Role of 2′,6′-dimethyl-l-tyrosine (Dmt) in some opioid lead compounds

Here we evaluated how the interchange of the amino acids 2′,6′-dimethyl-l-tyrosine (Dmt), 2′,6′-difluoro-l-tyrosine (Dft), and tyrosine in position 1 can affect the pharmacological characterization of some reference opioid peptides and pseudopeptides. Generally, Dft and Tyr provide analogues with a similar pharmacological profile, despite different pK_a values. Dmt/Tyr(Dft) replacement gives activity changes depending on the reference opioid in which the modification was made. Whereas, H-Dmt-Tic-Asp1-Bid is a potent and selective δ agonist (MVD, IC₅₀ = 0.12 nM); H-Dft-Tic-Asp1-Bid and H-Tyr-Tic-Asp1-Bid are potent and selective δ antagonists (pA₂ = 8.95 and 8.85, respectively). When these amino acids are employed in the synthesis of deltorphin B and its Dmt¹ and Dft¹ analogues, the three compounds maintain a very similar δ agonism (MVD, IC₅₀ 0.32–0.53 nM) with a decrease in selectivity relative to the Dmt¹ analogue. In the less selective H-Dmt-Tic-Gly1-Bid the replacement of Dmt with Dft and Tyr retains the δ agonism but with a decrease in potency. Antagonists containing the Dmt-Tic pharmacophore do not support the exchange of Dmt with Dft or Tyr.     

Role of odour compounds in the attraction of gamete vectors in endophytic Epichloë fungi

Grass-infecting Epichlo? endophytes (Ascomycota, Calvicipitaceae) depend on Botanophila flies for gamete transfer, while fly larvae feed and develop on the fertilized fungal fruiting structures. Flies are known to be attracted by volatile signals, but the exact mechanisms of chemical communication and the degree of specialization are unknown. Headspace samples collected from five different Epichlo? species were analysed with respect to physiologically active substances using Botanophila flies. In field bioassays using synthetic compounds, their attractiveness and the specificity of the Epichlo?-Botanophila attraction were investigated. The identification of a new natural product, methyl (Z)-3-methyldodec-2-enoate, attracting Botanophila flies is reported here, and chokol K is confirmed as an attractive compound. Different blends of the two compounds attracted Botanophila flies under field conditions, but the three fly taxa present at the study site showed no preference for specific blends of volatiles. Chemical communication in the Epichlo?-Botanophila system relies on a few specific compounds, known as a communication system with 'private channels'. Although ratios of emitted compounds vary in different Epichlo? species, this seems not to lead to specialized attraction of Botanophila flies. Low selective pressure for specialization may have maintained a more generalist interaction between fungi and flies.     

Synthesis of α-allylated α,β-unsaturated carbonyl compounds using vanadium/palladium contemporaneous dual catalysis

This protocol describes a new approach for the preparation of α-allylated α,β-unsaturated carbonyl compound by chemoselective cross-coupling of propargyl alcohols with allyl carbonates using an unprecedented vanadium/palladium contemporaneous dual catalysis. This process involves 1,3-transposition of propargyl alcohols by an oxyvanadium catalyst to generate vanadium allenoates and the activation of allyl carbonates by a palladium catalyst to generate π-allylpalladium species. These two active intermediates trap each other more rapidly to afford the observed product, rather than being intercepted by the large excess of starting propargyl alcohol. One example for the preparation of this type of α-allylated α,β-unsaturated carbonyl compound is included in the text. It takes ~20 h to complete the protocol: 1.0 h to set up the reaction, 16 h for the reaction and 2.0 h for isolation and purification. This chemistry has been applied to obtain a wide range of α-allylated α,β-unsaturated ketones, esters and amides, which are highly valuable building blocks in organic synthesis.     

