4-HYDROXY-7,8-DIHYDRO-BETA-IONONE AND ISOMERIC MEGASTIGMA-6,8-DIEN-4-ONES - NEW C-13 NORISOPRENOIDS IN QUINCE (CYDONIA-OBLONGA, MILL) FRUIT

In a polar fraction of an extract obtained from quince fruit juice (Cydonia oblonga, Mill.) by solvent extraction and subsequent liquid chromatographic separation on silica gel, capillary gas chromatography (HRGC) and capillary gas chromatography-mass spectrometry (HRGC-MS) revealed the occurrence of 4-hydroxy-7,8-dihydro-β-ionone. The identification was verified by comparison of HRGC and MS data of the new natural product with those of a synthesized reference compound. In addition, biomimetic studies with another 4-oxygenated ionone derivative from quince fruit, i.e., 4-hydroxy-β-ionol, were carried out. Heat treatment of this diol at pH 3.5 gave a number of volatile C13norisoprenoids, including 2,2,6,7-tetramethylbicyclo[4.3.0]nona-4,7,9(l)-triene, isomeric retro-α-ionones, megastigma-5,8(E)-dien-4-one, and megastigma-5,8(Z)-dien-4-one. As major degradation products (70%) a mixture of four isomeric ketones was obtained. After preparative HPLC separation1H and13C NMR analyses in combination with NOE experiments revealed the structure of the main isomer as megastigma-6 (is),8(E)-dien-4-one. This component was also detected as trace constituent in quince fruit juice. © 1990, American Chemical Society. All rights reserved.