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

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.

Using chemical genetics and ATP analogues to dissect protein kinase function

Protein kinases catalyze the transfer of the gamma-phosphate of ATP to a protein substrate and thereby profoundly alter the properties of the phosphorylated protein. The identification of the substrates of protein kinases has proven to be a very difficult task because of the multitude of structurally related protein kinases present in cells, their apparent redundancy of function, and the lack of absolute specificity of small-molecule inhibitors. Here, we review approaches that utilize chemical genetics to determine the functions and substrates of protein kinases, focusing on the design of ATP analogues and protein kinase binding site mutants.

Anti-malarial activity of N6-modified purine analogues

Plasmodium falciparum causes one of the deadliest forms of malaria and resistance to the currently available drugs makes it imperative to develop new, safe and potent drugs. Parasites such as P. falciparum are unable to synthesise purines de novo and to this end often have multiple purine uptake and salvage systems. With this in mind, we have designed and synthesised libraries of purine analogues as potential anti-malarial agents. Herein, we report three compounds with promising activity against the highly chloroquine-resistant VS1 P. falciparum namely: N(6)-hydroxyadenine (1c), 2-amino-N(6)-aminoadenosine (2b) and 2-amino-N(6)-amino-N(6)-methyladenosine (4b).

Molecular recognition of adeninium cations on anionic metal-oxalato frameworks: an experimental and theoretical analysis

Reactions of adenine with water-soluble oxalato complexes at acidic pH give the compounds (1H,9H-ade)2[Cu(ox)2(H2O)] (1) [H2ade=adeninium cation (1+), ox=oxalato ligand (2-)] and (3H,7H-ade)2[M(ox)2(H2O)2].2H2O [M(II)=Co (2), Zn (3)]. The X-ray single crystal analyses show that the supramolecular architecture of all compounds is built up of anionic sheets of metal-oxalato-water complexes and ribbons of cationic nucleobases among them to afford lamellar inorganic-organic hybrid materials. The molecular recognition process between the organic and the inorganic frameworks determines the isolated tautomeric form of the adeninium cation found in the crystal structures: the canonical 1H,9H for compound 1, and the first solid-state characterized 3H,7H-adeninium tautomer for compounds 2 and 3. Density functional theory calculations have been performed to study the stability of the protonated nucleobase forms and their hydrogen-bonded associations by comparing experimental and theoretical results.

Identification of intracellular targets of small molecular weight chemical compounds using affinity chromatography

Efforts to characterize small molecular weight chemical inhibitors of pharmacological interest tend to identify molecules with high efficiency and selectivity, to meet the two criteria required for the clinical development of a drug: efficacy and harmlessness. Drug candidates are expected to inhibit efficiently the target they have been optimized against (for example, a particular type of protein kinase). These hits are also designed to not interfere (or as little as possible) with the activity of other cellular enzymes/proteins to reduce undesired side effects. Here we discuss the use of immobilized drugs as affinity chromatography matrices to purify and identify their bona fide intracellular targets. This method not only allows the systematic investigation of the selectivity of pharmacological compounds but also the anticipation of their putative adverse effects.

Solid-phase synthesis of 7-substituted 3H-imidazo[2,1-i]purines

A method for solid-supported synthesis of N,N-disubstituted (3H-imidazo[2,1-i]purin-7-yl)methyl amines has been developed. The key features of this library synthesis are: (i) immobilization of commercially available N6-benzoyl-5'-O-(4,4'-dimethoxytrityl)-2'-deoxyadenosine 3'-(2-cyanoethyl N,N-diisopropylphosphoramidite) by phosphitylation to a hydroxyl-functionalized support, (ii) quantitative conversion of the deprotected adenine base to 3H-imidazo[2,1-i]purine-7-carbaldehyde with bromomalonaldehyde in DMF in the presence of formic acid and 2,6-lutidine, (iii) reductive amination of the formyl group followed by N-alkylation or N-acylation, and (iv) release from the support by acidolytic cleavage of the N-glycosidic bond. Steps (ii) and (iii) have been optimized in some detail by using (adenin-9-yl)acetic acid anchored to a Phe-Wang resin as a model compound.