Amino acids from imides

Alternatively, an electrochemical procedure was employed in the synthesis of amino acids from nitridomolybdenum complex 4 via nitrogen-carbon and carbon-carbon bond formations involving imide 5 and nitrogen ylides 6. trans-[MoCl(N)(Ph2PCH2CH2PPh2)] 4 reacted with methyl iodoacetate to give the cationic complex 5. Complex 6 was obtained by the deprotonation of 5 at the a-carbon followed by treatment with Mel to afford the cationic methyl derivative 7. Electrochemical cleavage of the Mo-N bond of the complex 5 or 7 proceeded in the presence of acetic acid to release amino acid esters in 70-80% yield (Scheme 2) [12]. 

Combination of several molecules accompanied by relocation of a polyatomic radical The formation of sulfuric acid hydrate from-S -3 and H, of Nordhauser s oil of vitriol [H2S2O7] from anhydrous sulfuric acid and sulfuric acid hydrate, the production of hydrates of dibasic acids when water reacts with the anhydride, the formation of amino acids from the action of water on imiiies, and of amides when NH3 acts on imides, etc., belong here. For instance ... 

The most general protocol (eq 10) has therefore been based on potassium hexamethyldisilazide (KHMDS) as the base addition of trisyl azide at —78 °C and then acetic acid at the same temperature. Excellent levels of diastereoselectivity are ohsCTved with most substrates and the method has been used widely in the enantioselective synthesis of a-amino acids from chiral iniides. Chemoselective azidation of an imide enolate in the presence of an ester function has been demonstrated (eq 11). The product distribution is nevertheless finely balanced, as discovered with the respective dimethyl and dihenzyl ethers of the 3,5-substituted phenylacetyl imide (3) (eq 12). ... 

Just as a lactam can be opened to give an amino acid, an imide gives a similar reaction. A simple example is the hydrolysis of glutarimide, in this case prepared from furfural in four steps, to 5-amino-4-oxo-pentanoic acid (5-aminolevulinic acid, 2.81). This latter compound showed relatively high herbicidal activity. ... 

For other recent reviews of phthalimide photochemistry, see Griesbeck, AG., Chimia, 52, 272-283, 1998 Griesbeck, A.G., Photochemical Activation of Amino Acids. From the Synthesis of Enantiomer-icaUy Pure P,Y-Unsaturated Amino Adds to Macrocychc Ring Systems, Liebigs Ann., 1951-1958,1996. Yoon, U.C., Kim, H.J., and Mariano, P.S., Eledron Transfer Induced Photochemical Reactions in Imide Systems. Photoaddition of a-Trimethylsilyl Substituted Heteroatom Containing Compounds to Phthalimides. Heterocycles, 29,1041-1064. 1989. 

This imide system can also be used for the asymmetric synthesis of optically pure a,a-disubstituted amino aldehydes, which can be used in many synthetic applications.31 These optically active a-amino aldehydes were originally obtained from naturally occurring amino acids, which limited their availability. Thus, Wenglowsky and Hegedus32 reported a more practical route to a-amino aldehydes via an oxazolidinone method. As shown in Scheme 2 20, chiral diphenyl oxazolidinone 26 is first converted to allylic oxazolidinone 27 subsequent ozonolysis and imine formation lead to compound 28, which is ready for the a-alkylation using the oxazolidinone method. The results are shown in Table 2-6. 

The formation of tluorinated Q -hydroxy-jS-imino esters (180) by treatment of fluorinated imino ethers (179) with lithium 2,2,6,6-tetramethylpiperidide has been reported. A possible explanation for this interesting intramolecular rearrangement is proposed in Scheme 64. Acyclic imides derived from primary benzylic amines and amino acid esters have been found to undergo a novel nitrogen to carbon acyl migration via a base-generated carbanion to yield the corresponding a-amino... 

Due to these limitations Evans et al. focussed on the exploration of imide-derived enolates (165). They expected these systems to react stereoselective in carbon-carbon bond formation and that the derived imides might be readily hydrolized or reduced under the mild conditions required for the construction of complex products, One of the two chiral 2-oxazolidones (175) chosen for study by Evans et al.179) is derived from (S)-valine and was readily prepared from this inexpensive commercially available a-amino acid having an optical purity exceeding 99 %. The preparation of the related imide-derived enolate (165) is shown in the next scheme. Alkylation reactions employing (175) resulted in excellent diastereoface selection, as summarized in Table 4 179). 

