Design, synthesis and evaluation of novel dihydrostilbene derivatives as potential anti-melanogenic skin-protecting agents.

The stems of Dendrobium orchids (Orchidaceae), also known as Shi Hu, have been used for medicinal purposes for centuries in oriental countries. In fact, the health benefits of Shi Hu have been evidenced by its modern pharmacological actions on conquering oxidative stress in pathological conditions. From the extracts of two commonly used Dendrobium species, we obtained discernible amounts of stilbenoids, explicitly trans-resveratrol (1) and dihydro-resveratrol (2), which are prototypical antioxidants. When applied to cultured melanocytes, these stilbenoids, dihydro-resveratrol (2) in particular, significantly reduced melanin formation via inhibiting tyrosinase activity and expression of tyrosinase-related proteins. By utilizing dihydro-resveratrol (2) as the basic structural unit, we synthesized 11 novel dihydrostilbene derivatives (3-13) in good yields and purity, with manipulative steps. In addition to their anti-melanogenic activity, some of the novel derivatives are indeed potential antioxidants as they quenched intracellular oxidative radicals in a manner more efficient than Trolox, a water-soluble analogue of vitamin E, and thus premeditated beneficial to skin protection.