The Molecular Basis of Different Approaches for the Study of Cancer Stem Cells and the Advantages and Disadvantages of a Three-Dimensional Culture

Cancer stem cells (CSCs) are a rare tumor subpopulation with high differentiation, proliferative and tumorigenic potential compared to the remaining tumor population. CSCs were first discovered by Bonnet and Dick in 1997 in acute myeloid leukemia. The identification and isolation of these cells in this pioneering study were carried out through the flow cytometry, exploiting the presence of specific cell surface molecular markers (CD34⁺/CD38⁻). In the following years, different strategies and projects have been developed for the study of CSCs, which are basically divided into surface markers assays and functional assays; some of these techniques also allow working with a cellular model that better mimics the tumor architecture. The purpose of this mini review is to summarize and briefly describe all the current methods used for the identification, isolation and enrichment of CSCs, describing, where possible, the molecular basis, the advantages and disadvantages of each technique with a particular focus on those that offer a three-dimensional culture.     

Vicinal Difunctionalization of Alkenes with Iodine(III) Reagents and Catalysts

Hypervalent iodine(III) reagents have been known for over a century, and their reaction profile is still actively investigated. Recent years have seen impressive improvements in the area of alkene difunctionalization reactions, where new methodologies have become available. Especially chiral non‐racemic hypervalent iodine(III) reagents and catalysts have emerged as versatile tools for the realization of important enantioselective transformations.     

η3‐Allyl Coordination at Tin(II)—Reactivity towards Alkynes and Benzonitrile

We herein report the synthesis and characterization of a terphenyl‐substituted Sn^II allyl compound featuring an η³ coordination mode in solution and in the solid state. Two examples for the interesting reactivity of the allyl Sn^II molecule are presented: Reactions with terminal alkynes result in the formation of tricyclic compounds by C? C bond formation and the dimerization of two Sn moieties whereas the reaction with benzonitrile leads to a sixteen‐membered ring system through C? H activation.     

An Iodine‐Catalyzed Hofmann–Löffler Reaction

Iodine reagents have been identified as economically and ecologically benign alternatives to transition metals, although their application as molecular catalysts in challenging C? H oxidation reactions has remained elusive. An attractive iodine oxidation catalysis is now shown to promote the convenient conversion of carbon–hydrogen bonds into carbon–nitrogen bonds with unprecedented complete selectivity. The reaction proceeds by two interlocked catalytic cycles comprising a radical chain reaction, which is initiated by visible light as energy source. This unorthodox synthetic strategy for the direct oxidative amination of alkyl groups has no biosynthetic precedence and provides an efficient and straightforward access to a general class of saturated nitrogenated heterocycles.     

Enhanced conductivity and dielectric absorption in discotic liquid crystalline columnar phases of a vanadyl complex

A liquid crystalline vanadyl complex has been studied by DSC, polarizing optical microscopy, the reversal current technique, X-ray diffraction and frequency domain dielectric spectroscopy. The compound exhibits three columnar phases: rectangular ordered (Col_ro), rectangular disordered (Col_rd), and hexagonal disordered (Col_hd), all of which show a dielectric relaxation process at low frequencies. In the Col_ro low temperature phase this process seems to be connected with a slow relaxation of polarized polymeric chains inside the columns (mHz frequency range). However, in the Col_hd high temperature disordered phase this relaxation is faster (Hz range). It is interesting that the liquid crystalline phases studied show enhanced conductivity which changes by four orders of magnitude from 10^-9 S m^-1 in the orientationally disordered crystal (an ODIC phase) to 10^-5 S m^-1 in the Col_hd high temperature phase. Such a value of the conductivity is typical for semiconducting materials.     

Synthesis and cleavage of core‐labile poly(alkyl methacrylate) star polymers

Core‐cleavable star polymers were synthesized by the coupling of living anionic poly(alkyl methacrylate) arms with either dicumyl alcohol dimethacrylate (DCDMA) or 2,5‐dimethyl‐2,5‐hexanediol dimethacrylate (DHDMA). This synthetic methodology led to the formation of star polymers that exhibited high molecular weights and relatively narrow molecular weight distributions. The labile tertiary alkyl esters in the DCDMA and DHDMA star polymer cores were readily hydrolyzed under acidic conditions. High‐molecular‐weight star polymer cleavage led to well‐defined arm polymers with lower molecular weights. Hydrolysis was confirmed via ¹H NMR spectroscopy and gel permeation chromatography. Thermogravimetric analysis (TGA) of the star polymers demonstrated that the DCDMA and DHDMA star polymer cores also thermally degraded in the absence of acid catalysts at 185 and 220 °C, respectively, and the core‐cleavage temperatures were independent of the arm polymer composition. The difference in the core‐degradation temperatures was attributed to the increased reactivity of the DCDMA‐derived cores. TGA/mass spectrometry detected the evolution of the diene byproduct of the core degradation and confirmed the proposed degradation mechanism. The DCDMA monomer exhibited a higher degradation rate than DHDMA under identical reaction conditions because of the additional resonance stabilization of the liberated byproduct, which made it a more responsive cleavable coupling monomer than DHDMA. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3083–3093, 2003