In solution-phase peptide synthesis, acylation of amino acids or peptides with N-protected azetidine-2-carboxylic acid is performed via the active esters, e.g. A-hydroxysuccin-imide 100 111-112 or pentachlorophenyl ester, m 117 as well as by the mixed anhydride 101114 or carbodiimide 118 methods. An attempt to prepare the A-carbonic acid anhydride by cycli-zation of A-(chloroformyl)azetidine-2-carboxylic acid with silver oxide in acetone or by addition of triethylamine in situ failed, presumably due to steric hindrance. 111 In SPPS, activation of the Fmoc-protected imino acid by HBTU 119,120 is reported. In solution-phase peptide synthesis, coupling of N-protected amino acids or peptides to C-protected azetidine-2-carboxylic acid or related peptides may be performed by active esters, 100 118 121 mixed anhydrides, 95 or similar methods. It may be worth mentioning that the probability of pip-erazine-2,5-dione formation from azetidine-2-carboxylic acid dipeptides is significantly reduced compared to proline dipeptides. 111 ... 

In analogy to proline dipeptides, A1-unprotected 2-carbonylpyrazolidine amino acid dipeptide esters 37 on storage at ambient temperature are prone to conversion into the related triazines 38 that correspond to the aza analogues of piperazine-2,5-diones (Scheme 5). 160 161 An additional side reaction is reported for the 2-azaproline peptides 161 which leads to formation of the cyclic imide 40 from methyl TV -lbenzyloxycarbonylj -carbonylpyra-zolidine glycinate (39) upon treatment with methanolic ammonia (Scheme 6). 

The application of antibiotics as chiral selectors has resulted in the successful resolution of almost all types of neutral, acidic, and basic racemic molecule. These antibiotics have been used for the enantiomeric resolution of amino acids, their derivatives, peptides, alcohols, and other pharmaceuticals. The selectivities of the most commonly used antibiotic-based (vancomycin, teicoplanin, and ristocetin A) CSPs varied from one racemate to another and are given in Table 1. Vancomycin was used for the chiral resolution of amino acids, amines, amides, imides, cyclic amines, amino alcohols, hydantoins, barbiturates, oxazolidinones, acids, profens, and other pharmaceuticals. Teicoplanin was found to be excellent chiral selector for the enantiomeric resolution of amino acids, amino alcohols, imides, peptides, hydantoins, a-hydroxy and halo acids, and oxazolidinones, whereas ristocetin A is capable of chiral resolution of amino acids, imides, amino... 

The search for other amino acid-based catalysts for asymmetric hydrocyanation identified the imidazolidinedione (hydantoin) 3 [49] and the e-caprolactam 4 [21]. Ten different substituents on the imide nitrogen atom of 3 were examined in the preparation, from 3-phenoxybenzaldehyde, of (S)-2-hydroxy-2-(3-phenoxy-phenyl)acetonitrile, an important building block for optically active pyrethroid insecticides. The N-benzyl imide 3 finally proved best, affording the desired cyanohydrin almost quantitatively, albeit with only 37% enantiomeric excess [49]. Interestingly, the catalyst 3 is active only when dissolved homogeneously in the reaction medium (as opposed to the heterogeneous catalyst 1) [49]. With the lysine derivative 4 the cyanohydrin of cyclohexane carbaldehyde was obtained with an enantiomeric excess of 65% by use of acetone cyanohydrin as the cyanide source [21]. 

Stereoselective rearrangement reactions can involve sugar-linked functionalities. An example of this type is the Overman rearrangement of allylic trichloracetimidates formed from a D-glucofuranose derivative 20 [36]. This methods affords (L)-a-ami-no acids 25 from (Z)-allylic imidate 23 and (R)-a-amino acids 25 from ( )-imidates 23 with a diastereoselectivity of about 16 1. The oxidative cleavage of compound 24 with Ru04 yields the a-amino acid 25, (Scheme 15). 

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