Binding site for fungal beta-lactone hymeglusin on cytosolic 3-hydroxy-3-methylglutaryl coenzyme A synthase

We studied the molecular mechanism through which the fungal beta-lactone, hymeglusin, potently and specifically inhibits 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase. [(14)C]Hymeglusin covalently bound to purified rat liver and to recombinant hamster cytosolic HMG-CoA synthases. The enzyme activity was completely inhibited at a binding ratio of 1.6-2.0 mol [(14)C]hymeglusin/mol HMG-CoA synthase. Incubating the enzyme with 2 mM iodoacetamide (IAA) or 2 mM N-ethylmaleimide (NEM) but not with 1.0 mM diisopropyl fluorophosphates (DFP) completely inhibited the binding, suggesting that hymeglusin binds to a Cys residue of HMG-CoA synthase. Recombinant hamster HMG-CoA synthase labeled with [(3)H]hymeglusin was digested with V8 protease, and the [(3)H]peptide was purified by high performance liquid chromatography (HPLC). The sequence of the peptide was Ser-Gly-Asn-Thr-Asp-Ile-Glu-Gly-Ile-Asp-Thr-Thr-Asn-Ala-[(3)H]hymeglusyl Cys-Tyr-Gly-Gly-Thr-Ala-Ala-Val-Phe-Asn-Ala-Val-Asn-, which corresponds to the active site sequence (from Ser 115 to Asn 141) of hamster HMG-CoA synthase. These findings showed that hymeglusin inhibits hamster cytosolic HMG-CoA synthase by covalently modifying the active Cys 129 residue of the enzyme.     

Binding site for fungal β-lactone hymeglusin on cytosolic 3-hydroxy-3-methylglutaryl coenzyme A synthase

We studied the molecular mechanism through which the fungal β-lactone, hymeglusin, potently and specifically inhibits 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase. [¹⁴C]Hymeglusin covalently bound to purified rat liver and to recombinant hamster cytosolic HMG-CoA synthases. The enzyme activity was completely inhibited at a binding ratio of 1.6–2.0 mol [¹⁴C]hymeglusin/mol HMG-CoA synthase. Incubating the enzyme with 2 mM iodoacetamide (IAA) or 2 mM N-ethylmaleimide (NEM) but not with 1.0 mM diisopropyl fluorophosphates (DFP) completely inhibited the binding, suggesting that hymeglusin binds to a Cys residue of HMG-CoA synthase. Recombinant hamster HMG-CoA synthase labeled with [³H]hymeglusin was digested with V8 protease, and the [³H]peptide was purified by high performance liquid chromatography (HPLC). The sequence of the peptide was Ser-Gly-Asn-Thr-Asp-Ile-Glu-Gly-Ile-Asp-Thr-Thr-Asn-Ala-[³H]hymeglusyl Cys-Tyr-Gly-Gly-Thr-Ala-Ala-Val-Phe-Asn-Ala-Val-Asn-, which corresponds to the active site sequence (from Ser 115 to Asn 141) of hamster HMG-CoA synthase. These findings showed that hymeglusin inhibits hamster cytosolic HMG-CoA synthase by covalently modifying the active Cys 129 residue of the enzyme.     

Stereoselective synthesis of (22R)- and (22S)-castasterone/ponasterone A hybrid compounds and evaluation of their molting hormone activity

Two stereoisomers of a castasterone/ponasterone A hybrid compound, the (20R,22R) and (20R,22S)-isomers of 2alpha,3alpha,20,22-tetrahydroxy-5alpha-cholestan-6-one, were synthesized stereoselectively and their binding activity to the ecdysteroid receptor was determined. From the concentration-response curve for the inhibition of the incorporation of tritiated ponasterone A into ecdysteroid receptor containing insect cells, the concentration (IC50) required to inhibit 50% of the incorporation of radioactivity into cells was evaluated. The IC50 values of the (22R)- and (22S)-isomers were determined to be 0.30 and 38.9 microM against Kc cells, respectively, indicating that the (22R)-isomer is about 100 times more potent than the corresponding (22S)-isomer. IC50 values of these compounds against lepidopteran Sf-9 cells were determined to be 0.36 and 12.9 microM, respectively. The molting hormonal effect was examined in a Chilo suppressalis integument system and the 50% effective concentration for the stimulation of N-acetylglucosamine incorporation into the cultured integument was determined to be 2.7 microM for the (22R)-isomer, while the (22S)-isomer was inactive. On the other hand, both isomers did not show brassinolide-like activity in the rice lamina inclination assay.     

