1. Sci-Finder, Properties of 2,3-dimethoxybenzoic acid, https://origin-scifinder.cas.org/scifinder/view/scifinder/scifinderExplore.jsf, 2021 (accessed 08 July 2021).
2. T. Mikel, S. Gunther, S. Bella, J. Kansas, A. Martin, Benzoic acid conjugate of hydromorphone, benzoic acid derivative conjugate and heteroaryl carboxylic acid conjugate, prodrug thereof, preparation and use method, CN. Pat. Appl. CN 106999487 A, 2017-08-01.
3. T. Mikel, S. Gunther, S. Bella, Benzoic acid conjugate, benzoic acid derivative conjugate and heteroaryl carboxylic acid conjugate of oxycodone, CN. Pat. Appl. CN 106999486 A, 2017-08-01.
4. T. Mikel, S. Gunther, G. Chi, J. Kansas, A. Martin, S. Bella, Benzoic acid conjugate of hydromorphone, benzoic acid derivative conjugate and heteroaryl carboxylic acid conjugate, prodrug thereof, preparation and use method, CN. Pat. Appl. CN 104136031 B, 2016-05-04.
5. H. Yang, Y. Feng, C. Chen, An important intermediate of Berberine, CN. Pat. Appl. CN 107840840 B, 2019-11-12.