Sesquiterpene Lactones from Varthemia candicans

Abstract

I. racemosa [8] and Plucbea dioscoridis

Sesquiterpene lactones from Centaurea tweediei

“…The predominant secondary metabolite of C. tweediei was onopordopicrin (1) which has so far not been found in other New World Centaurea endemics and has in fact been reported previously from only four Old World Centaurea taxa out of 99 studied so far for sesquiterpene lactone content (El-Masry et al, 1985, Lonergan et al, 1992, Bruno et al, 1996, Youssef, 1998. On the other hand onopordopicrin is a characteristic constituent of Onopordon (Carduae, subtribe Carduinae), having been reported from seventeen out of nineteen Onopordon species studied so far for sesquiterpene lactone content (Drozdz et al, 1968, Drozdz and Piotrowski, 1973, Khafagy et al, 1977, Rustaiyan et al, 1979a, b, 1986, Gonzalez Collado et al, 1984, Miski et al, 1988, Eid and El-Dahmy, 1989, Meric¸li and Tuzlaci, 1989, Cardona et al, 1992, Garcı´a et al, 1996, Lazari et al, 1998, Braca et al, 1999. Lactones or acids of types 2 and 3 have been encountered in both genera, although again more commonly in Onopordon and so far not in New World Centaurea endemics, while heliangolides and melampolides are rare in the entire tribe.…”

Cycloartane-Type Triterpenes from Amberboa ramosa

“…Five protons were exchangeable with D20 in base in the 'H-nmr spectrum of the diketone of 1. In a 'H-'H homonuclear chemical shift correlation spectrum (COSY-45) of 1 the comparatively upfield carbinol methine proton at [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] showed cross peaks with two other protons and hence could be assigned to C-3. The large coupling (_/ax,ax = 9.8 and Vax.eq = 4.11 Hz) allowed us to assign ß and equatorial orientation to the hydroxyl group at C-3.…”