Discovery of a Novel Series of Pyrazolo[1,5-a]pyrimidine-Based Phosphodiesterase 2A Inhibitors Structurally Different from N-((1S)-1-(3-Fluoro-4-(trifluoromethoxy)phenyl)-2-methoxyethyl)-7-methoxy-2-oxo-2,3-dihydropyrido[2,3-b]pyrazine-4(1H)-carboxamide (TAK-915), for the Treatment of Cognitive Disorders

Phototoxicity─Medicinal Chemistry Strategies for Risk Mitigation in Drug Discovery

Phototoxicity is a common safety concern encountered by project teams in pharmaceutical research and has the potential to stop progression of an otherwise promising candidate molecule. This perspective aims to provide an overview of the approaches toward mitigation of phototoxicity that medicinal chemists have taken during the lead optimization phase in the context of regulatory standards for photosafety evaluation. Various strategies are laid out based on available literature examples in order to highlight how structural modification can be utilized toward successful mitigation of a phototoxicity liability. A proposed flowchart is presented as a guidance tool to be used by the practicing medicinal chemist when facing a phototoxicity risk. The description of available tools to consider in the drug design process will include an overview of the evolution of in silico methods and their application as well as structure alerts for consideration as potential phototoxicophores.

Interaction Patterns of Pyrazolopyrimidines with Receptor Proteins

Heterocyclic compounds have a prominent role in medicinal chemistry and drug design. They are not only useful as medicinally active compounds but also as a modular structural scaffold for drug design. Therefore, heterocycles are present in many ligands that exhibit a broad spectrum of biological activities. Pyazolopyrimidines are nitrogen heterocycles and are part of many biologically active compounds and marketed drugs. This study examines the non-covalent interactions between the pyrazolopyrimidine rings and receptor proteins through data mining and analysis of high-resolution crystal structures deposited in the Protein Data Bank. The Protein Data Bank contains 471 crystal structures with pyrazolopyrimidine derivatives as ligands, among which 50% contains 1H-pyrazolo[3,4-d]pyrimidines (Pyp1), while 38% contains pyrazolo[1,5-a] pyrimidines (Pyp2). 1H-Pyrazolo[4,3-d]pyrimidines (Pyp3) are found in 11% of the structures, and no structural data is available for pyrazolo[1,5-c]pyrimidine isomers (Pyp4). Among receptor proteins, transferases are found in most examples (67.5%), followed by hydrolases (13.4%) and oxidoreductases (8.9%). Detailed analysis of structures to identify the most prevalent interactions of pyrazolopyrimidines with proteins shows that aromatic π···π interactions are present in ∼91% of the structures and hydrogen bonds/other polar contacts are present in ∼73% of the structures. The centroid-centroid distances (d_cent) between the pyrazolopyrimidine rings and aromatic side chains of the proteins have been retrieved from crystal structures recorded at a high resolution (data resolution <2.0 Å). The average value of d_cent in pyrazolopyrimidine-protein complexes is 5.32 Å. The information on the geometric parameters of aromatic interactions between the core pyrazolopyrimidine ring and the protein would be helpful in future in silico modeling studies on pyrazolopyrimidine-receptor complexes.

PDE2A Inhibition Enhances Axonal Sprouting, Functional Connectivity, and Recovery after Stroke

