Three one-handed helical poly(phenylacetylene) derivatives bearing L-amino acid ethyl ester pendants

PPA-S-Phe

PPA-S-Leu and PPA-A-Leu were respectively synthesized by the polymerization of the corresponding monomers using Rh(nbd)BPh4 as a catalyst

and their chiral recognition abilities for seven racemates were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) after coating them on silica gel.The difference between PPA-S-Phe and PPA-S-Leu is the chiral pendants.The chiral pendant of PPA-S-Phe is L-phenylalanine ethyl ester

while that of PPA-S-Leu is L-leucine ethyl ester.The difference between PPA-S-Leu and PPA-A-Leu is the linkage groups between polymer main chains and chiral pendants.The linkage of PPA-S-Leu is sulphonamide group

while that of PPA-A-Leu is amide group.PPA-S-Phe

PPA-S-Leu and PPA-A-Leu possess their characteristic helical conformation and show their characteristic chiral recognition depending on the chiral pendants and the linkage groups.When linkage is a sulphonamide group

PPA-S-Leu with L-leucine ethyl ester pendants shows higher chiral recognition abilities than PPA-S-Phe with L-phenylalanine ethyl ester pendants.When chiral pendant is L-leucine ethyl ester

PPA-A-Leu with amide linkage shows higher chiral recognition abilities than PPA-S-Leu with sulphonamide linkage.It is concluded that the linkage groups play an important role in chiral recognition as well as the chiral pendants.