On the inhibitory potency of imidazole and its derivatives on thromboxane synthetase

The relative inhibitory potency of imidazole and derivatives on thromboxane synthetase from human platelets was found to be increased by substitution of the 1-position and abolished in other positions. The potency of 1-substituted imidazoles was increased as the side chain became more hydrophobic. Among the imidazole derivatives tested 1-nonyl-imidazole and 1-(2-isopropyl phenyl)-imidazole showed the highest potency with I₅₀ in the range of 10^?8 M. Inhibition by imidazole and its derivatives appeared to be very specific for thromboxane synthetase since other enzymes in prostaglandin endoperoxide metabolism were not affected. Kinetic studies indicated that inhibition was competitive with respect to prostaglandin endoperoxide substrate.     

Axial histidyl imidazole non-exchangeable proton resonances as indicators of imidazole hydrogen bonding in ferric cyanide complexes of heme peroxidases

Proton NMR spectra of a model of low-spin cyanide complexes of ferric hemoproteins indicate that two broad single-protein resonances from the axial imidazole can be resolved outside the diamagnetic spectral region. Upon deprotonation of the imidazole in the model, the upfield resonance shifts dramatically to higher field, suggesting that its position may reflect the degree of hydrogen bonding or proton donation of the imidazole. Met-cyano myoglobin reveals a pair of such broad peaks in the regions expected for an essentially neutral axial imidazole. In the cyano complexes of horseradish peroxidase and cytochrome c peroxidase, a pair of single-proton resonances are located which are assigned to the same imidazole protons on the basis of their linewidth and shift changes upon altering the heme substituents. The upfiled proton, however, is found at much higher field than in metMbCN. The upfield bias of this resonance is taken as evidence for appreciable imidazolate character for the axial ligand in these heme peroxidases.     

Enzyme inhibition potency enhancement by active site metal chelating and hydrogen bonding induced conformation-restricted cyclopropanecarbonyl derivatives

Two cyclopropanecarbonyl derivatives were independently found to be 15 and 14 times more potent than the corresponding isopropylcarbonyl analogues as inhibitors of 4-hydroxyphenylpyruvate dioxygenase and dihydroorotate dehydrogenase, respectively. A thorough examination of the co-crystal structures of available enzyme inhibitor complexes and the conformation of X-ray crystal structures of several synthesized cyclopropanecarbonyl derivatives revealed that this enhancement by one order of magnitude of inhibition potency exhibited by cyclopropanecarbonyl derivatives in both enzymes is probably caused by respective metal chelating and hydrogen bonding interactions at the ligand-receptor binding site. These specific interactions subsequently cause the cyclopropyl group of the molecules to adopt a fixed bisected conformation, which is unavailable for isopropylcarbonyl derivatives.     

Water as a hydrogen bonding bridge between a phenol and imidazole. A simple model for water binding in enzymes

The X-ray crystal structure of the mono-hydrate of 2,2-bis(imidazol-1-ylmethyl)-4-methylphenol has been determined. Three hydrogen bonds hold water very tightly in the crystal, as determined by deuterium solid-state NMR. The hydrogen bond between the phenolic hydroxyl and water appears to have about the same strength as the direct hydrogen bond to imidazole, suggesting that the structure can be a good model for hydrogen bonds that are mediated by a water molecule in enzymes.     

Water as a hydrogen bonding bridge between a phenol and imidazole. A simple model for water binding in enzymes

The X-ray crystal structure of the mono-hydrate of 2,2-bis(imidazol-1-ylmethyl)-4-methylphenol has been determined. Three hydrogen bonds hold water very tightly in the crystal, as determined by deuterium solid-state NMR. The hydrogen bond between the phenolic hydroxyl and water appears to have about the same strength as the direct hydrogen bond to imidazole, suggesting that the structure can be a good model for hydrogen bonds that are mediated by a water molecule in enzymes.     