Phosphodiesterase (PDE) inhibitors have been safely and effectively used in the clinic and increase the concentration of intracellular cyclic nucleotides (cAMP/cGMP). These molecules activate downstream mediators, including the cAMP response element-binding protein (CREB), which controls neuronal excitability and growth responses. CREB gain of function enhances learning and allocates neurons into memory engrams. CREB also controls recovery after stroke. PDE inhibitors are linked to recovery from neural damage and to stroke recovery in specific sites within the brain. PDE2A is enriched in cortex. In the present study, we use a mouse cortical stroke model in young adult and aged male mice to test the effect of PDE2A inhibition on functional recovery, and on downstream mechanisms of axonal sprouting, tissue repair, and the functional connectivity of neurons in recovering cortex. Stroke causes deficits in use of the contralateral forelimb, loss of axonal projections in cortex adjacent to the infarct, and functional disconnection of neuronal networks. PDE2A inhibition enhances functional recovery, increases axonal projections in peri-infarct cortex, and, through two-photon in vivo imaging, enhances the functional connectivity of motor system excitatory neurons. PDE2A inhibition after stroke does not have an effect on other aspects of tissue repair, such as angiogenesis, gliogenesis, neurogenesis, and inflammatory responses. These data suggest that PDE2A inhibition is an effective therapeutic approach for stroke recovery in the rodent and that it simultaneously enhances connectivity in peri-infarct neuronal populations.SIGNIFICANCE STATEMENT Inhibition of PDE2A enhances motor recovery, axonal projections, and functional connectivity of neurons in peri-infarct tissue. This represents an avenue for a pharmacological therapy for stroke recovery.

Medicinal Chemistry of Pyrazolopyrimidine Scaffolds Substituted with Different Heterocyclic Nuclei

BACKGROUND

Medicinal chemistry of pyrazolopyrimidine scaffolds substituted with different heterocyclic nuclei has attracted great attention due to their wide range of biological activities that have been reported. Pyrazolopyrimidine scaffold is an important privileged heterocycle nucleus in drug discovery.

METHODS

All pharmacological activities of pyrazolopyrimidine scaffold have been mentioned, such as anticancer, anti-inflammatory, antihypertensive, antitubercular, antiviral, antibacterial, antifungal, antidiabetic, and anti-obesity agents. In addition, it was used in both osteoporosis and neurological disorders. The difference in potency and bioavailability of pyrazolopyrimidine derivatives refers to the substituent groups that can increase the activity against specific targets and enhance their selectivity.

RESULTS

This review provides an overview of different synthetic pathways, structure activity relationships, and preclinical studies of pyrazolopyrimidine scaffolds substituted with a variety of heterocyclic nuclei, as well as it provides a discussion on the significant biological findings of these important scaffolds. In addition, it provides some insights on the different macromolecular targets that pyrazolopyrimidine scaffold can effectively work on, such as; cyclin dependent kinases; CDK2, CDK7, and CDK9, checkpoint kinases; CHK1 and CHK2 and their correlation with the anticancer activity, PI3Kα, transient receptor potential canonical 6, B-Raf kinase, Interleukin- 1 receptor-associated kinase 4, B-cell lymphoma 6, TRKA-C kinase, potent kDa ribosomal protein S6 kinase, colon cancer cell line (CaCo-2), domain receptor kinase (KDR), HepG-2 carcinoma cell, FLT3. The antibacterial activity against B. subtilis and E. coli and antifungal activity against C. albicans, C. tropicalis, A. niger, and A. clavatus are discussed.

CONCLUSION

This review provides an overview of the different pharmacological activities of the pyrazolopyrimidine scaffold and its correlation with chemical structure. Some exciting new developments in pyrazolopyrimidine scaffolds are also presented in this review.

Efficient Access to 3,5-Disubstituted 7-(Trifluoromethyl)pyrazolo[1,5-a]pyrimidines Involving SNAr and Suzuki Cross-Coupling Reactions

An efficient and original synthesis of various 3,5-disubstituted 7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidines is reported. A library of compounds diversely substituted in C-3 and C-5 positions was easily prepared from a common starting material, 3-bromo-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-5-one. In C-5 position, a S_NAr type reaction was achieved by first activating the C–O bond of the lactam function with PyBroP (Bromotripyrrolidinophosphonium hexafluorophosphate), followed by the addition of amine or thiol giving monosubstituted derivatives, whereas in C-3 position, arylation was performed via Suzuki–Miyaura cross-coupling using the commercially available aromatic and heteroaromatic boronic acids. Moreover, trifluoromethylated analogues of potent Pim1 kinase inhibitors were designed following our concise synthetic methodology.

