Compound 15a is a novel MDM2 inhibitor and represents a significant milestone towards the identification of the clinical candidate NVP-HDM201.  Compound 15a displayed good in vitro properties and metabolic stability across species in liver microsomal incubations.  The activity compound 15a was investigated in preclinical tumor models against a panel of 405 cell lines.  Compound 15a was shown to have an anti-proliferative effect on wt p53 expressing cell lines.  Compound 15a has good oral bioavailability, was efficacious in the mechanistic SJSA1 tumor model and was well tolerated in rat models.  MDM2 IC50 = 0.08nM.