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The development of a new fluorous-tagged ammonia-equivalent for the synthesis of N-alkylated amino acids is described. The required building blocks were readily accessed in high yield and purity using F-SPE purification technique. Coupling of the fluorous-tagged hydroxylamines with a selection of boronic acids and glyoxalic acid gave the desired N-alkylated amino acids. Subsequent removal of the fluorous tag via catalytic hydrogenation was investigated using a number of different catalysts and solvents. A more robust de-tagging procedure involves the transformation of the amino acid to the corresponding methyl ester followed by a Mo(CH3CN)3(CO)3 mediated N–O bond cleavage.

Positron emission tomography (PET) imaging of serotonin 2A (5-HT(2A)) receptors with agonist tracers holds promise for the selective labelling of 5-HT(2A) receptors in their high-affinity state. We have previously validated [(11)C]Cimbi-5 and found that it is a 5-HT(2A) receptor agonist PET tracer. In an attempt to further optimize the target-to-background binding ratio, we modified the chemical structure of the phenethylamine backbone and carbon-11 labelling site of [(11)C]Cimbi-5 in different ways. Here, we present the in vivo validation of nine novel 5-HT(2A) receptor agonist PET tracers in the pig brain.Each radiotracer was injected intravenously into anaesthetized Danish Landrace pigs, and the pigs were subsequently scanned for 90 min in a high-resolution research tomography scanner. To evaluate 5-HT(2A) receptor binding, cortical nondisplaceable binding potentials (BP(ND)) were calculated using the simplified reference tissue model with the cerebellum as a reference region.After intravenous injection, all compounds entered the brain and distributed preferentially into the cortical areas, in accordance with the known 5-HT(2A) receptor distribution. The largest target-to-background binding ratio was found for [(11)C]Cimbi-36 which also had a high brain uptake compared to its analogues. The cortical binding of [(11)C]Cimbi-36 was decreased by pretreatment with ketanserin, supporting 5-HT(2A) receptor selectivity in vivo. [(11)C]Cimbi-82 and [(11)C]Cimbi-21 showed lower cortical BP(ND), while [(11)C]Cimbi-27, [(11)C]Cimbi-29, [(11)C]Cimbi-31 and [(11)C]Cimbi-88 gave rise to cortical BP(ND) similar to that of [(11)C]Cimbi-5.[(11)C]Cimbi-36 is currently the most promising candidate for investigation of 5-HT(2A) receptor agonist binding in the living human brain with PET.

A new convenient three-step synthesis of the privileged CNS scaffold1,2,3,4,10,10a-hexahydropyrazino[1,2- A]indoleshas been developed. The method makes use of an intramolecular carbene-mediatedC-H insertion in phenylpiperazine-derived tosyl-hydrazonesmade from 2-fluorobenzaldehydes. Notably, the piperazine can bereplaced with other cyclic nitrogen bases and the methodology issuccessfully extended to pyrrolidine, piperidine, azepane, morpholine,and homopiperazine.

A novel direct, flexible, and robust approach to the iso-ergoline tetracyclic system in which a five or six-membered ring is established by intramolecular carbene C–H insertion is reported. The protocol involves a two step conversion of an aromatic aldehyde to the corresponding hydrazone and without purification further conversion to the diazo-compound followed by thermal carbene formation and C–H insertion α to a nitrogen.

The tautomeric composition of 4- and 5-hydroxy-1,2,3-triazoles in the gas phase has been investigated by comparison with the fragmentation of their fixed forms.

With emphasis on mono- and regio-selectively, methods for introduction of substituents at nitrogen and carbon atoms of 5-membered aza-heteroaromatics have been developed. The methods involve application of activation and of assistant groups for direction and protection. Activation has been achieved by the use of quaternary azolium ions and azol-N-oxides as reactive intermediates. If necessary, the N-oxides were further activated by alkylation or acylation.

A fluorous-tagged ammonia equivalent for the Cu-catalyzed amination of aryl iodides is described in which N-Boc-protected anilines are produced in high overall yield and purity. All purification steps are performed using Fluorous Solid-Phase Extraction (F-SPE) greatly simplifying and speeding up the isolation of the desired products.

Benzo[h]-1,6-naphthyridines and 5-ones, selectively functionalized at C-2, C-3, C-5 and C-10, were obtained by alkyllithium-, lithium amide- or potassium hydroxide-induced anionic cyclization of 3-cyano-2-(2-fluorophenyl)pyridine, which was functionalized regioselectively at positions 4, 5, 6, and 6′.

