Four Novel QuassinoidSkeletons from Brucea mollis via Guided Separation and Biomimetic Synthesis

Seven undescribed quassinoids (1–7) and one known quassinoid (8) were obtained from Brucea mollis by molecular networking integrated with DeepSAT and SIRIUS. Compound 1 is the first alkaloid–quassinoid adduct featuring a novel 6/5/5/6/6/6-fused hexacyclic skeleton. Compounds 2 and 3 are unprecedented skeleton C19 quassinoids. Biosynthetic pathways were proposed, which guided the successful biomimetic synthesis of compound 1, affording an optimized yield of 23.2%. Byproduct 1a with a rare 5/6/5/6/6/6 core was also formed.