Penicillin is a naturally occurring antibiotic, containing a fused
thiazolidine and beta lactam ring, interfering with the growth or metabolism
of many microorganisms of harmful nature. The substance was first observed by
A. Fleming in 1929, however the chemical structure was determined in 1945 and
the first chemical synthesis was performed by Sheehan only in 1957. Penicillin
has a very low toxicity for mankind. Penicillin being acid labile, is having
restricted therapeutic use. However, Penicillin is the starting compound for
many higher molecular weight derivatives of common therapeutic use like
amoxicillin, ampicillin, cephalexin etc. Two Penicillins are mainly used:
Penicillin G and Penicillin V (phenylacetic acid side chain and phenoxy acetic
acid side chain respectively).
