Metabolites from the Euryhaline Ciliate Pseudokeronopsis 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.