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Efficient synthesis of nevirapine analogs to study its metabolic profile by click fishing
Abstract
Knowledge of the biotransformation and pharmacokinetics of the antiretroviral agent nevirapine is still insufficient. In order to trace rash inducing metabolites of nevirapine, we devised a short and efficient multi-gram synthesis of a nevirapine analog that can be coupled to azide containing compounds by click chemistry.
... Palaniappan et al., reported that Nevirapine alters the cleavage specificity of ribonuclease H of human immunodeficiency virus I reverse transcriptase [5]. Although innumerous articles exist in the literature about the medical aspects of Nevirapine, relatively few have appeared on the chemistry, structure, synthesis and other uses of it [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. ...
Nevirapine is a dipyridodiazepinone and representative of a new class of anti-HIV agents, the non-nucleoside reverse transcriptase inhibitors. The effect of some centric perturbations on some properties of nevirapine have been investigated within the limitations of density at the level of B3LYP/6-31++G(d,p). The calculations have revealed that the isomers constructed are all thermally favorable and electronically stable. Various calculated properties of the isomers including geometrical, electronic, thermo chemical, quantum chemical and some spectral properties have been harvested and discussed. Additionally, nucleus-independent chemical shift, NICS(0), calculations have been performed and the effect of perturbations on the local aromaticity of six-membered rings have been investigated. The effect of monocentric carbon to nitrogen perturbations on the chemical function descriptors have been determined. Also, the variation of polar surface areas (PSA) of the isomers have been considered in relation to their ability to penetrate the blood-brain barrier.
... [15] Similarly, the coupling reaction ern azide intermediates 42, 43, 44 and 45 and acrylamides 51-53 (Scheme 4). [22] A number of the reactions for the synthesis of hybrid 11 followed procedures reported by Weisner et al. (Scheme 5). [6a] The synthesis started with the nitration of commercially available 5-chloro-1-(piperidine-4-yl)-1,3-dihydro-2H-benzo[d]imidazol-2-one 54 to afford 55. [23] Simultaneous reduction and hydrodehalogenation of 55 then afforded 56. ...
Akt is a protein kinase that has been implicated in the progression of cancerous tumours. A number of covalent allosteric Akt inhibitors are known, and based on these scaffolds, a small library of novel potential covalent allosteric imidazopyridine‐based inhibitors was designed. The envisaged compounds were synthesised, with click chemistry enabling a modular approach to a number of the target compounds. The binding modes, potencies and antiproliferative activities of these synthesised compounds were explored, thereby furthering the structure activity relationship knowledge of this class of Akt inhibitors. Three novel covalent inhibitors were identified, exhibiting moderate activity against Akt1 and various cancer cell lines, potentially paving the way for future covalent allosteric inhibitors with improved properties.
A simple and general approach to nitrogen-containing heterocycles via copper-catalyzed domino reaction has been developed, the corresponding 2-aminopyridylbenzoxazole derivatives were obtained in good to excellent yields using the readily available starting materials.
Les toxidermies médicamenteuses sont des réactions de toxicité cutanée déclenchées par la prise d’un ou de plusieurs médicament(s). Dans les cas les plus graves, ces effets indésirables médicamenteux menacent la vie des patients. La plupart des toxidermies ne seraient pas déclenchées par la substance médicamenteuse elle-même, mais par un ou plusieurs de ses métabolites cutanés suffisamment réactif(s) pour former un complexe antigénique avec les protéines épidermiques. Cette étape-clé serait le point de départ des mécanismes immunitaires à l’origine des toxidermies. L’objectif de ce travail de thèse a été d’étudier l’activation métabolique in situ de la Névirapine, un antirétroviral à l’origine de toxidermies chez 20% des patients. En utilisant une technique non invasive, la RMN HRMAS associée aux épidermes humains reconstruits, il a été possible de suivre l’éventuelle bioactivation épidermique de la Névirapine et de ses dérivés ainsi que la fixation de l’un d’eux dans l’épiderme.
