Synthesis and Characterization of a Click-Assembled 18-Atom Macrocycle That Displays Selective AXL Kinase Inhibitory Activity

Abstract

A novel macrocyclic construct consisting of a pyrazolopyrimidine scaffold concatenated to a benzene ring through two triazoles has been developed to investigate uncharted chemical space with bioactive potential. The 18-atom macrocycle was assembled via a double copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction between 1,3-bis(azidomethyl)benzene and a bis-propargylated pyrazolo[3,4-d]pyrimidine core. The resulting macrocycle was functionalized further into a multicyclic analog that displays selective inhibitory activity against the receptor tyrosine kinase AXL.

Figure 1

Structure and synthesis/retrosynthetic strategy of eSM119 (left) and macrocycle 1 (right). The novel compound 1 was designed by the incorporation of a second triazole group to enclose the cyclophene ring.

Scheme 1. Synthesis of the 18-Atom Macrocycle 1 from 6-Chloro-1H-pyrazolo[3,4-d]pyrimidine, 2

Figure 2

Representative three-dimensional (3D) structure models (superimposed through the pyrazolopyrimidine ring) of four of the most significant types of conformers found for 1 after macrocyclic sampling with MacroModel.

Figure 3

(A) ¹H NMR spectra of 1 at different temperatures. (B, C) two-dimensional (2D) HSQC analysis of 1 at 27 and 80 °C.

Figure 4

(A) Columbic surface representation of the AXL active site with the predicted binding pose of 1 (light yellow). Red and blue areas represent negatively and positively polarized areas, respectively. (B) Antiproliferative activity of compound 1 (30 μM) against a panel of cancer cell lines. The cell viability was analyzed with PrestoBlue at day 5. Error bars: ± standard deviation (SD) from n = 2.