Scheme 2.
Synthesis of C-16 substituted compounds (25, 28 and 31)a
aReagents and conditions: (i) substituted amines, molecular sieves, EtOH, Ar, reflux (3 – 7 h); (ii) MeOH, NaBH4, ice cold (2 h), rt (3 h); (iii) MeOH, 10% methanolic-KOH, Ar, rt (2 – 3 h);