A Toxoplasma gondii Oxopurine Transporter Binds Nucleobases and Nucleosides Using Different Binding Modes

Toxoplasma gondii is unable to synthesize purines de novo, instead salvages them from its environment, inside the host cell, for which they need high affinity carriers. Here, we report the expression of a T. gondii Equilibrative Nucleoside Transporter, Tg244440, in a Trypanosoma brucei strain from which nucleobase transporters have been deleted. Tg244440 transported hypoxanthine and guanine with similar affinity (Km ~1 µM), while inosine and guanosine displayed Ki values of 4.05 and 3.30 µM, respectively. Low affinity was observed for adenosine, adenine, and pyrimidines, classifying Tg244440 as a high affinity oxopurine transporter. Purine analogues were used to probe the substrate-transporter binding interactions, culminating in quantitative models showing different binding modes for oxopurine bases, oxopurine nucleosides, and adenosine. Hypoxanthine and guanine interacted through protonated N1 and N9, and through unprotonated N3 and N7 of the purine ring, whereas inosine and guanosine mostly employed the ribose hydroxy groups for binding, in addition to N1H of the nucleobase. Conversely, the ribose moiety of adenosine barely made any contribution to binding. Tg244440 is the first gene identified to encode a high affinity oxopurine transporter in T. gondii and, to the best of our knowledge, the first purine transporter to employ different binding modes for nucleosides and nucleobases.

Aza-Reversine Promotes Reprogramming of Lung (MRC-5) and Differentiation of Mesenchymal Cells into Osteoblasts

Reversine or 2-(4-morpholinoanilino)-N6-cyclohexyladenine was originally identified as a small organic molecule that induces dedifferentiation of lineage-committed mouse myoblasts, C2C12, and redirects them into lipocytes or osteoblasts under lineage-specific conditions (LISCs). Further, it was proven that this small molecule can induce cell cycle arrest and apoptosis and thus selectively lead cancer cells to cell death. Further studies demonstrated that reversine, and more specifically the C2 position of the purine ring, can tolerate a wide range of substitutions without activity loss. In this study, a piperazine analog of reversine, also known as aza-reversine, and a biotinylated derivative of aza-reversine were synthesized, and their potential medical applications were investigated by transforming the endoderm originates fetal lung cells (MRC-5) into the mesoderm originated osteoblasts and by differentiating mesenchymal cells into osteoblasts. Moreover, the reprogramming capacity of aza-reversine and biotinylated aza-reversine was investigated against MRC-5 cells and mesenchymal cells after the immobilization on PMMA/HEMA polymeric surfaces. The results showed that both aza-reversine and the biofunctionalized, biotinylated analog induced the reprogramming of MRC-5 cells to a more primitive, pluripotent state and can further transform them into osteoblasts under osteogenic culture conditions. These molecules also induced the differentiation of dental and adipose mesenchymal cells to osteoblasts. Thus, the possibility to load a small molecule with useful “information” for delivering that into specific cell targets opens new therapeutic personalized applications.

A New Smoothened Antagonist Bearing the Purine Scaffold Shows Antitumour Activity In Vitro and In Vivo

The Smoothened (SMO) receptor is the most druggable target in the Hedgehog (HH) pathway for anticancer compounds. However, SMO antagonists such as vismodegib rapidly develop drug resistance. In this study, new SMO antagonists having the versatile purine ring as a scaffold were designed, synthesised, and biologically tested to provide an insight to their mechanism of action. Compound 4s was the most active and the best inhibitor of cell growth and selectively cytotoxic to cancer cells. 4s induced cell cycle arrest, apoptosis, a reduction in colony formation and downregulation of PTCH and GLI1 expression. BODIPY-cyclopamine displacement assays confirmed 4s is a SMO antagonist. In vivo, 4s strongly inhibited tumour relapse and metastasis of melanoma cells in mice. In vitro, 4s was more efficient than vismodegib to induce apoptosis in human cancer cells and that might be attributed to its dual ability to function as a SMO antagonist and apoptosis inducer.

Regioselective synthesis of triazolo[3,4-e]purine derivatives and their anti-cancer activity against NCI-60 cell-lines

Introduction: Due to the vast medicinal importance of purine nucleoside, a hybrid molecule of triazole with purine ring might explode a lead molecule in the pharma sector and based on the last decade’s studies suggested that the nitrogen-rich molecules possess a wide range of medicinal importance. Aim: Due to the vast application of purine nucleoside itself in the field of cancer research, we synthesized triazolo[3,4-e]purines and screened them for their anti-cancer study against NCI-60 cell lines by the protocol used by NIH. Materials and methods: The targeted molecules, 4-chloro-5a,6-dihydro-8-substitutedphenyl-1H-[1,2,4]triazolo[3,4-e]purine derivatives (4a-4h) were synthesized in a two-step procedure by nucleophilic substitution (SN) at C-2 chlorine followed by formation of the triazole ring by acid-catalyzed reaction in the polar protic solvent. Results: It was observed that the regioselective approach followed in C-2 chlorine replacement instead of C-6 chlorine during SN reaction. One-dose response of selected three molecules (4a, 4b, and 4c) showed that 4b (K-562: 64.47 µM & SR: 63.38 µM; mean GI50: 99.09 µM) was found to be more potent than 4a and 4c. Conclusions: We have described in this study the general synthetic method for triazolo[3,4-e]purines as an innovative class of potential anticancer agents. The dose-response curve in the sense of mean GI50 for three compounds across all 60 cell lines, 4b can be served as lead after necessary modification.

