Many bacterial species use quorum sensing for cell-cell communication. Gram-(-) bacteria predominantly use two types of signaling compounds. One class is derived from acylhomoserine lactones (AHLs) and convey information within individual species. A proposed interspecies signal, autoinducer-2, which is derived from (S)-4,5-dihydroxy-2,3-pentanedione (DPD) is also present in many bacteria. Methods for detecting these signals are primarily based on qualitative bioassays, and more quantitative chemical methods for detection are needed. To this end, we have developed a synthesis of stable isotope labeled AHL internal standards for mass spectrometric (MS) quantitation, in which the isotope is incorporated into the conserved lactone core to facilitate late stage diversification. Also, due to the properties of DPD that hinder detection, we have synthesized a derivatizing agent to convert this molecule to a form more amenable to MS quantitation. Herein, we report syntheses of these compounds used for detection and quantitation of Gram-(-) quorum sensing molecules.