Just in case my other fact had too much to do with biological testing... I didn't know what isocyanate derivates were. Isocyanates contain the N-C-O functional group, with both links being a double bond to the carbon. Isocyanates are highly reactive, and primarily used to create polyurethanes. In this case, an amine on intermediate 3 is acting as a nucleophile to attack the electrophilic carbon on the isocyanate group, giving the urea derivative.

QUESTION: Here, thioguanine is inserted into the C14 side chain of pleuromutilin. Why was thioguanine chosen over other purine derivatives, like a thioadenine? Would the different hydrogen-bonding pattern of donors and acceptors affect this choice? This could become a complicating factor; we do NOT fully know whether most of the antibacterial activity can be explained by the R side-chain of the purine, the hydrogen-bonding pattern or the thiol chemistry.

The synthesis of the target compounds illustrates a lot of the simple reactions we have learned about in class. In the first step, we see the use of a tosylate to convert an alcohol into a great leaving group, exhibited on the left side of the pleuromutilin. We see the alcohol replaced with a thioester in the second arrow, using reagents we have seen before; triethyl amine in a solvent DMF. In the next set of three arrows, we see the addition of acyl chlorides (or benzoyls) to secondary amines, producing tertiary amides. The penultimate arrow contains another example of this carbonyl chemistry, with another nucleophilic attack on an acyl chloride by a primary amine to create a secondary amide.

FACT: The cytotoxicity of a substance indicates how toxic or damaging to cells that substance is. This toxicity may lead to programmed cell death in the form of apoptosis or uncontrolled cell death (necrosis). Low cytotoxicity is thus favorable in the synthesis of antibiotics, and is often measured by using fluorescent dyes to detect dead cells, measuring metabolic activity, and/or measuring the release of lactate dehydrogenase from plasma membranes injured by the substance.