Isolation of Salsolinol, a Tetrahydroisoquinoline Alkaloid, from the Marine Sponge Xestospongia cf. vansoesti as a Proteasome Inhibitor

Salsolinol (1), a tetrahydroisoquinoline alkaloid, was isolated from the marine sponge Xestospongia cf. vansoesti collected in Indonesia as a proteasome inhibitor, along with three salsolinol derivatives, norsalsolinol (2), cis-4-hydroxysalsolinol (3), and trans-4-hydroxysalsolinol (4). Compounds 1 and 2 inhibited the chymotrypsin-like activity of the proteasome with IC50 values of 50 and 32 μg/ml, respectively, but 3 and 4 showed no inhibitory effect even at 100 μg/ml.