C2 Substituent Research Articles

Unusual Stabilization of 1,2‐Diamino Derivatives of Quincorine and Quincoridine by Carbon Dioxide: Persistent Crystalline prim‐Ammonium‐Carbamate Salts and Their Reactivity towards Isatoic Acid Anhydride

AbstractThe reaction of N‐methylisatoic anhydride 1 with a series of quincorine (QCI) and quincoridine (QCD) derivatives furnished the corresponding QCI‐ and QCD‐substituted anthranilic acid amides 4−9. In the synthesis of 4−9, we investigated the influence of the C5 substituent of 2‐aminomethyl derivatives of QCI and QCD on their basicity and polarity and, therefore, on their reactivity towards isatoic acid anhydride. By exposing a number of 2‐aminomethyl derivatives of QCI and QCD to (carbon dioxide from) air, the formation of carbon dioxide adducts 10−15 was observed. In an unusual reaction, we obtained the first set of chiral ammonium carbamates derived from primary amines, which provides a convenient method for purifying and stabilizing aminomethyl derivatives of QCI and QCD. All compounds were fully characterized by spectroscopic methods. In addition, the structure of 11 was proved by X‐ray crystal structure determination. The heterocyclic nitrogen atoms display trigonal‐pyramidal coordination geometries; the amido group is essentially planar. N‐2′ of the ammonium ion is a triple hydrogen bond donor to the carboxylato oxygen atoms of three different carbamate anions. The resulting net effect is a hydrophilic plane parallel to the ab plane. The crystal packing involves six classical hydrogen bonds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Ultrahigh Resolution Structure of a Class A β-Lactamase: On the Mechanism and Specificity of the Extended-spectrum SHV-2 Enzyme

Bacterial β-lactamases hydrolyze β-lactam antibiotics such as penicillins and cephalosporins. The TEM-type class A β-lactamase SHV-2 is a natural variant that exhibits activity against third-generation cephalosporins normally resistant to hydrolysis by class A enzymes. SHV-2 contains a single Gly238Ser change relative to the wild-type enzyme SHV-1. Crystallographic refinement of a model including hydrogen atoms gave R and Rfree of 12.4% and 15.0% for data to 0.91Å resolution. The hydrogen atom on the Oγ atom of the reactive Ser70 is clearly seen for the first time, bridging to the water molecule activated by Glu166. Though hydrogen atoms on the nearby Lys73 are not seen, this observation of the Ser70 hydrogen atom and the hydrogen bonding pattern around Lys73 indicate that Lys73 is protonated. These findings support a role for the Glu166–water couple, rather than Lys73, as the general base in the deprotonation of Ser70 in the acylation process of class A β-lactamases. Overlay of SHV-2 with SHV-1 shows a significant 1–3Å displacement in the 238–242 β-strand-turn segment, making the β-lactam binding site more open to newer cephalosporins with large C7 substituents and thereby expanding the substrate spectrum of the variant enzyme. The OH group of the buried Ser238 side-chain hydrogen bonds to the main-chain CO of Asn170 on the Ω loop, that is unaltered in position relative to SHV-1. This structural role for Ser238 in protein–protein binding makes less likely its hydrogen bonding to oximino cephalosporins such as cefotaxime or ceftazidime.

Synthesis and Biological Evaluation of 6‐Bromo‐6‐Substituted Penicillanic Acid Derivatives as β‐Lactamase Inhibitors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Iron-mediated preparation of vinylcyclopropanecarboxylates: scope, mechanism, and applications.

The addition of stabilized carbon nucleophiles to tricarbonyl(1-methoxycarbonylpentadienyl)iron(1+) cation (1a) proceeds via attack at C2 on the face of the ligand opposite the Fe(CO)(3) group to generate tricarbonyl(pentenediyl)iron complexes 2. Oxidation of complexes 2 affords vinylcyclopropanecarboxylates in good yield. In general, the relative stereochemistry about the cyclopropane ring reflects reductive elimination with retention of configuration. In cases where the C2 substituent is bulky (i.e., 2b) the major cyclopropane product 9b represents ring closure with inversion at C3. A mechanism involving pi-sigma-pi rearrangement of the initially oxidized (pentenediyl)iron species is proposed to account for these results. Experiments which probe the stereochemistry of deuterium labeling in the vinyl group of the vinylcyclopropanecarboxylate products were carried out, and these results are consistent with the proposed mechanism. This methodology for the preparation of vinylcyclopropanecarboxylates was applied to the synthesis of 2-(2'-carboxycyclopropyl)glycines (+)-22 and (-)-23 and the cyclopropane triester (-)-26.

