Diastereoselective Synthesis of Enantiopure Cyclic α-Aminophosphonic Acids

A new and efficient route for the synthesis of cyclic aminophosphonic acids by the reaction of dialkylchlorophosphites with β-aldiminoalcohols has been described.     

Ring-Closing Metathesis in the Synthesis of Cyclic α-Amino Acids

The review summarizes recent advances in the synthesis of cyclic -amino acids via intramolecular ring-closing metathesis of dienes and enynes.     

The Synthesis of Cyclic Amino Acids

Several cyclic amino acids (1-4) were synthesized from glycine. Isocyanate ester was prepared as the key intermediate and reacted with dibromoalkanes to afford the target compounds.     

An Improved Synthesis of α,β Methylenic Cyclic Ketones

This communication describes a convenient two steps procedure for the preparation of α,β methylenic cyclic ketones from arylmethyl ketones involving a preformed Mannich reagent.     

Switchable Synthesis of 7- and 14-Membered Cyclic Peptides Containing N-Methyl- and β-Amino Acids Utilizing Microflow Technology

Smaller cyclic peptides containing non-proteinogenic amino acids have garnered much attention for use as drugs, but their chemical synthesis is extremely challenging. In this study, a rapid (60.5 min) synthesis of 7- and 14-membered cyclic peptides containing N-methyl- and β-amino acids was achieved by only switching the concentrations (0.20 M or 0.01 M) of the substrates. The developed approach required neither expensive transition-metals nor expensive coupling agents. As far as we could ascertain, this is the first report of the synthesis of smaller (≤16-membered) cyclic N-methylated peptides via dimerization-cyclization strategy.     

Enantioselective Synthesis of α-Thiocarboxylic Acids by Nitrilase Biocatalysed Dynamic Kinetic Resolution of α-Thionitriles

The enantioselective synthesis of α-thiocarboxylic acids by biocatalytic dynamic kinetic resolution (DKR) of nitrile precursors exploiting nitrilase enzymes is described. A panel of 35 nitrilase biocatalysts were screened and enzymes Nit27 and Nit34 were found to catalyse the DKR of racemic α-thionitriles under mild conditions, affording the corresponding carboxylic acids with high conversions and good-to-excellent ee. The ammonia produced in situ during the biocatalytic transformation favours the racemization of the nitrile enantiomers and, in turn, the DKR without the need of any external additive base.     

Synthesis of α-N-Ethylamino Acids and their Derivatives

 A new synthesis of α-N-ethylamino acids starting from α-amino acids using hexafluoroacetone as protecting and activating agent is described. The hexafluoroacetone-protected N-ethylamino acid derivatives obtained are activated lactons. Therefore, they can be directly transformed without the need of an additional activation step with various nucleophiles into the corresponding carboxylic acid derivatives.     

Synthesis of α-N-Ethylamino Acids and their Derivatives

Summary.  A new synthesis of α-N-ethylamino acids starting from α-amino acids using hexafluoroacetone as protecting and activating agent is described. The hexafluoroacetone-protected N-ethylamino acid derivatives obtained are activated lactons. Therefore, they can be directly transformed without the need of an additional activation step with various nucleophiles into the corresponding carboxylic acid derivatives. Received March 24, 2000. Accepted (revised) April 20, 2000     

Polyenolates of Unsaturated Carboxylic Acids in Synthesis. Synthesis of Unsaturated α-Amino Acids and β-Hydrazing Acids

Regioselective reaction of lithium diene-and triene-diolates 1 and 2 with O-diphenylphosphinyl hydroxylamine affords unsaturated α-amino acids 3 and 4. Addition to DEAD leads selectively to γ-hydrazino unsaturated acids 5 and 6.     

