Optimization of Orally Bioavailable Antileishmanial 2,4,5-Trisubstituted Benzamides

Abstract

Leishmaniasis, a neglected tropical disease caused by Leishmania species parasites, annually affects over 1 million individuals worldwide. Treatment options for leishmaniasis are limited due to high cost, severe adverse effects, poor efficacy, difficulty of use, and emerging drug resistance to all approved therapies. We discovered 2,4,5-trisubstituted benzamides (4) that possess potent antileishmanial activity but poor aqueous solubility. Herein, we disclose our optimization of the physicochemical and metabolic properties of 2,4,5-trisubstituted benzamide that retains potency. Extensive structure-activity and structure-property relationship studies allowed selection of early leads with suitable potency, microsomal stability, and improved solubility for progression. Early lead 79 exhibited an 80% oral bioavailability and potently blocked proliferation of Leishmania in murine models. These benzamide early leads are suitable for development as orally available antileishmanial drugs.

Figure 1

Structures of miltefosine and other potential antileishmanial agents.

Figure 2

Design strategy for optimizing 2,4,5-trisubstituted benzamides.

Scheme 1. Synthesis of Compounds 7–30

Reagents and reaction conditions: (a) polyphosphoric acid, 12 h, 170 °C, 63% yield; (b) substituted benzoic acid or nicotinic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (1.2 equiv), N,N-diisopropylethylamine (1.2 equiv), DMF, 14 h, room temperature, 17–82% yield; (c) substituted benzoyl chloride or nicotinoyl chloride, N,N-diisopropylethylamine (1.2 equiv), dichloromethane, 14 h, room temperature, 49–76% yield.

Scheme 2. Synthesis of Compounds 31–41

Reagents and reaction conditions: (a) cyclic or acyclic aliphatic amines (1.2 equiv), N,N-diisopropylethylamine (1.3 equiv), dioxane, 14 h, room temperature, 36–62% yield; (b) TFA, dichloromethane, 1 h, 0 °C, room temperature, 48–59% yield.

Scheme 3. Synthesis of Compounds 44–97

Reagents and reaction conditions: (a) oxalyl chloride (1.2 equiv), DMF (0.02 equiv), dichloromethane, 1–4 h, refluxed at 50 °C, 61–85% yield; (b) appropriately substituted aromatic amines, N,N-diisopropylethylamine (1.2 equiv), dichloromethane, 14 h, room temperature, 43–68% yield; (c) piperazine or methyl piperazine (1.1 equiv), N,N-diisopropylethylamine (1.1 equiv), dioxane, 14 h, room temperature, 47–56% yield.

Figure 3

In vivo pharmacokinetic profiling of compound 79 in mice administered intravenously at 3 mg/kg and orally at 10 mg/kg.

Figure 4

In vivo efficacy study of compound 79 in mice. BALB/c mice (BALB/c strain, 5 per group) were infected with L. mexicana and treated with either the vehicle or compound 79 (PO, 50mg/kg/day) for 10 consecutive days beginning on day 18 postinfection. Lesion sizes were measured by caliper and are plotted as mean ± SD. Compound-treated animals had significantly smaller lesions at weeks 4 and 5 (asterisks, p < 0.0001, Mann–Whitney). Vehicle control animals were sacrificed in the following week 5 due to the large lesion size.

Figure 5

SAR summary of antileishmanial 2,4,5-trisubstituted benzamide derivatives.