Thiazolides as novel antiviral agents. 1. Inhibition of hepatitis B virus replication

Abstract

We report the syntheses and activities of a wide range of thiazolides [viz., 2-hydroxyaroyl-N-(thiazol-2-yl)amides] against hepatitis B virus replication, with QSAR analysis of our results. The prototypical thiazolide, nitazoxanide [2-hydroxybenzoyl-N-(5-nitrothiazol-2-yl)amide, NTZ] 1 is a broad spectrum antiinfective agent effective against anaerobic bacteria, viruses, and parasites. By contrast, 2-hydroxybenzoyl-N-(5-chlorothiazol-2-yl)amide 3 is a novel, potent, and selective inhibitor of hepatitis B replication (EC(50) = 0.33 μm) but is inactive against anaerobes. Several 4'- and 5'-substituted thiazolides show good activity against HBV; by contrast, some related salicyloylanilides show a narrower spectrum of activity. The ADME properties of 3 are similar to 1; viz., the O-acetate is an effective prodrug, and the O-aryl glucuronide is a major metabolite. The QSAR study shows a good correlation of observed EC(90) for intracellular virions with thiazolide structural parameters. Finally we discuss the mechanism of action of thiazolides in relation to the present results.

Figure 1

Basic thiazolide structures 1-3.

Figure 2

Thiazolide O-glucuronides.

Figure 3

Predicted vs Experimental pEC₉₀ RI as predicted by the QSAR model01A for pEC₉₀ RI.

Scheme 1

^a General synthetic procedures for thiazolides. ^a i) Coupling step: Carboxylic acid reacted with SOCl₂/ pyridine or (COCl)₂/ DMF, DCM, then either add acid Cl to amine in aq. NaHCO_3⁻ organic solvent with stirring, or add to amine in dry THF with Et₃N: or BrPyBOP or BOP-Cl, NMM, CH₂Cl₂; deprotection: aq. HCl, 60°C or aq. NH₃.

Scheme 2

^a Syntheses of 5′-acetamido and 5′-fluorothiazolides ^a i) H₂-Raney Ni, Ac₂O; ii) aq. NH₃; iii) SelectFluor, MeCN, heat; iv) aq. NaOH/EtOH.

Scheme 3

^a Syntheses of 4′-and 5′- methanesulfonylthiazolides ^a i) MeSO²Na, CuI, DMF, heat; ii) MeSNa, EtOH; iii) acetylsalicyloyl chloride; iv) 3-ClC₆H₄CO₃H (2 eq.); v) aq. NH³.

Scheme 4

^a Syntheses of 5′- aryl, alkyl, cyano and methoxycarbonylthiazolides. ^a i) N-bromosuccinimide, MeOH; ii), iii) (H₂N)₂C=S.

Scheme 5

^a Synthesis of 5′-trifluoromethylthiazolide 28. a) i) MCPBA, K₂CO₃, CH₃CN, RT to 40 ⁰C; ii) NH₂C(=S)NH₂ (2 equiv.) DMF, 75 ⁰C; iii) Acetylsalicyloyl chloride, Et₃N, CH₂Cl₂; iv) HCl, H₂O, THF, 50 ⁰C

Scheme 6

^a Synthesis of the O-glucuronide of 3. ^a i) 2-amino-5-chlorothiazole hydrochloride, NMM, EDCI, DMAP, HOBt, CH₂Cl₂; ii) NaOH, aq. MeOH, then pH 6.