A chiral switch: balancing between equilibrium and non-equilibrium states

2019 ◽  
Vol 55 (48) ◽  
pp. 6910-6913 ◽  
Author(s):  
Iaroslav Baglai ◽  
Michel Leeman ◽  
Bernard Kaptein ◽  
Richard M. Kellogg ◽  
Willem L. Noorduin
Keyword(s):  
Amino Acid ◽  
Absolute Configuration ◽  
Equilibrium States ◽  
Chiral Center ◽  
Equilibrium Conditions ◽  
The Absolute ◽  
Amino Acid Precursors ◽  
Non Equilibrium

Herein we introduce a “chiral switch” – a sequence of operations that alternate between equilibrium and non-equilibrium conditions to switch the absolute configuration of a chiral center. The generality and practical potential of the technique are demonstrated with three unnatural α-amino acid precursors.

Enantioselective Synthesis and Photoreactivity of a Diazirinyl-substituted (R)-β-Phenylalanine

2014 ◽  
Vol 69 (11-12) ◽  
pp. 1088-1096 ◽  
Author(s):  
Jan-Niklas Schäckermann ◽  
Thomas Lindel
Keyword(s):  
Amino Acid ◽  
Absolute Configuration ◽  
Enantioselective Synthesis ◽  
Thermally Stable ◽  
Standard Laboratory ◽  
Laboratory Conditions ◽  
Quantumchemical Calculations ◽  
Valence Tautomers ◽  
The Absolute

Abstract The first enantioselective synthesis of a photoreactive (R)-β-phenylalanine is described. In the key step, m-diazirinyl-substituted benzaldehyde is converted to a chiral sulfinimine in a Ti(OEt)4- mediated reaction, followed by diastereoselective enolate addition. The absolute configuration of photo (R)-β-phenylalanine was confirmed by Mosher analysis. The photo amino acid proved to be thermally stable under standard laboratory conditions. Irradiation in toluene afforded cycloheptatriene=norcaradiene valence tautomers, together with carbene benzylation. Quantumchemical calculations indicate a small triplet-singlet gap.

scholarly journals Absolute Stereochemistry of the β-Hydroxy Acid Unit in Hantupeptins and Trungapeptins

2016 ◽  
Vol 11 (1) ◽  
pp. 1934578X1601100 ◽  
Author(s):  
Deepak Kumar Gupta ◽  
Gary Chi Ying Ding ◽  
Yong Chua Teo ◽  
Lik Tong Tan
Keyword(s):  
Amino Acid ◽  
Structural Feature ◽  
Absolute Configuration ◽  
Hydroxy Acid ◽  
Hplc Analysis ◽  
The Absolute ◽  
Absolute Stereochemistry ◽  
Common Structural Feature ◽  
Acid Unit

The β-hydroxy/amino acid unit is a common structural feature of many bioactive marine cyanobacterial depsipeptides. In this study, the absolute stereochemistry of the β-hydroxy acid moieties in hantupeptins and trungapeptins were determined through their synthesis and HPLC analysis of the Mosher ester derivatives. Synthesis of two3-hydroxy-2-methyloctanoic acid (Hmoa) stereoisomers, (2 S,3 R)-Hmoa and (2 S,3 S)-Hmoa, were achieved using diastereoselective asymmetric method and the retention times of all four Hmoa isomers were established indirectly by RPLC-MS analysis of their Mosher ester derivative standards. Based on the retention times of the standards, the absolute configuration of the Hmoa unit in hantupeptin C (3) and trungapeptin C (6) was assigned as (2 R,3 S)- and (2 S,3 R)-Hmoa, respectively. The use of the Mosher's reagents, coupled with HPLC analysis, provided a viable alternative to the absolute stereochemical determination of β-hydroxy acid units in depsipeptides.

scholarly journals A tryptophan C-methyltransferase involved in streptonigrin biosynthesis in Streptomyces flocculus

1984 ◽  
Vol 220 (1) ◽  
pp. 309-313 ◽  
Author(s):  
D L Hartley ◽  
M K Speedie
Keyword(s):  
High Pressure ◽  
Liquid Chromatography ◽  
Amino Acid ◽  
Stationary Phase ◽  
High Pressure Liquid Chromatography ◽  
Absolute Configuration ◽  
Specific Activity ◽  
Shake Culture ◽  
Methyl Group ◽  
The Absolute

A C-methyltransferase that catalyses the transfer of a methyl group from S-adenosylmethionine to C-3 of tryptophan, resulting in beta-methyltryptophan, has been identified in cell-free extracts of streptonigrin-producing Streptomyces flocculus. The absolute configuration of the product was shown to be (2S,3R)-beta-methyltryptophan by high-pressure liquid chromatography and reactivity with D- and L-amino acid oxidases. In shake culture, maximum specific activity occurs after S. flocculus enters stationary phase, but before significant streptonigrin accumulates.

