Following our report that A 3 adenosine receptor (AR) antagonist 1 exhibited a polypharmacological profile as a dual modulator of peroxisome proliferator-activated receptor (PPAR)γ/δ, we discovered a new template, 1′homologated adenosine analogues 4a−4t, as dual PPARγ/δ modulators without AR binding. Removal of binding affinity to A 3 AR was achieved by 1′homologation, and PPARγ/δ dual modulation was derived from the structural similarity between the target nucleosides and PPAR modulator drug, rosiglitazone. All the final nucleosides were devoid of AR-binding affinity and exhibited high binding affinities to PPARγ/δ but lacked PPARα binding. 2-Cl derivatives exhibited dual receptor-binding affinity to PPARγ/δ, which was absent for the corresponding 2-H derivatives. 2-Propynyl substitution prevented PPARδ-binding affinity but preserved PPARγ affinity, indicating that the C2 position defines a pharmacophore for selective PPARγ ligand designs. PPARγ/δ dual modulators functioning as both PPARγ partial agonists and PPARδ antagonists promoted adiponectin production, suggesting their therapeutic potential against hypoadiponectinemia-associated cancer and metabolic diseases.

a b s t r a c tWe have reported on aristeromycin (1) and 6 0 -fluorinated-aristeromycin analogues (2), which are active against RNA viruses such as Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV), Zika virus (ZIKV), and Chikungunya virus (CHIKV). However, these exhibit substantial cytotoxicity. As this cytotoxicity may be attributed to 5 0 -phosphorylation, we designed and synthesized one-carbon homologated 6 0 -fluorinated-aristeromycin analogues. This modification prevents 5 0 -phosphorlyation by cellular kinases, whereas the inhibitory activity towards S-adenosyl-L-homocysteine (SAH) hydrolase will be retained. The enantiomerically pure 6 0 -fluorinated-5 0 -homoaristeromycin analogues 3a-e were synthesized via the electrophilic fluorination of the silyl enol ether with Selectfluor, using a base-build up approach as the key steps. All synthesized compounds exhibited potent inhibitory activity towards SAH hydrolase, among which 6 0 -b-fluoroadenosine analogue 3a was the most potent (IC 50 ¼ 0.36 mM). Among the compounds tested, 6 0 -b-fluoro-homoaristeromycin 3a showed potent antiviral activity (EC 50 ¼ 0.12 mM) against the CHIKV, without noticeable cytotoxicity up to 250 mM. Only 3a displayed anti-CHIKV activity, whereas both3a and 3b inhibited SAH hydrolase with similar IC 50 values (0.36 and 0.37 mM, respectively), which suggested that 3a's antiviral activity did not merely depend on the inhibition of SAH hydrolase. This is further supported by the fact that the antiviral effect was specific for CHIKV and some other alphaviruses and none of the homologated analogues inhibited other RNA viruses, such as SARS-CoV, MERS-CoV, and ZIKV. The potent inhibition and high selectivity index make 6 0 -b-fluoro-homoaristeromycin (3a) a promising new template for the development of antivirals against CHIKV, a serious re-emerging pathogen that has infected millions of people over the past 15 years.

Modulators of the G protein-coupled A 2A adenosine receptor (A 2A AR) have been considered promising agents to treat Parkinson’s disease, inflammation, cancer, and central nervous system disorders. Herein, we demonstrate that a thiophene modification at the C8 position in the common adenine scaffold converted an A 2A AR agonist into an antagonist. We synthesized and characterized a novel A 2A AR antagonist, 2 (LJ-4517), with K i = 18.3 nM. X-ray crystallographic structures of 2 in complex with two thermostabilized A 2A AR constructs were solved at 2.05 and 2.80 Å resolutions. In contrast to A 2A AR agonists, which simultaneously interact with both Ser277 7.42 and His278 7.43 , 2 only transiently contacts His278 7.43 , which can be direct or water-mediated. The n -hexynyl group of 2 extends into an A 2A AR exosite. Structural analysis revealed that the introduced thiophene modification restricted receptor conformational rearrangements required for subsequent activation. This approach can expand the repertoire of adenosine receptor antagonists that can be designed based on available agonist scaffolds.

An alternative and efficient approach to neplanocin A analogs 1b and 1d has been developed using electrophilic fluorination and Pd-catalyzed dehydrosilylation.

To determine which sugar conformation is favorable in binding to peroxisome proliferator-activated receptors, the conformationally locked south (S) and north (N) analogues were asymmetrically synthesized using a bicyclo[3.1.0]hexane template. The (S)-conformer was synthesized by employing "reagentcontrolled" Charette asymmetric cyclopropanation in a 100% stereoselective manner, whereas the (N)-conformer was stereoselectively synthesized by using "substrate-controlled" hydroxyldirected Simmons−Smith cyclopropanation as a key step.