- Practical syntheses of both enantiomers of cyclopropylglycine and of methyl 2-cyclopropyl-2-N-Boc-iminoacetate
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A facile three-step synthesis of racemic cyclopropylglycine in multigram quantities from inexpensive cyclopropyl methyl ketone has been elaborated. Enzymatic hydrolysis of the N-Boc-protected methyl ester of cyclopropylglycine 9 with the inexpensive enzyme papain from Carica papaya affords both enantiomers of cyclopropylglycine (8) with enantiomeric excesses of 99% or better after deprotection under acidic conditions. Furthermore, the new cyclopropyl group-containing building block methyl 2-cyclopropyl-2-N-Boc-iminoacetate (13) was prepared by N-chlorination and subsequent dehydrochlorination with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Addition of nucleophiles to 13 offers a ready access to an unusual, orthogonally bisprotected α,α-diamino acid derivative and interesting components of rigid peptide backbones.
- Larionov, Oleg V.,De Meijere, Armin
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p. 1071 - 1078
(2007/10/03)
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- SYNTHESIS OF α-AMINO ACIDS WITH β,γ-UNSATURATED SIDE CHAINS
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α-Amino acids with allenyl, vinyl and acetylenic side chains can be synthesized using non-enolate based strategies.The ester enolate-Claisen rearrangement applied to propargylic esters of N-protected α-amino acids is of limited utility since only poor yields of allenic product are obtained with the N-Boc glycine esters, the system which give the most reproducible results.However, α-allenyl-α-amino acids that are fully functionalized on the α-carbon are available through the agency of 4-allenyl-2-phenyloxazolones 4 ( obtained from propargyl esters of N-benzoyl protected amino acids via cyclization and Claisen rearrangement ) provided that Meerwein's reagent is used to facilitate hydrolysis of the benzamide function in 5.A variety of α-substituted glycinates, including those with α-vinyl and α-acetylenic functions, can be prepared using a two step sequence involving condensation of the cationic glycine synthon 22 with various organomagnesium reagents, followed by hydrolysis.
- Castelhano, Arlindo L.,Horne, Stephen,Taylor, Gregg J.,Billedeau, Roland,Krantz, Allen
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p. 5451 - 5466
(2007/10/02)
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- REACTIONS OF AN ELECTROPHILIC GLYCINE CATION EQUIVALENT WITH GRIGNARD REAGENTS A SIMPLE SYNTHESIS OF β,γ-UNSATURATED AMINO ACIDS
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A simple and general synthesis of α-amino acids employing vinyl and alkyl Grignard reagents with a glycine cation equivalent is described.
- Castelhano, Arlindo L.,Horne, Stephen,Billedeau, Roland,Krantz, Allen
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p. 2435 - 2438
(2007/10/02)
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