1137 Assessment of the diagnostic scale for drug induced liver injury (DILI) by the International Consensus Meeting (ICM) and a proposal of its modifications

Several barbiturates and primidone were equilibrated with polyethylene glycol 4000 in pyridine. IR spectral properties of these samples indicate that seven disubstituted barbiturates complex with polyethylene glycol 4000 while five disubstituted barbiturates and two trisubstituted barbiturates as well as primidone do not. Forces responsible for complexation of barbiturates with polyethylene glycol 4000, as inferred from spectral data, consist of hydrogen bonds formed between N1 and N3 hydrogens of the barbiturate ring and two oxygen atoms of the —O—CH2CH2—O—moiety. Also, there appear to be three configurations of intermolecular hydrogen bonding sites between disubstituted barbiturates. Several factors affect the barbiturate-polyethylene glycol 4000 interaction, including the nature of the solvent, C5 substituents, the number of hydrogen bonds formed between reactants, and the 2-carbonyl group of the barbiturate ring. Complexes of polyethylene glycol 4000 with phenobarbital, butabarbital, and cyclobarbital are stable in water at 26° or below, but complexes of polyethylene glycol 4000 with butethal, cyclopentenyl allylbarbituric acid, pento barbital, and probarbital are not.

Crystal and molecular structures of 4-aryl-1,4-dihydropyrimidines: Novel calcium channel antagonists

Abstract The solid-state structures of three calcium channel antagonists viz. 1,4-dihydro-6-methyl-5-N-methyl-carbamoyl-4-(3′,4′-dichlorophenyl)-2(3 H)-pyrimidinethione, C13H13N3OSCl2 (1); 1,4-dihydro-6-methyl-5-N-methyl-carbamoyl-4-(4′-methoxyphenyl)-2(3 H)-pyrimidinethione, C14H17N3O2S (2) and 1,4-dihydro-6-methyl-5-N-methyl-carbamoyl-4-(2′,4′-dichlorophenyl)-2(3 H)-pyrimidineone monohydrate, C13H13N3O2Cl2·H2O (3), are reported here. The structures show that these compounds can adopt the important structural features of 1,4-dihydropyridine calcium channel blockers. In (2), the compound crystallized with three molecules in the asymmetric unit. The dihydropyrimidine ring adopts a half-chair in (1) and boat conformation in (2) and (3). The 4-aryl substituents occupies a pseudo-axial position approximately orthogonal to the plane of the dihydropyrimidine ring [95.1(2)° (1); 97.5(3)°, 79.8(2)° & 88.2(2)° (2) and 78.8(3)° (3)]. The C3 substituent, carbamoyl group, is in an extended conformation and oriented anticlinical in (1) and (3), but in (2) two molecules are anticlinal and the other one is synperiplanar, respectively. Intra- and inter- molecular interactions may be influencing the orientation of the C3 carbamoyl group. The 2-chlorophenyl substituent in (3) is in the axial synperiplanar orientation.

Microencapsulated methylrhenium trioxide (MTO)/H2O2 systems for the oxidation of cardanol derivatives

Abstract A convenient and efficient application of microencapsulated/methylrhenium trioxide (MTO) and MTO/pyridine systems for the selective oxidation of cardanol derivatives is reported. Environmentally friendly and low-cost H2O2 was used as the oxygen atom donor. The catalysts were stable systems for at least five recycling experiments. In the oxidation of C2 alkyl-substituted cardanol derivatives, high conversion and yields of the corresponding para-benzoquinones were obtained. By contrast, in the absence of the C2 substituent, an unprecedented oxidative degradation to di-γ-lactone derivative was observed.

N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A) interaction with LYS 3.28(192) is crucial for its inverse agonism at the cannabinoid CB1 receptor.

