Sulawesins A–C, Furanosesterterpene Tetronic Acids That Inhibit USP7, from a Psammocinia sp. Marine Sponge

Three new furanosesterterpene tetronic acids, sulawesins A–C (1–3), were isolated from a Psammocinia sp. marine sponge, along with the known compounds ircinins-1 (4) and -2 (5). Although ircinins-1 and -2 were previously isolated as (+)- or (−)-enantiomers from marine sponges, we isolated them as enantiomeric mixtures. Sulawesins A and B possess a new carbon skeleton with a 5-(furan-3-yl)-4-hydroxycyclopent-2-enone moiety and were also found to be diastereomeric mixtures of four isomers by an HPLC analysis with a chiral-phase column. Sulawesin C has a dimeric structure of ircinin-1 and is the first dimer in this family. USP7, a deubiquitinating enzyme, is an emergent target of cancer therapy, and the isolated compounds inhibited USP7 with IC₅₀ values in the range of 2.7–4.6 μM.