Complex sentence: A major breakthrough was achieved with the discovery of the first well-tolerated orally available diuretics, the first of which was chlorothiazide, which was derived from the antibiotic sulfanilamide and became available in 1958.
Split into simpler sentences: A major breakthrough was achieved in the 1950's with the discovery of the first well-tolerated orally available diuretics, the first of which was chlorothiazide. This was derived from the antibiotic sulfanilamide and became available in 1958.