Separation and SAR study of HIF-1alpha inhibitory tubulosines from Alangium cf. longiflorum.

A crude organic solvent extract of Alangium cf. longiflorum exhibited potent inhibition of hypoxia-induced HIF-1 transcriptional activity in human U251 glioma cells. Dereplication and bioactivity-guided fractionation, including Sephadex LH-20 and chiral HPLC chromatographies, led to the isolation of tubulosine ( 1), 9-desmethyltubulosine ( 2), and isotubulosine ( 3). Structures were verified by complete (1)H and (13)C assignments using 1D- and 2D-NMR techniques. Tubulosine strongly inhibited HIF-1 transcriptional activity, isotubulosine was devoid of activity, and 9-desmethyltubulosine possessed 6-fold less potency than tubulosine.