Enzymes catalysing conjugations of glutathione with αβ-unsaturated carbonyl compounds

1. Heat-inactivation experiments, ammonium sulphate-fractionation studies, enzyme-inhibition studies with S-(alphabeta-diethoxycarbonylethyl)glutathione, and evidence from the distribution of activities in rat liver, in rat kidney and in the livers of other animals, indicate that reactions of glutathione with (i) trans-benzylideneacetone, (ii) cyclohex-2-en-1-one, (iii) trans-cinnamaldehyde, (iv) diethyl maleate, (v) diethyl fumarate and (vi) 2,3-dimethyl-4-(2-methylenebutyryl)phenoxyacetic acid are catalysed by different enzymes. 2. Evidence is presented that the enzymes catalysing the reactions of glutathione with substrates (i)-(iv) are different from glutathione S-alkyltransferase, S-aryltransferase and S-epoxidetransferase. 3. The name ;glutathione S-alkenetransferases' is proposed for enzymes catalysing reactions of glutathione with alphabeta-unsaturated compounds. 4. The Arrenhius plot for the enzyme-catalysed reaction of diethyl maleate with glutathione is discontinuous, with lower energy of activation at 38 degrees .     

Biosynthesis of phloroglucinol compounds in microorganisms—review

Phloroglucinol derivatives are a major class of secondary metabolites of wide occurrence in biological systems. In the bacteria kingdom, these compounds can only be synthesized by some species of Pseudomonads. Pseudomonas spp. could produce 2,4-diacetylphloroglucinol (DAPG) that plays an important role in the biological control of many plant pathogens. In this review, we summarize knowledge about synthesis of phloroglucinol compounds based on the DAPG biosynthetic pathway. Recent advances that have been made in understanding phloroglucinol compound biosynthesis and regulation are highlighted. From these studies, researchers have identified the biosynthesis pathway of DAPG. Most of the genes involved in the biosynthesis pathway have been cloned and characterized. Additionally, heterologous systems of the model microorganism Escherichia coli are constructed to produce phloroglucinol. Although further work is still required, a full understanding of phloroglucinol compound biosynthesis is almost within reach. This review also suggests new directions and attempts to gain some insights for better understanding of the biosynthesis and regulation of DAPG. The combination of traditional biochemistry and molecular biology with new systems biology and synthetic biology tools will provide a better view of phloroglucinol compound biosynthesis and a greater potential of microbial production.     

On the structures of some adducts of biotin with electrophiles: Does sulfur transannular interaction with the carbonyl group play a role in the chemistry or biochemistry of biotin?

Biotin methyl ester (1), 1′-N-carbomethoxy biotin methyl ester (2) and 1′-N-trifluoroacetylbiotin methyl ester (3) were treated with boron trifluoride etherate and triethyloxonium tetrafluoroborate. Whereas no reaction could be observed in the case of 3, coordination of the electrophiles to the urea oxygen could be deduced from the IR, ¹H-NMR, and ¹³C-NMR spectra of the adducts obtained from 1 and 2. X-Ray analysis of the 1/BF₃-adduct (4) confirmed the O-coordination, but showed no transannular sulfur-carbonyl interaction. From comparison of the spectral data obtained for all addition products it is concluded that none of them shows a significant transannular sulfur-carbonyl interaction. Reaction of 3 with SbF₅ also formed an O-coordinated adduct (10) without sulfur transannular bonding. In magic acid (FSO₃H/SbF₅/SO₂) both 1 and 3 added a proton to the urea oxygen, to the sulfur atom, and to the ester group, as reported previously for biotin itself. The relationship of these findings to the kinetics of acid-catalyzed NH exchange in biotin, and to possible mechanisms of biochemical biotin-catalyzed reactions, are discussed.     

