Synthesis and evaluation of polycyclic pyrazolo[3,4-d]pyrimidines as PDE1 and PDE5 cGMP phosphodiesterase inhibitors

Advances in targeting Phosphodiesterase 1: From mechanisms to potential therapeutics

Phosphodiesterase 1 (PDE1) is an enzyme entrusted with the hydrolysis of the second messengers cAMP and cGMP, thereby governing a plethora of metabolic processes, encompassing ion channel modulation and cellular apoptosis. Recent advancements in the realm of small molecule structural variations have greatly facilitated the exploration of innovative applications for PDE1. Remarkably, a recent series of PDE1 inhibitors (PDE1i) have been meticulously formulated and devised, showcasing enhanced selectivity and potency. Among them, ITI-214 has entered Phase II clinical trials, holding promise for the treatment of Parkinson's disease and heart failure. Nevertheless, the majority of current PDE1 inhibitors have encountered substantial side effects in clinical trials attributable to their limited selectivity, this predicament presents a formidable obstacle in the development of specific small molecule inhibitors targeting PDE1. This Perspective endeavors to illuminate the potential design approaches, structure-activity relationships, and biological activities of current PDE1i, aiming to offer support and insights for clinical practice and the development of novel PDE1i.

Structure-based development of potent and selective type-II kinase inhibitors of RIPK1

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) functions as a key regulator in inflammation and cell death and is involved in mediating a variety of inflammatory or degenerative diseases. A number of allosteric RIPK1 inhibitors (RIPK1i) have been developed, and some of them have already advanced into clinical evaluation. Recently, selective RIPK1i that interact with both the allosteric pocket and the ATP-binding site of RIPK1 have started to emerge. Here, we report the rational development of a new series of type-II RIPK1i based on the rediscovery of a reported but mechanistically atypical RIPK3i. We also describe the structure-guided lead optimization of a potent, selective, and orally bioavailable RIPK1i, 62, which exhibits extraordinary efficacies in mouse models of acute or chronic inflammatory diseases. Collectively, 62 provides a useful tool for evaluating RIPK1 in animal disease models and a promising lead for further drug development.

Silver/chiral pyrrolidinopyridine relay catalytic cycloisomerization/(2 + 3) cycloadditions of enynamides to asymmetrically synthesize bispirocyclopentenes as PDE1B inhibitors

Significant progress has been made in asymmetric synthesis through the use of transition metal catalysts combined with Lewis bases. However, the use of a dual catalytic system involving 4-aminopyridine and transition metal has received little attention. Here we show a metal/Lewis base relay catalytic system featuring silver acetate and a modified chiral pyrrolidinopyridine (PPY). It was successfully applied in the cycloisomerization/(2 + 3) cycloaddition reaction of enynamides. Bispirocyclopentene pyrazolone products could be efficiently synthesized in a stereoselective and economical manner (up to >19:1 dr, 99.5:0.5 er). Transformations of the product could access stereodivergent diastereoisomers and densely functionalized polycyclic derivatives. Mechanistic studies illustrated the relay catalytic model and the origin of the uncommon chemoselectivity. In subsequent bioassays, the products containing a privileged drug-like scaffold exhibited isoform-selective phosphodiesterase 1 (PDE1) inhibitory activity in vitro. The optimal lead compound displayed a good therapeutic effect for ameliorating pulmonary fibrosis via inhibiting PDE1 in vivo.

The long and winding road of designing phosphodiesterase inhibitors for the treatment of heart failure

Cyclic nucleotide phosphodiesterases (PDEs) are a superfamily of enzymes known to play a critical role in the indirect regulation of several intracellular metabolism pathways through the selective hydrolysis of the phosphodiester bonds of specific second messenger substrates such as cAMP (3',5'-cyclic adenosine monophosphate) and cGMP (3',5'-cyclic guanosine monophosphate), influencing the hypertrophy, contractility, apoptosis and fibroses in the cardiovascular system. The expression and/or activity of multiple PDEs is altered during heart failure (HF), which leads to changes in levels of cyclic nucleotides and function of cardiac muscle. Within the cardiovascular system, PDEs 1-5, 8 and 9 are expressed and are interesting targets for the HF treatment. In this comprehensive review we will present a briefly description of the biochemical importance of each cardiovascular related PDE to the HF, and cover almost all the "long and winding road" of designing and discovering ligands, hits, lead compounds, clinical candidates and drugs as PDE inhibitors in the last decade.

