Bioinspired Synthesis of Pinoxaden Metabolites Using a Site-Selective C-H Oxidation Strategy.

A bioinspired synthesis of Pinoxaden metabolites 2-5 is described herein. A site-selective C-H oxidation strategy validated by density functional theory (DFT) calculations was devised for preparing metabolites 2-4. Oxidation of the benzylic C-H bond in tertiary alcohol 7 using K2S2O8 and catalytic AgNO3 formed the desired metabolite 2 that enabled access to metabolites 3 and 4 in a single step. Unlike most metal/persulfate-catalyzed transformations reported for the C-C and C-O bond formation reactions wherein the metal acts as a catalyst, we propose that Ag(I)/K2S2O8 plays the role of an initiator in the oxidation of intermediate 7 to 2. Metabolite 2 was subjected to a ruthenium tetroxide-mediated C-H oxidation to form metabolites 3 and 4 as a mixture that were purified to isolate pure standards of these metabolites. Metabolite 5 was synthesized from readily available advanced intermediate 9 via a House-Meinwald-type rearrangement in one step using a base.

N-Ammonium Ylide Mediators for Electrochemical C-H Oxidation.

The site-specific oxidation of strong C(sp3)-H bonds is of uncontested utility in organic synthesis. From simplifying access to metabolites and late-stage diversification of lead compounds to truncating retrosynthetic plans, there is a growing need for new reagents and methods for achieving such a transformation in both academic and industrial circles. One main drawback of current chemical reagents is the lack of diversity with regard to structure and reactivity that prevents a combinatorial approach for rapid screening to be employed. In that regard, directed evolution still holds the greatest promise for achieving complex C-H oxidations in a variety of complex settings. Herein we present a rationally designed platform that provides a step toward this challenge using N-ammonium ylides as electrochemically driven oxidants for site-specific, chemoselective C(sp3)-H oxidation. By taking a first-principles approach guided by computation, these new mediators were identified and rapidly expanded into a library using ubiquitous building blocks and trivial synthesis techniques. The ylide-based approach to C-H oxidation exhibits tunable selectivity that is often exclusive to this class of oxidants and can be applied to real-world problems in the agricultural and pharmaceutical sectors.

Design, Synthesis, and Biological Evaluation of Structurally Rigid Analogues of 4-(3-Hydroxyphenyl)piperidine Opioid Receptor Antagonists.

In order to gain additional information concerning the active conformation of the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine (1) class of opioid receptor antagonists, procedures were developed for the synthesis of structurally rigid N-substituted-6-(3-hydroxyphenyl)3-azabicyclo[3.1.0]hexane and 3-methyl-4-(3-hydroxyphenyl)-4-azabicyclo[4.1.0]heptanes. Evaluation of the conformationally constrained series in a [35S]GTPγS assay showed that structural rigid compounds having the 3-hydroxyphenyl group locked in the piperidine equatorial orientation had potencies equal to or better than similar compounds having more flexible structures similar to 1. The studies of the rigid compounds also suggested that the 3-methyl group present in compound 1 type antagonists may not be necessary for their pure opioid antagonist properties.

Design, synthesis, and pharmacological evaluation of JDTic analogs to examine the significance of replacement of the 3-hydroxyphenyl group with pyridine or thiophene bioisosteres.

The potent and selective KOR antagonist JDTic was derived from the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of pure opioid antagonists. In previous studies we reported that compounds that did not have a hydroxyl on the 3-hydroxyphenyl group and did not have methyl groups at the 3- and 4-position of the piperidine ring were still potent and selective KOR antagonists. In this study we report JDTic analogs 2, 3a-b, 4a-b, and 5, where the 3-hydroxyphenyl ring has been replaced by a 2-, 3-, or 4-pyridyl or 3-thienyl group and do not have the 3-methyl or 3,4-dimethyl groups, remain potent and selective KOR antagonists. Of these, (3R)-7-hydroxy-N-(1S)-2-methyl-[4-methyl-4-pyridine-3-yl-carboxamide (3b) had the best overall binding potency and selectivity in a [(35)S]GTPγS functional assay, with a Ke=0.18nM at the KOR and 273- and 16,700-fold selectivity for the KOR relative to the MOR and DOR, respectively. Calculated physiochemical properties for 3b suggest that it will cross the blood-brain barrier.

