(A) Structure of 106, highlighting the cap group (purple),
left amide, and linker region. Brain penetration can be improved by elimination
of the left amide, and replacement with an ether, olefin, or ketone. Metabolic
stability can be improved by introducing a non-saturated linkage adjacent to the
right amide, which prevents formation of a benzimidazole. Cu(I)-catalyzed click
chemistry was used to generate compound click-1, where a triazole is generated
in the linker region of the histone deacetylase inhibitor [81]. (B) Efficacy of click-1 in neuronal cells
derived from FRDA iPSCs, as measured by qRT-PCR, compared to HDACi
109.