Δδ SR values at H2-11 and Me-14 and negative Δδ SR values at H2-1 and H2-2. Thus, the configuration at C-1 was assigned as (S) and the absolute configuration of 4 as (1S,4R,5R,10R). In order to verify the absolute configuration independently from Mosher's NMR analysis, TDDFT-ECD calculations were performed on the (1S,4R,5R,10R)-4. 20 low-energy conformers above 1% Boltzmann population (Figure ). Boltzmann-averaged ECD spectra computed at four different levels of theory reproduced all transitions of the experimental ECD spectrum suggesting an absolute configuration for 4 of (1S,4R,5R,10R) (Figure ). It is interesting to note that depending on how the 8-OH coordinates to the C-7 carbonyl oxygen with an intramolecular hydrogen bond, there are two major groups of conformers with considerably different computed ECD spectra (group A: conformers A, C, D, F, I, L, O and P; group B: conformers B, E, G, H, J, K, M, Q and R). This manifested in oppositely singed ECD transitions or shoulders at about 325 nm and 240 nm, while the positive Cotton effect (CE) at around 220 nm seems to be unchanged and it can serve for the solid assignment of the absolute configuration (Figures and). Accordingly, compound 4 was confirmed to be a new sesquiterpene derivative that was named as abundisporin C. the previously reported hemi-synthetic fungal metabolite 7-ketoeuryfuran. The relative configuration of 5 was determined by the ROESY spectrum (Figure ) that revealed key NOE correlation from two methyl groups at δH 1. ) also disclosed the presence of a methoxy group at δH 3.64 (Me-16) that was directly correlated to an oxygenated primary carbon at δC 51.9 ppm. The HMBC spectrum (Figure ) revealed key correlations from both methoxy group and methine proton at δH 3.23 (H-9; δC 59.1) to a carboxycarbonyl carbon at δC 174.7 (C-11) indicating its existence as a methyl ester moiety at C-9. In addition, HMBC spectrum revealed correlations from the deshielded proton at δH 6.99 (H-7)