Thiadiazoles and other 5-Membered Systems

A final type of 5-membered heterocycle to be considered has the 1,3,4-thiadiazole stmcture. It is noted, however, that other less common medicinally useful compounds with 5-membered ring systems exist that have two or three heteroatoms and are not included in this chapter. These include 1,2-oxazoles (isoxazoles), 1,2-thiazoles, 1,3-dithioles, 1,2,5-thiadiazoles, and 1,2,4-oxadiazoles. Examples of drugs based on these systems can be found in the series The Organic Chemistry of Drug Synthesis by Daniel Lednicer.  

SYNTHETIC METHODS FOR SOME PROMINENT HETEROCYCLIC FAMILIES 

Derivatives of indole are connnon in nature. Alkaloids based on indole were discussed in Chapter 3. Indole itself is a colorless solid with a melting point (m. p.) of 52°C, and its derivatives also are solids. Unless a polar group is present, water solubility is low indole itself has the solubility of 1 part in 540 parts of water at 20°C, but it is freely soluble in many organic solvents. Resonance properties and behavior with electrophilic agents were discussed in Chapter 7. 

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