Hirseins A and B, daphnane diterpenoids from Thymelaea hirsuta that inhibit melanogenesis in B16 melanoma cells.

Two new daphnane diterpenoids, hirseins A (1) and B (2), were isolated from the aerial parts of Thymelaea hirsuta, and their structures were elucidated on the basis of spectroscopic data interpretation. Hirsein B (2) is an unusual daphnane in possessing a coumaroyl moiety. NOESY correlations of 2 implied that isomerization of the coumaroyl group in 2 was caused by equilibrium between the E (2e) and Z (2z) forms. Compounds 1 and 2 were found to inhibit melanogenesis in B16 murine melanoma cells.