Construction of Nitrated Benzo[3.3.1]bicyclic Acetal/Ketal Core via Nitration of o-Carbonyl Allylbenzenes

One-pot synthesis of benzofused 8-oxabicyclo[3.3.1]nonanes via GaCl3-mediated cyclocondensation of o-allylbenzaldehydes and 1,3-dicarbonyl synthons

GaCl3-mediated one-pot cyclocondensation of o-allylbenzaldehydes and 1,3-dicarbonyls generates benzofused 8-oxabicyclo[3.3.1]nonanes in moderate to good yields in refluxing MeNO2 under easy-operational conditions. A plausible mechanism is proposed and discussed here. In the overall reaction process, various metal chloride-promoted conditions were investigated for one-pot cyclocondensation.

6-n-Butoxy-10-nitro-12,13-dioxa-11-azatricyclo[7.3.1.02,7]trideca-2,4,6,10-tetraene Improves the X-ray Sensitivity on Inhibiting Proliferation and Promoting Oxidative Stress and Apoptosis of Oral Cancer Cells

This in vitro study examines the anti-oral cancer effects and mechanisms of a combined X-ray/SK2 treatment, i.e., X-ray and 6-n-butoxy-10-nitro-12,13-dioxa-11-azatricyclo[7.3.1.02,7]trideca-2,4,6,10-tetraene (SK2). ATP cell viability and flow cytometry-based cell cycle, apoptosis, oxidative stress, and DNA damage assessments were conducted. The X-ray/SK2 treatment exhibited lower viability in oral cancer (Ca9-22 and CAL 27) cells than in normal (Smulow-Glickman, S-G) cells, i.e., 32.0%, 46.1% vs. 59.0%, which showed more antiproliferative changes than with X-ray or SK2 treatment. Oral cancer cells under X-ray/SK2 treatment showed slight subG1 and G2/M increments and induced high annexin V-monitored apoptosis compared to X-ray or SK2 treatment. The X-ray/SK2 treatment showed higher caspase 3 and 8 levels for oral cancer cells than other treatments. X-ray/SK2 showed a higher caspase 9 level in CAL 27 cells than other treatments, while Ca9-22 cells showed similar levels under X-ray and/or SK2. The X-ray/SK2 treatment showed higher reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) depletion than other treatments. Meanwhile, the mitochondrial superoxide (MitoSOX) and glutathione levels in X-ray/SK2 treatment did not exhibit the highest rank compared to others. Moreover, oral cancer cells had higher γH2AX and/or 8-hydroxy-2-deoxyguanosine levels from X-ray/SK2 treatment than others. All these measurements for X-ray/SK2 in oral cancer cells were higher than in normal cells and attenuated by N-acetylcysteine. In conclusion, X-ray/SK2 treatment showed ROS-dependent enhanced antiproliferative, apoptotic, and DNA damage effects in oral cancer cells with a lower cytotoxic influence on normal cells.

Antioral Cancer Effects by the Nitrated [6,6,6]Tricycles Compound (SK1) In Vitro

A novel nitrated [6,6,6]tricycles-derived compound containing nitro, methoxy, and ispropyloxy groups, namely SK1, was developed in our previous report. However, the anticancer effects of SK1 were not assessed. Moreover, SK1 contains two nitro groups (NO2) and one nitrogen-oxygen (N-O) bond exhibiting the potential for oxidative stress generation, but this was not examined. The present study aimed to evaluate the antiproliferation effects and oxidative stress and its associated responses between oral cancer and normal cells. Based on the MTS assay, SK1 demonstrated more antiproliferation ability in oral cancer cells than normal cells, reversed by N-acetylcysteine. This suggests that SK1 causes antiproliferation effects preferentially in an oxidative stress-dependent manner. The oxidative stress-associated responses were further validated, showing higher ROS/MitoSOX burst, MMP, and GSH depletion in oral cancer cells than in normal cells. Meanwhile, SK1 caused oxidative stress-causing apoptosis, such as caspases 3/8/9, and DNA damages, such as γH2AX and 8-OHdG, to a greater extent in oral cancer cells than in normal cells. Siilar to cell viability, these oxidative stress responses were partially diminished by NAC, indicating that SK1 promoted oxidative stress-dependent responses. In conclusion, SK1 exerts oxidative stress, apoptosis, and DNA damage to a greater extent to oral cancer cells than in normal cells.

Combined Treatment of Nitrated [6,6,6]Tricycles Derivative (SK2)/Ultraviolet C Highly Inhibits Proliferation in Oral Cancer Cells In Vitro

