Cancers 2019, 11, 957
11 of 18
4.2.2. Synthesis of 4-(((2-(2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)ethoxy)ethoxy)diisopropylsilyl)-oxy)
benzaldehyde (3)
Compound 2 (0.5 g, 2.7 mmol) and triethylamine (0.55 g, 5.4 mmol) were dissolved in
dichloromethane (20 mL) and the mixture was cooled to 0 ◦C. A solution of dichlorodiisopropylsilane
(0.6 g, 2.7 mmol) in DCM (10 mL) was slowly added dropwise. After 40 min, p-hydroxybenzaldehyde
(0.33 g, 2.7 mmol) in tetrahydrofuran (5 mL) was slowly added dropwise for an additional 1 h of
reaction. After completion of the reaction, the solvent was concentrated to give a crude material, which
was purified by column chromatography to obtain compound 3 as a white solid (0.86 g, 76% yield).
1H-NMR (400 MHz, CDCl3):
3.92 (t, J = 5.1 Hz, 2H), 3.72 (t, J = 5.1 Hz, 2H), 3.64 (t, J = 5.3 Hz, 2H), 3.58 (t, J = 5.3 Hz, 2H), 1.16 (m,
δ 9.90 (s, 1H), 7.80 (dt, J = 8.4 Hz, 2H), 7.08 (dt, J = 8.4 Hz, 2H), 6.69 (s, 2H),
2H), 1.05 (m, 12H). 13C-NMR (100 MHz, CDCl3):
δ 191.10, 170.73, 161.05, 134.23, 132.07, 130.58, 120.26,
71.84, 67.98, 62.99, 37.31, 17.20, 12.39. HRMS (ESI) m/z (M + H)+ calculated for C21H30NO6Si 420.1842;
found 420.1838. HRMS (ESI) m/z (M + Na)+ calculated for C21H29NNaO6Si 442.1662; found 442.1655.
4.2.3. Synthesis of 1-(2-(2-(((4-(hydroxymethyl)phenoxy)diisopropylsilyl)oxy)ethoxy)ethyl)-1H-
pyrrole-2,5-dione (4)
Compound 3 (0.5 g, 1.19 mmol) was dissolved in dry THF (15 mL) and the mixture was cooled to
-5 ◦C after dissolution. Sodium borohydride (18 mg, 0.48 mmol) was added to the reaction mixture
and the mixture was reacted for 2 h and then filtered to remove the insoluble salt; the filtrate was
concentrated under reduced pressure and evaporated to dryness to give a crude product, which
was purified by column chromatography to obtain compound 4 as a colorless oil (0.1 g, 23% yield).
1H-NMR (400 MHz, CDCl3):
δ 7.25 (t, 2H), 6.93 (m, 2H), 6.67 (s, 2H), 4.61 (s, 2H), 3.90 (t, J = 5.2 Hz,
2H), 3.69 (t, J = 5.0 Hz, 2H), 3.61 (t, J = 5.3 Hz, 2H), 3.56 (t, J = 5.2 Hz, 2H), 1.73 (br, 1H), 1.13 (m, 2H),
1.05 (m, 12H). ESI m/z (M + Na)+ calculated for C21H31NNaO6Si 444.5; found 444.4.
4.2.4. Synthesis of 4-(((2-(2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)ethoxy)ethoxy)diisopropylsilyl)-oxy)
benzyl(4-nitrophenyl) carbonate (5)
Compound 4 (253 mg, 0.6 mmol) was dissolved in dry DMF (15 mL) and bis(p-nitrophenyl)
carbonate (360 mg, 1.2 mmol) and DIPEA (104 mg, 0.9 mmol) were added; the reaction was stirred at
room temperature for 12 h. After the completion of the reaction, the solvent was concentrated under
reduced pressure to remove the solvent. The obtained residue was subjected to diethyl ether dispersion
and then filtered to obtain crude product, which was further purified by column chromatography to
1
obtain compound 5 as a white solid powder (253 mg, 72% yield). H-NMR (400 MHz, CDCl3):
δ 8.28
(dt, J = 9.0 Hz, 2H), 7.38 (dt, J = 9.2 Hz, 2H), 7.33 (dt, J = 8.4 Hz, 2H), 6.98 (dt, J = 8.7 Hz, 2H), 6.68 (s,
2H), 5.23 (s, 2H), 3.91 (t, J = 5.2 Hz, 2H), 3.72 (t, J = 5.6 Hz, 2H), 3.65 (t, J = 5.6 Hz, 2H), 3.58 (t, J = 5.2
Hz, 2H), 1.14 (m, 2H), 1.06 (dd, 12H). ESI m/z (M + NH4)+ calculated for C28H38N3O10Si 604.3; found
604.6. ESI m/z (M + Na)+ calculated for C28H34N2NaO10Si 609.2; found 609.5.
4.2.5. Synthesis of the Linker-MMAE Conjugate (Compound 6)
Compound 5 (35.2 mg, 0.06 mmol) was dissolved in dry DMF (3 mL), then HOBt (8.28 mg, 0.06
mmol), MMAE (40 mg, 0.06 mmol), and DIPEA (10.68 µL) were added; the reaction was stirred at
room temperature for 18 h. After the reaction, the solvent was concentrated under reduced pressure to
remove the solvent. The obtained residue was further purified by column chromatography to afford
1
compound 6 as a white solid powder (43.4 mg, 62% yield). H-NMR (400 MHz, CDCl3):
δ 7.38-7.31 (m,
6H), 7.25-7.20 (t, J = 8.12 Hz, 2H), 7.13 (d, J = 8.12 Hz, 0.5H), 7.02 (d, J = 9.28 Hz, 0.5H), 6.90 (d, J = 8.44
Hz, 2H), 6.68 (s, 2H), 6.55 (m, 1H), 5.15-5.03 (m, 2H), 4.95 (d, J = 2.8 Hz, 1H), 4.69 (m, 2H), 4.28-4.05 (m,
5H), 3.91 (t, J = 5.05 Hz, 2H), 3.72 (t, J = 5.50 Hz, 2H), 3.64 (t, J = 5.50 Hz, 2H), 3.57 (t, J = 5.05 Hz, 2H),
3.52-3.50 (m, 2H), 3.40 (m, 4H), 3.30 (s, 3H), 3.11 (m, 1H), 3.01 (m, 3H), 2.87 (m, 3H), 2.49-2.32 (m, 3H),
2.21 (m, 1H), 2.04 (m, 3H), 1.85 (m, 2H), 1.33-1.24 (m, 5H), 1.04 (m, 19H), 0.98-0.77 (m, 26H). 13C-NMR
(100 MHz, CDCl3):
δ 174.78, 170.77, 170.54, 169.98, 169.70, 157.58, 155.18, 141.21, 134.21, 130.07, 129.55,