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India has the task of eliminating tuberculosis (TB) by 2025. This translates to curing about two million TB cases present today as well as reducing the TB infection rates rapidly (WHO Global Tuberculosis Report 2017). The ‘standard treatment regimen’ being administered today is a combination of drugs discovered and developed in the 1950s and 1960s. This regimen falls short of an ideal therapy in many ways including the requirement of prolonged treatment period of 6 months with unpleasant and toxic drug side effects (Yee et al. 2003). However, the characteristic of the TB patient population has changed considerably in the last few decades—coexistence of diabetes and HIV (human immunodeficiency virus) being the main drivers (Balganesh et al. 2008). In addition, India has a significant number of drug-resistant TB patients (Indian TB report 2018) who need novel drugs and regimens for faster and permanent cure. Thus there is an urgent unmet medical need for which TB drug discovery and development efforts globally and in India need to rise to this occasion.

We report the discovery of benzothiazoles, a novel anti-mycobacterial series, identified from a whole cell based screening campaign. Benzothiazoles exert their bactericidal activity against Mycobacterium tuberculosis (Mtb) through potent inhibition of decaprenylphosphoryl-β-d-ribose 2'-oxidase (DprE1), the key enzyme involved in arabinogalactan synthesis. Specific target linkage and mode of binding were established using co-crystallization and protein mass spectrometry studies. Most importantly, the current study provides insights on the utilization of systematic medicinal chemistry approaches to mitigate safety liabilities while improving potency during progression from an initial genotoxic hit, the benzothiazole N-oxides (BTOs) to the lead-like AMES negative, crowded benzothiazoles (cBTs). These findings offer opportunities for development of safe clinical candidates against tuberculosis. The design strategy adopted could find potential application in discovery of safe drugs in other therapy areas too.

M. tuberculosis thymidylate kinase (Mtb TMK) has been shown in vitro to be an essential enzyme in DNA synthesis. In order to identify novel leads for Mtb TMK, we performed a high throughput biochemical screen and an NMR based fragment screen through which we discovered two novel classes of inhibitors, 3-cyanopyridones and 1,6-naphthyridin-2-ones, respectively. We describe three cyanopyridone subseries that arose during our hit to lead campaign, along with cocrystal structures of representatives with Mtb TMK. Structure aided optimization of the cyanopyridones led to single digit nanomolar inhibitors of Mtb TMK. Fragment based lead generation, augmented by crystal structures and the SAR from the cyanopyridones, enabled us to drive the potency of our 1,6-naphthyridin-2-one fragment hit from 500 μM to 200 nM while simultaneously improving the ligand efficiency. Cyanopyridone derivatives containing sulfoxides and sulfones showed cellular activity against M. tuberculosis. To the best of our knowledge, these compounds are the first reports of non-thymidine-like inhibitors of Mtb TMK.

Short and efficient route for the synthesis of oxazinone- and thiazinone-containing bicyclic heteroaromatic aldehydes, which involves the key step of palladium-catalyzed reductive carbonylation, is described. Overall routes for the synthesis of these aldehydes are short, versatile, and scalable with good yields of the product. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

Cytotoxic nucleosides have proven to be ineffective for the treatment of hepatocellular carcinoma (HCC) due, in part, to their inadequate conversion to their active nucleoside triphosphates (NTP) in the liver tumor and high conversion in other tissues. These characteristics lead to poor efficacy, high toxicity, and a drug class associated with an unacceptable therapeutic index. Cyclic 1-aryl-1,3-propanyl phosphate prodrugs selectively release the monophosphate of a nucleoside (NMP) into CYP3A4-expressing cells, such as hepatocytes, while leaving the prodrug intact in plasma and extrahepatic tissues. This prodrug strategy was applied to the monophosphate of the well-known cytotoxic nucleoside cytosine-1-beta-D-arabinofuranoside (cytarabine, araC). Compound 19S (MB07133), in mice, achieves good liver targeting compared to araC, generating >19-fold higher cytarabine triphosphate (araCTP) levels in the liver than levels of araC in the plasma and >12-fold higher araCTP levels in the liver than in the bone marrow, representing a >120-fold and >28-fold improvement, respectively, over araC administration.