Introduction Several dopamine D 2 agonist radioligands have been used with positron emission tomography (PET), including [ 11 C-]-(−)-MNPA, [ 11 C-]-(−)-NPA and [ 11 C]-(+)-PHNO. These radioligands are considered particularly powerful for detection of endogenous dopamine release, but they either provide PET brain images with limited contrast or have affinity for both D 2 and D 3 receptors. We here present the carbon-11 radiolabeling and ex vivo evaluation of 2-Cl-(−)-NPA, a novel PET-tracer candidate with high in vitro D 2 /D 3 selectivity. Methods 2-Cl-[ 11 C]-(−)-NPA and [ 11 C]-(−)-NPA were synthesized by a two step N -acylation-reduction process using [ 11 C]-propionyl chloride. Awake rats were injected with either tracer, via the tail vein. The rats were decapitated at various times, the brains were removed and quickly dissected, and plasma metabolites were measured. Radioligand specificity, and P-glycoprotein involvement in brain uptake, was also assessed. Results 2-Cl-[ 11 C]-(−)-NPA and [ 11 C]-(−)-NPA were produced in high specific activity and purity. 2-Cl-[ 11 C]-(−)-NPA accumulated slower in the striatum than [ 11 C]-(−)-NPA, reaching maximum concentrations after 30 min. The maximal striatal uptake of 2-Cl-[ 11 C]-(−)-NPA (standard uptake value 0.72±0.24) was approximately half that of [ 11 C]-(−)-NPA (standard uptake value 1.37±0.18). Nonspecific uptake was similar for the two compounds. 2-Cl-[ 11 C]-(−)-NPA was metabolized quickly, leaving only 17% of the parent compound in the plasma after 30 min. The specific binding of 2-Cl-[ 11 C]-(−)-NPA was completely blocked and inhibition of P-glycoprotein did not alter the brain uptake. Conclusion Ex vivo experiments showed, despite a favorable D 2 /D 3 selectivity, that 2-Cl-[ 11 C]-(−)-NPA is inferior to [ 11 C]-(−)-NPA as a PET tracer in rat, because of slower brain uptake and lower specific to nonspecific binding ratio.

Oral absorption of tripeptides is generally mediated by the human intestinal di-/tri-peptide transporter, hPEPT1. However, the bioavailability of tripeptides is often limited due to degradation in the GI-tract by various peptidases. The aim of the present study was to evaluate the general application of N-methyl amide bioisosteres as peptide bond replacements in tripeptides in order to decrease degradation by peptidases and yet retain affinity for and transport via hPEPT1. Seven structurally diverse N-methyl amide tripeptidomimetics were selected based on a principal component analysis of structural properties of 6859 N-methyl amide tripeptidomimetics. In vitro extracellular degradation of the selected tripeptidomimetics as well as affinity for and transepithelial transport via hPEPT1 were investigated in Caco-2 cells. Decreased apparent degradation was observed for all tripeptidomimetics compared to the corresponding natural tripeptides. However, affinity for and transepithelial transport via hPEPT1 were only seen for Gly-Sar-Sar, AsnPsi[CONCH(3)]PhePsi[CONCH(3)]Trp, and Gly-Sar-Leu. This implies that tripeptidomimetics originating from tripeptides with neutral side chains are more likely to be substrates for hPEPT1 than tripeptidomimetics with charged side chains. The results of the present study indicate that the N-methyl amide peptide bond replacement approach for increasing bioavailability of tripeptidomimetic drug candidates is not generally applicable to all tripeptides. Nevertheless, retained affinity for and transport via hPEPT1 were shown for three of the evaluated N-methyl amide tripeptidomimetics.

2-Fluoronorapomorphine, the PET labelling precursor to 2-fluoro-N-[11C]propylnorapomorphine, was prepared in 13 steps from codeine in a total yield of 10 %. Codeine was converted in four steps into N-benzylnorcodeine which was oxidised by using the Swern protocol. Subsequent acid-catalysed rearrangement afforded N-benzylnormorphothebaine which was selectively triflylated at the 2-position and pivaloylated at the 11-position. The triflate underwent palladium-catalysed amination with benzophenone imine. Amination conditions required sequential base addition to give substantial conversion of the triflate to the corresponding N-substituted benzophenone imine. After acidic hydrolysis the resulting aniline was transformed into the 2-fluoro compound via the Balz–Schiemann reaction. Hydrogenolysis of the N-benzyl group followed by deprotection of the catechol moiety using BBr3 provided 2-fluoronorapomorphine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

A new and convergent synthesis of azaphenanthridines via an anionic ring closure is reported. Ortho -lithiation/in situ borylation of cyanopyridines produces the corresponding cyanopyridylboronic esters, which undergo a Suzuki–Miyaura cross-coupling to give the key intermediates. Addition of lithium morpholide produces the azaphenanthridines.