Iminosugars: potential inhibitors of liver glycogen phosphorylase

The first synthesis of the single isomers (3R,4R,5R); (3S,4S,5S): (3R,4R,5S) and (3S,4S,5R) of 5-hydroxymethyl-piperidine-3,4-diol from Arecolin is reported, including the synthesis of a series of N-substituted derivatives of the (3R,4R,5R)-isomer (Isofagomine). The inhibitory effect of these isomers as well as of a series of N-substituted derivatives of the (3R,4R,5R)-isomer and selected hydroxypiperidine analogues on liver glycogen phosphorylase (GP) showed that the (3R,4R,5R) configuration was essential for obtaining an inhibitory effect at submicromolar concentration. The results also showed that all three hydroxy groups should be present and could not be substituted, nor were extra OH groups allowed if sub-micromolar inhibition should be obtained. Some inhibitory effect was retained for N-substituted derivatives of Isofagomine; however, N-substitution always resulted in a loss of activity compared to the parent compound, IC50 values ranging from 1 to 100 microM were obtained for simple alkyl, arylalkyl and benzoylmethyl substituents. Furthermore, we found that it was not enough to assure inhibitory effect to have the (R,R,R) configuration. Fagomine, the (2R,3R,4R)-2-hydroxymethylpiperidine-3,4-diol analogue, showed an IC50 value of 200 microM compared to 0.7 microM for Isofagomine. In addition, Isofagomine was able to prevent basal and glucagon stimulated glycogen degradation in cultured hepatocytes with IC50 values of 2-3 microM.     

Stereoselectivity for the (R)-Enantiomer of HA-966 (l-Hydroxy-3-Aminopyrrolidone-2) at the Glycine Site of the N-Methyl-d-Aspartate Receptor Complex

HA-966 (1-hydroxy-3-aminopyrrolidone-2) is an antagonist at the glycine allosteric site of the N-methyl-D-aspartate receptor ionophore complex. Unlike presently known glycine antagonists, HA-966 is chiral. We report stereoselectivity for the (R)-enantiomer at the glycine antagonist site. In [3H]glycine binding, the (R)-enantiomer has an IC50 of 4.1 +/- 0.6 microM. The racemic mixture has an IC50 of 11.2 +/- 0.5 microM, whereas (S)-HA-966 has an IC50 greater than 900 microM. In glycine-stimulated [3H]1-[1-(2- thienyl)cyclohexyl]piperidine binding, the (R)-enantiomer inhibits with an IC50 of 121 +/- 61 microM, whereas the racemic mixture has an IC50 of 216 +/- 113 microM and (S)-HA-966 is inactive. The inhibition by (R)-HA-966 can be prevented by the addition of glycine. (R)-HA-966 and racemic HA-966, but not (S)-HA-966, also prevent N-methyl-D-aspartate cytotoxicity in cortical cultures. The (R)-enantiomer and, less potently, the (S)-enantiomer inhibit N-methyl-D-aspartate-evoked [3H]norepinephrine release from rat hippocampal slices (IC50 values of about 0.3 mM and 1.6 mM, respectively), but only the inhibition by (R)-HA-966 is reversed by added glycine. In glutamate-evoked contractions of the guinea pig ileum, (R)-HA-966 causes a glycine-reversible inhibition (IC50 of about 150 microM), whereas (S)-HA-966 is much less potent (IC50 of greater than 1 mM). These results demonstrate stereoselectivity of the glycine antagonist site of the N-methyl-D-aspartate receptor complex in a variety of tissues and assays. The stereoselectivity also confirms the specificity of N-methyl-D-aspartate receptors in glutamate-evoked contractions of the guinea pig ileum, and supports their similarity to central N-methyl-D-aspartate receptors.     

