Oxazole-containing macrolides

Phorboxazole A (34) is an unusual oxazole-containing macrolide isolated from a sponge Phorbas sp. (18). It is highly antifungal and cytostatic. 

Bacteria other than actinomycetes also produce macrolides. About 100 macrolides have been produced by myxobacteria, and about 40 by other bacteria (Tables IV and V). Myxobacteria produce macrolides with up to 42-membered rings including polyene macrolides, macrodiolides, macrolide lactams, and oxazole-containing macrolides. The other bacteria produce macrolides with up to 26-membered rings including polyene macrolides, macrodiolides, and macrotriolides. 

Fig. 17. Structures of oxazole-containing macrolides produced by bacteria.

A cytotoxic compound, rhizopodin (Fig. 17, 92), is a 19-membered ring mac-rolide whose skeleton contains an oxazole [115]. It is produced by Myxococcus stipitatus. It caused formation of rhizopodia-like structures in animal cells and caused reorganization of the actin cytoskeleton [116]. Chivosazols (chivosazol A, 93) are oxazole-containing macrolides having 31-membered ring tetraene [117], They are produced by S. cellulosum. 

Chattopadhyay, S. K., and Pattenden, G. (1998). Total synthesis of ulapualide A, a novel tris-oxazole containing macrolide from the marine nudibranch Hexabranchus sanguineus. Tetrahedron Lett. 39,6095-6098. 

Several nitrogen-containing macrolides were reported to be obtained from marine sources. Ulapualides A (254) and B (255), possessing unique structures with three contiguous oxazoles, were isolated from the egg... 

Other notable oxazole-containing natural products that have received intense scrutiny include macrolide phorbox-azoles and cyclic peptide diazonamide (Figure 6). The structure of diazonamide has been revised from the original assignments as the result of an elegant total synthesis study <2003AGE4961>. 

A large variety of macrolides have been isolated from natural sources. Macrolides have various ring sizes up to 62 and exhibit various characters spiroacetal-fused macrolides, polyene macrolides, macropolylides, and macrolides containing amino nitrogen, amide nitrogen, oxazole rings, or thiazole rings in their skeletons. 

Theonezolides A-C are cytotoxic macrolides containing an oxazole and a sulfate group in the lactone ring with 37 members the configurations of 23 chiral centers are not yet fully determined (Kobayashi et al, 1993c Kondo, Ishibashi, and Kobayashi, 1994). 

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