Enantioseparation of racemic organic ammonium perchlorates by a silica gel bound optically active di-tert-butylpyridino-18-crown-6 ligand
摘要:
Both enantiomers of the novel chiral di-tert-butylpyridino-18-crown-6 ligand (R,R)-7 and (S,S)-7 containing an allyloxy group on the pyridine subcyclic unit were prepared by the reaction of 4-allyloxy-2,6-pyridinedimethyl ditosylate 9 and the enantiomers of di-tert-butyl-substituted tetraethylene glycol (R,R)-8 and (S,S)-8 in the presence of a strong base. One of them, (R,R)-7, was covalently attached to silica gel, and this chiral stationary phase (CSP) separated four selected racemic organic ammonium perchlorates into their enantiomers by column chromatography. (C) 1999 Elsevier Science Ltd. All rights reserved.
Seven new enantiomerically pure chiral pyridino-crown ethers (S,S)-4-(R,R)-10 were prepared. Three of them [(S,S)-4, (S,S)-7 and (R,R)-10] contain one, and two of them [(S,S)-5 and (S,S)-8] contain two linker chains with a terminal double bond. These linker chains were connected to the carbon atom at position 9 (opposite the pyridine moiety) of the macrocycle. The terminal double bond of the linker makes it possible to attach these ligands to silica gel to obtain chiral stationary phases (CSPs). The enantioselectivity of the new ligands toward the enantiomers of alpha-(1-naphthyl)ethylammonium perchlorate (NEA) was also determined by a titration H-1 NMR method. (C) 1999 Elsevier Science Ltd. All rights reserved.