The intestinal di- and tripeptide transporter hPEPT1 is considered responsible for the absorption of di- and tripeptides arising from digestion, along with several drugs and prodrugs. In order to gather information on the binding site of the protein, several structure-affinity relationships have been suggested. However, these are not necessarily predictive of compounds that are actually translocated by hPEPT1. More information on affinity to and translocation via hPEPT1 of side-chain-modified dipeptides may be gained by conducting a study of selected dipeptide derivatives with variety in size, hydrophobicity, and bond type. The aim of the present study was to synthesize new esters and amides based on L-Glu-Sar and investigate the effects that bond type and size of modification of the N-terminal side chain of sarcosine-containing dipeptides have on the affinity to and translocation via hPEPT1. The esters L-Glu(O-i-Bu)-Sar and L-Glu(OCH(2)Ada)-Sar and the amides L-Gln(N,N-dimethyl)-Sar and L-Gln(N-piperidinyl)-Sar were synthesized, and affinity to and translocation via hPEPT1 were investigated in mature Caco-2 cell monolayers, grown on permeable supports. Affinity was estimated in a competition assay using (14)C-labeled Gly-Sar. Translocation was measured as fluorescence ratios induced by the substrates using the fluorescent probe BCECF and an epifluorescence microscope setup. All compounds showed high affinity to hPEPT1, but only the amides L-Gln(N,N-dimethyl)-Sar and L-Gln(N-piperidinyl)-Sar were translocated by hPEPT1. hPEPT1 is very susceptible to modifications of the N-terminal amino acid side chain of dipeptidomimetic substrates, in terms of achieving compounds with high affinity for the transporter. However, as affinity is not predictive of translocation, derivatization in this position must be performed with great caution since some of the compounds investigated turn out not to be translocated by the transporter.

The mucolytic agent bromhexine is useful in the evaluation of the performance of inductively coupled plasma mass spectrometry (ICP-MS) as compared to radiolabelling. A prerequisite for this comparison is access to radiolabelled bromhexine. [3H2]-bromhexine was synthesized in three steps introducing tritium in the final step by reduction of 2-amino-3,5-dibromo-N-methyl-N-cyclohexylbenzamide. Good chemical yields, high specific activity (54 Ci/mmol) and high radiochemical purity (98.5%) were achieved. Reduction with LiB3H4 in dichloromethane proved to be very efficient and easy to handle. Copyright © 2005 John Wiley & Sons, Ltd.

An enzymatically activated liposome-based drug-delivery concept involving masked antitumor ether lipids (AELs) has been investigated. This concept takes advantage of the cytotoxic properties of AEL drugs as well as the membrane permeability enhancing properties of these molecules, which can lead to enhanced drug diffusion into cells. Three prodrugs of AELs (proAELs) have been synthesized and four liposome systems, consisting of these proAELs, were investigated for enzymatic degradation by secretory phospholipase A(2) (sPLA(2)), resulting in the release of AELs. The three synthesized proAELs were (R)-1-O-hexadecyl-2-palmitoyl-sn-glycero-3-phosphocholine (1-O-DPPC), (R)-1-O-hexadecyl-2-palmitoyl-sn-glycero-3-phosphoethanolamine poly(ethylene glycol)(350) (1-O-DPPE-PEG(350)), and 1-O-DPPE-PEG(2000) of which 1-O-DPPC was the main liposome component. All three phospholipids were synthesized from the versatile starting material (R)-O-benzyl glycidol. A phosphorylation method, employing methyl dichlorophosphate, was developed and applied in the synthesis of two analogues of (R)-1-O-hexadecyl-2-palmitoyl-sn-glycero-3-phosphoethanolamine poly(ethylene glycol). Differential scanning calorimetry has been used to investigate the phase behavior of the lipid bilayers. A release study, employing calcein encapsulated in non-hydrolyzable 1,2-bis-O-octadecyl-sn-glycero-3-phosphocholine (D-O-SPC) liposomes, showed that proAELs, activated by sPLA(2), perturb membranes because of the detergent-like properties of the released hydrolysis products. A hemolysis investigation was conducted on human red blood cells, and the results demonstrate that proAEL liposomes display a very low hemotoxicity, which has been a major obstacle for using AELs in cancer therapy. The results suggest a possible way of combining a drug-delivery and prodrug concept in a single liposome system. Our investigation of the permeability-enhancing properties of the AEL molecules imply that by encapsulating conventional chemotherapeutic drugs, such as doxorubicin, in liposomes consisting of proAELs, an increased effect of the encapsulated drug might be achievable due to an enhanced transmembrane drug diffusion.

