Ma Cruz Caballero

A macrocyclic receptor for the chiral recognition of hydroxycarboxylates

Good chiral recognition of hydroxycarboxylates such as lactic or mandelic acids has been achieved with a macrocyclic receptor, readily available from a known bis-chromenylurea and a spirobifluorene linker. Resolution of the receptor racemic mixture was carried out taking advantage of its complexing properties with (R)-mandelic acid tetramethylammonium salt on a TLC plate.

A CYCLOHEXANE SPACER FOR PHOSPHATE RECEPTORS

Abstract A cyclohexane tricarboxylic acid is shown to be a good spacer for phosphate guests. The combination of 8-aminochromenone-2-carboxamide groups with the cyclohexane spacer leads to a versatile receptor which sets six hydrogen bonds with either phosphonic acids or phosphates. Large association constants are obtained for this receptor in DMSO and methanol when tetraalkylammonium phosphates are used as guests.

Readily available chromenone receptors for carboxylates

Abstract Several carboxylate group receptors able to bind syn and anti electron lone pairs have been prepared making use of an aminochromenone fragment. Symmetric ureas and sulfuryl amides permit the establishment of four linear hydrogen bonds with the carboxylate. The flat geometry of the sulfuryl amides complexes and the higher acidity of their hydrogens yield the best association constants.

Catalysis of nucleophilic addition of pyrrolidine to 2-(5H)-furanone through chromenone cleft-type receptors

Abstract Several H-bonding receptors are shown to significantly catalyze the nucleophilic addition of pyrrolidine to 2-(5 H )-furanone to a significant extent. Combination of these receptors with a sulfonamide group affords a further increase in the catalytic effect of these molecules.

New enantioselective synthesis of 4-hydroxy-2-oxopyrrolidine-N-acetamide (oxiracetam) from malic acid

Abstract The enantioselective synthesis of oxiracetam has been accomplished from readily available optically active D(+) and L(−) malic acids. The key step of the described method involves the selective reduction of a chiral cyclic diimide; in this way, both enantiomers of 4-hydroxy-2-oxopyrrolidine-N-acetamides were prepared.

A receptor for aromatic acids and amides

A dinitrotoluic residue has been introduced onto an hydrogen bonding aromatic acid receptor to achieve stacking and charge-transfer interactions. This new receptor shows large differences in association constants with aromatic guests in CDCl3 ranging from 1.6 × 103 with isophthalic acid methyl ester to 1.5 × 106 with p-dimethylamino benzoic acid.

Three complexing agents for ureas and formamides

Abstract Three cleft type hydrogen bonding receptors were prepared, with slightly different geometries due to the presence of either methylene, oxygen, or sulfur. All three are able to complex urea, one with the methylene group being the best suited. Benzyl formamide, probably due to its smaller cleft, is better associated to the oxygen compound.

Benzimidazole receptors for carboxylic acids

Combination of an aminobenzimidazole with a chromenone unit provides a receptor for carboxylic acids or primary amides. This host is highly selective for carboxylic acids with Kass above 106 M−1 while amides only bind weakly with association constants in the order of hundreds of M−1.

Improved receptors for dibutylmalonic acid

Abstract New molecular receptors with a dibenz[c,h]acridine skeleton bearing functional groups complementary to dibutylmalonic acid have been developed.

Lactone receptors with catalytic activity

Abstract Three cleft-type receptors have been prepared that associate 2(5H)-furanone in benzene. These complexes show greater reactivity toward pyrrolidine nucleophilic addition than the furanone itself, probably due to stronger hydrogen bonds in going to the transition state.