Norisoprenoids in Vitis vinifera White Wine Grapes and the Identification of a Precursor of Damascenone in These Fruits

Twenty-four norisoprenoids , which are either free volatile components of juices of Vitis vinifera cvv . Chardonnay, Semillon and Sauvignon Blanc, or are liberated by glycosidase enzyme, or acid hydrolysis of extracts of these juices, have been identified. Eleven of these norisoprenoids are reported as grape products for the first time. The hypothetical 7-oxomegastigmane precursors, grasshopper ketone (5) and megastigm-5-en-7-yne-3,9-diol (10), as well as the related allene, 9-hydroxymegastigma-4,6,7-trien-3-one (6), have been observed for the first time, cooccurring with damascenone (1), 3-hydroxy- β- damascone (2) 3-oxo-β-damascone (3) and 3-oxo-α-damascone (4). Hydrolytic studies have shown that megastigm-5-en-7-yne-3.9-diol (10) is a precursor of damascenone (1) and 3-hydroxy- β- damascone (2) during wine conservation.