Structure and Property Based Design of Pyrazolo[1,5-a]pyrimidine Inhibitors of CK2 Kinase with Activity in Vivo

Abstract

In this letter, we describe the design, synthesis, and structure−activity relationship of 5-anilinopyrazolo [1,5-a]pyrimidine inhibitors of CK2 kinase. Property-based optimization of early leads using the 7-oxetan-3-yl amino group led to a series of matched molecular pairs with lower lipophilicity, decreased affinity for human plasma proteins, and reduced binding to the hERG ion channel. Agents in this study were shown to modulate pAKT S129 , a direct substrate of CK2, in vitro and in vivo, and exhibited tumor growth inhibition when administered orally in a murine DLD-1 xenograft. KEYWORDS: CK2 kinase, pyrazolo[1,5-a]pyrimidine, matched molecular pair, oxetane T he serine/threonine protein kinase CK2, a tetrameric complex containing two catalytic (α or α′) and two regulatory (β) subunits, controls cell growth, proliferation, and evasion of apoptosis by phosphorylation of a range of substrates in critical cellular signaling pathways including PI3K (phosphatidylinositol 3-kinase)/AKT (protein kinase B), NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells) and Wnt (wingless type MMTV integration site family).1−3 Overexpression of the CK2α subunit correlates with tumor aggressiveness and disease severity in certain cancers, while compensatory increases in CK2α′ levels have been observed in response to RNAi treatment in mice.4,5 Several academic and industrial research groups have been actively engaged in developing small molecule inhibitors of CK2 to provide further pharmacological validation of the compelling in vitro and in vivo data amassed to date. 6 The recent discovery of CX-4945, a selective, orally available inhibitor of CK2 by researchers from Cylene, represents an important first step in evaluating the clinical potential of this novel target in man. 7 We have recently described the design of a series of conformationally constrained inhibitors of CK2 containing the pyrazolo[1,5-a]pyrimidine nucleus.8 Members of this series of compounds exhibited potent inhibition of the enzyme, possessed a high degree of kinase selectivity, and depleted cellular levels of pAKT S129 , a direct substrate of CK2 believed to hyperactivate the AKT pathway.9 Although our attempts to enhance both cellular potency and physical properties in this series were unsuccessful, these studies resulted in an understanding of the structure−property relationships within the scaffold and provided additional insights into ligand−receptor binding. In particular, we found that N-methylation of the acetamide of 1a, to give ring-constrained analogue 1b, preserved enzymatic and cellular activity. In subsequent designs, we proposed to release the constraint in 1b and introduce a new conformational constraint, exemplified by indoline 2, that would enforce the crystallographically observed cisoid conformation of the acetamide in 1 (Figure 1). Compound 2 is a potent inhibitor

Structurally Divergent Lithium Catalyzed Friedel–Crafts Reactions on Oxetan‐3‐ols: Synthesis of 3,3‐Diaryloxetanes and 2,3‐Dihydrobenzofurans

“…Alternative 3-aryl-oxetan-3-ol substrates were prepared (5-10), each with a para-donating aromatic groups (see the Supporting Information). Using either catecholo r2 -methylphenol gave the desired oxetane products in each case (11)(12)(13)(14)i n3 3-77 %y ields. Importantly,h eterocyclesw ere also suitable as the preinstalled aromatic group.2 -Methylfuran was capable of stabilizing the carbocationic intermediate affording oxetane 15 in 58 %y ield, providing another functionalizable handle.…”

“…[11,12] In drug discovery settings, the incorporation of the polar,l ow molecular weighto xetane moiety has often afforded compounds with enhanced properties such as improved metabolic stability, solubility and lipophilicity. [13] As part of our interest in the synthesis of novel oxetane derivatives, [14] we were intrigued by possible approaches to 3,3-diaryloxetanes, designedt op rovide isosteres for diarylketonea nd diarylmethanes tructures with improvedp roperties ford rug discovery.A tt he outset of this work, there were no reported examples of disubstituted 3,3-diaryloxetanesi nt he literature. [15,16] Indeed,i nternal efforts within Pfizer corroborated this observation, with this motif being recognized as difficult to access.…”

Oxetanes: Recent Advances in Synthesis, Reactivity, and Medicinal Chemistry

“…Dowling et al 81 at AstraZeneca compared 3-aminooxetane motifs with other small rings through a series of matched pairs ( Figure 9). It was found that introduction of oxetane lowered logD by ∼0.8 unit in comparison to aminocyclopropane and aminocyclobutane derivatives.…”

“…Incorporation of an oxetane resulted in the greatest improvement in metabolic stability and lipophilicity. Overall, 2,4,4- Dowling et al 81 at AstraZeneca described a series of 5anilinopyrazolo[1,5-a]pyrimidine inhibitors of CK2 kinase (Figure 9, section 2). An N-oxetanyl group was used in place of a N-cyclopropyl group to reduce lipophilicity without the introduction of a basic group.…”

SGC-CK2-1: The First Selective Chemical Probe for the Pleiotropic Kinase CK2

“…They further evaluate this series for both mechanistic and phenotypic endpoints, including pAKT levels and antiproliferative activity. [13][14][15][16] While the compounds are potent, even one of their best compounds (17) also has offtargets (HIPK1-4, DAPK1-3, DYRK2, and BMPR1B) that may confound interpretation of biological results. 15 Due to its narrow kinome profile as well as potency, we started our CK2 probe project utilizing this promising scaffold.…”