2-Amino-4-methylpyridine as a potent inhibitor of inducible NO synthase activity in vitro and in vivo.

1. The ability of 2-amino-4-methylpyridine to inhibit the catalytic activity of the inducible NO synthase (NOS II) enzyme was characterized in vitro and in vivo. 2. In vitro, 2-amino-4-methylpyridine inhibited NOS II activity derived from mouse RAW 264.7 cells with an IC50 of 6 nM. Enzyme kinetic studies indicated that inhibition is competitive with respect to arginine. 2-Amino-4-methylpyridine was less potent on human recombinant NOS II (IC50 = 40 nM) and was still less potent on human recombinant NOS I and NOS III (IC50 = 100 nM). NG-monomethyl-L-arginine (L-NMMA), N6-iminoethyl-L-lysine (L-NIL) and aminoguanidine were much weaker inhibitors of murine NOS II than 2-amino-4-methylpyridine but, unlike 2-amino-4-methylpyridine, retained similar activity on human recombinant NOS II. L-NMMA inhibited all three NOS isoforms with similar potency (IC50S 3-7 microM). In contrast, compared to activity on human recombinant NOS III, L-NIL displayed 10 x selectivity for murine NOS II and 11 x selectivity for human recombinant NOS II while aminoguanidine displayed 7.3 x selectivity for murine NOS II and 3.7 x selectivity for human recombinant NOS II. 3. Mouse RAW 264.7 macrophages produced high levels of nitrite when cultured overnight in the presence of lipopolysaccharide (LPS) and interferon-gamma. Addition of 2-amino-4-methylpyridine at the same time as the LPS and IFN-gamma, dose-dependently reduced the levels of nitrite (IC50 = 1.5 microM) without affecting the induction of NOS II protein. Increasing the extracellular concentration of arginine decreased the potency of 2-amino-4-methylpyridine but at concentrations up to 10 microM, 2-amino-4-methylpyridine did not inhibit the uptake of [3H]-arginine into the cell. Addition of 2-amino-4-methylpyridine after the enzyme was induced also dose-dependently inhibited nitrite production. Together, these data suggest that 2-amino-4-methylpyridine reduces cellular production of NO by competitive inhibition of the catalytic activity of NOS II, in agreement with results obtained from in vitro enzyme kinetic studies. 4. When infused i.v. in conscious unrestrained rats, 2-amino-4-methylpyridine inhibited the rise in plasma nitrate produced in response to intraperitoneal injection of LPS (ID50 = 0.009 mg kg-1 min-1). Larger doses of 2-amino-4-methylpyridine were required to raise mean arterial pressure in untreated conscious rats (ED50 = 0.060 mg kg-1 min-1) indicating 6.9 x selectivity for NOS II over NOS III in vivo. Under the same conditions, L-NMMA was nonselective while L-NIL and aminoguanidine displayed 5.2 x and 8.6 x selectivity respectively. All of these compounds caused significant increases in mean arterial pressure at doses above the ID50 for inhibition of NOS II activity in vivo. 5. 2-Amino-4-methylpyridine also inhibited LPS-induced elevation in plasma nitrate after either subcutaneous (ID50 = 0.3 mg kg-1) or oral (ID50 = 20.8 mg kg-1) administration. 6. These data indicate that 2-amino-4-methylpyridine is a potent inhibitor of NOS II activity in vitro and in vivo with a similar degree of isozyme selectivity to that of L-NIL and aminoguanidine in rodents.

5,7-dihydro-3-[2-[1-(phenylmethyl)-4-piperidinyl]ethyl]-6H- pyrrolo[3,2-f]-1,2-benzisoxazol-6-one: a potent and centrally-selective inhibitor of acetylcholinesterase with an improved margin of safety.

A series of N-benzylpiperidines (2a-d, 10) with novel isoxazole-containing tricycles has been prepared. This series has shown potent in vitro inhibition of the enzyme acetylcholinesterase (AChE), with IC50S = 0.33 - 3.6 nM. Compound 2a was the most potent inhibitor with an IC50 = 0.33 +/- 0.09 nM. Derivatives 2a-d and 10 displayed weak in vitro inhibition of butyrylcholinesterase (BuChE) with IC50S = 600 - 23,000 nM. The most selective compound was 2a with a BuChE/AChE ratio in excess of 4 orders of magnitude (> 10,000). Pyrrolobenzisoxazole 2a also displayed a favorable profile in vivo. In microdialysis experiments, 2a produced a 200% increase in extracellular levels of acetylcholine (ACh) at a dose of 0.4 mg/kg in freely moving, conscious rats. Peripheral side effects (salivation ED50 = 26 +/- 1.5 mg/kg) and acute lethality (LD50[1 h] = 42 mg/kg) were observed at > 60-fold higher doses. These data indicate that 2a is an AChE inhibitor with good central selectivity and a favorable margin of safety. Compound 2a, designated as CP-118,954, is currently in clinical development for the treatment of cognitive disorders.

