The protein kinase DYRK1A has been suggested to act as one of the intracellular regulators contributing to neurological alterations found in individuals with Down syndrome. For an assessment of the role of DYRK1A, selective synthetic inhibitors are valuable pharmacological tools. However, the DYRK1A inhibitors described in the literature so far either are not sufficiently selective or have not been tested against closely related kinases from the DYRK and the CLK protein kinase families. The aim of this study was the identification of DYRK1A inhibitors exhibiting selectivity versus the structurally and functionally closely related DYRK and CLK isoforms. Structure modification of the screening hit 11H-indolo[3,2-c]quinoline-6-carboxylic acid revealed structure–activity relationships for kinase inhibition and enabled the design of 10-iodo-substituted derivatives as very potent DYRK1A inhibitors with considerable selectivity against CLKs. X-ray structure determination of three 11H-indolo[3,2-c]quinoline-6-carboxylic acids cocrystallized with DYRK1A confirmed the predicted binding mode within the ATP binding site.

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a potential drug target because of its role in the development of Down syndrome and Alzheimer’s disease. The selective DYRK1A inhibitor 10-iodo-11H-indolo[3,2-c]quinoline-6-carboxylic acid (KuFal194), a large, flat and lipophilic molecule, suffers from poor water solubility, limiting its use as chemical probe in cellular assays and animal models. Based on the structure of KuFal194, 7-chloro-1H-indole-3-carbonitrile was selected as fragment template for the development of smaller and less lipophilic DYRK1A inhibitors. By modification of this fragment, a series of indole-3-carbonitriles was designed and evaluated as potential DYRK1A ligands by molecular docking studies. Synthesis and in vitro assays on DYRK1A and related protein kinases identified novel double-digit nanomolar inhibitors with submicromolar activity in cell culture assays.

Since hyperactivity of the protein kinase DYRK1A is linked to several neurodegenerative disorders, DYRK1A inhibitors have been suggested as potential therapeutics for Down syndrome and Alzheimer’s disease. Most published inhibitors to date suffer from low selectivity against related kinases or from unfavorable physicochemical properties. In order to identify DYRK1A inhibitors with improved properties, a series of new chemicals based on [b]-annulated halogenated indoles were designed, synthesized, and evaluated for biological activity. Analysis of crystal structures revealed a typical type-I binding mode of the new inhibitor 4-chlorocyclohepta[b]indol-10(5H)-one in DYRK1A, exploiting mainly shape complementarity for tight binding. Conversion of the DYRK1A inhibitor 8-chloro-1,2,3,9-tetrahydro-4H-carbazol-4-one into a corresponding Mannich base hydrochloride improved the aqueous solubility but abrogated kinase inhibitory activity.

2-tert- 6,7,8,9,indole was synthesized by reaction of cycloheptanone and (4-tert-butylphenyl)hydrazine hydrochloride in the presence of sodium acetate and sulfuric acid in glacial acetic acid via Fischer indole synthesis. . Recently paullone chalcone hybrid structures 1 were reported to inhibit the growth of Leishmania amastigotes in vitro [7]. In order to study structure-activity relationships regarding this antiparasitic activity congeners related to 1 are currently investigated. In the course of these studies we were interested in 2-tert-butyl-5, 6,7,8,9,10-hexahydrocyclohepta[b]indole (2) representing the tert-butyl substituted indole fragment reminiscent of the paullone substructure in 1. A thorough survey of the literature revealed that 2 was hitherto unknown. KeywordsThe synthesis of 2 was accomplished by a straightforward Fischer indole synthesis [8,9] protocol from cycloheptanone (3) and (4-tert-butylphenyl)hydrazine hydrochloride (4). OPEN ACCESS

Abstract:The title compound was prepared by a Friedel-Crafts acylation-oxime synthesis-decarboxylation/dehydration sequence starting from commercially available 7-iodoindole with 2-(7-iodo-1H-indol-3-yl)-2-oxoacetic acid as isolated intermediate. The structural identity of the title compound was proven by elemental analysis and spectroscopic methods (IR, NMR, EI-MS), and purity was assessed by two independent HPLC methods.