Antityrosinase and Antioxidant Activities of Guanidine Compounds and Effect of Guanylthiourea on Melanogenesis

•Four guanidine compounds (GCs) exhibited significant antityrosinase activities.•Dynamic and quantitative observation on the interaction of tyrosinase and GCs were studied.•The models and theories of structural functional relationships of GCs were developed.•Guanylthiourea exhibited a significantly inhibitory effect on melanin synthesis.