Synthesis and biological activity of N(alpha)-[4-[N-[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinyl)methyl]-N-propargylamino]phenylacetyl]-L-glutamic acid

2-Deamino-2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI 198583) is a potent inhibitor of thymidylate synthase. Its analogue, N(alpha)-[4-[N-[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinyl)methyl]-N-propargylamino]phenylacetyl]-L-glutamic acid, containing p-aminophenylacetic acid residue substituting p-aminobenzoic acid residue, was synthesized. The new analogue exhibited a moderately potent thymidylate synthase inhibition, of linear mixed type vs. the cofactor, N(5,10)-methylenetetrahydrofolate. The Ki value of 0.34 microM, determined with a purified recombinant rat hepatoma enzyme, was about 30-fold higher than that reported for inhibition of thymidylate synthase from mouse leukemia L1210 cells by ICI 198583 (Hughes et al., 1990, J. Med. Chem. 33, 3060). Growth of mouse leukemia L5178Y cells was inhibited by the analogue (IC50 = 1.26 mM) 180-fold weaker than by ICI 198583 (IC50 = 6.9 microM).     

Asymmetric synthesis and stereochemical structure-activity relationship of (R)- and (S)-8-[1-(2,4-dichlorophenyl)-2-imidazol-1-yl-ethoxy] octanoic acid heptyl ester, a potent inhibitor of allene oxide synthase

The preparation of both enantiomers of 8-[1-(2,4-dichlorophenyl)-2-imidazol-1-yl-ethoxy] octanoic acid heptyl ester (JM-8686), a potent inhibitor of allene oxide synthase, has been achieved using 2,4-dichlorophenacyl bromide as a starting material. The key step was the asymmetric reduction of 1-(2,4-dichlorophenyl)-2-imidazol-1-yl-ethanone with chiral BINAL-H. The products were purified by chiral high-performance liquid chromatography (HPLC) to afford pure (R)-JM-8686 and (S)-JM-8686. The inhibitory activities and binding affinities of these enantiomers toward allene oxide synthase were determined. We found that the inhibition potency of (R)-JM-8686 is approximately 200 times greater than that of (S)-JM-8686, with IC(50) values of approximately 5+/-0.2 nM and 950+/-18 nM, respectively. The dissociation constants of (R)-JM-8686 and (S)-JM-8686 with respect to the recombinant allene oxide synthase were approximately 1.4+/-0.3 microM and 4.8+/-0.6 microM, respectively.     

Acidic nonsteroidal anti-inflammatory drugs inhibit rat brain fatty acid amide hydrolase in a pH-dependent manner

Previous studies have demonstrated that fatty acid amide hydrolase, the enzyme responsible for the metabolism of anandamide, is inhibited by the acidic non-steroidal anti-inflammatory drug (NSAID) ibuprofen with a potency that increases as the assay pH is reduced. Here we show that (R)-, (S)- and (R,S)-flurbiprofen, indomethacin and niflumic acid show similar pH-dependent shifts in potency to that seen with ibuprofen. Thus, (S)-flurbiprofen inhibited 2 microM [3H]anandamide metabolism with IC50 values of 13 and 50 microM at assay pH values of 6 and 8, respectively. In contrast, the neutral compound celecoxib was a weak fatty acid amide hydrolase inhibitor and showed no pH dependency (IC50 values approximately 300 microM at both assay pH). The cyclooxygenase-2-selective inhibitors nimesulide and SC-58125 did not inhibit fatty acid amide hydrolase activity at either pH. The data are consistent with the conclusion that the non-ionised forms of the acidic NSAIDs are responsible for the inhibition of fatty acid amide hydrolase.     

Pharmacological evaluation of the novel thromboxane modulator BM-567 (I/II). Effects of BM-567 on platelet function

The aim of this work was to evaluate the effects of BM-567 (N-pentyl-N'-[(2-cyclohexylamino-5-nitrobenzene)sulfonyl]urea), a torasemide derivative, on both thromboxane A(2) (TXA(2)) receptors (TP) and thromboxane synthase of human platelets. The drug affinity for TP receptors of human washed platelets has been determined. In this test, BM-567 showed a high affinity (IC(50): 1.1+/-0.1nM) for the TP receptors in comparison with BM-531 (IC(50): 7.8+/-0.7nM) and sulotroban (IC(50): 931+/-85nM), two TXA(2) antagonists. We also demonstrated that BM-567 prevented platelet aggregation induced by arachidonic acid (AA) (600 microM) (ED(100): 0.20+/-0.10 microM), U-46619, a stable TXA(2) agonist (1 microM) (ED(50): 0.30+/-0.04 microM) and collagen (1microgram ml(-1)) (% of inhibition: 44.3+/-4.3% at 10 microM) and inhibited the second wave of ADP (2microM). Moreover, when BM-567 was incubated in whole blood from healthy donors, the closure time measured by the Platelet Function analyzer (PFA-100((R))) was significantly prolonged (closure time: 215+/-21s) by using collagen/epinephrine cartridges. Finally, at the concentration of 1 microM, BM-567 completely reduced the TXB(2) production from human platelets stimulated with AA (600 microM). These results indicate that BM-567 is a novel combined TXA(2) receptor antagonist and thromboxane synthase inhibitor characterized by a powerful antiplatelet potency.     

