Peptide Coupling between Amino Acids and the Carboxylic
Acid of a Functionalized Chlorido-gold(I)-phosphane
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Abstract
We
have developed a protocol for the direct coupling between methyl ester
protected amino acids and the chlorido-gold(I)-phosphane (<i>p</i>-HOOC(C<sub>6</sub>H<sub>4</sub>)PPh<sub>2</sub>)AuCl.
By applying the EDC·HCl/NHS strategy (EDC·HCl = <i>N</i>-ethyl-<i>N</i>′-(3-(dimethylamino)propyl)carbodiimide
hydrochloride, NHS = <i>N</i>-hydroxysuccinimide), the methyl
esters of l-phenylalanine, glycine, l-leucine, l-alanine, and l-methionine are coupled with the carboxylic
acid of the gold complex in moderate to good yields (62–88%).
All amino acid tagged gold complexes were characterized by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy and high-resolution mass spectrometry.
As corroborated by measurement of the angle of optical rotation, no
racemization occurred during the reaction. The molecular structure
of the leucine derivative was determined by single-crystal X-ray diffraction.
In the course of developing an efficient coupling protocol, the acyl
chlorides (<i>p</i>-Cl(O)C(C<sub>6</sub>H<sub>4</sub>)PPh<sub>2</sub>)AuX (X = Cl, Br) were also prepared and characterized
