An Updated Organic Classification of Tyrosinase Inhibitors on Melanin Biosynthesis

Tyrosinase (EC 1.14.18.1) is known to be the rate-limiting enzyme responsible for catalyzing the first two steps in the synthesis of melanin pigments that determine the coloring of hair, skin and eyes. Tyrosinase catalyzes two- sequence distinct bio-reactions in pigment productions: L-tyrosine to L-dopa (hydroxylation); and L-dopa to dopaquinone (oxidation). The inhibition of tyrosinase has been established as one of the major strategies to regulate the production of melanin and the inhibitors are used to treat hyper-pigmentation and other unwanted effects from melanogenesis. There are now a variety of medicaments inhibiting melanin synthesis to treat excess melanin production or hyper-pigmentation of human skin, including the usage of natural plant extracts or chemically synthesized compounds. Recently, due to an increasing emphasis on healthy concepts, attention has been drawn to the usage of naturally produced crude materials and drugs in cosmetics and pharmaceutical applications. In this review, we demonstrate melanogenic inhibitory factors such as flavonoids, stilbenes, simple phenolics, furans, triterpenes, alkaloids, and other synthetic compounds. The structure-activity relationships are classified in terms of their inhibition of tyrosinase functions and copper chelating activity.