Synthesis of pyrazolo[4,3-e][1,2,4]triazine sulfonamides, novel Sildenafil analogs with tyrosinase inhibitory activity.

Tyrosinase is a multifunctional, glycosylated and copper-containing oxidase which catalyzes the first two steps in mammalian melanogenesis and is responsible for enzymatic browning reactions in damaged fruits during post-harvest handling and processing. Neither hyperpigmentation in human skin nor enzymatic browning in fruits are desirable. These phenomena have encouraged researchers to seek new potent tyrosinase inhibitors for use in foods and cosmetics. This article surveys tyrosinase inhibitors, newly discovered from natural and synthetic sources. The inhibitory strength is comparable to that of the standard inhibitor kojic acid. Also their inhibitory mechanisms are discussed. The new obtained compounds were also tested as PDE5 inhibitors and did not show significant inhibitory effect.