N-(4-bromobenzoyl)-S,S-dimethyliminosulfurane, a potent dermal penetration enhancer

Asymmetric Synthesis of Chiral Sulfimides through the O-Alkylation of Enantioenriched Sulfinamides and Addition of Carbon Nucleophiles

Chiral sulfimides, the aza-analogues of sulfoxides, are valuable compounds in organic synthesis and medicinal chemistry. Herein, we report an efficient method for preparing chiral sulfimides from easily available enantioenriched sulfinamides. The key step of this method is a stereospecific oxygen-selective alkylation of enantioenriched sulfinamides, which is accomplished by using isopropyl iodide, K₂ CO₃ , and DMPU. The resulting chiral sulfinimidate esters are transformed to chiral sulfimides by the nucleophilic addition of the Grignard reagents under simple conditions. This transformation enables access to the enantioenriched diaryl or dialkyl sulfimides bearing two similar carbon substituents, which are difficult to synthesize by previous methods.

Ligand-Free, Quinoline N-Assisted Copper-Catalyzed Nitrene Transfer Reaction To Synthesize 8-Quinolylsulfimides

An efficient copper-catalyzed, quinolyl N-directed nitrene transfer reaction to 8-quinolylsulfides was described. A variety of 8-quinolylsulfimides with different functional groups were synthesized in moderate to high yields. The obtained 8-quinolylsulfimides were proved to be promising novel type of bidentate ligands in Pd(II)-catalyzed allylic alkylation.

Discriminant analysis as a tool to identify compounds with potential as transdermal enhancers

Structure-activity relationships were sought for 73 enhancers of hydrocortisone permeation from propylene glycol across hairless mouse skin. Enhancers had chain lengths (CC) from 0 to 16 carbon atoms, 1 to 8 H-bonding atoms (HB), molecular weight 60 to 450, log P (calculated) −1.7 to 9.7 and log S (calculated) −7.8 to 0.7. These predictive properties were chosen because of their ready availability. Enhancement ratio (ER) was defined as hydrocortisone transferred after 24 h relative to control. Values for the ER ranged from 0.2 to 25.3. Multiple regression analysis failed to predict activity; ER values for the ‘good’ enhancers (ER>10) were underestimated. Simple guidelines suggested that high ER was associated with CC>12 and HB 2–5. This was refined by multivariate analysis to identify significant predictors. Discriminant analysis using CC, HB, and molecular weight correctly assigned 11 of the 12 ‘good’ enhancers (92%). The incorrectly assigned compound was a known, idiosyncratic Br compound. Seventeen of the 61 ‘poor’ enhancers (28%) were incorrectly assigned but four could be considered marginal (ER>8). The success of this simple approach in identifying potent enhancers suggested its potential in predicting novel enhancer activity.

Cutaneous biotransformation of N-(4-bromobenzoyl)-S,S-dimethyliminosulfurane and its product, 4-bromobenzamide, leading to percutaneous penetration enhancement of drugs: initial evidence using hydrocortisone

The role of the skin's metabolism of N-(4-bromobenzoyl)-S,S-dimethyliminosulfurane (DMBIS), an effective penetration enhancer, on its enhancement activity was investigated. It has been found that DMBIS hydrolyzes very fast in physiological buffer to 4-bromobenzamide (BBA), and even faster and almost completely in the presence of skin tissue. It was further shown that in the presence of skin from different species incubated at physiological conditions, the concentration of BBA (DMBIS' immediate product) dropped sharply to 70-80% in 10 min followed by a slower decrease of 0.35-0.50 microg/h. This metabolism was partially inhibited by a continuous application of iodine, and more profoundly, by iodoacetic acid (IAA) and dithiothreitol (DTT) combination treatment. This indicates that at least a part of the metabolism of BBA involves enzymes that are sensitive to reactions with their sulfhydryl groups. In an in vitro permeation study using human epidermis and conventional diffusion cells, we compared between the permeabilities of untreated epidermis and IAA/DTT-treated epidermis to hydrocortisone in the presence of BBA. Due to its metabolic inhibition, we noted a higher penetration of BBA through IAA/DTT-treated epidermis than through the untreated epidermis. Contrary to these results, the extent of the penetration of hydrocortisone was higher through the untreated epidermis with only 1.6 h lag time relative to its penetration through IAA/DTT-treated epidermis, which exhibited a lag time of 12.4 h. It is evident, therefore, that the skin enhancement activity of DMBIS/BBA depends on BBA metabolism in the skin, presumably through its in situ biotransformation into an active enhancer.

Mechanistic studies on percutaneous penetration enhancement by N-(4-halobenzoyl)-S,S-dimethyliminosulfuranes

Halogen-substituted iminosulfuranes are transdermal penetration enhancers (TPEs) in permeation studies using hairless mouse or human cadaver skin. The interaction of N--(4--R-benzoyl)-S,S-dimethyliminosulfuranes 1--4, where R=H, Cl, Br, and I, with l-alpha-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) has been studied using differential scanning calorimetry, isothermal titration calorimetry, nuclear Overhauser effect spectroscopy (NOESY), and NMR spectroscopy, and by calculation of the iminosulfurane polarizabilities in order to elucidate the molecular basis of the TPE activity. The active compounds reduce the melting temperature of the gel-to-liquid-crystal phase transition and induce multiple components in the transition excess heat capacity profile. The partitioning of the bromo derivative 3, the most active compound, into DMPC is unique in that 3 may be trapped in the bilayer, affording an enhanced residence time and a reason for its high TPE activity. The entropy decrease associated with the transfer of 3 to the bilayer is much lower than that for the other compounds, indicating that 3 occupies or induces sites that afford it considerable local motional freedom. Correlations between the iminosulfurane TPE activities, the partition coefficients, and NOESY crosspeak volume were observed. Molecular polarizabilities are not consistent with a TPE mode of action involving interaction of these agents with protein side chains.

Investigation of Iminosulfuranes as Novel Transdermal Penetration Enhancers: Enhancement Activity and Cytotoxicity

PURPOSE

Very few chemical enhancers for transdermal drug delivery have been approved for clinical use due to irritancy and toxicity concerns. Novel chemical enhancers (iminosulfuranes) were synthesized and studied for their activity and toxicity.

METHODS

Skin was treated with 0.4 M 1-5 for 1 h before hydrocortisone was applied. Samples were taken over 24 h and analyzed by high-performance liquid chromatography. Dermal fibroblasts and epidermal keratinocytes were treated with 0-1.2 M 1-5 for 24 h and cytotoxicity assay [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)] was performed. Furthermore, enhancement activity of 0-0.4 M 2 was studied. Partition coefficient of the model drugs into stratum corneum (SC) was measured and confocal Raman microscopy was used to study the penetration process and possible mechanisms of action of the enhancers. Quantitative structure-activity relationship (QSAR) was analyzed to study the contribution of different intramolecular descriptors to enhancement activity.

RESULTS

Iminosulfurane 2 showed the highest enhancement activity. All compounds below 0.2 M were safe to skin cells, and 2 was effective at the concentration of 0.1 and 0.2 M. Mechanisms of action of 2 may include increasing partition coefficient of the model drug into SC and interaction between the enhancer and lipids and protein in the SC. QSAR study indicated contribution of several factors to activity: partition coefficient, hydrogen-bond acceptor, and optimal molecular size.

CONCLUSIONS

Enhancement activity of 2 was achieved without any cytotoxicity.