Microwave-assisted preparation of cyclic ketals from a cineole ketone as potential cosmetic ingredients: solvent-free synthesis, odour evaluation, in vitro cytotoxicity and antimicrobial assays

Some cyclic ketals derived from (+)1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-one were obtained in excellent yields by microwave activation under solvent-free conditions, as a 'green chemistry' procedure. The results obtained using acidic alumina containing 7% p-toluenesulfonic acid, as mineral support, are reported and compared with those obtained by classical methods. The new compounds were tested for their olfactive character and for a potential cosmetic use. In vitro skin cytotoxicity tests were carried out on the most promising compounds, by using NCTC 2544 human keratinocytes as target cells. They all displayed slight cytotoxic effects which were one order of magnitude lower than those found with sodium dodecylsulphate positive control. Two compounds that resulted interesting as toothpaste aromas, were submitted to antimicrobial assays and showed their activity against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus hominis, Propionibacterium acnes and Candida albicans.