Evidence for two concurrent mechanisms and a kinetically significant proton transfer process in acid-catalyzed O-methyloxime formation

Rate and equilibrium constants for formation and hydrolysis of 9-formylfluorene oxime: diffusion-controlled trapping of a protonated aldehyde by hydroxylamine

Equilibrium constants Kadd = 440 and Kox = 3.0 × 108 for formation of a carbinolamine adduct and oxime, respectively from 9-formylfluorene and hydroxylamine, and pKa = –1.62 for protonation of the oxime, have been evaluated at 25°C in aqueous solution, based on measurements in hydroxylamine buffers, acetic acid buffers, and dilute HCl. Rate constants for hydrolysis of the oxime have been measured in the acidity range pH 4–12 M HClO4. At the highest acidities, a reaction pathway via protonated carbinolamine has been identified: evidence is presented that the reverse of this reaction involves rate-determining attack of hydroxylamine upon protonated 9-formylfluorene. By assuming that the attack of hydroxylamine is diffusion-controlled, with rate constant 3 × 109 M –1 s–1, a pKa for O-protonation of the aldehyde (–4.5) is derived. Taking account of the equilibrium constant for enolization of 9-formylfluorene (KE = 16.6), a pKa for for C-protonation of the enol tautomer ((–5.7) may also be obtained. Comparison of this pKa with that of the enol of acetophenone shows that the enol of 9-formylfluorene is less basic by a factor of 1010. By combining pKas for protonation of the aldehyde and oxime with measured or estimated equilibrium constants for addition of water, hydroxide ion, and hydroxylamine to 9-formylfluorene, it is also possible to obtain values of pKR = –5.3, 4.1, and 12.25 for the protonated 9-formylfluorene, protonated oxime, and 9-formylfluorene, respectively. The usefulness of pKR in providing a general measure of equilibrium constants for electrophile-nucleophile combination reactions is discussed.Key words: oxime, formyfluorene, hydrolysis, protonation, diffusion-control.

Derivatization of prostaglandins and related compounds to (methoxime) alkyl ester alkyl ether derivatives for gas chromatographic analysis

Rapid and convenient methods are described for the exhaustive derivatization of carbonyl, carboxyl and hydroxyl groups of prostaglandins and related compounds to methoxime, alkyl ester and alkyl ether compounds respectively. Optimal reaction conditions were established for each group. The reactions were carried out in polar aprotic solvents. Alkyl ester alkyl ether derivatives were obtained quantitatively and rapidly in one step with n-alkyl (C1-C4) halides in the presence of sodium hydroxide. Methyl ester methyl ether derivatives have the highest volatility, but propyl ester propyl ether derivatives improved the separation of complex mixtures. The carbonyl group sometimes induced side-products, so the carbonyl group was converted into methoxime. Methoximation was achieved quantitatively by using methoxylamine in the presence of hydrochloric acid or sodium hydroxide, followed by alkylation in same reaction medium. Methoximation gave syn- and anti-isomers, which were separated chromatographically, decreasing the resolution for complex samples.

A role of oxidative DNA sugar damage in mutagenesis by neocarzinostatin and bleomycin

The anti-tumor antibiotics neocarzinostatin and bleomycin specifically oxidize deoxyribose in DNA at the C-5' and C-4' positions, respectively. The resulting DNA lesions include strand breaks and apyrimidinic sites. Both agents are broad specificity mutagens, inducing, in various systems, base substitutions, frameshifts and deletions. Sequencing studies in bacterial systems have suggested that the base substitutions may result primarily from replicative bypass of the oxidized apyrimidinic sites.