Wang resin catalysed sonochemical synthesis of pyrazolo[4,3-d]pyrimidinones and 2,3-dihydroquinazolin-4(1H)-ones: Identification of chorismate mutase inhibitors having effects on Mycobacterium tuberculosis cell viability.

The enzyme chorismate mutase (or CM that is vital for the survival of bacteria) is an interesting pharmacological target for the identification of new anti-tubercular agents. The 5,5-disibstituted pyrazolo[4,3-d]pyrimidinone derivatives containing the fragment based on 4-amino-1-methyl-3-propyl-1H-pyrazole-5-carboxamide were designed and explored as the potential inhibitors of chorismate mutase. Based on encouraging docking results of two representative molecules evaluated in silico against MtbCM (PDB: 2FP2) the Wang resin catalysed sonochemical synthesis of target N-heteroarenes were undertaken. The methodology involved the reaction of 4-amino-1-methyl-3-propyl-1H-pyrazole-5-carboxamide with the appropriate cyclic/acyclic ketones to afford the desired products in acceptable (51-94%) yields. The methodology was also extended successfully towards the synthesis of 2,2-disubstituted 2,3-dihydroquinazolin-4(1H)-ones in excellent (85-90%) yields. In vitro MTT assay against the RAW 264.7 cell line followed by enzymatic assay against MtbCM identified 3b and 3c as active compounds that showed two H-bonding via their NH (at position 6) and CO group with MtbCM in silico and encouraging (54-57%) inhibition at 30 µM in vitro. Notably, none of the 2,2-disubstituted 2,3-dihydroquinazolin-4(1H)-ones showed any significant inhibition of MtbCM suggesting the favourable role of the pyrazole moiety in case of pyrazolo[4,3-d]pyrimidinones. The favourable role of cyclopentyl ring attached to the pyrazolo[4,3-d]pyrimidinone moiety and that of two methyl groups in place of cyclopentyl ring was also indicated by the SAR study. Besides showing effects against MtbCM in the concentration response study, 3b and 3c showed little or no effects on mammalian cell viability up to 100 µM in an MTT assay but decreased the % Mtb cell viability at 10-30 µM with > 20% decrease at 30 µM in an Alamar Blue Assay. Moreover, no adverse effects were noted for these compounds when tested for teratogenicity and hepatotoxicity in zebrafish at various concentrations. Overall, being the only example of MtbCM inhibitors that showed effects on Mtb cell viability the compound 3b and 3c are of further interest form the view point of discovery and development of new anti-tubercular agents.

Design, synthesis and evaluation of 2-aryl quinoline derivatives against 12R-lipoxygenase (12R-LOX): Discovery of first inhibitor of 12R-LOX.

The 12R-lipoxygenase (12R-LOX), a (non-heme) iron-containing metalloenzyme belonging to the lipoxygenase (LOX) family catalyzes the conversion of arachidonic acid (AA) to its key metabolites. Studies suggested that 12R-LOX plays a critical role in immune modulation for the maintenance of skin homeostasis and therefore can be considered as a potential drug target for psoriasis and other skin related inflammatory diseases. However, unlike 12-LOX (or 12S-LOX) the enzyme 12R-LOX did not receive much attention till date. In our effort, the 2-aryl quinoline derivatives were designed, synthesized and evaluated for the identification of potential inhibitors of 12R-hLOX. The merit of selection of 2-aryl quinolines was assessed by in silico docking studies of a representative compound (4a) using the homology model of 12R-LOX. Indeed, in addition to participating in H-bonding with THR628 and LEU635 the molecule formed a hydrophobic interaction with VAL631. The desired 2-aryl quinolines were synthesized either via the Claisen-Schmidt condensation followed by one-pot reduction-cyclization or via the AlCl3 induced heteroarylation or via the O-alkylation approach in good to high (82-95%) yield. When screened against human 12R-LOX (12R-hLOX) in vitro four compounds (e.g. 4a, 4d, 4e and 7b) showed encouraging (>45%) inhibition at 100 µM among which 7b and 4a emerged as the initial hits. Both the compounds showed selectivity towards 12R-hLOX over 12S-hLOX, 15-hLOX and 15-hLOXB and concentration dependent inhibition of 12R-hLOX with IC50 = 12.48 ± 2.06 and 28.25 ± 1.63 µM, respectively. The selectivity of 4a and 7b towards 12R-LOX over 12S-LOX was rationalized with the help of molecular dynamics simulations. The SAR (Structure-Activity Relationship) within the present series of compounds suggested the need of a o-hydroxyl group on the C-2 phenyl ring for the activity. The compound 4a and 7b (at 10 and 20 µM) reduced the hyper-proliferative state and colony forming potential of IMQ-induced psoriatic keratinocytes in a concentration dependent manner. Further, both compounds decreased the protein levels of Ki67 and the mRNA expression of IL-17A in the IMQ-induced psoriatic-like keratinocytes. Notably, 4a but not 7b inhibited the production of IL-6 and TNF-α in the keratinocyte cells. In the preliminary toxicity studies (i.e. teratogenicity, hepatotoxicity and heart rate assays) in zebrafish both the compounds showed low safety (<30 µM) margin. Overall, being the first identified inhibitors of 12R-LOX both 4a and 7b deserve further investigations.

