Andrew J. Pratt

Escherichia coli dihydrodipicolinate synthase and dihydrodipicolinate reductase: kinetic and inhibition studies of two putative herbicide targets

Dihydrodipicolinate synthase (DHDPS) (EC 4.2.1.52) and dihydrodipicolinate reductase (DHDPR) (EC 1.3.1.26) have attracted much recent attention as potential herbicide targets. DHDPS was feedback-inhibited by (S)-lysine; inhibition was reversible and uncompetitive with respect to both (S)-ASA and pyruvate. Homoserine lactone was a reversible non-competitive inhibitor of DHDPS with respect to both (S)-ASA and pyruvate. (R)-Cysteine sulfinic acid and (S)-glutamic acid were reversible uncompetitive inhibitors of DHDPS with respect to (S)-ASA. (S)-Aspartic acid was a reversible mixed-type inhibitor. Dipicolinic acid was a reversible competitive inhibitor of DHDPR with respect to the substrate (4S)-4-hydroxy-2,3,4,5-tetrahydro-(2S)-dipicolinic acid, as was isophthalic acid. Δ3-Tetrahydroisophthalic acid was a moderate inhibitor of both DHDPS and DHDPR. These compounds represent possible leads in the development of novel herbicides. © 1999 Society of Chemical Industry

(S)-Aspartate semi-aldehyde: Synthetic and structural studies

Abstract We report a novel synthesis of (S)-aspartate semi-aldehyde, (S)-ASA, 1, a key intermediate in the biosynthesis of lysine, based on hydrolysis of an enol ether precursor, (S)-2-amino-4-methoxybut-3-enoic acid, 10. (S)-ASA is conveniently and quantitatively liberated from this stable intermediate and can be used in biological studies directly, since methanol is the only side-product. Enzyme inhibition studies and chemical precedent imply a cyclic lactol structure might be significant; heteronuclear multibond coupling (HMBC) measurements, however, are consistent with the hydrate being the predominant species in aqueous solution.

Photolabile benzoin and furoin esters of a biologically active peptide

Abstract Benzoin and furoin esters of N-carbobenzyloxyglycylphenylalanine were prepared and photolyzed under a variety of conditions. The photochemistry of peptide-derived benzoin esters is more efficient than that of furoin esters and is appropriate for the photolytic initiation of biochemical processes. Methodology to assess the enantiomeric purity of the resulting free peptide was developed and used to monitor the protection-deprotection chemistry. Synthesis based on alkylation of the cesium salt of the peptide proved more effective than DCCI-mediated chemistry on stereochemical grounds.

AN-nitrosochloroethyl-cephalosporin carbamate prodrug for antibody-directed enzyme prodrug therapy (ADEPT)

Abstract N-Nitrosochloroethyl-cephem7 was prepared via acylation and selective nitrosation of a cephalothin derivative. This cephalosporin is an efficient substrate for Enterobacter cloacae P99 β-lactamase. Kinetic parameters were determined for enzyme-catalysed hydrolysis. This cephalosporin is a potential prodrug for the delivery of bis-alkylating chloroethyldiazo species to tumours by antibody-β-lactamase conjugates. Download : Download full-size image

Synthesis and Diels–Alder reactions of thioisobenzofurans

Anions prepared by deprotonation of benzofused thionolactones reacted with alkylating agents preferentially on sulfur. The resulting isobenzofurans underwent Diels–Alder reactions with dienophiles. This chemistry was developed as a one-pot procedure for the synthesis of bridged precursors of polycyclic aromatic compounds. The structure of one of the adducts, dimethyl 9-exo-10-endo-1-methylsulfanyl-8-phenyl-11-oxatricyclo[6.2.1.02.7]undeca-2,4,6-triene-9,10-dicarboxylate 5a, was determined by single-crystal X-ray diffraction. The versatility of this approach was extended by lithiation of the intermediate anion whereby alkylation introduced a further substituent on the aromatic nucleus. This methodology may be appropriate for the synthesis of anti-tumour prodrugs.

Mediation of a plant-spider association by specific volatile compounds.