An assessment study of known pyrazolopyrimidines: Chemical methodology and cellular activity

Heterocyclic compounds with nitrogen atom play a key role in the normal life cycle of a cell. Pyrazolopyrimidine is a privileged class of nitrogen containing fused heterocyclic compound contributing to a major portion of all lead molecules in medicinal chemistry. The thumbprint of pyrazolopyrimidine as a pharmacophore is always noticeable due to its analogy with the adenine base in DNA. Pyrazolopyrimidines are divided into five types [I, II, III, IV, V] based on the mechanism of action on the specific target conferring a wide scope of research which has accelerated the interest of researchers to investigate its biological profile. In 1956, the anti-cancer activity of pyrazolopyrimidine was evaluated for the first time with appreciable results. Since then, medicinal chemists centered their work on various methods of synthesis and evaluating the biological profile of pyrazolopyrimidine isomers. This report consists of novel methodologies followed to synthesize pyrazolopyrimidine isomers along with a note on their biological significance. To the best of our knowledge, this review article will be first of its kind to encompass different synthetic procedures along with anti-cancer, kinase inhibition, phosphodiesterase inhibition and receptor blocking activity of pyrazolopyrimidine moieties. IC₅₀ values of potent compounds are added wherever necessary to understand the suitability of pyrazolopyrimidine skeletons for a specific biological activity.

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

The condensation of 5-aminopyrazole with various bielectrophilic moieties results in the formation of pyrazoloazines, an interesting array of fused heterocyclic systems. The development of new synthetic routes towards pyrazoloazines for their biological and medicinal exploration is an attractive area for researchers throughout the world. The present review focuses on various synthetic methods developed in the last decade for the synthesis of differently substituted pyrazoloazines by a broad range of organic reactions by means of 5-aminopyrazole as a precursor.

Synthesis, modeling and biological evaluation of hybrids from pyrazolo[1,5c]pyrimidine as antileishmanial agents

Aim: A new series of pyrazolo[1,5-c]pyrimidines were synthesized by different hybridization strategies. Methodology: All structures were confirmed by IR, 1H, 13C, 1H-13C heteronuclear multiple-quantum correlation (HMQC) spectra and microanalysis. They were evaluated for their in vitro antileishmanial activity against miltefosine and amphotericin B deoxycholate as reference drugs. Results: The most active compounds 2a and 9a demonstrated superior potencies to miltefosine by ten- and six-fold, respectively, for the promastigote form, and by 5.5-fold for the amastigote form. Their binding scenario to Leishmania major pteridine reductase was rationalized by docking experiments. In addition, all compounds were safe for the experimental animals orally up to 150 mg/kg and parenterally up to 75 mg/kg. Conclusion: This study provides novel chemotype class for antileishmanial activity.

[Formula: see text]

Crystal structure of N,N-dimethyl-N′-(2-methyl-4-oxo-5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-3(4H)-yl)formimidamide, C14H18N4OS

C14H18N4OS, monoclinic, P21/c (no. 14), a = 15.479(4) Å, b = 13.203(3) Å, c = 7.3147(17) Å, β = 99.385(7)°, V = 1474.9(6) Å3, Z = 4, R gt(F) = 0.070, wR ref(F 2) = 0.197, T = 296(2).

Synthesis, in vitro and in vivo anticancer activity of novel 1-(4-imino-1-substituted-1H-pyrazolo[3,4-d]pyrimidin-5(4H)-yl)urea derivatives

A series of pyrazolo[3,4-d]pyrimidine and urea hybrids have been designed, synthesized and evaluated for their anticancer activity in vitro and in vivo cancer models.