CD exciton chirality method for determination of the absolute configuration of ?-hydroxy-?-amino acid derivatives

Chirality ◽  
2001 ◽  
Vol 13 (5) ◽  
pp. 266-271 ◽  
Author(s):  
Lee-Chiang Lo ◽  
Jean-Yin Chen ◽  
Chun-Tzu Yang ◽  
Der-Shang Gu
Keyword(s):  
Amino Acid ◽  
Absolute Configuration ◽  
Amino Acid Derivatives ◽  
Hydroxy Amino Acid ◽  
Hydroxy Amino ◽  
The Absolute

scholarly journals The Assignment of the Absolute Configuration of C-22 Chiral Center in the Aglycones of Triterpene Glycosides from the Sea Cucumber Cladolabes schmeltzii and Chemical Transformations of Cladoloside C

2015 ◽  
Vol 10 (7) ◽  
pp. 1934578X1501000 ◽  
Author(s):  
Anatoly I. Kalinovsky ◽  
Alexandra S. Silchenko ◽  
Sergey A. Avilov ◽  
Vladimir I. Kalinin
Keyword(s):  
Absolute Configuration ◽  
Sea Cucumber ◽  
Triterpene Glycosides ◽  
Chiral Center ◽  
Biosynthetic Pathways ◽  
Chemical Transformations ◽  
Chemical Structures ◽  
Different Types ◽  
The Absolute ◽  
Chiral Centers

The absolute R-configuration of the C-22 chiral center in cladoloside C (1) and therefore in all related glycosides isolated from the sea cucumber Cladolabes schmeltzii has been assigned by Mosher‘s method. Some chemical transformations of the native glycoside 1 were carried out to apply this method. This resulted in the isolation and elucidation of chemical structures of progenin 2 and artefact aglycones 3 and 4, obtained from 1 and assignment of the absolute R-configuration of C-22 in the progenin 2. The coincidence of C-22 configurations in the studied compounds with those of the earlier known lanostane-type aglycone of frondoside C and holostane-type aglycone of cladoloside C (1) confirms the generic biosynthetic pathways to different types of sea cucumber glycoside aglycones. It suggests the same R-configuration of C-22 chiral centers in all the sea cucumber glycosides having C-22 functionalities.

Nucleic acid and protein content of Bact . lactis aerogenes . I. Equilibrium and non-equilibrium conditions

1962 ◽  
Vol 155 (961) ◽  
pp. 580-588 ◽  
Keyword(s):  
Nucleic Acid ◽  
Protein Content ◽  
Continuous Culture ◽  
Growth Cycle ◽  
Equilibrium States ◽  
Logarithmic Phase ◽  
Equilibrium Conditions ◽  
Aerobacter Aerogenes ◽  
Non Equilibrium

The variations in the size and in the RNA , DNA and protein content of cells of Bact . lactis aerogenes ( Aerobacter aerogenes ) during a growth cycle are compared with the corresponding values obtained in continuous culture. The results are discussed in terms of the economy of the cell and in particular with regard to how far the levels of RNA , DNA and protein in a growth cycle differ from equilibrium values. When non-equilibrium states occur in the growth cycle explanations are suggested for the ‘overshoot’ phenomena. The results obtained when cultures are started with cells from the logarithmic phase of the growth cycle agree more closely with the equilibrium (continuous culture) values than those obtained when inocula from 24 h glucose-exhausted cultures are used. The results emphasize the disadvantages of comparing analyses of cells from cultures sampled at arbitrarily chosen times.

Enantioselective synthesis of 1-substituted tetrahydroisoquinoline-1-carboxylic acids

1992 ◽  
Vol 70 (5) ◽  
pp. 1555-1561 ◽  
Author(s):  
Zbigniew Czarnocki ◽  
Dennis Suh ◽  
David B. MacLean ◽  
Philip G. Hultin ◽  
Walter A. Szarek
Keyword(s):  
Amino Acid ◽  
Carboxylic Acids ◽  
Absolute Configuration ◽  
Enantioselective Synthesis ◽  
Synthetic Route ◽  
Acid Hydrochloride ◽  
The Absolute

The 3,4-dihydroisoquinolinium salt 1 and its enantiomer have been converted readily and stereoselectively into (+)-and (−)-1,2,3,4-tetrahydro-6,7-dimethoxy-1-methylisoquinoline-1-carboxylic acids. The synthetic route described should be applicable to the enantioselective synthesis of a variety of 1-alkyl- or 1-aryl-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acids. The absolute configuration of the amino acid hydrochloride 11 was established to be as depicted in Scheme 2.

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