Enantiomeric Purity and Odor Characteristics of 2- and 3-Acetoxy-1,8-cineoles in the Rhizomes of <i>Alpinia </i><i>g</i><i>alanga</i> Willd.

Abstract

( S )-(+)- O -methylmandelate esters of trans - and cis -1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-5- and 6-ols (2- and 3-hydroxy-1,8-cineoles) were prepared, and eight diastereomers were separated. The absolute configuration of the asymmetric carbons of the cineole moiety of each diastereomer was determined by 1 H NMR data according to the Mosher theory. Each mandelate was reduced with LiAlH 4 to obtain optically pure hydroxy-1,8-cineoles, this being followed by acetylation to afford optically pure acetoxy-1,8-cineoles. These acetates were subjected to chiral GC, using a cyclodextrin column, and the enantiomeric purity of trans - and cis -1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-5- and 6-yl acetates in the aroma concentrate from the rhizomes of Alpinia galanga was determined as 93.9 (5 S ), 19.4 (5 R ), 63.5 (6 R ), and 100 (6 R ) % ee, respectively. The aroma character of each enantiomer was also evaluated by GC-sniffing. Keywords: Alpinia galanga W.; rhizome; enantiomeric purity; odor; acetoxy-1,8-cineole; 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-yl acetate; 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-5-yl acetate; O -methylmandelate