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Bacteria ingested by a neutrophil are located in phagosomes in which H(2)O(2) is produced through the NADPH oxidase-dependent respiratory burst. Myeloperoxidase (MPO) plays important role in the bactericidal action of phagosomes. MPO catalyses the reaction of H(2)O(2) and Cl(-) to produce HClO. The chemical mechanism behind the bactericidal action of the MPO-H(2)O(2)-Cl(-) system is unclear. Bactericidal action may result from (a) the direct reactions of HOCl with biological components (through amine chlorination) or (b) (1)O(2), formed non-enzymatically from HOCl and H(2)O(2), that mainly works to kill microorganisms through bacterial respiratory chain injury. To answer this question, we developed a Cypridina luciferin analogue (MCLA)-dependent chemiluminescence method to determine the rate of formation of (1)O(2) from a (1)O(2) source at pH 4.5-9.0. Using the MCLA-dependent chemiluminescence method, we found that the rate of formation of (1)O(2) from the MPO-H(2)O(2)-Cl(-) system peaked at pH 7.0. Segal et al. (28) reported that almost all Staphylococcus aureus is killed 2 min after phagocytosis by neutrophils where the phagosomal pH is 7.4-7.75. However, amine chlorination by HOCl did not proceed at pH > 7.0. Moreover, the bactericidal activities of the MPO-H(2)O(2)-Cl(-) system with Escherichia coli at pH 4.5 and 8.0 were paralleled by the rate of formation of (1)O(2). Combining these observations and the results reported by Segal et al., we concluded that (1)O(2) is a major chemical species in the killing of bacteria in neutrophil phagosomes.

Rates for the reaction between L-S-nitrosocysteine and L-cysteine were found to be first order with respect to concentrations of the two reactants in the pH range of 4.85 – 9.41. The second order rate constant was determined to be 3.10 × 10−2 M−1s−1 at pH = 7.4 at 37 °C. Spontaneous decomposition of L-S-nitrosocysteine proceeded with the first order rate constant, 1.46 × 10−5 s−1 under the same conditions.

Our study of the kinetics of deprotonation and decomposition of spiro[adamantane-1,3′-(4′-(m-hydroxy-phenyl)-4′-methoxy-1′,2′-dioxetane)] (I) showed kinetic parameters for decomposition of tetrabutylammmonium salt of I to be ΔH‡=85.4±1.1 kJ mol-1; ΔS‡=16.0±3.5 J mol-1 K-1.

meso-Tetraphenylporphinatoiron chloride (TPPFeIIICl) has been found to catalyse the reductive cleavage of semipolar S–O and S–N bonds in aromatic sulphoxides and sulphilimines respectively with both 1-benzyl-1,4-dihydronicotinamide (BNAH) and sodium borohydride. Sulphoxides bearing electron-withdrawing substituents are much more readily reduced than those with electron-donating groups. The rate of reduction by the TPPFeIII/BNAH system decreases in the following order: N-unsubstituted sulphilimines > N-tosylsulphilimines > aromatic sulphoxides. During the reaction with sulphoxides, the formation of the µ-oxo dimer of TPPFeIII has been observed. Under the same conditions, concurrent reductive cleavage of the S–C bond was observed with sulphoxides bearing an electron-withdrawing group at the α-position. Control experiments revealed that the reductive S-dealkylation of these sulphides is accompanied by the major S-deoxygenation reaction. Plausible mechanisms are discussed.

Treatment of azoxybenzene with p-toluenesulfonic acid in acetic anhydride gave tosylates of 4- and 2-(phenylazo)phenols, and the corresponding acetates as by-product, besides azobenzene. However, a similar reaction of 4,4′-difluoroazoxybenzene gave 2-tosyloxy-4,4′-difluoroazobenzene as rearrangement product, besides 4-fluorophenyl tosylate and 4-fluorophenyl acetate. Meanwhile, the reaction of 4,4′-diacetoxyazoxybenzene afforded 4-acetoxyphenyl tosylate and hydroquinone diacetate in high yields. These unique reactions involve C–N bond cleavage, and may proceed through a pathway involving formation of benzenediazonium ion as the key intermediate.

Reduction of Schiff bases with selenophenol proceeded at room temperature to yield the corresponding sec. amines quantitatively. The reaction of either prim. amine or sec. amine with carbonyl compound and selenophenol gave sec. or tert. amines, respectively. Different alkyl groups can be introduced successively on nitrogen of prim. amines to afford tert. amines bearing three different alkyl groups desired by one pot reaction.

The reactions of 4-methylbenzyl thiocyanate (1) with several nucleophiles have been investigated. Compound 1 possesses three electrophilic sites, i.e., benzylic carbon, sulfur and cyano carbon, to receive nucleophilic attack. PhS− and CN− which have HOMO’s of high energy levels appear to attack preferentially the sulfur atom. MeO− was found to attack preferably the cyanide carbon, while amines which have HOMO’s of low energy levels prefer benzylic carbon to attack. The nucleophilic substitution on the sulfur or the cyanide carbon generates CN− or p-xylene-α-thiolate anion, strong nucleophiles, as the primary products, which then initiate the complex secondary reactions. The selective reactivities of three attacking sites for nucleophiles in 1 have been rationalized in terms of MO theory.

