Raghu Babu Korupolu

Pd-PEPPSI-IPentCl: a new highly efficient ligand-free and recyclable catalyst system for the synthesis of 2-substituted indoles via domino copper-free Sonogashira coupling/cyclization

A pyridine-containing decidedly resourceful Pd-N-heterocyclic carbene complex, Pd-PEPPSI-IPentCl (PEPPSI = pyridine enhanced precatalyst preparation, stabilization, and initiation), is used as a first class recyclable catalytic system for the synthesis of 2-substituted indoles via domino copper-free Sonogashira coupling/cyclization. The catalyst showed a greater performance in the cascade reaction of various 2-bromo anilines with different terminal acetylenes under mild (60 °C) and green conditions (ethanol : water) even in the absence of a copper catalyst and an inert atmosphere. The catalyst is used for the first time in these reactions. The findings suggest that 0.1 mol% of the catalyst is sufficient, and that the catalyst is recyclable and can be reused for up to six cycles.

Mn(II) Catalyzed Oxidation of Atenolol by Cerium(IV) in Aqueous Sulfuric Acid Medium: A Spectrophotometer Aided Kinetic, Mechanistic and Thermodynamic Study

Abstract The kinetics and mechanism of manganese(II) catalyzed oxidation of atenolol by cerium(IV) sulfate in aqueous H2SO4 at a constant ionic strength of 0.50 mol dm-3 was studied spectrophotometrically. The reaction showed first order kinetics in cerium(IV) whereas fractional order in both manganese(II) and atenolol. Addition of products showed no effect on the rate of the reaction. The main product, 2-(4-(2-hydroxy-3-oxopropoxy)phenyl)acetamide, was identified with the aid of IR and mass spectral data. Stoichiometry with respect to the drug substrate and reagent was established as 2:1. Added H2SO4, SO42− and HSO4− showed negligible effect on the rate of the reaction. HCe(SO4)3− was found to be the predominant reactive species under the specified experimental conditions. The rate constants (k), catalytic constant (kc) and equilibrium constant (K6) for the proposed mechanism were determined. The kinetic and thermodynamic activation parameters were computed for both the slow rate determining step and complex forming equilibrium step.

Resolution of racemic Vigabatrin using tartaric acid

Abstract An efficient and simple resolution methodology for the preparation of (S)- and (R)-Vigabatrin has been developed. In addition, a method of preparation for the novel compounds Vigabatrin-l-tartarate and Vigabatrin-d-tartarate is also described. The title compounds have been synthesized via resolution of Vigabatrin using commercially available l-(+)- and d-(−)-tartaric acids respectively. Graphical Abstract

Degradation study of irbesartan: Isolation and structural elucidation of novel degradants

HIGHLIGHTSBase mediated hydrolysis of Irbesartan resulted in formation of three degradants.Structures of all the three degradants were established by extensive analysis of HRMS and 1D and 2D NMR spectra.Two of the three isolated degradants were found to be new.The structure of DP‐3 was found to be different compared to that of earlier proposed one with same molecular weight. ABSTRACT To assess the stability of Irbesartan under stress conditions, and identify the degradation products, it was subjected to hydrolytic and oxidative stress, according to ICH guideline Q1A (R2). The drug showed degradation only in basic conditions, while it was stable to other stress conditions. Three degradation products were formed, which were separated on a C‐8 column employing prep HPLC using gradient elution. The structures were established by extensive 1D and 2D NMR spectroscopic studies and mass spectra. The products were identified as (2′‐(2H‐tetrazol‐5‐yl)‐[1,1′‐biphenyl]‐4‐yl)methanamine (DP‐1), N‐((2′‐(2H‐tetrazol‐5‐yl)‐[1,1′‐biphenyl]‐4‐yl)methyl)pentanamide (DP‐2) and N‐((2′‐(2H‐tetrazol‐5‐yl)‐[1,1′‐biphenyl]‐4‐yl)methyl)‐1‐pentanamidocyclopentane‐1‐carboxamide (DP‐3). One of the three, DP‐1, was reported earlier. However, its structure has not been elucidated by NMR. The other two degradants are novel and are being reported here for the first time.

Hydrolytic Degradation Study of Dabigatran Etexilate Mesylate: Isolation and Structural Elucidation of New Degradants

Abstract Dabigatran etexilate mesylate is a prodrug salt prescribed to prevent stroke with atrial fibrillation. It was subjected to stability testing by hydrolysis in both acid and basic media at room temperature. The degradation resulted in two degradants in each medium and one of which was found to be common in both the media. The degradants have been isolated by mass based preparative HPLC and SFC. All of them were unambiguously characterized by HRMS and extensive NMR (including 2D) spectroscopic techniques. Of the three impurities isolated (referred as DP-1, 2 and 3), DP-2 and DP-3 are being reported for the first time. DP-1 was identified earlier but was not characterized by NMR. DP-3 was obtained in both acid and base mediated hydrolysis. Based on 1D-NMR, 2D-NMR and HRMS spectral data, the structures of degradation products were confirmed as (Z)-3-(2-((4-(N’-(hexyloxycarbonyl) carbamimidoyl) phenylamino)methyl)-1-methyl-N-(pyridin-2-yl)-1H-benzo[d]imidazole-5-carboxamido) propanoicacid for DP-1 (Known); 2-((4-carbamimidoylphenyl amino)methyl)-1-methyl-1H-benzo[d]imidazole-5-carboxylic acid for DP-2 (New); (Z)-2-((4-(N’-(hexyloxycarbonyl) carbamimidoyl) phenylamino)methyl)-1-methyl-1H-benzo[d]imidazole-5-carboxylic acid for DP-3 (New).