Minor constituents from the tubers of Gymnadenia conopsea.

Four new minor constituents including two cyclodipeptides (1 and 2) and two cyclopentene derivatives (3 and 4), together with four known cyclodipeptides, have been isolated from an ethanolic extract of the tubers of Gymnadenia conopsea. Their structures including absolute configurations were determined by spectroscopic data interpretation combined with chemical methods. Among them, compound 1 contains an abnormal S-(4''-hydroxybenzyl)cysteine residue, 3 and 4 possess [(4-methylcyclopentyl)methyl]benzene and (4-hydroxymethylcyclopentyl)benzene carbon skeletons, respectively, both of which are first found from the natural source.