300 Macromolecules, Vol. 44, No. 2, 2011
Xu et al.
Polysciences Inc., 97%) were used as received. N,N-dimethylacry-
lamide (DMA, Aldrich, 99%) was passed through a basic alumi-
num oxide column to remove inhibitor prior to use. 4-(Dimethyl-
amino)-pyridinium-4-toluene sulfonate (DPTS) was prepared
according to the procedure described in the literature.32
N-Acryloxysuccinimide (NAS) was synthesized according to
the literature procedure by the direct esterification of NHS and
acryloyl chloride in the presence of triethylamine.33 All other
chemicals were used as received.
Synthesis of N,N0-Bis(2-(cholesteryl butyric-1-carbonyloxo)-
ethyl)cyanopentanoic Amide Dithiobenzoate, CTA4. The RAFT
CTAs CTA4 and CTA5 (Scheme S1 in Supporting Information),
were prepared from the precursor dithioesters 4,40-((((4-cyano-
4-((phenylcarbonothioyl)thio)pentanoyl)azanediyl)bis(ethane-2,
1-diyl))bis(oxy))bis(4-oxobutanoic acid) (CTA3) and 5-(bis(2-
hydroxyethyl)amino)-2-cyano-5-oxopentan-2-yl benzodithio-
ate (CTA2) respectively which were themselves prepared according
to previously published procedures.34,35
reaction mixture was left to stir overnight at room temperature.
After removal of the undissolved solid, the solution was con-
centrated and the product, 16-hydroxyhexadecyl(4-pyren-1-yl)
butanoate, purified by column chromatography on silica gel,
eluting with DCM (Rf = 0.3) to give the target compound
1
(0.41 g, 36.1% yield). H NMR (300 MHz, CDCl3): δ (ppm)
8.32-7.80, (m, 9H, pyrenyl group), 4.10, (t, 2H, CH2CH2OCO),
3.62 (q, 2H, HOCH2(CH2)14CH2OCO), 3.39 (t, 2H,CH2CH2-
CH2-pyrene), 2.46 (t, 2H, CH2OCOCH2CH2CH2-pyrene),
2.22 (m, 2H, CH2CH2CH2-pyrene), 1.58 (m, 4H), 1.24 (m,
24H). ESI MS: 551.12 (MNaþ).
Subsequently, 16-hydroxyhexadecyl(4-pyren-1-yl)butanoate
(0.36 g, 0.68 mmol) and DCC (0.13 g, 0.62 mmol) were dissolved
in DCM (3.0 mL). In a separate flask, CTA3 (0.16 g, 0.29 mmol)
and DPTS (0.01 g, 0.039 mmol) were dissolved in DCM (3.0 mL)
and were added to the above solution. The reaction mixture was
stirred overnight at room temperature. After removal of the
undissolved solid, the solution was concentrated and the target
product purified by column chromatography on silica gel,
eluting with n-hexane/ethyl acetate (2/1) (Rf = 0.25) to give
the RAFT agent CTA6 as a pink solid (0.34 g, 74.1% yield). 1H
NMR (300 MHz, CDCl3): δ (ppm) 8.29-7.90, (m, 18H, pyrenyl
group), 7.81 (d, 2H, phenyl group), 7.48 (t, 1H, phenyl group), 7.30
(t, 2H, phenyl group), 4.25 (q, 4H), 4.11 (m, 8H), 3.59 (m, 4H), 3.38
(m, 4H), 2.72 (t, 2H), 2.60 (m, 9H), 2.45 (t, 5H), 2.22 (m, 4H), 1.96
(s, 3H), 1.58 (m, 8H), 1.24 (m, 48H). ESI MS: 1612.3 (MNaþ).
Synthesis of 2-(4-Cyano-4-((phenylcarbonothioyl)thio)penta-
namido)ethyl 4-(Pyren-1-yl) Butanoate, CTA7. For the general
scheme see Scheme S3 in the Supporting Information.
Precursor CTA3 (0.40 g, 0.706 mmol) and DCC (0.32 g,
1.55 mmol) were dissolved in dichloromethane (DCM, 6.0 mL).