Design, synthesis, and pharmacological evaluation of JDTic analogs to examine the significance of the 3- and 4-methyl substituents.

The design and discovery of JDTic as a potent and selective kappa opioid receptor antagonist used the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine pharmacophore as the lead structure. In order to determine if the 3-methyl or 4-methyl groups were necessary in JDTic and JDTic analogs for antagonistic activity, compounds 4a-c, and 4d-f which have either the 3-methyl or both the 3- and 4-methyl groups removed, respectively, from JDTic and analogs were synthesized and evaluated for their in vitro opioid receptor antagonist activities using a [(35)S]GTPγS binding assay. Other ADME properties were also assessed for selected compounds. These studies demonstrated that neither the 3-methyl or 3,4-dimethyl groups present in JDTic and analogs are required to produce potent and selective κ opioid receptor antagonists.

Design, synthesis, and biological evaluation of (3R)-1,2,3,4-tetrahydro-7-hydroxy-N-[(1S)-1-[[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl]-2-methylpropyl]-3-isoquinolinecarboxamide (JDTic) analogues: in vitro pharmacology and ADME profile.

JDTic analogues 4-15 which have the hydroxyl groups replaced with other groups were synthesized and their in vitro efficacy at the µ, δ, and κ opioid receptors determined and compared to JDTic using [(35)S]GTPγS assays. Compounds 4, 5, 6, 13, 14, and 15 had Ke = 0.024, 0.01, 0.039, 0.02, 0.11, and 0.041 nM compared to the Ke = 0.02 nM for JDTic at the κ receptor and were highly selective for the κ receptor relative to the µ and δ opioid receptors. Unexpectedly, replacement of the 3-hydroxyl substituent of the 4-(3-hydroxyphenyl) group of JDTic with a H, F, or Cl substituent leads to potent and selective KOR antagonists. In vitro studies to determine various ADME properties combined with calculated TPSA, clogP, and logBB values suggests that the potent and selective κ opioid receptors 4, 5, 13, and 14 deserve consideration for further development toward potential drugs for CNS disorders.

Effect of the 3- and 4-methyl groups on the opioid receptor properties of N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines.

N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines (2a,b) are opioid receptor antagonists where the antagonist properties are not due to the type of N-substituent. In order to gain a better understanding of the contribution that the 3- and 4-methyl groups make to the pure antagonist properties of 2a,b, we synthesized analogues of 2a,b that lacked the 4-methyl (5a,b), 3-methyl (6a,b), and both the 3- and 4-methyl group (7a,b) and compared their opioid receptor properties. We found that (1) all N-methyl and N-phenylpropyl substituted compounds were nonselective opioid antagonists (2) all N-phenylpropyl analogues were more potent than their N-methyl counterparts, and (3) compounds 2a,b which have both a 3- and 4-methyl substituent, were more potent antagonists than analogues 5a,b, 6a,b, and 7a,b. We also found that the removal of 3-methyl substituent of N-methyl and N-phenylpropyl 3-methyl-4-(3-hydroxyphenyl)piperazines (8a,b) gives (4a,b), which are opioid antagonists.

4ß-Methyl-5-(3-hydroxyphenyl)morphan opioid agonist and partial agonist derived from a 4ß-methyl-5-(3-hydroxyphenyl)morphan pure antagonist.

In previous studies we reported that addition of 7α-acylamino groups to N-phenylpropyl-4ß-methyl-5-(3-hydroxyphenyl)morphan (4) led to compounds that were pure opioid receptor antagonists. In contrast to these findings we report in this study that addition of a 7α-amino (5a), 7α-alkylamino (5b-e), or 7α-dialkylamino (5f-h) group to 4 leads to opioid receptor ligands with varying degrees of agonist/antagonist activity. The 7α-amino and 7α-methylamino analogues were full agonists at the µ and δ receptors and antagonists at the κ receptor. The 7α-cyclopropylmethylamino analogue 5h was a full agonist at the µ receptor with weaker agonist activity at the δ and κ receptors. Whereas the addition of a 7α-acylamino group to the pure nonselective opioid receptor antagonist N-phenylpropyl-4ß-methyl-5-(3-hydroxyphenyl)morphan (4) led to κ selective pure opioid receptor antagonist, the addition of a 7α-amino, 7α-alkylamino, or 7α-dialkylamino group to 4 leads to opioid ligands that are largely µ or δ agonist with mixed agonist/antagonist properties.

