Medicinal chemical optimization of fluorescent pyrrole-based COX-2 probes

Abstract

Recent studies have demonstrated the ability of human prostaglandin-endoperoxide synthase 2 (COX-2) to guide the formation of fluorescent pyrroles through the Paal-Knorr reaction resulting in the discovery of a central motif. This initial discovery prompted further exploration of this motif for the design of COX-2 inhibitors through the modifications of the substituents on the pyrrole core. This effort led to the discovery of a set of pyrroles whose activity was comparable to Celecoxib, an orally prescribed nonsteroidal anti-inflammatory COX-2 inhibitor. Furthermore, structure-activity relationship (SAR) data, important for the discovery of COX-2 inhibitors, has been obtained.

Keywords: COX-2; Celecoxib; Fluorescent probes; Paal-Knorr; Pyrroles.

Fig. 1.

Comparable to Celecoxib, the two motifs A and B explored herein are comprised of two aryl units Ar1 (blue) and Ar2 (red) attached through a heterocyclic (pyrrole in A and B or pyrazole in Celecoxib) core (black).

Fig. 2.

Synthesis and structures of motif A analogs. Structures are provided with modifications in Ar1 (blue) and Ar2 (red) as well as the R group within the core.

Fig. 3.

Synthesis and structures of motif B analogs. Structures are provided with modifications in Ar1 (blue) and Ar2 (red).

Fig. 4.

A heatmap showing COX-2 inhibitory screening. Blue denotes (light to dark) compounds with increased relative fluorescence (increased enzymatic activity) and thus reduced efficacy when compared to Celecoxib. Green indicates (light to dark) compounds that demonstrated improved efficacy (reduced fluorescence) as compared to Celecoxib. All compounds were screened at 50 μM. Data represents an average of the relative fluorescence obtained every 5 min over 1 h (see Supporting Information for a description of the assay methods and data processing).

Fig. 5.

A comparison activity of a subset of the pyrrole analogs against COX-2. Structures of the best three inhibitors (green) are shown at the top. All compounds were screened at 50 μM and compared with Celecoxib (C, positive) and DMSO (D, negative) as controls. Data represents an average of the relative fluorescence obtained every 5 min over 1 h (see Supporting Information for a description of the assay methods and data processing). Five repetitions were conducted for each compound and control.

Fig. 6.

Evaluation of compounds 3aa, 3bf, and 3bg on COX-2 activity as compared to Celecoxib (C, black). Five repetitions were conducted for each compound and data was collected using the CoxFluor screen (Fig. 4) and single dose assay (Fig. 5).

Fig. 7.

The 1,4-diketone 1a were synthesized using procedure A [21] and 1,4-diketones 1b-1g were synthesized using (procedure B) a similar synthetic procedure that reported in the literature [22]. Characterization data of 1a, 1b-1c, and 1g were matching with those reported in the literature [21,22].

Fig. 8.

The following 1,4-diketones 1h-k were synthesized using similar synthetic procedure [23]. Characterization data of 1h, 1j and 1k were matching with those reported in the literature [23].

Fig. 9.

Pyrroles 3aa-ko were synthesized using similar procedure. This procedure was adapted from the literature [22].