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The acetylome is important for maintaining the homeostasis of cells. Abnormal changes can result in the pathogenesis of immunological or neurological diseases, and degeneration can promote the manifestation of cancer. In particular, pharmacological intervention in the acetylome with pan‐histone deacetylase (HDAC) inhibitors is clinically validated. However, these drugs exhibit an undesirable risk‐benefit profile due to severe side effects. Selective HDAC inhibitors might promote patient compliance and represent a valuable opportunity in personalised medicine. Therefore, we envisioned the development of HDAC6‐selective inhibitors. During our lead structure identification, we demonstrated that an alkoxyurea‐based connecting unit proves to be beneficial for HDAC6 selectivity and established the synthesis of alkoxyurea‐based hydroxamic acids. Herein, we report highly potent N‐alkoxyurea‐based hydroxamic acids with improved HDAC6 preference compared to nexturastat A. We further validated the biological activity of these oxa analogues of nexturastat A in a broad subset of leukaemia cell lines and demonstrated their superior anti‐proliferative properties compared to nexturastat A., A hydroxylamine connecting unit facilitates HDAC6 preference: The derivatization of nexturastat A with alkoxyurea connecting units is reported. This modification resulted in an increased preference for HDA6 and increased antiproliferative properties in haematological cancer cell lines.

Inhibition of more than one cancer‐related pathway by multi‐target agents is an emerging approach in modern anticancer drug discovery. Here, based on the well‐established synergy between histone deacetylase inhibitors (HDACi) and alkylating agents, we present the discovery of a series of alkylating HDACi using a pharmacophore‐linking strategy. For the parallel synthesis of the target compounds, we developed an efficient solid‐phase‐supported protocol using hydroxamic acids immobilized on resins (HAIRs) as stable and versatile building blocks for the preparation of functionalized HDACi. The most promising compound, 3 n, was significantly more active in apoptosis induction, activation of caspase 3/7, and formation of DNA damage (γ‐H2AX) than the sum of the activities of either active principle alone. Furthermore, to demonstrate the utility of our preloaded resins, the HAIR approach was successfully extended to the synthesis of a proof‐of‐concept proteolysis‐targeting chimera (PROTAC), which efficiently degrades histone deacetylases., Hydroxamic acids immobilized on resins (HAIRs) were developed and utilized for the library synthesis of DNA‐alkylating HDAC inhibitors and a proof‐of‐concept HDAC degrader (PROTAC). A hybrid compound based on the pharmacophores of chlorambucil and panobinostat was identified as the most promising chimeric HDAC inhibitor and demonstrated improved anticancer properties compared to the sum of the activities of either pharmacophore alone.

Histone deacetylase 6 (HDAC6) is an emerging target for the treatment of cancer, neurodegenerative diseases, inflammation, and other diseases. Here, we present the multicomponent synthesis and structure-activity relationship of a series of tetrazole-based HDAC6 inhibitors. We discovered the hit compound NR-160 by investigating the inhibition of recombinant HDAC enzymes and protein acetylation. A cocrystal structure of HDAC6 complexed with NR-160 disclosed that the steric complementarity of the bifurcated capping group of NR-160 to the L1 and L2 loop pockets may be responsible for its HDAC6-selective inhibition. While NR-160 displayed only low cytotoxicity as a single agent against leukemia cell lines, it augmented the apoptosis induction of the proteasome inhibitor bortezomib in combination experiments significantly. Furthermore, a combinatorial high-throughput drug screen revealed significantly enhanced cytotoxicity when NR-160 was used in combination with epirubicin and daunorubicin. The synergistic effect in combination with bortezomib and anthracyclines highlights the potential of NR-160 in combination therapies.

[Image: see text] A chiral, hybrid bioisostere of the CF(3) and Et groups (BITE) was installed in a series of vorinostat (Zolinza) analogues, and their histone deacetylase (HDAC) inhibitory behavior was studied relative to that of their nonfluorinated counterparts. Several of these compounds containing the 1,2-difluoroethylene unit showed in vitro potency greater than that of the clinically approved drug itself against HDAC1. This trend was found to be general with the BITE-modified HDAC inhibitors performing significantly better than the ethyl derivatives. Installed by the direct, catalytic vicinal difluorination of terminal alkenes using an I(I)/I(III) manifold, this underexplored chiral bioisostere shows potential in drug discovery.

