Isolation, Structure Elucidation, and Antioxidant Evaluation of Cydonioside A, an Unusual Terpenoid from the Fruits of Cydonia vulgaris

A novel terpenoid, cydonioside A ( 1 ), was isolated from the fruits of Cydonia vulgaris Pers . Its structure and relative configuration were elucidated on the basis of in‐depth spectroscopic analyses, including 2D‐NMR experiments as well as MM+ calculations. Compound 1 was assayed for its radical‐scavenging activity towards the DPPH radical and the superoxide radical anion (O ${{_{2}^{{^\cdot} -}}}$ ), as well as for its overall antioxidant activity, as assessed by the formation of a phosphomolybdenum complex.