Halogenated Meroditerpenoids from a South Pacific Collection of the Red Alga Callophycus serratus

A detailed examination of the red alga Callophycus serratus collected in Tonga led to the isolation of six new halogenated meroditerpenoids: callophycol C (1), callophycoic acid I (2), iodocallophycols E (3) and F (4), iodocallophycoic acid B (5), and callophycoic acid J (6). Of these, compounds 3-5 are new iodinated additions to the growing family of Callophycus meroditerpenoids. The relative configurations of compounds 1-6 were deduced by analyses of 1D NOE data and H-1-H-1 scalar coupling constants, and 3-6 are proposed to differ from the closely related compounds reported in the literature, iodocallophycoic acid A and iodocallophycols A-D. Iodocallophycol E (3) exhibited moderate cytotoxicity against the promyelocytic leukemia cell line HL-60 with an IC50 value of 6.0 mu M.