Ramesh Anna Joshi

Design, Synthesis, Structural Characterization by IR, 1H, 13C, 15N, 2D-NMR, X-Ray Diffraction and Evaluation of a New Class of Phenylaminoacetic Acid Benzylidene Hydrazines as pfENR Inhibitors

Recent studies have revealed that plasmodial enoyl‐ACP reductase (pfENR, FabI), one of the crucial enzymes in the plasmodial type II fatty acid synthesis II (FAS II) pathway, is a promising target for liver stage malaria infections. Hence, pfENR inhibitors have the potential to be used as causal malarial prophylactic agents. In this study, we report the design, synthesis, structural characterization and evaluation of a new class of pfENR inhibitors. The search for inhibitors began with a virtual screen of the iResearch database by molecular docking. Hits obtained from the virtual screen were ranked according to their Glide score. One hit was selected as a lead and modified to improve its binding to pfENR; from this, a series of phenylamino acetic acid benzylidene hydrazides were designed and synthesized. These molecules were thoroughly characterized by IR, 1H, 13C, 15N, 2D‐NMR (COSY, NOESY, 1H‐13C, 1H‐15N HSQC and HMBC), and X‐ray diffraction. NMR studies revealed the existence of conformational/configurational isomers around the amide and imine functionalities. The major species in DMSO solution is the E, E form, which is in dynamic equilibrium with the Z, E isomer. In the solid state, the molecule has a completely extended conformation and forms helical structures that are stabilized by strong hydrogen bond interactions, forming a helical structure stabilized by N‐H…O interactions, a feature unique to this class of compounds. Furthermore, detailed investigation of the NMR spectra indicated the presence of a minor impurity in most compounds. The structure of this impurity was deduced as an imidazoline‐4‐one derivative based on 1H‐13C and 1H‐15H HMBC spectra and was confirmed from the NOESY spectra. The molecules were screened for in vitro activity against recombinant pfENR enzyme by a spectrophotometric assay. Four molecules, viz. 17, 7, 10, and 12 were found to be active at 7, 8, 10, and 12 μm concentration, respectively, showing promising pfENR inhibitory potential. A classification model was derived based on a binary QSAR approach termed recursive partitioning (RP) to highlight structural characteristics that could be tuned to improve activity.

Total synthesis of cis and trans-hydroxyglimepiride: active metabolite of glimepiride

Syntheses of trans-hydroxyglimepiride 2b, a human metabolite of the blood glucose lowering agent glimepiride 1 and its corresponding cis-stereoisomer 2a, are described.

Regioselective and diastereoselective iodocyclization reaction of alkene-thioureas: an efficient approach to bicyclic β-lactams

Bicyclic β-lactams, i.e. 3-thia-1-dethiacephams, were synthesized via a highly regioselective and diastereoselective iodocyclization reaction of alkene-thioureas with molecular iodine. Furthermore, the structure of 3-thia-1-dethiacepham was confirmed by a chemical method, the dehydrohalogenation reaction using DBU.

Targeting dormant tuberculosis bacilli: results for molecules with a novel pyrimidone scaffold.

Our inability to completely control TB has been due in part to the presence of dormant mycobacteria. This also renders drug regimens ineffective and is the prime cause of the appearance of drug‐resistant strains. In continuation of our efforts to develop novel antitubercular agents that especially target dormant mycobacteria, a set of 55 new compounds belonging to the pyrimidone class were designed on the basis of CoMFA and CoMSIA studies, and these were synthesized and subsequently tested against both the dormant and virulent BCG strain of M. tuberculosis. Some novel compounds have been identified which selectively inhibit the dormant tuberculosis bacilli with significantly low IC50 values. This study reports the second molecule after TMC‐207, having the ability to inhibit tuberculosis bacilli exclusively in its dormant phase. The synthesis was accomplished by a modified multicomponent Biginelli reaction. A classification model was generated using the binary QSAR approach – recursive partitioning (RP) to identify structural characteristics related to the activity. Physicochemical, structural, topological, connectivity indices, and E‐state key descriptors were used for generation of the decision tree. The decision tree could provide insights into structure–activity relationships that will guide the design of more potent inhibitors.

Continuous-Flow Meerwein Arylation

The continuous-flow Meerwein arylation is demonstrated for a set of few aryl donors (anilines and m-amino-acetophenone) and specific radical acceptors. Homogeneous catalyst (CuBr in HBr and CuCl in HCl) was used to facilitate the reaction. The effect of parameters, viz., temperature, catalyst concentration, residence time, and concentration of the radical acceptor on the yield of the arylated product, was studied. The yield of the aryl derivative obtained by continuous-flow syntheses was always better than the respective experiments in batch mode. Flow synthesis allows easy variation in these parameters and thus allows going close to the maximum possible yields in a system where the relative rates of different reactions create a complex situation. Temperature plays a crucial role by affecting the rates as well as by governing the system homogeneity. The nitrogen bubbles generated in the reaction helped to avoid any channel blockage.