New delta8(14)-ketosterols with an oxygenated side chain

New analogues of 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one (15-ketosterol) with modified 17-chains [(22S,23S,24S)- and (22R,23R,24S)-3beta-hydroxy-24-methyl-22,23-oxido-5alpha-cholest-8(14)-en-15-ones and (22RS,23xi,24S)-24-methyl-5alpha-cholesta-3beta,22,23-triol-15-one] were synthesized from (22E,24S)-3beta-acetoxy-24-methyl-5alpha-cholesta-8(14),22-dien-15-one. The chiralities of their 22 and 23 centers were determined by NMR spectroscopy. The isomeric 22,23-epoxides effectively inhibited cholesterol biosynthesis in hepatoma Hep G2 cells (IC50 0.9 +/- 0.2 and 0.7 +/- 0.2 microM, respectively), and their activities significantly exceeded those of 15-ketosterol (IC50 4.0 +/- 0.5 microM), (22E,24S)-3beta-hydroxy-24-methyl-5alpha-cholesta-8(14),22-dien-15-one (IC50 3.1 +/- 0.4 microM), and the 3beta,22,23-triol synthesized (IC50 6.0 +/- 1.0 microM). The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 3; see also http://www.maik.ru.     

Pharmacological evaluation of both enantiomers of (R,S)-BM-591 as thromboxane A2 receptor antagonists and thromboxane synthase inhibitors

The aim of this work is to evaluate the anti-thromboxane activity of two pure enantiomers of (R,S)-BM-591, a nitrobenzene sulfonylurea chemically related to torasemide, a loop diuretic. The drug affinity for thromboxane A2 receptor (TP) of human washed platelets has been determined. In these experiments, (R)-BM-591 (IC50 = 2.4+/-0.1 nM) exhibited a significant higher affinity than (S)-BM-591 (IC50 = 4.2+/-0.15 nM) for human washed platelets TP receptors. Both enantiomers were stronger ligands than SQ-29548 (IC50 = 21.0+/-1.0 nM) and sulotroban (IC50 = 930+/-42 nM), two reference TXA2 receptor antagonists. Pharmacological characterisations of (S)-BM-591 and (R)-BM-591 were compared in several models. Thus, (R)-BM-591 strongly prevented platelet aggregation induced by arachidonic acid (AA) (600 microM) and U-46619 (1 microM) while (S)-BM-591 showed a lower activity. On isolated tissues pre-contracted by U-46619, a stable TXA2 agonist, (S)-BM-591 was more potent in relaxing guinea-pig trachea (EC50 = 0.272+/-0.054 microM) and rat aorta (EC50 = 0.190+/-0.002 microM) than (R)-BM-591 (EC50 of 9.60+/-0.63 microM and 0.390+/-0.052 microM, respectively). Moreover, at 1 microM, (R)-BM-591 totally inhibited TXA2 synthase activity, expressed as TXB2 production from human platelets, while at the same concentration, (S)-BM-591 poorly reduced the TXB2 synthesis (22%). Finally, in rats, both enantiomers lost the diuretic activity of torasemide. In conclusion, (R)-BM-591 exhibits a higher affinity and antagonism on human platelet TP receptors than (S)-BM-591 as well as a better thromboxane synthase inhibitory potency. In contrast, (S)-BM-591 is more active than the (R)-enantiomer in relaxing smooth muscle contraction of rat aorta and trachea guinea pig. Consequently, (R)-BM-591 represents the best candidate for further development in the field of thrombosis disorders.     

3-Hydroxy-3-methylglutaryldithio-coenzyme A: a potent inhibitor of Pseudomonas mevalonii HMG-CoA reductase.

