Doisy employed state-of-the-art techniques such as chromatography and molecular distillation to isolate vitamin K in high purity. Elemental analysis and stepwise hydrogenation demonstrated that the molecule was 3-phytyl-menadione, later called phylloquinone. This precise structural identification opened the way to chemically synthesize vitamin K3 (menadione). The synthetic compound was more stable and could be produced in bulk, greatly aiding surgical hemostasis and supplementation for patients with cholestatic jaundice. Doisy’s achievement transformed the previously “black-box” field of vitamin research into an interdisciplinary arena of organic chemistry and biochemistry. His analytical methods were later applied to the structural elucidation of vitamins E and B12, becoming textbook examples in analytical chemistry.

Doisy extracted alfalfa with ethanol and combined silica-gel chromatography with vacuum molecular distillation to obtain a single yellow oily compound. Elemental analysis established the molecular formula C31H46O2, and redox behavior suggested a 1,4-naphthoquinone core. Ozonolysis and decarboxylation clarified that the side chain was a phytyl group. Doisy further synthesized a methyl-substituted analogue (menadione, K3) and demonstrated that it retained hemostatic activity. This observation initiated discussion on the biological equivalence of natural (K1) and bacterial (K2) forms. Shifts in the UV maximum upon chemical reduction provided a method to monitor hydroquinone formation. Structural information from Doisy’s work later became foundational for studies on vitamin K epoxide reductase substrate specificity and inhibitor development. The research is regarded as pioneering because it treated synthesis, physiological function and pharmacological application of essential lipid-quinones as one continuum.

Targeting only ~0.5 mg kg-1 of phylloquinone in alfalfa, Doisy devised a sequential purification scheme combining Al2O3 adsorption chromatography with molecular distillation, greatly enhancing recovery. He then applied Fieser-type aromatic quinone synthesis to build an analogue library with systematically varied side-chain lengths and analyzed activity correlations in in-vivo clotting assays. The reduced activity of ε-menadione and stereochemical differences among phytyl isomers indicated that membrane permeability and local redox potential were major determinants. Although X-ray structures were unavailable, Doisy used UV, IR and Diels–Alder derivative analysis to assign configurations, setting a benchmark for pre-NMR structural elucidation. His samples were later re-examined in 14C-labeling experiments by Suttie et al., serving as reference compounds in discussions of the stereoelectronic requirements of the carboxylase reaction. The synthetic route he proposed was notable for both yield and cost, allowing direct transition to wartime mass production lines. These chemical contributions bridged mechanistic biochemistry and clinical application, a quality highlighted by the Nobel Committee.