Cholesterol (1.08 g, 2.87 mmol) and DPTS (0.024 g, 0.078 mmol)
dissolved in DCM (6.0 mL) were added slowly. The reaction
mixture was warmed to 40 °C and stirred overnight. After
removal of the undissolved solid, the solution was concentrated
and purified by column chromatography on silica gel, eluting with
n-hexane/ethyl acetate (1/1) (Rf = 0.8) to give the RAFT agent
1
CTA4 as a pink solid powder (0.52 g, 56.6% yield). H NMR
(300 MHz, CDCl3): δ (ppm) 7.92 (d, 2H, phenyl group), 7.56
(t, 1H, phenyl group), 7.39 (t, 2H, phenyl group), 5.36 (d,
2H, protons on double bond of cholesterol), 4.59 (m, 2H,
CH2COOCH(CH2)(CH2)), 4.26 (m, 4H, CON(CH2CH2OCO)2),
3.68 (t, 2H), 3.62 (t, 2H, CON(CH2CH2OCO)2), 2.76 (t, 2H,
(CN)C(CH3)CH2CH2CON), 2.60 (m, 8H, CH2OCOCH2CH2-
COOCH), 2.47-2.39 (m, 2H, (CN)C(CH3)CH2CH2CON), 2.30
(d, 4H, CH2COOCH(CH2)(CH2)), 1.97, 1.83, 1.56, 1.49, 1.32,
1.12, 0.92, 0.88, 0.87, 0.85, 0.67. ESI MS: 1327.10 (MNaþ).
Synthesis of N,N0-Bis(2-(1-pyrenebutyrate)ethyl)cyanopen-
tanoic Amide Dithiobenzoate, CTA5. Precursor CTA2 (0.401 g,
1.07 mmol) and DCC (0.606 g, 2.94 mmol) were dissolved in
tetrahydrofuran (THF, 6 mL). 1-Pyrenebutyric acid (0.77 g,
2.68 mmol) and DPTS (0.046 g, 0.146 mmol), dissolved in THF
(6 mL), were added slowly. The reaction mixture was stirred
overnight at room temperature. After removal of the undis-
solved solid the solution was concentrated and purified by column
chromatography on silica gel, eluting with n-hexane/ethyl
acetate (2/1) (Rf = 0.5) to give the RAFT agent CTA5 as a pink
solid powder (0.70 g, 72.4% yield). 1H NMR (300 MHz, CDCl3): δ
(ppm) 8.29-7.90, (m, 18H, pyrenyl group), 7.81 (d, 2H, phenyl
group), 7.48 (t, 1H, phenyl group), 7.30 (t, 2H, phenyl group), 4.21,
4.11 (m, 4H, N(CH2CH2OCO)2), 3.53(m, 4H, N(CH2CH2OCO)2),
3.34 (m, 4H,CH2CH2CH2-pyrene), 2.67 (t, 2H, (CN)C(CH3)CH2-
CH2CON), 2.43 (t, 4H, CH2OCOCH2CH2CH2-pyrene), 2.40-
2.31 (m, 2H, (CN)C(CH3)CH2CH2CON), 2.14 (m, 4H, CH2CH2-
CH2-pyrene), 1.78 (s, 3H, (CH3)C(CN)S). 13C NMR (75 MHz,
CDCl3): 222.4 (PhCdS), 173.4 (CdO), 144.4, 135.3, 132.9, 131.3,
130.75, 129.9, 128.7, 128.5, 127.4, 127.3, 126.7, 126.6, 125.8, 125.0,
124.9, 124.8, 123.1, 118.6, 63.0, 45.9, 38.9, 33.9, 33.5, 32.6, 31.7, 26.5,
24.1. UV-vis absorption: 267, 278, 314, 328, 344 nm. ESI MS:
930.23 (MNaþ).