3-Hydroxy-3-methyl-1-thionoglutaryl-coenzyme A, a dithioester analog of 3-hydroxy-3-methylglutaryl-CoA, has been enzymatically synthesized using the HMG-CoA synthase catalyzed condensation of acetyl-CoA with 3-oxo-1-thionobutyryl-CoA. HMGdithio-CoA is a potent inhibitor of Pseudomonas mevalonii HMG-CoA reductase. Inhibition was mainly competitive with respect to HMG-CoA with a Kis of 0.086 +/- .01 microM and noncompetitive with respect to NADH with a Kis of 3.7 +/- 1.5 microM and a Kii of 0.65 +/- .05 microM in the presence of 110 microM (R.S)-HMG-CoA.     

Resolution, absolute stereochemistry, and enantiopharmacology of the GluR1-4 and GluR5 antagonist 2-amino-3-[5-tert-butyl-3-(phosphonomethoxy)-4-isoxazolyl]propionic acid

The phosphono amino acid, (RS)-2-amino-3-[5-tert-butyl-3-(phosphonomethoxy)-4-isoxazolyl+ ++]propio nic acid (ATPO), is a structural hybrid between the NMDA antagonist (RS)-2-amino-7-phosphonoheptanoic acid (AP7) and the AMPA and GluR5 agonist, (RS)-2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl)propionic acid (ATPA). ATPO has been resolved into (S)-ATPO and (R)-ATPO using chiral HPLC, and the absolute stereochemistry of the two enantiomers was established by an X-ray crystallographic analysis of (R)-ATPO. (S)-ATPO and (R)-ATPO were characterized pharmacologically using rat brain membrane binding and electrophysiologically using the cortical wedge preparation as well as homo- or heteromeric GluR1-4, GluR5-6, and KA2 receptors expressed in Xenopus oocytes. (R)-ATPO was essentially inactive as an agonist or antagonist in all test systems. (S)-ATPO was an inhibitor of the binding of [(3)H]AMPA (IC(50) = 16 +/- 1 microM) and of [(3)H]-6-cyano-7-nitroquinoxaline-2,3-dione ([(3)H]CNQX) (IC(50) = 1.8 +/- 0.2 microM), but was inactive in the [(3)H]kainic acid and the [(3)H]-(RS)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid ([(3)H]CPP) binding assays. (S)-ATPO did not show detectable agonist effects at any of the receptors under study, but antagonized AMPA-induced depolarization in the cortical wedge preparation (IC(50) = 15 +/- 1 microM). (S)-ATPO also blocked kainic acid agonist effects at GluR1 (K(i) = 2.0 microM), GluR1+2 (K(i) = 3.6 microM), GluR3 (K(i) = 3.6 microM), GluR4 (K(i) = 6.7 microM), and GluR5 (K(i) = 23 microM), but was inactive at GluR6 and GluR6+KA2. Thus, although ATPO is a structural analog of AP7 neither (S)-ATPO nor (R)-ATPO are recognized by NMDA receptor sites.     

Irreversible inhibition of sodium current and batrachotoxin binding by a photoaffinity-derivatized local anesthetic

We have synthesized a model local anesthetic (LA), N-(2-di-N-butyl- aminoethyl)-4-azidobenzamide (DNB-AB), containing the photoactivatable aryl azido moiety, which is known to form a covalent bond to adjacent molecules when exposed to UV light (Fleet, G.W., J.R. Knowles, and R.R. Porter. 1972. Biochemical Journal. 128:499-508. Ji, T.H. 1979. Biochimica et Biophysica Acta. 559:39-69). We studied the effects of DNB-AB on the sodium current (INa) under whole-cell voltage clamp in clonal mammalian GH3 cells and on 3[H]-BTX-B binding to sheep brain synaptoneurosomes. In the absence of UV illumination, DNB-AB behaved similarly to known LAs, producing both reversible block of peak INa (IC50 = 26 microM, 20 degrees C) and reversible inhibition of 3[H]-BTX- B (50 nM in the presence of 0.12 microgram/liter Leiurus quinquestriatus scorpion venom) binding (IC50 = 3.3 microM, 37 degrees C), implying a noncovalent association between DNB-AB and its receptor(s). After exposure to UV light, both block of INa and inhibition of 3[H]-BTX-B binding were only partially reversible (INa = 42% of control; 3[H]-BTX-B binding = 23% of control) showing evidence of a light-dependent, covalent association between DNB-AB and its receptor(s). In the absence of drug, UV light had less effect on INa (post exposure INa = 96% of control) or on 3[H]-BTX-B binding (post exposure binding = 70% of control). The irreversible block of INa was partially protected by coincubation of DNB-AB with 1 mM bupivacaine (IC50 = 45 microM, for INa inhibition at 20 degrees C, Wang, G.K., and S.Y. Wang. 1992. Journal of General Physiology. 100:1003-1020), (post exposure INa = 73% of control). The irreversible inhibition of 3[H]-BTX- B binding also was partially protected by coincubation with bupivacaine (500 microM, 37 degrees C) (post exposure binding = 51% of control), suggesting that the site of irreversible inhibition of both INa and 3[H]-BTX-B binding is shared with the clinical LA bupivacaine.     

