Respiratory syncytial virus (RSV) is a major cause of respiratory tract infections in infants, young children and adults. 1,2,3,9b-Tetrahydro-5H-imidazo[2,1-a]isoindol-5-ones with general structure 1 were previously identified as promising inhibitors of RSV targeting the fusion glycoprotein. In particular, the introduction of a nitrogen at the 8-position of the tricyclic core yielded lead compounds 2 and 3. Extensive exploration of the R² group established that certain heterocyclic amides conferred potent RSV A&B activity and a good balance of physicochemical and pharmacokinetic properties. The antiviral activity was found to reside in a single enantiomer and compound 33a, (9bS)-9b-(4-chlorophenyl)-1-(pyridin-3-ylcarbonyl)-1,2,3,9b-tetrahydro-5H-imidazo[1′,2′:1,2]pyrrolo[3,4-c]pyridin-5-one (known as BTA9881), was identified as a candidate for preclinical development.

呼吸道合胞病毒（RSV）是婴儿，幼儿和成人呼吸道感染的主要原因。先前已鉴定出具有一般结构1的1,2,3,9 b-四氢-5 H-咪唑并[2,1- a ] isoindol-5 -ones是靶向融合糖蛋白的有希望的RSV抑制剂。特别地，在三环核的8位引入氮产生了铅化合物2和3。R ^2的广泛探索该小组确定某些杂环酰胺具有强大的RSV A＆B活性，并在理化和药代动力学特性之间取得了良好的平衡。发现抗病毒活性存在于单一对映异构体和化合物33a，（9b S）-9b-（4-氯苯基）-1-（吡啶-3-基羰基）-1,2,3,9 b-四氢-5 H-咪唑并[1'，2'：1,2]吡咯并[3,4- c ]吡啶-5-酮（称为BTA9881）被确定为临床前开发的候选药物。