A Sonochemical Access to 5-Aryl Substituted Pyrazolo[1,5-a]Pyrimidines as Potential Inhibitors of TNF-α

In spite of various and extensive studies known for pyrazolo[1,5-a]pyrimidines the synthesis, in silico studies and biological evaluation of their 5-(het)aryl analogs remained underexplored. The TNF-α inhibitors on the other hand has considerable therapeutic potential for autoimmune and inflammatory diseases in addition to cancer, diabetes and possibly COVID-19. In the current study 5-aryl pyrazolo[1,5-a]pyrimidines were explored as potential inhibitors of TNF-α that was supported by the in silico studies. This class of compounds was accessed via a sonochemical synthesis involving the acid catalyzed cyclocondensation reaction of aminopyrazoles with acrylophenones in the presence of aerial oxygen. The study indicated that the overall rate of the reaction was enhanced by ultrasound in the absence of which a longer duration and higher temperature was necessary. The current catalyst/promoter/ligand free and scalable method afforded a range of compounds. Some of these compounds showed good inhibition of TNF-α in vitro where ester/amide moiety at the C-3 position played a key role in interacting with the protein dimer as suggested by the in silico studies. Indeed, these groups formed H-bonds with A: GLY121 and B: TYR151 residues of TNF-α dimer in silico. A brief SAR within the series and in silico ADME/toxicity prediction for best active compounds is presented. Compounds 3a-c were identified as initial hits for further pharmacological evaluations. A sonochemical method has been developed for the facile synthesis of pyrazolo[1,5-a]pyrimidines that were evaluated as potential inhibitors of TNF-α. [ABSTRACT FROM AUTHOR] Copyright of Polycyclic Aromatic Compounds is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ultrasound assisted Cu-catalyzed Ullmann-Goldberg type coupling-cyclization in a single pot: Synthesis and in silico evaluation of 11H-pyrido[2,1-b]quinazolin-11-ones against SARS-CoV-2 RdRp.

The in silico evaluation of 11H-pyrido[2,1-b]quinazolin-11-one derivatives against SARS-CoV-2 RdRp was undertaken based on the reports on antiviral activities of this class of compounds in addition to the promising interactions of the antiviral drug penciclovir as well as quinazoline derivatives with SARS-CoV-2 RdRp in silico. The target compounds were prepared via an Ullmann-Goldberg type coupling followed by the subsequent cyclization (involving amidation) in a single pot. The methodology involved a CuI-catalyzed reaction of 2-iodobenzoate ester with 2-aminopyridine or quinolin-2-amine or thiazol-2-amine under ultrasound to give the expected products in acceptable (51-93%) yields. The molecular interactions of the synthesized 11H-pyrido[2,1-b]quinazolin-11-one derivatives with the SARS-CoV-2 RdRp (PDB: 7AAP) were evaluated in silico. The study suggested that though none of these compounds showed interactions better than penciclovir but the compound 3a and 3n appeared to be comparable along with 3b seemed to be nearly comparable to favipiravir and remdesivir. The compound 3n with the best binding energy (-79.85 Kcal/mol) participated in the H-bond interactions through its OMe group with THR556 as well as ARG624 and via the N-5 atom with the residue SER682. The in silico studies further suggested that majority of the compounds interacted with the main cavity of active site pocket whereas 3h and 3o that showed relatively lower binding energies (-66.06 and -66.28 Kcal/mol) interacted with the shallow cavity underneath the active site of SARS CoV-2 RdRp. The study also revealed that a OMe group was favourable for interaction with respect to its position in the order C-8 > C-1 > C-2. Further, the presence of a fused quinoline ring was tolerated whereas a fused thiazole ring decreased the interaction significantly. The in silico predictions of pharmacokinetic properties of 3a, 3b and 3n indicated that besides the BBB (Blood Brain Barrier) penetration potential these molecules may show a good overall ADME. Overall, the regioisomers 3a, 3b and 3n have emerged as molecules of possible interest in the context of targeting COVID-19.

Recent advances in transition metal-catalyzed reactions of chloroquinoxalines: Applications in bioorganic chemistry.

