Streptomyces lasaliensis

A mixture of ionophoric polyether antibiotics produced by Streptomyces lasaliensis, from which the components A to E have been separated. L. exert antibacterial and antiviral (HIV) activities, LD50 (mouse p.o.) 146 mg/kg. L. A mp. 110-114°C, (aJo -7.5° (CH3OH), which preferentially forms complexes with divalent cations, is formed biosynthetically by the polyketide pathway from five acetate units, four propionate units, and three butanoate units, the benzene ring arises through cyclization. L. A (Bovatec ) in the form of its sodium salt (Avatec ) is used in fowl breeding as a coccidostatic. 

Lasalocid A, an antibiotic produced by Streptomyces lasaliensis, is unique in that it is a polyether antibiotic and that it contains 3 C-ethyl groups. Studies on the incorporation of sodium [l- C]acetate, sodium [l- C]propionate, and sodium [l- C]butyrate, and examination of the labelled antibiotic with C-NMR, confirmed that the lasalocid A skeleton was derived from 5 acetate, 4 propionate, and 3 butyrate residues. This work provided the first example of C-ethyl groups arising from complete butyrate units. Indeed, all 3 C-ethyl groups arose in this way [219,220]. 

---