6 research outputs found
Computational Methods to Predict the Regioselectivity of Electrophilic Aromatic Substitution Reactions of Heteroaromatic Systems
The
validity of calculated NMR shifts to predict the outcome of
electrophilic aromatic substitution reactions on different heterocyclic
compounds has been examined. Based on an analysis of >130 literature
examples, it was found that the lowest predicted <sup>13</sup>C and/or <sup>1</sup>H chemical shift of a heterocycle correlates qualitatively
with the regiochemical outcome of halogenation reactions in >80%
of
the investigated cases. In the remaining cases, the site of electrophilic
aromatic substitution can be explained by the calculated HOMO orbitals
obtained using density functional theory. Using a combination of these
two methods, the accuracy increases to >95%
Fast and Accurate Prediction of the Regioselectivity of Electrophilic Aromatic Substitution Reactions
While computational prediction of chemical reactivity is possible it usually requires expert knowledge and there are relatively few computational tools that can be used by a bench chemist to help guide synthesis. The RegioSQM method for predicting the regioselectivity of electrophilic aromatic substitution reactions of heteroaromatic systems is presented in this paper. RegioSQM protonates all aromatic C-H carbon atoms and identifies those with the lowest free energies in chloroform using the PM3 semiempirical method as the most nucleophilic center. These positions are found to correlate qualitatively with the regiochemical outcome in a retrospective analysis of 96% of more than 525 literature examples of electrophilic aromatic halogenation reactions. The method is automated and requires only a SMILES string of the molecule of interest, which can easily be generated using chemical drawing programs such as ChemDraw. The computational cost is 1-10 minutes per molecule depending on size, using relatively modest computational resources and the method is freely available via a web server at regiosqm.org. RegioSQM should therefore be of practical use in the planning of organic synthesis
The Molecular Basis for Inhibition of Stemlike Cancer Cells by Salinomycin
Tumors
are phenotypically heterogeneous and include subpopulations
of cancer cells with stemlike properties. The natural product salinomycin,
a K<sup>+</sup>-selective ionophore, was recently found to exert selectivity
against such cancer stem cells. This selective effect is thought to
be due to inhibition of the Wnt signaling pathway, but the mechanistic
basis remains unclear. Here, we develop a functionally competent fluorescent
conjugate of salinomycin to investigate the molecular mechanism of
this compound. By subcellular imaging, we demonstrate a rapid cellular
uptake of the conjugate and accumulation in the endoplasmic reticulum
(ER). This localization is connected to induction of Ca<sup>2+</sup> release from the ER into the cytosol. Depletion of Ca<sup>2+</sup> from the ER induces the unfolded protein response as shown by global
mRNA analysis and Western blot analysis of proteins in the pathway.
In particular, salinomycin-induced ER Ca<sup>2+</sup> depletion up-regulates
C/EBP homologous protein (CHOP), which inhibits Wnt signaling by down-regulating
β-catenin. The increased cytosolic Ca<sup>2+</sup> also activates
protein kinase C, which has been shown to inhibit Wnt signaling. These
results reveal that salinomycin acts in the ER membrane of breast
cancer cells to cause enhanced Ca<sup>2+</sup> release into the cytosol,
presumably by mediating a counter-flux of K<sup>+</sup> ions. The
clarified mechanistic picture highlights the importance of ion fluxes
in the ER as an entry to inducing phenotypic effects and should facilitate
rational development of cancer treatments
The Molecular Basis for Inhibition of Stemlike Cancer Cells by Salinomycin
Tumors
are phenotypically heterogeneous and include subpopulations
of cancer cells with stemlike properties. The natural product salinomycin,
a K<sup>+</sup>-selective ionophore, was recently found to exert selectivity
against such cancer stem cells. This selective effect is thought to
be due to inhibition of the Wnt signaling pathway, but the mechanistic
basis remains unclear. Here, we develop a functionally competent fluorescent
conjugate of salinomycin to investigate the molecular mechanism of
this compound. By subcellular imaging, we demonstrate a rapid cellular
uptake of the conjugate and accumulation in the endoplasmic reticulum
(ER). This localization is connected to induction of Ca<sup>2+</sup> release from the ER into the cytosol. Depletion of Ca<sup>2+</sup> from the ER induces the unfolded protein response as shown by global
mRNA analysis and Western blot analysis of proteins in the pathway.