The importance of the quinoxaline framework is exemplified by its presence in the well-known drugs such as varenicline, brimonidine, quinacillin, etc. In the past few years, preparation of a variety of organic compounds containing the quinoxaline framework has been reported by several research groups. The chloroquinoxalines were successfully used as substrates in many of these synthetic approaches due to their easy availability along with the reactivity especially towards a diverse range of metal and transition metal-catalyzed transformations including Sonogashira, Suzuki, Heck type of cross-coupling reactions. The transition metals e.g., Pd, Cu, Fe and Nb catalysts played a key role in these transformations for the construction of various CX (e.g., CC, CN, CO, CS, CP, CSe, etc) bonds. These approaches can be classified based on the catalyst employed, type of the reaction performed and nature of CX bond formation during the reaction. Several of these resultant quinoxaline derivatives have shown diverse biological activities which include apoptosis inducing activities, SIRT1 inhibition, inhibition of luciferace enzyme, antibacterial and antifungal activities, cytotoxicity towards cancer cells, inhibition of PDE4 (phosphodiesterase 4), potential uses against COVID-19, etc. Notably, a review article covering the literature based on transition metal-catalyzed reactions of chloroquinoxalines at the same time summarizing the relevant biological activities of resultant products is rather uncommon. Therefore, an attempt is made in the current review article to summarize (i) the recent advances noted in the transition metal-catalyzed reactions of chloroquinoxalines (ii) with the relevant mechanistic discussions (iii) along with the in vitro, and in silico biological studies (wherever reported) (iv) including Structure-Activity Relationship (SAR) within the particular series of the products reported between 2010 and 2022.

Synthesis and characterization of two known and one new impurities of dolutegravir: In silico evaluation of certain intermediates against SARS CoV-2 O-ribose methyltransferase (OMTase).

Besides its use against HIV infection the marketed anti-retroviral drug dolutegravir attracted attention as a potential agent against COVID-19 in multiple AI (artificial intelligence) based studies. Due to our interest in accessing the impurities of this drug we report the synthesis and characterization of three impurities of dolutegravir one of which is new. The synthesis of O-methyl ent-dolutegravir was accomplished in three-steps the first one involved the construction of fused 1,3-oxazinane ring. The cleavage of -OEt ether moiety followed by methylation afforded the target compound. The second impurity i.e. N-(2,4-difluorobenzyl)-4-methoxy-3-oxobutanamide was synthesized via a multi-step method involving sequentially the keto group protection, ester hydrolysis, acid chloride formation followed by the reaction with amine and finally keto group deprotection. The synthesis of new or dimer impurity was carried out via another multi-step method similar to the previous one starting from ethyl 4-chloro acetoacetate. The methodology involved preparation of ether derivative, keto group protection, ester hydrolysis, preparation of amide derivative via acid chloride formation in situ and then keto group deprotection for a longer duration. The last step afforded the target compound for which a plausible reaction mechanism has been proposed. All three impurities were prepared in gram scale (minimum 2 g and maximum 8 g). The in silico evaluation of three selected synthesized intermediates e.g. 7, 8 and 9 (structurally similar to dolutegravir) against SARS CoV-2 O-ribose methyltransferase (OMTase) (PDB: 3R24) indicated that compound 7 could be of interest as a possible inhibitor of this protein.

Pyrrolo[2,3-b]quinoxalines in attenuating cytokine storm in COVID-19: their sonochemical synthesis and in silico / in vitro assessment.

In view of the recent global pandemic caused by COVID-19 intense efforts have been devoted worldwide towards the development of an effective treatment for this disease. Recently, PDE4 inhibitors have been suggested to attenuate the cytokine storm in COVID-19 especially tumour necrosis factor alpha (TNF-α). In our effort we have explored the 2-substituted pyrrolo[2,3-b]quinoxalines for this purpose because of their potential inhibitory properties of PDE-4 / TNF-α. Moreover, several of these compounds appeared to be promising in silico when assessed for their binding affinities via docking into the N-terminal RNA-binding domain (NTD) of N-protein of SARS-CoV-2. A rapid and one-pot synthesis of this class of molecules was achieved via the Cu-catalyzed coupling-cyclization-desulfinylation of 3-alkynyl-2-chloroquinoxalines with t-butyl sulfinamide as the ammonia surrogate under ultrasound irradiation. Most of these compounds showed good to significant inhibition of TNF-α in vitro establishing a SAR (Structure Activity Relationship) within the series. One compound e.g. 3i was identified as a promising hit for which the desirable ADME and acceptable toxicity profile was predicted in silico.

