Arylation goes platinum: The synthesis of the ABCD ring fragments of the kibdelones has been achieved through a novel PtIV‐catalyzed arylation of a quinone monoketal followed by photocyclization (see scheme). Biological evaluation in the NCI 60‐cell screen revealed that the kibdelone ABCD ring analogues were about 2000 times less active than kibdelones B and C, suggesting that the tetrahydroxanthone structure of the kibdelones is crucial for cytotoxicity.
Phenotypic cell-based screening is a powerful approach to small-molecule discovery, but a major challenge of this strategy lies in determining the intracellular target and mechanism of action (MoA) for validated hits. Here, we show that the small-molecule BRD0476, a novel suppressor of pancreatic β-cell apoptosis, inhibits interferon-gamma (IFN-γ)-induced Janus kinase 2 (JAK2) and signal transducer and activation of transcription 1 (STAT1) signaling to promote β-cell survival. However, unlike common JAK-STAT pathway inhibitors, BRD0476 inhibits JAK-STAT signaling without suppressing the kinase activity of any JAK. Rather, we identified the deubiquitinase ubiquitin-specific peptidase 9X (USP9X) as an intracellular target, using a quantitative proteomic analysis in rat β cells. RNAi-mediated and CRISPR/Cas9 knockdown mimicked the effects of BRD0476, and reverse chemical genetics using a known inhibitor of USP9X blocked JAK-STAT signaling without suppressing JAK activity. Site-directed mutagenesis of a putative ubiquitination site on JAK2 mitigated BRD0476 activity, suggesting a competition between phosphorylation and ubiquitination to explain small-molecule MoA. These results demonstrate that phenotypic screening, followed by comprehensive MoA efforts, can provide novel mechanistic insights into ostensibly well-understood cell signaling pathways. Furthermore, these results uncover USP9X as a potential target for regulating JAK2 activity in cellular inflammation.
We previously reported the discovery of BRD0476 (1), a small molecule generated by diversity-oriented synthesis that suppresses cytokine-induced β-cell apoptosis. Herein, we report the synthesis and biological evaluation of 1 and analogs with improved aqueous solubility. By replacing naphthyl with quinoline moieties, we prepared active analogs with up to a 1400-fold increase in solubility from 1. In addition, we demonstrated that compound 1 and analogs inhibit STAT1 signal transduction induced by IFN-γ.
Turn up the heat: An asymmetric total synthesis of the epoxykinamycin FL-120B’ is reported. The synthesis establishes a route to epoxide-containing diazobenzofluorenes which could potentially serve as monomers to the dimeric lomaiviticins. Key steps include Sharpless asymmetric epoxidation, Stille coupling, and intramolecular Friedel-Crafts acylation of atropisomeric carboxylic acids at elevated temperatures to construct the FL-120B’ core structure.
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