Wang and Advincula
138.9, 119.6, 119.2, 119.1, 118.9, 114.2, 113.8. Anal. Calcd for
C16H10N2O8: C, 53.64; H, 2.81; N, 7.82. Found: C53.26; H,
2.92; N, 7.98.
dichloromethane (15 mL) was added the AB2 monomer (10)
(1 mmol), followed by 4-dimethylaminopyridinum toluene-4-
sulfonate (DPTS) (1 mg). The mixture was stirred at room
temperature under nitrogen for 15 min. Dicyclohexylcarbodi-
imide (DCC) (2.2 mmol) was then added and stirring continued
at room temperature until the reaction was complete. The
reaction mixture was filtered to remove the precipitate dicy-
clohexylurea and evaporated to dryness under reduced pres-
sure. The crude product was purified by silica gel chromatog-
raphy using dichloromethane/ethyl acetate (30/1) as an eluent
to give G-3-OTBDPS (yield: 91%). MALDI-TOF-MS: [M +
H] 2307.9 (calcd for C137H122 N14O29Si, 2454.83). 1H NMR (300
MHz, CDCl3): δ 8.89-8.88 (m, 3H), 8.80-8.77 (m, 9H), 8.73-
8.68 (m, 9H), 8.01 (d, 12H, J ) 8.8 Hz), 7.95 (d, 2H, J ) 8.5
Hz), 7.71-7.68 (m, 4H), 7.66 (d, 12H, J ) 8.2 Hz), 7.52 (d, 2H,
J ) 8.1 Hz), 7.44-7.36 (m, 6H), 5.44 (s, 12H), 4.85 (s, 2H),
4.46 (q, 6H, J ) 7.0 Hz), 1.44 (t, 24H, J ) 7.0 Hz), 1.10 (s,
9H). 13C NMR (300 MHz, CDCl3): δ 165.3, 165.0, 164.9, 152.7,
152.6, 152.2, 139.5, 139.2, 135.5, 133.2, 132.4, 132.0, 131.6,
131.5, 129.8, 128.9, 128.2, 127.8, 127.7, 126.6, 123.6, 123.5,
123.3, 66.7, 61.7, 14.3.
Dendron G-3-OH and General Procedure for Desilyla-
tion. To a solution of G-3-OTBDPS (1 equiv) in CH2Cl2 in a
polyethylene bottle was added HF-pyridine (2 equiv), and the
mixture was vigorously stirred at room temperature. After
being stirred overnight, the mixture was diluted with twice
the volume of water, CH2Cl2 was added, and the solution was
washed with saturated NaHCO3 (aq). After the solvent was
dried (MgSO4) and evaporated, an orange solid was obtained,
which was washed with methanol and purified by silica gel
chromatography using a mixture of CH2Cl2/EtOAc from 100:1
to 10:1 (v/v) (yield 86%). MALDI-TOF: [M + K] 2257.4 (calcd
for C121H104 N14O29, 2218.2). 1H NMR (300 MHz, CDCl3): δ
8.89-8.88 (m, 3H), 8.80-8.77 (m, 9H), 8.72-8.65 (m, 9H), 8.01
(d, 12H, J ) 8.8 Hz), 7.87 (d, 2H, J ) 8.4 Hz), 7.55 (d, 12H, J
) 8.4 Hz), 7.53 (d, 2H, J ) 8.7 Hz), 5.44 (s, 12H), 4.81 (s, 2H),
4.44 (q, 16H, J ) 7.0 Hz), 1.44 (t, 24H, J ) 7.0 Hz). 13C NMR
(300 MHz, CDCl3): δ 165.3, 164.9, 152.8, 152.7, 152.6, 152.2,
152.1, 145.1, 139.4, 139.2, 132.4, 132.0, 131.6, 131.5, 129.0,
128.9, 128.2, 127.7, 127.4, 123.6, 123.5, 123.4, 66.7, 64.7, 61.7,
14.3. Anal. Calcd for C121H104N14O29: C, 65.52; H, 4.73; N, 8.84
Found: C, 65.38; H, 4.92; N, 8.96.
