Malbrumpenoids A-N, unusually cyclized triterpenoids from the Euphorbia endophyte Malbranchea umbrina D16

Molecular networking-guided chemical investigation of the Euphorbia endophyte Malbranchea umbrina D16 led to the isolation of 14 novel unusually cyclized triterpenoids (UCT) involving three different skeletal types. Compounds 1–10 are tricyclic triterpenoids featuring a 1-cyclohexyloctahydro-1H-indene core, in which 1 incoporates an unusual 7,7-dimethyl-6,8-dioxabicyclo[3.1.2]octane motif. Compounds 11–13 represent a rare class of bicyclic triterpenes (6/5 ring system) containing various O-heterocycles at the side chain. Compound 14 is an acyclic triterpenoid with O-heterocycles at both ends. Their structures were assigned by spectroscopic, chemical, computational, and crystallographic means, which also allowed the stereochemical revisions of three previously reported analogues. Compound 1 significantly inhibited the adipogenesis in 3T3-L1 adipocytes via activating the AMP-activated protein kinase (AMPK) signalling.