Natural diarylfluorene derivatives: isolation, total synthesis, and phosphodiesterase-4 inhibition

Abstract

In our previous study, selaginpulvilins A–D (1–4) featuring an unprecedented 9,9-diphenyl-1-(phenylethynyl)-9H-fluorene skeleton were identified as potent phosphodiesterase-4 (PDE4) inhibitors from Selaginella pulvinata. In the current work, a large-scale reinvestigation of the same plant led to the isolation of six additional new analogues, selaginpulvilins E–J (5–10), among which 5 features a rare 6-(4-hydroxyphenyl)-2H-pyran-2-one unit. Compounds 5–10 exhibited remarkable inhibitory activities against PDE4 with IC₅₀ values in the range of 0.22–1.38 μM. The first total synthesis of selaginpulvilins A–F (1–6) was developed in 7–11 steps involving a Friedel–Crafts reaction as the key reaction, which provides a feasible access to this scaffold.