Growth Regulatory Response of Parthenin and its Derivatives

Parthenin, a pseudoguaianolide sesquiterpene lactone and a major component of the ethanol extract of Parthenium hysterophorus was converted to C₁₆-derivative through its pyrazoline derivative to know more about structure-activity relationship. For selected chemical reduction of one of the C=Cs, two reducing reagents i) Na-MeOH, ii) Na₂S₂O₄ were attempted. Na-MeOH treatment of parthenin and its C₁₆-cyclopropyl derivative resulted in addition of two methoxyl groups on C₂ and C₄. Interestingly, Na₂S₂O₄ chemoselectively reduced only the C=C that is conjugated to lactone moiety. The reagent also did not harm the cyclopropyl ring of C₁₆ derivative of parthenin. It is presumed that both the reductions proceed through free radical mechanism. The stereostructures of these products were ascertained on the basis of 1H NMR, IR and related studies. The transformed products of parthenin were subsequently tested for their biological activity. The bioefficacy of parthenin and its transformed products on germination and early seedling growth of maize and mungbean showed that the chemical modification altered growth regulatory properties. The transformed products, especially at lower concentrations, stimulated root growth and development in both maize and mungbean. However, promotion of shoot growth was seen only in mungbean.