In addition to simple polyacetylenes [1] and an unusual sesquiterpene [2], so far two guaianolides [3,4] have been isolated from Arctotis grandis Thunb. We have now isolated a further sesquiterpene lactone, C₁₅H₂₀O₄, its ¹H NMR data (see Table 1) clearly showing that it is the 6,12-lactone I, while the two other lactones are 8,12-lactones [2,3]. Intensive decoupling experiments in CDCl₃ and C₆D₆, as well as addition of Eu(fod)₃, clearly establish the configurations at all asymmetric centres. Irradiation at δ 3.95 ppm (in CDCl₃) collapses the fourfold doublet at 2.05 to a three-fold one and changes the multiplet at 2.30, while irradiation at 2.05 collapses the three-fold doublet at 1.35 to a doublet of doublets and changes the multiplet at 2.54. The two corresponding protons are further coupled with the proton on the hydroxy group-bearing carbon, which also shows an allylic coupling with an exomethylene proton (5.44, d). The signal at 2.05 is further coupled with a multiplet at 2.30 (in C₆D₆ 1.52, dq, J = 11, 7 Hz), which must be assigned to 11-H. These observations establish sequence A. Two double doublets at δ 2.61 and 2.48 obviously have to be assigned to a methylene group α to a keto group; its presence also follows from the IR band at 1730 cm⁻¹. These two hydrogens are coupled with a proton, which gives rise to a three-fold doublet at 2.97, as can be shown by irradiation at this frequency. Furthermore, the multiplet at 2.30 is changed, indicating that these two signals can only be assigned to 1- and 5-H. Irradiation of the 5-H signal changes a multiplet at 1.33 (in C₆D₆), which itself is coupled with the second methyl doublet. These experiments show that sequence A can be extended to I. The observed couplings clearly establish the given configurations. If we look at a corresponding Dreiding model, J₁,₂ and J₁,₃ are both large. This is only in agreement with an α-orientation of the methyl groups. Also the α-orientation of 1- and 5-H, the presence of a 6,12-trans-lactone and the β-orientation of the 9-OH-group follow from the observed couplings. In addition to kaurane derivatives, we have already isolated from A. revoluta Jacq. the corresponding 8-desoxy compound 2 [5] and further guaianolides with a 6,12-lactone ring, while A. repens Jacq. afforded the germacranolide parthenolide [5]. The chemotaxonomic situation is still therefore complicated.