Selective and facile deacetylation of pentacyclic triterpenoid under methanolic ammonia condition and unambiguous NMR analysis

• Published in: Chinese chemical letters Vol. 31; no. 2; pp. 333 - 336
• Main Authors: Wang, Han, Xu, Renyang, Liang, Shuobin, Ran, Fuxiang, Zhang, Lihe, Zhang, Yongmin, Zhou, Demin, Xiao, Sulong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-02-2020; Department of Pharmacy, The Second Affiliated Hospital, Dalian Medical University, Dalian 116023, China%State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China%Sorbonne Université, Institut Parisien de Chimie Moléculaire, CNRS UMR 8232, 4 place Jussieu, 75005 Paris, France%State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China; State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China; State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China; Elsevier
• Subjects: Chemical Sciences; Deacetylation; Methanolic ammonia; Pentacyclic triterpenoid; Selectivity; Synthesis; Selectivity; Synthesis; Pentacyclic triterpenoid; Deacetylation; Methanolic ammonia
• ISSN: 1001-8417; 1878-5964
• DOI: 10.1016/j.cclet.2019.06.007

Different reactivities of acetyl groups of pentacyclic triterpenoid under methanolic ammonia condition were observed and a plausible route for the deacetylation reaction was proposed.
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The acetyl ester plays an important role for protection of the hydroxyl groups in carbohydrates synthesis. In the present study, we described an efficient deprotection of acetyl group of pentacyclic triterpenoid by using methanolic ammonia in THF solution. Good selectivity for cleaving gal-C2-OAc group of 3β-hydroxy-olean-12-en-28-oic acid 28-N-2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (3) was achieved in the presence of methanolic ammonia within 4 h at low temperature (−60 °C) in a yield of 56%. The reaction disclosed here provides a new method for the synthesis of C2 selective modified carbohydrates, which is more useful than conventional synthesis procedure that usually requires many steps including temporary regioselective protection and deprotection. When the reaction temperature was increased from −60 °C to room temperature, the cleavage of the other three acetyl groups of galactose in an order of C4-OAc > C3-OAc > C6-OAc was observed. Based on this study, a plausible route for the deacetylation reaction has been proposed.