An efficient solid-phase protocol for the synthesis of substituted (5-biphenyltetrazolyl)-hydantoins and -thiohydantoins has been developed. Suzuki cross-coupling between resin-bound 2-(tetrazol-5-yl)-phenylborinane and 4-bromobenzaldehyde gave the corresponding tetrazolylbiphenyl aldehyde. Subsequent reductive amination using amino acid esters gave the pivotal resin bound amino acid esters which were transformed to hydantoins or thiohydantoins via two routes: (i) treatment with isocyanates or isothiocyanates or (ii) successive treatment with triphosgene and primary amines. Using molecular modeling, we were able to jump from L-692,429, a well known non-peptidyl growth hormone secretagogue (GHS), to biphenyltetrazolyl hydantoins, obtaining compounds with IC50 values below 600 nM after two iterative cycles only.

We have previously used homologation of (S)-glutamic acid (Glu) and Glu analogs as an approach to the design of selective ligands for different subtypes of Glu receptors. (RS)-2-Amino-3-(3-carboxy-5-methyl-4-isoxazolyl)propionic acid (ACPA), which is an isoxazole homolog of Glu, is a very potent agonist at the (RS)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) subgroup of Glu receptors and a moderately potent ligand for the kainic acid (KA) subgroup of Glu receptors. The enantiomers of ACPA were previously obtained by chiral HPLC resolution. Prompted by pharmacological interest in ACPA, we have now prepared the (S)- and (R)-enantiomers of ACPA by stereocontrolled syntheses using (1R,2R,5R)- and (1S,2S,5S)-2-hydroxy-3-pinanone, respectively, as chiral auxiliaries. Furthermore, the 5-ethyl analog of ACPA, Ethyl-ACPA, was synthesized, and (S)- and (R)-Ethyl-ACPA were also prepared using this method. The absolute configurations of (S)- and (R)-ACPA were established by X-ray crystallographic analysis of a protected (1S,2S,5S)-2-hydroxy-3-pinanone imine derivative of (R)-ACPA. The absolute stereochemistry of (S)- and (R)-Ethyl-ACPA was assigned on the basis of a comparison of their properties with those of the enantiomers of ACPA, employing elution order on chiral HPLC columns, as well as circular dichroism (CD) spectroscopy in combination with time-dependent density functional theory. The structural and electronic basis for the Cotton effect observed for such analogs is examined. The lower homolog of ACPA, (RS)-2-amino-2-(3-carboxy-5-methyl-4-isoxazolyl)acetic acid (1), which is a Glu analog, was also synthesized. Affinities and neuroexcitatory effects were determined using rat brain membranes and cortical wedges, respectively, at native AMPA, KA, and N-methyl-D-aspartic acid (NMDA) receptors. The molecular pharmacology of (S)- and (R)-ACPA and (S)- and (R)-Ethyl-ACPA was evaluated at homomeric cloned subtypes of AMPA receptors (iGluR1o,3o,4o) and of KA receptors (iGluR5,6), expressed in Xenopus laevis oocytes. The cloned receptors mGluR1α, mGluR2, and mGluR4a, expressed in CHO cell lines, were used to study the effects of the five compounds at metabotropic Glu receptors. In accordance with ligand–receptor complexes known from X-ray crystallography, the conformationally restricted Glu analog 1 was inactive at all Glu receptors studied, and the R-forms of ACPA and Ethyl-ACPA were very weak or inactive at these receptors. At AMPA receptor subtypes, (S)-ACPA and (S)-Ethyl-ACPA showed equally potent agonist effects at iGluR1o and iGluR3o, whereas (S)-Ethyl-ACPA was 6-fold more potent than (S)-ACPA at iGluR4o. (S)-ACPA and (S)-Ethyl-ACPA were approximately an order of magnitude less potent at iGluR5 than at AMPA receptor subtypes, and neither compound showed detectable effects at iGluR6. The binding mode of (S)-Ethyl-ACPA at iGluR2 was examined by docking to the (S)-ACPA–iGluR2 complex. Chirality 16:452–466, 2004. © 2004 Wiley-Liss, Inc.

A novel, mild method for the synthesis of di- and trisubstituted N-acyl ureas on solid support is described. Addition of carboxylic acids to a resin-bound carbimidoyl chloride gave, initially, an O-acyl isourea which subsequently rearranged to the corresponding N-acyl urea. Trisubstituted N-acyl ureas were assembled on a Wang resin from a wide range of Fmoc amino acids, secondary amines and carboxylic acids. Acid mediated cleavage yielded the products in good yields and excellent purities. In addition, the regioselective synthesis of disubstituted N-acyl ureas is demonstrated with four examples.

