Steroidal guanidines as enantioselective receptors for N-acyl alpha-amino acids. Part 1. 3 alpha-Guanylated carbamates derived from cholic acid

Receptors 5-11, bearing guanidinium, carbamate and (in some cases) other fu nctional groups, were synthesized from cholic acid 1. These cations were sh own to extract chiral carboxylate anions from aqueous buffer into chlorofor m with significant enantioselectivities. The most successful receptors bore two carbamate substituents and achieved, in the best cases, ratios (L:D) o f 7-10:1 for a series of five N- acetyl alpha -amino acids.