4-(Phenylamino)-5-phenyl-7-(5-deoxy-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine 1 and related compounds known as "diaryltubercidin" analogues are potent inhibitors of adenosine kinase (AK) and are orally active in animal models of pain such as the rat formalin paw model (GP3269 ED50= 6.4 mg/kg). However, the utility of this compound class is limited by poor water solubility that can be attributed to the high energy of crystallization caused by stacking of the parallel C4 and C5 aryl rings in the solid state (compound 1 and GP3269 each with pH 7.4 solubility0.05 microg/mL). To increase water solubility, the hydrophobic C4-phenylamino substituent was replaced with a more hydrophilic group, glycinamide. This modification resulted in improved water solubility while retaining AK inhibition potency. Analogues were studied where changes in the glycinamide moiety were combined with changes to the base and sugar. A lead compound, 4-N-(N-cyclopropylcarbamoylmethyl)amino-5-phenyl-7-(5-deoxy-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine (16c) (IC50= 3 nM and water solubility = 32 +/- 9 microg/mL at pH 7.4), was further characterized in biological assays. Compound 16c exhibited strong oral efficacy in the rat formalin paw model (ED50 of 2.5 mg/kg). In the most advanced assay, 16c was found to inhibit bradykinin-induced licking in marmoset monkeys with an ED50 estimated at 0.9 mg/kg without producing evidence of side effects such as ataxia, sedation, and emesis at this dose. However, lethal toxicity in the rat formalin paw model occurred with high doses of 16c, and further work on this series was discontinued.

Sugar intermediates 4- C -methyl-2,3,5-tri- O -benzyl- d -ribofuranose ( 8b ) and 4- C -methyl-2,3,5-tri- O -benzyl- l -lyxofuranose ( 8a ) were synthesized by addition of alkylithium reagents to pentanones 3a , b . The nucleophilic additions proceeded with good stereoselectivity and good yields to give the titled compounds in four steps from perbenzylated methyl d -ribofuranoside and methyl 5′-deoxy- d -ribofuranoside.

Adenosine receptor agonists produce a wide variety of therapeutically useful pharmacologies. However, to date they have failed to undergo successful clinical development due to dose-limiting side effects. Adenosine kinase inhibitors (AKIs) represent an alternative strategy, since AKIs may raise local adenosine levels in a more site- and event-specific manner and thereby elicit the desired pharmacology with a greater therapeutic window. Starting with 5-iodotubercidin (IC50 = 0.026 microM) and 5'-amino-5'-deoxyadenosine (IC50 = 0.17 microM) as lead inhibitors of the isolated human AK, a variety of pyrrolo[2,3-d]pyrimidine nucleoside analogues were designed and prepared by coupling 5-substituted-4-chloropyrrolo[2,3-d]pyrimidine bases with ribose analogues using the sodium salt-mediated glycosylation procedure. 5'-Amino-5'-deoxy analogues of 5-bromo- and 5-iodotubercidins were found to be the most potent AKIs reported to date (IC50S0.001 microM). Several potent AKIs were shown to exhibit anticonvulsant activity in the rat maximal electric shock (MES) induced seizure assay.

The pyrrolopyrimidine nucleoside GP3269 (12) was shown to be a potent and selective inhibitor of human adenosine kinase (IC50 = 11 nM) and to exhibit anticonvulsant activity in rats after oral administration. Synthesis of GP3269 was accomplished in 4 steps from 4-chloro-5-iodopyrrolopyrimidine (9) and the protected 5-deoxy-1-α-chlororibose (8) using a base-catalyzed nucleoside coupling reaction and the Suzuki reaction to replace the 5-iodo substituent with phenyl.

A convenient methodology has been developed for the synthesis of substituted 2-amino-1,3,4-oxadiazoles from corresponding acylthiosemicarbazides using catalytic amount of iodine/KI in the presence ...

