ABSTRACT
Binding of anions using macrocyclic structures with a nonpolar interior using the CH···anion interaction as the recognition motif has gained popularity in the past few years, and such receptors often rely on a subtle interplay between enthalpic and entropic factors. For these types of receptors solvation of both the anion and the binding pocket of the macrocyclic host play important roles in the overall energetic picture of the binding event. Systematic chemical modifications of synthetic receptors that are able to bind anions in a variety of solvents is an important tool to gain understanding of the factors that determine the supramolecular chemistry of anions. Here we present the chiral macrocyclic structure biotin-l-sulfoxide[6]uril as a host molecule that binds anions in both water and in organic solvents. Biotin-l-sulfoxide[6]uril is prepared in a highly diastereoselective one-pot synthesis from the macrocycle biotin[6]uril. We compare the binding properties with that of biotin[6]uril, also studied in acetonitrile and in aqueous buffer at neutral pH. The biotin-l-sulfoxide[6]uril generally exhibits stronger recognition of anions in acetonitrile, but weaker binding in water as compared to the biotin[6]uril macrocycle. We have studied the binding events using a combination of NMR spectroscopy, isothermal titration calorimetry (ITC), and computational methods.
ABSTRACT
Confinement of reactive chemical species uniquely affects chemical reactivity by restricting the physical space available and by restricting access to interactions with the solvent. In Nature, for example, confined protein binding pockets govern processes following photoisomerization reactions and the isomerizations themselves. Here we describe the first example of a dihydroazulene/vinylheptafulvene (DHA/VHF) photo-switch functioning in water, and we show how its switching behavior is strongly influenced by supramolecular interactions with a series of cucurbit[n]uril (CB) host molecules. In CB7 inclusion complexes, the kinetics of the thermal VHF-to-DHA back-reaction is accelerated, while in CB8 inclusion complexes, the kinetics is slowed down as compared to the free photo-switch. The effect of the CB encapsulation of the photo-switch can be effectively canceled by introducing a guest that binds the CB more strongly. According to DFT calculations, a stabilization of the reactive s-cis VHF conformer relative to the s-trans VHF appears to be a contributing factor responsible for the accelerated back-reaction when encapsulated in CB7.
ABSTRACT
PURPOSE: We conducted a phase II study to evaluate the efficacy and safety of the combination of irinotecan and paclitaxel in patients with advanced stage non-small cell lung cancer (NSCLC). PATIENTS AND METHODS: Patients were eligible if they had histologically confirmed chemotherapy naïve stage IV NSCLC or stage IIIB disease that was not suitable for combined modality therapy. Patients were treated with irinotecan 50 mg/m2 and paclitaxel 75 mg/m2 on days 1 and 8 of a 21-day cycle. If the patient did not experience >grade 1 toxicity during the first cycle, the dose of irinotecan could be escalated to 60 mg/m(2). Patients were evaluated for tumor response rate, time to progression (TTP), overall survival (OS) and toxicity. RESULTS: Twenty-three eligible patients were treated. Two (9%) patients achieved a partial response. Eight patients (35%) had stable disease. The median number of cycles given per patient was four (range 1-29). The major toxicities were grade >or=3 neutropenia (26%) and grade 3 diarrhea (5%). The median time to progression was 2.8 months (range 0.5-21.8 months) for all patients and 4.3 months for the patients who had either stable disease or a partial response. The median overall survival was 9.2 months (range 0.5-40 months). The one- and two-year survival rates were 39% and 13%, respectively. CONCLUSION: The combination of irinotecan and paclitaxel is safe in advanced NSCLC and affords a survival similar to other non-platinum as well as platinum-based doublets. However, this combination does not have sufficient activity to justify further study in an unselected population. If biomarkers are developed that can guide the selection of chemotherapy in an individual patient, there may be a rationale for further evaluation of this regimen.
