Organix, a Symeres company, developed scale up conditions of the synthesis of 25-hydroxy cholesterol 3-monosulfate (sodium salt) from cholesterol.
After the protection of the hydroxy group (acetate) and double bond (debromination), the hydroxy group in position 25 was introduced using oxone and trifluoromethylethylketone. Then the 3-hydroxy group and double bond were deprotected, and the resulting 25-hydroxy cholesterol was selectively converted into the 3-mono sulfate (triethylammonium salt). Finally, a counterion exchange provided the required sodium salt.
The key step of this synthesis was the hydroxylation in position 25. This reaction required very controlled conditions (batch size, addition of the reagents, post-addition reaction time) to the point that other CROs were unable to scale it up beyond our batch size (70 g). A different sequence which involved the construction of the chain in position 17 was utilized for GMP scale up.
