Merck Research Labs

In work on a tumor-cell inhibitor, chemists in Merck’s technology enabled synthesis (TES) group in West Point, Pa., found that microwave chemistry—they use Biotage instruments—has not only sped up reaction times but also has brought a structural diversity strategy into library design. As senior research chemist Scott E. Wolkenberg says, he and his colleagues view microwave synthesizers as “diversity engines” and as “an enabling technology that can get us to the analogs quicker.”

Rather than work with very large compound libraries, TES chemists advance their projects with many iterations of smaller libraries of 10 to 100 compounds. Group leader Craig W. Lindsley and Zhijian Zhao, along with colleagues in the TES group, were studying a protein, a biochemical survival broker in tumor pathways called protein kinase B/PKB, or Akt. When activated, this kinase affects a number of growth factors and receptors involved in tumor-cell growth and proliferation.

Akt comes in functionally distinct isozymes: Akt1, Akt2, and Akt3. Inhibiting Akt in a specific way could hamper tumor cells. As Lindsley and his colleagues point out (Bioorganic & Medicinal Chemistry Letters, in press), the study of Akt as a potential anticancer therapeutic has been hampered by a lack of Akt-specific inhibitors. So first, the chemists sought to help answer how the isozymes differed from each other.

From high-throughput screening aimed at finding Akt inhibitors, a compound called 2,3-diphenylquinoxaline emerged. One research strategy focused on replacing the primary amine in 2,3-diphenylquinoxaline with functionalized amines while doing away with the gem-dimethyl functionality. The chemists used microwave syntheses to create amino-functionalized quinoxalines. The resulting compounds, while structurally close to the lead, were 10 to 100 times more potent and acted generally as selective dual inhibitors of Akt1 and Akt2.

Again applying microwave-assisted organic synthesis, an approach was taken to incorporate diverse structures to develop more selective agents. As Wolkenberg explains, the success of the microwave quinoxaline synthesis led the team to use similar conditions for the preparation of a diverse set of heterocycles from a single 1,2-diketone intermediate. The ease of microwave synthesis was pivotal in driving the project in these diverse directions, he says.

As a result of this work, the chemists have developed microwave protocols to prepare quinoxalines, imidazoles, and pyrazinones from 1,2-diketone intermediates. These intermediates act, as Wolkenberg says, as “diversification elements.” Microwave synthesis, he says, helps to broaden library design beyond the decoration of a heterocyclic template with monomer units. The library that is created can contain a number of heterocyclic scaffolds, which also offer a broader intellectual property position.

While continuing library work on the amino-functionalized quinoxaline, the scientists created new libraries around a 5,6-diphenylpyrazin-2(1H)-one core. As Wolkenberg says, further microwave-assisted syntheses and assays yielded two novel series of Akt kinase inhibitors based on either a 2,3-diphenylquinoxaline or 5,6-diphenylpyrazin-2(1H)-one core. These compounds turned out to be selective Akt1 and selective Akt2 inhibitors.

Along with the dual Akt1/Akt2 inhibitors, research proceeded to see which one has the higher antitumor activity. As it turns out, inhibiting Akt1 and Akt2, either with two selective compounds or a single dual Akt1/Akt2 inhibitor, leads to antitumor activity. Merck continues to develop these Akt inhibitors as potential drug candidates.