Syntheses of Calcium-Selective, Substituted Diaza-Crown Ethers: A Novel, One-Step Formation of Bibracchial Lariat Ethers (BiBLEs)

Article abstract of DOI:10.1021/ja00338a038

Ten N,N-disubstituted derivatives of 4,13-diaza-18-crown-6 (7) have been prepared, three of which exhibit Ca²⁺, over either Na⁺ or K⁺, selectivity.This selectivity has been achieved by utilizing polar, yet uncharged, donor groups such as carbethoxymethyl.Several of these compunds have been prepared by a novel, one-step reaction of aliphatic primary amines with triethylene glycol diiodide.The compounds prepared by this method include examples having the following substituents on nitrogen: benzyl, 2-methoxybenzyl, 2-hydroxyethyl, allyl, 2-furylmethyl, and 2-pyridylmethyl.Isolated yields of pure product for the one-step reaction were in the range 26 +/- 4percent.The corresponding derivatives of 7 having 2-methoxyethyl, carbethoxymethyl, carboxymethyl, and 2-hydroxybenzyl sidearms were also prepared so that cation selectivity as a function of structure could be assessed.Homogeneous stability constants (K_s) for the association between the various ligands and Na⁺, K⁺, and Ca²⁺ were determined and are reported.Significant Ca²⁺ selectivity is achieved for the first time in these systems which should retain a high degree of binding dynamics since the donor groups of primary interest in this study are non-ionizable.