The importance of side chain intramolecular interaction on the stereochemical course of the 2-carbon deuteration of amino acids complexed to cobalt(III)

We, Keyes; Re, Caputo; Rd, Willett; Ji, Legg

doi:10.1021/ja00438a032

Cited by 16 publications

(7 citation statements)

References 5 publications

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“…It is known 18 that the most likely mechanism for the inversion of the chirality of amino acids is the momentary formation of a C᎐ ᎐ C bond caused by the temporary, reversible, ionization of a proton. The temporary species resulting from such an ionization step is planar as a result of its double bond character.…”

Section: Resultsmentioning

confidence: 99%

Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a Co^III–amine complexes: reaction, structure and mechanism

2004

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Cleavage of the peptide bond occurs when beta]-alanyl-L-histidine (carnosine) reacts with [Co(tren)Cl2]+ (tren = tris(2-aminoethyl)amine) to give [Co(tren)(histidine)](2+) 1 and [Co(tren)(beta-alanine)](2+) 2. [Co(tren)(histidine)](2+) 1 crystallizes in the enantiomorphic space group P2(1)2(1)2(1) and 2 crystallizes in the P2(1)/c space group. The mechanism of the cleavage reactions were studied in detail for the precursor [Co(tren)Cl2]+ and [Co(trien)Cl2]+, which convert into [Co(tren)(OH)2]+/[Co(tren)(OH)(OH2)]2+ and [Co(trien)(OH)2]+/[Co(trien)(OH)(OH2)]2+ in water at basic pH (trien = 1,4,7,10-tetraazadecane). At a slightly basic pH, the initial coordination of the substrate (beta-alanyl-L-histidine) is by the carboxylate group for the reaction with [Co(tren)Cl2]+. This is followed by a rate-limiting nucleophilic attack of the hydroxide group at the beta-alanyl-L-histidine carbonyl group. In a strongly basic reaction medium substrate, binding of the metal was through carboxylate and amine terminals. On the other hand, for the reaction between [cis-beta-Co(trien)Cl2]+ and beta-alanyl-L-histidine, the initial coordination of the substrate takes place via an imidazole ring nitrogen, independently, and followed by a nucleophilic attack of the hydroxide group at the beta-alanyl-L-histidine carbonyl group. The circular dichroism spectrum for 1 suggests that a very small extent of racemization of the amino acid (L-histidine) takes place during the cleavage reaction between [Co(tren)Cl2]+ and beta-alanyl-L-histidine. Reaction between [cis-beta-Co(trien)Cl2]+ and beta-alanyl-L-histidine also causes cleavage of the peptide bond, producing a free beta-alanyl molecule and a cationic fragment [cis-alpha-Co(trien)(histidine)](2+) 3 that crystallizes in the optically active space group P2(1)2(1)2(1). Unlike the previous case an appreciable degree of racemization of the L-histidine takes place during the reaction between [cis-beta-Co(trien)Cl2]+ and beta-alanyl-L-histidine. Crystals containing L-histidine and D-histidine fragments in the [cis-alpha-Co(trien)(histidine)]2+ moiety were crystallographically documented by mounting a number of randomly selected crystals.

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Section: Resultsmentioning

confidence: 99%

Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a Co^III–amine complexes: reaction, structure and mechanism

2004

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“…Crystal structures of relevant complexes, for example, Ã(+) 495 -[Co(en) 2 {S-Glu(O À )O}]ClO 4 (en is ethane-1,2-diamine; Gillard et al, 1970), Ã(+) 578 -[Co(en) 2 {S-Asp (OH)O}](ClO 4 ) 2 (Barfod et al, 1999) and rac-(Á-R,Ã-S)-[Co(en) 2 {O 2 CCH[CH(CO 2 Et) 2 ]NH 2 }](ClO 4 ) 2 (Bendahl et al, 2002), reveal firm intramolecular hydrogen-bonding interactions from coordinated ligand amine groups to side-chain acceptor sites. However, in the structure of the asparagine complex, Ã-[Co(en) 2 (S-AsnO)]I 1.6 (NO 3 ) 0.4 , the amino acid side chain is not engaged in intramolecular hydrogen bonding with coordinated ethane-1,2-diamine (Keyes et al, 1976). These structures each represent only one of two possible diastereoisomers and, incidentally, this is the thermodynamically favoured diastereoisomer (Á-R,Ã-S) in all four instances.…”

Section: Commentmentioning

confidence: 99%

Diastereoisomeric β-ethyl aspartate–cobalt(III) complexes: Λ(+)₅₇₈- and Δ(−)₅₇₈-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato]cobalt(III) bis(perchlorate) monohydrate

et al. 2010

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The structures of the diastereoisomers Λ(+)(578)-, (I), and Δ(-)(578)-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato-κ(2)N,O(1)]cobalt(III) bis(perchlorate) monohydrate, (II), both [Co(C(6)H(10)N(2)O(4))(C(2)H(8)N(2))(2)](ClO(4))(2)·H(2)O, are compared. In both structures, the ester group of the amino acid side chain is engaged only in intramolecular hydrogen bonding to coordinated amine groups. This interaction is stronger in (I) and correlates with previously observed diastereoisomeric equilibrium ratios for related metal complex systems in aqueous media. The two perchlorate anions of (II) are located on twofold axes. Both perchlorates in (I) and one of the perchlorates in (II) are affected by disorder. Both structures exhibit extensive three-dimensional hydrogen-bonding networks.