A convenient four-component one-pot strategy toward the synthesis of pyrazolo[3,4-d]pyrimidines

An efficient one-pot synthesis of pyrazolo[3,4-d]pyrimidine derivatives by the four-component condensation of hydrazines, methylenemalononitriles, aldehydes and alcohols has been developed via two different reaction pathways. The structures of target products were characterized by IR spectroscopy, NMR (¹H and ¹³C) spectroscopy and HRMS (ESI) spectrometry. The crystal structure of 4-ethoxy-6-(2-nitrophenyl)-1-phenyl-1H-pyrazolo[3,4-d]pyrimidine was determined by single crystal X-ray diffraction.

Novel pyrazolopyrimidine derivatives targeting COXs and iNOS enzymes; design, synthesis and biological evaluation as potential anti-inflammatory agents

A novel set of 4-substituted-1-phenyl-pyrazolo[3,4-d]pyrimidine and 5-substituted-1-phenyl-pyrazolo[3,4-d]pyrimidin-4-one derivatives were synthesized and evaluated as potential anti-inflammatory agents. The newly prepared compounds were assessed through the examination of their in vitro inhibition of four targets; cyclooxygenases subtypes (COX-1 and COX-2), inducible nitric oxide synthase (iNOS) and nuclear factor kappa B (NF-κB). Compounds 8a, 10c and 13c were the most potent and selective ligands against COX-2 with inhibition percentages of 79.6%, 78.7% and 78.9% at a concentration of 2 μM respectively, while compound 13c significantly inhibited both COX subtypes. On the other hand, fourteen compounds showed high iNOS inhibitory activities with IC50 values in the range of 0.22-8.5μM where the urea derivative 11 was the most active compound with IC50 value of 0.22 μM. Most of the tested compounds were found to be devoid of inhibitory activity against NF-kB. Moreover, almost all compounds were not cytotoxic, (up to 25 μg/ml), against a panel of normal and cancer cell lines. The in silico docking results were in agreement with the in vitro inhibitory activities against COXs and iNOS enzymes. The results of in vivo anti-inflammatory and antinociceptive studies were consistent with that of in vitro studies which confirmed that compounds 8a, 10c and 13c have significant anti-inflammatory and analgesic activities comparable to that of the control, ketorolac. Taken together, dual inhibition of COXs and iNOS with novel pyrazolopyrimidine derivatives is a valid strategy for the development of anti-inflammatory/analgesic agents with the probability of fewer side effects.

PF-04859989 as a template for structure-based drug design: identification of new pyrazole series of irreversible KAT II inhibitors with improved lipophilic efficiency

The structure-based design, synthesis, and biological evaluation of a new pyrazole series of irreversible KAT II inhibitors are described herein. The modification of the inhibitor scaffold of 1 and 2 from a dihydroquinolinone core to a tetrahydropyrazolopyridinone core led to discovery of a new series of potent KAT II inhibitors with excellent physicochemical properties. Compound 20 is the most potent and lipophilically efficient of these new pyrazole analogs, with a k(inact)/K(i) value of 112,000 M(-1)s(-1) and lipophilic efficiency (LipE) of 8.53. The X-ray crystal structure of 20 with KAT II demonstrates key features that contribute to this remarkable potency and binding efficiency.

Chemoenzymatic Asymmetric Total Synthesis of Phosphodiesterase Inhibitors: Preparation of a Polycyclic Pyrazolo[3,4-d]pyrimidine from an Acylnitroso Diels−Alder Cycloadduct-Derived Aminocyclopentenol

[reaction: see text] Enzymatic resolution of Boc-protected 4-aminocyclopenten-1-ol 4c gave both enantiomers 5c and 6c in high ee. Boc removal and separate condensation with chloropyrazolopyrimidine 18 provided elaborated 1,4-aminocyclopentenol derivatives 20 and 26, respectively. Separate treatment of 20 and 26 with Pd(0) under basic conditions induced cyclization to unsaturated polycycles 22 and 27, which, upon catalytic hydrogenation, were transformed to new cyclopentane-containing pyrazolopyrimidines 24 and 28, analogues of recently described novel phosphodiesterase inhibitors.