A series of 21 analogues of tetrahydrolipstatin (THL, 1) were synthesized and tested as inhibitors of the formation or hydrolysis of the endocannabinoid 2-arachidonoylglycerol (2-AG). Three of the novel compounds, i.e., 11, 13, and 15, inhibited 2-AG formation via the diacylglycerol lipase alpha (DAGLalpha) with IC 50 values lower than 50 nM (IC 50 of THL = 1 microM) and were between 23- and 375-fold selective vs 2-AG hydrolysis by monoacylglycerol lipase (MAGL) as well as vs cannabinoid CB 1 and CB 2 receptors and anandamide hydrolysis by fatty acid amide hydrolase (FAAH). Three other THL analogues, i.e., 14, 16, and 18, were slightly more potent than THL against DAGLalpha and appreciably selective vs MAGL, CB receptors, and FAAH (15-26-fold). One compound, i.e., 8, was a potent inhibitor of MAGL-like activity (IC 50 = 0.41 microM), and relatively ( approximately 7-fold) selective vs the other targets tested.