We report the structure of a new sesquiterpene l.SCtOnS isolated from Artemisia annua L. (collected in October 1970, Belgrade area, 1Pugoslavla). The structure of this lactone (I) (OOlOrlSSS crystals, mow. 248, IU*P* 152', cd.3;0 -6'), which we named Arteannuin B, belongs to the new type of sesquiterpene lactone with the cadinane skeleton. This structure is suggested based upon the following arguments:
Arteannuin B iI> has molecular formula Cl54oO3 (h.r.m.8. and combustion analysis). Bands in i.r. at 1780 at 1780 Cr-laotone ycso> and 1665 cm-' (QzCH2),Xmax at 215 m)~ (E 5820) in U.V. and two doublets in n.n.r. (J = 3Hs) at P5.41 and 6.61 (~&vinyl protons) confirm Glactone ring. In n.m.r. spectrum (220 MC, CDC13, Me,Si), there are no other signals below $2.73, indicating that lactonic oxygen is bonded to a tertiary C-atom (double bond at C-6 is excluded by both hydrogenation and brute formula). C-6 can be a tertiary atom e&her if it belongs to the three rings or if the substituents like OH, CH3 or CH3C0 are attached to it. Howewr, there is no OH band in i.r., and the other two substituents are excluded for the follwing reasons: n.m.r. spectrum shows only two methyl groups indicated by a doublet at SO.98 (J = 6Hs; 10-CH3) and a singlet at sl.33 (CH3CO), and a wry sharp singlet (1H) at 82.66 is asigned_; the epoxide proton (epoxide ring is also confirmed by 1260, 938 and 863 cm bands in the i.r.). When r-lactonic ring is inVOlWd in chemical transformations (hydrogenation , isomerieation of C=C, formation of pyr'asolone derivative, NaBH4 reduction to diol) and epoxide is kept unchanged the abow two singlets retain their positions. Howewr, when acid hydrolisia is carried out these two signals disappear, and the new 3H singlet appears at $1.85 (C$ attached to double bond). These facts lead to the conclusion that the tertiary methyl group is on epoxide ring and not linked to C-6 atom. Consequently, it can be concluded that C-6 belongs to the three rings as it is shown ti fory (I), Such a position of the lactone ring together with the "isoprene rule" ilLply the cadinane skeleton (i.e. two fused six-membered rings). Each of the