Evarcha culicivora, an East African jumping spider (Salticidae), is the only spider for which there is evidence of innate olfactory affinity for particular plant species. Evarcha culicivora also actively chooses as preferred prey the females of Anopheles mosquitoes, and both sexes of Anopheles are known to visit plants for nectar meals. Here, we identified compounds present in the headspace of one of these species in Kenya, Lantana camara, and then used 11 of these compounds in olfactometer experiments. Our findings show that three terpenes [(E)-β-caryophyllene, α-humulene and 1,8 cineole] can be discriminated by, and are salient to, E. culicivora. The spiders experienced no prior training with plants or the compounds we used. This is the first experimental demonstration of specific phytochemicals being innately attractive to a spider, a group normally characterized as predators.

Prebiological evolution and the metabolic origins of life

The chemoton model of cells posits three subsystems: metabolism, compartmentalization, and information. A specific model for the prebiological evolution of a reproducing system with rudimentary versions of these three interdependent subsystems is presented. This is based on the initial emergence and reproduction of autocatalytic networks in hydrothermal microcompartments containing iron sulfide. The driving force for life was catalysis of the dissipation of the intrinsic redox gradient of the planet. The codependence of life on iron and phosphate provides chemical constraints on the ordering of prebiological evolution. The initial protometabolism was based on positive feedback loops associated with in situ carbon fixation in which the initial protometabolites modified the catalytic capacity and mobility of metal-based catalysts, especially iron-sulfur centers. A number of selection mechanisms, including catalytic efficiency and specificity, hydrolytic stability, and selective solubilization, are proposed as key determinants for autocatalytic reproduction exploited in protometabolic evolution. This evolutionary process led from autocatalytic networks within preexisting compartments to discrete, reproducing, mobile vesicular protocells with the capacity to use soluble sugar phosphates and hence the opportunity to develop nucleic acids. Fidelity of information transfer in the reproduction of these increasingly complex autocatalytic networks is a key selection pressure in prebiological evolution that eventually leads to the selection of nucleic acids as a digital information subsystem and hence the emergence of fully functional chemotons capable of Darwinian evolution.

Dehydroascorbic Acid Mediated Crosslinkage of Proteins Using Maillard Chemistry - Relevance to Food Processing

Dehydroascorbic acid (DHA) is the first stable oxidation product of ascorbic acid and can participate in redox reactions such as the oxidative crosslinking of proteins through disulfide bonds. Emphasis on the redox chemistry of ascorbic acid and DHA has led to its Maillard type chemistry being somewhat over-shadowed. Model studies of DHA with both amino acids and proteins have demonstrated that dehydroascorbic acid is particularly susceptible to Maillard reactions and can crosslink proteins by mechanisms that do not involve disulfide bonding This may partly explain the improver action of ascorbic acid in flour-based products.

Potential mechanism-based tyrosine kinase inhibitors. Part 2. Design and synthesis of peptides containing heterocyclic tyrosine analogues

The Fmoc derivatives of two homochiral tyrosine analogues, a pyridine N-oxide and a pyridone, have been prepared in high stereochemical purity. Solid-phase synthesis has been used to prepare a decapeptide substrate for the tyrosine kinase domain of epidermal growth factor. Two decapeptides, which incorporate the tyrosine analogues in place of tyrosine, and thereby have the potential to act as mechanism-based inhibitors of epidermal growth factor tyrosine kinase, have been synthesised and found to inhibit the aforementioned kinase.

Anticancer Prodrug Studies: Diels–Alder Chemistry of 1-Methylthio-1-(p-tolylsulfonyl)ethene

The reactivity of 1-methylthio-1-(p-tolylsulfonyl)ethene (1) as a dienophile in Diels–Alder chemistry is investigated. Cycloaddition reactions were carried out with a range of pyran-2-ones and isobenzofurans. The initial Diels–Alder adducts have the potential of undergoing fragmentation in chemistry that is relevant to the design of anticancer intercalator prodrugs. The nature of the final products of the reactions provided insights into both the cycloaddition reactions and fragmentation pathways of the adducts. By comparison with a thioether group, the sulfonyl substituent of the dienophile was found to decrease the reactivity and regioselectivity of the cycloaddition chemistry and to facilitate fragmentation of the initial adducts by the elimination of p-toluenesulfinic acid.