Copper-catalyzed amino acid condensation in water — A simple possible way of prebiotic peptide formation

The recently reported condensation reaction of glycine to di- and triglycine in aqueous solution in the presence of higher concentrations of sodium chloride and copper ions has been investigated systematically and quantitatively using HPLC analytical methods. The influence of environmental factors (temperature, concentration, atmosphere) are discussed. Numerous other metal ions have been investigated with respect to similar catalytic effects, and molybdenum results as the only one inducing peptide condensation, although to a much lesser extent. Experiments based on evaporation of water and redissolution lead to peptide condensation up to (gly)₆ in concentrated solutions and produces peptides even starting from initially low concentrations.     

Synthesis of some racemicγ-fluoro-α-amino acids

Summary Versatile three-step procedures for syntheses of seven racemi-fluoro-a-amino acids are described. Alkylation oftert-butyl N-(diphenylmethylene) glycinate with 1-bromo-2-fluoroalkanes gave N-protected aminoacid esters both in anhydrous medium using lithium-diisopropylamide as base at low temperature or in a two phase system of 50% aqueous sodium hydroxide and methylene chloride with triethylbenzylammonium chloride as the phase transfer catalyst at room temperature. Subsequent two-step deprotection with citric acid and hydrochloric acid gave the title compounds in 13–33% overall yields.Dedicated to Professor Dr.mult., Dr.h.c. Alois Haas on the occasion of his 65th birthday     

Cytokines in Brain Ischemia—The Role of TNFα

1. The role of cytokines and other inflammatory mediators in the progression of ischemic brain injury is a new and exciting era of research. Evidence in support for a role for TNF in this respect is emerging as evidence on de novo upregulation of TNF following ischemia is now well established.2. TNF administered directly to the brain parenchyma elicits local microvascular injury in the form of pericapillary edema and leukocyte adhesion to cerebral capillaries.3. TNF administered into the cerebroventricular space prior to ischemia augment the extent of tissue damage and neurological deficits.4. Specific and potent inhibitors of TNF synthesis or TNF receptors must be developed and tried to prove firmly a role for TNF in ischemic brain injury.     

The catalytic promiscuity of a microbial 7α-hydroxysteroid dehydrogenase. Reduction of non-steroidal carbonyl compounds

A thermostable 7α-hydroxysteroid dehydrogenase from Bacteroides fragilis ATCC 25285 was found to catalyze the reduction of various benzaldehyde analogues to their corresponding benzyl alcohols. The enzyme activity was dependent upon the substituent on the benzene ring of the substrates. Benzaldehydes with electron-withdrawing substituent usually showed higher activity than those with electron-donating groups. Furthermore, this enzyme was tolerant to some organic solvents. These results together with previous studies suggested that 7α-hydroxysteroid dehydrogenase from B. fragilis might play multiple functional roles in biosynthesis and metabolism of bile acids, and in the detoxification of xenobiotics containing carbonyl groups in the large intestine. In addition, its broad substrate spectrum offers great potential for finding applications not only in the synthesis of steroidal compounds of pharmaceutical importance, but also for the production of other high-value fine chemicals.     

Synthesis,characterization and antitumour properties of some metal(II) complexes of 2-pyridinecarboxaldehyde 2′-pyridylhydrazone and related compounds

Metal complexes of 2-pyridinecarboxaldehyde 2′-pyridylhydrazone (PCPH) and related compounds with manganese(II), iron(II), cobalt(II), nickel(Il), copper(II), zinc(II) and platinum(II) were synthesized and characterized by magnetic susceptibility measurements down to liquid nitrogen temperature and also by electronic, infrared, electron spin resonance and Mössbauer spectra. All the metal(II) complexes appeared to be monomeric, high-spin, five-coordinate (square-pyramidal) (X = Cl⁻ or OAc⁻), except for Ni(PCPH)Cl₂ which is polymeric, high-spin, six-coordinate. Each ligand behaved as a tridentate NNN donor, via the pyridine nitrogen, azomethine nitrogen, and pyridine or quinoline nitrogen. One of the most active agents of this series, Cu(PCPH)Cl₂, showed antitumour activity against a variety of transplanted tumours, including Sarcoma 180, Ehrlich carcinoma and L1210 leukaemia sensitive to α(N)-heterocyclic carboxaldehyde thiosemicarbazones. This agent caused inhibition of ³H-thymidine and ³H-uridine incorporation into DNA and RNA, respectively, of Sarcoma 180 ascites cells; protein biosynthesis was relatively insensitive to the action of this agent.     

