Cyclopericodiol and new chlorinated melleins isolated from Periconia macrospinosa KT3863

Abstract

Cyclopericodiol (1) and two new chlorinated melleins (2 and 3) were isolated from Periconia macrospinosa KT3863. The results of density functional theory (DFT)-based calculations while estimating the values of the 13C chemical shifts and the spin coupling constants allowed to determine the relative configurations of 1 and 2. The absolute configurations of these compounds were established by comparing the experimental electronic circular dichroism (ECD) spectra with those obtained while performing time-dependent DFT calculations. Interestingly, the methyl and hydroxy groups at C3 and C4, respectively, of 2 assume an 1,2-anti-diaxial conformation due to absence of 1,3-diaxial repulsion. This conclusion was supported by the observation that 2 afforded an ECD spectrum that was almost the mirror image of that of 3. Furthermore, the theoretical spin coupling constants 3JH-3/C1, 2JH-3/C4, 3JH-3/C4a, and 2JH-3/C9 were in agreement with the heteronuclear multiple-bond correlation (HMBC) intensities of H-3 with C1, C4, C4a, and C9.