Synthesis and sedative-hypnotic effects of N3-allyl- and N1-allyl-5,6-substituted 2-thiouracil derivatives in mice.

Twenty four thiouracil derivatives, including N3-allyl- (19) and N1-allyl-2-thiouracil (20) were synthesized and their pharmacological effects [sedative-hypnotic activity (loss of righting reflex and spontaneous activity), convulsant activity, effect on pentobarbital (PB)-induced sleep and mortality] were evaluated in mice at doses of 320 mg/kg, i.p. and 2 mumol/mouse by intracerebroventricular (i.c.v.) injections, respectively. N3-Allyl-6-propyl-2-thiouracil (3), N3-allyl-5,6-dimethyl-2-thiouracil (10), N3-allyl-1,2,3,4,5,6,7,8,9-nonahydro-4-oxo-2-thiocyclohepta [d]pyrimidine (16) and N3-allyl-5-methyl-2-thiouracil (18) exhibited sedative-hypnotic activity, whereas N3-allyl-6-ethyl-5-methyl-2-thiouracil (11), N1-allyl-5-methyl-2-thiouracil (21), N1-allyl-1,2,3,4,5,6,7,8,9-nonahydro-4-oxo-2-thiocyclohepta[ d]pyrimidine (23) and N1-allyl-5,6-dimethyl-2-thiouracil (24) conversely displayed clonic- and/or tonic-convulsant seizures. N3-Allyl-6-propyl-2-thiouracil (3) and N3-allyl-5-methyl-2-thiouracil (18) decreased spontaneous activity. Other compounds examined were inactive, or only slightly active in the sedative-hypnotic assay even at high doses. Fifteen compounds (1-4, 7, 10, 11, 14-16, 18-21, and 23) significantly prolonged the PB-induced sleeping time. Interestingly, only N1-allyl-5,6-dimethyl-2-thiouracil (24) shortened the PB-induced sleeping time. These results showed that these thiouracils possessed many different effects such as sedative-hypnotic, anticonvulsant and/or convulsant, and that N3-allyl-5-methyl-2-thiouracil (18) and N1-allyl-5,6-dimethyl-2-thiouracil (24) had the most potent hypnotic activity and antagonistic effect against PB, respectively.