Discovery of a pyrazolo[1,5-a]pyrimidine derivative (MT-3014) as a highly selective PDE10A inhibitor via core structure transformation from the stilbene moiety

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.

Insights into the medicinal chemistry of heterocycles integrated with a pyrazolo[1,5-a]pyrimidine scaffold

Pyrazolo[1,5-a]pyrimidines are the dominant motif of many drugs; for instance, zaleplon and indiplon are sedative agents and ocinaplon was identified as an anxiolytic agent. The importance of this class of compounds lies in its varied and significant biological activities, and accordingly, considerable methods have been devised to prepare these compounds. Hence, other derivatives of this class of compounds were prepared by substitution reactions with different nucleophiles exploiting the activity of groups linked to the ring carbon and nitrogen atoms. The methods used vary through the condensation reactions of the aminopyrazoles with 1,2-allenic, enaminonitriles, enaminones, 1,3-diketones, unsaturated nitriles, or unsaturated ketones. Alternatively, these compounds are prepared through the reactions of acyclic reagents, as these methods were recently developed efficiently with high yields. The current review highlighted the recent progress of the therapeutic potential of pyrazolo[1,5-a]pyrimidines as antimicrobial, anticancer, antianxiety, anti-proliferative, analgesic, and antioxidant agents, carboxylesterase, translocator protein and PDE10A inhibitors, and selective kinase inhibitors.

Bicyclic 5-6 Systems: Comprehensive Synthetic Strategies for the Annulations of Pyrazolo[ 1,5-a]pyrimidines

Pyrazolopyrimidines are a privileged class of 5-6 bicyclic systems with three or four nitrogen atoms, including four possible isomeric structures. The significance of this class of compounds is that they can be applied in medical and pharmaceutical fields due to their unlimited biological aptitude, hence it is the basic skeleton of several synthetic drugs. The current review aimed to highlight all the synthetic routes that have been applied to construct the pyrazolo[1,5-a]pyrimidine ring systems up to date. The sections in this study included the synthesis of pyrazolo[1,5- a]pyrimidines by condensation reactions of 5-aminopyrazoles with each of β-diketones, 1,5-diketones, β- ketoaldehydes, α-cyanoaldehydes, β-enaminones, enamines, enaminonitriles, ethers, with unsaturated ketones, unsaturated thiones, unsaturated esters, unsaturated dienones "1,2-allenic", unsaturated aldehydes, unsaturated imines, and unsaturated nitriles. The routes adopted to synthesize this class of heterocyclic compounds were extended for ring construction from acyclic reagents and multicomponent reactions under catalytic or catalyst-free conditions.

Synthesis and preclinical evaluation of [11C]MTP38 as a novel PET ligand for phosphodiesterase 7 in the brain

Purpose

Phosphodiesterase (PDE) 7 is a potential therapeutic target for neurological and inflammatory diseases, although in vivo visualization of PDE7 has not been successful. In this study, we aimed to develop [¹¹C]MTP38 as a novel positron emission tomography (PET) ligand for PDE7.

Methods

[¹¹C]MTP38 was radiosynthesized by ¹¹C-cyanation of a bromo precursor with [¹¹C]HCN. PET scans of rat and rhesus monkey brains and in vitro autoradiography of brain sections derived from these species were conducted with [¹¹C]MTP38. In monkeys, dynamic PET data were analyzed with an arterial input function to calculate the total distribution volume (V_T). The non-displaceable binding potential (BP_ND) in the striatum was also determined by a reference tissue model with cerebellar reference. Finally, striatal occupancy of PDE7 by an inhibitor was calculated in monkeys according to changes in BP_ND.

Results

[¹¹C]MTP38 was synthesized with radiochemical purity ≥99.4% and molar activity of 38.6 ± 12.6 GBq/μmol. Autoradiography revealed high radioactivity in the striatum and its reduction by non-radiolabeled ligands, in contrast with unaltered autoradiographic signals in other regions. In vivo PET after radioligand injection to rats and monkeys demonstrated that radioactivity was rapidly distributed to the brain and intensely accumulated in the striatum relative to the cerebellum. Correspondingly, estimated V_T values in the monkey striatum and cerebellum were 3.59 and 2.69 mL/cm³, respectively. The cerebellar V_T value was unchanged by pretreatment with unlabeled MTP38. Striatal BP_ND was reduced in a dose-dependent manner after pretreatment with MTP-X, a PDE7 inhibitor. Relationships between PDE7 occupancy by MTP-X and plasma MTP-X concentration could be described by Hill’s sigmoidal function.

