Enantioselective Extraction of Dinitrophenyl Amino Acids Mediated by Lipophilic Deoxyguanosine Derivatives: Chiral Discrimination by Self-Assembly
✍ Scribed by Vincenza Andrisano; Giovanni Gottarelli; Stefano Masiero; Erik H. Heijne; Silvia Pieraccini; Gian Piero Spada
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 100 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0044-8249
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✦ Synopsis
The lipophilic deoxyguanosine derivatives 1 are versatile molecules which, depending on to the experimental conditions, undergo different self-assembly patterns. In the presence of K ions, octamers or columnar oligomers are formed based on the G-quartet structure. In these aggregates the quartets constitute the inner part of the structure, whereas the sugars with their lipophilic pendants are on the outside and in contact with the organic solvent. Alkali metal ions act like cement to keep the quartets Q together: If the K :1 molar ratio is 1:8 or lower, the octamer O is the most abundant species observed, while for higher ratios oligomeric or polymeric columnar aggregates P are progressively observed. Lipophilic guanosines and isoguanosines are able to transfer alkali metal ions from water to organic solvents and act as self-assembled ionophores. Apparently the anion is also dragged into the organic phase, and, considering that the cation is inside a chiral cage, it was thought that the anion could be in contact with the chiral surface of the octamer or of the columnar oligomer. Chiral anions could possibly be discriminated by the chiral surface formed by the substituted deoxyribose moieties.
The potassium salts of the N-2,4-dinitrophenyl (DNP) derivatives of amino acids tryptophan (K(DNP-Trp), 2), phenylalanine (K(DNP-Phe), 3), alanine (K(DNP-Ala), 4), isoleucine (K(DNP-Ile), 5), and proline (K(DNP-Pro), 6) were chosen to test the validity of this hypothesis: They are