Heterocycle-based MMP inhibitors with P2' substituents

Potent and selective inhibition of matrix metalloproteinases was demonstrated for a series of sulfonamide-based hydroxamic acids. The design of the heterocyclic sulfonamides incorporates a six- or seven-member central ring with a P2' substituent that can be modified. Binding interactions of this substituent at the S2' site are believed to contribute to high inhibitory potency against stromelysin, collagenase-3 and gelatinases A and B, and to provide selectivity against collagenase-1 and matrilysin. An X-ray structure of a stromelysin inhibitor complex was obtained to provide insights into the SAR and selectivity trends observed for the series.     

Pyrazolopyridine inhibitors of B-RafV600E. Part 2: structure-activity relationships

Structure-activity relationships around a novel series of B-Raf(V600E) inhibitors are reported. The enzymatic and cellular potencies of inhibitors derived from two related hinge-binding groups were compared and3-methoxypyrazolopyridine proved to be superior. The 3-alkoxy group of lead B-Raf(V600E) inhibitor 1 was extended and minimally affected potency. The propyl sulfonamide tail of compound 1, which occupies the small lipophilic pocket formed by an outward shift of the αC-helix, was expanded to a series of arylsulfonamides. X-ray crystallography revealed that this lipophilic pocket unexpectedly enlarges to accommodate the bulkier aryl group.     

Synthesis and SAR of potent inhibitors of the Hepatitis C virus NS3/4A protease: Exploration of P2 quinazoline substituents

Novel NS3/4A protease inhibitors comprising quinazoline derivatives as P2 substituent were synthesized. High potency inhibitors displaying advantageous PK properties have been obtained through the optimization of quinazoline P2 substituents in three series exhibiting macrocyclic P2 cyclopentane dicarboxylic acid and P2 proline urea motifs. For the quinazoline moiety it was found that 8-methyl substitution in the P2 cyclopentane dicarboxylic acid series improved on the metabolic stability in human liver microsomes. By comparison, the proline urea series displayed advantageous Caco-2 permeability over the cyclopentane series. Pharmacokinetic properties in vivo were assessed in rat on selected compounds, where excellent exposure and liver-to-plasma ratios were demonstrated for a member of the 14-membered quinazoline substituted P2 proline urea series.     

Factor Xa inhibitors based on a 2-carboxyindole scaffold: SAR of neutral P1 substituents

A series of novel, highly potent 2-carboxyindole-based factor Xa inhibitors is described. Structural requirements for neutral ligands, which bind in the S1 pocket of factor Xa were investigated with the 2-carboxyindole scaffold. This privileged fragment assembly approach yielded a set of equipotent, selective inhibitors with structurally diverse neutral P1 substituents.     

Aryl-indolyl maleimides as inhibitors of CaMKIIdelta. Part 2: SAR of the amine tether

A family of aryl-substituted maleimides was prepared and studied for their activity against calmodulin-dependant kinase. Inhibitory activities against the enzyme ranged from 34nM to >20microM and were dependant upon both the nature of the aryl group and the tether joining the basic amine to the indolyl maleimide core. Key interactions with the kinase ATP site and hinge region, predicted by homology modeling, were confirmed.     

The Antioxidant Trolox Enhances the Oxidation of 2', 7'-Dichlorofluorescin to 2', 7'-Dichlorofluorescein

