Peptide aldehydes as inhibitors of HIV protease.

We have recently shown that alpha-MAPI, a peptidic aldehyde of microbial origin, inhibits the HIV protease with a potency comparable to pepstatin, having, differently from pepstatin, no activity on other aspartic proteases. In this study different peptide derivatives containing a C-terminal aldehyde have been tested to assess the potential of this function for the inhibition of HIV protease. The results of our analysis correspond with the recently published subsite preferences of the viral enzyme, indicating that aldehydes bind to the active site of the HIV protease. Our data suggest that peptide aldehydes can act in their hydrated forms as transition state analogues with the most potent inhibitor having an IC50 of 0.9 microM.

Recent advances in neurokinin receptor antagonists.

The structurally related neuropeptides, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), which belong to a family of molecules termed tachykinins and are widely distributed in the central and peripheral nervous systems, influence the function of many tissues. SP and NKA have links to the following chronic diseases: asthma, inflammatory bowel disorders, rheumatoid arthritis, pain and psychiatric disorders. These peptides exert their effects through three G-protein coupled receptor subtypes, namely, the NK1, NK2, and NK3 receptors. Non-peptide antagonists of these receptors may provide opportunities for disease treatments. In this review, the very recent advances in nonpeptide neurokinin receptor antagonists will be described with an emphasis on structure-activity relationships which have been developed.

Tetracyclines induce apoptosis in osteoclasts.

Chemically modified tetracyclines (CMTs) are thought to inhibit bone resorption through inhibition of matrix metalloproteinases. Here we report that some tetracyclines also induce apoptosis in rabbit osteoclasts and inhibit differentiation and activity of osteoclasts in murine osteoblast/marrow cocultures. Apoptosis of mature rabbit osteoclasts increased from 5.5 +/- 1.4% (mean +/- SD) in control cultures to 44.9 +/- 6.3% (p < 0.001) and 18.9 +/- 4.0% (p < 0.005) with CMT-3 and doxycycline (10 microg/mL), respectively. CMT-2 or CMT-5 did not alter osteoclast viability even at 25 microg/mL. In murine osteoblast/marrow cocultures over 11 days, CMT-3 and doxycycline (5 microg/mL) reduced the formation of mature osteoclasts and inhibited resorption to 21 +/- 9% (p < 0.01) and 49 +/- 4% (p < 0.01) of untreated cultures. Induction of osteoclast apoptosis is an additional property of tetracyclines that may contribute to their ability to inhibit bone resorption.

Synthesis and antiallergic activity of some quinolinones and imidazoquinolinones.

A group of 1,4-dihydro-4-oxoquinoline-2- and -3-carboxylic acid esters with nitrogen functionality at the 8-position was synthesized, and 6-oxo-6H-imidazo[4,5,1-ij]quinoline-4- and -5-carboxylic acid esters were elaborated from these. Several of the compounds displayed activity in the rat passive cutaneous anaphylaxis (PCA) test for antiallergic activity. However, PCA activity in this series was accompanied by rat toxicity, as measured by a decrease in percent of normal weight gain over a 2-week period, following a single oral dose.

Benzo[1,2-c:5,4-c']dipyrazoles: non-xanthine adenosine antagonists.

3,5-Dimethylbenzo[1,2-c:5,4-c']dipyrazoles, optionally substituted in the 1-, 7-, and 8-positions, were synthesized from resorcinols. These compounds display affinity for adenosine A1 (rat brain) and A2 (human platelet) receptors. In addition, these compounds reverse contractions of guinea pig tracheal cylindrical segments induced by potassium chloride, histamine, acetylcholine, and 5-hydroxytryptamine, as well as reverse bronchospasm induced by aerosolized histamine in the conscious guinea pig.

Conformationally restrained, chiral (phenylisopropyl)amino-substituted pyrazolo[3,4-d]pyrimidines and purines with selectivity for adenosine A1 and A2 receptors.