A Sonochemical Access to 5-Aryl Substituted Pyrazolo[1,5-a]Pyrimidines as Potential Inhibitors of TNF-α

In spite of various and extensive studies known for pyrazolo[1,5-a]pyrimidines the synthesis, in silico studies and biological evaluation of their 5-(het)aryl analogs remained underexplored. The TNF-α inhibitors on the other hand has considerable therapeutic potential for autoimmune and inflammatory diseases in addition to cancer, diabetes and possibly COVID-19. In the current study 5-aryl pyrazolo[1,5-a]pyrimidines were explored as potential inhibitors of TNF-α that was supported by the in silico studies. This class of compounds was accessed via a sonochemical synthesis involving the acid catalyzed cyclocondensation reaction of aminopyrazoles with acrylophenones in the presence of aerial oxygen. The study indicated that the overall rate of the reaction was enhanced by ultrasound in the absence of which a longer duration and higher temperature was necessary. The current catalyst/promoter/ligand free and scalable method afforded a range of compounds. Some of these compounds showed good inhibition of TNF-α in vitro where ester/amide moiety at the C-3 position played a key role in interacting with the protein dimer as suggested by the in silico studies. Indeed, these groups formed H-bonds with A: GLY121 and B: TYR151 residues of TNF-α dimer in silico. A brief SAR within the series and in silico ADME/toxicity prediction for best active compounds is presented. Compounds 3a-c were identified as initial hits for further pharmacological evaluations. A sonochemical method has been developed for the facile synthesis of pyrazolo[1,5-a]pyrimidines that were evaluated as potential inhibitors of TNF-α. A sonochemical method has been developed for the facile synthesis of pyrazolo[1,5-a]pyrimidines that were evaluated as potential inhibitors of TNF-α.

CuCl2-catalyzed inexpensive, faster and ligand/additive free synthesis of isoquinolin-1(2H)-one derivatives via the coupling-cyclization strategy: Evaluation of a new class of compounds as potential PDE4 inhibitors.

In spite of possessing a wide range of pharmacological properties the anti-inflammatory activities of isoquinolin-1(2H)-ones were rarely known or explored earlier. PDE4 inhibitors on the other hand in addition to their usefulness in treating inflammatory diseases have been suggested to attenuate the cytokine storm in COVID-19 especially TNF-α. In our effort, a new class of isoquinolin-1(2H)-ones derivatives containing an aminosulfonyl moiety were designed and explored as potential inhibitors of PDE4. Accordingly, for the first time a CuCl2-catalyzed inexpensive, faster and ligand/additive free approach has been developed for the synthesis of these predesigned isoquinolin-1(2H)-one derivatives via the coupling-cyclization strategy. Thus, the CuCl2-catalyzed reaction of 2-iodobenzamides with appropriate terminal alkynes proceeded with high chemo and regioselectivity affording the desired compounds in 77-84% yield within 1-1.5 h. The methodology also afforded simpler isoquinolin-1(2H)-ones devoid of aminosulfonyl moiety showing a broader generality and scope of this approach. Several of the synthesized compounds especially 3c, 3k and 3s showed impressive inhibition (83-90%) of PDE4B when tested at 10 µM in vitro whereas compounds devoid of aminosulfonyl moiety was found to be less active. In spite of high inhibition showed at 10 µM these compounds did not show proper concertation dependent inhibition below 1 µM that was reflected in their IC50 values e.g. 2.43 ± 0.32, 3.26 ± 0.24 and 3.63 ± 0.80 µM for 3k, 3o and 3s respectively. The anti-inflammatory potential of these compounds was indicated by their TNF-α inhibition (60-50% at 10 µM). The in silico docking studies of these molecules suggested good interactions with PDE4B and selective inhibition of PDE4B by 3k over PDE4D that was supported by in vitro assay results. These observations together with the favorable ADME and safety predicted for 3kin silico not only suggested 3k as an interesting hit molecule for further studies but also reveal the first example of isoquinolin-1(2H)-one based inhibitor of PDE4B.