NDH-2 is an essential respiratory enzyme in Mycobacterium tuberculosis (Mtb), which plays an important role in the physiology of Mtb. Herein, we present a target-based effort to identify a new structural class of inhibitors for NDH-2. High-throughput screening of the AstraZeneca corporate collection resulted in the identification of quinolinyl pyrimidines as the most promising class of NDH-2 inhibitors. Structure–activity relationship studies showed improved enzyme inhibition (IC50) against the NDH-2 target, which in turn translated into cellular activity against Mtb. Thus, the compounds in this class show a good correlation between enzyme inhibition and cellular potency. Furthermore, early ADME profiling of the best compounds showed promising results and highlighted the quinolinyl pyrimidine class as a potential lead for further development.

The pyrrolopyrimidine nucleoside GP3269 (12) was shown to be a potent and selective inhibitor of human adenosine kinase (IC50 = 11 nM) and to exhibit anticonvulsant activity in rats after oral administration. Synthesis of GP3269 was accomplished in 4 steps from 4-chloro-5-iodopyrrolopyrimidine (9) and the protected 5-deoxy-1-α-chlororibose (8) using a base-catalyzed nucleoside coupling reaction and the Suzuki reaction to replace the 5-iodo substituent with phenyl.

Adefovir dipivoxil, a marketed drug for the treatment of hepatitis B, is dosed at submaximally efficacious doses because of renal toxicity. In an effort to improve the therapeutic index of adefovir, 1-aryl-1,3-propanyl prodrugs were synthesized with the rationale that this selectively liver-activated prodrug class would enhance liver levels of the active metabolite adefovir diphosphate (ADV-DP) and/or decrease kidney exposure. The lead prodrug (14, MB06866, pradefovir), identified from a variety of in vitro and in vivo assays, exhibited good oral bioavailability (F = 42%, mesylate salt, rat) and rate of prodrug conversion to ADV-DP. Tissue distribution studies in the rat using radiolabeled materials showed that cyclic 1-aryl-1,3-propanyl prodrugs enhance the delivery of adefovir and its metabolites to the liver, with pradefovir exhibiting a 12-fold improvement in the liver/kidney ratio over adefovir dipivoxil.

Adenosine is an endogenous neuromodulator that when produced in the central and the peripheral nervous systems has anticonvulsant, anti-inflammatory, and analgesic properties. However, efforts to use adenosine receptor agonists are plagued by dose-limiting cardiovascular side effects. As an alternative, we explored the use of adenosine kinase inhibitors (AKIs) as potential antiseizure agents and demonstrated an adenosine receptor mediated therapeutic effect in the absence of overt cardiovascular side effects. These activities were associated with elevation of extracellular adenosine concentrations due to inhibition of AK in a site and event specific manner. Several tubercidin based AKIs, including the ribo- and lyxo-furanosyltubercidin analogues as well as the newly discovered erythro-furanosyltubercidin analogues, designed to prevent 5'-O-phosphorylation and associated toxicities, were tested for their analgesic activity in the rat formalin paw model. Described herein are the synthesis, enzyme inhibition structure-activity relationships (SARs) of erythro-furanosyltubercidin analogues, and SARs of analgesic activity of various classes of AKIs. Also reported is the characterization of a lead AKI, 19d (GP3966), an orally bioavailable compound (F% = 60% in dog) which exhibits broad-spectrum analgesic activities (ED50or = 4 mg/kg, per os) that are reversible with an adenosine receptor antagonist (theophylline).

A convenient methodology has been developed for the synthesis of substituted 2-amino-1,3,4-oxadiazoles from corresponding acylthiosemicarbazides using catalytic amount of iodine/KI in the presence of Oxone® as a bulk oxidant. This offers the advantage of short reaction times and substrate variability which is suitable for the rapid production of analogues required for lead optimisation programmes. The method could also be useful for large-scale synthesis because of the mild reaction conditions and the use commercially inexpensive and safe reagents.

