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

Desilylative activation of TMSCN in chemoselective Strecker–Ugi type reaction: functional fused imidazoles as building blocks as an entry route to annulated purines

Nucleophilic activation of TMSCN as an isocyanide equivalent by DABCO–THF in the Strecker–Ugi reaction facilitates the synthesis of functional imidazoles which, as building blocks, afford access to C8–N9 annulated purines.

Subtle Mitsunobu couplings under super-heating: the role of high-throughput continuous flow and microwave strategies

Fragile Mitsunobu reaction can efficiently be performed under super-heating.

Exploration of aziridine- and β-lactam-based hybrids as both bioactive substances and synthetic intermediates in medicinal chemistry

The concept of pharmacophore hybridization is attracting an increasing interest from medicinal chemists. Whereas the main motivation for the application of this methodology relates to the pharmacological advantages associated with hybrid molecules, molecular hybridization can also deliver a synthetic advantage through selective chemical modification of the more reactive entity within hybrid systems. Moreover, if both features are combined, new hybrid structures result displaying both a biological and a synthetic benefit, and elaboration of this methodology might culminate in structural diversity and chemical novelty. In this perspective, a new approach based on hybrid structures combining a biologically interesting yet rather chemically reactive nucleus with a privileged heterocyclic scaffold is discussed by means of β-lactam-purine chimeras useful in antiviral research and aziridine-(iso)quinoline hybrids for antimalarial purposes.

Sequential three-component synthesis of 1,4-bis[6,9-dihydro-6-oxo-9-phenyl-1H-purin-2-yl]piperazines

A simple one-pot efficient method for the synthesis of 1,4-bis[6,9-dihydro-6-oxo-9-phenyl-1 H-purin-2-yl]piperazines by a domino three-component process involves an aza-Wittig reaction/heterocyclisation in the presence of sodium ethoxide as catalyst. Ethyl 1-phenyl-5-[(triphenylphosphoranylidene)amino]-1H-imidazole-4-carboxylate reacted with aromatic isocyanate to give carbodiimide intermediates, followed by addition of piperazines to give the corresponding guanidine intermediates. The guanidine intermediates were cyclised in the presence of a catalytic amount of sodium ethoxide to give 1,4-bis(6,9-dihydro-6-oxo-9-phenyl-1 H-purin-2-yl)piperazine derivatives in good yields.

2-Chloro-N-ethyl-9-isopropyl-9H-purin-6-amine

In the title compound, C(10)H(14)ClN(5), the purine ring system is essentially planar, with an r.m.s. deviation from the least-squares plane defined by the nine constituent atoms of 0.0063 (11) Å. In the crystal, mol-ecules are linked by weak N-H⋯N and C-H⋯π inter-actions.

The selective synthesis of metallanucleosides and metallanucleotides: a new tool for the functionalization of nucleic acids

Nucleobases team up: the efficient and selective preparation of purine-derived metallanucleosides, metallanucleotides, and metalladinucleotides having M-C bonds (M=Ir(III), Rh(III)) is reported for the first time. The results presented may be applied to the synthesis of functionalized nucleic acids, or DNA/RNA-modified segments.

Design, synthesis, and antiviral evaluation of purine-β-lactam and purine-aminopropanol hybrids

Purine-β-lactam chimera were prepared as a novel class of hybrid systems through N-alkylation of 6-benzylamino- or 6-benzyloxypurine with (ω-haloalkyl)-β-lactams, followed by reductive ring opening of the β-lactam ring by LiEt(3)BH to provide an entry into the class of purine-aminopropanol hybrids. Both new types of hybrid systems were assessed for their antiviral activity and cytotoxicity, resulting in the identification of eight purine-β-lactam hybrids and two purine-aminopropanol hybrids as promising lead structures.

