Anticonvulsant activity of paeonimetabolin-I adducts obtained by incubation of paeoniflorin and thiol compounds with Lactobacillus brevis.

Seventeen thiopaeonimetabolin-I adducts were obtained as mixtures of diastereoisomers after incubation of paeoniflorin with Lactobacillus brevis in the presence of various thiols. The anticonvulsant activity of the adducts was investigated in mice using the maximal subcutaneous pentylenetetrazol seizure test and sodium valproate (1.5 mmol/kg) as a positive control. Thirteen adducts showed dose-dependent prolongation of latencies of clonic and tonic convulsions. Maximal protection against convulsions was effectively demonstrated by 8-(n-hexylthio)paeonimetabolin I (8) and 8-benzoylthiopaeonimetabolin I (18) at doses of 0.125 and 0.25 mmol/kg, respectively, while 100% protection was only achieved at 0.5 mmol/kg of 8-cyclopentylthiopaeonimetabolin I and 8-(p-tolylthio)paeonimetabolin I. The principal anticonvulsant activity of the diastereoisomers of 8 and 18 was attributed to their 7S-isomers [ED50 values of 0.09 and 0.12 mmol/kg, and protective indices of 5.0 and 4.0 for 8 (7S) and 18 (7S), respectively], while the 7R counterparts [8 (7R) and 18 (7R)] showed a muscle relaxation effect.