Histone deacetylases (HDACs) have been identified as promising epigenetic drug targets for the treatment of neuroblastoma and glioblastoma. In this work, we have rationally designed a novel class of peptoid-based histone deacetylase inhibitors (HDACi). A mini library of β-peptoid-capped HDACi was synthesized using a four-step protocol. All compounds were screened in biochemical assays for their inhibition of HDAC1 and HDAC6 and docking studies were performed to rationalize the observed selectivity profile. The synthesized compounds were further examined for tumor cell-inhibitory activity against a panel of neuroblastoma and glioblastoma cell lines. In particular, non-selective compounds with potent activity against HDAC1 and HDAC6 showed strong antiproliferative effects. The most promising HDACi, compound 6i, displayed submicromolar tumor cell-inhibitory potential (IC(50): 0.21–0.67 μM) against all five cancer cell lines investigated and exceeded the activity of the FDA-approved HDACi vorinostat.

Histone deacetylases (HDACs) have been identified as emerging antiplasmodial drug targets. In this work, we report on the synthesis, structure-activity relationships, metabolic stability and in vivo efficacy of new peptoid-based HDAC inhibitors with dual-stage antiplasmodial activity. A mini library of HDAC inhibitors was synthesized using a one-pot, multi-component protocol or submonomer pathways. The screening of the target compounds for their activity against asexual blood stage parasites, human cell cytotoxicity, liver stage parasites, and selected human HDAC isoforms provided important structure-activity relationship data. The most promising HDAC inhibitor from this series, compound 3n, demonstrated potent activity against drug-sensitive and drug-resistant asexual stage P. falciparum parasites and was selective for the parasite versus human cells (Pf3D7 IC50 0.016 μM; SIHepG2/Pf3D7 573; PfDd2 IC50 0.002 μM; SIHepG2/PfDd2 4580) combined with activity against P. berghei exoerythrocytic liver stages (PbEEF IC50 0.48 μM). While compound 3n displayed high stability in human (Clint 5 μL/min/mg) and mouse (Clint 6 μL/min/mg) liver microsomes, only modest oral in vivo efficacy was observed in P. berghei infected mice. Together these data provide a foundation for future work to improve the properties of these dual-stage inhibitors as drug leads for malaria.

The multicomponent synthesis of a mini-library of histone deacetylase inhibitors with imidazo[1,2- a]pyridine-based cap groups is presented. The biological evaluation led to the discovery of the hit compound MAIP-032 as a selective HDAC6 inhibitor with promising anticancer activity. The X-ray structure of catalytic domain 2 from Danio rerio HDAC6 complexed with MAIP-032 revealed a monodentate zinc-binding mode.

Novel malaria intervention strategies are of great importance due to the development of drug resistance in malaria endemic countries. In this regard, histone deacetylases (HDACs) have emerged as new and promising malaria drug targets. In this work, we present the design, synthesis and biological evaluation of 20 novel HDAC inhibitors with antiplasmodial activity. Based on a previously discovered peptoid-based hit compound, we modified all regions of the peptoid scaffold by utilizing a one-pot multicomponent pathway and submonomer routes to gain a deeper understanding of the structure-activity as well as structure-toxicity relationships. Most compounds displayed potent activity against asexual blood stage P. falciparum parasites with IC(50) values ranging from 0.0052–0.25 µM and promising selectivity over mammalian cells (SI(Pf3D7/HepG2): 170–1483). In addition, several compounds showed encouraging submicromolar activity against P. berghei exo-erythrocytic forms (PbEEF). Our study led to the discovery of the hit compound (N-(2-(benzylamino)-2-oxoethyl)-N-(4-(hydroxycarbamoyl)benzyl)-4-i-propylbenzamide, 2h) as a potent and parasite-specific dual-stage antiplasmodial HDAC inhibitor (IC(50) (Pf3D7) = 0.0052 µM, IC(50) (PbEEF) = 0.016 µM).