Chiroptical properties of fluorescamine and MDPF condensation compounds with amino acids, amino acid esters and dipeptides

Abstract

2-Methoxy-2,4-diphenyl-3(2H)furanone (MDPF) and 4-phenylspiro[furan 2(3H),1′-phthalan]-3,3′-dione (fluorescamine, Fluram®) react efficiently with primary amino groups to form pyrrolinone type (N-substituted 3,5-diphenyl-5-hydroxy-2-pyrrolin-4-ones) chromophores with UV absorption maxima at 270–280 nm and 380–390 nm regions. In Circular Dichroism (CD) measurements, in ethanol, the synthesized MDPF derivatives of twenty-four L-, and D-amino acids showed three characteristic Cotton effects: first at 400–370 nm, second at 335–315 nm, and third at 290–270 nm displaying in L-series (+)-, (−)-, (+)-, signs. Chromophoric reactions of MDPF and fluorescamine with α-amino acids, their esters and dipeptides can be performed in test tubes. CD spectra are obtained from the resulting reaction mixtures in situ. Investigations showed that in configurational studies of fluorescamine derivatives only the second and third Cotton effects should be used following the empirical rule: in L-series the second CD band at 340–315 nm is negative, whereas the third one at 290–270 nm is positive. For the MDPF condensation compounds with dipeptides, only the sign of the third Cotton effect is reliable. A pyrrolinone chirality rule is proposed. The experimental parameters, solvent, and pH effects on the sign of the Cotton effects are discussed. The main advantage of these chromophoric reactions is their simplicity, reliability and the fact that they can he carried out under mild conditions within minutes.