| Recent papers report that extracts of the plant, Lepidium meyenii, called Maca, contain eighteen macamides. These compounds are non-polar N-benzylamides of long chain fatty acids containing mostly 15 and 18 carbons with zero to three double bonds, and in some cases conjugated ketone functions. We have synthesized eleven of these macamides and also some structurally related compounds for in vitro biological evaluation as inhibitors of the cloned human enzyme Fatty Acid Amide Hydrolase (FAAH).;The following four most active macamides inhibited FAAH with IC 50 values in the 10-14 micromolar range: the N-benzylamide of linoleic acid and the N-(3 methoxybenzyl)amides of oleic, linoleic and linolenic acids. Somewhat less active were the N-benzylamide of oleic acid (IC50 = 17 micromolar) and the N-benzylamide of linolenic acid (IC50 = 42 micromolar). The preeminence of the 3-methoxybenzylamides among active macamides is attributable to hydrogen-bonding from the Thr236 hydroxyl present in the binding pocket of FAAH. Indeed replacement of the 3-methoxybenzyl group with a more-strongly H-bond accepting N-(3-pyridylmethyl) group lowered the IC50 to 7-8 micromolar in both the resulting oleamide and the linoleamide. Lesser inhibitory activities were observed for the macamides of palmitic acid and several saturated synthetic analogs. One unusual macamide, E,E,N-benzyl-5-keto-6,8-octadecadienamide, was prepared in a five-step synthesis, and was found to be only weakly active as an FAAH inhibitor. The preparation of macamide analogs from chain-shortened omega phenyl fatty acids resulted in amides with dramatically less of inhibitory activity. Syntheses of urea analogs of 9Z-octadecenylamine and 8Z-heptadecenylamine gave compounds not as active as the best macamides. However, the carbamate synthesized from (Z)-1-isocyanatoheptadec-8-ene and 3-hydroxymethylpyridine showed a 67-fold decrease in its IC50 value (to 150 nanomolar). In an experiment to distinguish reversible from irreversible enzyme inhibition, the most inhibitory macamide (HW-70) was tested with the carbamate (HW-88). Only the carbamate showed a decrease in its IC50 value at a longer preincubation time. The result implied irreversible binding of the carbamate, and suggested reversible binding of macamides to the enzyme. Biological testing methods were validated using the heteroaromatic ketone, OL-135 (IC50 =30 nanomolar), and the urea, PF-622 (IC50 =1 micromolar), as standards. |
