1. Homopeptides Antibiotics

2. Examples of homopeptide antibiotics Gramicidin A (linear pentadecapeptides) 15 amino acid residues L-val- L-gly-L-ala-D-leu-L-ala- D-val-L-val-D-val- L-try-D-leu-L-try-D-leu-L-try- D-leu-L-try- NH.CH2.CH2.OH. It is produced by Bacillus brevis

3. Cyclic homopeptides Gramicidin S

4. Heteromer peptide antibiotics Polymyxin type: Is the best known heteromer peptide antibiotics produced by Bacillus polymyxa The cyclic portion of their molecules is linked to a tripeptide bearing a fatty acid residue

5. Polymyxin B

6. Peptolides e.g: actinomycin -Consists of hetero-tricyclic chromophore called actinocin, which is responsible for the yellow-red color of the antibiotic linked to - Two pentapeptide lactone rings which are responsible for the solubility of the antibiotics. - Different actinomycin all have the same chromophore but differ only in one or two amino acid sites.

7. Structure of Dactinomycin - Actinomycins were the first antibiotics isolated from the culture broth of Streptomyces. - Have activity against gram-positive and gram-negative bacteria and some fungi. -Dactinomycin and other related antibiotics were subsequently found to have both antineoplastic and antibacterial activities.

8. Dose and adminstration Dactinomycin is administered by intravenous injection. The usual adult daily dose is 10 to 15 μg/kg daily for 5 days repeated at intervals of 4 to 6 weeks. Following intravenous administration, dactinomycin is rapidly bound to tissues. It undergoes minimal biotransformation and is found excreted unchanged in the bile and urine. Dactinomycin does not cross the blood-brain barrier.

9. Actinomycin D