Deuterium and Tritium Labelling ofN-Acyl-<scp>L</scp>-homoserine Lactones (AHLs) by Catalytic Reduction of a Double Bond in the Layer-by-Layer Method

N-Acyl-L-homoserine lactones (AHLs) are signalling molecules found in Gram-negative bacteria that enable bacteria to communicate with each other through quorum sensing and with their eukaryotic host cells through inter-kingdom signalling. Very little is known about inter-kingdom signalling mechanisms. Deuterium- and tritium-labelled AHLs were synthesized in an effort to detect the cellular distribution and monitor the membrane transport of AHLs. Most tritium labelling methods use tritium gas, which is difficult to handle, however, here we present a novel, gas-free method with which to obtain deuterium- and tritium-label terminally unsaturated AHLs through catalytic reduction of the double bond. This uncommon double bond reduction employs either sodium borohydride-[2H] or sodium borohydride-[3H] and is performed in the presence of palladium(II) acetate, which acts as a catalyst in the unique layer-by-layer system. Moreover, detailed NMR analysis of the resulting isotopologues is presented.