Identification of a tetrahydroquinoline analog as a pharmacological inhibitor of the cAMP-binding protein Epac.

The cAMP-binding protein Epac is a therapeutic target for the treatment of various diseases such as cardiac hypertrophy and tumor invasion. This points out the importance to develop Epac inhibitors to better understand the involvement of these cAMP sensors in physiology and pathophysiology. Here, we have developed a functional fluorescence-based high-throughput assay with a Z' value around 0.7 for screening Epac-specific antagonists. We identified an Epac1 inhibitor compound named CE3F4 that blocked Epac1 guanine nucleotide exchange activity toward its effector Rap1 both in cell-free systems and in intact cells. CE3F4 is a tetrahydroquinoline analog that fails to influence protein kinase A holoenzyme activity. CE3F4 inhibited neither the interaction of Rap1 with Epac1 nor directly the GDP exchange on Rap1. The kinetics of inhibition by CE3F4 indicated that this compound did not compete for binding of agonists to Epac1 and suggested an uncompetitive inhibition mechanism with respect to Epac1 agonists. A structure-activity study showed that the formyl group on position 1 and the bromine atom on position 5 of the tetrahydroquinoline skeleton were important for CE3F4 to exert its inhibitory activity. Finally, CE3F4 inhibited Rap1 activation in living cultured cells, following Epac activation by either 8-(4-chlorophenylthio)-2'-O-methyl-cAMP, an Epac-selective agonist, or isoprenaline, a non-selective ß-adrenergic receptor agonist. Our study shows that CE3F4 and related compounds may serve as a basis for the development of new therapeutic drugs.

The (R)-enantiomer of CE3F4 is a preferential inhibitor of human exchange protein directly activated by cyclic AMP isoform 1 (Epac1).

Isoform 1 and isoform 2 of exchange protein directly activated by cAMP (Epac1 and Epac2) contribute to cAMP signaling in numerous cellular processes. Their guanine-nucleotide exchange factor (GEF) activity toward the small GTP-binding protein Rap1 is stimulated by the agonist cAMP. CE3F4, a tetrahydroquinoline analog, prevents Epac1 activation in vitro and in living cultured cells by inhibiting the GEF activity of Epac1. However, the activity of the (R)- and (S)-enantiomers of CE3F4, as well as the ability of CE3F4 and its analogs to inhibit Epac2 GEF activity, have not yet been investigated. In this study, we report that (R)-CE3F4 is a more potent cAMP antagonist than racemic CE3F4 and (S)-CE3F4, inhibiting the GEF activity of Epac1 with 10-times more efficiency than (S)-CE3F4. Epac2, in contrast to Epac1, is activated more efficiently by cAMP than by 8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (007), an Epac-selective cAMP analog. (R)-CE3F4 displays Epac isoform preference, with 10-fold selectivity for Epac1 over Epac2. Deletion of the N-terminal cyclic nucleotide-binding domain of Epac2 does not affect the characteristics of activation of Epac2 by cAMP and by 007, nor its inhibition by CE3F4. Finally, the evaluation of a series of CE3F4 structural analogs as GEF inhibitors allowed identifying structural features that are important for high Epac1 inhibitory activity of CE3F4. We conclude that the (R)-enantiomer of CE3F4 is a preferential inhibitor of Epac1 with high potency in the low micromolar range, and we suggest that this compound may be a useful pharmacological tool for investigating the functional role of Epac1 in cAMP signaling.

Nucleophilic addition onto methyl-4H-1,4-oxazine-3-carboxylate moiety: short access to 1,4-diazine privileged substructures.

To determine the synthetic potential of the original 1,4-oxazine ring, which appears as a valuable building block for the synthesis of more complex derivatives, Michael-type nucleophilic additions were studied. According to the nature of the nucleophile, either acyclic or cyclic derivatives were isolated. In the presence of primary amines, a short and efficient access to diazinic hemiaminals was described.

Diversity-oriented synthesis of polycyclic diazinic scaffolds.

An efficient and versatile synthesis of a polycyclic diazinic system starting from oxazine has been developed using a two-step Michael/retro Michael and cyclization sequence. The substrates were synthesized with good to high yields giving rapid access to molecular diversity.

Synthesis and reactivity of imide-derived bisvinyl phosphates. Reactivity of 2,6-disubstituted 1,4-dihydropyridines.

Symmetrical and unsymmetrical 2,6-disubstituted dihydropyridines were prepared in high yields under mild conditions using the Suzuki and Stille Pd-catalyzed coupling reactions of imide-derived bisvinyl phosphates with a range of aryl, heteroaryl, and alkenyl moieties. The alkylation reaction at C-4 easily afforded original tri- and tetrasubstituted dihydropyridines. Hydrolysis of the latter under acidic condition provided efficiently either open-chain 1,5-diketones or di- or trisubstituted pyridines.