Polypeptide antibiotics

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Chapter: Medicinal Chemistry : Antibiotics

The compounds have complex polypeptide structure. These are resistant to animal and plant proteases.


Polypeptide antibiotics

The compounds have complex polypeptide structure. These are resistant to animal and plant proteases. These contain lipid moieties besides amino acids that are not found in peptides of animal and plant origins. Examples: bacitracin, polymycin, amphomycin, tyrothricin, and vancomycin.

 

i. Bacitracin


Properties and uses: Bacitracin is a white hygroscopic powder, soluble in water and alcohol. Bacitracin antibiotic is isolated from the fermentation broth of a culture of tracyl-1 strain of Bacillus subtilis. It is found to be a complex mixture of at least 10 polypeptides (A, A1, B, C, D, E, F1, F2, F3, and G), of which bacitracin A fraction is believed to be the most abundant and the most potent. A divalent ion Zn++ enhances its activity. Although bacitracin is occasionally employed for topical application (often in combination with neomycin, polymycin, and tyrothicin) for the treatment of burns, ulcer, and wounds, it can cause serious necrosis of the kidney tubules; if it is given systematically (i.e. I.V route) an oral administration is not feasible due to its lack of absorption from the GI tract. A variety of gram-positive cocci and bacilli are sensitive to bacitracin. It should be stored in airtight containers due to its hygroscopic nature.

Assay: It is assayed by microbiological method.

 

ii. Polymyxin


Properties and uses: Polymycin sulphate is a white hygroscopic powder, soluble in water, and slightly soluble in ethanol. The polymyxins are cyclic peptides holding a fatty acid side chain. This is a group of relatively simple basic, cationic, detergent peptides that are produced by Bacillus polymyxia. At least, five polymyxins (A, B, C, D, and E) are known, but only polymyxin B and polymyxin E are of clinical utility. Both polymyxin B and polymyxin E (colistin) are mixtures of two components and is used in the treatment of bacterial meningitis, urinary tract infection, burns, wounds, and gastroenteritis. Polymyxin may affect renal tubules and central nervous system (CNS), and because of their nephrotoxicity associated with their systemic use, they are primarily employed to treat topical infections.

Assay: It is assayed by adopting liquid chromatography technique.

 

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