Medicinal Chemistry Optimization of a Diaminopurine Chemotype: Toward a Lead for Trypanosoma brucei Inhibitors

Abstract

Human African trypanosomiasis (HAT), or sleeping sickness, is caused by the protozoan parasite Trypanosoma brucei and transmitted through the bite of infected tsetse flies. The disease is considered fatal if left untreated. To identify new chemotypes against Trypanosoma brucei, previously we identified 797 potent kinase-targeting inhibitors grouped into 59 clusters plus 53 singleton compounds with at least 100-fold selectivity over HepG2 cells. From this set of hits, a cluster of diaminopurine-derived compounds was identified. Herein, we report our medicinal chemistry investigation involving the exploration of structure-activity and structure-property relationships around one of the high-throughput screening (HTS) hits, N²-(thiophen-3-yl)-N⁶-(2,2,2-trifluoroethyl)-9H-purine-2,6-diamine (1, NEU-1106). This work led to the identification of a potent lead compound (4aa, NEU-4854) with improved in vitro absorption, distribution, metabolism, and excretion (ADME) properties, which was progressed into proof-of-concept translation of in vitro antiparasitic activity to in vivo efficacy.

Figure 1.

Structure of NEU-1106 (1) and our medicinal chemistry strategy

Figure 2.

Key SAR and SPR points around this series for anti T. brucei activity (4aa, NEU-4854)

Figure 3.

(A) in vivo pharmacokinetics data of 4aa at dose 10 mg/kg ip in non-infected female NMRI mice; (B) in vivo pharmacokinetics data of 4aa at dose 30 mg/kg ip after ABT-pretreatment in Tbb STIB795 infected mice (N1-N3) and uninfected mice (N7-N9) on day 1 of treatment; (C) percentage survival of animals in acute in vivo murine HAT model (NMRI mice; T. brucei brucei STIB795 parasites); (D) Parasitemia levels graph in murine HAT model, cross indicates the day of death, values represented on the x axis indicate undetected parasitemia (values below 10⁴ parasites/ml which cannot be detected by counting in the Neubauer chamber). Start of infection (arrow) and treatment period (orange box) indicated.

Scheme 1.

Synthetic route for compounds 4a-4ab. Reagents and conditions: (a) 2,2,2-trifluoroethylamine, DIPEA, n-BuOH, 90 °C, 16 h (17%); (b) secondary amine, IPA, 80 °C, 16h; (c) amine, HCl, dioxane, microwave, 150 °C, 40 min.; (d) amine, Pd₂dba₃, XPhos, KOtBu, t-BuOH, 100 °C, 16h; (e) boronic acid, Cs₂CO₃, Pd(PPh₃)₄, 2:1 DME/H₂O, 150 °C, microwave, 60 min.

Scheme 2.

Synthetic route for compounds 5a-5ae. Reagents and conditions: (a) amine, THF, rt, 16 h; (b) amine THF:IPA (1:1), 80 °C, 4h; (c) amine, HCl, dioxane, microwave, 150 °C, 40 min.; (d) amine, Pd₂dba₃, XPhos, KOtBu, t-BuOH, 100 °C, 16h.

Scheme 3.

Synthetic route for compounds 9–11. Reagents and conditions: (a) 2,2,2-tifluoroethylamine, DIPEA, n-BuOH, 90 °C, 16 h; (b) amine, Pd₂dba₃, XPhos, KOtBu, t-BuOH, 100 °C, 16h.

Scheme 4.

Synthetic route for compounds 13a-13b. Reagents and conditions: (a) 2,2,2-tifluoroethylamine, DIPEA, n-BuOH, 90 °C, 16 h; (b) aniline, HCl, dioxane, microwave, 150 °C, 40 min.; (c) 3-aminothiophene, Pd₂dba₃, XPhos, KOtBu, t-BuOH, 100 °C, 16h.