Continuous flow telescopic oxidation of alcohols via generation of chlorine and hypochlorite

A 3-step continuous flow oxidation of alcohols is demonstrated with continuous generation of chlorine as the first step followed by its use for the flow synthesis of high strength sodium hypochlorite. The solution is subsequently used for oxidation of alcohols in the presence of a catalytic amount of the nitroxyl radical “TEMPO”, which inhibits oxidation at the aldehyde stage. Selective oxidations of eight different alcohols were demonstrated. To achieve identical yields, the aromatic alcohols containing electron withdrawing groups needed a longer residence time than aliphatic alcohols.

Synthesis, Biological Evaluation and Molecular Docking studies of Novel 3-aryl-5-(alkyl-thio)-1H-1,2,4-triazoles Derivatives targeting Mycobacterium tuberculosis

A small library of new 3‐aryl‐5‐(alkyl‐thio)‐1H‐1,2,4‐triazoles was synthesized and screened for the antimycobacterial potency against Mycobacterium tuberculosis H37Ra strain and Mycobacterium bovis BCG both in active and dormant stage. Among the synthesized library, 25 compounds exhibited promising anti‐TB activity in the range of IC500.03–5.88 μg/ml for dormant stage and 20 compounds in the range of 0.03–6.96 μg/ml for active stage. Their lower toxicity (>100 μg/ml) and higher selectivity (SI = >10) against all cancer cell lines screened make them interesting compounds with potential antimycobacterial effects. Furthermore, to rationalize the observed biological activity data and to establish a structural basis for inhibition of M. tuberculosis, the molecular docking study was carried out against a potential target MTB CYP121 which revealed a significant correlation between the binding score and biological activity for these compounds. Cytotoxicity and in vivo pharmacokinetic studies suggested that 1,2,4‐triazole analogues have an acceptable safety index, in vivo stability and bio‐availability.

Continuous two step flow synthesis of m-amino acetophenone

Abstract The continuous flow nitration of acetophenone followed by reduction of the meta isomer has been demonstrated using simple tubular reactors. Because of ease of separation of the desired isomer from the first step, both steps are made continuous, but separately. The continuous flow nitration was carried out in a safe manner in a shorter reaction time than the conventional approach. The choice of micromixer was seen to affect the performance of the nitration reaction. The effect of different parameters on the yield of the desired product was studied. The reduction step with sodium sulfide was found to be economical and could be carried out efficiently at 70°C using sodium sulfide in ethanol, using a silicone tube. Both steps were demonstrated for several hours, yielding a sufficiently large quantity (∼100 g) of m-aminoacetophenone at lab scale in a single day using simple tubular reactors.

Continuous flow synthesis of β-amino α, β-unsaturated esters in aqueous medium

Abstract Continuous flow synthesis of many β-amino α, β-unsaturated esters has been demonstrated, through the reaction of a β-ketoester compound with ammonia and primary amines. Several combinations have been studied in detail in batch mode and a few have been taken for continuous flow synthesis based on their suitability. Upon studying the feasibility of continuous flow synthesis of different β-amino crotonates, the synthesis of methyl amino crotonate in the presence of a recyclable and reusable homogeneous acid catalyst has been studied in detail. Tubular reactors were seen to overcome the heat and mass transfer limitations, thereby providing a simple device for even a pilot scale production. A similar approach can be used for the synthesis of other β-amino crotonates. The continuous flow synthesis approach for producing methyl amino crotonate, in the absence of any external solvent, makes it a green process technology.

Synthesis and biological evaluation of 1,2,4-triazole-3-thione and 1,3,4-oxadiazole-2-thione as antimycobacterial agents

Resistance among dormant mycobacteria leading to multidrug‐resistant and extremely drug‐resistant tuberculosis is one of the major threats. Hence, a series of 1,2,4‐triazole‐3‐thione and 1,3,4‐oxadiazole‐2‐thione derivatives (4a–5c) have been synthesized and screened for their antitubercular activity against Mycobacterium tuberculosis H37Ra (H37Ra). The triazolethiones 4b and 4v showed high antitubercular activity (both MIC and IC50) against the dormant H37Ra by in vitro and ex vivo. They were shown to have more specificity toward mycobacteria than other Gram‐negative and Gram‐positive pathogenic bacteria. The cytotoxicity was almost insignificant up to 100 μg/ml against THP‐1, A549, and PANC‐1 human cancer cell lines, and solubility was high in aqueous solution, indicating the potential of developing these compounds further as novel therapeutics against tuberculosis infection.