Transkarbam 12 (5-(dodecyloxycarbonyl) pentylammonium-5-(dodecyloxycarbonyl) pentylcarbamate, T12) is a highly effective skin permeation enhancer. In this study, ester groups in the molecule of T12 were replaced by carbonate and carbamate ones, respectively. The in vitro permeation-enhancing activities were evaluated using porcine skin and compared with those of T12 and previously prepared series of amide, ketone, and ...