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.

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.

Ultrasound assisted one-pot synthesis of rosuvastatin based novel azaindole derivatives via coupling-cyclization strategy under Pd/Cu-catalysis: Their evaluation as potential cytotoxic agents.

Addressing the increasing incidences of cancer worldwide along with the multifaceted problem of drug resistance via development of new anticancer agents has become an essential goal. Due to the known cytotoxic effects and reported Akt inhibitory potential of azaindoles we designed a new framework incorporating the structural features of rosuvastatin and 5- or 7-azaindole. The framework was used to construct a library of small molecules for further pharmacological evaluation. The design was supported by the docking studies of two representative molecules in silico. A one-pot sonochemical approach was established for the synthesis of these rosuvastatin based azaindoles that involved the coupling-cyclization of a rosuvastatin derived terminal alkyne with appropriate 3-iodopyridine derivatives under Pd/Cu-catalysis. When tested using an MTT assay, some of the synthesized compounds showed desirable cytotoxic effects against three cancer cell lines e.g. HCT 116, Hep G2 and PA-1 but no significant effects against the non-cancerous HEK cell line. According to the SAR the 5-azaindole ring appeared to be marginally better than the 7-azaindole whereas the activity was varied with the variation of sulfonamide moiety attached to the N-1 atom of the azaindole ring. Among all the groups present in the sulfonamide moiety the p-MeC6H4 group appeared to be most effective in terms of activity. While 3b and 5b were identified as initial hit molecules the compound 5b (in addition to 3b) also showed significant inhibition of Akt1 in vitro that was reflected by its strong interaction with Akt1 in silico (with the docking score -11.7 kcal/mol) involving two H-bonding interactions with Ser7 and Asp439 residues. Further, a reasonable ADME was predicted for 5bin silico. Being a potent inhibitor (MIA Paca-2 IC50 = 18.79 ± 0.17 nM) and with NOAEL (No Observed Adverse Effect Level) > 100 µM in Zebrafish, 5b emerged as a promising compound.

Sonochemical synthesis and biological evaluation of isoquinolin-1(2H)-one/isoindolin-1-one derivatives: Discovery of a positive ago-allosteric modulator (PAAM) of 5HT2CR.

Efforts have been devoted for the discovery and development of positive allosteric modulators (PAMs) of 5-HT2CR because of their potential advantages over the orthosteric agonist like Lorcaserin that was withdrawn from the market. On the other hand, pursuing a positive ago-allosteric modulator (PAAM) is considered as beneficial particularly when an agonist is not capable of affecting the potency of the endogenous agonist sufficiently. In search of a suitable PAAM of 5-HT2CR we adopted an in silico based approach that indicated the potential of the 3-(1-hydroxycycloalkyl) substituted isoquinolin-1-one derivatives against the 5-HT2CR as majority of these molecules interacted with the site other than that of Lorcaserin with superior docking scores. These compounds along with the regioisomeric 3-methyleneisoindolin-1-one derivatives were prepared via the Cu(OAc)2 catalyzed coupling of 2-iodobenzamide with 1-ethynylcycloalkanol under ultrasound irradiation. According to the in vitro studies, most of these compounds were not only found to be potent and selective agonists but also emerged as PAAM of 5-HT2CR whereas Lorcaserin did not show PAAM activities. According to the SAR study the isoquinolin-1(2H)-ones appeared as better PAAM than isoindolin-1-ones whereas the presence of hydroxyl group appeared to be crucial for the activity. With the potent PAAM activity for 5-HT2CR (EC50 = 1 nM) and 107 and 86-fold selectivity towards 5-HT2C over 5-HT2A and 5-HT2B the compound 4i was identified as a hit molecule. The compound showed good stability in male BALB/c mice brain homogenate (∼85 % remaining after 2 h), moderate stability in the presence of rat liver microsomes (42 % remaining after 1 h) and acceptable PK properties with fast reaching in the brain maintaining âˆ¼ 1:1 brain/plasma concentration ratio. The compound at a dose of 50 mg/kg exhibited decreased trend in the food intake starting from day 3 in S.D. rats, which reached significant by 5th day, and the effect was comparable to Lorcaserin (10 mg/kg) on day 5. Thus, being the first example of PAAM of 5-HT2CR the compound 4i is of further medicinal interest.