Addition–elimination reactions involving a nucleophile and a remote leaving group [SHN(AE)tele] are well-known under basic conditions, especially amongst electron-poor six-membered heterocycles, but are less commonly encountered for five-membered heterocycles and are rare under acidic conditions. Concentrated HCl converts 1-hydroxy-1H-pyrazolo[3,4-c] isoquinoline and 1-hydroxy-1H-pyrazolo[3,4-c]quinoline into 3-chloro-1H-pyrazolo[3,4-c]isoquinoline and 3-chloro-1H-pyrazolo[3,4-c]quinoline, respectively. However, apparently neither the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)-quinolines nor the parent 1-hydroxypyrazole undergo this reaction. Additionally, all these systems are refractory under basic conditions. We present a plausible mechanism for the reaction, involving the 3-addition of Cl- to the diprotonated heterocycle, followed by the elimination of water. Calculations of the initial transition states and intermediates, using optimisation at B3LYP/6-311+G(d,p), including thermochemistry [HF/6-31+G(d)], and single-point Poisson–Boltzmann self-consistent reaction field determination of the free energy of solvation (Jaguar Poisson–Boltzmann self-consistent reaction field), support this mechanism and reproduce the observed order of reactivity, the addition step being 2–4 kcal less favourable for the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)quinolines and provide a rationalisation for the role of strong acid.

Hapten derivatives of 1α,25-dihydroxyvitamin D3 and its 20-epimer were synthesized and conjugated to a carrier protein for raising polyclonal antibodies. The haptens were linked through spacers at C-16, thereby exposing both the A-ring and the side chain of the molecules, to maximize antibody specificity. The spacers were introduced via stereoselective hydroboration of 16-ene intermediates as the key step. In immunoassays, the antibodies raised toward the natural hormone were selective to this compound over derivatives with modifications in the A-ring or the side chain. The antibodies toward the 20-epimer, however, were unable to recognize modifications in the side chain.

The synthesis of a new class of azaxanthones is presented. The N–O functionality of 1-hydroxypyrazole and 1-hydroxy-1,2,3-triazole was used to direct metalation and subsequently incorporated in the new ring systems.

A series of novel α-amino acids containing the 1-hydroxypyrazole ring has been prepared by addition of organomagnesium or organolithium intermediates to diethyl N-Boc-iminomalonate as an electrophilic glycine equivalent. Electrophiles, aryl and heteroaryl substituents were introduced in the pyrazole ring.

A range of C-4 and C-5 acylated 1-benzyloxypyrazoles (7a–e) and (4) have been prepared via Pd(0) catalysed cross-coupling between acid chlorides and 1-benzyloxy-4-(tributylstannyl)pyrazole (8) or 1-benzyloxypyrazol-5-ylzinc chloride. 3-Acylated 2-(4-methoxybenzyl)-2H-pyrazole 1-oxides (15a–f) were formed by reaction between the 3-magnesiated 2H-pyrazole 1-oxide (14) and acid chlorides. The benzyl group of 4 and 7a and the 4-methoxybenzyl (PMB) group of 15a were removed by treatment with conc. HCl or TFA in the presence of water, furnishing the corresponding C-acylated 1-hydroxypyrazoles.

Sequential regioselective N-arylations through high-yielding catalyst-free direct SNAr reactions of pentafluorobenzene derivatives with azole or indole derivatives are described. The N-arylated derivatives were further functionalized through a microwave-assisted cross-coupling reaction via C–H bond activation or Suzuki conditions. The order of the reactions could be reversed, proving full orthogonality between the reactions which led to well-defined fully substituted benzene derivatives.

A number of 1-hydroxyazole derivatives were synthesized as bioisosteres of (S)-glutamic acid (Glu) and as analogues of the AMPA receptor agonist (R,S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA, 3b). All compounds were subjected to in vitro pharmacological studies, including a series of Glu receptor binding assays, uptake studies on native as well as cloned Glu uptake systems, and the electrophysiological rat cortical slice model. Compounds 7a,b, analogues of AMPA bearing a 1-hydroxy-5-pyrazolyl moiety as the distal carboxylic functionality, showed only moderate affinity for [3H]AMPA receptor binding sites (IC(50) = 2.7 +/- 0.4 microM and IC(50) = 2.6 +/- 0.6 microM, respectively), correlating with electrophysiological data from the rat cortical wedge model (EC(50) = 280 +/- 48 microM and EC(50) = 586 +/- 41 microM, respectively). 1-Hydroxy-1,2,3-triazol-5-yl analogues of AMPA, compounds 8a,b, showed high affinity for [3H]AMPA receptor binding sites (IC(50) = 0.15 +/- 0.03 microM and IC(50) = 0.13 +/- 0.02 microM, respectively). Electrophysiological data showed that compound 8a was devoid of activity in the rat cortical wedge model (EC(50) > 1000 microM), whereas the corresponding 4-methyl analogue 8b was a potent AMPA receptor agonist (EC(50) = 15 +/- 2 microM). In accordance with this disparity, compound 8a was found to inhibit synaptosomal [3H]D-aspartic acid uptake (IC(50) = 93 +/- 25 microM), as well as excitatory amino acid transporters (EAATs) EAAT1 (IC(50) = 100 +/- 30 microM) and EAAT2 (IC(50) = 300 +/- 80 microM). By contrast, compound 8b showed no appreciable affinity for Glu uptake sites, neither synaptosomal nor cloned. Compounds 9a-c and 10a,b, possessing 1-hydroxyimidazole as the terminal acidic function, were devoid of activity in all of the systems tested. Protolytic properties of compounds 7a,b, 8b, and 9b were determined by titration, and a correlation between the pK(a) values and the activity at AMPA receptors was apparent. Optimized structures of all the synthesized ligands were fitted to the known crystal structure of an AMPA-GluR2 construct. Where substantial reduction or abolition of affinity at AMPA receptors was observed, this could be rationalized on the basis of the ability of the ligand to fit the construct. The results presented in this article point to the utility of 1-hydroxypyrazole and 1,2,3-hydroxytriazole as bioisosteres of carboxylic acids at Glu receptors and transporters. None of the compounds showed significant activity at metabotropic Glu receptors.

