3-Aminoazetidin-2-one derivatives as N-acylethanolamine acid amidase (NAAA) inhibitors suitable for systemic administration

Abstract

N-Acylethanolamine acid amidase (NAAA) is a cysteine hydrolase that catalyzes the hydrolysis of endogenous lipid mediators such as palmitoylethanolamide (PEA). PEA has been shown to exert anti-inflammatory and antinociceptive effects in animals by engaging peroxisome proliferator-activated receptor α (PPAR-α). Thus, preventing PEA degradation by inhibiting NAAA may provide a novel approach for the treatment of pain and inflammatory states. Recently, 3-aminooxetan-2-one compounds were identified as a class of highly potent NAAA inhibitors. The utility of these compounds is limited, however, by their low chemical and plasma stabilities. In the present study, we synthesized and tested a series of N-(2-oxoazetidin-3-yl)amides as a novel class of NAAA inhibitors with good potency and improved physicochemical properties, suitable for systemic administration. Moreover, we elucidated the main structural features of 3-aminoazetidin-2-one derivatives that are critical for NAAA inhibition.

Keywords: N-acylethanolamine acid amidase; cysteine hydrolase; inhibitors; structure-activity relationships; β-lactams.

Figure 1

Structures of (S)–OOPP (1) and ARN077 (2)

Figure 2

Summary of key structural features for β-lactam based inhibitors of NAAA.

Scheme 1

Synthetic pathway for the preparation of amide derivatives 11a–q and 12h. Reagents and conditions: a) p–anisidine, EDC, THF/DCM (3:1), r.t., 16 h [85–92%]; b) ImSO₂Im, 0 °C, 1 h, then NaH, DMF, −20 °C, 1 h [75%]; c) CAN, MeCN/H₂O (1:1), 0 °C, 1 h [80–85%]; d) 1,4–cyclohexadiene, 10% Pd on charcoal, EtOH, r.t., 12 h, then AcOH, EtOAc [79%]; Method A [for 11a, 11f–h, 11l, 11o and 12h]: RCOCl, Et₃N, DCM or DCM/DMF (3:1), r.t., 16 h [15–65%]; Method B [for 11b–e, 11i–k, 11m–n and 11p–q]: RCOOH, TBTU, Et₃N, DCM/DMF (3:1), r.t., 16 h [30–62%].

Scheme 2

Syntheses of carboxylic acids 13, 14 and 15. Reagents and conditions: a) LiOH, THF/MeOH/H₂O (1:1:1), r.t., 1 h [quant.]; b) Dess–Martin Periodinane, DCM, 0 °C, 1 h, then r.t, 1 h. [94%]; c) NaClO₂, NaH₂PO₄, 2–methyl–2–butene, tBuOH/H₂O 4:1, r.t. 1.5 h [quant.]; d) DMSO, oxalyl chloride, DCM, −78°C, 15 min then 17, −78 °C, 1 h, then Et₃N, r.t. [quant.]; e) (EtO)₃POCH₂CO₂Et, NaH (95%), THF, 0 °C to r.t. [77%]; f) H₂, 10% Pd/C cartridge (H–Cube^®, EtOH, 45 °C, 20 bar, flow: 1.0 mL/min), 92%; g) LiOH, THF/MeOH/H₂O (1:1:1), r.t., 1 h [quant.].

Scheme 3

Syntheses of compounds 21h-24h. Reagents and conditions: a) 1N NaOH, 35%, H₂O₂, 60% tBuOH–H₂O, r.t., 16 h [82%]; b) 2N HCl.Et₂O, 1,2–bis(trimethylsiloxy)cyclobutene, THF, reflux, 3 h [37%]; c) nonanoyl chloride, Et₃N, DCM, r.t., 2 h [94%]; d) TFA/DCM (1:3), 0 °C, 30 min, then r.t. 45 min [quant.]; e) 2N HCl, r.t., 30 min then THF, r.t., 16 h [79%]; Method A: nonanoyl chloride, Et₃N, DCM, r.t., 16 h [83%].

Scheme 4

Syntheses of N–methylated compounds 27h-28h. Reagents and conditions: a) NaH (60% in mineral oil), MeI, THF, 0° C, 1 h then r.t., 4 h [25%]; b) NaH (95%), MeI, THF, 0° C, 1 h then r.t., 1 h [90%]; c) CAN, MeCN/H₂O (1:1), 0 °C, 1 h [92%]; d) H₂, 10% Pd/C cartridge (H–Cube, EtOAc, 30 °C, 1.0 bar, flow: 1.0 mL/min) then AcOH, EtOAc [78%]; Method A: nonanoyl chloride, Et₃N, DCM, r.t., 16 h [33%].

Scheme 5

Syntheses of amine, urea and carbamate derivatives 32–34. Reagents and conditions: a) DMSO, oxalyl chloride, DCM, −78 °C, 15 min then n–nonanol −78 °C, 1 h, then Et₃N, r.t. [quant.]; b) 9, Et₃N, dichloroethane, 10 min, then Na(OAc)₃BH, r.t., 1.5 h [21%]; c) nonyl isocyanate, DMAP, pyridine, r.t., 16 h [59%]; d) DMAP, 2-DPC, DCM, r.t., 16 h [quant.]; e) 9, DIPEA, DCM, r.t., 16 h [36%].