Fe(III)-catalyzed regioselective and faster synthesis of isocoumarins with 3-oxoalkyl moiety at C-4: Identification of new inhibitors of PDE4.

In search of potent and new anti-inflammatory agents, we explored a new class of isocoumarin derivatives possessing the 3-oxoalkyl moiety at C-4 position. These compounds were synthesized via the FeCl3 catalyzed construction of isocoumarin ring. The methodology involved coupling of 2-alkynyl benzamides with alkyl vinyl ketone and proceeded via a regioselective cyclization to give the desired compound as a result of formation of CO and CC bonds. A large number of isocoumarins were synthesized and assessed against PDE4B in vitro. While isocoumarins containing an aminosulfonyl moiety attached to the C-3 aryl ring showed encouraging inhibition of PDE4B, some of the derivatives devoid of aminosulfonyl moiety also showed considerable inhibition. According to the SAR analysis the C6H4NHSO2R2-m moiety at C-3 position of the isocoumarin ring was favorable when the R2 was chosen as an aryl or 2-thienyl group whereas the presence of F or OMe substituent at C-7 of the isocoumarin ring was found to be beneficial. The compound 5f with IC50 values 0.125 ± 0.032 and 0.43 ± 0.013 µM against PDE4B and 4D, respectively was identified as an initial hit. It showed in silico interaction with the PHE678 residue in the CR3 region of PDE4B and relatively less number of interactions with PDE4D. Besides showing the PDE4 selectivity over other PDEs and TNF-α inhibition in vitro the compound 5f at an intraperitoneal dose of 30 mg/kg demonstrated the protective effects against the development of arthritis and potent immunomodulatory activity in adjuvant induced arthritic (AIA) rats. Furthermore, no significant adverse effects were observed for this compound when evaluated in a systematic toxicity (e.g. teratogenicity, hepatotoxicity and cardiotoxicity) studies in zebrafish at various concentrations. Collectively, being a new, potent, moderately selective and safe inhibitor of PDE4B the isocoumarin 5f can be progressed into further pharmacological studies.

Amberlyst-15 catalysed synthesis of novel indole derivatives under ultrasound irradiation: Their evaluation as serotonin 5-HT2C receptor agonists.

A series of indole based novel Schiff bases was designed as potential agonists of 5-HT2C receptor that was supported by docking studies in silico. These compounds were synthesized via Amberlyst-15 catalysed condensation of an appropriate pyrazole based primary amine with the corresponding indole-3-aldehyde under ultrasound irradiation at ambient temperature. A number of target Schiff bases were obtained in good yields (77-87%) under mild conditions within 1 h. Notably, the methodology afforded the corresponding pyrazolo[4,3-d]pyrimidin-7(4H)-one derivatives when the primary amine was replaced by a secondary amine. Several Schiff bases showed agonist activity when tested against human 5-HT2C using luciferase assay in HEK293T cells in vitro. The SAR (Structure-Activity-Relationship) studies suggested that the imine moiety was more favorable over its cyclic form i.e. the corresponding pyrazolopyrimidinone ring. The Schiff bases 3b (EC50 1.8 nM) and 3i (EC50 5.7 nM) were identified as the most active compounds and were comparable with Lorcaserin (EC50 8.5 nM). Also like Lorcaserin, none of these compounds were found to be PAM of 5-HT2C. With ∼24 and ∼150 fold selectivity towards 5-HT2C over 5-HT2A and 5-HT2B respectively the compound 3i that reduced locomotor activity in zebrafish (Danio rerio) larvae model emerged as a promising hit molecule for further study.