Involvement of calcium in the mevalonate-accelerated degradation of 3-hydroxy-3-methylglutaryl-CoA reductase

3-Hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase), the rate-limiting enzyme in the biosynthesis of cholesterol and isoprenoids, is subject to rapid degradation which is regulated by mevalonate (MVA)-derived metabolic products. HMG-CoA reductase is an integral membrane protein of the endoplasmic reticulum, the largest nonmitochondrial pool of cellular Ca2+. To assess the possible role of Ca2+ in the regulated degradation of HMG-CoA reductase, we perturbed cellular Ca2+ concentration and followed the fate of HMG-CoA reductase and of HMGal, a fusion protein consisting of the membrane domain of HMG-CoA reductase and the soluble bacterial enzyme beta-galactosidase. The degradation of HMGal mirrors that of HMG-CoA reductase, demonstrating that the membrane domain of HMG-CoA reductase is sufficient to confer regulated degradation (Skalnik, D.G., Narita, H., Kent, C., and Simoni, R.D. (1988) J. Biol. Chem. 263, 6836-6841; Chun, K.T., Bar-Nun, S., and Simoni, R.D. (1990) J. Biol. Chem. 265, 22004-22010). In this study we show that the MVA-dependent accelerated rates of degradation of HMG-CoA reductase and HMGal in cells maintained in Ca(2+)-free medium are 2-3-fold slower than the rate of degradation in cells grown in high (1.8-2 mM) Ca2+ concentration. This effect is reversed upon addition of Ca2+ to the medium. Furthermore, when cells maintained in high Ca2+ are treated with 1 microM ionomycin, the MVA-dependent accelerated degradation of HMG-CoA reductase and HMGal is also reduced about 2-3-fold. This inhibition is not due to a Ca(2+)-dependent uptake or incorporation of MVA into sterols, since these processes are not affected in the absence of external Ca2+. In addition, cobalt, a known antagonist of Ca(2+)-dependent cellular functions, totally abolishes (IC50 = 520 microM in the presence of 1.8 mM extracellular Ca2+) the MVA-accelerated degradation of HMGal. These results suggest that Ca2+ plays a major role in the regulated degradation of HMG-CoA reductase.     

Synthesis of N-benzyl- and N-phenyl-2-amino-4,5-dihydrothiazoles and thioureas and evaluation as modulators of the isoforms of nitric oxide synthase

Inhibition of the isoforms of nitric oxide synthase (NOS) has important applications in therapy of several diseases, including cancer. Using 1400 W [N-(3-aminomethylbenzyl)acetamidine], thiocitrulline and N(delta)-(4,5-dihydrothiazol-2-yl)ornithine as lead compounds, series of N-benzyl- and N-phenyl-2-amino-4,5-dihydrothiazoles and thioureas were designed as inhibitors of NOS. Ring-substituted benzyl and phenyl isothiocyanates were synthesised by condensation of the corresponding amines with thiophosgene and addition of ammonia gave the corresponding thioureas in high yields. The substituted 2-amino-4,5-dihydrothiazoles were approached by two routes. Treatment of simple benzylamines with 2-methylthio-4,5-dihydrothiazole at 180 degrees C afforded the corresponding 2-benzylamino-4,5-dihydrothiazoles. For less nucleophilic amines and those carrying more thermally labile substituents, the 4,5-dihydrothiazoles were approached by acid-catalysed cyclisation of N-(2-hydroxyethyl)thioureas. This cyclisation was shown to proceed by an S(N)2-like process. Modest inhibitory activity was shown by most of the thioureas and 4,5-dihydrothiazoles, with N-(3-aminomethylphenyl)thiourea (IC(50)=13 microM vs rat neuronal NOS and IC(50)=23 microM vs rat inducible NOS) and 2-(3-aminomethylphenylamino)-4,5-dihydrothiazole (IC(50)=13 microM vs rat neuronal NOS and IC(50)=19 microM vs human inducible NOS) being the most potent. Several thioureas and 4,5-dihydrothiazoles were found to stimulate the activity of human inducible NOS in a time-dependent manner.     

