Enantiomeric recognition of carboxylic anions by a library of neutral receptors derived from α-amino acids and o-phenylenediamine

A library of eight neutral anion receptors consisting of α-amino acid esters attached to o-phenylenediamine by urea groups was synthesized and analysed in terms of capacity for chiral recognition of carboxylates. The NMR titrations revealed that the association constants of complexes consisting of a chiral guest and a chiral host are two orders of magnitude lower than those of achiral partners. Diverse substituents in the receptor structure modify both the affinities and enantioselectivities.

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(2R,2′R)-Dimethyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-methylbutanoate)C20H30N4O6ee = 99%[α]D20 = −2.8 (c 0.5, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)

(2R,2′R)-Diisopropyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-methylbutanoate)C24H38N4O6ee = 99%[α]D20 = −9.1 (c 0.5, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)

(2R,2′R)-Dibutyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-methylbutanoate)C26H42N4O6ee = 99%[α]D20 = +1.6 (c 0.5, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)

(2R,2′R)-Dibenzyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-methylbutanoate)C32H38N4O6ee = 99%[α]D20 = +2.0 (c 0.45, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)

(2R,2′R)-Dimethyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-phenylpropanoate)C28H30N4O6ee = 99%[α]D20 = +7.2 (c 0.45, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)

(2R,2′R)-Diisopropyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-phenylpropanoate)C32H38N4O6ee = 99%[α]D20 = +16.3 (c 0.5, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)

(2R,2′R)-Dibutyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-phenylpropanoate)C34H42N4O6ee = 99%[α]D20 = +4.0 (c 0.5, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)

(2R,2′R)-Dibenzyl 2,2′-(((1,2-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))bis(3-phenylpropanoate)C40H38N4O6ee = 99%[α]D20 = −2.0 (c 0.5, MeCN)Source of chirality: starting materialsAbsolute configuration: (2R,2′R)