Boc-gly-gly-gly-OH → Glycylglycylglycine

t-Boc-GlyGlyGly (1.359 g, 4.7 mmol) was dissolved in 350 mL of anhydrous methylene chloride at room temperature and to this solution were added DIPC (0.75 mL, 4.7 mmol), DMAP (382 mg, 3.13 mmol) and camptothecin (0.55 g, 1.57 mmol) at 0° C. The reaction mixture was allowed to warm to room temperature and left for 16 h. The solution was washed with 0.1 N HCl, dried and evaporated under reduced pressure to yield a white solid, which was recrystallized from methanol to give camptothecin-20-ester of t-Boc-GlyGlyGly: 1H NMR(DMSO-d6) δ 8.40 (s), 8.25 (d), 7.91 (d), 7.78 (m), 7.65 (t), 7.26 (s), 7.05 (br, s), 5.65 (d), 5.40 (d), 5.25 (s), 5.10 (br, s), 3.75-4.42 (m), 2.15-2.35 (m), 1.45 (s), 0.95 (t) Camptothecin-20-ester of t-Boc-GlyGlyGly (1.5 g, 1.06 mmol) was dissolved in a mixture of methylene chloride (10 mL) and TFA (10 mL) and stirred at room temperature for 1 h. Solvent was removed under vacuum and the residue was re-dissolved in methylene chloride. The solution was poured into ether to give instant precipitate (yellow). The precipitate was filtered and washed with cold ether to give 1.31 g of 12. 1H NMR (DMSO-d6) δ 8.79 (s), 7.75-8.61 (m), 7.10 (s), 5.55 (s), 3.90-4.37 (m), 3.86 (s), 3.54 (s), 2.11-2.23 (m), 0.95 (t). ESI/MS (m/z) expected 519; Found 520 (M+H).