Two modes of tethering a chiral (phenylisopropyl)amino substituent in pyrazolo[3,4-d]pyrimidines and purines have been explored. One mode gave (S)-2,7-dihydro-7-phenyl-2-(phenylmethyl)-5- propoxy-3H-imidazo[1,2-c]pyrazolo-[4,3-e]pyrimidine (12a) and its corresponding R-enantiomer 12b, which were selective for A2 and A1 adenosine receptors, respectively. The corresponding diimidazo[1,2-c:4',5'-e]pyrimidines 12e and 12f were analogously selective. This is the first example where a single chiral recognition unit provides enantiomers with opposite selectivities for adenosine receptors. The second mode gave (2S-trans)-2,7-dihydro-2-methyl-3,7-diphenyl-5- propoxy-3H-imidazo[1,2-c]-pyrazolo[4,3-e]pyrimidine (12c) and its corresponding R-enantiomer 12d. Compounds 12c and 12d were significantly less potent than 12a and 12b at A1 receptors, and were nonselective.

Evaluation of rotenone and related compounds as antagonists of slow-reacting substance of anaphylaxis.

Rotenone (1), dihydrorotenone (2), isorotenone (3), mutarotenone (4), and deguelin (12) were found to be potent antagonists of slow-reacting substance of anaphylaxis (SRS-A) in vitro. However, these compounds were also shown to inhibit histamine, serotonin, and acetylcholine at only ten times their IC50 concentrations for SRS-A antagonism. Rotenone (1) and several related compounds were also evaluated in an in vivo guinea pig anaphylaxis model. Several of these compounds and FPL 55712 (I) were effective in prolonging collapse times of animals which received an aerosol challenge of an antigen to which they had been sensitized.

Xanthines with C8 chiral substituents as potent and selective adenosine A1 antagonists.

Several 8-substituted 1,3-dipropylxanthines were synthesized, and their receptor binding affinities at adenosine A1 and A2 receptors were measured. When enantiomeric pairs of compounds were examined, the R enantiomers were significantly more potent than the corresponding S enantiomers. The most potent compound at the A1 receptor was (R)-3,7-dihydro-8-(1-methyl-2-phenylethyl)-1,3-dipropyl-1H-purine-2,6-di one (5a; MDL 102,503), whose Ki value at the A1 receptor was 6.9 nM. However, a more selective compound was (R)-3,7-dihydro-8-(1-phenylpropyl)-1,3-dipropyl-1H-purine-2,6-dione (5d; MDL 102,234), which had a Ki value of 23.2 nM at the A1 receptor and an A2/A1 ratio of 153.

3-(1H-tetrazol-5-yl)-4(3H)-quinazolinone sodium salt (MDL 427): a new antiallergic agent.

Syntheses for 3-(1H-tetrazol-5-yl)-4(3H)-quinazolinone sodium salt monohydrate (9; MDL 427) and the related formamido compound, 2-(formylamino)-N-1H-tetrazol-5-ylbenzamide (10), are described. Both compounds are active in the rat passive cutaneous anaphylaxis and passive peritoneal anaphylaxis tests. A 94:6 equilibrium mixture of 9 and ionized 10, respectively, forms in aqueous buffer systems at a pH-dependent rate. In addition, analogues of 3-(1H-tetrazol-5-yl)-4(3H)-quinazolinone (8) bearing substituents on the benzene ring, substituents at the 2-position, and heteroaryl groups at the 3-position other than tetrazole were prepared. These analogue sets demonstrated that an accessible electrophilic center and an acidic functionality were requirements for good antiallergic activity.

Synthesis of peptidyl fluoromethyl ketones and peptidyl alpha-keto esters as inhibitors of porcine pancreatic elastase, human neutrophil elastase, and rat and human neutrophil cathepsin G.

Comparison of MeO-Suc-Val-Pro-Phe-CO2Me (29) and MeO-Suc-Ala-Ala-Pro-Phe- CO2Me (25) with their corresponding trifluoromethyl ketones 9a and 9b, respectively, in rat and human neutrophil cathepsin G assays showed the alpha-keto esters to be more potent inhibitors. Likewise, Ac-Pro-Ala-Pro-Ala-CO2Me (21) was more potent than its corresponding trifluoromethyl ketone (9c) in both porcine pancreatic elastase and human neutrophil elastase assays. Within a set of Ala-Ala-Pro-Val-CF3 elastase inhibitors, the carbobenzyloxy (Cbz) N-protecting group conferred greater potency as a P5 site recognition unit for elastase than did dansyl, methoxysuccinyl, or tert-butyloxycarbonyl. Initial inhibition of elastase was greater when trifluoromethyl ketone 9f was added from a stock solution of dimethyl sulfoxide than when it had been buffer-equilibrated prior to assay, which suggests that the nonhydrated ketone is the more effective form of the inhibitor. The most potent elastase inhibitor we report is Na-(Ad-SO2)-N epsilon-(MeO-Suc)Lys-Pro-Val-CF3 (16) which has a Ki of 0.58 nM.

