Aminoimidazo[1,2-a]pyridines as a new structural class of cyclin-dependent kinase inhibitors. Part 1: Design, synthesis, and biological evaluation.

We have identified a novel structural class of protein serine/threonine kinase inhibitors comprised of an aminoimidazo[1,2-a]pyridine nucleus. Compounds from this family are shown to potently inhibit cyclin-dependent kinases by competing with ATP for binding to a catalytic subunit of the protein. Structure-based design approach was used to direct this chemical scaffold toward generating potent and selective CDK2 inhibitors. The discovery of this new class of ATP-site directed protein kinase inhibitors, aminoimidazo[1,2-a]pyridines, provides the basis of new medicinal chemistry tool in search for an effective treatment of cancer and other diseases that involve protein kinase signaling pathways.

Aryl[a]pyrrolo[3,4-c]carbazoles as selective cyclin D1-CDK4 inhibitors.

The synthesis of new analogues of Arcyriaflavin A in which one indole ring is replaced by an aryl or heteroaryl ring is described. These new series of aryl[a]pyrrolo[3,4-c]carbazoles were evaluated as inhibitors of Cyclin D1-CDK4. A potent and selective D1-CDK4 inhibitor, 7a (D1-CDK4 IC(50)=45 nM), has been identified. The potency, selectivity profile against other kinases, and structure-activity relationship (SAR) trends of this class of compounds are discussed.

Studies on cyclin-dependent kinase inhibitors: indolo-[2,3-a]pyrrolo[3,4-c]carbazoles versus bis-indolylmaleimides.

A series of indolo[2,3-a]pyrrolo[3,4-c]carbazoles and their bis-indolylmaleimides precursors have been prepared in order to compare their activity as D1-CDK4 inhibitors. Both enzymatic and antiproliferative assays have shown that the structurally more constrained indolo[2,3-a]pyrrolo[3,4-c]carbazoles are consistently more active (8-42-fold) in head-to-head comparison with their bis-indolylmaleimides counterparts. Cell-cycle analysis using flow cytometry have also shown that the indolocarbazoles are selective G1 blockers while the bis-indolylmaleimides arrest cells in the G2/M phase.

Synthesis of aryl- and heteroaryl[a]pyrrolo[3,4-c]carbazoles.

Synthesis of aryl- and hetero[a]pyrrolo[3,4-c]carbazoles by photochemical oxidation and Heck cyclization are described. Photochemical oxidation of 2-naphthyl indolyl maleimide affords two different carbazole regioisomers, depending on the reaction conditions. The regiochemistry of the cyclization can be controlled using the Heck reaction.

Imidazo[1,2-b]pyridazines, novel nucleus with potent and broad spectrum activity against human picornaviruses: design, synthesis, and biological evaluation.

A novel structural class of picornavirus inhibitors comprising an imidazo[1,2-b]pyridazine nucleus was discovered. 2-Aminoimidazo[1,2-b]pyridazines (6d, (E/Z)-7b, (E)-7d, (Z)-7d, (E/Z)-8b, (E)-10b, (E)-13a, (Z)-13a, (E)-13b, (Z)-13b, (E)-13c, and (Z)-13c) were designed and synthesized in an effort to identify potent broad spectrum antirhinoviral agents. A practical synthetic route to this chemical scaffold has been developed. The target compounds were evaluated in a plaque reduction assay and in a cytopathic effect assay. Our preliminary SAR studies highlight the minimum structural features required for antirhinovirus activity. Our data suggest that the nature of the linker between the phenyl and the imidazopyridazine moieties has a significant influence on the activity of these compounds. Oximes are slightly better than vinyl carboxamides at this position. The oximes are the most potent analogues against human rhinovirus 14 (HRV-14), and at the concentrations evaluated, no apparent cellular toxicity is noted. Furthermore, the E geometry appears to be a key element for activity; the Z isomer leads to a considerable loss in potency. Of particular interest, analogue 7b exhibits potent broad-spectrum antirhinoviral and antienteroviral activity when evaluated against a panel of seven additional rhino- and enteroviruses. The chemistry and the biological evaluations are discussed.

Novel, potent and selective cyclin D1/CDK4 inhibitors: indolo[6,7-a]pyrrolo[3,4-c]carbazoles.

The synthesis and CDK inhibitory properties of a series of indolo[6,7-a]pyrrolo[3,4-c]carbazoles is reported. In addition to their potent CDK activity, the compounds display antiproliferative activity against two human cancer cell lines. These inhibitors also effect strong G1 arrest in these cell lines and inhibit Rb phosphorylation at Ser780 consistent with inhibition of cyclin D1/CDK4.