Orobanone analogues from acid-promoted aromatization rearrangement of curcumol inhibit hypoxia-inducible factor-1 (HIF-1) in cell-based reporter assays

In this paper, the mechanism of orobanone analogues formation via aromatization rearrangement of curcumol was minutely explored. Aromatization of curcumol with acetone under acidic condition was selected as the model reaction. The formation of a stable aromatic system was the driving force for this reaction. Based on the model reaction, other four new orobanone analogues were prepared through curcumol reacting with different carbonyl compounds. The results showed that the stability of carbocation, which was generated from the carbonyl compounds, and the steric hindrance were main factors affecting the aromatization. We also synthesized the analogue of aromaticane B using compound 2. In vitro anti-proliferative activity of some derivatives were tested by MTT assay. Two derivatives showed weak anti-tumor effect on two cancer cell lines (HepG2 and MCF7) under normoxia. Four orobanone analogue 2, 5, 6 and 9 significantly inhibited hypoxia-induced HIF-1 luciferase reporter activity in HeLa cells with the IC50 values of 13.6, 6.6, 2.4 and 18.2 μM, respectively.