Two aza-analogues of the marine pyrroloquinoline alkaloids wakayin and tsitsikammamines A and B have been synthesized. The strategy used was based on a 1,3-dipolar cycloaddition reaction between indole 4,7-dione and a diazo-aminopropane derivative. One of the two analogues partially inhibits human topoisomerase 1, whereas synthetic intermediates inhibit the enzyme DNA cleavage activity at a concentration comparable to that of the control drug camptothecin. (c) 2005 Elsevier Ltd. All rights reserved.