Design and synthesis of fluorescent beta-cyclodextrins for the enantioselective sensing of alpha-amino acids.
Fluorescent monofunctionalized beta-cyclodextrins bearing a copper(II) binding side arm and a dansyl group (CD-NH-AA-CH(2)CH(2)NH-DNS) were designed as enantioselective sensors for unmodified alpha-amino acids. The side arm was derived from amino acid synthons (AA = L- and D-phenylalanine (1 and 2), L- and D-phenylglycine (3 and 4), L-proline (5), and L-cyclohexylglycine (6)) and was chosen in order to contain an amide, an amine, and a sulphonamide group. Enantioselectivity was evaluated by addition of copper(II) complexes of D- or L-valine and D- or L-proline. Chiral discrimination in the fluorescence response was observed in all cases, due to a ligand exchange process. The best conditions for these experiments were found to be the use of an excess (10:1) of the copper complex. The cyclodextrin 4 containing a D-phenylglycine unit was found to be poorly enantioselective, as found for 2, suggesting that the best design can be obtained by using L-amino acids. All L-amino acid containing cyclodextrins showed good enantioselectivities, some of which were higher than those already reported for 1. Other analytes related to amino acids were studied using cyclodextrins 1 and 3. Enantiomers of alpha,alpha-disubstituted amino acids, N-methylamino acids, and amino acid amides were found to be discriminated, while beta-phenylalanine and other molecules bearing a poor anchoring group at the alpha-carbon gave poor enantioselectivity. On the basis of the present data a model for the recognition process, based on the formation of ternary diastereomeric complexes, is proposed.
Corradini
R
R
Dipartimento di Chimica Organica e Industriale, Parma, Italy.
Paganuzzi
C
C
Marchelli
R
R
Pagliari
S
S
Sforza
S
S
Dossena
A
A
Galaverna
G
G
Duchateau
A
A
D000596:Amino Acids / Q000737:chemistry*; D003505:Cyclodextrins / Q000138:chemical synthesis* / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000494:pharmacology*; D005998:Glycine / Q000031:analogs & derivatives / Q000737:chemistry; D008024:Ligands; D008956:Models, Chemical; D010649:Phenylalanine / Q000737:chemistry; D011392:Proline / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D047392:beta-Cyclodextrins
D000596:Amino Acids; D003505:Cyclodextrins; D005456:Fluorescent Dyes; D008024:Ligands; D047392:beta-Cyclodextrins; D010649:Phenylalanine; D011392:Proline; C031215:betadex; D005998:Glycine