the present invention encompasses structures of the formula : ## str1 ## and the pharmaceutically acceptable non - toxic salts thereof wherein : ## str2 ## and w , x , a , b , c , d , e , r 3 , r 4 are variables . these compounds are highly selective agonists , antagonists or inverse agonists for gabaa brain receptors or prodrugs thereof and are useful in the diagnosis and treatment of anxiety , sleep , and seizure disorders , overdose with benzodiazepine drugs , and enhancement of memory .