The use of antioxidants to prevent intracellular free radical damage is an area currently attracting considerable research interest. The compound 2',7'-dichlorofluorescin diacetate (DCFH-DA) is a probe for intracellular peroxide formation commonly used in such studies. During our studies we unexpectedly found that incubation of Trolox, a water soluble vitamin E analog, with DCFH-DA in cell-free physiological buffers resulted in the deacetylation and oxidation of DCFH-DA to form the fluorescent compound, 2',7'-dichlorofluororescein (DCF). The reaction was time-, temperature-, and pH-dependent. Fluorescence intensity increased with an increase in either Trolox or DCFH-DA concentration. These results indicate that even at physiological pH, DCFH-DA can be deacetylated to form 2',7'-dichlorofluorescin (DCFH). DCFH can then be oxidized to DCF by abstraction of a hydrogen atom by the phenoxyl radical of Trolox. Exposure of the reaction mixture to 10 Gy of ⁶⁰Co gamma radiation greatly increased production of DCF. Antioxidant compounds reported to “repair” the Trolox phenoxyl radical (e.g., ascorbic acid, salicylate) can also prevent the Trolox-induced DCFH-DA fluorescence. However, compounds that cannot repair the Trolox phenoxyl radical (e.g., catechin) or can themselves form a radical (e.g., uric acid, TEMPOL) either have no effect or can increase levels of DCF. These results demonstrate that experimental design must be carefully considered when using DCFH-DA to measure peroxide formation in combination with certain antioxidants.     

Semi-synthetic qualestatins: Squalene synthase inhibition and antifungal activity. The SAR of C6 and C7 modifications

We describe herein a protection/deprotection strategy that enables efficient transformation of natural Squalestatin S1 into C6 and C7 acyl analogues. We present the mammalian and fungal SQS enzyme activity and whole cell antifungal activity of the semi-synthetic Squalestatins.     

Phototriggerable 2',7-caged Paclitaxel

Three different variants of photoactivatable caged paclitaxel (PTX) have been synthesized and their bioactivity was characterized in in vitro assays and in living cells. The caged PTXs contain the photoremovable chromophore 4,5-dimethoxy-2-nitrobenzyloxycarbonyl (Nvoc) attached to position C7, C2' and to both of these positions via a carbonate bond. Single caged PTXs remained biologically active even at low dosages. Double caging was necessary in order to fully inhibit its activity and to obtain a phototriggerable PTX that can be applied successfully at commonly used concentrations. Irradiation of solutions containing the double caged PTX allowed dose-dependent delivery of functional PTX. Light-triggered stabilization of microtubule assemblies in vitro and in vivo by controlled light exposure of tubulin solutions or cell cultures containing caged PTX was demonstrated. Short light exposure under a fluorescence microscope allowed controlled delivery of free PTX during imaging.     

Synthesis and properties of ApU analogues containing 2'-halo-2'-deoxyadenosines. Effects of 2' substituents on oligonucleotide conformation

Five A-U analogues containing deoxyadenosine or 2'-halo-2'-deoxyadenosines, which are known to have widely different C3'-endo conformer populations according to their electronegativities of the halogen substituents, dAfl-U, dAcl-U, dAbr-U, dAio-U, and dA-U, were synthesized chemically. Characterization of these dimers has been performed by UV absorption, circular dichroism, and proton nuclear magnetic resonance spectroscopy. The results show that the dimers containing 2'-halo-2'-deoxyadenosines have stacked conformations with a geometry similar to that of A-U and the degree of stacking decreases in the order dAfl-U greater than dAcl-U greater than dAbr-U greater than dAio-U. dAcl-U is assumed to have the same degree of stacking as A-U. dA-U takes a more stacked conformation than does dAio-U, but the mode of stacking is different from those of the other dimers. The effects of the 2' substituents on dimer conformation are discussed in terms of electronegativity, molecular size, and hydrophobicity.     

Pyrazolo[1,5-a]pyridine antiherpetics: effects of the C3 substituent on antiviral activity

A recently disclosed series of pyrazolo[1,5-a]pyridine inhibitors of herpes virus replication has been closely examined herein for effects of the C3 substituent on antiviral activity. Significant changes in activity are observed by alterations of the heteroatom basicity and orientation of the group at C3. These results in combination with previous studies have served to further elaborate the minimal pharmacophore required for potency of this novel series of antiviral agents. During the course of these studies, several novel synthetic approaches were developed and are described.     