Chronic inflammatory diseases, such as arthritis and rheumatoid arthritis, remain major health problems worldwide. We previously demonstrated that adenosine kinase inhibitors (AKIs) exhibit antiinflammatory effects by inhibiting TNF-alpha production, neutrophil accumulation, and edema formation. Although adenosine receptor agonists produce similar effects, AKIs showed the antiinflammatory activity without the cardiovascular side effects that prevented the development of adenosine receptor specific agonists. However, previously described potent AKIs, such as 5-iodotubercidin, are nucleosides which have the potential to undergo in vivo 5'-O-phosphorylation and therefore produce cytotoxicity. In an effort to eliminate toxicities produced by phosphorylated nucleosides, l-lyxofuranosyl analogues of tubercidin were tested as potential AKIs since the opposite stereochemical orientation of the CH(2)OH was expected to eliminate intracellular phosphorylation. Described herein are the discovery of a new series of AKIs based on alpha-l-lyxofuranosyl nucleosides, their SAR, as well as the antiinflammatory activity of the lead compound GP790 (IC(50) = 0.47 nM, 47% inhibition of paw swelling at 10 mg/kg in rat carrageenan paw edema model). In addition, a study showing that in the skin lesion model the antiinflammatory activity is reversed by an A2 selective adenosine receptor antagonist 3,7-dimethyl-1-propargyl xanthine [correction of propylxanthine] (DMPX) is also described.

In the preceding article (Ugarkar et al. J. Med. Chem. 2000, 43) we reported that analogues of tubercidin are potent adenosine kinase (AK) inhibitors with antiseizure activity in the rat maximum electroshock (MES) model. Despite the discovery of several highly potent AK inhibitors (AKIs), e.g., 5'-amino-5'-deoxy- 5-iodotubercidin (1c) (IC50 = 0.0006 microM), no compounds were identified that exhibited a safety, efficacy, and side effect profile suitable for further development. In this article, we demonstrate that substitution of the tubercidin molecule with aromatic rings at the N4- and the C5-positions not only retains AKI potency but also improves in vivo activity. Synthesis of such compounds entailed transformation of 4-arylamino-5-iodotubercidin analogues to their corresponding 5-aryl derivatives via the Suzuki reaction. Alternatively, 4-N-arylamino-5-arylpyrrolo[2,3-d]pyrimidine bases were constructed and then glycosylated with appropriately protected alpha-ribofuranosyl chlorides using a phase-transfer catalyst. Several compounds exhibited potent activity in the rat MES seizure assay with ED50sor = 2.0 mg/kg, ip, and showed relatively mild side effects.

A facile synthesis of 7-amino-5-chloro-3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine (5-chloroformycin A, 6), 7-amino-5-chloro-3-(2-deoxy-beta-D-erythro-pentofuranosyl) pyrazolo [4,3-d]-pyrimidine (5-chloro-2'-deoxyformycin A, 13) and certain related 5,7-disubstituted pyrazolo[4,3-d]pyrimidine ribonucleosides is described starting with formycin A. Thiation of tri-O-acetyloxoformycin B (4b) with phosphorus pentasulfide, followed 3-beta-D-ribofuranosyl-7-thioxopyrazolo[4,3-d] pyrimidin-5(1H,4H,6H)-one (3b) in excellent yield. Chlorination of 4b with either phosphorus oxychloride or phenyl phosphonicdichloride furnished the key intermediate 5,7-dichloro-3-(2,3, 5-tri-O-acetyl-beta-D-ribofuranosyl)pyrazolo[4,3-d]pyrimidine (5a), which on deacetylation afforded 5,7-dichloro-3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine (5b). Ammonolysis of 5a with liquid ammonia gave 6, whereas with MeOH/NH3, a mixture of 6 and 7-methoxy-5-chloro-3-beta-D-ribofuranosylpyrazolo[4,3-d]pyrimidine (7) was obtained. Reaction of 6 with lithium azide and subsequent hydrogenation afforded 5-aminoformycin A (10). Treatment of 5a with thiourea gave 5-chloro-3-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl) pyrazolo[4,3-d]pyrimidine-7(1H,6H)-thione (8a), which on further reaction with sodium hydrosulfide furnished 3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine-5,7(1H,4H,6H)-dithione (11). The four-step deoxygenation procedure using phenoxythiocarbonylation of the 2'-hydroxy group of the 3', 5'-protected 6 gave 5-chloro-2'-deoxyformycin A (13).

