Detailed ¹H and ¹³C NMR structural assignment of ent-polyalthic acid, a biologically active labdane diterpene

In this paper, a complete H-1 and C-13 NMR data assignment of ent-polyalthic acid, a biologically active labdane-type diterpene, is presented. The assignments were carried on the basis of spectroscopic data from H-1 NMR, C-13{H-1} NMR, gCOSY, gHMQC, and gHMBC experiments. Furthermore, a software-assisted methodology, using FOMSC3_rm_NB and NMR_MultSim programs, supported the detailed and unequivocal assignment of H-1 and C-13 signals, allowing all hydrogen coupling constants to be determined and thus clarifying all hydrogen signal multiplicities.