This Thesis introduces a collection of novel synthetic transformations applied to pentacyclic triterpenoids. The design of previously unexplored ionogenic phosphonate derivatives of betulinic, oleanolic and ursolic acids was established, and a scalable, convenient synthetic procedure suitable for PCT derivatives was developed, which afforded a series of differently linked PCT phosphonates. For the first time, synthetic procedures for regioselective palladium-catalysed C-H arylation and azetidination of pentacyclic triterpenoids have been developed. A novel catalytic method has been developed for achieving regioselective C-H amination on the betulin molecular scaffold using a rhodium catalyst. The compound design proposed in this Doctoral Thesis, along with the developed synthetic methods for their preparation, provides preparative access to novel structural motifs previously unavailable in the chemistry of pentacyclic triterpenoids, thereby opening new opportunities for research in medicinal chemistry within this field.