Combined treatment is an effective strategy to improve anticancer therapy, but severe side effects frequently limit this application. Drugs inhibiting the proliferation of cancer cells, but not normal cells, display preferential antiproliferation to cancer cells. It shows the benefits of avoiding side effects and enhancing antiproliferation for combined treatment. Nitrated [6,6,6]tricycles derivative (SK2), a novel chemical exhibiting benzo-fused dioxabicyclo[3.3.1]nonane core with an n-butyloxy substituent, exhibiting preferential antiproliferation, was chosen to evaluate its potential antioral cancer effect in vitro by combining it with ultraviolet C (UVC) irradiation. Combination treatment (UVC/SK2) caused lower viability in oral cancer cells (Ca9-22 and OC-2) than single treatment (20 J/m² UVC or 10 μg/mL SK2), i.e., 42.3%/41.1% vs. 81.6%/69.2%, and 89.5%/79.6%, respectively. In contrast, it showed a minor effect on cell viability of normal oral cells (HGF-1), ranging from 82.2 to 90.6%. Moreover, UVC/SK2 caused higher oxidative stress in oral cancer cells than normal cells through the examination of reactive oxygen species, mitochondrial superoxide, and mitochondrial membrane potential. UVC/SK2 also caused subG1 increment associated with apoptosis detections by assessing annexin V; panaspase; and caspases 3, 8, and 9. The antiproliferation and oxidative stress were reverted by N-acetylcysteine, validating the involvement of oxidative stress in antioral cancer cells. UVC/SK2 also caused DNA damage by detecting γH2AX and 8-hydroxy-2′-deoxyguanosine in oral cancer cells. In conclusion, SK2 is an effective enhancer for improving the UVC-caused antiproliferation against oral cancer cells in vitro. UVC/SK2 demonstrated a preferential and synergistic antiproliferation ability towards oral cancer cells with little adverse effects on normal cells.

Antiproliferation- and Apoptosis-Inducible Effects of a Novel Nitrated [6,6,6]Tricycle Derivative (SK2) on Oral Cancer Cells

The benzo-fused dioxabicyclo[3.3.1]nonane core is the central framework in several natural products. Using this core, we had developed a novel nitrated [6,6,6]tricycle-derived compound containing an n-butyloxy group, namely, SK2. The anticancer potential of SK2 was not assessed. This study aimed to determine the antiproliferative function and investigated possible mechanisms of SK2 acting on oral cancer cells. SK2 preferentially killed oral cancer cells but caused no harmful effect on non-malignant oral cells. After the SK2 exposure of oral cancer cells, cells in the sub-G1 phase accumulated. This apoptosis-like outcome of SK2 treatment was validated to be apoptosis via observing an increasing annexin V population. Mechanistically, apoptosis signalers such as pancaspase, caspases 8, caspase 9, and caspase 3 were activated by SK2 in oral cancer cells. SK2 induced oxidative-stress-associated changes. Furthermore, SK2 caused DNA damage (γH2AX and 8-hydroxy-2'-deoxyguanosine). In conclusion, a novel nitrated [6,6,6]tricycle-derived compound, SK2, exhibits a preferential antiproliferative effect on oral cancer cells, accompanied by apoptosis, oxidative stress, and DNA damage.

Construction of Sulfonyl Dihydrobenzo[c]xanthen-7-ones Core via NH4OAc/PdCl2/CuCl2-Mediated Double Cyclocondensation of α-Sulfonyl o-Hydroxyacetophenones with 2-Allylbenzaldehydes

NH₄OAc/PdCl₂/CuCl₂ mediated domino double cyclocondensation of α-sulfonyl o-hydroxyacetophenones and 2-allylbenzaldehydes provides tetracyclic sulfonyl dihydrobenzo[c]xanthen-7-one core with good to excellent yields in MeOH. The intermediates contain a 3-sulfonyl flavanone motif. Only water is generated as a byproduct. The use of various catalysts and reaction conditions is studied for the facile-operational conversion.

Direct access to substituted benzo[b]carbazoles through cascade annulation of 2-vinylbenzaldehydes with indoles

A highly efficient palladium-catalyzed cascade annulation of 2-vinylbenzaldehydes with indoles has been achieved to afford 6-(3-indolyl)benzo[b]carbazoles under mild conditions in good yield and with excellent regioselectivity.

mCPBA-Mediated Intramolecular Oxidative Annulation of ortho-Crotyl or Cinnamyl Arylaldehydes: Synthesis of Benzofused Five-, Six-, and Seven-Membered Oxacycles

mCPBA-mediated intramolecular oxidative annulation of ortho-crotyl or cinnamyl arylaldehydes provides chroman, coumaran, isochroman, and tetrahydrobenzo[ c]oxepine under different reaction conditions. This research investigates the reaction conditions for facile and efficient transformation.

Construction of Sulfonyl Oxabenzo[3.3.1]bicyclic Core via Cyclocondensation of β-Ketosulfones and o-Formyl Allylbenzenes

NH₄OAc mediated domino Knoevenagel/Diels-Alder cyclocondensation of β-ketosulfones 1 and o-formyl allylbenzenes 2 provides sulfonyl oxabenzo[3.3.1]bicyclic core 4 in a cosolvent of toluene and HOAc (v/v = 1/1) at reflux for 3 h. The intermediate 3 contains a chalcone motif. The uses of various ammonium salts and solvent systems are investigated for facile and efficient transformation. The plausible mechanisms have been proposed and the DFT calculations have been included.

Metal triflate promoted synthesis of naphthalenes

A synthetic route to derive the skeleton of naphthalenes starting with isovanillin is described with modest total yields via the key transformation of metal triflate-mediated intramolecular benzannulation of o-formyl or o-benzoyl allylbenzenes in MeNO₂ at rt.