In superior cervical ganglion neurons, N-(piperidiny-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A) competitively antagonizes the Ca(2+) current effect of the cannabinoid (CB) agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN55212-2), and behaves as an inverse agonist by producing opposite current effects when applied alone. In contrast, in neurons expressing CB1 with a K-->A mutation at residue 3.28(192) (i.e., K3.28A), SR141716A competitively antagonizes the effects of WIN55212-2, but behaves as a neutral antagonist by producing no current effects itself. Receptor modeling studies suggested that in the CB1 inactive (R) state, SR1417A16A stabilizes transmembrane helix 6 in its inactive conformation via aromatic stacking with F3.36/W6.48. In this binding site, SR141716A would exhibit higher affinity for CB1 R due to a hydrogen bond between the SR141716A C3 substituent and K3.28(192), a residue available to SR141716A only in R. To test this hypothesis, a "mutant thermodynamic cycle" was constructed that combined the evaluation of SR141716A affinity at WT CB1 and K3.28A with an evaluation of the wild-type CB1 and K3.28A affinities of an SR141716A analog, 5-(4-chlorophenyl)-3-[(E)-2-cyclohexylethenyl]-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole (VCHSR), that lacks hydrogen bonding potential at C3. Binding affinities suggested that K3.28 is involved in a strong interaction with SR141716A in WT CB1, but does not interact with VCHSR. Thermodynamic cycle calculations indicated that a direct interaction occurs between the C3 substituent of SR141716A and K3.28 in WT CB1. Consistent with these results, VCHSR acted as a neutral antagonist at WT CB1. These results support the hypothesis that hydrogen bonding of the SR141716A C3 substituent with K3.28 is responsible for its higher affinity for the inactive R state, leading to its inverse agonism.

Photoelectron spectra and electronic structure of some diastereomeric quinuclidine derivatives.

The molecular and electronic structure of three pairs of diastereomeric quinuclidine derivatives (1-6) have been investigated by quantum chemical calculations and UV photoelectron (PE) spectroscopy. Compounds 1-6 each possess a hydroxymethyl group at C2 and an ethyl (1, 2), vinyl (3, 4) or ethynyl group (5, 6) at C5. The diastereomeric pairs differ only in the configuration of carbon C2 to which the hydroxymethyl group is attached. The 1-azabicyclo[2.2.2]octane cages of 1-6 are slightly twisted. The torsion angles show opposite signs in the pseudoenantiomeric pairs and vary only little with the degree of unsaturation in the C5 substituent. In all compounds the hydroxymethyl group forms an intramolecular hydrogen bond with the nitrogen atom of the bicycle in the gas phase (in contrast to the crystalline and liquid state). The PE spectra of the diastereomers are nearly identical. Compared to unsubstituted quinuclidine, the orbital of the nitrogen lone pair electrons n(N) is stabilized by 0.3-0.4 eV, which is a result of partially compensating contributions of the OH...N hydrogen bond and substituent effects. Among these a substantial through-bond interaction of the n(N) with a pi(CC) orbital is detected for 3-6. The marked differences of the properties of 1-6 in the gas phase versus solid state and solution are emphasised. In solution the ethynyl azabicyclics 5 and 6 are more polar than the vinyl analogues 3 and 4.

New hydrogenated and didehydrogenated 1,2-diamines of quincorine and quincoridine

Four new members of the family of 1,2-diamines of quincorine and quincoridine have been synthesized, being hydrogenated and didehydrogenated at the C10–C11 fragment. The alkynes, containing an additional amino group at C9, are potentially useful building blocks for cross-coupling reactions. Additional investigations concerning the chemical properties of the molecules point to a significant impact of the remote C5 substituent on the basicity of the bridgehead nitrogen.

Synthesis and biological evaluation of 6-bromo-6-substituted penicillanic acid derivatives as β-lactamase inhibitors

The synthesis of a selected set of 6-bromopenicillanic acid derivatives with an additional C6 substituent is reported. All these substances were tested as inhibitors of class A and C β-lactamase enzymes derived from Escherichia coli (TEM-1) and E. cloacae (P99). As 6-(1-hydroxyethyl) derivatives 4c and 6c were found to be weak β-lactamase inhibitors, they were further investigated in combination with amoxicillin against a series of β-lactamase-producing bacterial strains. Some structure-activity relationships are discussed.

Cephalosporin-derived inhibitors of β-Lactamase. Part 4: The C3 substituent

New C3-substituted β-lactamase inhibitors were prepared and evaluated against representative class A and class C enzymes. It was possible to improve simultaneous inhibitory activity of both classes of serine hydrolase. Other inhibitors showed high selectivity for either the class C cephalosporinases or the class A penicillinases. This represents the first time that cephalosporin-derived inhibitors have demonstrated selectivity for the class A β-lactamases.

Antiproliferative effect of plant cytokinin analogues with an inhibitory activity on cyclin-dependent kinases.

