Biocatalytic approaches toward the synthesis of both enantiomers of trans-cyclopentane-1,2-diamine

Synthesis of Fmoc-Protected ( S, S)- trans-Cyclopentane Diamine Monomers Enables the Preparation and Study of Conformationally Restricted Peptide Nucleic Acids

An efficient synthesis of Fmoc-protected ( S, S)- trans-cyclopentane PNA ( tcypPNA) monomers starting from mono-Boc-protected ( S, S)-1,2-cyclopentanediamine is reported. A general synthetic strategy was developed so that tcypPNA monomers with each nucleobase can be made in sufficient quantity and purity for use in solid-phase peptide synthesis (SPPS). The newly synthesized monomers were then successfully incorporated into 10-residue PNA oligomers using standard Fmoc chemistry for SPPS. The different tcypPNAs allow different positions in the sequence to be conformationally constrained with ( S, S)- trans-cyclopentane to determine the effects on binding to complementary DNA.

Enzymatic synthesis of L-norephedrine by coupling recombinant pyruvate decarboxylase and ω-transaminase

L-Norephedrine, a natural plant alkaloid, possesses similar activity as ephedrine and can be used as a vicinal amino alcohol for the asymmetric synthesis of a variety of optically pure compounds, including pharmaceuticals, fine chemicals, and agrochemicals. Because of the existence of two asymmetric centers, efficient synthesis of L-norephedrine has been challenging. In the present study, an R-selective pyruvate decarboxylase from Saccharomyces cerevisiae and an S-selective ω-transaminase from Vibrio fluvialis JS17 were coupled to develop a sequential process for the stereoselective biosynthesis of L-norephedrine. After systematic optimization of the reaction conditions, a green, economic, and practical biocatalytic method to prepare L-norephedrine was established to achieve de and ee values of greater than 99.5 % and a molar yield over 60 %. The present coupling approach can facilitate the development of sequential reactions by various biocatalysts.

New generation of biocatalysts for organic synthesis

The use of enzymes as catalysts for the preparation of novel compounds has received steadily increasing attention over the past few years. High demands are placed on the identification of new biocatalysts for organic synthesis. The catalysis of more ambitious reactions reflects the high expectations of this field of research. Enzymes play an increasingly important role as biocatalysts in the synthesis of key intermediates for the pharmaceutical and chemical industry, and new enzymatic technologies and processes have been established. Enzymes are an important part of the spectrum of catalysts available for synthetic chemistry. The advantages and applications of the most recent and attractive biocatalysts--reductases, transaminases, ammonia lyases, epoxide hydrolases, and dehalogenases--will be discussed herein and exemplified by the syntheses of interesting compounds.

Catalytic enantioselective desymmetrization of meso-diamines: a dual small-molecule catalysis approach

The desymmetrization of meso-diamines was accomplished via enantioselective monobenzoylation facilitated by the cooperative action of two small-molecule catalysts. A chiral acyl-transfer reagent is formed in situ through the interplay of benzoic anhydride, 4-(dimethylamino)pyridine as a nucleophilic catalyst, and a chiral amide-thiourea cocatalyst.

A Biocatalytic Approach to Synthesizing Optically Active Orthogonally Protected trans-Cyclopentane-1,2-Diamine Derivatives

A straightforward chemoenzymatic synthesis of optically active trans-N,N-dialkylcyclopentane-1,2-diamines has been efficiently developed starting out from their analogous (+/-)-trans-2-(N,N-dialkylamino)cyclopentanols. The route involves the one-pot stereospecific transformation of the racemic amino alcohols into racemic diamines and a subsequent kinetic resolution by means of lipase-B from Candida antarctica-catalyzed acylation reactions. The careful selection of both the alkyl substituents present in the diamine and the derivatization strategy applied to the enzymatic reaction enabled the easy preparation of other synthetically valuable optically active trans-cyclopentane-1,2-diamines derivatives.

Practical Synthesis of trans-tert-Butyl-2-aminocyclopentylcarbamate and Resolution of Enantiomers

Optically active trans-tert-butyl-2-aminocyclopentylcarbamate (1) has potential utility as a scaffold for chiral ligands and as a modified backbone unit for peptide nucleic acids (PNAs). We have developed a short and practical synthesis of 1 via aziridine opening of tosyl-activated cyclopentene aziridine 2 and optical resolution of racemic 1 with 10-camphorsulfonic acid (CSA). The route provides ready access to multigram quantities of both enantiomers without the need for chromatography.

Catalytic Asymmetric Synthesis of Vicinal Diamine Derivatives through Enantioselective N-Allylation Using Chiral π-Allyl Pd-Catalyst

[reaction: see text] N-monoallylation of meso-vicinal diamine bistrisylamides using a chiral pi-allyl-Pd catalyst proceeded in an enantioselective manner (up to 90% ee) to give desymmetrization products in good yields. The product was converted to the known sigma-receptor agonist in short steps. In addition, the present catalytic asymmetric N-allylation was applied to kinetic resolution of racemic-diamide.

Transacylation of α-Aryl-β-keto Esters

The acyl group of an alpha-aryl-beta-keto ester was readily transferred to N-, O-, and S-nucleophiles. The transacylation from arylated diethyl 3-oxoglutarate to amines led to unsymmetrical malonic acid amide esters in high yields. The present reaction proceeded under mild conditions without formation of detectable byproducts. Only simple experimental manipulations were required. This reaction was also found to be sensitive to steric factors, which enabled the chemoselective monoacylation of diamines and amino alcohols without any modifications such as protection.

A cyclopentane conformational restraint for a peptide nucleic acid: design, asymmetric synthesis, and improved binding affinity to DNA and RNA

[structure: see text] A strategy to restrict the highly flexible backbone conformation of a peptide nucleic acid (PNA) by incorporation of a cyclopentane ring is proposed. An asymmetric synthesis of cyclopentane-modified PNA is reported, and its binding properties were determined. The cyclopentane ring leads to a significant improvement in the binding properties of the resulting PNA to DNA and RNA.