BAY-73-6691 is a novel, potent, and selective PDE9 inhibitor that was developed by Bayer for the treatment of Alzheimer's disease. The PDE9A enzyme is expressed primarily in the brain, with high concentrations in the cerebellum, neocortex, striatum, and hippocampus, and acts to limit the cGMP-mediated signal transduction which occurs following glutamate binding to NMDA receptors. Consequently, selective PDE9A inhibitors were predicted to prolong intracellular responses to glutamate and enhance glutamate signaling, and since this process is known to be involved in learning and memory, PDE9A inhibitors should have a nootropic effect and may be useful in the treatment of Alzheimer's. Animal studies have confirmed these expectations, and BAY 73-6691 has been shown to improve learning and memory in rats. As the first selective PDE9A inhibitor to be developed, it is also widely used in research into the function of this enzyme subtype. However pre-clinical research is at an early stage and it is not yet known whether BAY 73-6691 will prove suitable to progress to human trials, or if it will remain merely a laboratory research tool.

BAY 61-3606 is a potent inhibitor of spleen tyrosine kinase (Syk) which is playing essential roles in receptors for Fc portion of immunoglobulins and B cell receptor complex signaling in various inflammatory cells. In addition, BAY61-3606 could inhibit the inhibitor of nuclear factor kappa B kinase (IKK-alpha) kinase activity. The compound is able to inhibit neoplastic phenotype of leukemia cells as well as of colon and breast cancer cells in vitro. BAY 61-3606 also exrets antiinflammatory and antiallergic properties in animal models.

BAY-41-2272 is a direct and NO-independent soluble guanylate cyclase (sGC) stimulator. It sensitizes sGC to nitric oxide (NO), its physiological stimulator, and contains antiplatelet activity. BAY-41-2272 is an inhibitor of GCS. BAY-41-2272 inhibits platelet aggregation (IC50 = 36 nM) and phenylephrine-induced contractions of rabbit aorta (IC50 = 0.30 uM). BAY-41-2272 also reduces vascular smooth muscle growth through cAMP- and cGMP-dependent PKA and PKG pathways. BAY-41-2272 not only sensitized NO-sensitive GC toward activation by NO but also, with comparable potency, inhibited cGMP degradation by PDE5. BAY-41-2272 may provide a novel therapeutic compound for treating chronic hypoxic pulmonary hypertension.

BAY 41-4109 (methyl (R)-4-(2-chloro-4-fluorophenyl)-2-(3,5-difluoro-2-pyridinyl)-6-methyl-1,4-dihydro-pyrimidine-5-carboxylate) is a heteroaryldihydropyrimidine (HAP) antiviral compound. BAY 41-4109 treatment disassembled the core capsids and separated them into monomers or dimers, the form in which they could be further degraded into peptides. The core protein assembled in a misdirected manner cannot function effectively. BAY 41-4109 was effective in animal models of HBV, however, its development was discontinued.