Inhibition of Protein Tyrosine Phosphatase 1B by Ursane-Type Triterpenes Isolated from Symplocos paniculata - Na, MinKyun; Yang, Seungmi; He, Long; Oh, Hyuncheol; Kim, Beom Seok; Oh, Won Keun; Kim, Bo Yeon; Ahn, Jong Seog (Planta Medica, 2006)