Electrophiles were introduced regioselectively at the 5-position of 1-(benzyloxy)imidazole by lithiation at C-5 after protection of C-2 with a chloro or a trimethylsilyl group. Subsequent treatment with an electrophile afforded 5-substituted 1-(benzyloxy)-2-chloroimidazoles 8-13 and 5-substituted 1-(benzyloxy)imidazoles 3-5, the 2-(trimethylsilyl) group being lost during workup. Electrophiles were introduced regioselectively at the 4-position of 1-(benzyloxy)imidazole by bromine-lithium exchange of 4-bromo-2-chloro-1-(benzyloxy)imidazoles, protected at C-5 with chloro or trimethylsilyl groups, followed by reaction with an electrophile. The 5-(trimethylsilyl) group was removed via base-catalyzed desilylation. Chlorine at C-2 and O-benzyl groups were removed by palladium-catalyzed hydrogenolysis.

The prevalence of allergic airway diseases is rapidly increasing in Western Europe and North America. This increase in disease prevalence may be associated with environmental pollutants. The present study investigated the adjuvant and immuno-suppressive effect of a series of monophthalates which are considered to be important metabolites of commonly used phthalate plasticizers. The effects were studied in a screening model. Ovalbumin (OA), used as the model antigen, was injected subcutaneously in the neck region of BALB/cJ mice with or without one of the test substances, mono-n-butyl phthalate (MnBP), monobenzyl phthalate (MBnP), mono-n-octyl phthalate (MnOP), mono-2-ethylhexyl phthalate (MEHP), mono-iso-nonyl phthalate (MiNP) or mono-iso-decyl phthalate (MiDP). The levels of OA-specific IgE, IgG1 and IgG2a in sera were measured by ELISA. Immuno-suppressive effect, defined as a statistically significant reduction in IgE or IgG1 antibody production, was observed with MEHP (1000 microg/ml, IgE and IgG1), MnOP (1000 microg/ml, IgE and IgG1), MiNP (1000 microg/ml, IgE and 10 microg/ml, IgG1) and MiDP (100 microg/ml, IgE and IgG1). Adjuvant effect, defined as a statistically significant increase in IgE or IgG1 antibody level, occurred with MEHP (10 microg/ml, IgE), MnOP (100 microg/ml, and 10 microg/ml, IgG1) and MiNP (100 microg/ml, IgE). No statistically significant immune modulating effect was seen with MBnP and MnBP.

Transport across the intestinal barrier of compounds with low permeability may be facilitated by targeting the human oligopeptide transporter, hPepT1. A flexible synthetic pathway for attaching compounds to dipeptides through ester or amide bonds was developed. Furthermore, a synthetic approach to functionalize model drugs from one key intermediate was generated and applied to a glucose-6-phosphatase active model drug. The model drug was coupled to D-Glu-Ala through various linkers, and the G-6-Pase activity as well as the aqueous solubility and transport properties of these prodrugs, as compared to those of the parent drugs, were examined. None of the peptide-coupled compounds seemed to be transported by hPepT1, though one of the peptide-coupled compounds had affinity for hPepT1. Interestingly, in one case the parent drug was actively effluxed, while the corresponding peptide-coupled prodrug was not. The low aqueous solubility of the parent compounds was not increased after attachment to a dipeptide. This suggests that only compounds with a certain intrinsic aqueous solubility should be targeted to hPepT1 by attachment to a dipeptide. Important information about the design of peptide-coupled drugs targeted for hPepT1 is presented.

