Photoprotective zoanthamine derivatives from the cultured zoantharian zoanthus sansibaricus

Zoanthus sansibaricus is a marine invertebrate native to the Indian and North Pacific Oceans. A chemical investigation of Z. sansibaricus, cultured in an aquafarm, led to the isolation of two new zoanthamine derivatives, named 3β-hydroxyzoanthamine (1) and 3α-hydroxynorzoanthaminone (2), along with five known derivatives (3‒7). Their structures were elucidated through quantum chemical calculations and a detailed analysis of spectroscopic data, including mass, IR, and NMR spectra. New compounds 1 and 2 represent additional examples of the oxidation of zoanthamine derivatives. The potential photoprotective effect of all isolated alkaloids (1‒7) was evaluated against UVA-induced damage in human dermal fibroblasts. Among the tested compounds, only 26-norzoanthamine (4) significantly attenuated UVA-induced oxidative stress. Notably, this antioxidant activity did not translate into sustained cell viability protection at 72 hours post-irradiation, suggesting that the photoprotective mechanism of compound 4 is limited to acute oxidative stress attenuation.