Dual N6/C7-Substituted 7-Deazapurine and Tricyclic Ribonucleosides with Affinity for G Protein-Coupled Receptors.

Various purine-based nucleoside analogues have demonstrated unexpected affinity for nonpurinergic G protein-coupled receptors (GPCRs), such as opioid and serotonin receptors. In this work, we synthesized a small library of new 7-deazaadenosine and pyrazolo[3,4-d]pyrimidine riboside analogues, featuring dual C7 and N6 modifications and assessed their affinity for various GPCRs. During the course of the synthesis of 7-ethynyl pyrazolo[3,4-d]pyrimidine ribosides, we observed the formation of an unprecedented tricyclic nucleobase, formed via a 6-endo-dig ring closure. The synthesis of this tricyclic nucleoside was optimized, and the substrate scope for such cyclization was further explored because it might avail further exploration in the nucleoside field. From displacement experiments on a panel of GPCRs and transporters, combining C7 and N6 modifications afforded noncytotoxic nucleosides with micromolar and submicromolar affinity for different GPCRs, such as the 5-hydroxytryptamine (5-HT)2B, κ-opioid (KOR), and σ1/2 receptor. These results corroborate that the novel nucleoside analogues reported here are potentially useful starting points for the further development of modulators of GPCRs and transmembrane proteins.

Targeted AURKA degradation: Towards new therapeutic agents for neuroblastoma.

Aurora kinase A (AURKA) is a well-established target in neuroblastoma (NB) due to both its catalytic functions during mitosis and its kinase-independent functions, including stabilization of the key oncoprotein MYCN. We present a structure-activity relationship (SAR) study of MK-5108-derived PROTACs against AURKA by exploring different linker lengths and exit vectors on the thalidomide moiety. PROTAC SK2188 induces the most potent AURKA degradation (DC50,24h 3.9 nM, Dmax,24h 89%) and shows an excellent binding and degradation selectivity profile. Treatment of NGP neuroblastoma cells with SK2188 induced concomitant MYCN degradation, high replication stress/DNA damage levels and apoptosis. Moreover, SK2188 significantly outperforms the parent inhibitor MK-5108 in a cell proliferation screen and patient-derived organoids. Furthermore, altering the attachment point of the PEG linker to the 5-position of thalidomide allowed us to identify a potent AURKA degrader with a linker as short as 2 PEG units. With this, our SAR-study provides interesting lead structures for further optimization and validation of AURKA degradation as a potential therapeutic strategy in neuroblastoma.

Efficient Divergent Synthesis of New Immunostimulant 4″-Modified α-Galactosylceramide Analogues.

A synthesis strategy for the swift generation of 4″-modified α-galactosylceramide (α-GalCer) analogues is described, establishing a chemical platform to comprehensively investigate the structure-activity relationships (SAR) of this understudied glycolipid part. The strategy relies on a late-stage reductive ring-opening of a p-methoxybenzylidene (PMP) acetal to regioselectively liberate the 4″-OH position. The expediency of this methodology is demonstrated by the synthesis of a small yet diverse set of analogues, which were tested for their ability to stimulate invariant natural killer T-cells (iNKT) in vitro and in vivo. The introduction of a p-chlorobenzyl ether yielded an analogue with promising immunostimulating properties, paving the way for further SAR studies.