Alkyne Two-Phase Strategy: Rapid Generation of TK-285-Derived PROTACs as BRD4 Degraders

This study introduces
a divergent synthetic strategy in linkerology
using preassembled linkers to generate structural diversity. The approach
was validated by developing bromodomain-containing protein 4 (BRD4)–targeting
proteolysis-targeting chimeras (PROTACs) based on an “alkyne
two-phase strategy,” employing the BRD4 inhibitor TK-285 as the binding ligand. In the initial screening phase, alkyne-modified TK-285 derivatives were subjected to click chemistry to optimize
linker length and the modification site, leading to the identification
of TKP-5 as a potent degrader. TKP-5 exhibited
stronger thymic stromal lymphopoietinmore suppressive activity
than TK-285 and markedly suppressed IL-33 mRNA expression in a tape-stripping-induced skin injury model.
In the subsequent optimization phase, late-stage diversification using
1,3-butadiyne-typed PROTAC intermediates revealed the critical contribution
of the triazole moiety, supported by in silico analysis suggesting
interaction with Trp81 of BRD4. The strategy is expected to be broadly
applicable to modular functional molecules accessible via click chemistry.