Metabolites from the Euryhaline CiliatePseudokeronopsis erythrina

Three new secondary metabolites (named erythrolactones A2, B2 and C2), that are characterized by a central 4-hydroxy-unsaturated δ lactone ring bearing an alkyl saturated chain at C(2) and a butyl-benzenoid group at C(5), together with their respective sulfate esters (erythrolactones A1, B1 and C1), have been isolated from cell cultures of Pseudokeronopsis erythrina, clone TL-1. The structures are assigned on the basis of extensive spectroscopic measurements (1D and 2D NMR, UV,IR and HR-MALDI-TOF). A plausible biogenetic route for their formation is also suggested. Cold-shock treatment was performed in order to induce the discharge of the metabolites contained in pigment granules lying on the ciliary organelles of this microorganism. HPLC-ESI-MS analysis of this granule discharge reveals that erythrolactones A2–C2 are actually therein contained, strongly suggesting a possible role for these metabolites in the chemical defence strategy of P. erythrina.