Yeast as a model system to screen purine derivatives against human CDK1 and CDK2 kinases.

Cyclin-dependent kinases (Cdk) play crucial roles in cell cycle progression. Aberrant activation of Cdk1 has been observed in a number of primary tumors and Cdk2 is deregulated in various malignancies. The therapeutic value of targeting Cdk1 and Cdk2 has been explored in a number of experimental systems. In the present study, taking advantage of the fact that deletion of the yeast CDC28 gene is functionally complemented by human CDK1 or CDK2, we set up an in vivo screen system to evaluate the inhibitory potency of purine derivatives against these two human Cdks. We constructed three isogenic strains highly sensitive to small molecules and harboring genes CDK1, CDK2 or CDC28, under the control of the CDC28 promoter. In a proof of principle assay, we determined the inhibitory effect of 82 purine derivatives on the growth rate of these strains. Thirty-three of them were revealed to be able to inhibit the Cdk1- or Cdk2-harboring strains but not the Cdc28-harboring strain, suggesting a specific inhibitory effect on human Cdks. Our data demonstrate that the yeast-based assay is an efficient system to identify potential specific inhibitors that should be preferentially selected for further investigation in cultured human cell lines.

New aminopyrimidine derivatives as inhibitors of the TAM family.

In this study, we describe the synthesis of new pyrimidine analogs of BMS-777607, a potent and selective inhibitor of Met kinase. Inhibition of Met and Axl remained high whereas inhibition of Tyro3 and Mer decreased to some extend. The preferential moderate inhibition of the non-phosphorylated form of Abl1 of some derivatives suggests that they behave as type II inhibitors. This hypothesis was confirmed by docking studies into the structure of Met (3F82) and in a Tyro3 model where key interactions with the hinge region, the DFG-out motif and the allosteric pocket explain this inhibition.

Inhibitors of the TAM subfamily of tyrosine kinases: synthesis and biological evaluation.

The TAM subfamily of Receptor Tyrosine Kinases (RTKs) contains three human proteins of therapeutical interest, Axl, Mer, and Tyro3. Our goal was to design a type II inhibitor specific for this family, i.e. able to interact with the allosteric pocket and with the hinge region of the kinase. We report the synthesis of several series of purine analogues of BMS-777607. The structural diversity of the designed inhibitors was expected to modify the interactions formed in the binding site and consequently to modulate their selectivity profiles. The most potent inhibitor 6g exhibits Kds of 39, 42, 65 and 200 nM against Axl, Mer, Met and Tyro3 respectively. Analysis of the affinity of 6g for active and inactive forms of Abl1, an RTK protein that does not belong to the TAM subfamily, together with the binding modes of 6g predicted by docking studies, indicates that 6g displays some selectivity for the TAM family and may act as a type II inhibitor.

Microwave-assisted Pd/Cu-catalyzed C-8 direct alkenylation of purines and related azoles: an alternative access to 6,8,9-trisubstituted purines.

An efficient microwave-assisted palladium/copper comediated C-8 direct alkenylation of purines with styryl bromides has been developed. The method is regioselective, functional group tolerant, rapid, and compatible with other related azoles. Combined with subsequent nucleophilic substitution, it provides an easy access to new 6,8,9-trisubstituted purines.

Novel 8-arylated purines as inhibitors of glycogen synthase kinase.

A series of 8-arylated purine derivatives bearing either an aniline or an alkyl amide at position 6 were found to inhibit glycogen synthase kinase-3, with good selectivity over ten kinases. Molecular modeling studies indicated that the most active compounds (8a and 8e), adopt a planar conformation, close to the shape of AMPPNP in the crystal structure of GSK-3. These compounds are stabilized by hydrophobic contacts between the 8-aromatic group and the protein adenine pocket and by electrostatic contacts.

Targeting the cell cycle and the PI3K pathway: a possible universal strategy to reactivate innate tumor suppressor programmes in cancer cells.

