. The aqueous phase was acidified with
1 M NaHSO4. The product was extracted with ethyl
acetate. The organic layer was washed with a satu-
rated NaCl solution, dried over anhydrous Na2SO4,
and evaporated; the residue was dried in a vacuum.
Yield 10.98 g (85.4%); white crystals.
Found, %: C 57.41, H 8.95, N 10.40.
C39H72N6O12.
Calculated, %: C 57.33, H 8.88, N 10.29.
MALDI, m/z: 818.1 [M + H]+, 840.1 [M + Na]+,
1
856.1 [M + K]+. IR spectrum, , cm : 3150 3500
(NH), 2978 (t-C4H9), 1693 (C=O, amide I), 1525
(amide II), 1170 (CO).
NH2CH2CH2NHLys(LysBoc2)2 IV. A solution of
1.58 g (1.93 mmol) of dendron III in 15 ml of abso-
lute methanol was added dropwise with stirring to
15 ml of ethylenediamine, cooled with ice. The mix-
ture was purged with nitrogen and left in the dark
at room temperature for 3 days. After that, the sol-
vent and excess ethylenediamine were distilled off in
a vacuum. The product was purified by preparative
adsorption chromatography on a column packed with
1H NMR spectrum (DMSO-d6), , ppm: 1.2 1.4 m
(20H, t-C4H9, CH2), 1.53 m (2H, CH2), 1.61 m (2H,
CH2), 2.88 m (2H, CH2NHBoc), 3.82 m (1H, OCCH),
6.72 t (1H, NH), 6.96 t (1H, NH), 12.35 s (1H, COOH).
Found, %: C 55.42, H 8.81, N 8.16.
C16H30N2O6.
Calculated, %: C 55.47, H 8.73, N 8.09.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 6 2005

SYNTHESIS OF A METHACRYLIC MONOMER CONTAINING AN L-LYSINE-BASED DENDRON 1005
silica gel (40 60 m), with chloroform methanol
(5 : 1) as eluent. A white crystalline product was
obtained; yield 1.38 g (83.8%).
1H NMR spectrum (DMSO-d6), , ppm: 1.10
1.75 m (56H), 2.54 m (2H, CH2 NH2), 2.87 m (4H,
CH2), 2.95 3.08 m (4H, CH2), 3.81 m (1H, CH),
3.85 m (1H, CH), 4.17 m (1H, CH), 6.66 d (1H, NH),
7.62 m (2H, NH), 6.86 d (1H, NH), 7.68 m (2H, NH),
7.79 t (1H, NH).
13C NMR spectrum (DMSO-d6), , ppm: 22.52,
22.83, 28.22, 28.32, 28.79, 29.24, 31.44, 31.89, 31.96,
38.41, 39.69, 41.25, 42.29, 52.38, 54.33, 54.54, 77.34,
77.93, 78.15, 155.29 (CO), 155.46 (CO), 155.61 (CO),
171.46 (CO), 171.90 (CO), 171.96 (CO).
1.167 g (1.6 mmol) of methacryloyl chloride in 2 ml
of THF. The mixture was stirred for 3 h and left over-
night. On the next day, the solvent was distilled off
in a vacuum. The residue was dissolved in dichloro-
methane and washed with water, dilute Na2CO3, and
again water. The organic layer was dried over Na2SO4
and concentrated. A white crystalline substance was
obtained; yield 1.1 g (83.3%).
1H NMR spectrum (DMSO-d6), , ppm: 1.1
1.75 m (52H), 1.98 s (3H, C=CCH3), 2.87 m (4H,
CH2NHCO), 3.03 m (2H), 3.15 m (4H), 3.82 m (2H),
4.18 m (1H, CH), 5.28 (1H), 5.62 (1H), 5.95 6.9
(a series of broad NH signals).
13C NMR spectrum (DMSO-d6), , ppm: 19.39,
21.55, 23.31, 23.66, 25.30, 25.97, 29.01, 29.10, 29.63,
30.06, 32.25, 32.71, 34.20, 39.81, 46.43, 48.37, 53.15,
55.15, 55.33, 55.70, 60.57, 67.86, 78.13, 78.72, 78.94,
119.93, 140.66, 156.09 (CO), 156.27 (CO), 156.40
(CO), 157.49 (CO), 168.37 (CO), 171.11 (CO), 172.62
(CO), 172.64 (CO).
