The nitro group in aliphatic and aromatic nitro compounds also containing reducible substituents such as ethene, nitrile, acid, phenol, halogen, ester, etc., are selectively and rapidly reduced at room temperature to corresponding amines in good yields by employing hydrazinium monoformate, in the presence of commercial zinc dust. It was observed that, hydrazinium monoformate is more effective than hydrazine or formic acid and reduction of nitro group occurs without hydrogenolysis in the low cost zinc dust compared to expensive metals like palladium.

The repeating sequence of elastin, valylprolylglycylvalylglycine (VPGVG), its permutation pentamer glycylvalylglycylvalylproline (GVGVP), and its more hydrophobic pentamer glycylphenylalanylglycylvalylproline (GFGVP) were synthesized by classical solution-phase methods and characterized. The kinetics of the oxidation of these pentapeptides (PP) by Mn(III) was studied in the presence of sulphate ions in acidic medium at 25°C. The reaction was followed spectrophotometrically at l max = 500 nm. A first-order dependence of rate on both [Mn(III)] and [PP] was observed. The rate is independent of concentration of the reduction product, Mn(II) and hydrogen ions. Effects of varying dielectric constant of the medium and addition of anions such as sulphate, chloride and perchlorate were studied. Activation parameters were evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of PP with Mn(III) in the rate-limiting step is suggested. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of these sequences where increased hydrophobicity results in an increased rate of oxidation. Further, it was observed that the pentamers with Pro as C-terminus are more susceptible to oxidation than the pentamer with Gly as C-terminus.

Reduction ReductionO 0220 Hydrazinium Monoformate: A New Hydrogen Donor. Selective Reduction of Nitrocompounds Catalyzed by Commercial Zinc Dust. -The nitro group in compounds also containing reducible substituents is selectively and rapidly reduced under mild conditions to the corresponding amines (II) by employing the title reaction. -(GOWDA, S.; GOWDA, B. K. K.; GOWDA*, D. C.; Synth. Commun. 33 (2003) 2, 281-289; Dep. Stud. Chem., Univ. Mysore, Manasagangotri, Mysore 570 006, India; Eng.) -H. Haber 22-054

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The fragments of elastin sequences, glycyl-alanyl-proline (GAP), glycyl-valyl-proline (GVP), glycyl-isoleucyl-proline (GIP) and glycyl-leucyl-proline (GLP) were synthesized by a classical solution phase method and characterized. The kinetics of oxidation of these tripeptides (TP) by Mn(III) has been studied in the presence of sulfate ions in acidic solution at 25 C. The reaction was followed spectrophotometrically at l max 500 nm. A ®rst-order dependence of rate on both [Mn(III)] and [TP] was observed. The rate is independent of the concentration of the reduction product, Mn(II), and hydrogen ions. The eects of varying the dielectric constant of the medium and addition of anions such as sulfate, chloride or perchlorate were studied. Activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of TP with Mn(III) in the rate-limiting step is suggested. The eect of hydrophobicity of the amino acids on the rate of oxidation is discussed. 1110 CHANNE GOWDA, KEMPE GOWDA, AND RANGAPPA Downloaded by [McMaster University]