1261024-88-7Relevant academic research and scientific papers
Origins of enantioselectivity during allylic substitution reactions catalyzed by metallacyclic iridium complexes
Madrahimov, Sherzod T.,Hartwig, John F.
, p. 8136 - 8147 (2012)
In depth mechanistic studies of iridium catalyzed regioselective and enantioselective allylic substitution reactions are presented. A series of cyclometalated allyliridium complexes that are kinetically and chemically competent to be intermediates in the allylic substitution reactions was prepared and characterized by 1D and 2D NMR spectroscopies and single-crystal X-ray difraction. The rates of epimerization of the less thermodynamically stable diastereomeric allyliridium complexes to the thermodynamically more stable allyliridium stereoisomers were measured. The rates of nucleophilic attack by aniline and by N-methylaniline on the isolated allyliridium complexes were also measured. Attack on the thermodynamically less stable allyliridium complex was found to be orders of magnitude faster than attack on the thermodynamically more stable complex, yet the major enantiomer of the catalytic reaction is formed from the more stable diastereomer. Comparison of the rates of nucleophilic attack to the rates of epimerization of the diastereomeric allyliridium complexes containing a weakly coordinating counterion showed that nucleophilic attack on the less stable allyliridium species is much faster than conversion of the less stable isomer to the more stable isomer. These observations imply that Curtin-Hammett conditions are not met during iridium catalyzed allylic substitution reactions by ≠3-≠1-≠3 interconversion. Rather, these data imply that when these conditions exist for this reaction, they are created by reversible oxidative addition, and the high selectivity of this oxidative addition step to form the more stable diastereomeric allyl complex leads to the high enantioselectivity. The stereochemical outcome of the individual steps of allylic substitution was assessed by reactions of deuterium-labeled substrates. The allylic substitution was shown to occur by oxidative addition with inversion of configuration, followed by an outer sphere nucleophilic attack that leads to a second inversion of configuration. This result contrasts the changes in configuration that occur during reactions of molybdenum complexes studied with these substrates previously. In short, these studies show that the factors that control the enantioselectivity of iridium-catalyzed allylic substitution are distinct from those that control enantioselectivity during allylic substitution catalyzed by palladium or molybdenum complexes and lead to the unique combination of high regioselectivity, enantioselectivity, and scope of reactive nucleophile.
Multifunctional novel Diallyl disulfide (DADS) derivatives with β-amyloid-reducing, cholinergic, antioxidant and metal chelating properties for the treatment of Alzheimer's disease
Manral, Apra,Saini, Vikas,Meena, Poonam,Tiwari, Manisha
, p. 6389 - 6403 (2015/10/05)
A series of novel Diallyl disulfide (DADS) derivatives were designed, synthesized and evaluated as chemical agents, which target and modulate multiple facets of Alzheimer's disease (AD). The results showed that the target compounds 5a-l and 7e-m exhibited significant anti-Aβ aggregation activity, considerable acetylcholinesterase (AChE) inhibition, high selectivity towards AChE over butyrylcholinesterase (BuChE), potential antioxidant and metal chelating activities. Specifically, compounds 7k and 7l exhibited highest potency towards self-induced Aβ aggregation (74% and 71.4%, 25 μM) and metal chelating ability. Furthermore, compounds 7k and 7l disaggregated Aβ fibrils generated by Cu2+-induced Aβ aggregation by 80.9% and 78.5%, later confirmed by transmission electron microscope (TEM) analysis. Besides, 7k and 7l had the strongest AChE inhibitory activity with IC50 values of 0.056 μM and 0.121 μM, respectively. Furthermore, molecular modelling studies showed that these compounds were capable of binding simultaneously to catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. All the target compounds displayed moderate to excellent antioxidant activity with ORAC-FL values in the range 0.546-5.86 Trolox equivalents. In addition, absorption, distribution, metabolism and excretion (ADME) profile and toxicity prediction (TOPKAT) of best compounds 7k and 7l revealed that they have drug like properties and possess very low toxic effects. Collectively, the results strongly support our assertion that these compounds could provide good templates for developing new multifunctional agents for AD treatment.
