ent-Labdane diterpenes from the aquatic plant Potamogeton pectinatus

Four new ent-labdane diterpenes were isolated from the freshwater aquatic plant Potamogeton pectinatus, together with two known furano-ent-labdanes. The new compounds were assigned the structures methyl-15,16-epoxy-12(R)-acetoxy- 8(17),13(16),14-ent-labdatrien-19-oate, 15,16-epoxy-12(R)-acetoxy-8(17),13(16),14-ent-labdatrien-19-oic acid, 8(17),13-ent-labdadien-15 → 16-lactone-19-oic acid and 16-hydroxy-8(17),13-ent-labdadien-15,16-olid-19-oic acid by spectroscopic means. Some of these labdanes showed a strong algicidal activity against Raphidocelis subcapitata. [Copyright &y& Elsevier]