Thirty compounds that are precursors, analogs, derivatives, or fragments of strigol were prepared and tested for their activity as witchweed [Striga asiatica (L.) Kuntze] seed-germination stimulators. Five compounds showed significant stimulatory activity. Among these were 5-ethoxy-3-methyl-2(5H)-furanone, 3-hydroxy-2,6,6-trimethylcyclohex-1-ene-1-carboxaldehyde, a two-ring analog of strigol, and two isomers of a three-ring analog. Several of the other 25 compounds showed slight and/or non-reproducible activity when dimethylsulfoxide was used as the carrier at 0.1% (v/v) in aqueous solutions. Compounds with such diverse structures as trimethylcyclohexenes, furanones, and bicycloheptenones were among those that possessed some stimulatory activity.
