The Chiral Recognition of Optically Active Poly(triphenylmethyl methacrylate) Derivatives as Stationary Phases for HPLC

Four meta-halogen- or meta-methyl-substituted optically active poly(triphenylmethyl methacrylate) [poly(TrMA)] derivatives with a one-handed helical structure were coated on macroporous silica gel and their chiral-recognition abilities as stationary phases for high-pherformance liquid chromatography were investigated with methanol or hexane–2-propanol (95:5(v/v)) as the eluent. The chiral-recognition abilities of poly(m-fluorophenyldiphenylmethyl methacrylate) and poly(m-chlorophenyldiphenylmethyl methacrylate) were slightly low compared with that of poly(TrMA) when methanol was used as the eluent. Poly[tris(m-chlorophenyl)methyl methacrylate] [poly(m-Cl3TrMA)] showed no resolving ability, although poly[tris(m-tolyl)methyl methacrylate] [poly(m-Me3TrMA)] had an effective chiral recognition ability and resolved some racemates more efficiently than poly(TrMA). When hexane–2-propanol (95/5) was used as the eluent, the optical-resolution abilities of all these chiral polymers except for poly(m-Cl3TrMA) were rather similar to that of poly(TrMA) under the same eluent system. The chiral-adsorbing sites are considered to be the chiral triarylmethyl propellers in the methanol system; carbonyl groups may also be involved in the hexane–2-propanol system. The difference in the chiral-recognition abilities of the two tri-substituted chiral polymers were ascribed to their different propeller structures and/or the different conformations of their carbonyl groups. The optical-resolution abilities of poly[TrMA-co-(m-Cl3TrMA)] and poly[TrMA-co-(m-Me3TrMA)] were also investigated. From the results, the mechanism of the separation of enantiomers on poly(TrMA) was discussed.