Some μ-oxo compounds of iron-hemiporphyrazine. Synthesis and properties

Details of the conditions necessary for preparing the recently reported μ-oxo-ironhemiporphyrazinate compounds (Fe(IV)hpO)_n and [(Fe(III)hp)₂O]H₂O are given. Two further homologous μ-oxo Fe(III)hemiporphyrazinates are described: an amorphous μ-oxo dimer and a μ-oxo dimer HCl adduct. The thermal and spectroscopic (UV-Vis, IR, Mössbauer, XPS) properties and magnetic susceptibilities of these compounds have been investigated. The reducibility of these species in solution, in the presence and absence of O₂, has been monitored. The results do not indicate a change in oxidation state of the iron in (FehpO)_n. Attempts to obtain the hemiporphyrazinato Fe(III) chloride are described.     

NEUROLOGICALLY HANDICAPPED CHILDREN—The Role of the Pediatrician in Rehabilitation

In the application of the broad services now available to assist a child having a major neurologic impairment, the pediatrician occupies an important role owing to his ability to consider the problem of the handicapped child in the context of his specialized knowledge of the developmental process. He thus has a large responsibility for interpretation of the problem to the child, to the parents and to his professional colleagues and for guidance of the rehabilitation regimen within the limits of the child''s developmental readiness for new experiences.The pediatrician has the opportunity to contribute significant clinical observations which may provide stimuli for future basic research and to exercise his skill as a practitioner of preventive medicine.Goals for the future achievement of the child having a major neurologic impairment must be set realistically and with great caution.     

In vitro inhibition of α-carbonic anhydrase isozymes by some phenolic compounds

Carbonic anhydrase inhibitors (CAIs) are a class of pharmaceuticals used as antiglaucoma agents, diuretics, antiepileptics, in the management of mountain sickness, gastric and duodenal ulcers, neurological disorders or osteoporosis. We report here the inhibitory capacities of some phenolic compounds against three human CA isozymes (hCA I, hCA II, and hCA VI) and the gill carbonic anhydrase of the teleost fish Dicentrarchus labrax (European seabass) (dCA). The isozymes showed quite diverse inhibition profiles with these compounds. These data may lead to design novel CAIs with a diverse inhibition mechanism compared to sulfonamide/sulfamate inhibitors.     

Synthesis of new simplified hemiasterlin derivatives with α,β-unsaturated carbonyl moiety

In this Letter, we report a convenient and efficient method for the synthesis of new simplified derivatives of hemiasterlin in which the α,α-dimethylbenzylic moiety A is replaced by α,β-unsaturated aryl groups as Michael acceptor. Most of these derivatives have a strong cytotoxic activity on three human tumor cell lines (KB, Hep-G₂ and MCF₇). Analogs 17b and 17f showed a high cytotoxicity against KB and Hep-G₂ cancer cell lines comparable to paclitaxel and ellipticine.     

Synthesis of two fluorescent GTPγS molecules and their biological relevance

Fluorescent GTP analogues are utilized for an assortment of nucleic acid and protein characterization studies. Non-hydrolysable analogues such as GTPγS offer the advantage of keeping proteins in a GTP-bound conformation due to their resistance to hydrolysis into GDP. Two novel fluorescent GTPγS molecules were developed by linking fluorescein and tetramethylrhodamine to the γ-thiophosphate of GTPγS. Chemical and biological analysis of these two compounds revealed their successful synthesis and ability to bind to the nucleotide-binding site of tubulin. These two new fluorescent non-hydrolysable nucleotides offer new possibilities for biophysical and biochemical characterization of GTP-binding proteins.