IDH1 and cancer: The combined absorbance, 1H NMR, and electrochemical assay results reveal that some C3- and C4-substituted 2OG derivatives (e.g. 3-butyl-2OG, 4) are efficient substrates of cancer-associated IDH1/2 variants, i.e. R132H IDH1, R132C/S280F IDH1, R172K IDH2, and R140Q IDH2, affording the corresponding alcohol products (Figs. 2 and S1), in accord with spectroscopic and crystallographic evidence showing their binding at the active site (Figs. 5 and S3).