Semi-synthesis of A23187 (calcimycin) analogs. III. Modification of benzoxazole ring substituents, ionophorous properties in an organic phase.

Ten semi-synthetic analogs of A23187 (calcimycin), with only the benzoxazole ring substituents modified together with the ionophore X14885A were studied with regard to their calcium and magnesium carrier properties through an organic phase (toluene - butanol, 70:30). The results indicate that the carboxylic group and the oxazolic nitrogen, maintained in the ortho position are essential for the ionophorous properties. Further, the introduction of a substituent in place of the NHCH3 group, producing steric hindrance of the carboxylic group leads to a destabilization of the 2:1 associations with cations.