Novel Benzothiazole-based Ureas as 17β-HSD10 Inhibitors, A Potential Alzheimer's Disease Treatment

Abstract

: It has long been established that mitochondrial dysfunction in Alzheimer's disease (AD) patients can trigger pathological changes in cell metabolism by altering metabolic enzymes such as the mitochondrial 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10), also known as amyloid-binding alcohol dehydrogenase (ABAD). We and others have shown that frentizole and riluzole derivatives can inhibit 17β-HSD10 and that this inhibition is beneficial and holds therapeutic merit for the treatment of AD. Here we evaluate several novel series based on benzothiazolylurea scaffold evaluating key structural and activity relationships required for the inhibition of 17β-HSD10. Results show that the most promising of these compounds have markedly increased potency on our previously published inhibitors, with the most promising exhibiting advantageous features like low cytotoxicity and target engagement in living cells.

Keywords: 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10), amyloid binding alcohol dehydrogenase (ABAD), benzothiazole; Alzheimer’s disease (AD), amyloid-beta peptide (Aβ), mitochondria.

Figure 1

Structure of previously identified benzothiazolylurea inhibitors.

Figure 2

Design of benzothiazolylurea-based 17β-HSD10 inhibitors.

Scheme 1

Synthesis of 2–11. Reagents and conditions: (a) CDI, DCM, RT; (b) aniline derivative, MeCN, reflux; (c) 4 M HCl, dioxane, RT (for N-Boc protected intermediates).

Scheme 2

Synthesis of aniline intermediate 12. Reagents and conditions: (a) Pd/C, H₂, EtOH, RT.

Scheme 3

Synthesis of intermediates 13 and 14. Reagents and conditions: (a) HNO₃/CH₃COOH, RT; (b) Fe, NH₄Cl, MeOH/H₂O, RT.

Scheme 4

Synthesis of intermediate 15. Reagents and conditions: (a) AlCl₃, DCM, reflux.

Scheme 5

Synthesis of intermediates 16–21. Reagents and conditions: (a) (Boc)₂O, DMAP, THF, RT; (b) Pd/C, H₂, EtOH, RT.

Scheme 6

Synthesis of intermediate 22. Reagents and conditions: (a) LiAlH₄, THF, −5 °C to RT.

Scheme 7

Synthesis of compounds 23–26. Reagents and conditions: (a) NMP, 160 °C; (b) CDI, DMF, RT; (c) AlCl₃, DCM, reflux.

Scheme 8

Synthesis of compounds 27–29. Reagents and conditions: (a) AlCl₃, DCM, reflux; (b) MeCN, reflux.

Scheme 9

Synthesis of phosphonate derivatives. Reagents and conditions: (a) toluene, reflux; (b) dimethyl phosphite, 1,1,3,3-tetramethylguanidine, THF, 65 °C.

Scheme 10

Synthesis of compound 41. Reagents and conditions: (a) MeNCS, TBABr, CuCl, DMSO, 60–80 °C; (b) triphosgene, Et₃N, DCM, 0 °C–reflux; (c) THF, RT; (d) AlCl₃, toluene, reflux.

Scheme 11

Synthesis of N-methylated aniline derivatives. Reagents and conditions: (a) CH₃I, NaH, THF, 0 °C–RT; (b) AlCl₃, toluene, reflux.

Scheme 12

Synthesis of compound with methylated urea linker. Reagents and conditions: (a) CDI, DCM, RT. (b) amine, MeCN, reflux. (c) CH₃I, NaH, DMF, 0 °C–RT; (d) AlCl₃, toluene, reflux.

Scheme 13

Synthesis of 6-substituted benzothiazoles. Reagents and conditions: (a₁) KSCN, Br₂, acetic acid, 10 °C–RT; (a₂) KSCN, tetramethylammonium dichloroiodate, DMSO/water, RT–70 °C; (b) CDI, DCM, RT; (c) 4-amino-2-chlorophenol, MeCN, reflux.

Scheme 14

One-pot synthesis of phenylureas 72, 75 and 76.

Scheme 15

Synthesis of symmetric urea derivative 78. Reagents and conditions: (a) CDI, DMF, 60 °C; (b) AlCl₃, toluene, reflux.

Figure 3

Compound screening pipeline.

Figure 4

Primary compound in vitro evaluation (relative remaining activity at 25 µM inhibitor concentration is displayed in percentage of six independent measurements ± SEM; detailed results in Supplementary data). * Authors’ previously published most potent enzymatic data from Hroch et al. 2016 (Design, synthesis and in vitro evaluation of benzothiazole-based ureas as potential ABAD/17β-HSD10 modulators for Alzheimer’s disease treatment) [9].