Corruption of the Rb and p53 pathways occurs in virtually all human cancers. This could be because it lends oncogene-bearing cells a surfeit of Cdk activity and growth, enabling them to elaborate strategies to evade tumor-suppressive mechanisms and divide inappropriately. Targeting both Cdk activities and the PI3K pathway might be therefore a potentially universal means to palliate their deficiency in cancer cells. We showed that the killing efficacy of roscovitine and 16 other purines and potentiation of roscovitine-induced apoptosis by the PI3K inhibitor, LY294002, decreased with increasing corruption of the Rb and p53 pathways. Further, we showed that purines differing by a single substitution, which exerted little lethal effect on distant cell types in rich medium, could display widely-differing cytotoxicity profiles toward the same cell types in poor medium. Thus, closely-related compounds targeting similar Cdks may interact with different targets that could compete for their interaction with therapeutically-relevant Cdk targets. In the perspective of clinical development in association with the PI3K pathway inhibitors, it might thus be advisable to select tumor cell type-specific Cdk inhibitors on the basis of their toxicity in cell-culture-based assays performed at a limiting serum concentration sufficient to suppress their interaction with undesirable crossreacting targets whose range and concentration would depend on the cell genotype.

High-yielding two-step synthesis of 6,8-disubstituted N-9-unprotected purines.

We report herein a convenient method for the synthesis of libraries of 6,8-disubstituted-9-H-purines in two steps, including cyclization of 6-chloro-4,5-diaminopyrimidine with various arylcarboxylic acids or chlorides, followed by S(N)Ar with amines and alkoxides or Pd-catalyzed amidations at C-6. These reactions were highly efficient and allowed the synthesis of a 32-member library of 6,8-disubstituted purines.

Synthesis of 6,7,8-trisubstituted purines via a copper-catalyzed amidation reaction.

We report herein an efficient method for the synthesis of 6,7,8-trisubstituted purines via a copper-catalyzed amidation reaction from easily accessible starting materials. Furthermore, the resulting 6-benzylsulfanyl-substituted purine derivatives may be readily oxidized for substitution by nucleophiles to give access to 6,7,8-trisubstituted purines for biological screening purposes.

Selective amidation of 2,6-dihalogenopurines: application to the synthesis of new 2,6,9-trisubstituted purines.

We report herein the palladium(0)/Xantphos-catalyzed cross-coupling of various amides with 2,6-dihalogenopurines, with substituent-dependent regioselectivity. Furthermore, subjecting the same 2,6-dihalogenopurines to SNAr conditions with amide/NaH in DMF leads to inverted regioselectivity albeit in lower yield. These methodologies allow the two-step synthesis of new 2,6,9-trisubstituted purines from readily available 2,6-dihalogenopurines.

A Pd(0) based cross-coupling approach to the synthesis of 2-amidopurines and their evaluation as CDK inhibitors.

Two new series of 2-amido- and 2-aminocarbonylpurines have been synthesized using a Pd catalyst cross-coupling reaction either with amides or amines in the presence of CO. Moderate in vitro inhibitory activity against CDK1 and CDK5 was observed with IC(50) of 0.9muM for the most active compound (18c).

Suzuki-type Pd(0) coupling reactions in the synthesis of 2-arylpurines as Cdk inhibitors.

A new series of 2-aryl-substituted purine derivatives has been synthesized by Suzuki Pd(0) coupling reactions. Moderate in vitro inhibitory activity against Cdk1 and Cdk5 was observed. These compounds are inactive against GSK3.

The purines: potent and versatile small molecule inhibitors and modulators of key biological targets.

The goal of this review is to highlight the wide range of biological activities displayed by purines, with particular emphasis on new purine-based agents which find potential application as chemical-biology tools and/or therapeutic agents. The expanding interest in the biological properties of polyfunctionalized purine derivatives issues, in large part, from the development of rapid high-throughput screening essays for new protein targets, and the corresponding development of efficient synthetic methodology adapted to the construction of highly diverse purine libraries. Purine-based compounds have found new applications as inducers of interferon and lineage-committed cell dedifferentiation, agonists and antagonists of adenosine receptors, ligands of corticotropin-releasing hormone receptors, and as inhibitors of HSP90, Src kinase, p38alpha MAP kinase, sulfotransferases, phosphodiesterases, and Cdks. The scope of application of purines in biology is most certainly far from being exhausted. Testing purine derivatives against the multitude of biological targets for which small molecule probes have not yet been found should thus be a natural reflex.