4-Substituted pyrazolo[4,3-c]quinolines 4a−i and 6a−b were prepared from pyrazole 3 whereas 9-substituted pyrazolo[3,4-c]quinolines 9a−d and 17 were prepared from pyrazole 13 utilizing anionic annelation techniques. 1,4-Dihydrochromeno[4,3-c]pyrazoles 7a−c were accessed from pyrazole 3, extending the method for the synthesis of 4a−i.

An efficient solid-phase synthesis of phthalides is described in which aromatic carboxylic acids or acid chlorides and ketones are used as building blocks. The carboxylic acid or acid chloride is tethered to aminomethylated polystyrene resin, forming a secondary amide, which functions as both the linker and the directing metalation group. This allows the resin-bound benzamides to be ortho-lithiated at 0 degrees C. The ortho-lithiated species can be quenched with benzaldehydes, benzophenones, and even acetophenones, affording resin-bound alcohols. A cyclative cleavage is induced by simply warming the resin in toluene or dioxane, yielding the desired phthalide compounds in exceptionally high purity.

A study of a series of compounds with agonistic effect at the alpha4beta2 nicotinic acetylcholine receptors resulted in an improved pharmacophore model as well as a CoMFA model. The pharmacophore was composed of three pharmacophoric elements: (1) a site point (a) corresponding to a protonated nitrogen atom, (2) a site point (b) corresponding to an electronegative atom capable of forming a hydrogen bond, and (3) the centre of a heteroaromatic ring or a C=O bond (c). The pharmacophoric elements were related by the following parameters: (a-b) 7.3-8.0 A, (a-c) 6.5-7.4 A, and the angle between the two distance vectors (delta bac) 30.4-35.8 degrees. In addition to this, a stereoselective CoMFA model was developed, which showed good predictability even for compound classes not present in the training set.

The Peterson reaction between a series of 2-substituted 1-azabicyclo[2.2.2]octan-3-ones and 3-methyl-5-trimethylsilanylmethyl isoxazole (1) was explored. (Z)-Stereoselectivity was obtained with all 2-substituents, ranging from 65:35 for benzyl to 95:5 for phenylsulphanyl. Different bases were investigated, revealing that an organolithium base is necessary for the reaction to occur. A transition state is suggested, involving a four-membered ring in which the lithium ion is covalently bound α to the silyl-group and chelated to the carbonyl oxygen.

A series of (isoxazole)methylene-1-azacyclic compounds was prepared. The compounds were tested for affinity to central nicotinic acetylcholine receptors (nAChRs) and central muscarinic receptors. The compounds covered a broad range of affinities for the nAChRs (IC(50) = 0.32 to >1000 nM), with selectivities for the nAChRs over the muscarinic receptors in the range of 3-183. The high-affinity compound (Z)-26 (3-(4-methyl-5-isoxazolyl)methylene-1-azabicyclo[2.2. 2]octane, IC(50) = 3.2 nM) having only one energy minimum was used as the reference structure in a computational study. This ligand has enabled definition of an important distance parameter, and the existence of this parameter was supported by showing that other potent nicotinic ligands (for example, nicotine and epibatidine) fit the model.

Two protocols for introduction of electrophiles at the 4-position of 1-hydroxypyrazoles have been developed. The first is deprotonation of 4-bromo-1-[(tert-butyldiphenylsilyl)oxy]pyrazole (6) with LDA to produce the 5-lithio derivative in which the silyl group migrates spontaneously from oxygen to C-5 affording 4-bromo-5-(tert-butyldiphenylsilyl)-1-lithoxypyrazole (8). Subsequent treatment with t-BuLi causes bromine-lithium exchange to give 5-tert-butyldiphenylsilyl-4-lithio-1-lithoxypyrazole which is trapped with electrophiles affording 4-substituted 5-(tert-butyldiphenylsilyl)-1-hydroxypyrazoles 9a-e in a one-pot sequence. The second is treatment of 4-bromo-1-hydroxypyrazole (5) with excess LDA and trimethylsilyl chloride to produce 3,5-bis(trimethylsilyl)-4-bromo-1-hydroxypyrazole (12), which upon sequential metalation with n-BuLi and reaction with electrophiles affords 4-substituted 3,5-bis(trimethylsilyl)-1-hydroxypyrazoles 13a-e. The tert-butyldiphenylsilyl group of 9a and the trimethylsilyl groups of 12 can be removed selectively by treatment with tetrabutylammonium fluoride in THF in the presence of trifluoroacetic acid.

The readily available S-(tert-butyl)-N-(trimethylsilyl)-S-phenylsulfoximine was prepared from S-methyl-N-(trimethylsilyl)-S-phenylsulfoximine via lithiation-methylation sequences. The reaction with n-butyllithium in THF at −78°C afforded the corresponding ortho-lithiated species which could be trapped with different electrophiles in good yields. Addition of benzaldehyde proceeded with a modest diastereoselectivity (de=52%).

