Isolation and NMR Scaling Factors for the Structure Determination of Lobatolide H, a Flexible Sesquiterpene from Neurolaena lobata .

A new flexible germacranolide ( 1 , lobatolide H) was isolated from the aerial parts of Neurolaena lobata . The structure elucidation was performed by classical NMR experiments and DFT NMR calculations. Altogether, 80 theoretical level combinations with existing 13 C NMR scaling factors were tested, and the best performing ones were applied on 1 . 1 H and 13 C NMR scaling factors were also developed for two combinations utilizing known exomethylene containing derivatives, and the results were complemented by homonuclear coupling constant ( J HH ) and TDDFT-ECD calculations to elucidate the stereochemistry of 1 . Lobatolide H possessed remarkable antiproliferative activity against human cervical tumor cell lines with different HPV status (SiHa and C33A), induced cell cycle disturbance and exhibited a substantial antimigratory effect in SiHa cells.