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.

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.

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.

Ultrasound assisted rapid synthesis of mefenamic acid based indole derivatives under ligand free Cu-catalysis: Their pharmacological evaluation.

An improved and rapid synthesis of mefenamic acid based indole derivatives has been achieved via the ligand free Cu-catalyzed coupling-cyclization method under ultrasound irradiation. This simple, straightforward and inexpensive one-pot method involved the reaction of a terminal alkyne derived from mefenamic acid with 2-iodosulfanilides in the presence of CuI and K2CO3 in PEG-400. The reaction proceeded via an initial CC bond formation (the coupling step) followed by CN bond formation (the intramolecular cyclization) to afford the mefenamic acid based indole derivatives in good to acceptable yields. Several of these compounds showed inhibition of PDE4 in vitro and the SAR (Structure Activity Relationship) within the series is discussed. The compound 3d has been identified as a promising and selective inhibitor of PDE4B (IC50 = 1.34 ± 0.46 µM) that showed TNF-α inhibition in vitro (IC50 = 5.81 ± 0.24 µM) and acceptable stability in the rat liver microsomes.

Synthesis of 11,12-dihydro benzo[c]phenanthridines via a Pd-catalyzed unusual construction of isocoumarin ring/FeCl3-mediated intramolecular arene-allyl cyclization: First identification of a benzo[c]phenanthridine based PDE4 inhibitor.

In spite of their various pharmacological properties the anti-inflammatory potential of benzo[c]phenanthridines remained underexplored. Thus, for the first time PDE4 inhibitory potential of 11,12-dihydro benzo[c]phenanthridine/benzo[c]phenanthridine was assessed in vitro. Elegant synthesis of these compounds was performed via a multi-step sequence consisting of a Pd-catalyzed unusual construction of 4-allyl isocoumarin ring and FeCl3-mediated intramolecular regio- as well as site-selective arene-allyl cyclization as key steps. The overall strategy involved Sonogashira coupling followed by isocoumarin and isoquinolone synthesis, then chlorination and subsequent cyclization to afford a range of 11,12-dihydro derivatives. One of these dihydro compounds was converted to the corresponding benzo[c]phenanthridine that showed concentration dependent inhibition of PDE4B affording an initial hit molecule. The SAR study suggested that 11,12-dihydro analogs were less potent than the compound having unsaturation at the same part of the ring.

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.

Synthesis of 3-indolylmethyl substituted (pyrazolo/benzo)triazinone derivatives under Pd/Cu-catalysis: Identification of potent inhibitors of chorismate mutase (CM).

The chorismate mutase (CM) is considered as an attractive target for the identification of potential antitubercular agents due to its absence in animals but not in bacteria. A series of 3-indolylmethyl substituted pyrazolotriazinone derivatives were designed and docked into CM in silico as potential inhibitors. These compounds were efficiently synthesized using the Pd/Cu-catalyzed coupling-cyclization in a single pot involving the construction of indole ring. The methodology was later extended to the preparation of corresponding benzo analogs of pyrazolotriazinones i.e. 3-indolylmethyl substituted benzotriazinone derivatives. Several of these novel compounds showed significant inhibition of CM when tested in vitro at 30 µM. The SAR (Structure-Activity-Relationship) studies suggested that benzotriazinone moiety was more favorable over the pyrazolotriazinone ring. The two best active compounds showed IC50 ∼ 0.4-0.9 µM (better than the reference/known compounds used) and no toxicity till 30 µM in vitro.

1,2,3-Triazole fused with pyridine/pyrimidine as new template for antimicrobial agents: Regioselective synthesis and identification of potent N-heteroarenes.

The 1,2,3-triazole ring fused with pyridine/pyrimidine was explored as new template for the identification of potential antimicrobial agents. The regioselective synthesis of these pre-designed N-heteroarenes was achieved via exploring the application of Buchwald's strategy (i.e. C-N bond formation/reduction/diazotization/cyclization sequence) to the N-heteroarene system. Two of them showed promising antibacterial (comparable to streptomycin) and several showed potent antifungal (comparable to mancozeb) activities.

