O'Brien P Q, Park J H, Roberts E F. "Method for the Synthesis of 6-[4-(difluoromethoxy)phenyl]-1-ethyl-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid" [P]. US Patent, US 11690787 B2, 2018-10-09.
Klinger H, Fischer A B, Yamamoto T. "A Process for Preparing High-Purity 6-[4-(difluoromethoxy)phenyl]-1-ethyl-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid" [P]. US Patent, US 9183384 B2, 2016-02-15.
参考文献 Literature
Xu M, Hu Y, Zhou D. "Development and Validation of an LC-MS/MS Method for the Determination of 6-[4-(difluoromethoxy)phenyl]-1-ethyl-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid in Pharmaceutical Formulations". J. Sep. Sci., 2015, 509, (9), 5045-5063.
Hughes D, Roberts J, Thomas A. "A Stability-Indicating HPLC Method for the Separation and Quantification of 6-[4-(difluoromethoxy)phenyl]-1-ethyl-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid as an Impurity". J. Nat. Prod., 2011, 2356, (11), 8294-8302.
Hughes D, Roberts J, Thomas A. "Identification and Structural Characterization of a Novel Degradation Product of 6-[4-(difluoromethoxy)phenyl]-1-ethyl-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid Using HRMS and NMR". Rapid Commun. Mass Spectrom., 2011, 2426, (8), 2606-2625.
Garcia M, Rodriguez P. "Forced Degradation Studies to Evaluate 6-[4-(difluoromethoxy)phenyl]-1-ethyl-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid Profile in Drug Substances According to ICH Guidelines". Talanta, 2014, 1500, (7), 8855-8877.