Several 3-beta-D-ribofuranosyl-1,2,4-triazolo[3,4-f]-1,2,4-triazines related to formycin were prepared and tested for their antitumor activity in cell culture. Dehydrative coupling of 3-amino-6-hydrazino-1,2,4-triazin-5(4H)-one (5) with 3,4,6-tri-O-benzoyl-2,5-anhydro-D-allonic acid (6a) and further ring closure of the reaction product (7) provided 6-amino-3-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)-1,2,4-triazolo[3,4- f]-1,2,4-triazin-8(7H)-one (8). Condensation of 5 with 3,4,6-tri-O-benzoyl-2,5-anhydro-D-allonic acid chloride (6b), followed by ring annulation, also gave 8 in good yield. Debenzoylation of 8 furnished the guanosine analogue 6-amino-3-beta-D-ribofuranosyl-1,2,4-triazolo[3,4-f]-1,2,4-triazin -8(7H)-one (4b). Thiation of 8 with P2S5, followed by debenzoylation of the thiated product (11a), afforded 6-amino-3-beta-D-ribofuranosyl-1,2,4-triazolo[3,4-f]-1,2,4-triazin -8(7H)- thione (11b). Methylation of the sodium salt of 11a gave the 8-methylthio derivative (10), which on ammonolysis furnished 6,8-diamino-3-beta-D-ribofuranosyl-1,2,4-triazolo[3,4-f]-1,2,4-triazine (9). Diazotization of 10 with tert-butyl nitrite (TBN) and SbCl3 in 1,2-dichloroethane gave the corresponding 6-chloro derivative (12a). Reaction of 10 with TBN in THF in the absence of a halogen source gave 8-(methylthio)-3-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)-1,2,4- triazolo[3,4-f]-1,2,4-triazine (12b). Ammonolysis of 12b gave the azaformycin A analogue 8-amino-3-beta-D-ribofuranosyl-1,2,4- triazolo[3,4-f]-1,2,4-triazine (3), which on deamination afforded 3-beta-D-ribofuranosyl-1,2,4-triazolo[3,4- f]-1,2,4-triazin-8(7H)-one (4a). The azaformycin A analogue (3) showed pronounced inhibitory effects against L1210, WIL2, and CCRF-CEM cell lines with ID50 values ranging from 5.0 to 7.3 microM.

1-Methy1-3-β-D-ribofuranosylpyrazolo[4, 3-d]pyrimidin-7(6H)-selone (6) and the corresponding thione analog (5) have been synthesized for the first time from l-methyl-3-(2, 3, 5-tri-O-acetyl-β-D]-ribo-furanosyl)pyrazolo[4, 3-d]pyrimidin-7(6H)-one (12). Thiation and deace-tylation of 12 gave 5. Compound 6 was prepared from 12 via the chloro intermediate (13) and selenourea followed by deacetylation. A convenient, high yield procedure for the preparation of 1-methylformycin B (4) from 1-methylformycin (7) is described. Phosphorylation of 7 provided 1-methylformycin 5′-phosphate (17). Compounds 6 and 17 were found to be potent inhibitors of growth of L1210 and P388 leukemia.

3-Phenylsydnone was subjected to chlorosulphonation for the first time. The resulting sydnone-sulphonyl chloride was treated with amines and phenols to obtain sulphonamides and sulphonates, respectively. Sulfonamid- und Sulfonatderivate von Sydnonen 3-Phenylsydnon wird erstmals der Chlorsulfonierung unterworfen und das erhaltene Sydnonsulfonylchlorid mit Aminen und Phenolen behandelt, um die Sulfonamide bzw. Sulfonate zu erhalten.

