Advances in ultra‐high load polymer‐supported peptide synthesis with phenolic supports: 2. Use of ‘hydrazinolysis‐hplc’ to check for racemization on c‐terminal amino acid loading and to determine peptide homogeneity during synthesis with selectively labile c‐terminal anchoring linkages

Abstract

2, 4‐Dinitrophenyl‐L‐phenylalanine has been coupled to L‐, D‐, and DL‐amino acid phenyl esters pendant upon a polymer matrix. The esters had been prepared by di‐isopropylcarbodiimide‐mediated condensation, catalyzed by 4‐dimethylaminopyridine. Reverse phase high pressure liquid chromatography (HPLC), using elution solvents consisting of 10 vol.‐% trifluoroacetic acid in water/acetonitrile mixtures, has been used to investigate the 2,4‐dinitrophenyl L‐L and L‐D dipeptide mixtures obtained on hydrazinolysis of each of the dipeptide‐matrix assemblies. ‘Hydrazinolysis‐HPLC’ has been used also to determine intermediate peptide homogeneity in ultra‐high load solid (gel) phase synthesis with Boc amino acids. Cross‐linked poly(N‐[2‐(4‐hydroxyphenyl)ethyl]acrylamide) and two derived polymers incorporating spacer groups have been used as supports. The spacer groups made possible peptide C‐terminal attachment by either HF‐labile benzyl ester or HF‐labile cyclohexyl ester bonds, while still incorporating the phenolic ester linkage susceptible to rapid hydrazinolytic scission.