Novel cytotoxic constituents of Orthosiphon diffusus

Chemical investigation on Orthosiphon diffusus resulted in the isolation of four relatively rare, novel polychiral furanopyrans, orthodiffenes A–D (1–4) which were characterized from detailed studies of their 1D and 2D NMR spectra. The X-ray crystallographic analysis of orthodiffene A (1) was accomplished. The in vitro cytotoxic activity of orthodiffenes A–C (1–3) was tested against Jurkat and HL-60 cells using camptothecin as a positive control. Orthodiffenes A (1) and B (2) showed comparable activity to camptothecin against HL-60 and Jurkat cells, respectively.