Design and Synthesis of 9-Dialkylamino-6-[(1H-1,2,3-triazol-4-yl)methoxy]-9H-purines

<p>The purine ring is a common structural component of a large variety of biomolecules with important roles in both physiological and pathological processes. The biological ubiquity and versatility of this heterocyclic scaffold makes it a privileged structure in drug design. Consequently, the development of novel purine analogs remains of great interest in the medicinal chemistry field. Here, we report the design and synthesis of a series of 9-dialkylamino-6-[(1<i>H</i>-1,2,3-triazol-4 yl)methoxy]-9<i>H</i>-purines and their intermediates. This series of compounds aims to diversify the chemical space around the purine scaffold in the search towards the discovery of new biologically active small molecules.</p>

Design and Synthesis of 9-Dialkylamino-6-[(1H-1,2,3-triazol-4-yl)methoxy]-9H-purines

<p>The purine ring is a common structural component of a large variety of biomolecules with important roles in both physiological and pathological processes. The biological ubiquity and versatility of this heterocyclic scaffold makes it a privileged structure in drug design. Consequently, the development of novel purine analogs remains of great interest in the medicinal chemistry field. Here, we report the design and synthesis of a series of 9-dialkylamino-6-[(1<i>H</i>-1,2,3-triazol-4 yl)methoxy]-9<i>H</i>-purines and their intermediates. This series of compounds aims to diversify the chemical space around the purine scaffold in the search towards the discovery of new biologically active small molecules.</p>

Excited State Dynamics of 8-Vinyldeoxyguanosine in Aqueous Solution Studied by Time-Resolved Fluorescence Spectroscopy and Quantum Mechanical Calculations

The fluorescent base guanine analog, 8-vinyl-deoxyguanosine (8vdG), is studied in solution using a combination of optical spectroscopies, notably femtosecond fluorescence upconversion and quantum chemical calculations, based on time-dependent density functional theory (TD-DFT) and including solvent effect by using a mixed discrete-continuum model. In all investigated solvents, the fluorescence is very long lived (3–4 ns), emanating from a stable excited state minimum with pronounced intramolecular charge-transfer character. The main non-radiative decay channel features a sizeable energy barrier and it is affected by the polarity and the H-bonding properties of the solvent. Calculations provide a picture of dynamical solvation effects fully consistent with the experimental results and show that the photophysical properties of 8vdG are modulated by the orientation of the vinyl group with respect to the purine ring, which in turn depends on the solvent. These findings may have importance for the understanding of the fluorescence properties of 8vdG when incorporated in a DNA helix.

Promising 2,6,9-Trisubstituted Purine Derivatives for Anticancer Compounds: Synthesis, 3D-QSAR, and Preliminary Biological Assays

We designed, synthesized, and evaluated novel 2,6,9-trisubstituted purine derivatives for their prospective role as antitumor compounds. Using simple and efficient methodologies, 31 compounds were obtained. We tested these compounds in vitro to draw conclusions about their cell toxicity on seven cancer cells lines and one non-neoplastic cell line. Structural requirements for antitumor activity on two different cancer cell lines were analyzed with SAR and 3D-QSAR. The 3D-QSAR models showed that steric properties could better explain the cytotoxicity of compounds than electronic properties (70% and 30% of contribution, respectively). From this analysis, we concluded that an arylpiperazinyl system connected at position 6 of the purine ring is beneficial for cytotoxic activity, while the use of bulky systems at position C-2 of the purine is not favorable. Compound 7h was found to be an effective potential agent when compared with a currently marketed drug, cisplatin, in four out of the seven cancer cell lines tested. Compound 7h showed the highest potency, unprecedented selectivity, and complied with all the Lipinski rules. Finally, it was demonstrated that 7h induced apoptosis and caused cell cycle arrest at the S-phase on HL-60 cells. Our study suggests that substitution in the purine core by arylpiperidine moiety is essential to obtain derivatives with potential anticancer activity.

Crystal structures of the synthetic intermediate 3-[(6-chloro-7H-purin-7-yl)methyl]cyclobutan-1-one, and of two oxetanocin derivatives: 3-[(6-chloro-8,9-dihydro-7H-purin-7-yl)methyl]cyclobutan-1-ol and 3-[(6-chloro-9H-purin-9-yl)methyl]cyclobutan-1-ol

The crystal structures of an intermediate, C10H9ClN4O, 3-[(6-chloro-7H-purin-7-yl)methyl]cyclobutan-1-one (I), and two N-7 and N-9 regioisomeric oxetanocin nucleoside analogs, C10H13ClN4O, 3-[(6-chloro-8,9-dihydro-7H-purin-7-yl)methyl]cyclobutan-1-ol (II) and C10H11ClN4O, 3-[(6-chloro-9H-purin-9-yl)methyl]cyclobutan-1-ol (IV), are reported. The crystal structures of the nucleoside analogs confirmed the reduction of the N-7- and N-9-substituted cyclobutanones with LiAl(OtBu)3 to occur with facial selectivity, yielding cis-nucleosides analogs similar to those found in nature. Reduction of the purine ring of the N-7 cyclobutanone to a dihydropurine was observed for compound (II) but not for the purine ring of the N-9 cyclobutanone on formation of compound (IV). In the crystal of (I), molecules are linked by a weak Cl...O interaction, forming a 21 helix along [010]. The helices are linked by offset π–π interactions [intercentroid distance = 3.498 (1) Å], forming layers parallel to (101). In the crystal of (II), molecules are linked by pairs of O—H...N hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif. The dimers are linked by O—H...N hydrogen bonds, forming chains along [001], which in turn are linked by C—H...π and offset π–π interactions [intercentroid distance = 3.509 (1) Å], forming slabs parallel to the ac plane. In the crystal of (IV), molecules are linked by O—H...N hydrogen bonds, forming chains along [101]. The chains are linked by C—H...N and C—H...O hydrogen bonds and C—H...π and offset π–π interactions [intercentroid distance = 3.364 (1) Å], forming a supramolecular framework.