Structure determination of two new compounds isolated from a marine sponge Haliclona(Gellius) sp.

Abstract

Two new sesterterpenes, including a known ses-terterpene, were isolated from the marine sponge Haliclona sp. collected in the Gageo island, Korea. One of the new sesterterpenes (1) was an unusual compound possessing a spiroketal moiety and the other (2) represented a four ring-fused skeleton. The planar structure of compound 1 was identical to gombaspiroketals A and B isolated from the marine sponge Clathria gombawuiensis, but the configuration for the two chiral centers was dif-ferent each other. On the other hand, the skeletal structure of compound 2 was similar to that of phorone A isolated from Phorbas sp. and a com-pound from C. gombawuiensis, except for one configuration at C-8. However, in comparing the 1H and 13C NMR spectral data, the proton and carbon chemical shifts for the three compounds were almost consistent. The NOESY spectrum re-vealed that the C-8 configuration of 2 was re-versed to that of the two reported compounds. The configuration for compound 2 was supported by quantum mechanical calculation for the carbon chemical shifts and DP4+ probability for the pro-tons and carbons of 2.