Synthesis and biological activity of new arenediyne-linked isoxazolidines
Graphical abstract
Introduction
Since the initial reports of the enediyne anticancer antibiotics in the late 1980s,1 an ever increasing attention has been addressed to the chemistry, biology and potential medicinal applications of this class of compounds.2 The antitumor activity of these substrates is linked to the presence of a highly unsaturated hex-1-ene-1,5-diyne system, which undergoes Bergman cyclization (BC)3 and generates a benzene-1,4-diradical, able to abstract H-atoms from the DNA backbone, thus causing cell death. BC is a thermal rearrangement of (Z)-hex-3-ene-1,5-diynes to benzene-1,5-diyls which, after quenching by H-atom donors, afford new benzene rings.4
Due to their highly interesting biological properties, the design of new low molecular weight enediynes, with good and multiple DNA-binding features, within a structurally well defined architecture, constitutes a research area of present interest. Thus, enediynes containing either DNA intercalating groups or DNA minor groove binding functions have been synthesized: all these derivatives are potent DNA-damaging agents due to their ability to generate benzenoid diradicals.
Apart their role in anticancer drug development, enediynes exhibit a wide spectrum of biological features, such as antibacterial,5 protein degradation,6 topoisomerase inhibiting activities.7
Recently, several new acyclic enediynes have been reported that do not undergo the Bergman or Myers cyclization under physiological conditions, but which still display interesting cancer cell cytotoxicity.8 Some possible mechanisms have been proposed: the most probable pathway to induce the death of cancer cells is the inhibition of physiological enzymes, especially the topological enzymes, although other targets such as MAPK pathway or the arrest or G2/M cell cycle have also been proposed.9
The isoxazolidine framework has successfully been applied as surrogate for a riboside ring in the synthesis of nucleoside analogs with anticancer or antiviral activity.10 In this context, we reasoned that arenediyne–isoxazolidine conjugates might provide a new scaffold for the development of bioactive mimics. Thus, the main focus of this paper is to design a new group of arenediynes and to verify whether this new hybrid agents induce antiproliferative effect, leading to cell growth perturbation.
The obtained results showed that some of the synthesized compounds are endowed with antiproliferative activity against three human cancer cell lines: the neuroblastoma SH-SY5Y, the HT-29 colon rectal adenocarcinoma and the HepG2 hepatocelluar carcinoma cells. Thermal reactivity shows that their biological activity probably could not be linked to the Bergman cyclization, that is, the formation of active biradical intermediates.
Section snippets
Chemistry
The synthetic approach towards acyclic arenediyne-linked isoxazolidines 9–11 involves the coupling of the arenediyne unit, the 1,2-bis(1-hydroxyprop-2-ynyl)benzene 3,11 with the isoxazolidine systems 7 and 8.
The arenediyne partner for the coupling reaction, the compound 3, was prepared by a Pd(0)-catalyzed Sonogashira coupling12 of 1,2-dibromobenzene 1 and propargyl alcohol 2 (1:3 ratio).
The coupling reaction, carried out in the absence of CuI to reduce the oxidative dimerization of the
Effects on cell proliferation
As shown in Figure 1, compounds 11 and 16 showed growth inhibitory activity, exerted in a time and concentration-dependent manner in every cell lines used in this study. In particular, the strongest antiproliferative effect was obtained in HT-29 colorectal adenocarcinoma cells, reaching the peak of reduction in cell proliferation after 72 h of treatment with 100 μM of 16 (63% in the MTT test; P < 0.001 vs control; Fig. 1C). A significant reduction of cell growth was obtained also after 48 h of
Conclusion
In summary, we report an efficient synthesis of arenediyne–isoxazolidine conjugates by the coupling of an arenediyne unit, prepared by using Sonogashira processes and glycosylation reactions. Some of the synthesized compounds are endowed with antiproliferative activity against three human cancer cell lines: the neuroblastoma SH-SY5Y, the HT-29 colon rectal adenocarcinoma and the HepG2 hepatocelluar carcinoma cells. Thermal reactivity data show that the biological activity of these compounds
General
Solvents and reagents were used as received from commercial sources. Melting points were determined with a Kofler apparatus. Elemental analyses were performed with a Perkin–Elmer elemental analyzer. NMR spectra (1H NMR recorded at 500 and 200 MHz, 13C NMR recorded at 126 and 50 MHz) were obtained with Varian instruments; chemical shifts are reported in ppm relative to TMS. Thin-layer chromatographic separations were performed on Merck silica gel 60-F254 precoated aluminum plates. Flash
Cell cultures and drug treatment
Experiments were carried out using three human cancer cell lines: the neuroblastoma SH-SY5Y, the HT-29 colorectal adenocarcinoma and the HepG2 hepatocellular carcinoma cells. All the cell lines were obtained originally from ATCC (Rockville, MD, USA). The cultures were grown in monolayer at 37 °C with 5% CO2 humidified atmosphere. The culture medium was a RPMI supplemented with 10% (v/v) heat-inactivated fetal bovine serum, l-glutamine (2 mM), sodium pyruvate (1 mM), penicillin (100 lU/ml) and
Acknowledgments
We gratefully acknowledge the Italian Ministry of Education, Universities, and Research (MIUR), the Universities of Messina and Catania, and the Interuniversity Consortium for Innovative Methodologies and Processes for Synthesis (CINMPIS) for partial financial support.
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