A study of the bioactive crude extract of the New Zealand ascidian Lissoclinum notti led to the isolation of the new pyridoacridine alkaloids isodiplamine (4), cystodytin K (5) and lissoclinidine (6), as well as the known pyridoacridine alkaloids diplamine (7) and cystodytin J (8) and the benzopentathiepin varacin (3) and related trithiane varacin A. The new alkaloids were characterised using standard spectroscopic techniques, including 2D H-1-N-15 NMR experiments. Pyridoacridine alkaloids 4-8 were assayed for a range of biological activities including antitumour and antibiotic properties. (C) 2002 Elsevier Science Ltd. All rights reserved.