Effect of the H-bonding on aromaticity of purine tautomers

Four tautomers of purine (1-H, 3-H, 7-H, and 9-H) and their equilibrium H-bonded complexes with F(-) and HF for acidic and basic centers, respectively, were optimized by means of the B3LYP/6-311++G(d,p) level of theory. Purine tautomer stability increases in the following series: 1-H < 3-H < 7-H < 9-H, consistent with increasing aromaticity. Furthermore, the presence of a hydrogen bond with HF does not change this order. For neutral H-bonded complexes, the strongest and the weakest intermolecular interactions occur (-14.12 and -10.49 kcal/mol) for less stable purine tautomers when the proton acceptor is located in the five- and six-membered rings, respectively. For 9-H and 7-H tautomers the order is reversed. The H-bond energy for the imidazole complex with HF amounts to -14.03 kcal/mol; hence, in the latter case, the fusion of imidazole to pyrimidine decreases its basicity. The ionic H-bonds of N(-)···HF type are stronger by ~10 kcal/mol than the neutral N···HF intermolecular interactions. The hydrogen bond N(-)···HF energies in pyrrole and imidazole are -32.28 and -30.03 kcal/mol, respectively, and are substantially stronger than those observed in purine complexes. The aromaticity of each individual ring and of the whole molecule for all tautomers in ionic complexes is very similar to that observed for the anion of purine. This is not the case for neutral complexes and purine as a reference. The N···HF bonds perturb much more the π-electron structure of five-membered rings than that of the six-membered ones. The H-bonding complexes for 7-H and 9-H tautomers are characterized by higher aromaticity and a much lower range of HOMA variability.

Long-range heteronuclear coupling constants in 2,6-disubstituted purine derivatives

Four- and five-bond heteronuclear J-couplings between the hydrogen H-8 and carbons C-6 and C-2 in a series of 7- and 9-benzyl substituted purine derivaties with variuous substituents in positions 2 and 6 were studied by coupled (13)  C NMR and H,C-HMBC experiments and by DFT calculations. We have found that for some of the derivatives, the five-bond coupling H8-C2 is higher than the four-bond H8-C6 coupling, which is also evidenced by a stronger crosspeak in the HMBC. This finding contradicts the generally accepted opinion that only strong three-bond crosspeaks and one weak four-bond H8-C6 crosspeak can be observed in the HMBC spectra of purine derivatives. The misinterpretation of HMBC spectra may lead to an incorrect determination of the purine derivatives' structure.

C6-substituted purine derivatives: an experimental and theoretical 1H, 13C and 15N NMR study

We measured the (1)H, (13)C and (15)N chemical shifts for a series of purine derivatives bearing a norbornane substituent in position 9 and various substituents in position 6. The experimental data were complemented with density functional theory (DFT) calculations. The comparison of the calculated and experimental chemical shifts provided us with information about the tautomer and conformational equilibria of the studied compounds.

Bis(7-amino-1,2,4-triazolo[1,5-a]pyrimidin-4-ium) bis-(oxalato-κO,O)cuprate(II) dihydrate

The structure of the title ionic compound, (C(5)H(6)N(5))(2)[Cu(C(2)O(4))(2)]·2H(2)O, consists of a centrosymmetric copper(II) oxalate dianion, two monoprotonated mol-ecules of the adenine analog 7-amino-1,2,4-triazolo[1,5-a]pyrimidine (7atp) and two water mol-ecules of crystallization. The Cu(II) ion, located on an inversion center, exhibits a sligthly distorted square-planar coordination geometry, in which two oxalate anions bind in a bidentate fashion. The triazolopyrimidine ligand is protonated at the N atom in position 4, instead of its most basic N atom in position 3. This fact may be explained by the network stability, which is provided through the formation of a two-dimensional wave-like network parallel to (50[Formula: see text]) by N-H⋯O, O-H⋯N and O-H⋯O hydrogen bonds. These nets are further connected via C-H⋯O inter-actions.

Direct C-H arylation of purine on solid phase and its use for chemical libraries synthesis

C(8)-H direct arylation of purine derivatives immobilized on Wang resin is described. The purine skeleton was immobilized via C(6)-regioselective substitution of 2,6-dichloropurine with polymer-supported amines. After N(9)-alkylation with two different alkyl iodides and C(2) substitution with two selected amines, reaction conditions for C(8)-H arylation were developed and optimized. Various aryl bromides and aryl iodides were used for the reaction affording the target 2,6,8,9-tetrasubstituted purines in very good purity. The same reaction conditions were also applied for the synthesis of 2,6,8-trisubstituted purines, however, yields were lower. The methodology is applicable for high throughput synthesis of chemical libraries comprised of purine scaffold.