Phosphodiesterases PDE2A and PDE10A both change mRNA expression in the human brain with age, but only PDE2A changes in a region-specific manner with psychiatric disease

Many studies implicate altered cyclic nucleotide signaling in the pathophysiology of major depressive disorder (MDD), bipolar disorder (BPD), and schizophrenia (SCZ). As such, we explored how phosphodiesterases 2A (PDE2A) and 10A (PDE10A)-enzymes that break down cyclic nucleotides-may be altered in brains of these patients. Using autoradiographic in situ hybridization on postmortem brain tissue from the Stanley Foundation Neuropathology Consortium, we measured expression of PDE2 and PDE10 mRNA in multiple brain regions implicated in psychiatric pathophysiology, including cingulate cortex, orbital frontal cortex (OFC), superior temporal gyrus, hippocampus, parahippocampal cortex, amygdala, and the striatum. We also assessed how PDE2A and PDE10A expression changes in these brain regions across development using the Allen Institute for Brain Science Brainspan database. Compared to controls, patients with SCZ, MDD and BPD all showed reduced PDE2A mRNA in the amygdala. In contrast, PDE2A expression changes in frontal cortical regions were only significant in patients with SCZ, while those in caudal entorhinal cortex, hippocampus, and the striatum were most pronounced in patients with BPD. PDE10A expression was only detected in striatum and did not differ by disease group; however, all groups showed significantly less PDE10A mRNA expression in ventral versus dorsal striatum. Across development, PDE2A mRNA increased in these brain regions; whereas, PDE10A mRNA expression decreased in all regions except striatum. Thus, PDE2A mRNA expression changes in both a disorder- and brain region-specific manner, potentially implicating PDE2A as a novel diagnostic and/or patient-selection biomarker or therapeutic target.

Therapeutic targeting of 3',5'-cyclic nucleotide phosphodiesterases: inhibition and beyond

Phosphodiesterases (PDEs), enzymes that degrade 3',5'-cyclic nucleotides, are being pursued as therapeutic targets for several diseases, including those affecting the nervous system, the cardiovascular system, fertility, immunity, cancer and metabolism. Clinical development programmes have focused exclusively on catalytic inhibition, which continues to be a strong focus of ongoing drug discovery efforts. However, emerging evidence supports novel strategies to therapeutically target PDE function, including enhancing catalytic activity, normalizing altered compartmentalization and modulating post-translational modifications, as well as the potential use of PDEs as disease biomarkers. Importantly, a more refined appreciation of the intramolecular mechanisms regulating PDE function and trafficking is emerging, making these pioneering drug discovery efforts tractable.

Phosphodiesterase inhibitors say NO to Alzheimer's disease

Phosphodiesterases (PDEs) consisted of 11 subtypes (PDE1 to PDE11) and over 40 isoforms that regulate levels of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), the second messengers in cell functions. PDE inhibitors (PDEIs) have been attractive therapeutic targets due to their involvement in diverse medical conditions, e.g. cardiovascular diseases, autoimmune diseases, Alzheimer's disease (AD), etc. Among them; AD with a complex pathology is a progressive neurodegenerative disorder which affect mostly senile people in the world and only symptomatic treatment particularly using cholinesterase inhibitors in clinic is available at the moment for AD. Consequently, novel treatment strategies towards AD are still searched extensively. Since PDEs are broadly expressed in the brain, PDEIs are considered to modulate neurodegenerative conditions through regulating cAMP and cGMP in the brain. In this sense, several synthetic or natural molecules inhibiting various PDE subtypes such as rolipram and roflumilast (PDE4 inhibitors), vinpocetine (PDE1 inhibitor), cilostazol and milrinone (PDE3 inhibitors), sildenafil and tadalafil (PDE5 inhibitors), etc have been reported showing encouraging results for the treatment of AD. In this review, PDE superfamily will be scrutinized from the view point of structural features, isoforms, functions and pharmacology particularly attributed to PDEs as target for AD therapy.