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Bergmann degradation
The Bergmann degradation is a series of chemical reactions designed to remove a single amino acid from the carboxylic acid (C-terminal) end of a peptide. First demonstrated by Max Bergmann in 1934, it is a rarely used method for sequencing peptides.〔 The later developed Edman degradation is an improvement upon the Bergmann degradation, instead cleaving the N-terminal amino acid of peptides to produce a hydantoin containing the desired amino acid.〔〔〔 The Bergmann degradation combines the azide degradation of the Curtius rearrangement with Bergmann and Zervas' carbobenzoxy method, which they designed to occur under relatively mild conditions so as to allow for peptide sequencing.〔 A single round of the Bergmann degradation yields an aldehyde containing the sought after amino acid residue and the remaining fragment of the original peptide in amide form.〔
The acyl azide of a peptide (1) undergoes a Curtius rearrangement in the presence of benzyl alcohol and heat(2) to give a benzyl carbamate (3). The Cbz group of intermediate 3 is removed by hydrogenolysis to give an unsubstituted amide (4) and an aldehyde (5).
==Mechanism==
The Bergmann degradation begins with benzoylation at the alpha-group of a peptide and subsequent conversion to an acyl azide.〔 As in the Curtius rearrangement, the acyl azide, in the presence of benzyl alcohol and heat, rearranges to a highly reactive isocyanate intermediate, releasing nitrogen gas in the process.〔 The isocyanate in turn reacts with benzyl alcohol to form a benzylurethane (also referred to as carboxybenzyl), a compound possessing a carbamate amine protecting group.〔〔 Subsequent removal of the carbamate protecting group is carried out by catalytic hydrogenation in the presence of hydrochloric acid followed by addition to boiling water,〔〔 yielding an unstable intermediate that rapidly rearranges to release carbon dioxide, driving the reaction forward. This leads to further rearrangement and subsequent hydrolysis, ultimately resulting in the formation of an aldehyde bearing the next amino acid residue in the sequencing series and the expulsion of the residual peptide in amide form.〔
A mechanism has been proposed which depicts catalytic hydrogenation of the benzylurethane as a concerted rearrangement that releases carbon dioxide concomitantly with formation of the amide.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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