Heat-shock protein 90 inhibitors as antitumor agents: a survey of the literature from 2005 to 2010

INTRODUCTION

Heat-shock protein 90 (Hsp90) is a validated novel anticancer target with unique features. As a molecular chaperone, Hsp90 is implicated in maintaining the conformation, stability, activity and cellular localization of several key oncogenic client proteins that are involved in signal transduction pathways leading to proliferation, cell-cycle progression, apoptosis, angiogenesis and metastasis. As a result, inhibitors of Hsp90 achieve their promising anticancer activity through disruption of the Hsp90 protein function, thereby freezing the chaperone cycle; this in turn decreases the affinity of Hsp90 for client proteins, thus leading to proteasome-mediated degradation of oncogenic client proteins within cancer cells.

AREAS COVERED

This review provides recent background information on Hsp90 inhibitors. It also highlights a panel of compounds of interest reported in patents and discusses the clinical results of the promising drug candidates.

EXPERT OPINION

In the past 5 years, Hsp90 inhibitors have remained the focus of much interest as new potential anticancer agents. A large variety of scaffolds were studied in both academia and industry. Consequently, these significant research efforts have provided several promising drug candidates for further clinical development. Further progress in the development of Hsp90 inhibitors, combined with a deeper understanding of the chaperon characteristics, strengthens their promise in cancer therapy.

CuBr catalyzed C-N cross coupling reaction of purines and diaryliodonium salts to 9-arylpurines

CuBr was found to be an efficient catalyst for the C-N cross coupling reaction of purine and diaryliodonium salts. 9-Arylpurines were synthesized in excellent yields with short reaction times (2.5 h). The method represents an alternative to the synthesis of 9-arylpurines via Cu(II) catalyzed C-N coupling reaction with arylboronic acids as arylating agents.

Targeting zebrafish and murine pituitary corticotroph tumors with a cyclin-dependent kinase (CDK) inhibitor

Cushing disease caused by adrenocorticotropin (ACTH)-secreting pituitary adenomas leads to hypercortisolemia predisposing to diabetes, hypertension, osteoporosis, central obesity, cardiovascular morbidity, and increased mortality. There is no effective pituitary targeted pharmacotherapy for Cushing disease. Here, we generated germline transgenic zebrafish with overexpression of pituitary tumor transforming gene (PTTG/securin) targeted to the adenohypophyseal proopiomelanocortin (POMC) lineage, which recapitulated early features pathognomonic of corticotroph adenomas, including corticotroph expansion and partial glucocorticoid resistance. Adult Tg:Pomc-Pttg fish develop neoplastic coticotrophs and pituitary cyclin E up-regulation, as well as metabolic disturbances mimicking hypercortisolism caused by Cushing disease. Early development of corticotroph pathologies in Tg:Pomc-Pttg embryos facilitated drug testing in vivo. We identified a pharmacologic CDK2/cyclin E inhibitor, R-roscovitine (seliciclib; CYC202), which specifically reversed corticotroph expansion in live Tg:Pomc-Pttg embryos. We further validated that orally administered R-roscovitine suppresses ACTH and corticosterone levels, and also restrained tumor growth in a mouse model of ACTH-secreting pituitary adenomas. Molecular analyses in vitro and in vivo showed that R-roscovitine suppresses ACTH expression, induces corticotroph tumor cell senescence and cell cycle exit by up-regulating p27, p21 and p57, and downregulates cyclin E expression. The results suggest that use of selective CDK inhibitors could effectively target corticotroph tumor growth and hormone secretion.

Synthesis of purin-2-yl and purin-6-yl-aminoglucitols as C-nucleosidic ATP mimics and biological evaluation as FGFR3 inhibitors

Two new series of C-nucleosidic ATP mimics have been synthesized using an efficient and versatile synthetic pathway. These compounds were designed as FGFR3 inhibitors using purine as a central scaffold. The two substituents, a polyhydroxylated ribose mimic and a lipophilic moiety, were linked either in position 2 or 6 of the purine ring in order to explore any possible binding mode. All the compounds were able to inhibit FGFR3 kinase activity at a concentration of 50 μM. Unexpectedly, the best inhibitor was found to be one of the synthetic intermediates 13 bearing an iodine atom in position 2. Docking studies have confirmed its location in the ATP binding site and revealed halogen bonding among key interactions.