We synthesized a series of novel macrocycles with diamide-diester groups (S,S)-1, (S,S)-2, (S,S)-3, and (R,R)-1, derived from dimethyloxalate and amino alcohols by high dilution technique, and evaluated enantiomeric recognition properties of these macrocycles toward primary alkyl ammonium salts by 1H NMR titration. Taking into account the host employed, important differences were observed in the Ka values of (R)-Am and (S)-Am for (S,S)-1 and (R,R)-1 hosts, KS/KR = 5.55 and KR/KS = 3.65, Delta Delta Go = 0.43 and -0.32 kJ mol-1, respectively. There seems a general tendency for the host to include the guests with the same absolute configuration.
This study consists of two parts. In the first part of the study; a Pirkle-type chiral stationary phase was prepared by synthesizing an aromatic amine derivative of (R)-2-amino-1-butanol as a chiral selector and binding to L-tyrosine-modified cyanogen bromide (CNBr)-activated Sepharose 4B and then, packed into the separation column. The chromatographic performance of the separation column was evaluated with racemic mandelic acid and 2-phenylpropionic acid by using phosphate buffers at three different pHs as mobile phase. In the resolution processes, the prepared solutions were loaded onto the separation column at two different concentrations and at three different pHs for each racemic organic acid, separately. Enantiomeric excess (ee%) of the eluates was determined on CHIRALPAK AD-H chiral analytical column by HPLC. The maximum ee% for mandelic acid and 2-phenylpropionic acid was determined to be 60.84 and 27.4, respectively. Separation factors (k 1 ' , k 2 ' , α, and Rs) were calculated for each acid. The structures of the obtained compounds were characterized using the spectroscopic methods (NMR, and elemental analysis). In the second part of the study; enantioselective interactions between the prepared CSP and the analytes have been widely studied by docking, molecular dynamics simulation and quantum mechanical computation methods. The reason of column eluation of rac-2-phenylpropionic acid with lower enantiomeric yield was explained by these techniques.
Two novel C2-symmetrical chiral tetraamide compounds derived from (S)-isoleucine were synthesised and their enantiomeric recognition abilities towards enantiomers of some amino acid esters and 1-arylethylamins were examined by UV-titration method. These receptor compounds exhibited strong complexation (with Ka up to 5787.23 M-1) and very good enantioselectivity (up to KaS/KaR= 13.98).
A new mixed-mode stationary phase derived from [2-(3,4epoxycyclohexyl)ethyl]trimethoxysilane as a coupling reagent was synthesized and evaluated for hydrophilic-interaction/ reversed-phase/ion-exchange HPLC. This phase bearing polar groups as well as nonpolar aliphatic and aromatic groups was synthesized starting from [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane and isoleucine amino acid, and it was characterized by elemental analysis, FTIR spectroscopy, SEM, and solid-state 13 C NMR. The new stationary phase offers hydrophilic interaction, reversed-phase and ion-exchange functionalities, which facilitate the simultaneous separation of polar, nonpolar, and ionic compounds. Several polar nonpolar compounds were tested to investigate the retention properties of the new phase. Seven water-soluble vitamins and five nucleobases/nucleosides were tested to investigate the effectiveness of the new phase in HILIC mode. Six water-soluble vitamins were separated successfully by gradient elution and the five nucleobases/ nucleosides were separated by isocratic elution. Numerous polar and nonpolar small compounds were tested under RPLC conditions, while six selected benzoic acids were tested for the IEC properties of the new phase, and these were also separated successfully. Quantitative structure-activity relationships between the test compounds and the new stationary phase are discussed according to logP, logD and pKa values.[a] M.
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