Towards cytotoxic derivatives of cafestol

Abstract

This study focuses on the extraction, characterization, and biological evaluation of diterpenes from green coffee beans, specifically, cafestol and kahweol. These compounds, known for their potential health benefits, were isolated via optimized extraction and saponification processes. Separation was achieved using silver nitrate-impregnated silica gel, and structural elucidation was performed through advanced 1D and 2D NMR techniques, including HSQC, HMBC, and (IN)ADEQUATE. Due to kahweol’s instability, the research prioritized cafestol for the synthesis of rhodamine B conjugates. Initial ester-linked conjugates proved unstable, prompting the development of more robust derivatives through amide linkage strategies and further functionalization via acetylation and oxidation reactions. Some oxidation methods led to furan ring cleavage, impacting structural integrity. Selected compounds were tested for cytotoxicity using SRB assays on human tumor cell lines (MCF7, A2780) and non-malignant fibroblasts (NIH 3T3). While the parent diterpenes and many derivatives showed minimal activity, several cafestol–rhodamine B conjugates demonstrated notable cytotoxic effects. Compound 6, in particular, exhibited selective activity against cancer cells with reduced toxicity toward non-malignant cells.