Steroidal ureas as enantioselective receptors for an N-acetyl alpha-amino carboxylate.

[reaction: see text] Cholic acid has been elaborated into three regioisomeric bis-carbamoylureas, which have been investigated as enantioselective receptors for N-acetyl phenylalanine. L/D selectivities, peaking at 5:1, have been determined by a sensitive and rapid MS-based extraction method that should be generalizable to related systems.