J . Med. Chem. 1992,35,743-750
stituted aryl group augments sweetness potency in the guanidine sweetener class. The sweet-tasting guanidines which lack this aryl moiety which we have described clearly indicate that the aryl group is not a requisite for sweetness. However, these analogues are in general 3 orders of magnitude less potent than corresponding aryl-substituted derivatives. Thus, we conclude that the essential pharmacophore in the guanidinoacetic acid sweeteners is a n N-substituted-N'-(cboxymethy1)guanidine. Important functionality for receptor binding is present in guanidinoacetic acid. However, i t appears to be insufficient for receptor activation and this critical role may be provided by either, or both, the aryl- or alkylguanidine substituents. Experimental Section Sensory data was obtained by evaluation of compounds at 0.01, 0.1, and 1.0 mg/mL in distilled water by two trained tasters, and the resulting sensory data was averaged. Melting pointa were obtained on a Thomas-Hoover Unimelt capillary apparatus and are not correded. IR spectra were taken as KBr pellets using a Perkin-Elmer Model 283 or 681. NMR spectra were obtained either on a Varian FT-80 or on a General Electric QE-300 spectrometer. Microanalyses were performed by Midwest Microlab, 7212 N. Shadeland Ave, Indianapolis, IN. Chromatography was performed according to the method of Stilllg on silica gel. The isothiocyanateswere p u r c h e d from Fairfield Chemical Company and Trans World Chemicals. Care should be taken in runningthe hydrogen peroxide oxidation reaction due to ita exothermicity. N-(Cyclohexylmethy1)thiourea (2a). To a stirred solution of cyclohexylmethyl isothiocyanate (9.14 g, 58.9 mmol) in 90 mL of acetonitrile was added 11.3 mL of 15 N ammonium hydroxide (170 mmol). After 19 h, the reaction mixture was filtered, and the white solid was washed with copious amounta of ether. The solid was air-dried to afford 4.60 g (45%) of the desired thiourea. The filtrate was concentrated and the residue was slurried in ether. The slurry was filtered to afford an additional 2.96 g (29%)of thiourea: mp 151-153 OC; 'H NMR (DMSO-d6)6 7.7-7.5 (m, 1 (19) Still, W. C.; Kahn,M.; Mitra, A. Rapid Chromatographic Technique for Preparative Separations with Moderate Resolution. J. Org. Chem. 1978,43, 2923.
743
H, NH), 7.5-6.65 (2 m, 2 H, NH2),3.3-3.1, 3.0-2.75 (2 m, 2 H), 1.8-1.4 (m, 6 H), 1.3-1.0 (m, 3 HI, 1.04.7 (m, 2 H); IR (KBr, cm-l) 3400, 3280, 3180, 2990, 2850, 1629, 1595, 1564, 1480. Anal. (CBH16N2) C, H, N.
[N-(Cyclohexylmethyl)~o]aminomethanesAcid
(3a). To a stirred, ice bath cooled suspension of 2a (7.11 g, 41.3 mmol) and sodium molybdate dihydrate (0.15 g, 0.62 mmol) in 40 mL of methanol was added 13.5 mL of 30% hydrogen peroxide at a rate such that the reaction temperature did not rise above 20 "C. After the addition was complete, the ice bath was removed. The reaction temperature r w . When the reaction exotherm was complete, the reaction mixture was cooled to 10 OC and filtered, and the solid was washed with water. The solid was dried in vacuo (40 OC, 100 4 14 3 3 2-CH3 29 1 3 3-CH3 12 3 3 40 f 3 4 4-CH3 38 f 12 3 >lo0 3 4-NOz 3 5615 13 f 3 4 H 19 f 6 3 >lo0 3 3 >100 >lo0 4-COCHe _.. Number of experiments. Concentration of compound which inhibited the binding of [3H]dihydroalprenolo1(4.5 nM) by 50% in partially purified membrane fractions from canine ventricular muscle in the presence of 1 r M zinterol. Concentrations of compound which inhibited the binding of [3H]dihydroalprenolo1(4.6 nM) by 50% in partially purified membrane fractions from canine lung tissue in the presence of 0.1 p M metoprolol.
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(IC,) for a series of substituted arylpiperazines. These compounds were used as models to indicate which type of aryl substitution might have the best /31/,92 selectivity. In Table 111, the IC, for each new compound is given. The new compounds were compared to sotalol. The electrophysiological assay was carried out in canine cardiac Purkinje fibers.16 Standard microelectrodetechniques with a cycle length of 1 s were used to determine the effects on action potential duration (APD) and the rate of depolarization of phase zero (Vm,J. In Table 111, we report the concentration necessary to prolong the APD at 95% repolarization by 20% from control (C20APDg5). Compounds that exhibited a C m APDgbof less than 10 pM were considered to show good activity as class III agents. We have found that such compounds generally show efficacy in in vivo models at reasonable doses (