Using 2,8-bis(trifluoromethyl)quinoline, the pharmacophore of mefloquine, as scaffold, eleven novel triazole-linked compounds have been synthesised by the application of CuAAC chemistry. The in vitro biological activity of the compounds on the Plasmodium falciparum chloroquine-sensitive strain NF54 was then determined. The compounds all showed IC50s in the lower μM range with (1R,3S,5R)-N-{[1-(2,8-bis(trifluoromethyl)quinoline-4-yl)-1H-1,2,3-triazol-4-yl]methyl}adamantan-2-amine (29) exhibiting the best activity of 1.00 μM.
Using 2-trichloromethylquinazoline as scaffold, seven novel triazole-linked compounds have been synthesized using CuAAC chemistry. The in vitro biological activity of four of the compounds on the P. falciparum chloroquine sensitive strain NF54 was then determined. The compounds which were tested showed moderate activity with 1.45 µM as the lowest inhibitory concentration.
A clickable alkyne tagged chloroacetamidyl chitobiose derivative was synthesized as a potential inhibitor of cytoplasmic peptide-N-glycanase (PNGase). Construction of a chitobiose structure containing both alkyne and azide functional groups was performed using a thioglycoside donor having a triisopropylsilyl (TIPS) protected alkyne group and a glycosyl azide acceptor. The resultant chitobiosyl azide derivative was reduced to the corresponding glycosyl amine and a chloroacetyl group was introduced. Finally, removal of the TIPS group using tetrabutylammonium fluoride (TBAF) gave the target compound. We conjugated the dansyl derivative, using click conditions and obtained the fluorescent labeled disaccharide derivative, selectively. Our probe can easily lead to a variety of compounds and should help in the understanding of the biological functions of cytoplasmic PNGase.
A scalable process for the preparation of 4,4,5,5-tetramethyl-2-(3-trimethylsilyl-2-propynyl)-1,3,2-dioxaborolane from trimethylsilylpropyne, isopropyl pinacol borate, and n-butyllithium is described. Problems associated with implementing a typical aqueous workup and batch process into production due to borolane “ate” equilibration and protonolysis are presented. To address these issues, a continuous-flow and distillation process was developed which efficiently produced 297 kg of the key propargylation reagent.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
A description of the ab initio quantum chemistry package GAMESS is presented. Chemical systems containing atoms through radon can be treated with wave functions ranging from the simplest closed-shell case up to a general MCSCF case, permitting calculations at the necessary level of sophistication. Emphasis is given to novel features of the program. The parallelization strategy used in the RHF, ROHF, UHF, and GVB sections of the program is described, and detailed speecup results are given. Parallel calculations can be run on ordinary workstations as well as dedicated parallel machines. © John Wiley & Sons, Inc.
By simply stirring in water, organic azides and terminal alkynes are readily and cleanly converted into 1,4-disubstituted 1,2,3-triazoles through a highly efficient and regioselective copper(I)-catalyzed process (see scheme for an example).
New protecting groups for the hydroxy function, 3-methoxybenzyl (3-MPM) and 3, 5-dimethoxybenzyl (3, 5-DMPM) groups are slowly removed by DDQ oxidation at room temperature and distinguished from readily removable 4-methoxybenzyl (MPM). They are stable to strong acids.
Novel pyrido[2,3-b][1,4]benzodiazepinones (I), pyrido[2,3-b][1,5]benzodiazepinones (II), and dipyrido[3,2-b:2',3'-e][1,4]diazepinones (III) were found to inhibit human immunodeficiency virus type 1 (HIV-1) reverse transcriptase in vitro at concentrations as low as 35 nM. In all three series, small substituents (e.g., methyl, ethyl, acetyl) are preferred at the lactam nitrogen, whereas slightly larger alkyl moieties (e.g., ethyl, cyclopropyl) are favored at the other (N-11) diazepinone nitrogen. In general, lipophilic substituents are preferred on the A ring, whereas substitution on the C ring generally reduces potency relative to the corresponding compounds with no substituents on the aromatic rings. Maximum potency is achieved with methyl substitution at the position ortho to the lactam nitrogen atom; however, in this case an unsubstituted lactam nitrogen is preferred. Additional substituents on the A ring can be readily tolerated. The dipyridodiazepinone derivative 11-cyclopropyl-5,11-dihydro-4-methyl-6H-dipyrido[3,2-b:2',3'-e][1,4]diazepin-6-one (96, nevirapine) is a potent (IC 50 =84 nM) and selective non-nucleoside inhibitor of HIV-1 reverse transcriptase, and has been chosen for clinical evaluation
Toward the goal of assigning function to the tens of thousands of protein products encoded by eukaryotic and prokaryotic genomes, the field of proteomics requires new technologies that can functionally characterize proteins within the dynamic environment of the cell, where these biomolecules are subject to myriad posttranslational modifications and the actions of endogenous activators and inhibitors. Here, we report an advanced strategy for activity-based protein profiling (ABPP) that addresses this important need. We show that several enzymes can be labeled in an activity-based manner both in vitro and in vivo by an azido-sulfonate ester probe and that these labeling events can be detected in whole proteomes by copper-catalyzed ligation with a rhodamine-alkyne reagent. This click chemistry-based strategy for ABPP represents a unique and versatile method for functional proteome analysis.
