Chemoenzymatic synthesis of the trans-dihydrodiol isomers of monosubstituted benzenes viaanti-benzene dioxides

Polyoxygenated Cyclohexenes and Their Chlorinated Derivatives from the Leaves of Uvaria cherrevensis

The chemical study of leaf extracts from Uvaria cherrevensis resulted in the identification of 11 new polyoxygenated cyclohexenes, cherrevenols A-K (1-11), and a new seco-cyclohexene derivative, cherrevenol L (12). Nine known compounds (13-21) were also isolated. Three of the isolated compounds are chlorinated polyoxygenated cyclohexenes. The structures of these compounds were determined using spectroscopic methods and, in some cases (compounds 2, 6, 8, and 10), single-crystal X-ray crystallographic structural analysis or chemical correlation (compounds 6 and 7). Compounds 6 and 7 were both isolated as scalemic mixtures (ee 23-24%).

NbCl3-catalyzed three-component [2 + 2 + 2] cycloaddition reaction of terminal alkynes, internal alkynes, and alkenes to 1,3,4,5-tetrasubstituted 1,3-cyclohexadienes

Three-component [2 + 2 + 2] cycloaddition of terminal alkynes, internal alkynes, and terminal alkenes is achieved using an NbCl(3)(DME) catalyst, leading to 1,3,4,5-substituted 1,3-cyclohexadienes in excellent yields with high chemo- and regioselectivity.

NbCl3-catalyzed intermolecular [2+2+2] cycloaddition of alkynes and alpha,omega-dienes: highly chemo- and regioselective formation of 5-omega-alkenyl-1,4-substituted-1,3-cyclohexadiene derivatives

Intermolecular [2+2+2] cycloaddition of tert-butylacetylene with alpha,omega-dienes was successfully achieved by NbCl(3)(DME) catalyst to afford 5-omega-alkenyl-1,4-disubstituted-1,3-cyclohexadienes in excellent yields with high chemo- and regioselectivity.

From scratch to value: engineering Escherichia coli wild type cells to the production of l-phenylalanine and other fine chemicals derived from chorismate

Recombinant strains of Escherichia coli K-12 for the production of the three aromatic amino acids (L-phenylalanine, L-tryptophan, L-tyrosine) have been constructed. The largest demand is for L-phenylalanine (L-Phe), as it can be used as a building block for the low-calorie sweetener, aspartame. Besides L-Phe, an increasing number of shikimic acid pathway intermediates can be produced from appropriate E. coli mutants with blocks in this pathway. The last common intermediate, chorismate, in E. coli not only serves for production of aromatic amino acids but can also be used for high-titer production of non-aromatic compounds, e.g., cyclohexadiene-transdiols. In an approach to diversity-oriented metabolic engineering (metabolic grafting), platform strains with increased flux through the general aromatic pathway were created by suitable gene deletions, additions, or rearrangements. Examples for rational strain constructions for L-phenylalanine and chorismate derivatives are given with emphasis on genetic engineering. As a result, L-phenylalanine producers are available, which were derived through several defined steps from E. coli K-12 wild type. These mutant strains showed L-phenylalanine titers of up to 38 g/l of L-phenylalanine (and up to 45.5 g/l using in situ product recovery). Likewise, two cyclohexadiene-transdiols could be recovered.

Chemoenzymatic synthesis of trans-dihydrodiol derivatives of monosubstituted benzenes from the corresponding cis-dihydrodiol isomers

Enantiopure trans-dihydrodiols have been obtained by a chemoenzymatic synthesis from the corresponding cis-dihydrodiol metabolites, obtained by dioxygenase-catalysed arene cis-dihydroxylation at the 2,3-bond of monosubstituted benzene substrates. This generally applicable, seven-step synthetic route to trans-dihydrodiols involves a regioselective hydrogenation and a Mitsunobu inversion of configuration at C-2, followed by benzylic bromination and dehydrobromination steps. The method has also been extended to the synthesis of both enantiomers of the trans-dihydrodiol derivatives of toluene, through substitution of a vinyl bromine atom of the corresponding trans-dihydrodiol enantiomers derived from bromobenzene. Through incorporation of hydrogenolysis and diMTPA ester diastereoisomer resolution steps into the synthetic route, both trans-dihydrodiol enantiomers of monohalobenzenes were obtained from the cis-dihydrodiols of 4-haloiodobenzenes.

syn-Benzene dioxides: chemoenzymatic synthesis from 2,3-cis-dihydrodiol derivatives of monosubstituted benzenes and their application in the synthesis of regioisomeric 1,2- and 3,4-cis-dihydrodiols and 1,4-dioxocins

cis-2,3-Dihydrodiol metabolites of monosubstituted halobenzenes and toluene have been used as synthetic precursors of the corresponding 3,4-cis-dihydrodiols. Enantiopure syn-benzene dioxide intermediates were reduced to the 3,4-cis-dihydrodiols and thermally racemised via the corresponding 1,4-dioxocins. The syn-benzene dioxide-1,4-dioxocin valence tautomeric equilibrium ratio was found to be dependent on the substituent position. The methodology has also been applied to the synthesis of both enantiomers of the 1,2-(ipso)- and 3,4-cis-dihydrodiols of toluene. This chemoenzymatic approach thus makes available, for the first time, all three possible cis-dihydrodiol regioisomers of a monosubstituted benzene.