Found, %: C 56.93, H 9.35, N 13.21.
C40H76N8O11.
Calculated, %: C 56.85, H 9.06, N 13.26.
MALDI, m/z: 846 [M + H]+, 868 [M + Na]+, 884
1
[M + K]+. IR spectrum, , cm : 3150 3500 (NH),
MALDI-TOF, m/z: 935.7 [M + Na]+, 951.7 [M +
2978 (t-C4H9), 1695 (C=O, amide I), 1525 (amide II),
1169 (CO).
1
K]+. IR spectrum, , cm : 3150 3500 (NH), 3085
(=C H), 2978 (t-C4H9), 1694 (C=O, amide I), 1642
(C=C), 1526 (amide II), 1169 (CO).
Methacrylic monomer V. To a solution of 0.97 g
(1.45 mmol) of dendron IV in 12 ml of dry THF,
cooled to 5 C, we added 0.223 ml (1.60 mmol) of
triethylamine. Then we slowly added a solution of
The poly-L-lysine dendritic macromonomer is pre-
pared in several steps:
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 6 2005

1006
KHIMICH, TENNIKOVA
MALDI-TOF data
MALDI-TOF data
[M + Na]+
Molar
weight
Dendron
Formula
[M + H]+
[M + K]+
III
IV
V
C39H72N6O12
C41H78N8O11
C44H80N8O12
817.02
845.08
913.15
818.02*
818.1**
846.08
846.1
840.02
840.1
868.08
868.1
935.7
935.7
856.02
856.1
884.08
884.1
951.7
951.7
*
Found.
**
Calculated.
First, we prepared by known procedures L-lysine
tion of a spacer to an acrylic or methacrylic monomer,
followed by its modification with a dendron contain-
ing an appropriate functional group [1, 18]. In this
study, we modified dendron III with ethylenediamine
to obtain NH2CH2CH2NHLys(LysBoc2)2 IV. This
compound contains a focal amino group. In the sub-
sequent step, it is brought into condensation with
methacryloyl chloride, i.e., the spacer is added direct-
ly to the dendritic fragment.
methyl ester dihydrochloride and di-Boc-L-lysine.
The carboxy group was protected by esterification
with methanol in the presence of SOCl2. The Boc
protection of the amino groups of L-lysine was per-
formed by a standard procedure with tert-butyl pyro-
carbonate (Boc2O) [17].
From L-lysine methyl ester hydrochloride I and
di(tert-butyloxycarbonyl)-L-lysine II, we prepared
a dendron of second generation, CH3OLys(LysBoc2)2
III, containing four Boc-protected amino groups. For
this reaction to be successful, the carboxy group
should be activated. Various activating agents are
used in the synthesis of dendritic poly-L-lysines.
Choi et al. [12] used, when preparing a hybrid copoly-
mer of poly(ethylene glycol) and polylysine dendron
by a divergent procedure, N- -N- -di-Fmoc-L-lysine
(Fmoc = 9-fluorenylmethoxycarbonyl) and HOBT in
the presence of diisopropylamine. Chapman et al. [11]
used as reagent pentafluorophenyl ester of N- -N- -
di-Boc-L-lysine in the presence of diisopropylethyl-
amine (DPEA).
The structures of dendrons III and IV and of mac-
1
romonomer V were confirmed by IR and H and 13C
NMR spectroscopy, and also by MALDI-TOF spec-
trometry (see table).
CONCLUSIONS
(1) A poly-L-lysine dendron of second generation,
containing a focal amino group and terminal Boc-
protected amino groups, was prepared.
(2) A procedure was developed for preparing
a methacrylic monomer linked to the poly-L-lysine
dendron of second generation through a spacer.
In the synthesis of L-lysine dendron III, we acti-
vated the carboxy group with dicyclohexylcarbodi-
imide and N-hydroxybenzotriazole (DCC/HOBT).
The reaction occurs within 3 days at room tempera-
ture. The product was purified by column chromatog-
raphy on silica gel, with chloroform methanol as
eluent; yield 86%.
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