Palladium-Catalyzed Animation of 6-Chloropurine. Synthesis of N6-Substituted Adenosine Analogues

Abstract

Room-temperature treatment of persilylated 6-chloro-9-β-D-ribofuranosyl-purine with a variety of aliphatic and aromatic amines, in the presence of Pd₂(dba)₃, BINAP and base, leads to N⁶-substituted adenosine analogues in fair to good yields. Coupling of chloropurine with a chiral aziridinyl diester is applied in the synthesis of a potential adenylosuccinate lyase inhibitor.     

Independent Validation of an Existing Model Enables Prediction of Hearing Loss after Childhood Bacterial Meningitis

Objective

This study aimed external validation of a formerly developed prediction model identifying children at risk for hearing loss after bacterial meningitis (BM). Independent risk factors included in the model are: duration of symptoms prior to admission, petechiae, cerebral spinal fluid (CSF) glucose level, Streptococcus pneumoniae and ataxia. Validation helps to evaluate whether the model has potential in clinical practice.

Study design

116 Dutch school-age BM survivors were included in the validation cohort and screened for sensorineural hearing loss (>25 dB). Risk factors were obtained from medical records. The model was applied to the validation cohort and its performance was compared with the development cohort. Validation was performed by application of the model on the validation cohort and by assessment of discrimination and goodness of fit. Calibration was evaluated by testing deviations in intercept and slope. Multiple imputation techniques were used to deal with missing values.

Results

Risk factors were distributed equally between both cohorts. Discriminative ability (Area Under the Curve, AUC) of the model was 0.84 in the development and 0.78 in the validation cohort. Hosmer-Lemeshow test for goodness of fit was not significant in the validation cohort, implying good fit concerning the similarity of expected and observed cases. There were no significant differences in calibration slope and intercept. Sensitivity and negative predicted value were high, while specificity and positive predicted value were low which is comparable with findings in the development cohort.

Conclusions

Performance of the model remained good in the validation cohort. This prediction model might be used as a screening tool and can help to identify those children that need special attention and a long follow-up period or more frequent auditory testing.     

Perturbation of the mutated EGFR interactome identifies vulnerabilities and resistance mechanisms

We hypothesized that elucidating the interactome of epidermal growth factor receptor (EGFR) forms that are mutated in lung cancer, via global analysis of protein–protein interactions, phosphorylation, and systematically perturbing the ensuing network nodes, should offer a new, more systems‐level perspective of the molecular etiology. Here, we describe an EGFR interactome of 263 proteins and offer a 14‐protein core network critical to the viability of multiple EGFR‐mutated lung cancer cells. Cells with acquired resistance to EGFR tyrosine kinase inhibitors (TKIs) had differential dependence of the core network proteins based on the underlying molecular mechanisms of resistance. Of the 14 proteins, 9 are shown to be specifically associated with survival of EGFR‐mutated lung cancer cell lines. This included EGFR, GRB2, MK12, SHC1, ARAF, CD11B, ARHG5, GLU2B, and CD11A. With the use of a drug network associated with the core network proteins, we identified two compounds, midostaurin and lestaurtinib, that could overcome drug resistance through direct EGFR inhibition when combined with erlotinib. Our results, enabled by interactome mapping, suggest new targets and combination therapies that could circumvent EGFR TKI resistance.     

The structure of an insect chymotrypsin

The South American imported fire ant (Solenopsis invicta), without natural enemies in the United States, widely infests the southern United States, causing more than a half billion dollars in health and agriculture-related damage annually in Texas alone. Fire ants are resistant to most insecticides, so control will require a more fundamental understanding of their biochemistry and metabolism leading to the design of selective, ecologically safe insecticides. The 4th instar larvae play a crucial role in the nutrition of the colony by secreting proteinases (especially chymotrypsin) which digest food products for the entire colony. The first structure of an ant proteolytic enzyme, fire ant chymotrypsin, was determined to atomic resolution (1.7 A). A structural comparison of the ant and mammalian structures confirms the "universality" of the serine proteinase motif and reveals a difference at residues 147-148, which are proteolytically removed in the bovine enzyme but are firmly intact in the ant chymotrypsin, suggesting a different activation mechanism for the latter. Likewise, the absence of the covalently attached propeptide domain (1-15) further suggests an uncharacteristic activation mechanism. The presence of Gly189 in the S1 site is an atypical feature of this chymotrypsin and is comparable only to human leukocyte elastase, hornet chymotrypsin and fiddler crab collagenase. Binding studies confirm the chymotrypsin nature of this novel enzyme.     

