Design and Synthesis of Potent Inhibitor of Apoptosis (IAP) Proteins Antagonists Bearing an Octahydropyrrolo[1,2-a]pyrazine Scaffold as a Novel Proline Mimetic

Abstract

To develop novel inhibitor of apoptosis (IAP) proteins antagonists, we designed a bicyclic octahydropyrrolo[1,2-a]pyrazine scaffold as a novel proline bioisostere. This design was based on the X-ray co-crystal structure of four N-terminal amino acid residues (AVPI) of the second mitochondria-derived activator of caspase (Smac) with the X-chromosome-linked IAP (XIAP) protein. Lead optimization of this scaffold to improve oral absorption yielded compound 45, which showed potent cellular IAP1 (cIAP1 IC(50): 1.3 nM) and XIAP (IC(50): 200 nM) inhibitory activity, in addition to potent tumor growth inhibitory activity (GI(50): 1.8 nM) in MDA-MB-231 breast cancer cells. X-ray crystallographic analysis of compound 45 bound to XIAP and to cIAP1 was achieved, revealing the various key interactions that contribute to the higher cIAPI affinity of compound 45 over XIAP. Because of its potent IAP inhibitory activities, compound 45 (T-3256336) caused tumor regression in a MDA-MB-231 tumor xenograft model (T/C: -53% at 30 mg/kg).

Synthesis of complex unnatural fluorine-containing amino acids

“…In 2013, Ishikawa and co-workers reported synthetic methodology that allowed for successful isolation of the 7,7-difluorooctahydropyrrolo[1,2- a ]pyrazine derivative 102 ( Scheme 23 ) [ 93 ]. Initial condensation of the commercially available (4R)-hydroxyproline derivative 96 and benzylamine using known conditions led to the successful formation of amide 97 .…”

“…The hydroxyl group could then be oxidised to the ketone before being treated with Deoxo-Fluor, yielding 7,7-difluoro derivative 102 ( Scheme 23 ).

Scheme 23 Synthesis of 7,7-difluorooctahydropyrrolo[1,2- a ]pyrazine derivatives, Ishikawa and co-workers [ 93 ].

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“… Synthesis of 7,7-difluorooctahydropyrrolo[1,2- a ]pyrazine derivatives, Ishikawa and co-workers [ 93 ]. …”

Screening and Characterization of Hydrate Forms of T-3256336, a Novel Inhibitor of Apoptosis (IAP) Protein Antagonist

“…T-3256336 is a highly potent and selective inhibitor of apoptosis (IAP) protein antagonist 15) and only the anhydrous form was obtained from the synthetic compounds by the medicinal chemists (Fig. 1).…”

“…The stability of the anhydrous/hydrate system is also affected by temperature because of the dependency of the equilibrium water activity (equilibrium K h ) on temperature. Understanding the anhydrous/hydrate phase transformation against temperature is important because crystallization from solution via cooling is most commonly applied to the manufacturing process.T-3256336 is a highly potent and selective inhibitor of apoptosis (IAP) protein antagonist 15) and only the anhydrous form was obtained from the synthetic compounds by the medicinal chemists (Fig. 1).…”