Calcimycin

Streptomyces chartreusisNRRL 3882 produces the polyether ionophore calcimycin and a variety of analogs, which originate from the same biosynthetic gene cluster. The role of calcimycin and its analogs for the producer is unknown, but calcimycin has strong antibacterial activity. Feeding experiments were performed in chemically defined medium systematically supplemented with proteinogenic amino acids to analyze their individual effects on calcimycin synthesis. In the culture supernatants, in addition to known calcimycin analogs, eight so far unknown analogs were detected using LC-MS/MS. Under most conditions cezomycin was the compound produced in highest amounts. The highest production of calcimycin was detected upon feeding with glutamine. Supplementation of the medium with glutamic acid resulted in a decrease in calcimycin production, and supplementation of other amino acids such as tryptophan, lysine, and valine resulted in the decrease in the synthesis of calcimycin and of the known intermediates of the biosynthetic pathway. We demonstrated that the production of calcimycin and its analogs is strongly dependent on amino acid supply. Utilization of amino acids as precursors and as nitrogen sources seem to critically influence calcimycin synthesis. Even amino acids not serving as direct precursors resulted in a different product profile regarding the stoichiometry of calcimycin analogs. Only slight changes in cultivation conditions can lead to major changes in the metabolic output, which highlights the hidden potential of biosynthetic gene clusters. We emphasize the need to further study the extent of this potential to understand the ecological role of metabolite diversity originating from single biosynthetic gene clusters.

Semisynthesis of two demethylamino A23187 with a methyl group in the 4- or 5-position on the benzene ring were carried out via the cleavage of A23187 oxazole ring and rebuilding of modified benzoxazoles. These compounds were shown to release Ca++ and MG++ from mitochondria and to keep part the antibacterial activity of the natural metabolite.

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.