Structure and anti-HIV activity of micrandilactones B and C, new nortriterpenoids possessing a unique skeleton from Schisandra micrantha - Li, R T; Han, Q B; Zheng, Y T; Wang, R R; Yang, L M; Lu, Y; Sang, S Q; Zheng, Q T; Zhao, Q S; Sun, H D (Chem Commun, 2005)