Microbial transformations of two lupane-type triterpenes and anti-tumor-promoting effects of the transformation products - Akihisa, T S; Takamine, Y S; Yoshizumi, K Z; Tokuda, H K; Kimura, Y K; Ukiya, M T; Nakahara, T R; Yokochi, T S; Ichiishi, E C; Nishino, H Y (J Nat Prod, 2002)