Separation of chiral primary amino compounds by forming a sandwiched complex in reversed-phase high performance liquid chromatography

Separation of chiral primary amino compounds was efficiently achieved under reversed-phase high performance liquid chromatography (RP-HPLC) conditions using a mixture of non-chiral crown ether (18-crown-6) and dimethyl-β-cyclodextrin (DM-β-CD) in the mobile phase. Under these conditions, the amino group of the chiral compound was protonated in a low pH mobile phase, and then interacted with 18-crown-6 and DM-β-CD to form a sandwiched complex [18-crown-6 + amine + CD]. Enantiomers of the compound in the sandwiched complex were separated with good enantioselectivity. Formation of the sandwiched complex among the chiral compound and additives in the mobile phase is a key step of the chiral separation. Four different chiral amino compounds namely, 1-aminoindan (AI), 1,2,3,4-tetrahydro-1-naphthylamine (THNA), tyrosine (Tyr), and phenylalanine (Phe), were selected to demonstrate the separation using the sandwiched complex mechanism in RP-HPLC.