LAUSR

Red pepper, Capsicum annuum (Solanaceae), is used as a spice all over the world. Red pepper is studied actively because its pungent principal component, capsaicin, has a dietary effect, analgesic activity, and antioxidant activity [1]. The pungent principal component of red peppers is a group of acid amides of vanillylamine and C8 to C13 fatty acids, which are known generally as capsaicin [2]. More than 16 other capsaicinoids have been found as minor components [3]. Numerous studies have been done on the red pepper fruit, but there are few studies on stems [2–4]. Previously, we isolated 19 compounds, including ten amides, four steroids, and six benzenoids from the stems of this plant [5]. We also isolated 17 compounds, including three chlorophylls, six steroids, one ionone, and seven benzenoids from the unripe fruits of this plant [6]. To further understand the chemotaxonomy and to continue searching for biologically and chemically novel agents from Solanaceous plants, the unripe fruits of C. annuum L. var. conoides (Mill.) Irish were chosen for further phytochemical investigation. In this paper, we report the isolation and structural elucidation of this new dimeric ionone. Conoidol (1) was obtained as a white amorphous powder from CHCl3. Its molecular formula was deduced as C27H36O5 by HR-ESI-MS (m/z 463.2458 ([M + Na]+; calcd 463.2460)). The UV spectrum of conoidol contained absorption bands typical of the -ionone derivatives [7]. The IR spectrum of conoidol showed characteristic absorption bands due to the presence of hydroxyl (3400 cm–1) and carbonyl (1665 cm–1) groups. The 1H NMR spectrum of conoidol contained two ethylenic protons indicated by two doublets each for 1H at 6.83 (2H, d, J = 16.0 Hz) and 6.47 (2H, d, J = 16.0 Hz), and their spin coupling pattern indicates the presence of one trans-disubstituted ethylene moiety in the molecule. It also represented one hydroxy proton at 5.70 (1H, s), three methine protons at 5.96 (2H, s) and 4.34 (1H, br.s), and four methylene protons at 2.34 (2H, d, J = 17.0 Hz) and 2.50 (2H, d, J = 17.0 Hz). The compound also illustrated four characteristic singlets for 24 protons at 2.31 (6H, s), 1.88 (6H, br.d, J = 1.0 Hz), 1.11 (6H, s), and 1.03 (6H, s). The 13C NMR and DEPT experiments of 1 showed 14 resonance lines consisting of four methyls, one methylene, four methines, and five quaternary carbons. The structure of conoidol was also confirmed by 2D NMR experiments. A COSY correlation was observed between H-1 and H-2 , and between H-1 and H-2 . The HETCOR experiment showed that the carbon signals at 49.3 for C-6 (C-6 ), 127.2 for C-2 (C-2 ), 130.6 for C-2 (C-2 ), and 145.5 for C-1 (C-1 ) were correlated to the proton signals at 2.34 and 2.50 for H-6 (H-6 ), 5.96 for H-2 (H-2 ), 6.47 for H-2 (H-2 ), and 6.83 for H-1 (H-1 ), respectively. Thus, 1 is a dimer of (S)-dehydrovomifoliol [8], which was further confirmed by NOESY and HMBC experiments.