Samik Nanda

Stereoselective synthesis of (R)-(−)-denopamine, (R)-(−)-tembamide and (R)-(−)-aegeline via asymmetric reduction of azidoketones by Daucus carota in aqueous medium

A simple and efficient stereoselective synthesis of (R)-denopamine and other naturally occurring hydroxy amides from optically active (R)-2-azido-1-arylethanols, is described for the first time via reduction of the corresponding α-azidoarylketones with enzymes from Daucus Carota root, under mild and environmentally friendly conditions. The products are formed with high degrees of enantioselectivity.

A facile synthesis of (R)-(−)-2-azido-1-arylethanols from 2-azido-1-arylketones using baker's yeast

Abstract A novel and efficient stereoselective reduction of 2-azido-1-aryl ketones using bakers yeast is described.

Characterization of a New (R)-Hydroxynitrile Lyase from the Japanese Apricot Prunus mume and cDNA Cloning and Secretory Expression of One of the Isozymes in Pichia pastoris

PmHNL, a hydroxynitrile lyase from Japanese apricot ume (Prunus mume) seed was purified to homogeneity by ammonium sulfate fractionation and chromatographic steps. The purified enzyme was a monomer with molecular mass of 58 kDa. It was a flavoprotein similar to other hydroxynitrile lyases of the Rosaceae family. It was active over a broad temperature, and pH range. The N-terminal amino acid sequence (20 amino acids) was identical with that of the enzyme from almond (Prunus dulcis). Based on the N-terminal sequence of the purified enzyme and the conserved amino acid sequences of the enzymes from Pr. dulcis, inverse PCR method was used for cloning of a putative PmHNL (PmHNL2) gene from a Pr. mume seedling. Then the cDNA for the enzyme was cloned. The deduced amino acid sequence was found to be highly similar (95%) to that of an enzyme from Pr. serotina, isozyme 2. The recombinant Pichia pastoris transformed with the PmHNL2 gene secreted an active enzyme in glycosylated form.

Lipoxygenase biocatalysis: a survey of asymmetric oxygenation

Lipoxygenases are a group of non-heme iron containing dioxygenases catalyzing the addition of molecular oxygen to poly unsaturated fatty acids in a stereospecific as well as regiospecific way and involved in the biosynthesis of inflammatory mediators, in cell differentiation and atherogenesis. Synthetic use of lipoxygenase over the last decade for total synthesis of several natural products, e.g. 6(R)-lopoxin A, 5(S)-HPETE, (R) and (S) coriolide is discussed in this review. In the second part of the review we have discussed on the LOX biocatalysis of unnatural substrates mimicking natural substrates, lipoxygenase biocatalysis in non-conventional media, the use of immobilized LOX and biocatalysis with engineered lipoxygenase. The factors governing the regiospecificity as well as stereospecificity of LOX biocatalysis will also be discussed here. From the synthetic chemists point of view, the asymmetric oxygenation reaction of unnatural substrates has a tremendous potential. The products of these reactions are important chiral building blocks for the total synthesis of numerous biological active natural products.

Enzyme catalysed kinetic resolution of racemic 2,2-dimethyl-3-(2,2-disubstituted vinyl) cyclopropane car☐ylic acids anchored on polymer supports

Kinetic resolution oftrans-substituted cyclopropane car☐ylic acids anchored on a solid support by lipase is described.

Novel chiral lipoxygenase substrates: design and synthesis. Part 2

A series of novel lipoxygenase substrates carrying a spacing modifier with a non-ionic hydroxyl terminus have been synthesized in an enantioselective fashion. One of the methylene hydrogens (flanked by the cis,cis-pentadienyl moiety) is replaced by alkyl, aryl and hydroxyl groups. The key steps in the synthesis involved enzymatic transesterification of 1,3-propanediol derivatives and two consecutive cis-selective Wittig olefinations.

Enzymatic asymmetric hydroxylation of unnatural substrates with soybean lipoxygenase

Abstract Surrogate substrates mimicking the natural substrate (linoleic acid) bearing a spacing prosthetic group with a non-ionic hydroxyl terminus undergo asymmetric hydroxylation with soybean lipoxygenase. The prosthetic modifier supplies the missing structural features needed for enzymatic recognition and controls the regiochemical outcome of the reaction by its high hydrophobic content. The effect of pH on the regiochemistry clearly shows that all the substrates can arrange themselves at the active site of soybean lipoxygenase in only one orientation leading to formation of hydroperoxides by oxygenation at the ω-6 carbon.

Design and synthesis of useful intermediates for novel lipoxygenase substrates through enzymatic resolution

Abstract Unnatural lipoxygenase substrates carrying spacing modifiers with a non-ionic hydroxy terminus and with methylene (flanked by the cis,cis diene moiety) pro-( S )-hydrogen can be synthesized from the intermediates 1a – 1c . These intermediates are conveniently synthesized via enzymatic resolution with lipase in organic solvents.

Asymmetric synthesis of unnatural (Z,Z,E)-octadecatrienoid and eicosatrienoid by lipoxygenase-catalyzed oxygenation

The asymmetric synthesis of unnatural 13-hydroxy-(6Z,9Z,11E,13S)-octadecatrienoid and 15-hydroxy-(8Z,11Z,13E,15S)-eicosatrienoid is described using a biomimetic oxidation route. The main highlights of this synthesis are the asymmetric hydroxylation of the substrate with soybean lipoxygenase and cis selective Wittig olefination.

Asymmetric Synthesis of Ramariolides A and C through Bimetallic Cascade Cyclization and Z–E Isomerization Reaction

A short and flexible asymmetric synthesis of ramariolides A and C was accomplished. A bimetallic catalytic system consisting of Pd-Cu-mediated cascade cyclization, unprecedented Z-E isomerization by a Ru-based metathesis catalyst, and late-stage stereoselective epoxidation are the key steps involved in the synthesis.