A highly potent and selective caspase 1 inhibitor that utilizes a key 3-cyanopropanoic acid moiety

Abstract

Herein, we examine the potential of a nitrile-containing propionic acid moiety as an electrophile for covalent attack by the active-site cysteine residue of caspase 1. The syntheses of several cyanopropanate-containing small molecules based on the optimized peptidic scaffold of prodrug VX-765 were accomplished. These compounds were found to be potent inhibitors of caspase 1 (IC(50) values < or =1 nM). Examination of these novel small molecules against a caspase panel demonstrated an impressive degree of selectivity for caspase 1 inhibition over other caspase isozymes. Assessment of hydrolytic stability and selected ADME properties highlighted these agents as potentially useful tools for studying caspase 1 down-regulation in various settings, including in vivo analyses.

Figure 1

A. The structure of VX-765 (1) and schematic representation of esterase cleavage of the 5-ethoxydihydrofuran-2(3H)-one moiety to yield the active drug VRT-043198 (2b). B. The structure of NCGC00185682 (3) and putative esterase cleavage of the ethyl-3-cyanopropanoate moiety to yield active agent NCGC00183434 (4).

Scheme 1

Conditions and reagents: (a) EDC, DMAP, CH₂Cl₂, 6 h (59%);(b) TFAA, DIPEA, CH₂Cl₂, 0 °C, 30 min. (90%); (c) thionyl chloride (excess), EtOH, 0 °C (95%); (d) TFAA, DIPEA, CH₂Cl₂, 0 °C, 30 min. (86%); (e) NMM, DME, then NH₄OH (73%); (f) TMSN₃, Bu₂SnO (0.6 equiv.), toluene, μW, 100 °C, 1h (77%); (g) TFAA, DIPEA, CH₂Cl₂, 0 °C, 30 min. (80%).

Scheme 2

Conditions and reagents: (a) EDC, HOBt, DMF, rt, 8 h; (b) DBU, CH₂Cl₂, rt(71% over 2 steps);(c) HATU, DIPEA, DMF, rt, 2 h; (d)TFA,CH₂Cl₂ (1:1), rt, 4 h (85% over 2 steps); (e) DBU, DMF, 5 min. then 15, HATU, DIPEA, DMF, 0 °C, 2h; (f) TBAF, THF, 0 °C (72% over 2 steps); (g) DBU, DMF, 5 min. then 15, HATU, DIPEA, DMF, 0 °C, 2h (91%); (h) DBU, DMF, 5 min. then 15, HATU, DIPEA, DMF, 0 °C, 2h (82%).

Scheme 3

Conditions and reagents: (a) SO₃-pyridine, Hunig's Base CH₂Cl₂, DMSO (75%); (b) (EtO)₃CH, PPTS, EtOH, 50 °C, 24 h; (c) DBU, CH₂Cl₂, (63% over 2 steps); (d) 19, DMF, 5 min. then 15, HATU, DIPEA, DMF, 0 °C, 1h; (e) TFA, CH₂Cl₂, 1 h (1:1 dr, 72% over 2 steps); (f) HCl, THF/H₂O (quant.).

Figure 2

Complete response curves for VRT-043198 (2b) ( IC₅₀ = 11.5 nM), NCGC00185682 (3) ( IC₅₀ = 144.7 nM), NCGC00183434 (4) (◆ IC₅₀ = 0.316 nM)and the tetrazole NCGC00183681 (16) (■ IC₅₀ = 20.4 nM).

Figure 3

Aqueous stability of prodrugs VX-765 (1)(◆) and NCGC00185682 (3)(X) and drugs VRT-043198 (2b)(▲), NCGC00183434 (4)(■) and NCGC00183681 (16)(●) at neutral (pH 7 - black), acidic (pH 2 - red), and basic (pH 8 - blue) conditions.

Figure 4

Molecular model (ribbon and space filling) of NCGC00183434 (4) bound to caspase 1.