4 research outputs found
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The Role of Catalyst-Catalyst Interactions in Asymmetric Catalysis with (salen)Co(III) Complexes and H-Bond Donors
In asymmetric catalysis, interactions between multiple molecules of catalyst can be important for achieving high catalyst activity and stereoselectivity. In Chapter 1 of this thesis, we introduce catalyst-catalyst interactions in the context of the classic Kagan nonlinear effect (NLE) experiment, and present examples of the strengths and drawbacks of the NLE experiment. For the remainder of the thesis, we explore catalyst-catalyst interactions in the context of two different reactions. First, in Chapter 2, we apply a combination of reaction kinetics and computational chemistry to a reaction that is well known to require the cooperative action of two molecules of catalyst: the (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides. In our investigation, we demonstrate that stereoselectivity in the HKR is achieved through catalyst-catalyst interactions and provide a model for how high selectivity and broad substrate scope are achieved in this reaction. In Chapter 3, we focus our attention on the thiourea-catalyzed enantioselective alkylation of alpha-chloroethers with silyl ketene acetal nucleophiles, a reaction that was not known to require the cooperative action of two molecules of catalyst at the outset of our investigation. By using a wide range of physical organic chemistry tools, we established that the resting state of the optimal thiourea catalyst is dimeric under typical reaction conditions, and that two molecules of catalyst work cooperatively to activate the alpha-chloroether electrophile. The implications of this mechanism for catalyst design are discussed.Chemistry and Chemical Biolog
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Mechanistic Basis for High Reactivity of (salen)Co–OTs in the Hydrolytic Kinetic Resolution of Terminal Epoxides
The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with a rate controlled by partitioning between a nucleophilic (salen)Co–OH catalyst and a Lewis acidic (salen)Co–X catalyst. The commonly used (salen)Co–OAc and (salen)Co–Cl precatalysts undergo complete and irreversible counterion addition to epoxide during the course of the epoxide hydrolysis reaction, resulting in quantitative formation of weakly Lewis acidic (salen)Co–OH, and severely diminished reaction rates in the late stages of HKR reactions. In contrast, (salen)Co–OTs maintains high reactivity over the entire course of HKR reactions. We describe here an investigation of catalyst partitioning with different (salen)Co–X precatalysts, and demonstrate that counterion addition to epoxide is reversible in the case of the (salen)Co–OTs. This reversible counterion addition results in stable partitioning between nucleophilic and Lewis acidic catalyst species, allowing highly efficient catalysis throughout the course of the HKR reaction.Chemistry and Chemical Biolog
Pioglitazone Therapy in Patients With Stroke and Prediabetes: A Post Hoc Analysis of the IRIS Randomized Clinical Trial.
Importance: In the Insulin Resistance Intervention After Stroke (IRIS) randomized clinical trial, pioglitazone, an insulin-sensitizing agent, reduced the risk for recurrent stroke or myocardial infarction (MI) among patients with insulin resistance. However, insulin resistance is not commonly measured in clinical practice.
Objective: To analyze the effects of pioglitazone in patients with good adherence as well as intention-to-treat effects of pioglitazone in patients with prediabetes in the IRIS trial.
Design, Setting, and Participants: The IRIS trial was a randomized multicenter clinical trial in patients with prior stroke or transient ischemic attack as well as insulin resistance but not diabetes. Patients were enrolled from February 2005 to January 2013, and the median follow-up was 4.8 years. The post hoc analyses reported here were performed from June to September 2018. Per American Diabetes Association criteria, prediabetes was defined as having a hemoglobin A1c level of 5.7% to 6.4% or fasting plasma glucose level of 100 mg/dL to 125 mg/dL (to convert to mmol/L, multiply by 0.0555). Good adherence was defined as taking 80% or more of the protocol dose. Fasting glucose and hemoglobin A1c, used to define prediabetes, and adherence of 80% or higher, stipulated in the protocol as defining good adherence, were prespecified subgroups in the analysis plan.
Interventions: Participants were randomized to 15 mg of pioglitazone, with dose titrated to target of 45 mg daily, or matching placebo.
Main Outcomes and Measures: The primary outcome was recurrent stroke or MI. Secondary outcomes included stroke, acute coronary syndrome, stroke/MI/hospitalization for heart failure, and progression to diabetes.
Results: Among 3876 participants analyzed in the IRIS trial, 2885 were included in this analysis (1456 in the pioglitazone cohort and 1429 in the placebo cohort). The mean (SD) age of patients was 64 (11) years, and 974 (66.9%) and 908 (63.5%) of patients were men in the pioglitazone and placebo cohort, respectively. In the prediabetic population with good adherence (644 of 1456 individuals [44.2%] in the pioglitazone group and 810 of 1429 [56.7%] in the placebo group), the hazard ratios (95% CI) were 0.57 (0.39-0.84) for stroke/MI, 0.64 (0.42-0.99) for stroke, 0.47 (0.26-0.85) for acute coronary syndrome, 0.61 (0.42-0.88) for stroke/MI/hospitalization for heart failure, and 0.18 (0.10-0.33) for progression to diabetes. There was a nonsignificant reduction in overall mortality, cancer, and hospitalization, a slight increase in serious bone fractures, and an increase in weight gain and edema. Intention-to-treat results also showed significant reduction of events but to a lesser degree. Hazard ratios (95% CI) were 0.70 (0.56-0.88) for stroke/MI, 0.72 (0.56-0.92) for stroke, 0.72 (0.52-1.00) for acute coronary syndrome, 0.78 (0.63-0.96), for stroke/MI/hospitalization for heart failure, and 0.46 (0.35 to 0.61) for progression to diabetes.
Conclusions and Relevance: Pioglitazone may be effective for secondary prevention in patients with stroke/transient ischemic attack and with prediabetes, particularly in those with good adherence.
Trial Registration: ClinicalTrials.gov identifier: NCT00091949