10.1246/cl.1982.1409
The research aimed to prepare and assess the chiral recognition of new chiral 18-crown-6 ethers, which are macrocyclic polyethers with phenyl, 1-naphthyl, or tetramethylphenyl substituents. The purpose was to enhance the chiral recognition capabilities of these compounds, particularly for 1-phenylethylamine, and to understand their complexation equilibria with racemic primary alkylammonium salts. The researchers synthesized four new chiral macrocyclic polyethers through a series of reactions starting from ethyl-(L)-tartarate and involving various reagents such as 1-naphthol, NaH, DMF, Grignard reagents, Li2CuCl4, and NaBH4. The chiral recognition was measured by distributing racemic 1-phenylethylamine salt between H2O and CHCl3 layers, with the organic layer containing the chiral crown ethers. The study concluded that crown ethers (3a), (3c), and (3d) recognized the chirality of the amine salt, with the exception of (3b), suggesting that the rigidity and size of the substituents play a crucial role in chiral recognition. The researchers are continuing their work to prepare other chiral 18-crown-6 type ethers with larger and more rigid substituents to further improve chiral recognition.
10.1016/S0040-4020(01)96536-6
The research investigates the enzyme-catalyzed hydrolysis of dialkylated propanedioic acid diesters, focusing on how the chain length of the alkyl substituents impacts enantioselectivity. Pig liver esterase and chymotrypsin were utilized as catalysts. A notable reversal of enantioselectivity from pro-5 to pro-1 was observed based on the alkyl chain length. For instance, substrates with short alkyl chains (1-3 and 8-10) yielded up to 73% enantiomeric excess (e.e.) of the R-enantiomer when hydrolyzed by pig liver esterase, while longer chain homologues (4-6 and 11) produced the L-enantiomer with almost 90% e.e. In the case of chymotrypsin, it selectively hydrolyzed benzylmethylpropanedioic acid diesters to yield optically pure monoesters. The study also involved the synthesis of dialkylated propanedioic acid diesters through reactions with sodium, methanol, propanedioic acid dimethyl ester, and various alkyl halides. The enantiomeric excess was determined using NMR spectroscopy in the presence of optically pure l-phenylethylamine. The absolute configuration was established through a series of chemical transformations, including acyl-azide formation and Curtius rearrangement, starting from the optically pure monoester obtained via chymotrypsin hydrolysis. The research provides valuable insights into the structural effects on the kinetics and enantioselectivity of enzyme-catalyzed reactions, which can be applied in the synthesis of chiral compounds with biological or pharmacological significance.
10.1021/jo00171a038
The purpose of this study is to explore the reaction pathways and products formed when primary amines react with organolithium compounds under mild conditions. The researchers used various primary amines, such as benzylamine, 1-hexanamine, and 1-phenylethanamine, along with organolithium reagents like n-butyllithium, tert-butyllithium, methyllithium, and phenyllithium. The study concluded that these reactions primarily involve three steps: mono- and dilithiation of the primary amine, elimination to form N-lithioimines, and addition of the organolithium compound to the lithioimine. The products include imines, α-substituted primary amines, and N-alkylimines.
10.1246/cl.1980.843
The research focuses on the synthesis and characterization of optically active perfluoro-2-propoxypropionic acid. The key chemicals involved include perfluoro-2-propoxypropionyl fluoride, which was prepared by the anionic dimerization of perfluoro-1,2-epoxypropane using tetramethylurea in diglyme. This fluoride reacted with (-)-1-phenylethylamine to form a mixture of diastereomeric amides. These amides were separated chromatographically, and their subsequent hydrolysis yielded the enantiomers of perfluoro-2-propoxypropionic acid, marking the first example of optically active organic perfluoro compounds. The study highlights the potential of these compounds as reagents for analyzing enantiomers and as solvents for 1H NMR analysis of chiral molecules, given their stability and lack of hydrogen atoms.
C