A new amidoalkynylation using alkynylzinc reagent was developed and successfully applied to various α-thio-lactams including 6.
Enantioselective hydrogenation of some alpha,beta -unsaturated nitriles and their corresponding methyl esters bearing a phthalimidomethyl substituent at the alpha -carbon using Rh-DuPHOS catalysts afforded beta -amino acid precursors with modest e.e.s of up to 48%. Hydrogenation of the alpha,beta -unsaturated methyl esters using a Ru-BINAP catalyst gave higher e.e.s of up to 84%. Method development for the determination of the enantiomeric excesses of these derivatives using chiral HPLC is also reported.
1,6‐bis‐(N‐phenothiazinyl)‐2,4‐hexadiyne (I) was synthesized in high yield by oxidative coupling of N‐propargyl phenothiazine. Grown from methylene chloride‐hexane solution, I is a monoclinic crystal, space group C2/c a=14.9500(18) Å; b=13.5512(15) Å; c=12.0116(10) Å; β=102.628(9)° Å; V=2374.6(4) Å3. The intermolecular distances and arrangement of I in the unit cell preclude the usual diacetylene reactivity. Nevertheless, heating of I at 145°C results in decomposition of I to phenothiazine and a dark brown solid. In addition, cation‐radicals of I were prepared by oxidation with nitrosonium tetrafluoroborate and iodine to give stable ion‐radical salts.
Gymnomitrol, a sesquiterpenic alcohol of unusual structure, has been synthesized in an efficient and stereoselective manner. Selective ketalization of the bicyclo[3.3.0]octanedione (4), followed by Wolff-Kishner reduction and deketalization, afforded the Cs symmetric ketone 5. Methylenation with paraformaldehyde and N-methylanilinium trifluoroacetate gave the exocyclic methylene derivative (6) which entered into copper-catalyzed 1,4 addition with the Grignard reagent from (E)-2-(bromovinyl)trimethylsilane and subsequent in situ methylation to deliver 12 in 66% yield. Epoxidation and dilute acid hydrolysis of this intermediate furnished hydroxy ketone 15 directly. The coproducts 14a and 14b could also be converted to 15 which was oxidized to diketone 16. The final stages of the synthesis involved regioselective addition of methyllithium to 16, dehydration of the tertiary carbinol functionality, and ultimate lithium aluminum hydride reduction.
Nevirapine (1) is a non-nucleoside reverse transcriptase inhibitor marketed for HIV treatment by Boehringer Ingelheim as Viramune® since 1996. In vitro studies of nevirapine biotransformation using human liver microsomes demonstrated the formation of five major metabolites. This paper describes the syntheses of these metabolites.
A new method for preparing 3-amino-2-chloropyridines with a substituent (methyl, phenyl, carbox-amide, methoxycarbonyl, acetyl, benzoyl and cyano) at the 4-position has been developed. An isoquinoline analogue of the reverse transcriptase inhibitor Nevirapine has been synthesized from the 4-amino-3-chloroisoquinoline.
Several synthetic methods were developed during the process optimization for the large scale synthesis of nevirapine (1), a non-nucleoside inhibitor of HIV-1 Reverse Transcriptase. The synthesis of its putative major metabolite 11-cyclopropyl-5,11-dihydro-4-hydroxymethyl-6H-[3,2-b:2′,3′-e][1,4]diazepin-6-one (2) and the oxidation of 2 to the corresponding aldehyde 3, are described.
