Azulene-based compounds for targeting orexin receptors

Abstract

A library of 70 000 synthetically accessible azulene-based compounds was virtually screened at the OX receptor. Based on the results, a series of azulene derivatives was synthesized and the binding to and activation of both orexin receptor subtypes were assessed. Two most promising binders were determined to have inhibition constants in the 3-9 μM range and two other compounds showed weak OX receptor agonism. Furthermore, three compounds exhibited a concentration-dependent potentiation of the response to orexin-A at the OX but not the OX receptors. Altogether this data opens new approaches for further development of antagonists, agonists, and potentiators of orexin response based on the azulene scaffold.

Structure–Activity Relationships of 1‐Benzoylazulenes at the OX1 and OX2 Orexin Receptors

“…Notably,t he assay cannot discriminate between weak agonists and ago-PAMs (compounds that have both agonist and positive allosteric modulator activities), as the increase of intracellularC a 2 + levels, which is ah allmark of the orexin receptora ctivation, directly potentiates the downstream signaling machinery and thus gives ap ositive signal. [12,21,[27][28][29][30] Compounds 5, 6,a nd 27 potentiated the response to orexin-A on OX 1 receptors by 1.4-, 1.6-, and 1.3-fold, respectively,a t1 0mm ( Figure S1 and Ta ble S1,S upporting Information). Additionally, compounds 10 (OX 1 ), 16 (both receptor subtypes), 19 (OX 2 ), and 24 (OX 1 )s howed aw eak potentiatinge ffect,b ut comparison with their effect on the control ATPr esponse suggested that these are not mediated specifically by orexin receptors (Table S1,S upportingI nformation).…”

“…The synthesis of the starting materials 4 and 20 was described previously. [12] Ketone derivatives of 4 were obtainedb ya pplying modified Vilsmeier-Haack reactionc onditions (Scheme 1). As the reactions gave only low to moderate yields, the unreacteds tartingm aterial was recovereda nd used in the synthesis of other ketone derivatives.…”

“…Additionally,w efurther studied the previously reported compound 37 (compound 19 in ref. [12]). In previousw ork, 37 demonstrated binding to orexin receptors (with functional K i values of 7.5 and 4.9 mm on the OX 1 and OX 2 receptors, respectively [12] ), but no Ca 2 + response in the agonistactivity screening we conducted at 10 mm.H ere we show that 37 acts as aw eak orexin receptor agonist at higher concentrations.…”

“…In contrast, the responses to compound 26 droppeda t3 2mm ( Figure 2D), which may be due to solubility issues at this high concentration. At 32 mm, 37 did not form colloidal aggregates, [12] cause af luorescenceo fi ts own at the wavelengths used, or show morphological changes indicating rapid cell death (as examined by visual inspection after running the assay similarlyt or ef. [26];d ata not shown).…”

“…Previously,w es uccessfully explored azulene-based compounds for targeting orexin receptors. [12] Following an in-silicoguided selection, we synthesized 33 compounds, among which we identified promising azulenes that act as orexin receptor antagonists with binding affinitiesa tt he low micromo-lar level, as weak orexin receptor agonists (compounds 1 and 2,F igure1), and/or as potentiatorso ft he orexin-A response at OX 1 (but not OX 2 )r eceptors. Azulene is an aromatic bicycle composed of fused five-and seven-membered hydrocarbon rings, and it resembles other ring systems found in drug molecules.…”