RESUMEN
A novel fluorescent probe based on a bisbinaphthyl structure has been designed and synthesized. This compound in combination with Zn(II) has exhibited highly enantioselective fluorescence enhancement with 13 common free amino acids. For example, its enantiomeric fluorescent enhancement ratios ( ef or Δ IL/Δ ID) in the presence of the following amino acids are extremely high: 177 for valine, 199 for methionine, 186 for phenylalanine, 118 for leucine, and 89 for alanine. The observed high enantioselectivity and the extent of the substrate scope are unprecedented in the fluorescent recognition of free amino acids. This fluorescent probe can be applied to determine the enantiomeric composition of the structurally diverse chiral amino acids. NMR and mass spectroscopic investigations have provided clues to elucidate the observed high enantioselectivity.
RESUMEN
A fluorophilic fluorescent probe based on a perfluoroalkyl-substituted bis(binaphthyl) compound was designed and synthesized. It displayed a highly enantioselective fluorescence response toward structurally diverse amino acids in a biphasic fluorous/aqueous system with enantiomeric fluorescent enhancement ratio (ef; ΔID /ΔIL ) values up to 45.2 (histidine). It can be used to determine the enantiomeric compositions of amino acids and also allows the amino acid enantiomers to be visually discriminated. NMR and mass-spectroscopic investigations provided insights into the observed high enantioselectivity. This biphasic fluorescent recognition was used to determine the enantiomeric composition of the crude phenylalanine products generated by an enzyme-catalyzed asymmetric hydrolysis under various reaction conditions. The fluorous-phase-based fluorescence measurement under the biphasic conditions was able to minimize the interference of other reaction components and thus has potential in asymmetric reaction screening.
RESUMEN
A 3,3'-di(1-diphenylmethylpiperazinyl)methyl H8BINOL compound, (S)-11, was prepared from the Mannich-type reaction of (S)-H8BINOL with paraformaldehyde and 1-(diphenylmethyl)piperazine. This compound can catalyze the asymmetric reaction of alkyl and aryl alkynes with N-(diphenylphosphinoyl)imines in the presence of Et2Zn and Ti(OiPr)4. It exhibits unprecedented high enantioselectivity (up to 85% ee) for a simple alkyl alkyne addition to the N-(diphenylphosphinoyl)imines. The easy removal of the N-(dipehenylphosphinoyl) protecting groups makes this method practically useful for the asymmetric synthesis of chiral propargyl amines.
RESUMEN
A new catalytic system based on the readily available Zn, (i)PrI, H8BINOL, and Ti(O(i)Pr)4 has been developed which avoids the use of pyrophoric ZnEt2. It can effectively catalyze the reaction of various terminal alkynes with aromatic, aliphatic, and vinyl aldehydes to generate chiral propargylic alcohols at room temperature with up to 98% yield and 98% enantiomeric excess. This new system signifciantly expands the substrate scope of the previously reported system using Zn, EtI, BINOL, and Ti(O(i)Pr)4.