Synthesis and determination of alkali metal binding selectivities of chiral macrocyclic bisamides derived from d-mannitol and l-threitol possessing 2,6-pyridinedicarboxamide subunits
Graphical abstract
Introduction
The chiral recognition and complexation properties of natural receptors have attracted considerable attention due to the design and synthesis of new chiral macrocyclic rings, for example, poliaza1 and polyoxacoronands.2 In the early 1990s, we found that α,ω-diaminoethers reacted under ambient conditions with dimethyl α,ω-dicarboxylates in methanol as a solvent, to afford the macrocyclic bisamides.3 This method was also extensively investigated by using the high-pressure technique.4 The amide group exhibits a dual complexing feature (CO and N or NH), thus meaning amide-based molecular receptors can bind metal5 and ammonium cations,6 neutral organic molecules7 as well as anionic species.8 Moreover, macrocyclic bisamides can be synthesized in their optically active forms and applied to chiral recognition processes.9 Recently, we published10, 11 an effective method for the synthesis of chiral bisamides using α,ω-diamines derived from d-mannitol and l-threitol. In contrast to achiral macrocyclic compounds, the synthesis of their chiral analogs is more difficult due to use of chiral α,ω-diaminoethers as substrates. Three diaminoethers 2–4 have been prepared by us previously.10 Herein, we report a useful synthetic way of preparing their analog 1. All four C2-symmetric α,ω-diaminoethers containing three or five ethylene units were applied for macrocyclization reactions leading to eight chiral bisamides. Electrospray ionization mass spectrometry (ESI-MS) was used to evaluate the alkali metal binding selectivities of these chiral bisamide compounds possessing 2,6-pyridine subunits.
Section snippets
Synthesis
1,2;5,6-Di-O-isopropylidene-d-mannitol and 1,4-di-O-benzyl-l-threitol were selected as inexpensive and convenient sources of chirality. These readily available building blocks were used for the synthesis of numerous chiral coronands.12 The synthesis of d-mannitol-derived α,ω-diaminoethers 2 and 4 containing three and five ethylene units and l-threitol-derived α,ω-diaminoether 3 possessing five ethylene units have been already reported10 (Fig. 1).
The synthesis of l-threitol-derived
Conclusions
As a result of our investigation, a new efficient method of macrocyclization leading to chiral macrocyclic bisamides has been developed. Moreover, we demonstrated that the ESI-MS technique can be successfully used for the preliminary determination of the selectivity of binding of the alkali metal cations by the prepared macrocyclic compounds.
General methods
Melting points were taken on a Köfler-type (Boetius) hot-stage apparatus and are uncorrected. Optical rotations were measured using a Perkin–Elmer 241 polarimeter equipped with a thermally-jacketed 10 cm cell. 1H NMR spectra were recorded with a Varian Gemini 200 (200 MHz) or a Varian Gemini 500 (500 MHz) spectrometer in CDCl3 using tetramethylsilane as an internal standard. 13C NMR spectra were also recorded using a Varian Gemini 200 (50 MHz) or a Varian Gemini 500 (125 MHz) spectrometer. All
Acknowledgments
This work was supported by the State Committee for Scientific Research (Project T09A 087 21). The authors wish to thank the Polish Science Foundation for additional financial support.
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