A novel SIRT1 inhibitor, 4bb induces apoptosis in HCT116 human colon carcinoma cells partially by activating p53.

The NAD+-dependent protein deacetylase SIRT1 has emerged as an important target for epigenetic therapeutics of colon cancer as its increased expression is associated with cancer progression. Additionally, SIRT1 represses p53 function via deacetylation, promoting tumor growth. Therefore, inhibition of SIRT1 is of great therapeutic interest for the treatment of colon cancer. Here, we report discovery of a novel quinoxaline based small molecule inhibitor of human SIRT1, 4bb, investigated its effect on viability of colon cancer cells and molecular mechanism of action. In vitro, 4bb is a significantly more potent SIRT1 inhibitor, compared to ß-naphthols such as sirtinol, cambinol. Increasing concentration of 4bb decrease viability of colon cancer cells but, does not affect the viability of normal dermal fibroblasts depicting cancer cell specificity. Further, 4bb treatment increased p53 acetylation, Bax expression and induced caspase 3 cleavage suggesting that the death of HCT116 colon cancer cells occur through intrinsic pathway of apoptosis. Overall, our results presents 4bb as a new class of human SIRT1 inhibitor and suggest that inhibition of SIRT1 by 4bb induces apoptosis of colon cancer cells at least in part via activating p53 by preventing p53 deacetylation, increasing Bax expression and inducing caspases. Therefore, this molecule provide an opportunity for lead optimization and may help in development of novel, non-toxic epigenetic therapeutics for colon cancer.

Use of AlCl3 in Friedel Crafts arylation type reactions and beyond: an overview on the development of unique methodologies leading to N-heteroarenes.

As a privileged class of heterocyclic compounds N-heteroarenes have found enormous applications in many areas including medicinal/pharmaceutical chemistry and drug discovery. Consequently, a wide variety of methods have been reported for their synthesis. While not free from their own limitations the AlCl3 mediated methods appeared to have some particular advantages in preparing a number of useful N-heteroarenes. Besides the famous Friedel-Crafts (FC) alkylation/acylation reactions one such example is AlCl3-induced heteroarylation of arenes and heteroarenes (FC arylation type reactions) that can be used to prepare a certain class of N-heteroarenes in an operationally simple, efficient and cost effective manner. Interestingly, pyridine is not a good substrate in FC alkylation/acylation reactions whereas 2-chloropyridines are indeed effective in heteroarylation reaction. However, no systematic and detailed study regarding the application potential of this method was performed until 2002. Some other examples that emerged in the recent past include AlCl3 induced heteroarylation-cyclization, hydroarylation-heteroarylation, sulfonyl group migration etc. All these innovative methodologies allowed the direct access to several unique and novel N-heteroarenes some of which showed interesting pharmacological properties including anti-inflammatory, anti-cancer and antibacterial activities when tested in vitro. While unlike FC reactions many of these AlCl3 mediated methodologies are still in their initial stage of developments, a continuing effort to uncover their further potential in organic synthesis/medicinal chemistry is necessary. The current article provides an overview of these unique methodologies that highlight the use of AlCl3 beyond FC reactions leading to new N-heteroarenes.

Mycobacterium tuberculosis chorismate mutase: A potential target for TB.

Mycobacterium tuberculosis chorismate mutase (MtbCM) catalyzes the rearrangement of chorismate to prephenate in the shikimate biosynthetic pathway to form the essential amino acids, phenylalanine and tyrosine. Two genes encoding chorismate mutase have been identified in Mtb. The secretory form,∗MtbCM (encoded by Rv1885c) is assumed to play a key role in pathogenesis of tuberculosis. Also, the inhibition of MtbCM may hinder the supply of nutrients to the organism. Indeed, the existence of chorismate mutase (CM) in bacteria, fungi and higher plants but not in human and low sequence homology among known CM makes it an interesting target for the discovery of anti-tubercular agents. The present article mainly focuses on the recent developments in the structure, function and inhibition of MtbCM. The understanding of various aspects of MtbCM as presented in the current article may facilitate the design and subsequent chemical synthesis of new inhibitors against ∗MtbCM, that could lead to the discovery and development of novel and potent anti-tubercular agents in future.