From MonoBINOL to BisBINOL: Expanded Enantioselective Fluorescent Recognition of Amino Acids.

Condensation of the methoxymethyl-protected (R)-3,3'-diformyl-1,1'-bi-2-naphthol (BINOL) with (pyridine-2,6-diylbis(methylene))bis(triphenyl phosphonium)dibromide in the presence of a base followed by deprotection gave a new bisBINOL-based fluorescent probe (R,R)-4. This compound showed expanded substrate scope in the recognition of amino acids with good enantioselective fluorescence responses toward 17 common amino acids. Two diastereomeric imines were synthesized from the condensation of (R,R)-4 with l- and d-valine, and the reactions of these imines with Zn(OAc)2 were investigated by various spectroscopic methods for a better understanding of the enantioselective fluorescent recognition process.

Opposite Enantioselectivity of Mg(II) Versus Zn(II) in the Fluorescent Recognition of Amino Acids.

The addition of Mg2+ is found to turn on the fluorescence response of a molecular probe, 3,3'-diformyl-1,1'-bi-2-naphthol, toward chiral amino acids with high enantioselectivity. It is further found that the enantioselective fluorescence responses of the molecular probe in the presence of Mg2+ toward certain amino acids are the opposite of those in the presence of Zn2+, that is, using Mg2+ with an l-amino acid generates much greater fluorescence enhancement than with the corresponding d-amino acid, but using Zn2+ with the d-amino acid gives much greater fluorescence than with the l-enantiomer. Thus, simply changing the metal cation additive allows the chirality sense of the fluorescence-based molecular recognition to be easily regulated.