Isoproturon Reappearance after Photosensitized Degradation in the Presence of Triplet Ketones or Fulvic Acids

Isoproturon (IPU) is a phenylurea herbicide used to control broad-leaf grasses on grain fields. Photosensitized transformation induced by excited triplet states of dissolved organic matter (³DOM*) has been identified as an important degradation pathway for IPU in sunlit waters, but the reappearance of IPU in the absence of light is observed after the initial photolysis. In this study, we elucidate the kinetics of this photodegradation and dark-reappearance cycling of IPU in the presence of DOM proxies (aromatic ketones and reference fulvic acids). Using mass spectrometry and nuclear magnetic resonance spectroscopic techniques, a semi-stable intermediate (IPU_int) was found to be responsible for IPU reversion and was identified as a hydroperoxyl derivative of IPU. IPU_int is photogenerated from incorporation of diatomic oxygen to IPU and is subjected to thermolysis whose rate depends on temperature, pH, the presence of DOM, and inorganic ions. These results are important to understand the overall aquatic fate of IPU and structurally similar compounds under diurnal conditions

Method for the Preparation of Derivatives of Heptiptycene: Toward Dual-Cavity Baskets

We have developed a novel synthetic method that enables the preparation of functional derivatives of heptiptycene, i.e., cavitands with two juxtaposed cavities. The homocoupling of bicyclic dibromoalkenes is promoted by Pd­(OAc)₂ (10%) in dioxane (100 °C) to give cyclotrimers in 27–77% yield under optimized reaction conditions (Ph₃P, K₂CO₃, <i>n</i>-Bu₄NBr, N₂, 4 Å MS). These dual-cavity baskets show a strong π → π* absorption at 241 nm (ε = 939 000 M^–1 cm^–1), along with a subsequent fluorescence emission at 305 nm

Chemistry of Ring-Substituted 4‑(Benzothiazol-2-yl)phenylnitrenium Ions from Antitumor 2‑(4-Aminophenyl)benzothiazoles

Ring-substituted derivatives of 2-(4-aminophenyl)­benzothiazole, <b>1a</b>, <b>1b</b>–<b>g</b>, are under development as antitumor agents. One derivative, <b>1f</b>, has reached phase 1 clinical trials as the prodrug <b>2f</b>, Phortress (NSC 710305). These amines are activated by CYP450 1A1, apparently into hydroxylamines <b>8a</b>–<b>g</b> that are likely metabolized into esters that ionize into nitrenium ions responsible for cellular damage. Previously we showed that <b>9a</b>, the acetic acid ester of <b>8a</b>, generates the long-lived (530 ns) nitrenium ion <b>11a</b> by hydrolysis or photolysis in water. In this study, azide trapping shows that <b>9b</b>–<b>g</b> generate <b>11b</b>–<b>g</b> via rate-limiting N–O heterolysis. Ion lifetimes, estimated from azide/solvent selectivities, range from 250 to 1150 ns with identical lifetimes for <b>11a</b> and <b>11f</b>. Differences in biological activity of the amines are likely not due to differences in the chemistry of the cations but to differences in metabolic activation/deactivation of individual amines. Unlike the nitrenium ions, lifetimes of the esters are strongly dependent on the 3′-Me substituent. Esters containing 3′-Me (<b>9b</b>, <b>9f</b>, <b>9g</b>) have lifetimes of 5–10 s compared to 400–800 s for esters without 3′-Me (<b>9a</b>, <b>9c</b>, <b>9d</b>, <b>9e</b>). This restricts 3′-Me esters to cells/tissues in which activation occurs, concentrating their effects in tumor cells if metabolism is restricted to those cells