1,1,6-TRIMETHYL-1,2-DIHYDRONAPHTHALENE (TDN) FORMATION IN WINE .1. STUDIES ON THE HYDROLYSIS OF 2,6,10,10-TETRAMETHYL-1-OXASPIRO[4.5]DEC-6-ENE-2,8-DIOL RATIONALIZING THE ORIGIN OF TDN AND RELATED C-13 NORISOPRENOIDS IN RIESLING WINE

In a glycosidic fraction of Riesling wine, obtained by retention of the glycosides on C18 reversed-phase adsorbent followed by enzymatic hydrolysis and trimethylsilylation of the liberated aglycons, capillary gas chromatography (HRGC) and capillary gas chromatography-mass spectrometry (HRGC-MS) revealed the occurrence of 2,6,10,10-tetramethyl-1-oxaspiro[4.5]dec-6-ene-2,8-diol. The identification was verified by comparison of HRGC and MS data of TMS derivatives of the new natural product with those of an authentic reference compound. Heating a diastereoisomeric mixture of synthetic 2,6,10,10-tetramethyl-1-oxaspiro[4.5]dec-6-ene-2,8-diols under simultaneous distillation/extraction (SDE) conditions at pH 3.2 gave a number of volatile C-13 norisoprenoid degradation products, including the important off-flavor-causing wine constituent 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN). Additional volatile degradation products, which have also been found in grape products, included 2,2,6,8-tetramethyl-7,11-dioxatricyclo[6.2.1.0(1,6)]undec-4-ene (Riesling acetal), 4-(2,3,6-trimethylphenyl)-2-butanone,2,10,10-trimethyl-6-methylene-1-oxaspiro[4.5]dec-7-en-2-ol, and, tentatively, 6-hydroxy-1,1,6-trimethyl-1,2,5,6-tetrahydronaphthalene.