A methylene chloride extract of Myoporum insulare R. Br. (Scrophulariaceae) root material was investigated by dual high-resolution PTP1B/α-glucosidase inhibition profiling and LC-PDA-HRMS. Subsequent analytical-scale separation of the crude extract afforded serrulatanes 1-9 of which 2 ((1R,11S,18R)-5,18-epoxyserrulat-3,14-dien-8,18-diol or myoporulatane A), 6 ((1R,4S,11S)-8-hydroxy-serrulat-14-en-18,5-olide or myoporulatane B), 7 ((1R,4S,11S)-serrulat-14-en-5,8,18-trione or myoporulatane C), and 9 ((1S, 2R,4S,11S)-2β-hydroxy-serrulat-14-ene or myoporulatane D) are previously unreported. The structures of all isolated compounds were established by HRMS as well as 1D and 2D NMR analysis. Relative configurations were determined from combined analyses of chemical shifts, J-coupling constants and ROESY correlations, and absolute configurations were tentatively assigned by comparison to previous studies and from biosynthetic arguments. Compounds correlated with PTP1B inhibitory activity in the high-resolution inhibition profile were tested after isolation. However, the pure compounds exhibited weak or essentially no inhibitory activity against PTP1B with IC₅₀ values of 97.4 μM for 2, 3.0 mM for 4, and > 100 μM for 7. This is the first study of the root chemistry of M. insulare.