Y.-J. Pu et al. / Chinese Chemical Letters 24 (2013) 917–920
919
deionized water, yield 75%. 8 was handled similarly with a yield of
8%.
Deprotection of 8 and 9: Taking 9 as an example, to a solution of 9
100 mg) in CH Cl (2 mL) was added TFA (200 L) in an ice bath.
The reaction was stirred for 6 h at r.t. Ethyl ether was added to
precipitate and the precipitate was dried under vacuum with a
high yield of 95%. Deprotection of 8 was similar.
completely alkynated. Notably, we had also tried another method
to synthesize alkynated POSS by reacting 2 with propargyl
bromide. However, the result was unsuccessful due to the poor
solubility of 2 in most organic solvents, and the basicity of the
reaction broke the Si–O–Si bond in the POSS matrix.
8
(
2
2
m
Dendritic poly(
synthesized by the divergent approach as previously reported [9].
Azido-functionalized poly( -lysine) dendrimers with generations 1
and 3 (G1-N and G3-N ) were synthesized by aminolysis,
L-lysine) with generations from 1 to 3 was
The product from deprotection of 8 and 9 was dissolved in
L
water and the pH was tuned to be basic by NaHCO
3
solution. The
3
3
solution was then dialysis against deionized water to remove salts
and the result solution was used for dynamic light scattering (DLS,
Malvern Zetasizer Nano ZS) test directly.
mesylation and finally azidotion of the corresponded dendrimers
(5a and 7a), which had the core carboxylic acid protected by
methanol ester and the peripheral amine group protected by tert-
butoxylcarbonyl (Boc). Ethanolamine was used to aminolysis in
55 8C [10]. The hydroxy group was converted to the ester group (–
Ms), which could be azided easily. The overall yield was about 80%.
1
H NMR spectra were recorded on a Bruker Avance II NMR
spectrometer at 400 MHz. Fourier transform infrared (FTIR)
spectra were recorded on a Perkin-Elmer spectrophotometer.
Gel permeation chromatography (GPC) measurements were
carried out using a Waters instrument that was equipped with a
model 515 pump, where THF was used as fluent with a speed of
3
Taking G3-N for example, the successful azidotion was directly
confirmed by FTIR spectrum (Fig. S2B in Supporting information).
À1
There was a characteristic peak at 2100 cm which corresponded
0
.35 mL/min at 40 8C.
to the typical stretching vibration absorbance of N
The POSS based generation 1 (8) and 3 (9) poly(
dendrimers were then synthesized via CuAAC click chemistry
where DMF–water solution (1:1, v/v) with 5% mol CuSO O and
10% mol sodium ascorbate used as catalyst. The reaction mixture
was precipitated with acetonitrile and dialyzed against dilute
3
.
L
-lysine)
3
. Results and discussion
4
Á5H
2
In the synthesis of the POSS core, we determined that a more
rapid synthesis of POSS-(NH
increasing the reaction temperature from room temperature to
0 8C. The reaction time was reduced from 5-10 days to only 16 h
2
ÁHCl)
8
(2) could be achieved by
EDTA solution and deionized water to remove copper. The
À1
9
obtained dendrimer showed no peaks at 2100 cm
in FTIR
while the yield was not changed (33% vs. traditional 30%). The
successful synthesis of 2 was demonstrated by MS as shown in
spectrum (Fig. S2C in Supporting information), suggesting that
alkyne and azide groups reacted completely and clearly removed.
The H NMR spectra of 8 and 9 are shown in Fig. 3, and
characteristic peaks of both POSS and amide bond in dendritic
lysine were observed. The structures of the dendrimers were
further confirmed by GPC (Fig. S3 in Supporting information). The
dendrimers of G1 and G3 both showed very narrow distribution
with low polydispersity of 1.03 and 1.06, respectively.
+
1
Fig. 2A. The molecular peak was observed at m/z 881 ([M+H] ). The
1
obtained POSS was also confirmed by H NMR and FTIR. As shown
in Fig. 2B, the signals at
d 0.6, 1.9, and 3.2 were assigned to the
protons adjacent to silicon atoms extending outward. The FTIR
spectrum (Fig. S1 in Supporting information) showed a character-
À1
istic absorbance peak at 1123 cm which corresponded to the
stretching vibration of Si–O–Si in the POSS matrix.
The deprotection of peripheral Boc groups on 8 or 9 was carried
The POSS was then alkyne-functionalized by two steps. Succinic
anhydride was first used to react with the amine group on 2 to
out in CH
triazole-G1lys(NH
2
Cl
2
/TFA solution. The resulting peptide dendrimers, POSS-
16 and POSS-triazole-G3lys(NH 64, were water
2
)
2
)
receive POSS-(COOH)
amine to synthesize POSS-(alkyne)
is shown in Fig. 2C. The peaks at 3.0 and 0.6 were ascribed to the
alkyne protons and -protons adjacent to POSS, respectively. The
8
(3), it was then reacted with 2-propynyl
soluble and their hydrodynamic diameters were investigated by
dynamic light scattering (DLS, Fig. S4 in Supporting information).
The mean diameters were less than 10 nm and the dendrimers were
monodisperse. The G3 showed a larger size than G1. The POSS core
itself was about 1 nm and the size of dendrimers with POSS cores
1
8
(4). The H NMR spectrum of 4
d
a
area ratio of the two peaks was 1:2, indicating that the POSS was
1
Fig. 2. (A) MS spectrum of 2 and H NMR spectra of (B) 2 and (C) 4 in D
2
O and DMSO-d
6
, respectively.