Robert Azerad

Synthesis of phosphono analogues of 3-deoxy -d-arabino-hept-2-ulosonic acid 7-phosphate☆

Abstract 3,7,8-Trideoxy-8-phosphono- d - arabino -octulosonic acid and 7,8-dedeoxy-8-phosphobno-D- gluco -octulosonic acid were synthesised in six step from known, protected derivatives of 2-deoxy- d - arabino -hexose and d -glucose. The protected 6- aldehydo -hexadialdoses were condensed with tetraethyl methylenediphosphonate, and hydrolysis of vinylphosphonate was effected indirectly by transesterification with bromotrimethylsilane. Cyanide addition to deprotected heptose phosphonates was followed by chlorate-vanadate oxidation to octulosonic acid derivatives. The corresponding 3,7-dideoxy-7-phosphono- d - arabino -heptulosonic acid and 7-deoxy-7-phosphono- d - gluco -heptulosonic acid were obtained by reaction of 6-bromo-6-deoxyhexoses with triethyl phosphite, followed by treatment with bromotrimethylsilane, hydrolysis with water, cyanide homologation, and chlorate-vanadate oxidation. All four, final phosphono compounds are competitive inhibitors of 3-dehydroquinate syntyhetase.

Biochemical study on ubiquinone biosynthesis in Escherichia coli: I. Specificity of para hydroxybenzoate polyprenyltransferase

Summary Experimental conditions to determine polyprenyl pyrophosphate p -hydroxybenzoate transferase activity with [ 14 C] p -hydroxybenzoate or [ 3 H]polyprenyl pyrophosphate have been elaborated in order to test E. coli strains carrying a ubi A − mutation in the ubiquinone biosynthetic pathway. The nature of prenylation products formed by extracts of 38-1 strain in the presence of different polyprenyl pyrophosphates indicates that solubilized 3-polyprenyl 4-hydroxybenzoate decarboxylase is highly specific for its octaprenyl substrate while p -hydroxybenzoate polyprenyltransferase is not.

Vitamin K‐dependent carboxylation: inhibition by a peptide containing 4‐methylene glutamic acid

Vitamin K Carboxylation 4‐Methylene glutamic acid γ‐Carboxyglutamic acid

The interaction of phosphonate and homophosphonate analogues of 3-deoxy-D-arabino heptulosonate 7-phosphate with 3-dehydroquinate synthetase from Escherichia coli

Abstract Phosphonate and homophosphonate analogues of 3-deoxy-D- arabino heptulosonate 7-phosphate and D- gluco heptulosonate 7-phosphate behave as competitive inhibitors of 3-dehydroquinate synthetase. Phosphonates have better affinities than homophosphonates and protect efficiently the enzyme against thermal denaturation. No evidence has been obtained for 5-keto phosphonate intermediate formation in the interaction of such analogues with 3-dehydroquinate synthetase and NAD+.

Enzymic properties of phosphonic analogues of D-erythrose 4-phosphate

Abstract 4-Deoxy-D- erythro tetrose 4-phosphonate and 4,5 dideoxy D- erythro pentose 5-phosphonate, the phosphonic analogues of D-erythrose 4-phosphate, have been prepared by oxidation of the corresponding analogues of glucose 6-phosphate and tested as substrates of 3-deoxy-D- arabino heptulosonate 7-phosphate synthetase, transaldolase and transketolase. Kinetic parameters of the reaction with the phosphonate analogues and the natural substrate have been compared.

The shikimate pathway. III. 3-dehydroquinate synthetase of E. coli. Mechanistic studies by kinetic isotope effect.

The conversion of 3-deoxy D-arabino heptulosonate 7-phosphate to 3-dehydroquinate by the 3-dehydroquinate synthetase from E. coli is characterized by a low but significant kinetic isotope effect for tritium carried in position-5 of DAHP, while no isotope effect was detectable for tritium in position-4. This effect was observed at different pH nad is interpreted as a result of theintermediary of a 5-ketonic form of the substrate, formed in a preliminary non limiting step during the enzymic cyclization reaction. A tentative scheme for the 3-DHQ synthetase reaction is proposed involving five steps: oxidation by NAD+ in position-5, phsophate elimination after enolization, reduction with precedently formed NADH and cyclization by attack of the 2-carbonyl by the C-7 methylene group.

The shikimate pathway: II. Stereospecificity of hydrogen transfer catalyzed by NADPH-dehydroshikimate reductase of E. coli*

Summary Dehydroshikimate reductase from E. coli is shown to transfer stereospecifically hydrogen-H A from NADPH, a stereospecificity identical to that demonstrated for plant enzyme. Some implications of this result are discussed.

Stereoselective synthesis of (1R,3S)-cis-chrysanthemic acid through microbiological reduction of 2,2,5,5-tetramethyl 1,4-cyclohexanedione

Abstract An efficient, highly stereoselective synthesis of (1 R ,3 S )- cis -chrysanthemic acid 6 is described. The crucial step of this synthesis was the microbiological reduction of dione 1 into ( S )-ketol 2.

Preparation of [1-3H]polyprenyl pyrophosphates

Summary Preparation of [1-3H]-polyprenylpyrophosphates is described using a lipophilic Sephadex converted to a diethylaminoethyoxylated form to separate inorganic phosphate, phosphate and pyrophosphate esters.

Synthesis of L-tryptophan by immobilized Escherichia coli cells

Enzymatic production of L-tryptophan has been studied in a system containing Escherichia coli cells (induced for tryptophanase) entrapped in a polyacrylamide gel, indole and excess pyruvate and ammonia. The influence of pH, substrate concentration and temperature on L-tryptophan production, in batch and flow reactor conditions, was investigated. In flow reactor conditions, inhibition of the reaction by indole resulted in a multi steady-state pattern characteristic of substrate inhibited reactions. Any increase in flow rate at indole concentrations higher than 17 mM resulted in a dramatic decrease in the conversion rate of indole to tryptophan.