Basic cholane derivatives. XI: Comparison between acid and basic derivatives

A series of hydroxycholan-24-amines was synthesized; the carboxyl group of starting unconjugated bile acids was transformed into a basic moiety [-NH2, -NHCH3, -N(CH3)2, or -NHCH2C6H5] at C-24. Solubilities, acidities, partition coefficients, and critical micellar concentrations were measured and compared with those of the corresponding bile acids. Because the steroid nucleus in the amines is the same as that in the bile acids, most of the physical-chemical properties of the two compound classes were similar. The amines were more soluble than the corresponding acids; solubilities depended mainly on the number of steroid hydroxyls and, to a lesser extent, on the side chain. Amines are strong bases in water, whereas unconjugated bile acids can be classified as weak acids. N-Benzylamino derivatives have higher log P (P is partition coefficient) values, as a consequence of the bulky hydrophobic substituent; the log P values were almost the same for the amines and the bile acids and depended on the steroid hydroxyls. Amines can self-aggregate at an acidic pH and form cationic micelles; the critical micellar concentrations of amines were of the same order of magnitude as those of bile acids. The introduction of a basic function in the side chain of the cholane moiety increased the antimicrobial activity toward most gram-positive strains.