In this study, analogues of olomoucine, a previously described plant cytokinin analogue with cyclin-dependent kinase (CDK) inhibitory activity, were investigated for effect on CDK1 and CDK2 and for effect on cell proliferation. Eight new compounds exhibit stronger inhibitory activity on CDK1 and CDK2 and on cell proliferation than olomoucine. Some active compounds showed low inhibition of proliferation of normal myeloid growth. Improvement of inhibitory activity of known compounds with a C6-benzylamino group was brought about by substitution with one hydroxyl. Also, new C2 substituents associated with inhibitory activity on CDK and on cell proliferation are described. There was a significant correlation between effect on CDK and antiproliferative effect on the KG1 and Molt3 cell lines and on primary human lymphocytes, strongly suggesting that at least part of the antiproliferative effect of cytokinin analogues was due to inhibition of CDK activity. Cytokinin analogues induced apoptosis in a time- and concentration-dependent manner and changes in cell cycle distribution. The antiproliferative and pro-apoptotic effects of plant cytokinin analogues suggest that they are a new class of cytostatic agents and that they may find an application in the chemotherapy of cancer.

Molecular interaction of the antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1- (2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide with the CB1 cannabinoid receptor.

N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716; 1) is a potent and selective antagonist for the CB1 cannabinoid receptor. Using the AM1 molecular orbital method, conformational analysis of 1 around the pyrazole C3 substituent identified four distinct conformations designated Tg, Ts, Cg, and Cs. The energetic stability of these conformers followed the order Tg > Cg > Ts > Cs for the neutral (unprotonated) form of 1 and Ts > Tg > Cs > Cg for its piperidine N-protonated form. Unified pharmacophore models for the CB1 receptor ligands were developed by incorporating the protonated form of 1 into the superimposition model for the cannabinoid agonists 4-[4-(1,1-dimethylheptyl)-2-hydroxyphenyl]perhydro-2alpha,6beta-dihydroxynaphthalene (CP55244; 2) and the protonated form of (R)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl](1-naphthalenyl)methanone (WIN55212-2; 3) reported previously (Shim et al. In Rational Drug Design Symposium Series; Parrill, A. L., Reddy, M. R., Eds.; American Chemical Society: Washington, DC, 1999; pp 165-184). Values of K(i) for 1 and a series of 31 structural analogues were determined from radioligand binding analyses by competitive displacement of [3H]CP55940 from cannabinoid receptors in a rat brain membrane preparation. Comparative molecular field analysis (CoMFA) was employed to construct three-dimensional (3D)-quantitative structure-activity relationship (QSAR) models for this data set as unprotonated species assuming the Tg, Cg, and Ts conformers and for the protonated species assuming the Ts, Tg, and Cs conformers. Values of the conventional r2 and cross-validated r2 (r(cv)2) associated with these CoMFA models exceeded the threshold for statistical robustness (r2 > or = 0.90) and internal predictive ability (r(cv)2 > or = 0.50) in each of these six cases except for the protonated species assuming the Tg conformer (i.e., r2 = 0.97; r(cv)2 = 0.36). Results from conformational analyses, superimposition models, and 3D-QSAR models suggest that the N1 aromatic ring moiety of 1 dominates the steric binding interaction with the receptor in much the same way as does the C3 alkyl side chain of cannabinoid agonists and the C3 aroyl ring of the aminoalkylindole agonists. We also determined that several of the conformers considered in this study possess the proper spatial orientation and distinct electrostatic character to bind to the CB1 receptor. We propose that the unique region in space occupied by the C5 aromatic ring of 1 might contribute to conferring antagonist activity. We further propose that the pyrazole C3 substituent of 1 might contribute to conferring either neutral antagonist or inverse agonist activity, depending upon the interaction with the receptor.

Synthesis and calcium channel antagonist activity of nifedipine analogues with methylthioimidazole substituent

Various diester analogues of nifedipine, in which the orthonitrophenyl group at position 4 is replaced by 1-methyl-2-methylthio-5-imidazolyl substituent, were synthesized and evaluated as calcium channel antagonists on guinea-pig ileal smooth muscle. Nifedipine was used as standard. Comparison of the activities of symmetrical esters ( 3a– e) indicate that increasing the length of alkyl chain in C3 and C5 ester substituents increases the antagonist activity and the n-propyl ester being preferred (IC 50=2.66×10 −9 M). In asymmetrical series ( 6a– g), compound 6g having ethyl and n-butyl ester at C3 and C5 positions of basic dihydropyridine structure was found to be the most active (IC 50=1.32×10 −9 M).

