Phytochemistry,Vol. 21, No. 8, pp. 2041-2044, 1982 Printed in Great Britain. 0031-9422/82/082041-04$03.00/0 @ 1982 Pergamon Press Ltd. zyxwv ZOAPATANOLIDE A AND B, TWO NEW HELIANGOLIDES FROM zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA MONTANOA TOMENTOSA” L. QUIJANO, J. S. CALDER~N, F. G~MEZ and T. Rios Institute de Quimica de la hive&dad National Authoma de MCxico, Circuit0 Exterior, Ciudad Universitaria, MCxico 20, D.F., Mexico (Revised received 9 November 1981) Key Word Index-Montanoa tomentosa; Compositae; Heliantheae; new heliangolides; sesquiterpene lactones; zoapatanolide A and B. Abstract-The re-investigation of Montanoa tomentosa afforded, in addition to known diterpenoids of the kaurene class, two new sesquiterpene lactones, zoapatanolide A and B, of the heliangolide type. INTRODUCTION Montanoa tomentosa and M. frutescens are Mexican plants commonly known as ‘zoapatles’, which have been user! in Mexico since ancient times in folk medicine for their putative oxytocic properties. In a previous paper, we described the isolation and structure elucidation of montafrusin (la), a ger- macrolide from M. frutescens [I]. Recently, an in- vestigation of the active components of M. tomen- toss, culminated in the structure elucidation of two biologically active oxepane diterpenoids, zoapatanol and montanol [2,3]. Previous studies of the plant demonstrated the presence of several diterpenoids [4] and the sesquiterpene lactone tomentosin (2), the structure of which was established by ‘H NMR stu- dies [5]. During our work on the structure elucidation of montafrusin (la) we realized that some of the pub- lished ‘H NMR data of tomentosin (2) were not in good agreement with the proposed structure, especi- ally the small values of J6,, and J7,13 which suggested that the molecule might be a heliangolide. A similar observation was recently made by Herz, but he sug- gested a truns-trans-germacra-1(10),4-cis-6,12-olide- type structure [6]. RESULTS AND DISCUSSION To verify the above hypothesis, we have under- taken a re-investigation of M. tomentosa Cerv. and isolated a new sesquiterpene lactone. The ‘H NMR and IR spectra of the new compound indicated that it was identical with the sesquiterpene lactone obtained during the isolation of the active components zoapa- tanol and montanol [2]. The ‘H NMR shifts, however, differed from those which have been published for tomentosin (2) [5]. This fact suggested that we were dealing with a different substance, which we named *Contribution No. 583from Institute de Quimica, U.N.A.M. zoapatanolide A (3a). Its structure was established by extensive ‘H NMR studies and spin-spin decoupling experiments as well as chemical evidence. Zoapatanolide A (3a), G0Hz606, mp 194-196”, [a],,- 83.5” was a conjugated y-lactone which showed UV absorption at 206nm (E 21358) and the typical IR absorption at 1770cm-‘. A strong ab- sorption band at 3440cm-’ indicated the presence of hydroxyl groups, which was confirmed by acetylation to give a diacetate (3b). The presence of an angelate (1710 cm-‘) was indicated by MS ion peaks at m/z 83 (&H,O, 100) and 55 (C4H,, 50.5) characteristic of this type of ester, and the typical vinyl proton quartet at S 6.14 in the ‘H NMR spectrum. The ‘H NMR spectrum of zoapatanolide A (3a) run in CDC& (Table 1) showed the typical signals of the exocyclic methylene at 6 6.29 as a broad doublet (4J = 2) and 5.62 as a broad doublet which might be considered as a doublet of doublets (4J = 2, *J = 1). The small allylic coupling constant suggested either a cis-fused lactone ring according to Samek’s rule [7] or a trans-fused heli- angolide type structure [8]. The ‘H NMR spectrum determined in acetone-de displayed a two-proton set of signals at 6 4.1-4.4 which were assigned to H-9 and the C-9-hydroxyl interaction since they collapsed to a one-proton doublet (J = 10) centred at 6 4.2 (H-9) upon D20 addition, besides the disappearance of a singlet at S 2.8. The remaining proton signals were assigned by spin-spin decoupling experiments; H-7 was located as a doublet of quartets at S 2.95 (J = 10, J = 1) since irradiation of this signal collapsed the exocyclic methylene signals to singlets, converted a triplet at 6 4.95 (J = 10) to a doublet and sharpened a broad doublet at 64.79 (J = 10). Irradiation at the frequency of H-9 (6 4.2) converted the triplet at S 4.95 into a doublet. Thus the signals at 6 4.95 and 4.79 were assigned to H-8 and H-6 respectively. Irradia- tion at the frequency of a vinyl methyl group doublet at 61.75 (J = 1) converted a broad doublet at S 5.08 (J = 10) into a thin doublet of doublets (J = 10, J = 1) 2041