Isolation and structure elucidation of seco-neokadsuranic acid A and 3,4-seco-(24Z)-lanosta-4(30),8,24-triene-3,26-dioic acid - Li, L N; Xue, H; Ge, D L; Kunio, K; Toshio, M; Sadafumi, O (Planta Med, 1989)