Vancomycin (Vancocin) - Red men and Borneo missionaries

Like penicillin and its brethren, vancomycin is an antibiotic that specifically beats up Gram-positive bacteria by disrupting their ability to make a cell wall. However, unlike most drugs, which are rather small (250-450 Da), it is a big (~1450 Da) glycopeptide (made up of sugars and amino acids). It's also notable because it includes two chlorine atoms in its structure, which is a relatively rare occurrence in biologically produced compounds (another biologically produced halocarbon of note is methyl bromide).

Vancomycin was initially isolated by scientists at Eli Lilly from a soil sample that was collected by a missionary converting heathens in the jungles of Borneo. It's nice to see that at least some good came of their work.

One of the nifty and yet entirely terrible things about vancomycin is that is can cause something called "red man" syndrome, which features flushing and a rash (thus the red part), if it is administered too rapidly. This is likely the result of excessive histamine (the stuff that makes you feel yucky when you get allergies such as hay fever) release.