Preparation of a Series of 5-Methyl-3-(substituted)-[1,2,4]triazines.

Procedures for the synthesis of thirty-six 5-methyl-3-(substituted)-[1,2,4]triazines have been described. These compounds were evaluated for antagonism at metabotropic glutamate receptor subtype 5. Two compounds, 5b and 3c, were determined to be low micromolar inhibitors of mGluR5.

Synthesis and evaluation of 1,2,4-methyltriazines as mGluR5 antagonists.

In previous studies we showed that 3-(substituted phenylethynyl)-5-methyl[1,2,4]triazine analogues of MPEP were potent antagonists of glutamate-mediated mobilization of internal calcium in an mGluR5 in vitro efficacy assay. In the present study we report the synthesis and evaluation of six 3-(substituted biphenylethynyl)-5-methyl[1,2,4]triazines (5a-f), and five 3-(substituted phenoxyphenylethynyl)-5-methyltriazines (6a-e). Compound 2-(4-fluorophenyl-5-[2-(5-methyl[1,2,4]triazine-3-yl)ethynyl]benzonitrile (5f) with an IC(50) of 28.2 nM was the most potent analogue.

Synthesis and Evaluation of Metabotropic Glutamate Receptor Subtype 5 Antagonists Based on Fenobam().

In an effort to discover potent and selective metabotropic glutamate receptor subtype 5 (mGluR5) antagonists, 15 tetrahydropyrimidinone analogues of 1-(3-chlorophenyl)-3-(1-methyl-4-oxo-4,5-dihydro-1H-imidazol-2-yl)-urea (fenobam) were synthesized. These compounds were evaluated for antagonism of glutamate-mediated mobilization of internal calcium in an mGluR5 in vitro efficacy assay. The IC(50) value for 1-(3-chlorophenyl)-3-(1-methyl-4-oxo-1,4,5,6-tetrahydropyridine)urea (4g) was essentially identical to that of fenobam.

Evaluating binuclear copper(II) complexes for glycoside hydrolysis.

Three binuclear copper(II) complexes were characterized as solids by X-ray diffraction and in solution by UV/vis spectrophotometric titration, and subsequently evaluated for their glycosidase-like activity. The structure analysis revealed comparable intermetallic Cu...Cu distances (approximately 3.5 A) for the complexes 2 and 3. Despite this similarity, the composition of the complexes differs significantly in aqueous solution as revealed by spectrophotometric titrations. The hydrolysis of selected nitrophenylglycopyranosides is up to 11,000-fold accelerated over background in the presence of the copper(II) complexes in 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS) buffer at pH 10.5 and 30 degrees C.

Disaccharide recognition by binuclear copper(II) complexes.

The sugar recognition by binuclear copper(II) complexes in solution is strongly dependent on secondary interactions and cannot be predicted from the intermetallic Cu...Cu distance.

Effect of water on the catalytic oxidation of catechols.

A dinuclear copper(II) complex derived from a new water-soluble pentadentate Schiff base backbone ligand has been prepared and characterized in solution and in the solid state. The complex has been found to accelerate the aerobic oxidation of 3,5-di- tert-butylcatechol (DTBC) into 3,5-di- tert-butylquinone (DTBQ) by 5 orders of magnitude, compared to the background reaction in aqueous methanol (k(cat)/k(non) = 160,000) at 30 degrees C. The transformation of the model substrate is considerably slower in pure methanol (k(cat)/k(non) = 60,000) under otherwise identical conditions. In-depth investigation of the catalytically active species revealed different structures for the copper(II) complex in methanol and in methanol/water mixtures.

Macromolecular salen catalyst with largely enhanced catalytic activity.

A dinuclear copper(II) Schiff-base complex was immobilized in a poly(acrylate) matrix by emulsion polymerization. The spheric microbeads were used for aerobic catalytic oxidation of 3,5-di-tert-butylcatechol into 3,5-di-tert-butylquinone in methanol at ambient temperature to study the contribution of the macromolecular matrix to the overall rate acceleration of the reaction. The polymeric catalyst catalyzes the oxidation about 1 order of magnitude faster (kcat/knon = 470,000) than its low molecular weight analogue (kcat/knon = 60,000).