Peptide Coupling between Amino Acids and the Carboxylic Acid of a Functionalized Chlorido-gold(I)-phosphane

We
have developed a protocol for the direct coupling between methyl ester
protected amino acids and the chlorido-gold­(I)-phosphane (p-HOOC­(C6H4)­PPh2)­AuCl.
By applying the EDC·HCl/NHS strategy (EDC·HCl = N-ethyl-N′-(3-(dimethylamino)­propyl)­carbodiimide
hydrochloride, NHS = N-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 1H and 13C 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 (p-Cl­(O)­C­(C6H4)­PPh2)­AuX (X = Cl, Br) were also prepared and characterized.