2-Cyano-5-((2-hydroxyethyl)amino)-5-oxopentan-2-yl benzo-
dithioate, was prepared from the reaction of 2-cyano-5-oxo-5-(2-
thioxothiazolidin-3-yl)pentan-2-yl benzodithioate with 2-amino-
ethanol as follows: Aminoethanol (0.092 g, 1.51 mmol) dissolved in
THF (2 mL) was added slowly to 2-cyano-5-oxo-5-(2-thioxothia-
zolidin-3-yl)pentan-2-yl benzodithioate (0.57 g, 1.52 mmol) also
dissolved in THF (2 mL). The reaction mixture was stirred over-
night. The mixture was concentrated and purified by column
chromatography on silica gel, eluting with gradient DCM/
methanol (40/0-40/1) to give the target compound as a pink oil
1
(0.42 g, 86.8% yield). H NMR (300 MHz, CDCl3): δ (ppm)
7.92 (d, 2H, phenyl group), 7.56 (t, 1H, phenyl group), 7.40 (t,
2H, phenyl group), 5.81 (t, 1H,CH2CONHCH2), 3.49 (m, 4H,
NHCH2CH2OH), 1.97 (s, 3H, (CH3)C(CN)S). 13C NMR (75
MHz, CDCl3): δ (ppm) 222.3 (PhCdS), 172.51 (CdO), 144.1,
132.8, 128.4, 126.3, 118.6 (CN), 65.3 (NHCH2CH2OH), 61.8, 45.8,
34.1, 27.5, 24.1. FT-IR: 3315-3100 (O-H and N-H), 1679
(CdO), 1568 (N-H), 1512 (N-C), 1160 (PhCdS). ESI MS:
344.90 (MNaþ).
2-Cyano-5-((2-hydroxyethyl)amino)-5-oxopentan-2-yl ben-
zodithioate (0.2 g, 0.62 mmol) and DCC (0.18 g, 0.85 mmol)
were dissolved in THF (3 mL). PyBA (0.22 g, 0.78 mmol) and
DMAP (0.005 g, 0.04 mmol), dissolved in THF (3 mL), were
added into the above solution. The reaction mixture was stirred
overnight at room temperature. After removal of the undis-
solved solid, the solution was concentrated and purified by
column chromatography on silica gel, eluting with n-hexane/
ethyl acetate (2/1) (Rf = 0.4) to give the RAFT agent CTA7 as a
pink powder (0.31 g, 84.3% yield). 1H NMR (300 MHz, CDCl3):
δ (ppm) 8.32-7.80, (m, 9H, pyrenyl group), 7.96 (d, 2H, phenyl
group), 7.53 (t, 1H, phenyl group), 7.36 (t, 2H, phenyl group),
5.81 ((t, 1H,CH2CONHCH2), 4.17, (t, 2H, NHCH2CH2OCO),
3.53 (m, 2H, NHCH2CH2OCO), 3.34 (t, 2H,CH2CH2CH2-
pyrene), 2.67 (t, 2H, (CN)C(CH3)CH2CH2CON), 2.41 (t, 2H,
CH2OCOCH2CH2CH2-pyrene), 2.40-2.31 (m, 2H, (CN)C(CH3)-
CH2CH2CON), 2.21 (m, 2H, CH2CH2CH2-pyrene), 1.86 (s, 3H,
(CH3)C(CN)S). 13CNMR (75 MHz, CDCl3): 222.4 (PhCdS), 173.4
(CdO), 144.4, 135.3, 132.9, 131.3, 130.75, 129.9, 128.7, 128.5, 127.4,
127.3, 126.7, 126.6, 125.8, 125.0, 124.9, 124.8, 123.1, 118.6, 63.0, 45.9,
38.9, 33.9, 33.5, 32.6, 31.7, 26.5, 24.1. UV-vis absorption: 267, 278,
314, 328, 344 nm. ESI MS: 615.33 (MNaþ).
Synthesis of O,O0-(((4-Cyano-4-((phenylcarbonothioyl)thio)-
pentanoyl)azanediyl)bis(ethane-2,1-diyl)) bis(((4-(pyren-1-yl)-
butanoyl)oxy)hexadecyl) Disuccinate, CTA6. CTA6 was prepared
via a two step procedure as follows (see Scheme S2 in Supporting
Information).
Initially, 16-hydroxyhexadecyl(4-pyren-1-yl) butanoate was
prepared via the reaction of PyBA with 1,16-hexadecanediol:
1,16-hexadecanediol (0.91 g, 3.56 mmol) and DCC (0.53 g,
2.58 mmol) were dissolved in THF (8.0 mL). In a separate flask,
PyBA (0.62 g, 2.15 mmol) and DMAP (0.013 g, 0.11 mmol) were
dissolved in THF (8.0 mL) and added to the above solution. The