• V N Rajasekharan Pillai

      Articles written in Journal of Chemical Sciences

    • Synthesis of amides and peptides using polymer-bound mixed carboxylic dithiocarbamic anhydrides

      K S Devaky V N Rajasekharan Pillai

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      The use of polymer-bound mixed carboxylic dithiocarbamic anhydrides in the synthesis of amides and peptides is illustrated. The introduction of acetyl, benzoyl andp-nitrobenzoyl and N-protected amino acyl groups into the polymer system, and acylation and peptide synthesis reactions using these polymeric acyl transfer reagents are described. Polystyrene crosslinked with hydrophilic tetraethyleneglycol diacrylate was chosen as the support for the preparation of the polymeric reagent. The reagent was prepared by a series of polymer-analogous reactions. Polystyrene resin was functionalized to aminomethyl polystyrene. The aminomethyl resin on treatment with carbondisulphide and sodium hydroxide resulted in polystyrene-supported sodium dithiocarbamate which on reaction with an acid chloride afforded the polymer-bound mixed carboxylic dithiocarbamic anhydride. The reagent on treatment with an amine or amino acid transfers its acyl group, forming the corresponding amide or peptide. In the case of acid-sensitive amino acids and amino acids containing acid-cleavable protecting groups, mixed amino acyl dithiocarbamic anhydride resins were prepared by treating sodium dithiocarbamate resin with the anhydride of the amino acid.

    • Synthesis of substance P partial sequential peptides on a photolytically removable 4-aminomethyl-3-nitrobenzoylaminomethyl polystyrene support

      V K Haridasan V N Rajasekharan Pillai

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      Sequential peptides corresponding to substance P (6–11) were synthesised on a photocleavable 4-aminomethyl-3-nitrobenzoylaminomethyl polystyrene resin. This photoremovable polymeric support, useful for the synthesis of C-terminal peptide amides, was prepared from 4-bromomethyl-3-nitrobenzoylaminomethyl polystyrene by treatment with potassium phthalimide followed by hydrazinolysis. Amino acid residues were incorporated onto this support following the standard solid-phase methodology of peptide synthesis. The protected peptide amides were cleaved from the resin by photolysis with light of wavelength 350 nm. The resin was used for the synthesis of peptides including the partial sequence corresponding to substance P (9–11) which was further subjected to stepwise synthesis to prepare substance P (6–11) in an overall yield of 88%. This approach combines the advantages of the photochemical deprotection of the 4-aminomethyl-3-nitro carboxyl protecting group, the polymer-supported peptide synthesis and the polymer-analogous functionalisation procedure to obtain the C-terminal peptide amide under mild conditions.

    • Polyethyleneglycol-catalysed benzil-benzilic acid rearrangement: A reaction in soluble macromolecular cavities

      Sunny Kuriakose V N Rajasekharan Pillai

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      Kinetics of benzil-benzilic acid rearrangement was investigated in the presence of polyethyleneglycols (PEG) at different concentrations. PEG of molecular weights 400 and 6000 were used for the studies. A set of solutions was prepared with varying PEG contents. The rearrangement was carried out in these systems and the rate constants were calculated. The rates surprisingly increased with PEG content instead of decreasing due to the reduced ionic movement in these viscous macromolecular solutions. In the presence of KOH and NaOH, PEG acts as a catalyst for the rearrangement. But in presence of LiOH, an inverse relation was observed between PEG content and the rate of reaction. These observations were explained on the basis of the cation-binding ability of polyethyleneglycols.

    • Metal ion complexation of hydrophilic polymeric amino ligands derived from tetraethyleneglycol diacrylate (TTEGDA)-crosslinked polyacrylamides

      Beena Mathew V N Rajasekharan Pillai

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      Complexation behaviour of amino ligands supported on polyacrylamides with 2–20 mol% of tetraethyleneglycol diacrylate crosslinks was investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) ions. The metal ion intake was dependent on the extent of crosslinking and followed the order: Hg(II)>Cu(II)>Zn(II)>Ni(II)>Co(II). The aminopolyacrylamides and their metal complexes were characterised by IR and EPR techniques. The absorptions of the ligands were shifted by complexation with metal ions and the EPR spectrum suggested distorted tetragonal geometry for the Cu(II) complex. The thermogravimetric analysis of the metal complexes revealed a pattern of variation of thermal stability on incorporation of metal ions. The kinetics and adsorption parameters of complexation, swelling characteristics, recyclability and specificity of metal-desorbed systems are also described.

    • A three-dimensional phase boundary model for diffusion processes involved in reactions of crosslinked polymeric amines with low molecular weight esters

      Desy P Koruthu P M Madhusudanan V N Rajasekharan Pillai

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      The reactivity of amino groups attached to N-N′-methylene-bis-acrylamide (NNMBA)-and triethyleneglycol dimethacrylate (TEGDMA)-crosslinked polyacrylamide gels (2–20 mol% crosslinked) has been investigated by following the aminolysis ofp-nitrophenyl ester of benzoyl glycine in a mixed solvent. A differential method was employed for following the rate of aminolysis reaction at definite intervals of time. The extent of aminolysis was found to be maximum between 25 and 35 min after initiation for these resins. The rate constants were calculated using the equation for three-dimensional phase boundary model with spherical symmetry and three-dimensional diffusion model. The reaction appears to be a phase boundary process up to 40 min after initiation and thereafter is fully controlled by three-dimensional diffusion. The rate constants do not show any dispersion when this model is used.

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