When the article was first published online, the below reference was not included and cited in the article. Yao B, Prinsep MR, Nicholson BK and Gordon DP, The Pterocellins, Novel Bioactive Alkaloids from the Marine Bryozoan Pterocella vesiculosa, J. Nat. Prod., 2003, 66, 1074–1077. This has now been corrected and published online.