Compound 2 (1 mmol) was refluxed with 6 ml of 1.0 Mborane/tetrahydrofuran solution for 36 h. Then, 5 ml of 4%hydrochloric acid solution was added and the mixture was againrefluxed for another 24 h. After completion of the reaction, the pHof the solution was maintained at ~7.0 by 10% aqueous sodiumhydroxide solution and the mixture was extracted with ethyl acetate(3×3 ml). The organic layer was washed with brine and watersuccessively. The pure product (compound 3) was isolated aftercolumn chromatography over silica gel (78% yield).
The diazo transfer reaction to 1,3-dicarbonyl compounds usually involves a combination of a sulfonyl azide and a base in a given organic solvent to furnish 2-diazo-1,3-dicarbonyl derivatives in good yields ( Scheme 1 ).
A Sc(OTf)3-catalyzed three-component cyclization reaction of arylamines, β,γ-unsaturated α-ketoesters and 1,3-dicarbonyl compounds was developed to synthesize highly substituted 1,4-dihydropyridines and fused bicyclic tetrahydropyridines carrying a quaternary all-carbon center.
T1 - Sc(OTf)3-catalyzed three-component cyclization of arylamines, β,γ-unsaturated α-ketoesters, and 1,3-dicarbonyl compounds for the synthesis of highly substituted 1,4-dihydropyridines and tetrahydropyridines
N2 - A Sc(OTf)3-catalyzed three-component cyclization reaction of arylamines, β,γ-unsaturated α-ketoesters and 1,3-dicarbonyl compounds was developed to synthesize highly substituted 1,4-dihydropyridines and fused bicyclic tetrahydropyridines carrying a quaternary all-carbon center.
β-1,3-Dicarbonyl aldehydes were synthesized by iron-catalyzed oxidative reactions between 1,3-dicarbonyl compounds and two molecules of tertiary amines in the presence of tert-butyl hydroperoxide (TBHP). α,β-Unsaturated aldehydes generated by tertiary amine oxidation in situ act as key intermediates under mild reaction conditions.
However, each compound was capable of reducing theviability of Hepa1–6, HeLa and NIH3T3 cells with an estimatedIC value of 16 μM or lower (). Although compound 2 was generallyslightly more cytotoxic than compound 1, little difference incytotoxicity was noted when comparing the pyrene () and chrysene () PAH-coupled compounds. Similarly, littledifference in cytotoxicity was observed when comparing compounds 2and 3, suggesting that reduction of the carbamate group had littleeffect on the pyrene-coupled PAHs.
Previous reports from our group and from otherauthors have shown that certain derivatives of PAHs, includingpyrene and chrysene derivatives, reduce the viability oftransformed cell lines (,,),and some of these PAH derivatives have been reported to reduce cellviability by induction of apoptosis (,).Therefore, we tested the effects of compounds 1, 2 and 3 on theviability of a small panel of human and mouse cell lines, includingliver cancer cell lines (HepG2 and Hepa1–6), colon cancer celllines (HT-29 and Caco-2), a cervical cancer cell line (HeLa) andNIH3T3 cells. Colon cancer and the HepG2 liver cancer cell lineswere less susceptible to the effects of the three compounds whencompared to other cell types; Caco-2 cells proved to beparticularly resistant to the effects of these three compounds().
Since each of the three compounds was capable ofreducing cell viability, at least of certain cancer and non-cancercell lines, we also aimed to determine whether this reduction incell viability occurred through the induction of apoptosis. Weexamined whether compounds 1, 2 and 3 treatment led to increasedcaspase 3/7 activity or increased DNA fragmentation (as measured bya TUNEL assay). We did not detect an increase in either of theseapoptotic features in either HepG2 or Hepa1–6 cells in response totreatment with any of the three compounds analyzed (data notshown). Taken together, these data suggest that the ability ofcompounds 1, 2 and 3 to reduce cell viability occurs through anapoptosis-independent mechanism.
Previous reports have identified that the peakemission wavelength of pyrene is less than 400 nM, with a shoulderfor that emission peak at approximately 420 nM (,).Similarly, chrysene was previously shown to exhibit a peak emissionwavelength of less than 400 nM, with a shoulder for its emissionpeak at approximately 425 nM ().Therefore, we aimed to determine whether PAH derivatives 1–3 wouldhave an impact on the absorption and spectral emission patterns ofthese molecules. Although no significant absorbance was detectedfor compounds in this study, i.e., compounds 1, 2 and 3, atwavelengths between 350 and 650 nM, we detected a fluorescenceemission spectrum for each of the PAH derivatives. The peakemission wavelength for both isobutyl pyren-4-ylcarbamate (compound2) and N-(isobutoxymethyl)pyren-4-amine (compound 3) occurredbetween 460 and 470 nM ( and). However, isobutylchrysen-6-ylcarbamate (compound 1) exhibited a much smalleremission spectra (), withshoulders for its peak at 420 and 525 nM, when compared tocompounds 2 and 3 (ig. 4 vs. and ). The limitedfluorescence of this compound was possibly due to its crystallizingin aqueous solution, since this emission peak was larger, albeit atthe same wavelength, when compound 3 was dissolved in an organicsolvent, DMSO (data not shown). Nonetheless, these data indicatethat the addition of the long chains to either chrysene or pyrenecaused a red-shift in spectral emission when compared to the PAHs(chrysene or pyrene).
Cells were plated onto a 96-well dish (5,000cells/well) and incubated overnight at 37°C. The following day,cells were treated with increasing dosages (3–100 μM) of eachcompound, which had been dissolved in DMSO. The DMSO concentrationof treatments was limited to 0.5%, and cells were treated with DMSOalone (0.5%) or 10 μM doxorubicin as negative and positive controlsfor cytotoxicity, respectively. After 48 h, cells were fixed andcell viability was analyzed using the Sulforhodamine B colorimetricassay as previously described (). Absorbance of SRB was measuredutilizing a SpextraMaxM5 plate reader and absorbance values werenormalized to non-treated cells. The normalized cell viability withincreasing drug doses was plotted on a four-parameter logisticalcurve, and the IC of each compound in each cell linewas calculated using SigmaPlot software (Systat Software, Inc.,Chicago, IL, USA). Each compound was synthesized in two independentreactions and used in cell viability assays to generatedose-response curves. The mean IC (in μM), with thecorresponding standard deviation of the two independent synthesisreactions, was then calculated.
A wide variety of planar ring systems are capable ofintercalating with DNA, giving rise to many drugs that possesschemotherapeutic activity. In this context, three new polyaromaticderivatives containing polar side chains were systematicallysynthesized and investigated. The primary mode of action of theseintercalators is believed to be their reversible binding to nuclearDNA, which causes inhibition of the replication process and, thus,cell death. As is well-known, cytotoxicity is not only dependent onthe ability to interact with DNA. Instead, the drug must be capableof interacting with DNA to form a stable ternaryDNA-intercalator-enzyme complex with a relatively long half-life insuch a way that the enzymatic process cannot progress (). Therefore, the low level ofcytotoxicity observed for compounds 1–3 may be ascribed to aninability to access nuclear DNA or a low binding association(including a low affinity or highly transient inter-action) toDNA.