Syntheses and anti-inflammatory activities of O-acyloximes. II

Organocatalytic dynamic kinetic resolution of azlactones to construct chiral N-acyl amino acid oxime esters

We have developed a chiral bisguanidinium salt catalyzed dynamic kinetic resolution of azlactones with oximes. A variety of chiral N-acyl amino acid oxime esters were generated with up to 97% ee and 99% yield. The products are useful in peptide synthesis.

Screening and evaluation of antioxidant activity of some amido-carbonyl oxime derivatives and their radical scavenging activities

The antioxidant activity of some amido-carbonyl oximes containing a C=O and -NH-R adjacent to the oxime group, [Phenyl-C(=O)-C(=N-OH)-N(-H)-Phenyl(-R)] where R= H, 4-chloro, 4-methyl, 4-methoxy, 3,4-dichloro, 3,4-dimethyl, 3-chloro-4-dimethyl, 3-chloro-4-methoxy, naphthyl and an amido-carbonyl dioxime were investigated in vitro by ferric thiocyanate, total reducing power by potassium ferricyanide reduction, 1,1-diphenyl-2- picryl-hydrazyl (DPPH(.)) free radical scavenging, ferrous ions chelating, superoxide anion radical scavenging and hydrogen peroxide scavenging activity assays. The results indicated that the amido-carbonyl oximes have powerful antioxidant capacity.

An α,β-unsaturated oxime identified as a strong contact allergen

The aim of this study was to examine the possible skin sensitizing effect of oximes, employing an alpha,beta-unsaturated oxime as the model compound. Oximes are not frequently used as biologically active compounds. However, they have been shown to possess both anti-inflammatory and anti-allergic activities. Furthermore, in a recent study, a number of oximes and oxime-ethers of hydroxylated benzaldehydes and acetophenones were found to be powerful antioxidants suggested to be used in consumer products such as cosmetics and food. Although there are only few reports on the sensitizing effect of oximes, their ability to be hydrolyzed to the corresponding ketones or aldehydes makes them potential contact allergens. The oxime investigated in this study was demonstrated to be a strong contact allergen in both mice and guinea pigs, capable of sensitize the control animals after only one dermal exposure. In order to elucidate the mechanisms for the formation of the complete antigen, a variety of analogues with different reactivity were tested. The results indicate that alpha,beta-unsaturated oximes can react with proteins via several different pathways. Most likely, a metabolic transformation is involved. Due to the strong allergenic effect of the oxime investigated, we strongly advise against the use of such oximes in consumer products until a better understanding of their interactions with biological macromolecules has been obtained.

Anti-inflammatory and anti-allergic activities of hydroxylamine and related compounds

The anti-inflammatory activities of several novel oximes and O-acyl oximes that we synthesized have been reported based on carrageenan-induced rat foot-pad swelling assay and histamine-induced rat vascular permeability assay. A cyclooxygenase (COX)-1 inhibitory effect has also been reported for 4'-piperidinoacetophenone and 4'-morpholinoacetophenone oximes and their O-acyl derivatives. To further search for more effective non-steroidal anti-inflammatory or anti-allergic drugs, 1-hydroxylamino-1-(4'-piperidinophenyl) ethane (P-HA) and 1-hydroxylamino-1-(4'-morpholinophenyl) ethane (M-HA) were synthesized from the corresponding oximes with sodium cyanoborohydride, and N,O-diacetyl hydroxylamines (P-HA-Ac and M-HA-Ac) were prepared from these hydroxylamines using acetyl chloride. These hydroxylamines and N,O-diacetyl hydroxylamines clearly exhibited inhibitory effects on mouse carrageenan-induced foot-pad swelling induced by oral administration (150, 37.5 mg/kg). An oral dose of P-HA-Ac (150 mg/kg) significantly inhibited the mouse anaphylactic reaction to ovalbumin measured by the abdominal wall (AW) method. Percutaneous administration of P-HA and M-HA significantly inhibited 2,4-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity reaction (type IV) in mice at a dose of 0.5 and 0.1 mg/ear, respectively. All tested hydroxylamines and N,O-diacetyl hydroxylamines clearly inhibited both COX-1 and COX-2 enzyme activities with IC(50) values of 1.9-28.7 and 1.6-2.9 micro M against COX-1 and COX-2, respectively. Hydroxylamines (P-HA and M-HA) also showed a 5-lipoxygenase inhibitory effect.

Solvents inducing oxidation of hydroxylamines

Hydroxylamines gradually undergo oxidation to their oximes on being dissolved in organic solvent (e.g. methanol). This phenomenon was followed by (1)H-NMR and liquid chromatography-mass spectrometry (LC-MS). The oxidation rate was estimated from the peak area observed on the mass chromatogram at the protonated molecule or fragment ion on LC-atmospheric pressure chemical ionization (APCI)-MS. The results showed that the oxidation rate of hydroxylamines depended on the solvent type.