Improved Synthesis and Resolution of α-N-Benzoyl-β(3-Qumolyl)-DL-α-Alanine Methyl Ester

The title compound has been synthesized and resolved previously by T. M. Kubiak. In our searching of new potent agonists of LH-RH(luteinizing hormone releasing hormone), α-N-t-butyloxycarbonyl-β-3-quinolyl)-D-α-alanine and its L-isomer were synthesized. The unprotected.optically active amino acids were obtained by enzymatic hydrolysis of the title compounds, followed by hydrolysis in 6 mol/L hydrochloric acid. The title compound was synthesized initially with 3-quinolinecar-     

New Enantioselective Routes to Cyclic and Acyclic S,O-acetals; Enzymatic Resolution of α-Acetoxy Sulfides and Enantioselective Synthesis of the Antiviral Agent Lamivudine

A new method for the synthesis of cyclic and acyclic optically active S,O-acetals is reported, along with subsequent stereocontrolled transformations, culminating in a synthesis of the important antiviral nucleoside Lamivudine.     

Enzymic Optical Resolution of α,α-Difluoro-β-Hydroxyketones

Kinetic resolution of various α,α-difluoro-β-hydroxyketones was conducted by enantioselective hydrolysis of the corresponding acetates with lipase MY to afford optically active products. Both enantiomers of 3,3-difluoro-2-hydroxy-4-decanone were obtained in a highly enantioselective manner by screening enzymes and acyl groups.     

Synthesis of (+)- and (−)-Tetrabenazine from the Resolution of α-Dihydrotetrabenazine

Abstract

Tetrabenazine (1) was reduced with NaBH₄ to α-dihydrotetrabenazine (2) and then resolved with di-p-toluoyl-L-tartrate and di-p-toluoyl-D-tartrate to subsequently give (+)- and (?)-α-dihydrotetrabenazine. The enantiomers were oxidized under Swern conditions to prepare samples of (+)-tetrabenazine and (?)-tetrabenazine. The samples were optically pure by chiral HPLC analysis.     

An Improved Synthesis of α-Phenylseleno Arsonium Ylides

The first a-seleno arsonium ylides have been synthesized by Typical procedure for the synthesis of compound sa. To a stirred suspension ofmethoxycarbonylmethylene triphenylarsorane (4a) (0.378 g, I mmol) and triethylamine(0. I I g, 1. 1 mmol) in MeOH-Et,O (0.6 mml, v/v=l f I ) was added dropwise the solutionof phenylselenenyl iodide 2 (0.85 mmol) in MeOH-Et,O (2.8 mml, v/v=l f l) at 0 "C for14 hrs. The mixture was stirred again for 6 hrs. After the solvent in the mixture wasevaporated un…     

Synthesis and Reaction of 4-Methyl-3,4-epithiotetrahydropyran with α-Amino Acids

4-Methyl-3,4-epithiotetrahydropyran was synthesized by the recyclization of 4-methyl-3,4-epoxytetrahydropyran by the action of thiourea. The product reacts with -amino acids in an alkaline medium with regioselective opening of the thiirane ring at the least substituted carbon atom.     

Synthesis of Phosphonic Acids Related to the Antibiotic Fosmidomycin from Allylic α- and γ-Hydroxyphosphonates

Abstract

Fosmidomycin is the most active compound of a group of natural phosphonic acid antibiotics bearing a unique hydroxamic acid functionality in the γ-position¹. We present here two efficient and novel routes to precursors and analogues of these compounds.     

Synthesis of Enantiomerically Enriched α-Bromonitriles from Amino Acids

Two methods were investigated for the preparation of six chiral α-bromonitriles with different optic purities. The nitrous deamination of amino acids gives α-bromoacids, which react with chlorosulfonyl isocyanate followed by triethylamine to afford α-bromonitriles with moderate enantiomeric excess. However, the dehydration of corresponding α-bromoamids using thionyl chloride gives α-bromonitriles with good enantiomeric excess up to 94%. The use of phosphoryl chloride instead of thionyl chloride results in more than 30% racemization as determined by high-performance liquid chromatograpic analysis.     

Synthesis and Stereochemistry of New Cyclic Phosphate-phosphonates

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