Meso-tetraphenylporphinatoiron(III)/imidazole catalyses the Polonovski type reaction of substituted N,N-dimethylanilne N-oxides to give mixtures of N-demethylated and N-deoxygenated products. Effect of substituent on the turnover number and the ratio of the demethylation to the deoxygenation, and other observations suggest that the Polonovski type N-demethylation reaction takes place via the rate determining N,N-dimethylanilinium cation radical formation.

Amines, especially imidazole, were found to be essential in the meso-tetraphenylporphinatoiron (III) promoted demethylation of N, N-dimethylaniline N-oxide through the Polonovski type reaction and in the cumene hydroperoxide dependent oxidative demethylation of N, N-dimethylaniline in dichloromethane. When benzenethoil was used instead of these amines, deoxygenation of N, N-dimethylaniline N-oxide took place very readily

The mechanism of the reaction between N,N-dimethylaniline N-oxide 1 and acetic anhydride to give 2-acetoxy-N,N-dimethylaniline 2a has been reinvestigated by means of our more refined 18O-tracer experiments. Other products of the reaction are 4-acetoxy-N,N-dimethylaniline, N,N-dimethylaniline 4, N-methylacetanilide, and bis(4-dimethylaminophenyl)methane. The reaction of 1 with 18O-labeled acetic anhydride is considered to involve the initial formation of carbonyl-18O-labeled N-acetoxy-N,N-dimethylanilinium ion 7a and the subsequent intramolecular rearrangement of 7a into 2a in which the original 18O-label in 7a is unequally partitioned into two oxygen atoms of 2a (phenolic oxygen: ethereal oxygen=ca. 4 : 1). The reaction of 1 with trichloroacetic anhydride gave solely 2-trichloroacetoxy-N,N-dimethylaniline but not any 4 which should be formed via the free radical mechanism. These observations suggest the occurrence of the two concerted path via polarized six-(major) and four-(minor) membered cyclic transit...

Mechanistic mode for the oxygenation of sulfides with the pig liver microsomal FAD-containing monooxygenase(EC 1.14.13.8) has been conveniently distinguished from that with the phenobarbital induced liver microsomal cytochrome P-450 by analyzing products of the oxygenation of phenacyl phenyl sulfide. Upon oxygenation of phenacyl phenyl sulfide, the FAD-containing monooxygenase gave solely phenacyl phenyl sulfoxide in contrast to the cytochrome P-450 promoted oxygenation which is known to give substantial amounts of C-S bond fission products. The observation suggests that the oxygenation of sulfide with FAD-containing monooxygenase involves the nucleophilic attack of the divalent sulfur on the reactive oxygen atom involved at the enzyme active site, namely electrophilic oxygenation of sulfide, though the oxygenation with the cytochrome P-450 is initiated by a single electron transfer from the sulfide to the enzyme active species.

Reduction of sulfoxides and sulfilimines to the corresponding sulfides by both BNAH and NaBH 4 have been found to proceed in the presence of a catalytic amount of metallo-mesotetraphenylporphins.

Specifically 18O-labeled p-substituted benzoyl cyclohexyl carbonates (1) were prepared and heated at 45, 70 and 75°C, and novel stepwise oxygen scrambling was found to take place in 1. On being heated at 45°C, the carbonic carbonyl oxygen atom and the oxygen atom sandwiched between the two carbonyl carbon atoms of 1 were found to scramble. The 18O-scrambling among the above two and carboxylic carbonyl oxygen atoms of 1 was found to take place at 70 or 75°C. A good first order kinetic dependence was observed for the first step of the scrambling at 45°C but no substituent effect. An intramolecular mechanism involving two steps of equilibration is proposed.

Treatment of azoxybenzene with p-toluenesulfonic acid in acetic anhydride gave tosylates of 4- and 2-(phenylazo)phenols, and the corresponding acetates as by-product, besides azobenzene. However, a similar reaction of 4,4′-difluoroazoxybenzene gave 2-tosyloxy-4,4′-difluoroazobenzene as rearrangement product, besides 4-fluorophenyl tosylate and 4-fluorophenyl acetate. Meanwhile, the reaction of 4,4′-diacetoxyazoxybenzene afforded 4-acetoxyphenyl tosylate and hydroquinone diacetate in high yields. These unique reactions involve C–N bond cleavage, and may proceed through a pathway involving formation of benzenediazonium ion as the key intermediate.

Specifically 18O-labeled p-substituted benzoyl cyclohexyl carbonates (1) were prepared and heated at 45, 70 and 75°C, and novel stepwise oxygen scrambling was found to take place in 1. On being heated at 45°C, the carbonic carbonyl oxygen atom and the oxygen atom sandwiched between the two carbonyl carbon atoms of 1 were found to scramble. The 18O-scrambling among the above two and carboxylic carbonyl oxygen atoms of 1 was found to take place at 70 or 75°C. A good first order kinetic dependence was observed for the first step of the scrambling at 45°C but no substituent effect. An intramolecular mechanism involving two steps of equilibration is proposed.

Diaryl disulfides were found to be reduced smoothly to the arenethiols by BNAH in the presence of a catalytic amount of 3-methyllumiflavin under mild conditions.