Intramolecular steric effects and hydrogen bonding in regular conformations of polyamino acids

A survey has been made, by using computer methods, of the types of helices which polypeptide chains can form, taking into account steric requirements and intramolecular hydrogen-bonding interactions. The influence on these two requirements, of small variations in the bond angles of the peptide residues, or of small changes in the overall dimensions of the helix (pitch and residues per turn), have been assessed for the special case of the α-helix. Criteria for the formation of acceptable hydrogen bonds have also been applied to helices of other types, viz., the 3, γ^?, ω^?, and π-helices. It was shown that the N? H … O and H … O? C angles in hydrogen bonds are sensitive to changes in either the NC^αC′ bond angle or in the rotational angles about the N? C^α and C^α? C′ bonds. However, the variants of the α-helix observed experimentally in myoglobin can all be constructed without distortion of the hydrogen bonds. For α-helices, the steric and hydrogen bonding requirements are more easily fulfilled with an NC^αC′ bond angle of 111°, rather than 109.5°. The decreased stability observed for the left-handed α-helix relative to the right-handed one for L -amino acids is due essentially only to interactions of the C^β atom of the side chains with atoms in adjacent peptide units in the backbone, and interactions with atoms in adjacent turns of the helical backbone are not significantly different in the two helices. Restrictions in the freedom of rotation of bulky side chains may have significant kinetic effects during the formation of the α-helix from the “random coil” state.     

Intramolecular hydrogen bonding: a potential strategy for more bioavailable inhibitors of neuronal nitric oxide synthase

Selective neuronal nitric oxide synthase (nNOS) inhibitors have therapeutic applications in the treatment of numerous neurodegenerative diseases. Here we report the synthesis and evaluation of a series of inhibitors designed to have increased cell membrane permeability via intramolecular hydrogen bonding. Their potencies were examined in both purified enzyme and cell-based assays; a comparison of these results demonstrates that two of the new inhibitors display significantly increased membrane permeability over previous analogs. NMR spectroscopy provides evidence of intramolecular hydrogen bonding under physiological conditions in two of the inhibitors. Crystal structures of the inhibitors in the nNOS active site confirm the predicted non-intramolecular hydrogen bonded binding mode. Intramolecular hydrogen bonding may be an effective approach for increasing cell membrane permeability without affecting target protein binding.     

Synthesis of N-alkylated derivatives of imidazole as antibacterial agents

N-Alkylation of imidazole, 2-methylimidazole and 2-methyl-4-nitroimidazole have been carried out to achieve effective antibacterial agents. The products were then investigated for antibacterial activity against Escherichia coil, Staphylococcus aureus and Pseudomonas aeruginosa. Antibacterial effects of 1-alkylimidazole derivatives increase as the number of carbons in alkyl chain increases up to nine carbons. Also substitution of 2-methyl and 2-methyl-4-nitro groups on imidazole ring increases the antibacterial activity.     

MGMT is a molecular determinant for potency of the DNA-EGFR-combi-molecule ZRS1

To enhance the potency of current EGFR inhibitors, we developed a novel strategy that seeks to confer them an additional DNA damaging function, leading to the design of drugs termed combi-molecules. ZRS1 is a novel combi-molecule that contains an EGFR tyrosine kinase targeting quinazoline arm and a methyltriazene-based DNA damaging one. We examined its effect on human tumor cell lines with varied levels of EGFR and O6-methylguanine DNA methyltransferase (MGMT). ZRS1 was more potent than the clinical methylating agent temozolomide in all cell lines, regardless of their MGMT status. However, its potency was in the same range as or less than that of Iressa, an EGFR inhibitor, against MGMT-proficient cells. In the MGMT-deficient or in MGMT-proficient cells exposed to the MGMT inhibitor O6-benzylguanine, its potency was superior to that of Iressa and temozolomide or a temozolomide+Iressa combination. Cell signaling analysis in A549 (MGMT(+)) and A427 (MGMT(-)) showed that ZRS1 strongly inhibited EGFR phosphorylation and related signaling pathways. In addition, the p53 pathway was activated by DNA damage in both cell lines, but apoptosis was significantly more pronounced in A427 cells. Using MGMT shRNA to block endogenous MGMT protein expression in A549 resulted in significant sensitization to ZRS1. Furthermore, transfection of MGMT into A427 greatly decreased the potency of ZRS1. These results conclusively show that MGMT is a critical molecular determinant for the full-blown potency of the dual EGFR-DNA targeting combi-molecule.     

