Despite moderate improvements in potency and selectivity, modifications on the two phenyl substituents failed to open an avenue to major optimization of the oxaprozin scaffold as inverse Nurr1 agonist. Thus, we turned our attention to structural modifications in the propanoic acid side chain of 6 (Table ) where variation of the carboxylic acid chain length enabled improvement in potency and selectivity towards Nurr1. While the shortest oxazolcarboxylic acid analogue 29 was equally potent as 6, the oxazolylacetic acid 30 provided a substantial improvement in potency and the extended oxazolylbutyric acid 31 was likewise more active than 6. The further elongated oxazolylpentanoic acid 32 comprised similar potency as 6 but weaker efficacy. This tolerance of various chain lengths by Nurr1 was attractive to achieve selectivity over RXR since chain shortening disrupted RXR agonism .