PdCl2-catalyzed synthesis of a new class of isocoumarin derivatives containing aminosulfonyl / aminocarboxamide moiety: First identification of a isocoumarin based PDE4 inhibitor.

While anti-inflammatory properties of isocoumarins are known their PDE4 inhibitory potential was not explored previously. In our effort the non-PDE4 inhibitor isocoumarins were transformed into the promising inhibitors via introducing an aminosulfonyl/aminocarboxamide moiety to the C-3 benzene ring attached to the isocoumarin framework. This new class of isocoumarins were synthesized via a PdCl2-catalyzed construction of the 4-allyl substituted 3-aryl isocoumarin ring starting from the appropriate 2-alkynyl benzamide derivative. Several compounds showed good inhibition of PDE4B in vitro and the SAR indicated superiority of aminosulfonamide moiety over aminocarboxamide in terms of PDE4B inhibition. Two compounds 3q and 3u with PDE4B IC50 = 0.43 ± 0.11 and 0.54 ± 0.19 µM and ≥ 2-fold selectivity over PDE4D emerged as initial hits. The participation of aminosulfonamide moiety in PDE4B inhibition and the reason for selectivity though moderate shown by 3q and 3u was revealed by the in silico docking studies. In view of potential usefulness of moderately selective PDE4B inhibitors the compound 3u (that showed PDE4 selectivity over other PDEs) was further evaluated in adjuvant induced arthritic rats. At an intraperitoneal dose of 30 mg/kg the compound showed a significant reduction in paw swelling (in a dose dependent manner), inflammation and pannus formation (in the knee joints) as well as pro-inflammatory gene expression/mRNA levels and increase in body weight. Moreover, besides its TNF-α inhibition and no significant toxicity in an MTT assay the compound did not show any adverse effects in a thorough toxicity studies e.g. teratogenicity, hepatotoxicity, cardiotoxicity and apoptosis in zebrafish. Thus, the isocoumarin 3u emerged as a new, safe and moderately selective PDE4B inhibitor could be useful for inflammatory diseases possibly including COVID-19.

In silico assessment and sonochemical synthesis of 2-alkynyl 3-chloropyrazines as prospective ligands for SARS-CoV-2.

The recent global pandemic caused by COVID-19 has triggered an intense effort worldwide towards the development of an effective cure for this disease. In our effort we have explored the 2-alkynyl substituted 3-chloropyrazine framework as a potential template for the design of molecules for this purpose. Our strategy was supported by the in silico studies of representative compounds to assess their binding affinities via docking into the N-terminal RNA-binding domain (NTD) of N-protein of SARS-CoV-2. Thus we created a small library of molecules based on the aforementioned template via an environmentally safer method that involved the rapid synthesis of 2-alkynyl 3-chloropyrazine derivatives under Cu-catalysis assisted by ultrasound. The reactions proceeded via the coupling of 2,3-dichloropyrazine with commercially available terminal alkynes in the presence of CuI, PPh3 and K2CO3 in PEG-400. Further molecular modelling studies helped in establishing a virtual SAR (Structure Activity Relationship) within the series and identification of three potential hits. The desirable ADME was also predicted for these three molecules suggesting their prospective medicinal value.

Ultrasound assisted synthesis of 3-alkynyl substituted 2-chloroquinoxaline derivatives: Their in silico assessment as potential ligands for N-protein of SARS-CoV-2.

In view of recent global pandemic the 3-alkynyl substituted 2-chloroquinoxaline framework has been explored as a potential template for the design of molecules targeting COVID-19. Initial in silico studies of representative compounds to assess their binding affinities via docking into the N-terminal RNA-binding domain (NTD) of N-protein of SARS-CoV-2 prompted further study of these molecules. Thus building of a small library of molecules based on the said template became essential for this purpose. Accordingly, a convenient and environmentally safer method has been developed for the rapid synthesis of 3-alkynyl substituted 2-chloroquinoxaline derivatives under Cu-catalysis assisted by ultrasound. This simple and straightforward method involved the coupling of 2,3-dichloroquinoxaline with commercially available terminal alkynes in the presence of CuI, PPh3 and K2CO3 in PEG-400. Further in silico studies revealed some remarkable observations and established a virtual SAR (Structure Activity Relationship) within the series. Three compounds appeared as potential agents for further studies.