Betulin-Amino Acid Molecular Hybrids: Synthesis, Structure and Pharmacological Potential

The multidirectional bioactivity of betulin (BN), its widespread occurrence in plants, relatively low toxicity, and acceptable safety profile make it an attractive scaffold for scientific research and potential therapeutic applications. Due to the presence of reactive functional groups (C-3-OH and C-28-OH), BN is an interesting source of new semisynthetic bioactive compounds obtained via structural modifications of the parent backbone. In our study, we designed new BN-amino acid (BNAA) molecular hybrids, aiming to exploit synergistically the properties of both components. We prepared and evaluated a total of 18 new compounds for antitumor activity against the two human cancer cell lines (HCT 116 and MCF-7) and one non-cancerous cell line (NHDF) using a standard Cell Counting Kit-8 (CCK-8) assay. The potential signaling pathways of the obtained BN derivatives were identified based on the measurement of p21 and Bax mRNA expression levels using the RT-qPCR method. We successfully synthesized a series of new BN hybrids by conjugation of the C-3 and C-28 hydroxyl groups via a succinyl (-CO-CH₂-CH₂-CO-, Suc) linker with selected amino acid methyl esters. The structures of all obtained BNAA molecular hybrids were confirmed by spectroscopic analysis (¹H and ¹³C NMR) and high-resolution mass spectrometry (HR-MS). Analysis of the biological activity of the obtained BN derivatives indicated that both the attached amino acids and the substituents at C3 carbon alter BN activity. The obtained BN-amino acid hybrids represent a useful platform for further optimization, especially derivatives (3a, 3e, 3f, and 7d), which showed the most relevant biological profiles in this study.