Absolute Configuration and Conformation of 1,3-Dioxanes from Cider

In extracts obtained by liquid-liquid extraction from French cider (2S,4R)- and (2R,4R)-2-methyl-4-pentyl-1,3-dioxane, 1a and 1b as well as (2S,4R)- and (2R,4R)-2-methyl-4-(2′(Z)-pentenyl)-1,3-dioxane, 2a and 2b, were identified by capillary gas chromatography (HRGC) and capillary gas chromatography-mass spectrometry (HRGC-MS). Absolute configuration and conformation of the 1,3-dioxanes was determined by nuclear magnetic resonance (NMR) spectrometry techniques [¹³C, ¹H, nuclear Overhauser enhancement (NOE), and H/H homonuclear decoupling], multidimensional gas chromatography (MDGC), and by comparison with synthesized reference compounds. A nonenzymatic formation of 1a and 1b and 2a and 2b during fermentation of apple juice was proposed leading to 22, 8, 2, and < 1 mg/L of 1a, 2a, 1b, and 2b, respectively in cider.