Examination of nature's favorite molecules reveals a striking preference for making carbon–heteroatom bonds over carbon–carbon bonds—surely no surprise given that carbon dioxide is nature's starting material and that most reactions are performed in water. Nucleic acids, proteins, and polysaccharides are condensation polymers of small subunits stitched together by carbon–heteroatom bonds. Even the 35 or so building blocks from which these crucial molecules are made each contain, at most, six contiguous C−C bonds, except for the three aromatic amino acids. Taking our cue from nature's approach, we address here the development of a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries through heteroatom links (C−X−C), an approach we call “click chemistry”. Click chemistry is at once defined, enabled, and constrained by a handful of nearly perfect “spring-loaded” reactions. The stringent criteria for a process to earn click chemistry status are described along with examples of the molecular frameworks that are easily made using this spartan, but powerful, synthetic strategy.
The15N-NMR-spectra of pyridine in presence of several proton donors are given. The concentration dependence of the chemical shifts can be described formally by a two step mechanism including proton transfer.Die15N-NMR-Spektren von Pyridin mit einigen Protonendonatoren sind angegeben. Die Konzentrationsabhngigkeit der chemischen Verschiebung kann formal durch ein zweistufiges Gleichgewicht, welches einen Protonenbergang beinhaltet, beschrieben werden.
An unexpected cyclization product was isolated in the final step of the synthesis of nevirapine, a non-nucleoside inhibitor of HIV-1 reverse transcriptase. Based on infrared spectrometry, mass spectrometry, and a number of two-dimensional nmr experiments, the structure of this product was assigned to be 2-((2′-cyclopropylamino)-3′-pyridyl)-7-methyloxazolo[5,4-b]pyridine, 9. Results of a single crystal X-ray analysis confirmed this structural assignment. This product arises from cyclization of N-(2-chloro-4-methyl-3-pyridyl)-2-(cyclopropylamine)-3-pyridinecarboxamide, 8, by displacement of the chlorine with the amide carbonyl oxygen. A competitive reaction occurs when 8 is deprotonated prior to cyclization to form nevirapine, 11-cyclopropyl-5,11-dihydro-4-methyl-6H-dipyrido[3,2-b:2′,3′-e][1,4]diazepin-6-one, 2.
The reverse transcriptase inhibitor, nevirapine (NVP), causes skin rashes and hepatotoxicity. We used a rat model to determine if the rash is caused by the parent drug or a reactive metabolite. By manipulation of metabolic pathways and testing analogues, we eliminated all but one pathway, 12-hydroxylation, which involves the oxidation of an exocyclic methyl group, as being responsible for the rash. Treatment with 12-OH-NVP caused a rash, and an analogue in which the methyl hydrogens were replaced by deuterium to inhibit the 12-OH pathway did not cause a rash; however, quite unexpectedly, blood levels of the deuterated analogue were very low. This is due to partitioning of the benzylic free radial intermediate between oxygen rebound to form 12-OH-NVP and loss of another hydrogen atom to form a reactive quinone methide, which inactivates P450. Cotreatment with the P450 inhibitor, 1-aminobenzotriazole, led to comparable levels of NVP and the deuterated analogue, and the deuterated analogue still caused a lower rash incidence. These data clearly point to the 12-hydroxy pathway being responsible for NVP skin rash. We propose that the hepatotoxicity of NVP in humans is due to the quinone methide formed by P450 in the liver, while the skin rash may be due to the quinone methide formed in the skin by sulfation of 12-OH metabolite followed by loss of sulfate. This is the first example in which a valid animal model of an idiosyncratic drug reaction was used to determine the metabolic pathway responsible for the reaction.
The lithium diisopropylamide (LDA)-mediated condensation of 2-fluoro-3-picoline and benzonitrile to form 2-phenyl-7-azaindole via a Chichibabin cyclization is described. Facile dimerization of the picoline via a 1,4-addition of the incipient benzyllithium to the picoline starting material and fast 1,2-addition of LDA to benzonitrile cause the reaction to be complex. Both adducts are shown to reenter the reaction coordinate to produce the desired 7-azaindole. The solution structures of the key intermediates and the underlying reaction mechanisms are studied by a combination of IR and NMR spectroscopies.
