Chemistry Reference
In-Depth Information
22
Gramicidins comprise several classes of peptide antibiotics, with gramicidin A,
B, and C referred to collectively as gramicidin D. Gramicidin D consists of linear
pentadecapeptides synthesized by
Bacillus brevis
. On the contrary, gramicidin
S(
24
) is a cyclodecapeptide with the pentapeptides joined head to tail. Two
uncommon amino acids form this structure: ornithine and the D-stereoisomer of
phenylalanine (15).
Polymixins, produced by
Bacillus polymyxa
, are cyclic peptides with a
hydrophobic chain. Polymixins are active against gram-negative bacteria
because of their ability to interact with cell membrane phospholipids. The most
representative antibiotic of this type is polymyxin B, which is a mixture of
polymyxin B1 (
25
)andB2(
26
).
3.2 ANTIFUNGALS
3.2.1 Polyene Antibiotics
Amphotericin B (
27
) is a macrocyclic polyene produced by
Streptomyces nodosus
with a heavily hydroxylated region on the ring opposite to the conjugated system.
