Four new cyclic octapeptides, hymenamides G, H, J, and K, (1 -4), have been isolated from the Okinawan marine sponge Hymeniacidon sp. and the structures elucidated on the basis of 2D NMR data and Edman degradation experiments of their partial hydrolysis products .
In our continuing studies on bioactive substances from marine organismsl, we isolated previously five new cyclic heptapeptides, hymenamides A -E2 , from the Okinawan marine sponge Hymeniacidon sp . Further investigation of extracts of this sponge resulted in isolation of four new cyclic octapeptides, designated hymenamides G, H, J, and K (1 -4) . In this paper we describe the isolation and structure elucidation of 1 4 .
The sponge of the genus Hymeniacidon was collected off Manza, Okinawa Island, and kept frozen until used . The MeOH extracts of the sponge were partitioned between EtOAc and H2O, and the aqueous layer was subsequently extracted with n-BuOH . The EtOAc soluble material was subjected to a silica gel column (CHC13/n-BuOH/AcOH/H2O) followed by repeated separation on a Sepadex LH-20 column (MeOH and CHC13/MeOH) . Further purification using a silica gel column (CHC13/MeOH), a Sep-Pak C18 cartridge, and/or Ct8 HPLC (CH3CN/H2O/CF3CO2H) afforded hymenamides G (1, 0 .0016%, wet weight) and H (2, 0 .0007%) as colorless amorphous solids. The n-BuOH soluble fraction was chromagraphed on a silica gel column (CHC13/n-BuOH/AcOH/H20), a Sephadex LH-20 column (MeOH), and C18 HPLC (CH3CN/H20/CF3CO2H) to give hymenamides J (3, 0 .0027%) and K (4, 0.0003%) as colorless amorphous solids .
Hymenamide G {1, [a]D 17 -127ยฐ (c 0.97, McOH)} showed the pseudomolecular ion peak at m/z 893 (M++H) in the FABMS spectrum.
The molecular formula, C47H72N809, of 1 was established by the HRFABMS (m/z 893 .5481, M++H, A -1 .9 mmu). The IR absorptions at 3400 and 1650 cm -l were attributed to hydroxy and amide carbonyl groups, respectively . Its peptide nature was suggested by five doublet amide 4667