The copper catalysis in the Huisgen reaction broadly known as the azide/ alkyne reaction or CuAAC reaction has been discussed. This simple and robust reaction, which involves clusters of Cu and ligands, has led to exclusive formation of the 1,4-isomer. It is vital to maintain a good concentration of Cu throughout the reaction medium particularly in the case of less reactive reaction components or dilute reactions. The ligands' role in protecting the copper from oxidation or disproportionation is also important. The ligands also influence the structure and equilibria of copper clusters and may promote the formation of the most catalytically active copper complexes. The CuAAC reaction may be designed to accommodate all types of protecting groups and reactive intermediates.
The ease of formation of cyclic structures shows some regularity which can be described by a set of 'rules' for ring closure. The restrictions on the endocyclic transfer of groups due to SN2 displacements having linear transition states are exemplified by studied on a biogenetic type synthesis of penicillin and, more generally, on the endocyclic attack of a nucleophile attached by a linking chain to an enone or polarized double bond. The formation of five-memebered rings is considered. In base, enones such as 4-hydroxy- and 4-amino-2-methylenebutanoates close exocyclically to give the corresponding five-membered lactones and lactams, respectively. Hydroxymethyl vinyl ketones, however, do not cyclize in base. In strong acid, hydroxy-enones close endocyclically to five-membered ring, as in the formation of cyclic ethylene ketals from acetone and ethanediol. The endocyclic closure of nucleophilic centres to polarized double bonds to give five-membered rings is impeded by restrictions of geometry; these restrictions can be overcome in acid through the generation of oxonium or protonated forms.
A series of dipyridodiazepinones have been shown to be potent inhibitors of human immunodeficiency virus-1 (HIV-1) reverse
transcriptase (RT). One compound, BI-RG-587, had a Ki of 200 nanomolar for inhibition of HIV-1 RT that was noncompetitive
with respect to deoxyguanosine triphosphate. BI-RG-587 was specific for HIV-1 RT, having no effect on feline and simian RT
or any mammalian DNA polymerases. BI-RG-587 inhibited HIV-1 replication in vitro as demonstrated by in situ hybridization,
inhibition of protein p24 production, and the lack of syncytia formation in cultured human T cell lines and freshly isolated
human peripheral blood lymphocytes. Cytotoxicity studies of BI-RG-587 on human cells showed a high therapeutic index (greater
than 8000) in culture.
Nevirapine (NVP) is a nonnucleoside reverse transcriptase inhibitor widely used in combination with other antiretroviral agents for the treatment of human immunodeficiency virus disease. To establish its safety profile, we conducted a review of data from prospective US and international clinical trials involving a total of 906 adult patients and 468 pediatric patients treated with NVP. Drug-related adverse events were similar in adults and children, with rash and nausea most frequently reported in adults and rash and granulocytopenia most frequently reported in children. A separate analysis of rash based on data from adult patients in controlled trials demonstrated a 16% rate of NVP-attributable rash in these patients. Of patients with NVP-associated rash, 65% developed rash within the first 6 weeks of therapy, and it has been shown that a lower lead-in dose (200 mg/d vs the standard 400 mg/d) for the first 2 weeks of NVP treatment reduces the frequency of drug-associated rash. Serious rash (Stevens-Johnson syndrome [SJS] or SJS/toxic epidermal necrolysis transition syndrome) occurred with an incidence of 0.3% and clinical hepatitis with an incidence of 1.0% among NVP-treated patients in clinical trials. Adverse event data from long-term clinical trials demonstrated a lower incidence of NVP-related adverse events than in short-term trials of NVP therapy. An analysis of abnormal laboratory findings using thresholds similar to those found in the prescribing information for other commonly used antiretroviral agents and data from controlled trials in adults showed that the most frequently observed laboratory abnormalities were elevations in liver function test results. Approximately 50,000 patients in the United States had been treated with marketed NVP at the time of writing, and postmarketing surveillance has supported the overall safety profile observed in clinical trials. NVP has been shown to be well tolerated in both adult and pediatric patients.
A correlation-energy formula due to Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)], in which the correlation energy density is expressed in terms of the electron density and a Laplacian of the second-order Hartree-Fock density matrix, is restated as a formula involving the density and local kinetic-energy density. On insertion of gradient expansions for the local kinetic-energy density, density-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calculations on a number of atoms, positive ions, and molecules, of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.
