Absolute configuration of phytocassanes as proposed on the basis of the CD spectrum of synthetic (+)-2-deoxyphytocassane A

Phytocassane A–E possess ent-cassane skeleton because synthetic (+)-2-deoxyphytocassane A with cassane skeleton showed the Cotton effects positive at 369 nm (due to the ring-C dienone chromophore) and negative at 289 nm (due to the ring-A carbonyl group), while the natural phytocassane A exhibited the opposite Cotton effects.