Method of preparing triterpenoid compound

A method of preparing a triterpenoid compound of formula (I), comprising:

• a step of converting a compound of formula (II) into a compound of formula (III) through sequentially oxidizing an aldehyde group of formula (II) to a carboxyl group by oxidation, and forming an oxygen protecting group on one oxygen atom of the carboxyl group by attaching a protecting group,
• a step of converting the compound of formula (III) into a compound of formula (IV) through epimerization, deprotection and oxidation sequentially, and
• a step of converting the compound of formula (IV) into the compound of formula (I) with deprotecting reaction,
• wherein R1 and R2 independently represent hydrogen or a protecting group selected from the group consisting of C1-C8 alkyl, allyl, C2-C8 alkenyl, C2-C8 alkynyl, (C6-C12)aryl(C1-C8)alkyl, tri(C1-C8)alkylsilyl, di(C1-C8)alkyl(C6-C12)arylsilyl, di(C6-C12)aryl(C1-C8)alkylsilyl, tri(C6-C12)arylsilyl, —C(O)R7, and —C(O)OR8, and each of which is substituted with from 0 to 4 substituents independently selected from the group consisting of hydroxy, cyano, halo, halo(C1-C6) alkyl, halo(C1-C6)alkyloxy, (C1-C6)alkylthio, C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C3-C7 cycloalkyl and C1-C6 alkoxy, wherein R7 and R8 are independently C1-C8 alkyl or C6-C12 aryl,
• wherein R3 is a protecting group selected from the group consisting of C1-C8 alkyl, C2-C8alkenyl, C2-C8 alkynyl, (C6-C12)aryl(C1-C8)alkyl, C6-C12 arylacyl, tri(C1-C8)alkylsilyl, di(C1-C8)alkyl(C6-C12)arylsilyl, di(C6-C12)aryl(C1-C8)alkylsilyl and tri(C6-C12)arylsilyl, and each of which is substituted with from 0 to 4 substituents independently selected from the group consisting of hydroxy, cyano, halo, halo(C1-C6)alkyl, halo(C1-C6)alkyloxy, (C1-C6)alkylthio, C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C3-C7 cycloalkyl and C1-C6 alkoxy.