A number of unknown disubstituted 3-phenylsydnones are synthesized and subjected for preliminary screening. Methyl, bromo and chloro groups in the phenyl ring of 3-tolylsydnones enhance the CNS depression action while the methyl group in the 4-position of the sydnone ring does not add to the CNS depression action shown by the original sydnone. Synthese und zentraldepressive Eigenschaften disubstituierter Sydnone Eine Anzahl noch nicht bekannter disubstituierter 3-Phenylsydnone wird synthetisiert und einem vorlaufigen Screening unterworfen. Methyl-, Brom- und Chlorsubstitution im Phenylring von 3-Tolyl-sydnonen verstarken die zentraldepressive Wirkung, wahrend eine Methylgruppe in 4-Stellung des Sydnonringes die zentraldepressive Wirkung im Vergleich zum Ausgangssydnon verringert.

Several pyrazolo[3,4-d]pyrimidine-4(5H)-selone ribonucleosides were prepared as potential antiparasitic agents. Treatment of 4-chloro-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)pyrazolo [3,4-d]pyrimidine (5a) with selenourea and subsequent deacetylation gave 1-beta-D-ribofuranosylpyrazolo[3,4-d] pyrimidine-4(5H)-selone (6a). A similar treatment of 3-bromo-4-chloro-1-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)pyrazolo [3,4-d]pyrimidine (5b) with selenurea, followed by debenzoylation, gave the 3-bromo derivative of 6a (6b). Glycosylation of persilylated 4-chloro-6-methyl-pyrazolo [3,4-d]pyrimidine (7) with tetra-O-acetylribofuranose (8) provided the key intermediate 4-chloro-6-methyl-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl) pyrazolo[3,4-d]pyrimidine (9). Ammonolysis of 9 gave 4-amino-6-methyl-1-beta-D-ribofuranosylpyrazolo[3,4-d]pyrimidine (10), whereas treatment with sodium hydroxide gave 6-methylallopurinol ribonucleoside (11a). Reaction of 9 with either thiourea or selenourea, followed by deacetylation, provided 6-methylpyrazolo[3,4-d]pyrimidine-4(5H)-thione ribonucleoside (11c) and the corresponding seleno derivative (11d), respectively. The structural assignment of these nucleosides was made on the basis of spectral studies. These compounds were tested in vitro against certain viruses and tumor cells. All the compounds except 11c exhibited significant activity against HSV-2 in vitro, whereas 11c exhibited the most potent activity against measles and has a very low toxicity. Compounds 6a, 6b, and 11d were found to be potent inhibitors of growth of L1210 and P388 leukemia in vitro.

Several pyrazolo[3,4-d]pyrimidine-4(5H)-selone ribonucleosides were prepared as potential antiparasitic agents. Treatment of 4-chloro-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)pyrazolo [3,4-d]pyrimidine (5a) with selenourea and subsequent deacetylation gave 1-beta-D-ribofuranosylpyrazolo[3,4-d] pyrimidine-4(5H)-selone (6a). A similar treatment of 3-bromo-4-chloro-1-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)pyrazolo [3,4-d]pyrimidine (5b) with selenurea, followed by debenzoylation, gave the 3-bromo derivative of 6a (6b). Glycosylation of persilylated 4-chloro-6-methyl-pyrazolo [3,4-d]pyrimidine (7) with tetra-O-acetylribofuranose (8) provided the key intermediate 4-chloro-6-methyl-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl) pyrazolo[3,4-d]pyrimidine (9). Ammonolysis of 9 gave 4-amino-6-methyl-1-beta-D-ribofuranosylpyrazolo[3,4-d]pyrimidine (10), whereas treatment with sodium hydroxide gave 6-methylallopurinol ribonucleoside (11a). Reaction of 9 with either thiourea or selenourea, followed by deacetylation, provided 6-methylpyrazolo[3,4-d]pyrimidine-4(5H)-thione ribonucleoside (11c) and the corresponding seleno derivative (11d), respectively. The structural assignment of these nucleosides was made on the basis of spectral studies. These compounds were tested in vitro against certain viruses and tumor cells. All the compounds except 11c exhibited significant activity against HSV-2 in vitro, whereas 11c exhibited the most potent activity against measles and has a very low toxicity. Compounds 6a, 6b, and 11d were found to be potent inhibitors of growth of L1210 and P388 leukemia in vitro.