Psammaplins from the sponge Pseudoceratina purpurea:: Inhibition of both histone deacetylase and DNA methyltransferase

Four novel bisulfide bromotyrosine derivatives, psammaplins E (9), F (10), G (11), and H (12), and two new bromotyrosine derivatives, psammaplins 1 (13) and J (14), were isolated from the sponge Pseudoceratina purpurea, along with known psammaplins A (4), B (6), C (7), and D (8) and bisaprasin (5). The structures of psammaplins E (9) and F (10), which each contain an oxalyl group rarely found in marine organisms, were determined by spectroscopic analysis. Compounds 4, 5, and 10 are potent histone deacetylase inhibitors and also show mild cytotoxicity. Furthermore, compounds 4, 5, and 11 are potent DNA methyltransferase inhibitors. The biogenetic pathway previously proposed for the psammaplins class is also revisited.