Extracts obtained by XAD solid-phase extraction of apple juice and cider we
re separated by liquid chromatography on silica gel. Several new 1,3-dioxan
es including the known 2-methyl-4-pentyl-1,3-dioxane and 2-methyl-4-[2'(Z)-
pentenyl]-1,3-dioxane, were identified in the nonpolar fractions by GC/MS a
nalysis and confirmed by chemical synthesis. The enantioselective synthesis
of the stereoisomers of the 1,3-dioxanes was performed using (R)- and (R,S
)-actane-1,3-diol and (R)- and (R,S)-5(Z)-octene-1,3-diol as starting mater
ial. Comparison with the isolated products indicated that the natural produ
cts consisted of a mixture of (2S,4R) and (2R,4R) stereoisomers in the rati
o of approximately 10:1, except for 1,3-dioxanes generated from acetone and
2-butanone. It is assumed that the 1,3-dioxanes are chemically formed in t
he apples and cider from the natural apple ingredients (R)-octane-1,3-diol,
(R)-5(Z)-octene-1,3-diol, (3R,7R)- and (3R,7S)-octane-1,3,7-triol, and the
appropriate aldehydes and ketones, which are produced either by the apples
or by yeast during fermentation of the apple juice.