1985 Volume 10 Issue 1 Pages 75-79
Optically pure ethyl (R)-(+) and (S)-(-)-2-[4-(6-chloro-2-quinoxalinyloxy) phenoxy] propanoate ((R)-(+)-1 and (S)-(-)-1) were synthesized from the corresponding propanoic acids ((R)-(+)-1-acid and (S)-(-)-1-acid), which were prepared from the racemic compound by optical resolution with cinchonidine and cinchonine. Both (R)-(+) and (S)-(-)-1-acid were converted into the corresponding acyl chlorides followed by the reaction with ethanol in the presence of pyridine to afford optically pure (R)-(+) and (S)-(-)-1, respectively. Optical purity was determined by the measurement of 200MHz NMR spectra using Eu(HFC)3 shift reagent and by the preferential crystallization. It became clear that optically pure (R)-(+)-1 had [α]20D+39.9° (CHCl3, c=1.20%). The growth inhibiting activity against rice plants in petridish and the post-emergence herbicidal activity against Echinochloa crus-galli and Digitaria adscendens were examined. The herbicidal activity was influenced mainly by chiral center at the propanoic acid moiety and the (R)-(+)-isomer was the most active.