<Emphasis Type="Italic">TRAF1/C5</Emphasis>polymorphism is not associated with increased mortality in rheumatoid arthritis: two large longitudinal studies

Introduction  

Recently an association between a genetic variation in TRAF1/C5 and mortality from sepsis or cancer was found in rheumatoid arthritis (RA). The most prevalent cause of death, cardiovascular disease, may have been missed in that study, since patients were enrolled at an advanced disease stage. Therefore, we used an inception cohort of RA patients to investigate the association between TRAF1/C5 and cardiovascular mortality, and replicate the findings on all-cause mortality. As TRAF1/C5 associated mortality may not be restricted to RA, we also studied a large cohort of non-RA patients.     

Mesenchymal stem cells in autoimmune diseases: hype or hope?

Intervention with mesenchymal stem cells (MSCs) represents a promising therapeutic tool in treatment-refractory autoimmune diseases. A new report by Schurgers and colleagues in a previous issue of Arthritis Research & Therapy sheds novel mechanistic insight into the pathways employed by MSCs to suppress T-cell proliferation in vitro, but, at the same time, indicates that MSCs do not influence T-cell reactivity and the disease course in an in vivo arthritis model. Such discrepancies between the in vitro and in vivo effects of potent cellular immune modulators should spark further research and should be interpreted as a sign of caution for the in vitro design of MSC-derived interventions in the setting of human autoimmune diseases.     

Pentacycloundecane lactam vs lactone norstatine type protease HIV inhibitors: binding energy calculations and DFT study

Background

Novel pentacycloundecane (PCU)-lactone-CO-EAIS peptide inhibitors were designed, synthesized, and evaluated against wild-type C-South African (C-SA) HIV-1 protease. Three compounds are reported herein, two of which displayed IC₅₀ values of less than 1.00 μM. A comparative MM-PB(GB)SA binding free energy of solvation values of PCU-lactam and lactone models and their enantiomers as well as the PCU-lactam-NH-EAIS and lactone-CO-EAIS peptide inhibitors and their corresponding diastereomers complexed with South African HIV protease (C-SA) was performed. This will enable us to rationalize the considerable difference between inhibitory concentration (IC₅₀) of PCU-lactam-NH-EAIS and PCU-lactone-CO-EAIS peptides.

Results

The PCU-lactam model exhibited more negative calculated binding free energies of solvation than the PCU-lactone model. The same trend was observed for the PCU-peptide inhibitors, which correspond to the experimental activities for the PCU-lactam-NH-EAIS peptide (IC₅₀ = 0.076 μM) and the PCU-lactone-CO-EAIS peptide inhibitors (IC₅₀ = 0.850 μM). Furthermore, a density functional theory (DFT) study on the natural atomic charges of the nitrogen and oxygen atoms of the three PCU-lactam, PCU-lactim and PCU-lactone models were performed using natural bond orbital (NBO) analysis. Electrostatic potential maps were also used to visualize the electron density around electron-rich regions. The asymmetry parameter (η) and quadrupole coupling constant (χ) values of the nitrogen and oxygen nuclei of the model compounds were calculated at the same level of theory. Electronic molecular properties including polarizability and electric dipole moments were also calculated and compared. The Gibbs theoretical free solvation energies of solvation (∆G_solv) were also considered.

Conclusions

A general trend is observed that the lactam species appears to have a larger negative charge distribution around the heteroatoms, larger quadrupole constant, dipole moment and better solvation energy, in comparison to the PCU-lactone model. It can be argued that these characteristics will ensure better eletronic interaction between the lactam and the receptor, corresponding to the observed HIV protease activities in terms of experimental IC₅₀ data.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-015-0115-5) contains supplementary material, which is available to authorized users.