2-Hydroxy-2,6,10,10-tetramethyl-1-oxaspiro[4.5]dec-6-en-8-one: Precursor of 8,9-Dehydrotheaspirone in White-Fleshed Nectarines

2-Hydroxy-2,6,10,10-tetramethyl-1-oxaspiro[4.5]dec-6-en-8-one ( 2 ) was identified as precursor of 2,6,10,10-tetramethyl-1-oxaspiro[4.5]deca-2,6-dien-8-one (8,9-dehydrotheaspirone, 1 ) in an Et 2 O extract from white-fleshed nectarine ( Prunus persica Batsch var. nucipersica Schneid) juice. The identification was verified by comparison of chromatographic and spectral data (MS, 1 H and 13 C NMR) of the new natural product with those of an authentic reference compound synthesized from dehydrovomifoliol ( 3 ). NMR spectral data revealed that the precursor compound 2 is present in 5:1 mixture of diastereomeric hemiacetals 2a/b . The absolute stereochemistry of the diastereoisomers (major isomer, 2 S,5 S; minor isomer, 2 R,5 S ) was elucidated by NOE experiments and dehydration to optically pure ( S -configured) spiroether 1 . In addition to hemiacetals 2a/b, (6 S )-dehydrovomifoliol ( 3 ) as well as the β- d -glucoside of (3 S,5 R,6 S )-3-hydroxy-5,6-epoxy-β-ionone ( 5 ) was also identified in nectarine juice. Keywords: 2-Hydroxy-2,6,10,10-tetramethyl-1-oxaspiro[4.5]dec-6-en-8-one; 2,6,10,10-tetramethyl-1-oxaspiro[4.5]deca-2,6-dien-8-one; 8,9-dehydrotheaspirone; enantiodifferentiation; dehydrovomifoliol; 3-hydroxy-5,6-epoxy-β-ionone 3- O -β- d -glucoside; white-fleshed nectarines; Prunus persica Batsch var. nucipersica Schneid; Rosaceae