Asymmetric syntheses of 1-amino-2-phenyl(alkyl)cyclopropanecarboxylic acids by diastereoselective cyclopropanation of highly functionalized monochiral olefines

Asymmetric Synthesis of α,α-Disubstituted α-Amino Acids by Diastereoselective Alkylation of Camphor-Based Tricyclic Iminolactone

A novel and convenient route for the preparation of chiral tricyclic iminolactones 9 and 10 from camphorquinone has been developed. Alkylation of iminolactones 9 and 10 provided iminolactones 16 and 17 in high yields which were, in turn, alkylated again to afford the alpha,alpha-disubstituted products in good yields (70-90%) and excellent diastereoselectivities (>98%). Hydrolysis of the alkylated iminolactones furnished the desired alpha,alpha-disubstituted alpha-amino acids in good yields and high enantiomeric excesses with good recovery yields of the chiral auxiliary 12 and 13. The extremely high endo-face selectivity for alkylation is discussed using semiempirical (MOPAC 93) calculations.

Diastereoselective Synthesis of Cyclopropane Amino Acids Using Diazo Compounds Generated in Situ

A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using aryl and unsaturated diazo compounds generated in situ from the corresponding tosylhydrazone salts. It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers. The synthetic utility of this process was demonstrated in the synthesis of (+/-)-(Z)-2,3-methanophenylalanine [(+/-)-(Z)-1], the anti-Parkinson (+/-)-(E)-2,3-methano-m-tyrosine [(+/-)-(E)-2], and the natural product (+/-)-coronamic acid [(+/-)-3].

Asymmetric synthesis of substituted 1-aminocyclopropane-1-carboxylic acids via diketopiperazine methodology

Diketopiperazinespirocyclopropane 12 is prepared in > 98% d.e. via the conjugate addition of a phosphorus ylide to (6S)-N,N'-bis(p-methoxybenzyl)-3-methylenepiperazine-2,5-dione 2. Deprotection and hydrolysis of adduct 12 and subsequent peptide coupling demonstrate the applicability of this methodology to the asymmetric synthesis of 1-aminocyclopropane-1-carboxylic acids for incorporation into novel peptides. A model for the high level of diastereofacial selectivity observed in the cyclopropanation reaction is presented. A highly selective asymmetric approach (> 98% d.e.) to (S)-[2,2-(2)H2]-1-aminocyclopropane-1-carboxylic acid 29 is also reported via a deuterated sulfur ylide addition to acceptor 2.

New chiral didehydroamino acid derivatives from a cyclic glycine template with 3,6-dihydro-2H-1,4-oxazin-2-one structure: applications to the asymmetric synthesis of nonproteinogenic alpha-amino acids

New chiral (Z)-alpha,beta-didehydroamino acid (DDAA) derivatives with 3,5-dihydro-2H-1,4-oxazin-2-one structure 11a-f have been stereoselectively prepared after condensation of chiral glycine equivalent 7 with aldehydes in the presence of K(2)CO(3) under mild solid-liquid phase-transfer catalysis reaction conditions. These new systems have been used in diastereoselective cyclopropanation reactions using Corey's ylide for the asymmetric synthesis of 1-aminocyclopropane-1-carboxylic acids (ACCs) such as allo-corononamic and allo-norcoronamic acids. The hydrogenation reaction of these systems at ambient pressure in the presence of formaldehyde affords saturated oxazinones and N-methylated oxazinones which have been transformed into the N-methyl-alpha-amino acids (N-MAAs) (S)-2-(methylamino)butanoic acid and (S)-N-methylleucine. In addition, the parent alpha, beta-didehydroalanine derivative 11g has been prepared by a direct aminomethylation-elimination sequence from 7 and Eschenmoser's salt and has been used in Diels-Alder cycloaddition with endo selectivity for the synthesis of the enantiomerically pure bicyclic alpha-amino acids (-)-2-aminobicyclo[2.2.1]heptane-2-carboxylic and (-)-2-aminobicyclo[2.2.2]octane-2-carboxylic acids.

Efficient access to all four stereoisomers of phenylalanine cyclopropane analogues by chiral HPLC

Bonded polysaccharide-derived chiral stationary phases were found to be useful for the preparation of the four stereoisomers of the cyclopropane analogue of phenylalanine (c(3)Phe) as well as for the direct determination of the enantiomeric purity of c(3)Phe derivatives by HPLC. Three chiral stationary phases, consisting of cellulose and amylose derivatives chemically bonded on allylsilica gel, were tested. The mixed 10-undecenoate/3, 5-dimethylphenylcarbamate of cellulose, 10-undecenoate/3, 5-dimethylphenylcarbamate of amylose and 10-undecenoate/p-methylbenzoate of cellulose were the starting polysaccharide derivatives for CSP-1, CSP-2, and CSP-3, respectively. Using mixtures of n-hexane/chloroform/2-propanol as mobile phase on a semi-preparative column (150 mm x 20 mm ID) containing CSP-2, we separated about 1.7 g of racemic cis-methyl 1-tert-butoxycarbonylamino-2-phenylcyclopropanecarboxylate (cis-6) and 1.2 g of racemic trans-methyl-1-tert-butoxycarbonylamino-2-phenylcycloprop-anecarboxyl ate (trans-6) by successive injections. Copyright 1999 Wiley-Liss, Inc.