The 13C chemical shifts and C–H coupling constants of a series of imidazole 1-oxides were compared with those of the parent imidazoles and imidazolium salts in order to show the influence of N-oxidation on these parameters. The 13C chemical shifts can be related to the electron density at the carbon atoms whereas long range C–H coupling constants can be related to the relative localization or delocalization of the π system in imidazoles, imidazolium salts and imidazole N-oxides. ©1998 John Wiley & Sons, Ltd.

Six new derivatives of 1-hydroxy-1,2,3-triazole (1-hydroxytriazole in the following) and N-hydroxytetrazole have been evaluated in a direct competition assay to investigate their efficiency as catalysts in the formation of peptide bonds. Furthermore, three well known catalysts, 1-hydroxy-7-azabenzotriazole (HOAt), 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (Dhbt-OH) and 1-hydroxybenzotriazole (HOBt) have been compared. All nine compounds have been used for activation in combination with N,N′-diisopropylcarbodiimide (DIPCDI) in solid-phase synthesis using the fluoren-9-ylmethoxycarbonyl (Fmoc) strategy. The capability of the catalysts to suppress racemization has also been analysed. The results demonstrate that three of the new compounds are competitive with HOAt and HOBt in the suppression of racemization. 5-Chloro-1-hydroxytriazole is found to be a highly efficient acylation catalyst; however, it does not show sufficient suppression of racemization. Its catalytic effect in the synthesis of Aib–Aib-containing peptides is superior to that of HOAt. Also, 2-hydroxytetrazole has a catalytic efficiency superior to that of HOAt and suppressed racemization as efficiently as HOBt. The hydroxytetrazoles are explosive in a hammer test whereas the triazoles are stable compounds.

1-(Benzyloxy)-1,2,3-triazole, prepared by selective benzylation of 1-hydroxy-1,2,3-triazole or by oxidative cyclization of 2-hydrazonoglyoxal O-benzyloxime, was metalated exclusively at the 5-position upon treatment with n-butyllithium. The anion formed reacted with a series of electrophiles. In this way carbon, halogen, sulfur, silicon, and tin substituents could be introduced at the 5-position. Subsequent removal of the benzyl group by palladium-catalyzed hydrogenolysis or by treatment with hydrochloric acid afforded the corresponding 5-substituted 1-hydroxy-1,2,3-triazoles.

Enol phosphates, synthesized from 4-piperidone, react by palladium catalyzed cross-coupling with arylboronic acids and by iron and palladium catalyzed cross-coupling with Grignard reagents to give 4-substituted tetrahydropyridines.

The crystal and molecular structure of meso -tetrakis 1-[2-(trimethylsilyl) ethoxymethyl]pyrazol-5-yl porphyrin 2 has been solved by X-ray analysis. The porphyrin core appears to be distorted from planarity and the conformation of the pyrazole rings is such that pyrazole N 2 atoms are situated up, up, down, down with regard to the macrocyclic ring (ααββ atropisomer). A new porphyrin meso -tetrakis[1-benzyloxy-3-methylpyrazol-5-yl]-porphyrin 3 has been obtained from 1-benzyloxy-5-formylpyrazole. Zn(II) and Co(III) complexes of meso -tetrakis-(1-benzylpyrazol-4-yl)porphyrin 1 have been prepared and characterized by MS, NMR and UV.

Various hemiesters of aliphatic dicarboxylic acids and paracetamol or phenol were prepared and assessed as potential prodrug forms with the aim of protecting phenolic drugs against first-pass metabolism after peroral administration. The degradation of the hemiesters was studied in aqueous buffer solutions and in various biological media. In buffer solutions the derivatives degraded via an intramolecular ring-closure reaction in addition to acid- or base-catalyzed ester hydrolysis. At physiological pH (7.4) the intramolecular ring-closure reaction is the major reaction contributing to the overall degradation and half-lives in the range of 1–350 min at pH 7.4 and 37°C were determined for the studied derivatives. The half-lives depended upon the degree of substitution in the acid moiety, the size of the formed anhydride and the p K a value of the patent phenol. Liver homogenates clearly catalyzed the degradation of the hemiesters, whereas plasma showed different results for the esters of paracetamol and phenol, respectively. The only derivative not subjected to any enzymatic catalysis was the hemi-3,3-dimethylglutarate of paracetamol. Although highly substituted hemiesters might be useful prodrugs for certain individual phenolic drugs, derivatization of phenolic drugs into hemiesters may not be a generally useful prodrug approach for protection against first-pass metabolism, due to the fact that the derivatives are subjected to marked enzymatic catalysis in liver homogenates.