Journal OfNatural P&s Vol. 51, No. 6,pp. 1153-1160, Nw-Da1988
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THE STRUCTURES OF PULICARAL AND RELATED SESQUITERPENOIDSFROM PULZCARZA PALUDOSA A. SAN FEUCIANO,*M.~~EDARDE, M.GORDALIW, E. DELOLMO,and J.M. MIGUELDELCORRAL Department of Organic Chemirtty, Faculty of Pharmacy, 37007 Sakamanca, Spain bSTRACT.-The structures of pulicaral and other related 13.3.33 propellane sesquiterpenoids isolated from PnlicariapaldJa were determined by interpretationof their spectral data, mainly homonuclear and heteronuclear two-dimensional n m r correlations and nOe difference results.
Two-dimensional n m r spectroscopy has become one of the most useful techniques for the natural products chemist devoted to the structural determination of new metabolites. This is particularly true for substances containing rare or previously unknown skeletons ( 1 , 2 ) , because in these cases little or no data for comparison are available. In the present paper we report how interpretation of some 1D- and 2D-nmr spectra, complemented with information obtained from other spectroscopic sources, permitted us to establish the constitution and stereochemistry of pulicaral and other related sesquiterpenoids isolated from Pulicaria paludosa Link (family Compositae; tribe Inuleae), a plant native to the western part of the Iberian peninsula. Previously, we reported the structural assignment of paludolon, another sesquiterpenoid with a novel skeleton, which was isolated from the same extract of this plant ( 3 ) . RESULTS AND DISCUSSION Pulicaral is a crystalline compound, unstable in air and light, located in the medium-polarity fraction of the n-hexane extract of aerial parts of P.paludosa. Its mass spectrum showed a molecular peak EM]+ at m/z 232.143 1 , in agreement with the molecular formula C15H2002(calcd 232.1463). This was confirmed by its 13C-nmr broad-band decoupled and DEPT spectra (Table 1 , Figure l ) , which revealed the existence in the molecule of three methyl groups (called A,B,and D for discussion in the text), four methylenes (C,E,F,and G),three methines (H, M,and N), and five nonprotonated carbon atoms (I,J, K,L,and 0).The chemical shift of signals above 100 ppm revealed the presence of two carbonyl groups, one ketone ( 2 18.2 ppm) and one aldehyde (189.0 ppm, CH), as well as a trisubstituted double bond (143.8 ppm, =C
