cis-Cinnamoyl glucoside as a major plant growth inhibitor contained in Spiraea prunifolia.

Crude extracts of the leaves of Spiraea prunifolia Sieb. showed high plant-growth-inhibiting activity comparable to S. thunbergii extracts. To isolate the causal compound in S. prunifolia, we performed bioassay-directed purification by monitoring the biological activity per unit weight of the organism containing the bioactive compound (total activity). We isolated I-O-cis-cinnamoyl-beta D-glucopyranose (cis-CG) and identified it as the most important growth-inhibiting constituent in the crude extracts. We did not detect 6–0 (4′-hydroxy-2′-methylenebutyroyl)-1-0-cis-cinnamoyl-β-D glucopyranose (cis-BCG) in S. prunifolia, though it is a major plant growth inhibitor in S. thunbergii together with cis-CG. We estimated the cis-CG content in S. prunifolia to be 3.84 mmol kg^−l F.W. This amount is comparable to the cis-CG plus cis-BCG content in S. thunbergii (3.59 mmol kg^−l F.W.). This indicates that S. prunifolia and S. thunbergii have equally high potential to inhibit plant growth, and cis-CG acts as the most important plant-growth inhibitor in S. prunifolia extracts.