Unsymmetrical cyclic ureas as HIV-1 protease inhibitors: novel biaryl indazoles as P2/P2' substituents

The preparation of unsymmetrical cyclic ureas bearing novel biaryl indazoles as P2/P2' substituents was undertaken, utilizing a Suzuki coupling reaction as the key step. Compound 6i was equipotent to the lead compound of the series SE063.     

Photosensitized oxidation of 2',7'-dichlorofluorescin: singlet oxygen does not contribute to the formation of fluorescent oxidation product 2',7'-dichlorofluorescein

2',7'-Dichlorofluorescin (DCFH) is often employed to assess oxidative stress in cells by monitoring the appearance of 2',7'-dichlorofluorescein (DCF), its highly fluorescent oxidation product. We have investigated the photosensitized oxidation of DCFH in solution and elucidated the role played by singlet molecular oxygen (1O(2)) in this reaction. We used rose bengal (RB), protoporphyrin, and DCF as photosensitizers. Irradiation (550 nm) of RB (20 microM) in 50 mM phosphate (pH 7.4) in the presence of DCFH (50 microM) resulted in the rapid formation of DCF, measured as an increase in its characteristic absorbance and fluorescence. The oxidation rate was faster in deoxygenated solution, did not increase in D(2)O, and even increased in the presence of sodium azide. The presence of antioxidants that react with 1O(2), thus removing oxygen, accelerated DCF formation. Such results eliminate any potential direct involvement of 1O(2) in DCF formation, even though DCFH is an efficient (physical) quencher of 1O(2) (k(q) = 1.4 x 10(8) M(-1)s(-1) in methanol). DCF is also a moderate photosensitizer of 1O(2) with a quantum yield of circa phi = 0.06 in D(2)O and phi = 0.08 in propylene carbonate, which unequivocally indicates that DCF can exist in a triplet state upon excitation with UV and visible light. This triplet can initiate photo-oxidization of DCFH via redox-and-radical mechanism(s) similar to those involving RB (vide supra). Our results show that, upon illumination, DCF can function as a moderate photosensitizer initiating DCFH oxidation, which may prime and accelerate the formation of DCF. We have also shown that, while 1O(2) does not contribute directly to DCF production, it can do so indirectly via reaction with cellular substrates yielding peroxy products and peroxyl radicals, which are able to oxidize DCFH in subsequent dark reactions. These findings suggest that DCFH should not be regarded as a probe sensitive to singlet molecular oxygen, and that care must be taken when using DCFH to measure oxidative stress in cells as a result of both visible and UV light exposure.     

Effect of P2' substituents on kinetic constants for hydrolysis by cysteine proteinases.

Intramolecularly quenched fluorogenic peptide substrates with the general sequence: DABCYL-Lys-Phe-Gly-Gly-Xxx-Ala-EDANS have been utilized to explore the effect of the hydrophobicity of amino acid side chains in the P2' position on the steady-state kinetic constants for papain catalyzed hydrolysis. The results demonstrate that subsite interactions between the enzyme and the peptide substrate modulate the enzyme specificity by slowing the release of the C-terminal product. This series of substrates can be used to characterize substrate specificity studies of other cysteine proteinases.     

Oxidation of 2',7'-Dichlorofluorescin by Peroxynitrite

The simultaneous production of nitric oxide and superoxide anion leads to the formation of peroxynitrite, a potent oxidant which may be an important mediator of cellular injury. Oxidation of dichlorofluorescin to the fluorescent dichlorofluorescein has been used as a marker for cellular oxidant production. The mechanisms of peroxynitrite-mediated oxidation of dichlorofluorescin to dichlorofluorescein were investigated. Chemically synthesized peroxynitrite (50-500 nM) induced the oxidation of dichlorofluorescin to dichlorofluorescein in a linear fashion. In addition, the simultaneous generation of nitric oxide and superoxide anion induced the oxidation of dichlorofluorescin to dichlorofluorescein, while nitric oxide (1-10 μM) alone under aerobic conditions did not. Peroxynitrite-mediated oxidation of dichlorofluorescin was not inhibited by the hydroxyl radical scavengers mannitol (100 mM) or dimethylsulfoxide (100 mM). Moreover, peroxynitrite-mediated oxidation of dichlorofluorescin was not dependent upon metal ion-catalyzed reactions. Furthermore, dichlorofluorescein formation was diminished at alkaline pH. These findings suggest that peroxynitrite-mediated dichlorofluorescein formation results directly from the protonation of peroxynitrite to form the conjugate peroxynitrous acid. L-cysteine was an efficient inhibitor (K₁ = 25 μM) of dichlorofluorescin oxidation through competitive oxidation of free sulfhydryls. Urate was a less efficient with a maximum inhibition of only 49%. These results demonstrate that dichlorofluorescin is efficiently oxidized by peroxynitrite.

