Valinomycin formula

C.4 Valinomycin is an antibiotic that has been used to treat tuberculosis. Valinomycin contains atoms of carbon, hydrogen, nitrogen, and oxygen in the ratio 9 15 1 3. Its molecules each have 18 oxygen atoms. Write the chemical formula of valinomycin. 

FIGURE 17.18. The ionophore valinomycin. (a) Chemical formula of valinomycin. 

Valinomycin, a cyclic 12-depsipeptide with the sequence cyc/o(LVal-DHyv-DVal-LLac)3, selectively transports K ions across natural and synthetic membranes. The conformations of the K complex and the uncomplexed form of valinomycin are different, but not as markedly different as the com-plexed and uncomplexed forms of antamanide. The molecular formula of valinomycin exhibits a threefold symmetry, which is maintained in the crystalline state for the K complex. If the differences in the side chains are overlooked, the approximate symmetry is raised to An early crystal structure determination of the KAUCI4 complex (Pinkerton et al, 1969) established that the ion is octahedrally coordinated to the carbonyl oxygen atoms of the six ester groups and that the carbonyl oxygen atoms from the six amide groups form hydrogen bonds with the six NH moieties (4 1 type... 

Valinomycin was first synthesized by Shemyakin (Plate 42) and coworkers in 1963 [19]. In their first attempt they tried to confirm the structure as originally published [15], corresponding to an incorrect molecular weight pointing to four instead of six valines per molecule. The discrepancy between the properties of the synthetic and the natural product, finally led to the correct formula of the depsipeptide. 

Figure 1.4. Structural formulae of some ionphores valinomycin (1), enniatin (2), monac-tin (3), dicyclohexyl-18-crown-6 (4), X537A (5) and A23187 (6). Only partial structures of valinomycin and enniatin are given, the sequences are repeated in the other two sectors. For the calcium ionphwes (5 and 6) two molecules of ionphore combine with one of calcium. The methyl ester of A23187is inactive. The affinity of A23187for Ca" is around 10 M ...

In the case of valinomycin and enniatin depsipeptides, the explanation for the structural origins of the more or less pronounced ion selectivities exhibited by these antibiotics was somewhat tentative. However, a detailed discussion of the structural features that lead to metal ion selectivities should be based on a whole set of comparable data on complex structures with various metal ions of different sizes. Fortunately, information of this kind has been provided for the macrote-trolide antibiotics [312-314]. The macrotetrolide antibiotics are 32-membered cyclic tetralactones that can be isolated from various Actinomyces species. Five homologues of the general formula. 

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