In particular, salinomycin-induced ER Ca<sup>2+</sup> depletion up-regulates
C/EBP homologous protein (CHOP), which inhibits Wnt signaling by down-regulating
β-catenin. The increased cytosolic Ca<sup>2+</sup> also activates
protein kinase C, which has been shown to inhibit Wnt signaling. These
results reveal that salinomycin acts in the ER membrane of breast
cancer cells to cause enhanced Ca<sup>2+</sup> release into the cytosol,
presumably by mediating a counter-flux of K<sup>+</sup> ions. The
clarified mechanistic picture highlights the importance of ion fluxes
in the ER as an entry to inducing phenotypic effects and should facilitate
rational development of cancer treatments
The Molecular Basis for Inhibition of Stemlike Cancer Cells by Salinomycin
Tumors
are phenotypically heterogeneous and include subpopulations
of cancer cells with stemlike properties. The natural product salinomycin,
a K<sup>+</sup>-selective ionophore, was recently found to exert selectivity
against such cancer stem cells. This selective effect is thought to
be due to inhibition of the Wnt signaling pathway, but the mechanistic
basis remains unclear. Here, we develop a functionally competent fluorescent
conjugate of salinomycin to investigate the molecular mechanism of
this compound. By subcellular imaging, we demonstrate a rapid cellular
uptake of the conjugate and accumulation in the endoplasmic reticulum
(ER). This localization is connected to induction of Ca<sup>2+</sup> release from the ER into the cytosol. Depletion of Ca<sup>2+</sup> from the ER induces the unfolded protein response as shown by global
mRNA analysis and Western blot analysis of proteins in the pathway.
In particular, salinomycin-induced ER Ca<sup>2+</sup> depletion up-regulates
C/EBP homologous protein (CHOP), which inhibits Wnt signaling by down-regulating
β-catenin. The increased cytosolic Ca<sup>2+</sup> also activates
protein kinase C, which has been shown to inhibit Wnt signaling. These
results reveal that salinomycin acts in the ER membrane of breast
cancer cells to cause enhanced Ca<sup>2+</sup> release into the cytosol,
presumably by mediating a counter-flux of K<sup>+</sup> ions. The
clarified mechanistic picture highlights the importance of ion fluxes
in the ER as an entry to inducing phenotypic effects and should facilitate
rational development of cancer treatments
The Molecular Basis for Inhibition of Stemlike Cancer Cells by Salinomycin
Tumors
are phenotypically heterogeneous and include subpopulations
of cancer cells with stemlike properties. The natural product salinomycin,
a K<sup>+</sup>-selective ionophore, was recently found to exert selectivity
against such cancer stem cells. This selective effect is thought to
be due to inhibition of the Wnt signaling pathway, but the mechanistic
basis remains unclear. Here, we develop a functionally competent fluorescent
conjugate of salinomycin to investigate the molecular mechanism of
this compound. By subcellular imaging, we demonstrate a rapid cellular
uptake of the conjugate and accumulation in the endoplasmic reticulum
(ER). This localization is connected to induction of Ca<sup>2+</sup> release from the ER into the cytosol. Depletion of Ca<sup>2+</sup> from the ER induces the unfolded protein response as shown by global
mRNA analysis and Western blot analysis of proteins in the pathway.
In particular, salinomycin-induced ER Ca<sup>2+</sup> depletion up-regulates
C/EBP homologous protein (CHOP), which inhibits Wnt signaling by down-regulating
β-catenin. The increased cytosolic Ca<sup>2+</sup> also activates
protein kinase C, which has been shown to inhibit Wnt signaling. These
results reveal that salinomycin acts in the ER membrane of breast
cancer cells to cause enhanced Ca<sup>2+</sup> release into the cytosol,
presumably by mediating a counter-flux of K<sup>+</sup> ions. The
clarified mechanistic picture highlights the importance of ion fluxes
in the ER as an entry to inducing phenotypic effects and should facilitate
rational development of cancer treatments