Sugars are organic compounds made of carbon, hydrogen, and oxygen, serving as energy sources and structural materials in living things. In the late 19th century, synthesizing sugars—previously obtainable only from nature—was a major challenge. Fischer invented ways to control the three-dimensional arrangement of atoms during reactions and, for the first time, produced several monosaccharides such as glucose and mannose in test tubes. Using similar strategies, he also synthesized purines (e.g., adenine), the building blocks of nucleic acids. His achievements ushered organic chemistry into an era of “make it and prove it,” laying the groundwork for drug discovery and genetic research.

Fischer employed protecting-group strategies and stepwise reactions to achieve regio- and stereoselective transformations of aldoses and ketoses. His “Fischer method,” which uses phenylhydrazone intermediates, enabled the systematic synthesis of a series of hexoses, including D-glucose, and determination of their stereochemistry via optical rotation measurements. He also combined acid anhydride chemistry with amidation to build the purine ring step by step, producing adenine, guanine, and related bases. These accomplishments led to the concept of stereochemistry embodied in the Fischer projection, later guiding the design of chiral catalysts and glycomedicines. Moreover, mechanistic insights gleaned from sugar and purine synthesis continue to influence nucleic acid chemistry and anticancer drug development.

Fischer established stereospecific epimerization of carbohydrates via phenylhydrazine intermediates, enabling interconversion and structural assignment of D- and L-series sugars. He introduced groundbreaking techniques such as formal 1,2-shift aldose→ketose transformations and oxime cleavage that preserved existing chiral centers. For purine synthesis he designed sequential ring-closure reactions of imidazole and pyrimidine fragments, achieving high yields through N-substitution control under acid catalysis. These contributions provided early guidelines for rational route design and stereochemical analysis in natural-product total synthesis. Modern glycoengineering, nucleic-acid analogue synthesis, and chirality-controlled fine-chemical manufacturing trace their methodological lineage directly to Fischer’s work.