A theoretical study on the influence of the frontier orbitals HOMO and LUMO and the size of C4 and C2 substituents in the psychoactivity of cannabinoid compounds

A theoretical study on the influence of the frontier orbitals HOMO and LUMO and on substitutions at the C4 and C2 regions, with known psychoactive and psychoinactive cannabinoid molecules, showed that the size (volume) of C4 substituents may have an important role to explain the presence or absence of psychoactivity in cannabinoid compounds. The calculated E LUMO values showed that this descriptor could be important for the separation between the psychoactive and psychoinactive compounds only when there is no substitution at the C4 position. The results indicate that there is a relationship between the volume of the C4 substituent and the activity of the compound. C4 substituents with a volume bigger than 83 Å 3 will always cause psychoinactivity.

POTENTIAL ENERGY SURFACES OF α-(1→3)-LINKED DISACCHARIDES CALCULATED WITH THE MM3 FORCE-FIELD

The adiabatic conformational surfaces of sixteen 4′,6′,6-trideoxy-α-d-(1→3)-linked disaccharides were obtained using the MM3 force-field at two different dielectric constants. Calculations were carried out on disaccharides with different configurations at C2, C4 and C2′, which are neighbors to the glycosidic linkage, as well as that of the linked carbon (C3). The resulting maps were similar, indicating that the substituents do not play a major role in the conformational features of these disaccharides. However, the preferred minimum conformation and the flexibility were found to be slightly dependant on the configurations of the carbons. Although equatorial bonds and vicinal axial substituents tend to increase the overall flexibility, it was found that these factors can have a cross over effect; i.e., an axial hydroxyl group on C2 may decrease the flexibility if the glycosyl group on C3 is also axial. The relative stabilities of the minimal energy conformations of the 16 compounds also show deviations of the predicted increased stabilities of equatorially substituted compounds over axially substituted ones: these deviations occur mainly for the C2 substituent.

Purification, characterization, and steady-state kinetics of a meta-cleavage compound hydrolase from Pseudomonas fluorescens IPO1

2-Hydroxy-6-oxo-7-methylocta-2,4-dienoate (6-isopropyl-HODA) hydrolase (CumD), an enzyme of the cumene biodegradation pathway encoded by the cumD gene of Pseudomonas fluorescens IP01, was purified to homogeneity from an overexpressing Escherichia coli strain. SDS-polyacrylamide gel electrophoresis and gel filtration demonstrated that it is a dimeric enzyme with a subunit molecular mass of 32 kDa. The pH optima for activity and stability were 8.0 and 7.0–9.0, respectively. The enzyme exhibited a biphasic Arrhenius plot of catalysis with two characteristic energies of activation with a break point at 20°C. The enzyme has a K m of 7.3 μM and a k cat of 21 s −1 for 6-isopropyl-HODA (150 mM phosphate, pH 7.5, 25°C), and its substrate specificity covers larger C6 substituents compared with another monoalkylbenzene hydrolase, TodR Unlike TodF, CumD could slightly hydrolyze 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate (6-phenyl-HODA). A mutant enzyme as to a putative active site residue, S103A, had 10 5-fold lower activity than that of the wild-type enzyme.

A versatile synthesis of substituted benzimidazolium salts by an amination/ring closure sequence.

[reaction: see text]. A new method to produce benzimidazolium salts based on a successive Buchwald-Hartwig amination and ring closure is reported. A variety of different benzimidazolium salts can be prepared using this procedure. Amines that bear an alpha-chiral group undergo the reaction to furnish chiral benzimidazolium salts. The salts that lack a C2 substituent on the heterocycle are readily deprotonated to give nucleophilic carbenes.

Spectroscopic analysis of imidazolidines. Part II: 1H NMR spectroscopy and conformational analysis of 1,2 and 1,3‐diarylimidazolidines

Abstract1H NMR spectra of a series of 1,2 and 1,3‐diarylimidazolidines are analyzed and correlated with their conformational features. Results were interpreted on the basis of chemical shifts and coupling constants of hydrogen atoms and confirmed by ID nOe difference experiments. 1,3‐Diarylimidazolidines (1–7) show a fast inversion of the N‐aryl nitrogen in all studied cases. 1,2‐Diaryl‐3‐methyl (or benzyl) imidazolidines (8–13) display a preferential conformation with a transoid orientation of N3 and C2 substituents.