Scheme 1.
Synthesis of betulinic acid (BA) from betulin (BE) using protecting groups [38]. Reagents and conditions: (i) DHP/CH2C12/PPTS (95%); (ii) Ac2O/pyridine (87%); (iii) EtOH/PPTS (95%); (iv) CrO3/H2SO4/acetone (80%); (v) K2CO3/MeOH/H2O (88%).
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