New 4-(aroyloxyalkanoyl)-2,3-dimethyl-1-phenyl-3-pyrazolin-5-ones (5) were
cyclized to 4-(2-aryl-5-unsubstituted/substituted oxazol-4-yl)-2,3-dimethyl
-1-phenyl-3-pyrazolin-5-ones (6) employing the Davidson procedure. Prelimin
ary evaluation of analgesic activity revealed that the effect of 4-(2-pheny
l-5-ethyloxazol-4-yl)-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and 4-[2-(4-c
hlorophenyl)-5-ethyloxazol-4-yl]-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one o
n acetic acid induced writhing was superior to that of antypyrine and amino
pyrine. 4-[2-(4-Chlorophenyl)-5-methyloxazol-4-yl]-2,3-dimethyl-1-phenyl-3-
pyrazolin-5-one and 4-[2-(4-methoxyphenyl)-5-ethyloxazol-4-yl]-2,3- dimethy
l-1-phenyl-3-pyrazolin-5-one were more potent than aminopyrine, whereas 4-(
2-phenyl-5-methyloxazol-4-yl)-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and 4
-[2-(4-methoxyphenyl)-5-methyl-oxazol-4-yl]-2,3-dimethyl-1-phenyl-3-pyrazol
in-5-one were not as active (modified Koster's Test; 0.19-0.21 mmol.kg(-1))
. None of the selected entries showed inhibition of formaldehyde-induced pa
w oedema. (C) 2000 Editions scientifiques et medicales Elsevier SAS.