Examination of nature's favorite molecules reveals a striking preference for making carbon-heteroatom bonds over carbon-carbon bonds-surely no surprise given that carbon dioxide is nature's starting material and that most reactions are performed in water. Nucleic acids, proteins, and polysaccharides are condensation polymers of small subunits stitched together by carbon-heteroatom bonds. Even the 35 or so building blocks from which these crucial molecules are made each contain, at most, six contiguous C-C bonds, except for the three aromatic amino acids. Taking our cue from nature's approach, we address here the development of a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries through heteroatom links (C-X-C), an approach we call "click chemistry". Click chemistry is at once defined, enabled, and constrained by a handful of nearly perfect "spring-loaded" reactions. The stringent criteria for a process to earn click chemistry status are described along with examples of the molecular frameworks that are easily made using this spartan, but powerful, synthetic strategy.
Form‐fitting chemistry in a protein mold is enabled by the use of the 1,3‐dipolar cycloaddition of azides and alkynes. The enzyme acetylcholinesterase preferentially assembles one pair of these reactants, each of which bears a group that binds to adjacent positions on the protein structure (see picture), into a 1,2,3‐triazole adduct that is the most potent noncovalent inhibitor of the enzyme yet developed.
Idiosyncratic drug reactions are difficult to study in humans due to their unpredictability. Unfortunately, this characteristic also hinders the development of animal models needed for mechanistic studies. Nevirapine, used to treat human immunodeficiency virus (HIV) infections, results in a severe idiosyncratic skin rash in some patients. We found that nevirapine can also cause a significant rash in some strains of rats. At a dose of 150 mg/kg/day, the incidence in female Sprague-Dawley rats was 6/28 (21%), in female Brown Norway rats 32/32 (100%), and in female Lewis rats 0/6 (0%) while no male Sprague-Dawley or Brown Norway rats developed a rash. Female SJL mice 0/7 also did not develop nevirapine-induced skin lesions. The first sign of a reaction in Brown Norway rats was red ears at days 7-10 followed by a rash with scabbing mainly on the back; this was a shorter time to onset than in Sprague-Dawley rats. Light microscopy of the skin revealed a primarily mononuclear inflammatory infiltrate and lesions typical of self-trauma. Immunohistochemistry results suggest that the infiltrate was composed of CD4 and CD8 T cells as well as macrophages. A lower dose of either 40 or 75 mg/kg/day did not lead to a rash and, in fact, 2 weeks of the lower doses induced tolerance to the 150 mg/kg/day dose in female Brown Norway rats. A dose of 100 mg/kg/day resulted in rash in 2/4 (50%) of female Brown Norway rats. Rechallenge of Brown Norway rats that had been allowed to recuperate after a nevirapine-induced rash led to red ears in less than 24 h followed by hair loss and occasional skin lesions. Although the skin rash was less evident on rechallenge, microscopically, the cellular infiltrate was more prominent, especially surrounding the hair follicles. Moreover, there were lesions of interface dermatitis with apoptosis and satellitosis, indicative of a cell-mediated immune attack on the epidermis. While systemic signs of illness did not accompany the rash on primary exposure, on rechallenge, the animals appeared generally unwell and this forced sacrifice after 2 weeks or less of treatment. Importantly, splenocytes isolated from rechallenged animals were able to transfer susceptibility to nevirapine-induced skin rash to naïve female Brown Norway recipients, which was illustrated by a faster time to onset of rash in the recipients. The characteristics of this adverse reaction are similar to that seen in humans; that is, it is idiosyncratic in that it only occurs in some strains of animals, is delayed in onset, is more common in females, is dose-dependent, and appears to be immune-mediated. Therefore, it may represent a good animal model for the study of idiosyncratic drug reactions.
[reaction: see text] A reagent combination of beta-SnO and catalytic [Rh(COD)Cl](2) in THF-H(2)O promotes the reaction of propargyl bromides and aldehydes and directs the regioselectivity toward the formation of either allenic alcohols or homopropargylic alcohols. This highly regioselective either/or transformation proceeds via a transmetalation from rhodium to tin, in which metallotropic rearrangement between a propargylmetal and allenylmetal is arrested.