Differential recognition of "enkephalinase" and angiotensin-converting enzyme by new carboxyalkyl inhibitors

New carboxylalkyl compounds derived from Phe-Leu and corresponding to the general formula C6H5-CH2-CH(R)CO-L.Leu with R = -COOH, 3, R = -CH2-COOH, 4, R = -NH-CH2-COOH, 5, R = -NH-(CH2)2-COOH, 6, have been found to inhibit the breakdown of the Gly3-Phe4 bond of [3H] Leu-enkephalin or [3H]D.Ala2-Leu-enkephalin resulting from the action of the mouse striatal metallopeptidases: "enkephalinase" or angiotensin-converting enzyme (A.C.E.). The carboxyl coordinating ability of the Zn atom seems to be significantly higher in ACE than in "enkephalinase". Moreover, IC50 values against "enkephalinase" were found in the same range whatever the length of the chain bearing the carboxyl group whereas a well-defined position of this group with respect to the Zn atom is required for strong ACE inhibition. These features suggest a larger degree of freedom of the carboxyalkyl moieties within the active site of "enkephalinase". Therefore the differential recognition of active sites of both peptidases leads to: i) N-(carboxymethyl)-L-Phe-L-Leu, 5, a competitive inhibitor of "enkephalinase" (KI = 0.7 microM) and ACE (KI = 1.2 microM) which could be used as mixed inhibitor for both enzymes; ii) N-[(R,S)-2-carboxy, 3-benzylpropanoyl]-L-Leucine, 3, a full competitive inhibitor of "enkephalinase" (KI = 0.34 microM) which does not interact with ACE (IC50 greater than 10,000 microM). This compound can be considered as the first example of a new series of highly potent and specific "enkephalinase" inhibitors.     

Resolution, configurational assignment, and enantiopharmacology of 2-amino-3-[3-hydroxy-5-(2-methyl-2H- tetrazol-5-yl)isoxazol-4-yl]propionic acid, a potent GluR3- and GluR4-preferring AMPA receptor agonist

We have previously shown that (RS)-2-amino-3-[3-hydroxy-5-(2-methyl-2H-tetrazol-5-yl)isoxazol -4-yl] propionic acid (2-Me-Tet-AMPA) is a selective agonist at (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors, markedly more potent than AMPA itself, whereas the isomeric compound 1-Me-Tet-AMPA is essentially inactive. We here report the enantiopharmacology of 2-Me-Tet-AMPA in radioligand binding and cortical wedge electrophysiological assay systems, and using cloned AMPA (GluR1-4) and kainic acid (KA) (GluR5, 6, and KA2) receptor subtypes expressed in Xenopus oocytes. 2-Me-Tet-AMPA was resolved using preparative chiral HPLC. Zwitterion (-)-2-Me-Tet-AMPA was assigned the (R)-configuration based on an X-ray crystallographic analysis supported by the elution order of (-)- and (+)-2-Me-Tet-AMPA using four different chiral HPLC columns and by circular dichroism spectra. None of the compounds tested showed detectable affinity for N-methyl-D-aspartic acid (NMDA) receptor sites, and (R)-2-Me-Tet-AMPA was essentially inactive in all of the test systems used. Whereas (S)-2-Me-Tet-AMPA showed low affinity (IC(50) = 11 microM) in the [(3)H]KA binding assay, it was significantly more potent (IC(50) = 0.009 microM) than AMPA (IC(50) = 0.039 microM) in the [(3)H]AMPA binding assay, and in agreement with these findings, (S)-2-Me-Tet-AMPA (EC(50) = 0.11 microM) was markedly more potent than AMPA (EC(50) = 3.5 microM) in the electrophysiological cortical wedge model. In contrast to AMPA, which showed comparable potencies (EC(50) = 1.3-3.5 microM) at receptors formed by the AMPA receptor subunits (GluR1-4) in Xenopus oocytes, more potent effects and a substantially higher degree of subunit selectivity were observed for (S)-2-Me-Tet-AMPA: GluR1o (EC(50) = 0.16 microM), GluR1o/GluR2i (EC(50) = 0.12 microM), GluR3o (EC(50) = 0.014 microM) and GluR4o (EC(50) = 0.009 microM). At the KA-preferring receptors GluR5 and GluR6/KA2, (S)-2-Me-Tet-AMPA showed much weaker agonist effects (EC(50) = 8.7 and 15.3 microM, respectively). It is concluded that (S)-2-Me-Tet-AMPA is a subunit-selective and highly potent AMPA receptor agonist and a potentially useful tool for studies of physiological AMPA receptor subtypes.     

