Antineoplastic agents 100. The marine bryozoan Amathia convoluta¹ 1 To refer to antineoplastic agents 99 see G.R. Pettit, V. Gaddamidi, A. Goswami and G.M. Cragg, J. Nat. Prod. in press.

An intensive investigation of the marine animal AAmathia convoluta (Bryozoa phylum) for antineoplastic constituents has led to the isolation and structural determination of bryostatin 8 (2). A total of 100 kg of Amathia convoluta was required to obtain some 4.2 mg of bryostatin 8. Evaluation of bryostatin 8 against the murine P388 lymphocytic leukemia showed substantial inhibition of growth (PS, cell line ED₅₀, 1.3 × 10^-3, T/C 174 at 0.11 mg kg). A major part of the very strong antineoplastic activity exhibited by fractions prepared from Amathia convoluta was accounted for by the isolation of bryostatins 4 (1a), 5 (1c) and 6 (1b). All three bryostatins were obtained in yields comparable to that of bryostatin 8 and appear derived from the closely related marine bryozoan Bugula neritina. The epiphytic-like relationship of Bugula neritina to Amathia convoluta is discussed.