Abibalsamins A and B, Two New Tetraterpenoids from <i>Abies balsamea</i> Oleoresin

Abibalsamins A (<b>1</b>) and B (<b>2</b>), two unprecedented tetraterpenoids featuring a 3,4-seco-rearranged lanostane system fused with a β-myrcene lateral chain <i>via</i> a [4 + 2] Diels–Alder cycloaddition, were isolated from the oleoresin of <i>Abies balsamea</i>. Their structures were elucidated by means of extensive 2D NMR, IR, and MS spectroscopy analyses. The absolute configuration of <b>1</b> was determined by single-crystal X-ray diffraction. Both compounds exhibited significant cytotoxic activity against cancer cell lines.