Solid-Phase Synthesis of Hydroxamic Acids and Identification of HDAC Inhibitors Using a Chemi-luminescence-based Assay.

We herein present broadly useful, readily available and non-integral hydroxylamine linkers for the routine solid-phase synthesis of hydroxamic acids. The Fmoc-protected linkers are readily made on multi-gram scale from simple starting materials and conveniently attached to solid support through standard amide bond forming reactions. The developed protocols enable the efficient synthesis and release of a wide range of hydroxamic acids from various resins, relying on high control and flexibility with respect to reagents and synthetic processes. The linkers show broad applicability to a range of reactions commonly employed in the solid-phase organic synthesis of molecular libraries, such as amination, acylation, sulfonylation, Cu-catalyzed click reactions, and Wittig reactions. The flexibility for the synthetic process was utilized to generate a proof-of-concept collection of 72 thiophene-based hydroxamic acids. The inhibitory effects of the compounds were examined for seven HDAC enzyme subtypes using a chemiluminescence-based assay, revealing several highly potent, and even subtype-selective, HDAC inhibitors, including single-digit nM inhibitors of HDAC6.