[3a,4]-Dihydropyrazolo[1,5a]pyrimidines: Novel, Potent, and Selective Phosphatidylinositol-3-kinase β Inhibitors

Abstract

A series of novel [3a,4]dihydropyrazolo[1,5a]-pyrimidines were identified, which were highly potent and selective inhibitors of PI3Kβ. The template afforded the opportunity to develop novel SAR for both the hinge-binding (R 3 ) and back-pocket (R 4 ) substitutents. While cellular potency was relatively modest due to high protein binding, the series displayed low clearance in rat, mouse, and monkey. KEYWORDS: PI3K-β inhibitor, PTEN-null, phosphatidylinositol-3-kinase, pyrazolopyrimidine, structure−activity relationship T he phosphatidylinositol 3-kinases (PI3Ks) are members of a larger family of lipid kinases that phosphorylate the inositol moiety of membrane-associated phosphatidyl inositols. 1 PI3Ks catalyze the conversion of phosphatidylinositol-4,5-diphosphate (PIP 2 ) to phosphatidylinositol-3,4,5-triphosphate (PIP 3 ), which allows recruitment of proteins containing the PIP 3 -binding pleckstrin homology (PH) domain to the plasma membrane. The PI3K class I family comprises four isoforms (α, β, δ, and γ), with the α and β isoforms most widely expressed. Each is a heterodimer consisting of an isoform-specific p110 catalytic subunit and a regulatory subunit.PI3Ks are an important mediator of receptor tyrosine kinase (RTK) and G-protein-coupled receptor (GPCR) signal transduction and are involved in the regulation of cellular metabolism, survival, and proliferation. 2 Aberrant activation of the PI3K pathway is strongly associated with malignant transformation, through either overexpression of PI3Kα, mutations that lead to constitutive activity of PI3Kα, or loss of function of the tumor suppressor PTEN (phosphatase and tensin homologue), which opposes PI3K function by converting PIP 3 to PIP 2 . 3−9 While the PI3K isoforms share the same substrate specificity, they have distinct biochemical roles and cellular functions. 10 In particular, there is considerable evidence that in PTEN-null tumors, malignant transformation is primarily driven by the PI3Kβ isoform. 11−15 The development of PI3Kβ-selective inhibitors is therefore an attractive target for the treatment of PTEN-null tumors.We have previously disclosed imidazopyrimidones (1) and triazolopyrimidones (2), as shown in Figure 1, which are potent and selective inhibitors of PI3Kβ. 16,17 However, the compounds were not suitable for in vivo studies due to high clearance in rat and mouse. Both 1 and 2 contain an embedded benzylamine moiety, a potential site for metabolism, which might contribute to the high clearance. We therefore designed a pyrazolo-pyrimidine scaffold, in which the benzyl group is attached to a carbon atom rather than a nitrogen, in an attempt to improve clearance.Pyrazolopyrimidines were generally prepared according to previously reported methods 18−20 as shown in Scheme 1. An α-cyanocarbonyl compound I is alkylated 21 with a benzyl bromide II and then condensed with hydrazine to afford the key aminopyrazole intermediate IV. The aminopyrazole is then condensed with a β-carbonyl-containing ester V to afford the 7-hydroxypyrazolopyrimi...

Structural Determinants of Isoform Selectivity in PI3K Inhibitors

“…This smaller binding motif may be important for PI3Kβ/δ selectivity in particular. In a series of dihydropyrazolo inhibitors, the replacement of a hydroxyl group ( 60 ) with the larger carboxyl group ( 61 ) reduces β/δ selectivity from 63x to only 8x (Figure 10) [137]. The clinical candidate, GSK2636771 ( 62 ) has a carboxyl group in the equivalent position.…”

Unconventional Rose Odorants: Serendipitous Discovery and Unique Olfactory Properties of 2,2-Bis(prenyl)-3-oxobutyronitrile and Its Derivatives

“…8 The crude sodium salt of cyanoacetone 8 was obtained in quantitative yield and then bis-prenylated with prenyl bromide (2.2 equiv) in DMF in the presence of Cs 2 CO 3 (1 equiv) as a base. 9 The corresponding target compound 6 was isolated in olfactory purity by flash chromatography in 74% yield.…”

“…As delineated in Scheme 5, the crude cyanoacetone enolate 8 was treated with benzyl bromide (2 equiv) in DMF in the presence of Cs 2 CO 3 (1 equiv) as a base. 9 After purification by flash chromatography, the corresponding target compound 15 was obtained as a colorless solid in 67% yield over two steps. Unfortunately, 15 turned out to be completely odorless, perhaps due to its relatively high molecular weight (C 18 H 17 ON, 263.34 u) compared to 6, though Rosacetol (1, C 10 H 9 O 2 Cl 3 267.54 u) has about the same.…”

“…Sodium 1-cyano-2oxopropan-1-ide (8) was prepared following literature precedence. 9 1 H NMR spectra were recorded on a Bruker AV 400 MHz spectrometer with the solvent resonance as the reference (CDCl 3 δ = 7.26). 13 C NMR spectra were recorded with 1 H-decoupling on a Bruker AV 100 MHz spectrometer with the solvent resonance as the reference (CDCl 3 δ = 77.0).…”

Isoform Selective PI3K Inhibitors for Treating Cancer

“…A series of publications from GSK detailed a number of different scaffolds possessing similar binding motifs (Scheme 5). Representative chemotypes included imidazopyrimidones (i.e., 15, Lin et al [27]), triazolopyrimidinones (i.e., 16, Sanchez et al [51]), pyrazolopyrimidines (i.e., 17, Yu et al [52]), and thiazolopyrimidinones (i.e., 18, Lin et al [53]).…”