Design, Synthesis, and Characterization of Sulfamide and Sulfamate Nucleotidomimetic Inhibitors of hHint1

Abstract

Hint1 has recently emerged to be an important target of interest due to its involvement in the regulation of a broad range of CNS functions including opioid signaling, tolerance, neuropathic pain, and nicotine dependence. A series of inhibitors were rationally designed, synthesized, and tested for their inhibitory activity against hHint1 using isothermal titration calorimetry (ITC). The studies resulted in the development of the first small-molecule inhibitors of hHint1 with submicromolar binding affinities. A combination of thermodynamic and high-resolution X-ray crystallographic studies provides an insight into the biomolecular recognition of ligands by hHint1. These novel inhibitors have potential utility as molecular probes to better understand the role and function of hHint1 in the CNS.

Keywords: CNS; ITC; central nervous system; hHint1; human histidine triad nucleotide binding protein 1; isothermal titration calorimetry.

Figure 1

(a) Chemical structures of the hHint1 substrates (compounds 1 and 2) and a previously reported hHint1 inhibitor (compound 3). (b) Design of the new generation hHint1 inhibitors with an acyl-sulfamate or sulfamide backbone to improve solubility and potency over compound 3.

Scheme 1

Reagents and conditions: (i) NH₂SO₂Cl, DMA, 85%; (ii) 22, DBU, DMF 55%; (iii) 80% aq. TFA quant.

Scheme 2

Reagents and conditions: (i) chloroacetaldehyde, NaOAc 0.1 M, pH 6.5, 40 °C, 30%; (ii) NH₂SO₂Cl, DMA, 85%; (iii) 22, DBU, overnight, 55%; and 80% aq. TFA, 1 h quant.

Scheme 3

Reagents and conditions: (i) MTPI, THF, −70 °C for 30 min and then RT for 4 h 92%; (ii) NaN₃, DMF, RT overnight, 55%; (iii) triphenyl phosphine/aq dioxane, triethylamine, 50 °C, 3 h, 54%; (iv) NH₂SO₂NH₂, 1,4-dioxane reflux for 2 h; and 4 N NaOH/MeOH for 2 h, 33%; (v) 22, DBU in DMF, overnight, 55%; and 80% aq. TFA, 1 h quant.

Figure 2

High-resolution X-ray crystal structure analysis of AMP (yellow; pdb: 3TW2) and overlaid with the compound 7 (cyan) in interaction with hHint1 (blue; pdb: 5I2E) complex. (A) H-bond interaction of the sugar and side chain are shown in dotted black lines. (B) Different orientations of isoleucine side chains observed in the hydrophobic nucleotide-binding pocket for AMP and compound 7 bound hHint1 structure is shown in yellow and blue, respectively.