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“…61 As an alternative to the Curtius rearrangement strategy adopted here with the aspartato complexes the Hofmann rearrangement may be applied to the related asparaginato complexes, [(en) 2 Co(AsnO)] 2ϩ . 62 However, the classical method employing bromine in aqueous base was not effective at generating coordinated 2,3-diaminopropanoic acid. In these conditions only epimerization at the α-carbon centre and hydrolysis of the amide functionality of the starting Λ-[(en) 2 Co(S-AsnO)] 2ϩ complex to yield the epimerized aspartato complex, Λ-[(en) 2 Co(R,S-Asp(O Ϫ )O)] ϩ , were observed.…”

Section: Synthesesmentioning

confidence: 99%

“…Contrasting these examples, the neutral carboxamide side chain of the related asparaginato complex, Λ-[(en) 2 Co(S-AsnO)]I 1.6 (NO 3 ) 0.4 , is conformationally extended in the crystal. 62…”

Section: Structure Of (؉) 578 -[(En) 2 Co(s-asp(oh)o)](clo 4 )mentioning

confidence: 99%

Novel metal complex synthons for chiral 4-azaleucine, 2,3-diaminopropanoic acid and its elaboration

Barfod¹,

Bendahl²,

Hammershøi³

et al. 1999

J. Chem. Soc., Dalton Trans.

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Efficient syntheses of chiral Co() complexes with 2,3-diaminopropanoic acid (A 2 pr) have been developed. In these complexes, the amino acid zwitterion [A 2 pr(H ϩ )O Ϫ ] is bound didentate through the carboxylate and N 2 -amine groups while the N 3 -ammonio group [pK a = 7.19(2)] is unprotected. Syntheses of Λ(ϩ) 578 -and ∆(Ϫ) 578 -[(en) 2 Co-(S-A 2 pr(H ϩ )O)]Cl 3 ؒH 2 O were effected stereoretentively from the similarly didentate aspartato complexes Λand ∆-[(en) 2 Co(S-Asp(OH)O)]Cl 2 in reaction sequences transforming the unbound β-carboxyl group into an amine by Curtius rearrangement. The absolute configuration of the Λ(ϩ) 578 -[(en) 2 Co(S-Asp(OH)O)](ClO 4 ) 2 complex was determined by X-ray crystallographic analysis and defined the absolute stereochemistry of diastereoisomers and derived products. Methylation of the N 3 -amine group of Λ(ϩ) 578 -[(en) 2 Co(S-A 2 pr(H ϩ )O)]Cl 3 ؒH 2 O gave the (S)-4azaleucine complex Λ(ϩ) 578 -[(en) 2 Co(S-A 2 pr(Me 2 H ϩ )O)](C 4 F 9 SO 3 ) 3 from which enantiopure (ϩ)-(S)-2-amino-3-(dimethylamino)propanoic acid dihydrochloride hemihydrate [=(ϩ)-(S)-A 2 pr(Me 2 )ؒ2HClؒ0.5H 2 O] was obtained upon reductive removal of the protecting Co(III) centre. Racemic 4-azaleucine was easily produced by an alternative, but also metal-dependent method and the intermediate rac-(p)-[(tren)Co(A 2 pr(Me 2 H ϩ )O)]Zn 2 Cl 7 ؒ3H 2 O obtained in a simple solid-phase synthesis by selective reduction of achiral (p)-[(tren)Co(2-amino-3-(dimethylamino)acrylyl chloride)] 3ϩ ion adsorbed on AG 50W-X2 cation exchange resin. The epimerization rate of the Λ-[(en) 2 Co(S-A 2 prO)] 2ϩ complex ion was first-order in [HO Ϫ ] [k E = 3.8 × 10 Ϫ2 dm 3 mol Ϫ1 s Ϫ1 , I = 1.00 M (NaClO 4 ), 25 ЊC] with the diastereoisomer ratio K C (=[Λ-R]/[Λ-S]) = 0.77(2) at equilibrium in 10 mM NaOH. However, no epimerization was observed after at least 3 hours in 6 M HCl at 45 ЊC.

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The importance of side chain intramolecular interaction on the stereochemical course of the 2-carbon deuteration of amino acids complexed to cobalt(III)

Cited by 16 publications

References 5 publications

Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a Co^III–amine complexes: reaction, structure and mechanism

Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a Co^III–amine complexes: reaction, structure and mechanism

Diastereoisomeric β-ethyl aspartate–cobalt(III) complexes: Λ(+)₅₇₈- and Δ(−)₅₇₈-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato]cobalt(III) bis(perchlorate) monohydrate

Novel metal complex synthons for chiral 4-azaleucine, 2,3-diaminopropanoic acid and its elaboration

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The importance of side chain intramolecular interaction on the stereochemical course of the 2-carbon deuteration of amino acids complexed to cobalt(III)

Cited by 16 publications

References 5 publications

Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a CoIII–amine complexes: reaction, structure and mechanism

Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a CoIII–amine complexes: reaction, structure and mechanism

Diastereoisomeric β-ethyl aspartate–cobalt(III) complexes: Λ(+)578- and Δ(−)578-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato]cobalt(III) bis(perchlorate) monohydrate

Novel metal complex synthons for chiral 4-azaleucine, 2,3-diaminopropanoic acid and its elaboration

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Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a Co^III–amine complexes: reaction, structure and mechanism

Cleavage of the peptide bond of β-alanyl-l-histidine (carnosine) induced by a Co^III–amine complexes: reaction, structure and mechanism

Diastereoisomeric β-ethyl aspartate–cobalt(III) complexes: Λ(+)₅₇₈- and Δ(−)₅₇₈-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato]cobalt(III) bis(perchlorate) monohydrate