Enantiomers of cis-constrained and flexible 2-substituted GABA analogues exert opposite effects at recombinant GABA(C) receptors

The effects of the enantiomers of a number of flexible and cis-constrained GABA analogues were tested on GABA(C) receptors expressed in Xenopus laevis oocytes using two-electrode voltage-clamp electrophysiology. (1S,2R)-cis-2-Aminomethylcyclopropane-1-carboxylic acid ((+)-CAMP), a potent and full agonist at the rho1 (EC(50) approximately 40 microM, I(max) approximately 100%) and rho 2 (EC(50) approximately 17 microM, I(max) approximately 100%) receptor subtypes, was found to be a potent partial agonist at rho3 (EC(50) approximately 28 microM, I(max) approximately 70%). (1R,2S)-cis-2-Aminomethylcyclopropane-1-carboxylic acid ((-)-CAMP), a weak antagonist at human rho1 (IC(50) approximately 890 microM) and rho2 (IC(50) approximately 400 microM) receptor subtypes, was also found to be a moderately potent antagonist at rat rho3 (IC(50) approximately 180 microM). Similarly, (1R,4S)-4-aminocyclopent-2-ene-1-carboxylic acid ((+)-ACPECA) was a full agonist at rho1 (EC(50) approximately 135 microM, I(max) approximately 100%) and rho2 (EC(50) approximately 60 microM, I(max) approximately 100%), but only a partial agonist at rho3 (EC(50) approximately 112 microM, I(max) approximately 37%), while (1S,4R)-4-aminocyclopent-2-ene-1-carboxylic acid ((-)-ACPECA) was a weak antagonist at all three receptor subtypes (IC(50)>300 microM). 4-Amino-(S)-2-methylbutanoic acid ((S)-2MeGABA) and 4-amino-(R)-2-methylbutanoic acid ((R)-2MeGABA) followed the same trend, with (S)-2MeGABA acting as a full agonist at the rho1 (EC(50) approximately 65 microM, I(max) approximately 100%), and rho2 (EC(50) approximately 20 microM, I(max) approximately 100%) receptor subtypes, and a partial agonist at rho3 (EC(50) approximately 25 microM, I(max) approximately 90%). (R)-2MeGABA, however, was a moderately potent antagonist at all three receptor subtypes (IC(50) approximately 16 microM at rho1, 125 microM at rho2 and 35 microM at rho3). On the basis of these expanded biological activity data and the solution-phase molecular structures obtained at the MP2/6-31+G* level of ab initio theory, a rationale is proposed for the genesis of this stereoselectivity effect.     

Biochemical and structural basis for inhibition of Enterococcus faecalis hydroxymethylglutaryl-CoA synthase, mvaS, by hymeglusin

Hymeglusin (1233A, F244, L-659-699) is established as a specific β-lactone inhibitor of eukaryotic hydroxymethylglutaryl-CoA synthase (HMGCS). Inhibition results from formation of a thioester adduct to the active site cysteine. In contrast, the effects of hymeglusin on bacterial HMG-CoA synthase, mvaS, have been minimally characterized. Hymeglusin blocks growth of Enterococcus faecalis. After removal of the inhibitor from culture media, a growth curve inflection point at 3.1 h is observed (vs 0.7 h for the uninhibited control). Upon hymeglusin inactivation of purified E. faecalis mvaS, the thioester adduct is more stable than that measured for human HMGCS. Hydroxylamine cleaves the thioester adduct; substantial enzyme activity is restored at a rate that is 8-fold faster for human HMGCS than for mvaS. Structural results explain these differences in enzyme-inhibitor thioester adduct stability and solvent accessibility. The E. faecalis mvaS-hymeglusin cocrystal structure (1.95 ?) reveals virtually complete occlusion of the bound inhibitor in a narrow tunnel that is largely sequestered from bulk solvent. In contrast, eukaryotic (Brassica juncea) HMGCS binds hymeglusin in a more solvent-exposed cavity.