Bioassay-guided fractionation of two phytotoxic extracts (a CH
2Cl
2–MeOH (1:1) and an aqueous) prepared from the aerial parts of
Hofmeisteria schaffneri led to isolation of thymol analogs
3–
5, along with seven known compounds,
1,
2 and
6–
10. Compounds
3–
5 were identified by spectroscopic methods as 1,4-bis(2′-hydroxy-4′-methylphenyl)butane-1,4-dione (
3), 2-isopropyl-5-methylphenyl (2
Z)-2-methylbut-2-enoate (
4) and 2-hydroxy-2-(2-hydroxy-4-methylphenyl)propane-1,3-diyl (2
Z,2′
Z)bis(2-methylbut-2-enoate) (
5) and designated trivial names of hofmeisterins II–IV, respectively. Their conformational behavior was also studied by molecular modeling using density functional theory calculations at the B3LYP/DGDZVP level. Compounds
1–
4 and
6–
10 significantly inhibited radicle growth of seedlings of
Amaranthus hypochondriacus and
Echinochloa crus-galli in the Petri dish bioassay with IC
50’s
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10
−4 M. Furthermore, the northymol analog
3 provoked significant bleaching of seedlings of
A. hypochondriacus. However, none of the isolates affected either seedling growth or germination of
Medicago sativa.