G-2-OH. G-1-Br (5) (1.12 g, 2.67 mmol) was combined with
pure 4-(5′-azoisophthalate acid)benzyl alcohol (4) (390 mg, 1.30
mmol), K2CO3 (369 mg, 2.67 mmol), 18-crown-6 (2 mg), and
acetone (50 mL) in a 100 mL three-necked round-bottomed
flask equipped with a magnetic stirrer, reflux condenser, and
N2 inlet. After the mixture was refluxed for 48 h, a large
amount of organic precipitate was observed. The reaction
mixture was cooled to room temperature, and the orange
precipitate was collected by suction filtration. The crude
product was recrystallized from THF/acetone and dried over-
night in a vacuum oven, yielding 968 mg of G-2-OH in 74%
yield. LC-MS: m/z [M + H] 977.3 (calcd for C53H48 N6O13,
976.4). 1H NMR (300 MHz, CDCl3): δ 8.90 (s, 1H), 8.80 (d,
4H, J ) 2.4 Hz), 8.77(s, 4H), 8.02 (d, 4H, J ) 8.5 Hz), 7.97 (d,
2H, J ) 8.5 Hz), 7.96 (d, 4H, J ) 8.3 Hz), 7.66 (d, 2H, J ) 8.4
Hz), 5.54 (s, 4H), 4.82(s, 2H), 4.46 (q, 8H, J ) 7.0 Hz), 1.44 (t,
12H, J ) 7.0 Hz). 13C NMR (300 MHz, CDCl3): δ 164.3, 163.9,
151.8, 151.6, 151.2, 150.7, 144.0, 138.3, 131.5, 131.3, 131.1,
130.6, 127.9, 127.1, 126.7, 126.4, 122.5, 122.4, 65.7, 63.7, 60.6,
13.3. Anal. Calcd for C53H48N6O13: C, 65.16; H, 4.95; N, 8.60.
Found: C, 65.15; H, 4.99; N, 8.45.
1-Nitro-4-(tert-butyldiphenylsiloxymethyl)benzene (8).
To a solution of 4-nitrobenzyl alcohol (15.3 g, 100 mmol) and
imidazole (13.4 g, 200 mmol) in DMF (50 mL) was added
dropwise a solution of tert-butyldiphenylsilyl chloride (41.1 g,
150 mmol) in DMF (50 mL) at 0 °C under nitrogen. The
mixture was stirred at room temperature for 12 h, and then
water was added to give a white precipitate. The precipitate
was collected by filtration and recrystallized from CH2Cl2/
hexane (20/100) to afford 37.6 g of 1-nitro-4-(tert-butyldiphen-
ylsiloxymethyl)benzene (8) as a colorless crystal in 96% yield.
EI-MS: m/z [M + H] 392.2 (calcd for C23H25 NO3Si, 391.1). 1H
NMR (300 MHz, CDCl3): δ 8.20 (d, 2H, J ) 8.2 Hz), 7.67 (m,
4H), 7.49 (d, 2H, J ) 8.4 Hz), 7.49-7.37 (m, 6H), 4.84 (s, 2H),
1.12 (s, 9H,). 13C NMR (300 MHz, CDCl3): δ 145.2, 145.0,
133.8, 131.2, 127.1, 127.0, 126.9, 126.5, 126.1, 126.2, 121.8,
66.3, 27.4, 20.1. Anal. Calcd for C23H25NO3Si: C, 70.55; H, 6.44;
N, 3.58. Found: C, 70.24; H, 6.62; N, 3.45.
1-Nitroso-4-(tert-butyldiphenylsiloxymethyl)ben-
zene (9). This was prepared from compound 8 using the
procedure described above for diethyl 5-nitrosoisophthalate (3)
and purified by flash chromatography using ethyl acetate/
hexane (1:5) as an eluent to give 1-nitroso-4-(tert-butyldiphen-
ylsiloxymethyl)benzene (9) as a white solid. Yield: 82%. EI-
MS: m/z [M + H] 376.1 (calcd for C23H25 NO2Si, 375.2). 1H
NMR (300 MHz, CDCl3): δ 7.71 (d, 2H, J ) 8.2 Hz), 7.67 (m,
4H), 7.45 (d, 2H, J ) 8.4 Hz), 7.49-7.37 (m, 6H), 4.84 (s, 2H),
1.12 (s, 9H). 13C NMR (300 MHz, CDCl3): δ 162.8, 145.9, 133.8,
131.2, 127.1, 126.1, 121.8, 66.3, 27.5, 20.1. Anal. Calcd for
C23H25NO2Si: C, 73.56; H, 6.74; N, 3.73. Found: C, 73.28; H,
6.82; N, 3.78.
