Racemic and (+)-ethyl 2-acetamido-2-carboxy-5-oxohexanoate

Racemic ethyl 2-acetamido-2-carboxy-5-oxohexanoate has been isolated by sin gle hydrolysis of the corresponding diethyl ester and resolved essentially quantitatively by diastereomeric salt formation with (-)-quinine. The (+)-i somer was retrieved from the less-soluble quininium salt. Racemate crystals , (+/-)-1, are monoclinic, space group P2(1)/c, a = 7.609(4)Angstrom, b = 1 6.731(7)Angstrom, c = 10.746(5)Angstrom, beta = 99,83(4); enantiomeric crys tals, (+)-1, are monoclinic, space group P2(1), a = 5.857(2)Angstrom, b = 1 5.282(4)Angstrom, c = 7.618(2)Angstrom, beta = 95.62(2)degrees. Molecular p acking is similar in the two structures; the enantiomer has a 0.7% higher v olume per molecule and the lower fusion temperatures by 3 degreesC. In both structures, carboxylic acids donate hydrogen bonds to the amide carbonyls of adjacent molecules without reciprocation. Amides form three-centered hyd rogen bonds to carboxy oxygen of an intramolecular carboxylic acid group an d to oxygen of a ketone carbonyl in an adjacent molecule.