The invention provides pyrazolo[1,5-a]pyrimidine derivatives which are useful as potent analgesics and represented by the formula
 wherein R1 is lower alkyl, lower alkenyl, hydroxy(lower)alkyl, (lower)alkylthio(lower)alkyl, (lower)alkanoyloxy(lower)alkyl, (lower)alkoxy(lower)alkyl, furyl or thienyl, R2 is pyridyl, 1-oxide-pyridyl, lower alkyl-substituted pyrazinyl, lower alkyl-substituted pyrimidinyl, or phenyl which may have 1 to 3 substituents selected from the group consisting of lower alkyl, lower alkoxy and halogen, R3 is hydrogen or halogen, and A is a single bond or lower alkylene; with the proviso that when R1 is lower alkyl, R2 is lower alkyl-substituted pyrazinyl or lower alkyl-substituted pyrimidinyl.
                            本发明提供了可用作强效镇痛剂的
吡唑并[1,5-a]
嘧啶衍
生物,其分子式为
 其中 R1 是低级烷基、低级烯基、羟基(低级)烷基、(低级)烷
硫基(低级)烷基、(低级)烷酰氧基(低级)烷基、(低级)烷氧基(低级)烷基、
呋喃基或
噻吩基,R2 是
吡啶基、1-氧化
吡啶基、低级烷基取代的
吡嗪基、R3是氢或卤素,A是单键或低级亚烷基;但 R1 为低级烷基时,R2 为低级烷基取代的
吡嗪基或低级烷基取代的
嘧啶基。