AB2 Monomer 10. A mixture of 5-aminoisophthalic acid
(484 mg, 2.67 mmol) in 50 mL of acetic acid and 1-nitroso-4-
(tert-butyldiphenylsiloxymethyl)benzene (9) (1000 mg, 2.67
mmol) in 10 mL of CH2Cl2 was stirred at room temperature
under nitrogen. After the mixture was stirred for 24 h, an
orange solid was obtained, collected by filtration, and washed
with water. The crude product was recrystallized from diethyl
ether/hexane to give 1.2 g (yield: 91%) of pure AB2 monomer
10 as an orange solid. EI-MS: m/z [M + H] 539.1 (calcd for
C31H30 N2O5Si, 538.2). 1H NMR (300 MHz, acetone-d6): δ 8.83
(s, 1H), 8.77 (s, 2H), 8.67 (d, 2H, J ) 8.2 Hz), 7.79-7.77 (m,
4H), 7.69 (d, 2H, J ) 8.4 Hz), 7.49-7.37 (m, 6H), 4.92 (s, 2H),
1.15 (s, 9H). 13C NMR (300 MHz, acetone-d6): δ 206.8, 166.7,
154.0, 152.7, 146.9, 136.7, 134.4, 133.7, 133.5, 131.3, 129.2,
128.6, 128.1, 125.9, 124.5, 66.3, 27.6, 20.8. Anal. Calcd for
C31H30N2O5Si: C, 69.12; H, 5.61; N, 5.20. Found: C, 69.08; H,
5.67; N, 5.41.
Dendrimer G-1-4. This compound was prepared by cou-
pling 5-dicarboxyl-(3′,5′-dicarboxylazophenyl)benzene (AB4) (1
equiv) with G-1-OH (4.2 equiv) for 6 h using the same coupling
conditions described above for dendron G-3-OSPDBT and
purified by chromatography eluted with dichloromethane/ethyl
acetate (25/1). Yield: 82%. MALDI-TOF-MS: [M + K] 1750.7
(calcd for C92H82 N10O24, 1711.7). 1H NMR (300 MHz, acetone-
d6): δ 8.95 (m, 2H), 8.87 (m, 3H), 8.77 (m, 3H), 8.71 (m, 4H),
8.02 (d, 8H, J ) 8.3 Hz), 7.67 (d, 8H, J ) 8.3 Hz), 5.55 (s, 8H),
4.44 (q, 16H, J ) 7.0 Hz), 1.46 (t, 24H, J ) 7.0 Hz). 13C NMR
(300 MHz, CDCl3): δ 165.3, 164.8, 152.5, 152.4, 152.2, 139.1,
133.4, 132.4, 132.0, 131.8, 129.1, 128.4, 127.7, 123.6, 66.8, 61.7,
14.3. Anal. Calcd for C92H82N10O24: C, 64.56; H, 4.83; N, 8.18.
Found: C, 64.26; H, 4.92; N, 8.38.
Acknowledgment. This work was supported in part
by the National Institute of Health (NIH) MBRS
SCORE (No. 1 S06 GM 63119-01), the Petroleum
Research Fund administrated by the American Chemi-
cal Society (No. 35036-G7) and the Robert A. Welch
Foundation (E-1551). Mr. Tony Gies (UAB) is gratefully
acknowledged for assistance with MALDI-TOF experi-
ment. We also thank Professor Henry Po (CSULB) and
Ms. Jacaqueline Corbeil (UCSD) for their comments.
Supporting Information Available: Additional copies of
1H NMR and 13C NMR for new compounds and the X-ray
crystal data of G-1-OH. This material is available free of
Dendron G-3-OTBDPS and General Procedure for
Ester Formation. To a solution of G-2-OH (2.1 mmol) in dry
JO0499773
9084 J. Org. Chem., Vol. 69, No. 26, 2004