Design and synthesis of 1-heteroaryl-3-(1-benzyl-4-piperidinyl)propan-1-one derivatives as potent, selective acetylcholinesterase inhibitors.

Herein is described the synthesis and structure--activity relationship of a novel series of aromatic and heteroaromatic 3-(1-benzyl-4-piperidinyl)propan-1-one derivatives that display potent and selective inhibition of the enzyme acetylcholinesterase (AChE). 1-(2-Methyl-6-benzothiazolyl)-3-(N-benzyl-4-piperidinyl)propan-1-one hydrochloride, 6d, is one of the most active compounds within this series exhibiting an IC50 for the inhibition of the AChE enzyme equal to 6.8 nM. Compound 6d has shown a dose-dependent elevation of total acetylcholine (ACh) levels in the mouse forebrain with an oral ED50 = 9.8 mg/kg. In addition, in vivo microdialysis experiments in the rat demonstrate that 6d increases extracellular ACh (100% over basal) 1-3 h postdose with an oral ED50 = 4.8 mg/kg.

Novel benzisoxazole derivatives as potent and selective inhibitors of acetylcholinesterase.

A series of N-benzylpiperidine benzisoxazoles has been developed as potent and selective inhibitors of the enzyme acetylcholinesterase (AChE). The benzisoxazole heterocycle was found to be an appropriate bioisosteric replacement for the benzoyl functionality present in the N-benzylpiperidine class of inhibitors. The title compounds were synthesized by alkylating 3-methyl-1,2-benzisoxazoles with an iodo piperidine derivatives as the key step. Benzisoxazoles 1b-j,o displayed potent inhibition of AChE in vitro with IC50's = 0.8-14 nM. Particularly interesting were N-acetyl and morpholino derivatives 1g (IC50 = 3 nM) and 1j (IC50 = 0.8 nM), respectively, which displayed outstanding selectivity for acetyl-over butyrylcholinesterase, in excess of 3 orders of magnitude. N-Acetyl 1g also displayed a favorable profile in vivo. This analog showed a dose-dependent elevation of total acetylcholine in mouse forebrain after oral administration with an ED50 = 2.4 mg/kg. In addition, 1g was able to reverse amnesia in a mouse passive avoidance model at doses of 3.2 and 5.6 mg/kg with an average reversal of 89.7%. Molecular dynamics simulations were used to study the possible binding modes of N-benzylpiperidine benzisoxazoles to AChE from Torpedo californica. Key structural insights were obtained regarding the potency of this class of inhibitors. Specifically, Asp-72, Trp-84, Trp-279, Phe-288, and Phe-330 are implicated in the binding of these inhibitors. The N-benzylpiperidine benzisoxazoles may be suitable compounds for the palliative treatment of Alzheimer's Disease.

Novel inhibitors of prolyl endopeptidase: effects of stereochemistry.

Prolyl endopeptidase is a serine protease that specifically cleaves peptides on the carboxyl side of proline residues. We have show that racemic 2-(2-formyl-pyrrolidine-1-carbonyl)-2,3-dihydro-indole-1-carboxylic acid benzyl ester (IP), racemic trans-2-(2-formyl-pyrrolidine-1-carbonyl-1-cyclohexane-carboxylic acid benzyl ester (cis-CP) are slow binding inhibitors of mouse brain prolyl endopeptidase with Ki values of 0.35, 2.4, and 3 nM, respectively. In order to determine whether IP and trans/cis-CP are stereoselective in their inhibition profile, five stereoisomers were synthesized and tested for inhibition. Kinetic analysis indicates that the 2S, 2'S-isomer is necessary for inhibition by racemic IP. trans/cis-CP also requires S-stereochemistry on two of its three chiral centres; the third can be either R or S. This suggests that our novel, non-peptide inhibitors bind at the same site as peptide inhibitors which require L-configuration at the P1 and P2 binding pockets.

1-Naphthylpiperazine derivatives as potential atypical antipsychotic agents.

The design and synthesis of a series of potential atypical antipsychotic agents based on the structure of 1-naphthylpiperazine are described. The incorporation of dopamine antagonist activity into the parent structure was achieved with heterocyclic surrogates for the catechol moiety of dopamine. Compound 4b from this series showed a biochemical profile that translated to behavioral activity in the rat predictive of an antipsychotic agent with a low propensity to cause extrapyramidal side effects in man.

Synthesis, in vitro binding profile, and central nervous system penetrability of the highly potent 5-HT3 receptor antagonist [3H]-4-(2-methoxyphenyl)-2-[4(5)-methyl-5(4)-imidazolylmethyl]thiazole.

