Antibiotics and Miscellaneous Natural Products

Antibiotics form a large proportion of the remaining natural products which have been examined by X-t y analysis. The crystallographic interest in antibiotics centres both on the ability to form a variety of complexes with different metal ions, and also on the polarization of hydrophobic and hydrophilic properties within the moiecuies, since it has been suggested that both these features may be implicated in the biological functions of such molecules. One antibiotic, monensin (158), has been studied both as the free acid, and also as the silver(i) salt. In the metal complex, the 

The cyclic conformation of the free acid is, however, slightly different from that of the silver salt, since in the former case one side of the cavity is drawn together by two intramolecular hydrogen bonds while the opposite side is dilated by the presence of a hydrogen-bonded water molecule. It is suggested 

The complexing of antibiotic X-206 (160) with silver(i) ions is rather more complicated than the complexing observed either for monensin or for grisorixin. In this case the anion is co-ordinated unsymmetrically to the 

The novel antibiotic boromycin (162) is the first well-defined boron-containing organic compound to have been found in Nature, and is a Boeseken complex of boric add with a macrolide which consists of two 

Yoshioka, T. Aold, H. Goko, K. Nakatsii, T. Noda, H. Sakakibara, T. Take, A. Nagata, J. Abe, T. Wakamiya, T. Shiba, and T. Kaneto, Tetrahedron Letters, 1971, 2043. 

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