98517-04-5Relevant articles and documents
Design of radical-resistant amino acid residues: A combined theoretical and experimental investigation
Croft, Anna K.,Easton, Christopher J.,Radom, Leo
, p. 4119 - 4124 (2007/10/03)
Ab initio calculations have been used to design radical -resistant amino acid residues. Optimized structures of free and protected amino acids and their corresponding β-carbon-centered radicals were determined with B3-LYP/6-31G(d). Single-point RMP2/6-31G
Selective Reaction of Glycine Residues in Hydrogen Atom Transfer from Amino Acid Derivatives
Burgess, Vicky A.,Easton, Christopher J.,Hay, Michael P.
, p. 1047 - 1052 (2007/10/02)
Relative rates of reaction of the N-benzoylamino acid methyl esters 1a-4a with N-bromosuccinimide and of 1a-4a with di-tert-butyl peroxide are reported.The selective reaction of glycine derivatives in these and other reactions of N-acylamino acid derivatives is attributed to the relative stability of intermediate radicals produced by hydrogen atom transfer.Radicals formed by hydrogen abstraction from N-acylglycine derivatives may adopt planar conformations which are relatively free of nonbonding interactions and in which there is maximum delocalization of the unpairedelectron, whereas radicals produced by similar reactions of derivatives of other amino acids are relatively unstable because of nonbonding interactions.In accord with this hypothesis, methyl pyroglutamate (5a) reacts at a faster rate than N-benzoylglycine methyl ester (1a) in reactions with either N-bromosuccinimide or di-tert-butyl peroxide.Anomalous rates of reaction of N-benzoylproline methyl ester (6a) are rationalized in terms of the regioselectivity of hydrogen atom transfer.Evidence for the mechanisms of reactions of 1a-6a is derived from product studies and by comparison of the relative rates of reactions of 1a-6a with those of the deuteriated amino acid derivatives 1b, 2b, 3b,c, 5b, and 6b,c.
REGIOSELECTIVE FORMATION OF AMIDOCARBOXY-SUBSTITUTED FREE RADICALS
Easton, Christopher J.,Hay, Michael P.,Love, Stephen G.
, p. 265 - 268 (2007/10/02)
Factors affecting the production of amidocarboxy-substituted free radicals have been investigated by examining reactions of derivatives of valine and sarcosine.Variations in the regioselectivity of reactions of these compounds are exemplified by the reactions of N-benzoylvaline methyl ester (4a) and N-benzoylsarcosine methyl ester (12a) with sulphuryl chloride and N-bromosuccinimide.Whereas the reaction of (4a) with sulphuryl chloride involves hydrogen-atom transfer from the β-position of (4a) with subsequent chlorine incorporation to give (4g), in direct contrast the reaction with N-bromosuccinimide proceeds via hydrogen-atom abstraction from the α-position of (4a) and yields the dibromide (4d).N-benzoylsarcosine methyl ester (12a), reacts with N-bromosuccinimide to give the α-bromosarcosine derivative (12b), whereas with sulphuryl chloride the product is the N-chloromethylglycine derivative (12c).These studies indicate that amidocarboxy-substituted radicals such as (3a) and (13) are considerably more stable than the tertiary alkyl radical (1a) and the amidosubstituted radical (14), respectively, but hydrogen-atom transfer reactions may afford the less stable products if electrophilic radicals are involved in the hydrogen-atom abstraction and if there is little development of radical character in the reaction transition state.
Preferential Reactivity of Glycine Residues in Free Radical Reactions of Amino Acid Derivatives
Easton, Christopher J.,Hay, Michael P.
, p. 55 - 57 (2007/10/02)
Reactions of amino acid derivatives, including a novel synthetic procedure for direct and selective functionalisation of glycine derivatives, indicate that the particular reactivity of glycine residues in free radical reactions is due to the stability of
