Lactone diterpenes from the aquatic plant Potamogeton natans

Four lactone diterpenes and two related glucosides with a labdane skeleton have been isolated from the aquatic plant Potamogeton natans. The structure s of three new compounds were determined as 19-acetoxy-20-oxo-8(17),13-ent- labdadien-15-->16 lactone, 8(17), 13-ent-labdadien-15-->16,19-->20 dilacton e and 6'-acetyl-19-glucopyranosyloxy-8(17),13-ent-labdadien-15-->16 lactone , respectively, by means of spectral analysis. Antialgal assays showed inhi bitory activity for some compounds. (C) 2001 Elsevier Science Ltd. All righ ts reserved.