Conclusion

We have provided the first successful preclinical demonstration of in vivo PDE7 imaging with a specific PET radioligand. [¹¹C]MTP38 is a feasible radioligand for evaluating PDE7 in the brain and is currently being applied to a first-in-human PET study.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05269-4.

Medicinal chemistry strategies for the development of phosphodiesterase 10A (PDE10A) inhibitors - An update of recent progress

Phosphodiesterase 10A is a member of Phosphodiesterase (PDE)-superfamily of the enzyme which is responsible for hydrolysis of cAMP and cGMP to their inactive forms 5'-AMP and 5'-GMP, respectively. PDE10A is highly expressed in the brain, particularly in the putamen and caudate nucleus. PDE10A plays an important role in the regulation of localization, duration, and amplitude of the cyclic nucleotide signalling within the subcellular domain of these regions, and thereby modulation of PDE10A enzyme can give rise to a new therapeutic approach in the treatment of schizophrenia and other neurodegenerative disorders. Limitation of the conventional therapy of schizophrenia forced the pharmaceutical industry to move their efforts to develop a novel treatment approach with reduced side effects. In the past decade, considerable developments have been made in pursuit of PDE10A centric antipsychotic agents by several pharmaceutical industries due to the distribution of PDE10A in the brain and the ability of PDE10A inhibitors to mimic the effect of D2 antagonists and D1 agonists. However, no selective PDE10A inhibitor is currently available in the market for the treatment of schizophrenia. The present compilation concisely describes the role of PDE10A inhibitors in the therapy of neurodegenerative disorders mainly in psychosis, the structure of PDE10A enzyme, key interaction of different PDE10A inhibitors with human PDE10A enzyme and recent medicinal chemistry developments in designing of safe and effective PDE10A inhibitors for the treatment of schizophrenia. The present compilation also provides useful information and future direction to bring further improvements in the discovery of PDE10A inhibitors.

Antipsychotic-like effects of a novel phosphodiesterase 10A inhibitor MT-3014 in rats

Phosphodiesterase (PDE) 10A is an attractive therapeutic target for schizophrenia. Here, we investigated the antipsychotic-like effects of a novel PDE10A inhibitor, 1-({2-(7-fluoro-3-methylquinoxalin-2-yl)-5-[(3R)-3-fluoropyrrolidin-1-yl]pyrazolo[1,5-α]pyrimidin-7-yl}amino)-2-methylpropan-2-ol hydrochloride (MT-3014) in rats. MT-3014 showed a potent and selective inhibitory effect against PDE10A (IC₅₀ = 0.357 nmol/L). Oral administration of MT-3014 (1.0-10 mg/kg) significantly increased the levels of cAMP, cGMP and cAMP response element-binding protein (CREB) phosphorylation in the rat striatum. MT-3014 decreased MK-801 (0.075 mg/kg)-induced hyperactivity (ED₅₀ = 0.30 mg/kg) in a dose-dependent manner, although it decreased spontaneous locomotion in control rats (ED₅₀ = 0.48 mg/kg); its effects were equivalent to those of risperidone. MT-3014 (0.3-3.0 mg/kg and 0.2 mg/kg) attenuated MK-801-induced prepulse inhibition deficits and cognitive deficits in rats, respectively, whereas risperidone attenuated MK-801-induced prepulse inhibition at only a high dose and failed to improve MK-801-induced cognitive deficits. Similar to risperidone (ID₅₀ = 0.63 mg/kg), MT-3014 suppressed the conditioned avoidance response (ID₅₀ = 0.32 mg/kg). Interestingly, MT-3014 did not elicit catalepsy and plasma prolactin increases at high doses. Furthermore, it also did not affect body weight. A positron emission tomography study using [¹¹C]IMA107 showed a plasma concentration-dependent increase in brain PDE10A occupancy after oral administration of MT-3014 within the pharmacological dose range in rats. Brain PDE10A occupancy corresponding to the ID₅₀ value in the conditioned avoidance response was approximately 60%, predicting the target occupancy in patients with schizophrenia. These results suggest that MT-3014 may be a novel antipsychotic drug, which is expected to have additional effects on cognitive impairment, without the prominent side effects associated with current atypical antipsychotics.

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.