title: Synthesis of enantiopure 2-aryl-2-methoxypropionic acids and determination of their absolute configurations by X-ray crystallography.
abstract: Racemic 2-aryl-2-methoxypropionic acids were enantioresolved by the use of (S)-(-)-phenylalaninol 4. For instance, racemic 2-methoxy-2-phenylpropionic acid (+/-)-7 was condensed with phenylalaninol (S)-(-)-4 yielding a diastereomeric mixture of amides, which was easily separated by HPLC on silica gel affording the first-eluted amide (-)-13a and the second-eluted amide (+)-13b: alpha = 3.19, Rs = 3.49. The absolute configuration of amide (-)-13a was determined to be (R;S) by X-ray crystallography by reference to the S configuration of the phenylalaninol moiety. Amide (R;S)-(-)-13a was converted to oxazoline (R;S)-(-)-14a, from which enantiopure 2-methoxy-2-phenylpropionic acid (R)-(-)-7 was recovered. Other 2-aryl-2-methoxypropionic acids, (R)-(-)-8, (R)-(-)-9, (R)-(+)-10, (R)-(-)-11, and (R)-(-)-12, were similarly prepared in enantiopure forms with the use of phenylalaninol (S)-(-)-4, and their absolute configurations were clearly determined by X-ray crystallography or by chemical correlation.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Sekiguchi
authors.forename: Junpei
authors.initials: J
authors.lastname: Naito
authors.forename: Hiromi
authors.initials: H
authors.lastname: Taji
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kasai
authors.forename: Akinori
authors.initials: A
authors.lastname: Sugio
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kuwahara
authors.forename: Masataka
authors.initials: M
authors.lastname: Watanabe
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Harada