Therefore, under conditions where nitric oxide and superoxide are produced simultaneously, oxidation of dichlorofluorescin may be mediated by the formation of peroxynitrite.     

Synthesis and SAR studies of bicyclic amine series GPR119 agonists

We disclosed a novel series of G-protein coupled receptor 119 (GPR119) agonists based on a bicyclic amine scaffold. Through the optimization of hit compound 1, we discovered that the basic nitrogen atom of bicyclic amine played an important role in GPR119 agonist activity expression and that an indanone in various bicyclic rings was suitable in this series of compounds. The indanone derivative 2 showed the effect of plasma glucose control in oGTT and scGTT in the rodent model.     

7-Substituted-melatonin and 7-substituted-1-methylmelatonin analogues: effect of substituents on potency and binding affinity

A series of 7-substituted melatonin and 1-methylmelatonin analogues were prepared and tested against human and amphibian melatonin receptors. 7-Substituents reduced the agonist potency of all the analogues in the Xenopus laevis melanophore assay, 7-bromomelatonin (5d) and N-butanoyl 7-bromo-5-methoxytryptamine (5f) being the most active compounds, but both were 42-fold less potent than melatonin (1). Whereas all the analogues bind with lower affinity at the human MT(1) receptor than melatonin, 5d, 5f and N-propanoyl 7-bromo-5-methoxytryptamine (5e) show a similar binding affinity to melatonin at the MT(2) receptor and consequently show some MT(2) selectivity. These results suggest that the receptor pocket around C-7 favours binding by an electronegative group, suggesting an electropositive region in this area of the receptor.     

Active oxygen chemistry within the liposomal bilayer. Part IV: Locating 2',7'-dichlorofluorescein (DCF), 2',7'-dichlorodihydrofluorescein (DCFH) and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) in the lipid bilayer

2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) is commonly used to detect the generation of reactive oxygen intermediates and for assessing the overall oxidative stress in toxicological phenomenon. It has been suggested that DCFH-DA crosses the cell membrane, subsequently undergoing deacetylation by intracellular esterases. The resulting 2',7'-dichlorodihydrofluorescein (DCFH) is proposed to react with intracellular hydrogen peroxide or other oxidizing ROS to give the fluorescent 2',7'-dichlorofluorescein (DCF). Using an NMR chemical shift-polarity correlation, we have determined that DCFH-DA and DCFH are located well within the lipid bilayer and certainly not at the interface. These results, therefore, put into serious question the proposed ability of DCFH to come in contact with the aqueous phase and thereby interact with aqueous intracellular ROS and components. However, H2O2 and superoxide can cross or at least penetrate the lipid bilayer and react with certain lipophilic substrates. This may well describe the mode of reaction of these and other ROS with DCFH.     

Anthranilate sulfonamide hydroxamate TACE inhibitors. Part 2: SAR of the acetylenic P1' group

The SAR of a series of potent sulfonamide hydroxamate TACE inhibitors bearing novel acetylenic P1' groups was explored. In particular, compound 4t bearing a butynyloxy P1' moiety has excellent in vitro potency against isolated TACE enzyme and in cells, good selectivity over MMP-1 and oral activity in an in vivo model of TNF-alpha production.