| abstract |
A stock solution comprising a compound of formula (I) wherein R 1 together with the carbonyl group to which it is attached is a residue of a carboxylic acid, and NR 2 R 3 , in which R 3 is H or together with R 2 and the N-atom to which they are attached, a 5-membered ring, is a residue of an amino acid, in particular a proteinogenic amino acid, ornithine, gamma-aminobutyric acid or beta alanine, or a 1-amino cycloalkyl carboxylic acid. |