5-OHKF and NorKA, depsipeptides from a Hawaiian collection of Bryopsis pennata: binding properties for NorKA to the human neuropeptide Y Y1 receptor.

Two new cyclic depsipeptides, 5-OHKF (1) and norKA (2), together with the known congeners kahalalide F (3) and isokahalalide F ((4S)- methylhexanoic kahalalide F) (4) were isolated from the green alga Bryopsis pennata. The structures of the new compounds were established on the basis of extensive 1D and 2D NMR spectroscopic analysis and mass spectrometric (ESIMS) data. The absolute configuration of each amino acid of 5-OHKF (1) and norKA (2) was determined by chemical degradation and Marfey's analysis. The biological activities of these two compounds are also reported.