Carbocyclic nucleosides as inhibitors of human tumor necrosis factor-alpha production: effects of the stereoisomers of (3-hydroxycyclopentyl)adenines.

A series of four structurally related carbocyclic nucleosides (6a, 6b, 10a, and 10b) were synthesized and evaluated for their ability to inhibit tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and interleukin-6 (IL-6) production from human primary macrophages. These compounds had little effect on the production of IL-1 beta and IL-6. It was determined that compound 10a was the most potent inhibitor of TNF-alpha production (IC50 = 10 microM), having 2-5-fold more activity compared to its enantiomer 10b or its diastereomers 6a and 6b. In addition, these compounds were also tested for their ability to protect mice against lethal challenges of lipopolysaccharide (LPS) and D-galactosamine (D-Gal). Compound 10a showed superior protective effects (100% protection) compared to its enantiomer 10b or its diastereomers 6a and 6b when it was administered to mice which were challenged with 3 times the LD100 dose of LPS.

Crystal structure of human cyclin-dependent kinase 2 in complex with the adenine-derived inhibitor H717.

Cyclin-dependent kinases (CDKs) are regulatory proteins of the eukaryotic cell cycle. They act after association with different cyclins, the concentrations of which vary throughout the progression of the cell cycle. As central mediators of cell growth, CDKs are potential targets for inhibitory molecules that would allow disruption of the cell cycle in order to evoke an antiproliferative effect and may therefore be useful as cancer therapeutics. We synthesized several inhibitory 2,6,9-trisubstituted purine derivatives and solved the crystal structure of one of these compounds, H717, in complex with human CDK2 at 2.6 A resolution. The orientation of the C2-p-diaminocyclohexyl portion of the inhibitor is strikingly different from those of similar moieties in other related inhibitor complexes. The N9-cyclopentyl ring fully occupies a space in the enzyme which is otherwise empty, while the C6-N-aminobenzyl substituent points out of the ATP-binding site. The structure provides a basis for the further development of more potent inhibitory drugs.

Inhibition of human neutrophil elastase. 4. Design, synthesis, X-ray crystallographic analysis, and structure-activity relationships for a series of P2-modified, orally active peptidyl pentafluoroethyl ketones.

A series of P2-modified, orally active peptidic inhibitors of human neutrophil elastase (HNE) are reported. These pentafluoroethyl ketone-based inhibitors were designed using pentafluoroethyl ketone 1 as a model. Rational structural modifications were made at the P3, P2, and activating group (AG) portions of 1 based on structure-activity relationships (SAR) developed from in vitro (measured Ki) data and information provided by modeling studies that docked inhibitor 1 into the active site of HNE. The modeling-based design was corroborated with X-ray crystallographic analysis of the complex between 1 and porcine pancreatic elastase (PPE) and subsequently the complex between 1 and HNE.

Neurokinin receptor antagonists.

Studies on tachykinin peptides and the corresponding neurokinin receptors (NKr) have increased dramatically recently due to the discovery of selective, orally-active, metabolically stable and sometimes CNS penetrating NKr antagonists. After demonstrating the potential use for NKr antagonists in animal models, some compounds have recently progressed into clinical trials and a few results have been published. NKr antagonists have demonstrated efficacy for the treatment of emesis and depression, while results in other areas have been disappointing. Nonetheless, this area is coming to the exciting time of proof of concept in humans. Demonstration of the involvement of tachykinin peptides in biological functions continues to grow, as do the potential indications for NKr antagonists. More drug candidates are undergoing clinical trials for various conditions and these results could widen the potential use for NKr antagonists.

A-ring bridged steroids as potent inhibitors of aromatase.