A diversity-oriented, enantioselective synthesis of new (monoprotected) carbocyclic nucleoside analogues (CNAs) with the nucleobase attached to a 3-hydroxymethyl-4-trialkylsilyloxymethylcyclopent-2-en-1-yl scaffold was developed. As a key intermediate, racemic (5SR,8RS)-8-allyloxy-2-trimethylsilyl-7-oxa-bicyclo[3.3.0]-oct-1-en-3-one was prepared from 1,1-diallyloxy-3-trimethylsilyl-2-propyne in a cobalt-mediated Pauson-Khand reaction. The enantiomerically pure material was obtained through efficient kinetic resolution (selectivity factor s >/= 40 at -78 degrees C) by means of an oxazaborolidine-catalyzed borane reduction (CBS reduction) with catecholborane. The absolute configuration of the resolved products was determined by CD spectroscopy, Mosher ester analysis, and chemical correlation. Subsequent steps involve diastereoselective ketone reduction and fully regio- and diastereoselective introduction of the nucleobase through Pd(0)-catalyzed allylic substitution. The generality of the method was demonstrated by preparation of CNAs in both enantiomeric series with all five natural nucleobases, as well as 5-bromouracil, 5-fluorouracil, and 6-chloropurine. Screening of the various compounds in a cytotoxicity assay with BJAB and ALL tumor cell lines revealed that some of the compounds possess pronounced antitumoral properties (LD50 values down to 9 microM, as determined by lactate dehydrogenase release after 48 h). By measuring DNA fragmentation, it could be shown that the activity results from induction of apoptosis.
A novel class of lymphocyte function-associated antigen-1 (LFA-1) inhibitors is described. Discovered during the process to improve the physicochemical and metabolic properties of BIRT377 (1, Figure 1), a previously reported hydantoin-based LFA-1 inhibitor, these compounds are characterized by an imidazole-based 5,5-bicyclic scaffold, the 1,3,3-trisubstituted 1H-imidazo[1,2-alpha]imidazol-2-one (i.e. structure 3). The structure-activity relationship (SAR) shows that electron-withdrawing groups at C5 on the imidazole ring benefit potency and that oxygen-containing functional groups attached to a C5-sulfonyl or sulfonamide group further improve potency. This latter gain in potency is attributed to the interaction(s) of the functionalized sulfonyl/sulfonamide groups with the protein, likely polar-polar in nature, as suggested by SAR data. X-ray studies revealed that these bicyclic inhibitors bind to the I-domain of LFA-1 in a pattern similar to that of compound 1.
Nevirapine, used for the treatment of HIV infection, is associated with development of skin rash and liver toxicity. The mechanism of these idiosyncratic reactions is unknown. We have previously reported the discovery of a new animal model of nevirapine-induced skin rash in rats. When treated with nevirapine, Brown Norway rats developed red ears on about day 7 and skin rash on about day 21. On rechallenge, ears turn red within 24 h, and skin lesions develop by day 9. In the current study, we analyzed the time course of the sequence of events involved in the development of skin rash. Rats were treated with nevirapine for 7, 14, or 21 days or rechallenged with it for 0, 1, or 9 days. This treatment led to an increase in the total number of auricular lymph node T, B, and macrophage cells. There was also an increase in the activation/infiltration marker ICAM-1 and activation/antigen presentation marker MHC II in these cells compared with those from control rats. Immunohistochemistry analysis showed macrophage infiltration and ICAM-1 expression in the ears of treated rats as early as day 7 of treatment. Macrophage infiltration preceded T cell infiltration, which was not apparent until the onset of rash. Both MHC I and MHC II expression increased in the skin of nevirapine-treated rats that developed rash. A major inducer of MHC is IFNgamma. Although rechallenge with nevirapine led to a large increase in serum levels of IFNgamma, this was not observed during the treatment of naïve rats with nevirapine. These observations provide further clues to the mechanism of nevirapine-induced skin rash.
A novel carbazolyldiacetylene derivative of 5-[1,2]dithiolan-3-ylpentanoic acid 1,6-bis((N-carbazol-3-yl)methyl)-2,4-hexadiyne ester (DCHD-HS) was synthesized. DCHD-HS showed unusual fluorescence enhancement when it was bound to gold nanoparticles. The studies also showed that varied solvents and ratios of ligand/gold particles that served as the driving forces to control aggregation resulted in emission enhancement. A rational explanation for this phenomenon was discussed and elucidated.