Holotrichones A and B, potent anti-leukemic lindenane-type sesquiterpene trimers with unprecedented complex carbon skeletons from a rare Chloranthus species

Two lindenane-type sesquiterpene (LDS) trimers with unprecedented carbon skeletons, holotrichones A (1) and B (2), were obtained from the whole plant of Chloranthus holostegius var. trichoneurus by a ultra performance liquid chromatography-photodiode array detector-mass spectrometry (UPLC-PDA-MS)-guided isolation strategy. Compound 1 represents the first LDS trimer incorporating a unique 3/5/6/6-fused framework, in which a lindenane-type monomer and the 2-methylbutyryl substituent of an LDS dimer is bridged by a six-membered ring system. Compound 2 is the first hetero-trimer fused by an LDS dimer with a p-benzoquinone-meroterpenoid, featuring an unusual 3/5/6/6/3/5/6/6/6 nonacyclic system fused by the sesquiterpenoid unit and a 2-geranyl-6-methyl-2,5-cyclohexadien-1,4-dione moiety. In compound 2, the dimeric LDS moiety is equipped with a rare oxaspiro[4.5]decane system. Their structures, including absolute configurations, were established by spectroscopic methods, GIAO NMR calculations and DP4+ probability analyses, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analysis. The plausible biogenetic pathway speculation indicated that hetero- and homo-Diels-Alder additions may dominate the formation of these highly fused polycyclic frameworks. Both compounds 1 and 2 induced the human acute myeloid leukemia MV-4-11 cell death via apoptosis induction, which deserves further investigation on this new chemical class of LDS oligomers for their anti-leukemic potential.