The design and syntheses of androstenedione derivatives with bridges spanning the 2,19-, 3,19-, 4,19- and 6, 19-positions are described. 2,19-Bridged compounds bearing hydroxyl groups on the two-carbon bridge (3a and 3b) were designed as stable carbon analogs of potential lactol intermediates in the enzymatic conversion of androgens to estrogens. Compounds 3a and 3b are competitive inhibitors of aromatase. Pyran 25 is a potent, time-dependent inhibitor of aromatase with partial NADPH dependence. These data suggest a mechanism of inhibition for 25 which involves both tight-binding competitive and mechanism-based components, with the former predominating. The sulfur, amino, and all carbon analogs of pyran 25 were prepared. Thiopyran 36, piperidine 42 and the all-carbon analog 47 are also time-dependent inhibitors of aromatase. Compound 47 is the most potent inhibitor and its time-dependent inhibition is not NADPH dependent. The kinetics of piperidine 42 suggest uncompetitive inhibition.

Biological characterization of A-ring steroids.

Hydroxylated 2,19-methylene-bridged androstenediones were designed as potential mimics of enzyme oxidized intermediates of androstenedione. These compounds exhibited competitive inhibition with low micromolar affinities for aromatase. These inhibitory constants (Ki values) were 10 times greater than the 2,19-methylene-bridged androstenedione constant (Ki = 35-70 nM). However, expansion of the 2,19-carbon bridge to ethylene increased aromatase affinity by 10-fold (Ki = 2 nM). Substitution of a methylene group with oxygen and sulfur in this expanded bridge resulted in Ki values of 7 and 20 nM, respectively. When the substituent was an NH group, the apparent inhibitory kinetics changed from competitive to uncompetitive. All of these analogs exhibited time-dependent inhibition of aromatase activity following preincubation of the inhibitor with human placental microsomes prior to measuring residual enzyme activity. Part of this inhibition was NADPH cofactor-dependent for the 2,19-methyleneoxy- but not for the 2,19-ethylene-bridged androstenedione. The time-dependent inhibition for these four analogs was very rapid since they exhibited tau 50 values, the t1/2 for enzyme inhibition at infinite inhibitor concentration, of 1 to 3 min. These A-ring-bridged androstenedione analogs represent a novel series of potent steroidal aromatase inhibitors. The restrained A-ring bridge containing CH2, O, S, or NH could effectively coordinate with the heme of the P450 aromatase to allow the tight-binding affinities reflected by their nanomolar Ki values.

Activation of adenosine A3 receptors on macrophages inhibits tumor necrosis factor-alpha.

Murine macrophage-derived tumor necrosis factor alpha (TNF-alpha) gene expression has been shown to be dramatically induced by bacterial lipopolysaccharide, and to be dependent upon nuclear factor-kappa B (NF-kappa B) binding sites in its promoter for the lipopolysaccharide induction. Murine J774.1 macrophage cells were found to predominantly express the adenosine A3 receptor RNA relative to adenosine A1 receptor or adenosine A2 receptor RNA. Adenosine receptor agonists, in a dose-dependent manner characteristic of the adenosine A3 receptor, blocked the endotoxin induction of the TNF-alpha gene and TNF-alpha protein expression in the J774.1 macrophage cell line. The adenosine A3 receptor antagonist BW-1433 dose-dependently reversed this adenosine inhibitory effect on TNF-alpha gene expression. Thus, the binding of adenosine receptor agonists to the adenosine A3 receptor interrupts the endotoxin CD14 receptor signal transduction pathway and blocks induction of cytokine TNF-alpha, revealing a novel cross-talk between the murine adenosine A3 receptor and the endotoxin CD14 receptor in J774.1 macrophages.

N-Demethylation of dextromethorphan.

In addition to providing an efficient synthesis of 3-methoxymorphinan hydrochloride, the use of 2,2,2-trichloroethyl chloroformate in the N-demethylation of dextromethorphan led to the isolation of two novel zinc salts of 3-methoxymorphinan.

The design and synthesis of purine inhibitors of CDK2. III.

Cyclin-dependent kinases (CDKs) belong to a class of enzymes that control the ability of a cell to enter into and proceed through the cell division cycle. Using purine as a scaffold, we have synthesized a number of nanomolar inhibitors of CDK-2/cyclin E. In this report, the synthesis of a series of piperidine-substituted purine analogs will be presented, as well as some of their in vitro and in vivo biological effects.