4-(2-Methoxyphenyl)-2-[4(5)-methyl-5(4)-imidazolylmethyl]thiazole (5) is a highly potent member of a structurally novel series of selective serotonin-3 receptor antagonists. The synthesis of tritiated 5 and its binding profile in neuroblastoma-glioma 108-15 cells are described. Furthermore, in vivo studies in rat with this radioligand indicate that it effectively penetrates the blood-brain barrier upon peripheral administration. Thus, 5 should be a useful pharmacological tool for both in vitro and in vivo studies of this class of compounds.

Thiazole as a carbonyl bioisostere. A novel class of highly potent and selective 5-HT3 receptor antagonists.

A novel structural class of highly potent and selective 5-HT3 receptor antagonists is described. The compounds in this new series contain a thiazole moiety linking an aromatic group and a nitrogen-containing basic region; the thiazole group appears to be acting as a carbonyl bioisostere in this system. An optimized member of this series, 4-(2-methoxyphenyl)-2-[[4(5)-methyl-5(4)-imidazolyl]methyl]thiazole (5), exhibits oral activity in the Bezold-Jarisch reflex paradigm comparable to or better than the standard agents ondansetron (1) and ICS-205-930 (2). Several of the structure-activity relationships are rationalized in terms of a computer pharmacophore model for 5-HT3 receptor binding.

An initial three-component pharmacophore for specific serotonin-3 receptor ligands.

With computer modeling, an initial three-component pharmacophore for specific 5-HT3 receptor ligands ICS-205-930 (1), ondansetron (2), zacopride (3), and 3-[2-(guanidinylmethyl)-4-thiazolyl]indol (4) has been identified. Two parts represent electrostatic interactions, one as a hydrogen-bond-donating interaction and the other as a hydrogen-bond-accepting interaction. The third part is represented by a plane in which the lipophilic aromatic groups align. The generation of the pharmacophore relies on the interactions of these ligands with probe atoms representative of a possible hydrogen-bond donor or hydrogen-bond acceptor within the receptor. A carboxylate oxygen was used as a hydrogen-bond-accepting probe and a serine-like hydroxyl was utilized as a hydrogen-bond-donating probe.

Synthesis, in vitro and in vivo activity of novel 9-deoxo-9a-AZA-9a-homoerythromycin A derivatives; a new class of macrolide antibiotics, the azalides.

A series of erythromycin A-derived semisynthetic antibiotics, featuring incorporation of a basic nitrogen atom into a ring expanded (15-membered) macrocyclic lactone, have been prepared and biologically evaluated. Semisynthetic modifications focused upon (1) varied substitution at the macrocyclic ring nitrogen and (2) epimerization or amine substitution at the C-4'' hydroxyl site within the cladinose sugar. In general, the new azalides exhibit improved Gram-negative potency, expanding the spectrum of erythromycin A to fully include Haemophilus influenzae and Neisseria gonorrhoeae. When compared to erythromycin A, the azalides exhibit substantially increased half-life and area-under-the-curve values in all species studied. The overall in vitro/in vivo performance of N-methyl, C-4'' epimers 3a and 9; and C-4'' amine 11 identify these compounds as the most interesting erythromycin A-superior agents. Compound 3a has been advanced to clinical study.

Synthesis and biological activities of 4"-deoxy-4"-sulfonamido-oleandomycin derivatives.

Chemical modification of the macrolide antibiotic oleandomycin (C-1) is described. Reductive amination of 11-acetyl-4"-deoxy-4"-oxo-oleandomycin (C-6) with ammonium acetate provides amino-oleandomycin derivative C-7 in which the 4"-amine is oriented in the axial configuration. The structure-activity relationship of a series of 4"-sulfonamide analogs prepared from amino-oleandomycin derivative C-7 is discussed. Noteworthy is the significant in vitro potency enhancement of the para-chlorobenzenesulfonamide analog C-12 over that of the parent oleandomycin. The absolute configuration of the 4"-amino-oleandomycin derivative C-7 was established through X-ray analysis of the para-iodobenzenesulfonamide analog C-14.

Ring contraction of oleandrose on the macrolide antibiotic oleandomycin with [(Methoxycarbonyl)sulfamoyl]triethylammonium hydroxide inner salt.

Ring contraction of the neutral oleandrose sugar in the 14-membered-ring macrolide antibiotic oleandomycin (2) has been accomplished using [(methoxycarbonyl)sulfamoyl]triethylammonium hydroxide inner salt (1). The product of this interesting rearrangement, after methanolic hydrolysis of the 2'-acetate, is the 11-acetyl-3-O-(3"-methoxy-4"-vinylfuranosyl)oleandomycin (12). The in vitro activity of furanoside 12 is only moderately less than that of 11-acetyloleandomycin (13).