Doxorubicin free base

Palmitic acid hydrazide was reacted with the ketone of doxorubicin, to produce the ph-sensitive hydrazone bond containing palmityl-doxorubicin (pDox), as synthesized previously (Fig. S1A)^{22 (link),26} . Briefly, 150 mg of doxorubicin free base (MedKoo Biosciences, Inc, NC, USA) and 82 mg of Palmitic acid hydrazide (1.1 eq) were added to 300 mL of MeOH:DCM solution (1:1) containing 15 uL of trifluoroacetic acid. The reaction proceeded for 24 hours and reaction progress monitored by thin layer chromatography (TLC) using MeOH:DCM (1:3). After the reaction was complete, the solvent was removed by rotary evaporation, and the crude was dissolved in a small volume of MeOH:DCM (1:20). The dissolved crude was purified by silica column chromatography using DCM, and eluting with increasing concentrations of MeOH until the product, pDox, was eluted. Fractions containing pDox were collected, solvent removed by rotary evaporation, and placed in a vacuum dry oven to yield a red oil (yield = 65%). The ¹H NMR spectrum of pDox exhibited chemical shifts of δ 10.01 (1H, s), 8.03 (1H, s), 7.78 (1H, s), 5.53–5.52(2H, d), 4.68 (2H, d), 3.91–4.09 (3H, m), 3.08–3.46 (6H, m), 2.03–2.60 (7H, m), 1.67–1.98 (8H, m), 1.02–1.42 (29H, m),0.85–0.88 (6H, m) ppm. (Fig. S1B) The molecular ion peak ([M + H]+) of pDox was 796.63. (Fig. S1C)