Intramolecular hydrogen bonding in articaine can be related to superior bone tissue penetration: a molecular dynamics study

Local anesthetics (LAs) are drugs that cause reversible loss of nociception during surgical procedures. Articaine is a commonly used LA in dentistry that has proven to be exceptionally effective in penetrating bone tissue and induce anesthesia on posterior teeth in maxilla and mandibula. In the present study, our aim was to gain a deeper understanding of the penetration of articaine through biological membranes by studying the interactions of articaine with a phospholipid membrane. Our approach involves Langmuir monolayer experiments combined with molecular dynamics simulations. Membrane permeability of LAs can be modulated by pH due to a titratable amine group with a pKa value close to physiological pH. A change in protonation state is thus known to act as a lipophilicity switch in LAs. Our study shows that articaine has an additional unique lipophilicity switch in its ability to form an intramolecular hydrogen bond. We suggest this intramolecular hydrogen bond as a novel and additional solvent-dependent mechanism for modulation of lipophilicity of articaine which may enhance its diffusion through membranes and connective tissue.     

Disulfide bonding as a determinant of the molecular composition of types I, II and III procollagen

Procollagen molecules have amino-terminal and carboxy-terminal propeptides at the respective ends of the collagenous triple helix. The carboxy-terminal propeptides enhance and direct the association of pro alpha-chains into procollagen molecules, but the mechanism of this registration function is still obscure. A hypothesis concerning the function of disulfide bonding in the assembly of types I, II and III procollagen is put forward here.     

Synthesis of C-ring-modified blebbistatin derivatives and evaluation of their myosin II ATPase inhibitory potency

(S)-Blebbistatin is a micromolar myosin II ATPase inhibitor that is extensively used in research. In search of analogs with improved potency, we have synthesized for the first time C-ring modified analogs. We introduced hydroxymethyl or allyloxymethyl functionalities in search of additional favorable interactions and a more optimal filling of the binding pocket. Unfortunately, the resulting compounds did not significantly inhibit the ATPase activity of rabbit skeletal-muscle myosin II. This and earlier reports suggest that rational design of potent myosin II inhibitors based on the architecture of the blebbistatin binding pocket is an ineffective strategy.     

Design and optimization of imidazole derivatives as potent CXCR3 antagonists

A series of imidazole derivatives have been designed and optimized for CXCR3 antagonism, pharmacokinetic properties, and reduced formation of glutathione conjugates. Our efforts led to the discovery of potent CXCR3 antagonists with good pharmacokinetic properties. These compounds are useful tools for in vivo studies of CXCR3 function.     

Synthesis of tetrocarcin derivatives with specific inhibitory activity towards Bcl-2 functions

Tetrocarcin A was recently identified as an inhibitor of the anti-apoptotic function of Bcl-2. We synthesized novel tetrocarcin derivatives in order to increase their selective inhibitory activity against Bcl-2. It was found that 21-acetoxy-9-glycosyloxy derivatives had potent Bcl-2 inhibitory activity without significant antimicrobial activity.     

Intramolecular catalysis of amide hydrolysis by carboxyl and metal ion/proton agents: I. Intramolecular reactions of imidazole or pyridine derivatives of maleamic acid

Kinetic studies on the hydrolysis of N-(2-imidazolylethyl)maleamic acid, N-(2-pyridylethyl)maleamic acid, and N-(2-pyridylmethyl)maleamic acid were carried out. In these maleamic acid derivatives, the amide nitrogens together with the heterocyclic nitrogens form bidentate ligands. The compounds were hydrolyzed through nucleophilic catalysis by carboxyl groups. The pH profiles for the hydrolysis at 65°C were descending sigmoids and were unaffected by the ionization of the heterocyclic nitrogens. The absence of rate enhancement due to the added divalent metal ions revealed that chelate formation by the bidentate leaving groups is not efficient. N-(2-Pyridylmethyl)maleamic acid underwent a dual intramolecular nucleophilic reaction through participation of both the carboxyl and the pyridyl groups.     

Specific configurations of hydrogen bonding. I. Hydrogen bonding and conformational preferences of N-acylamino-acids, peptides and derivatives

From a reexamination of the X-ray studies of the crystal structures of 27 N-acylamino acids, peptides and their derivatives and 30 linear peptides, it is concluded that specific formation of short intermolecular hydrogen bonds (2,5 to 2.6 A) from the carboxyl OH to the N-acyl oxygen is an important feature for N-acylamino acids. For N-acyl-N-amides, the formation of hydrogen bonds 2.7 to 2.9A long between N(acyl-H...O(amide) is strongly preferred. The dihedral angle delta between the N-acyl and carboxyl groups or adjacent amide groups shows a preference for values near 20 degrees or 90 degrees for N-acylamino acids and 90 degrees for N-acyl-N-amides.