151671-03-3Relevant articles and documents
Trading N and O. Part 4: Asymmetric synthesis of syn-β-substituted-α-amino acids
Davies, Stephen G.,Fletcher, Ai M.,Greenaway, Catherine J.,Kennedy, Matthew S.,Mayer, Christoph,Roberts, Paul M.,Thomson, James E.
, p. 5049 - 5061 (2018/05/08)
A total of nine enantiopure syn-β-substituted-α-amino acids have been synthesised, comprising both syn-β-hydroxy-α-amino acids and syn-β-fluoro-α-amino acids. The key step in the synthetic strategy towards these syn-β-substituted-α-amino acids involves a stereospecific rearrangement, which proceeds via the intermediacy of the corresponding aziridinium ions. The requisite enantiopure syn-α-hydroxy-β-amino esters were prepared via asymmetric aminohydroxylation of the corresponding α,β-unsaturated esters followed by epimerisation of the resultant anti-α-hydroxy-β-amino esters at the C(2)-position. Subsequent activation of the α-hydroxy moiety as a leaving group followed by displacement by the β-amino substituent gave the corresponding aziridinium species. Regioselective in situ ring-opening of the aziridinium intermediates with either water or fluoride gave the corresponding syn-β-hydroxy-α-amino ester or syn-β-fluoro-α-amino ester, respectively, and N-deprotection and ester hydrolysis afforded the target syn-β-substituted-α-amino acids as single diastereoisomers in good overall yield.
Trading N and O: Asymmetric syntheses of β-hydroxy-α-amino acids via α-hydroxy-β-amino esters
Davies, Stephen G.,Fletcher, Ai M.,Frost, Aileen B.,Lee, James A.,Roberts, Paul M.,Thomson, James E.
, p. 8885 - 8898 (2013/09/23)
Both diastereoisomers of 2-amino-3-hydroxybutanoic acid and 2-amino-3-hydroxy-3-phenylpropanoic acid have been prepared from enantiopure α-hydroxy-β-amino esters via the intermediacy of the corresponding cis- and trans-aziridines. Aminohydroxylation of two α,β-unsaturated esters produced enantiopure 2,3-anti-α-hydroxy-β-amino esters in >99:1 dr. Subsequent epimerisation at the C(2)-position via a sequential oxidation/diastereoselective reduction protocol gave the corresponding enantiopure 2,3-syn-α-hydroxy-β-amino esters in >99:1 dr. These syn- and anti-substrates were then converted into the corresponding N-Boc protected cis- and trans-aziridines, respectively, via a three step reaction sequence: (i) hydrogenolysis and in situ N-Boc protection; (ii) OH-activation; and (iii) aziridine formation. Subsequent regioselective ring-opening of the C(3)-methyl-aziridines with Cl3CCO2H proceeded with inversion of configuration to give the corresponding 2-amino-3-trichloroacetate esters, whereas the analogous reaction with the C(3)-phenyl-aziridines resulted in rearrangement to the corresponding oxazolidin-2-ones with retention of configuration. In each case, hydrolysis of the products from these ring-opening reactions produced the corresponding enantiopure β-hydroxy-α-amino acids as single diastereoisomers.
Asymmetric synthesis of α-amino carbonyls (aldehydes, ketones and acids) using lithium (R)-N-benzyl-N-α-methylbenzylamide
Davies,Epstein,Ichihara,Smith
, p. 1599 - 1601 (2007/10/03)
The diastereoselective conjugate addition of lithium (R)-N-benzyl-N-α-methylbenzylamide to α,β-unsaturated esters and subsequent enolate hydroxylation, followed by reduction and oxidative cleavage provides a facile route to N,N-protected α-amino aldehydes and ketones. Further manipulation furnishes α-amino acids in high enantiomeric excess.
