Department of Chemistry
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Item Copper-catalysed Csingle bondN/Csingle bondO coupling in water: a facile access to N-coumaryl amino acids and fluorescent tyrosine & lysine labels(Elsiever, 2016-06) Bajaj, Kiran; Sakhuja, RajeevA mild, efficient, ligand free and environmentally benign approach towards the construction of sp2 C-sp3 N bond has been developed via copper catalysed Ullmann type of coupling between 4-chlorocoumarin with N-terminus unprotected amino acids in microwave-aqua conditions, yielding a series of N-coumaryl amino acids in good to excellent yields. Excellent photo-physical properties exhibited by these N-coumaryl amino acids and their chemical applicability as C-terminus coupling partners for N-terminus peptides make them potential fluorescent probes in labelling studies. The methodology was extended towards the Csingle bondO and Csingle bondN coupling for the synthesis of fluorescent coumaryl labelled tyrosine and lysine labels respectively. Application of coumaryl labelled tyrosine was further explored towards the synthesis of fluorescent labelled opioid tetrapeptide, Endomorphin-2 derivative.Item Lewis Acid Promoted Synthesis of 2(3H)-Benzofuranones(Wiley, 2007-02-07) Sakhuja, RajeevChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDFItem A new flavone glycoside from Zanthoxylum acanthopodium DC(NISCAIR, 2007-05) Sakhuja, RajeevExamination of the dry fruits of Zanthoxylum acanthopodium has led to the isolation of a new flavone glycoside along with herbacetin-8,4'-dimethyl ether. The new flavone glycoside is characterized as 7-O-⍺-D-glucosyl-3,8-dihydroxy-2-(3-hydroxy-4-methoxyphenyl)-5-methoxy-4H-1-benzopyran-4-one on the basis of its spectral studies and that of its aglycone. This is the first report of the isolation of a 5-O-substituted flavone from the genus Zanthoxylum.Item Novel Fluorinated Spiro [Indole-indazolyl-thiazolidine]-2,4′-diones: Design and Synthesis(Taylor & Francis, 2004-09-07) Sakhuja, RajeevThe reaction of indol-2,3-diones ( 1a–i ) with 5-aminoindazole ( 2 ) has resulted in the formation of hitherto unknown 3-(indazol-5-yl)iminoindol-2-ones ( 3a–i ) in quantitative yields which, on 1,3-dipolar cyclocondensation with mercaptoacetic acid ( 4 ), has afforded a series of new spiro heterocycles, 3′-(indazol-5-yl) spiro[3H, indol-3, 2′ -thiazolidine]-2,4′-diones* ( 5a–i ).Item Microwave‐Assisted Synthesis of 10‐(Phthalimidoalkyl)‐halosubstitutedpyrido [3,2‐b][1,4]‐benzothiazine in Dry Media(Taylor & Francis, 2007-03-27) Sakhuja, RajeevN‐Alkylation of 10H‐9‐fluoropyrido[3,2‐b][1,4]‐benzothiazine 5a, 10H‐7‐fluoropyrido[3,2‐b][1,4]‐benzothiazine 5b, and 10H‐7‐chloropyrido[3,2‐b][1,4]‐benzothiazine 5c with different N‐(bromoalkyl)phthalimides using anhydrous K2CO3 and tetrabutylammonium bromide (TBAB) under dry conditions with microwave irradiation leads to the formation of 10‐(phthalimidoalkyl)‐halosubstitutedpyrido[3,2‐b][1,4]‐benzothiazine (6a–f) along with some unidentified product. Compound 5a is a new azaphenothiazine derivative and was obtained from hitherto unknown 2‐acetylamino‐3‐fluorophenyl‐3′‐nitro‐2′‐pyridylsulfide 4a via Smiles rearrangement. Compound 4a is required for the synthesis and has been prepared starting from 2‐amino‐3‐fluorobenzenethiol 1a in three steps.Item A facile synthesis of novel unsymmetrical bis-spiro[indole-pyrazolinyl-thiazolidine]-2,4'-diones (08-2933GP)(ARKAT, 2008-08-11) Sakhuja, RajeevAn elegant synthesis of some novel unsymmetrical bis-indol-2,3-diones (4a-d) has been achieved via 1-(6-bromohexyl)-1H-indol-2,3-diones (3a,b). These compounds have been further used for the synthesis of novel bis-spiroindoles (7a-d) via hitherto unknown bis Schiff‘s bases (6a-d).Item Gelation Behavior of 2H-Chromene N-Acylamino Acid Conjugates(ACS, 2009-03-18) Sakhuja, Rajeev2H-Chromene-based conjugates of N-acyl-1,ω-amino acids (5, 9a−f, 14a−f) of natural amino acids (10a,b) and of dipeptide (10c) are prepared (60−97%) by N-acylbenzotriazole methodology in aqueous media at 20 °C. Gelation properties of the corresponding sodium salts in DMF and DMSO are generalized with respect to an increase or decrease in the chain length of the spacer.Item Synthesis of boltorn 1,2,3-triazole dendrimers by click chemistry(Wiley, 2009) Sakhuja, RajeevSecond-, third-, and fourth-generation hyperbranched aliphatic polyols namely Boltorn® H20, Boltorn H30, and Boltorn H40 were endcapped with azido and activated acetylenic groups in good to excellent yields (75–95%) following an acid catalyzed procedure. The resultant terminally functionalized dendritic azido and acetylenic groups undergo 1,3-dipolar cycloaddition using methyl (or ethyl) propiolate and benzyl azide, respectively, under catalytic or noncatalytic conditions below 40 °C to yield 1,2,3-triazole dendrimeric polymers in 82–95% yield, under extremely mild conditions that could be applied for compounds sensitive to acid, base, or heat. The dendritic azido and activated acetylenic derivatives may act as novel scaffolds to tune the mechanical properties of different polymers.Item Effect of the crosslink functionality on the mechanical properties of crosslinked 1,2,3-triazole polymers as potential binders for rocket propellants(Wiley, 2010-03-30) Sakhuja, RajeevThe mechanical properties of crosslinked polymers depend on their structural features, one of which is the functionality of the crosslinks in a polymer network. To study the effect of crosslink functionality (ϕ) on the mechanical properties of 1,2,3-triazole polymers for potential application as rocket propellant binders, crosslinkers with different ϕ's (3, 4, 6, 16, 32, and 64) were used in the polymerization. As the percentage of acetylenic groups provided by crosslinker was kept constant and the functionality of the crosslinker increased, the resulting polymer showed a higher modulus but a lower strain. Compared to traditional polyurethane binders, 1,2,3-triazole polymers showed comparable mechanical properties, although the stress and modulus tended to be lower and the strain capability tended to be greater for the triazole-linked rubbers.Item Preparation and mechanical properties of crosslinked 1,2,3-triazole-polymers as potential propellant binders(Wiley, 2010-04-27) Sakhuja, RajeevThirteen triazole polymers were prepared as potential rocket propellant binders by the reactions of various diacetylenes and diazides. The reaction of E300 dipropiolate (1) with diazide (2) obtained from tetraethylene glycol was selected to study the effects of concentration of the tetraacetylene functionalized crosslinker (3) on the mechanical properties of resulting triazole polymers. The modulus of the polymers increased, whereas the strain (% elongation at failure) decreased with increasing percentage of crosslinker. The resulting triazole polymers also showed that the desired mechanical properties could be obtained by adjusting the crosslinker concentration during the polymerization. Addition of 43 wt % aluminum filler did not significantly affect the strain. The modulus of these triazole polymers was comparable with typical polyurethane elastomeric matrices for rocket propellants