Pyruvic acid Quinuclidine

Theoretical studies aimed at rationalizing the interaction between the chiral modifier and the pyruvate have been undertaken using quantum chemistry techniques, at both ab initio and semi-empirical levels, and molecular mechanics. The studies were based on the experimental observation that the quinuclidine nitrogen is the main interaction center between cinchonidine and the reactant pyruvate. This center can either act as a nucleophile or after protonation (protic solvent) as an electrophile. In a first step, NH3 and NH4 have been used as models of this reaction center, and the optimal structures and complexation energies of the pyruvate with NH3 and NHa, respectively, were calculated [40]. The pyruvate—NHa complex was found to be much more stable (by 25 kcal/mol) due to favorable electrostatic interaction, indicating that in acidic solvents the protonated cinchonidine will interact with the pyruvate. 

In order to reveal the importance of the basic quinuclidine N and the OH group of CD in the enantioselection, the efficiency of CD as chiral modifier of Pt was compared to those of some CD derivatives (Table 3). Two typical trifluoromethyl ketones, 1 and 4, were hydrogenated in an apolar solvent and in acetic acid. Data on ethyl pyruvate 9 hydrogenation are also schown in Table 3 for comparison. 

Protonation of the quinuclidine N by hydrochloric acid had only minor effect on the ee but quaternization led to a complete loss of enantioselection in all three reactions. This is a strong indication that the quinuclidine N of CD is involved in the crucial interaction between reactant and modifier. A H-bond (N-H-0 type interaction) has been proposed for the CD - ethyl pyruvate complex3, which interaction is not possible after methylation of the basic N atom of CD. 

In summary, in the presence of acetic acid and added amount of alkaloid the Pt nanocolloids prepared by using cinchona alkaloids appeared to be highly active and selective in the enantioselective hydrogenation of ethyl pyruvate. We consider that in this type of Pt nanocolloids both the quinuclidine nitrogen and the quinoline ring is involved in the stabilization of the colloidal form, however the presence of acetic acid seems to be also very cmcial in this process. The prepared Pt nanocol-... 

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