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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Chemical structures of betulinic acid, betulin, cyclic system skeleton derived from betulinic acid, COCONUT’s fragment with betulinic acid ring skeleton derived from the 24-nor-3α,11α-dihydroxy-lup-20(29)-en-23,28-dioic acid.