Total Synthesis and Biological Evaluation of 4α,9α,10α-Trihydroxyguaia-11(13)en-12,6α-olide

Abstract

Natural products remain central to therapeutic discovery, with nearly two-thirds of approved small-molecule drugs derived from or inspired by natural scaffolds. In addition to drug discovery, landmark examples of natural products functioning as chemical probes highlight their significant contributions to the field of chemical biology. These scaffolds, which have been refined through evolution, often demonstrate the ability to bind protein targets with strikingly high levels of selectivity. As a result, they not only provide excellent leads for the development of new drugs but also serve as indispensable research tools that allow researchers to interrogate and map biological pathways with precision. Within the diverse motifs found in bioactive molecules, the α-exo-methylene-γ-butyrolactone (AMGBL) is particularly prominent as an electrophilic handle, associated with potent bioactivity and often linked to anticancer effects. This dissertation describes the total synthesis and biological evaluation of 4α,9α,10α-trihydroxyguaia-11(13)en-12,6α-olide (1), a guaianolide-type sesquiterpene lactone containing an AMGBL unit. The natural product was originally isolated from Anvillea garcinii with an undetermined absolute stereochemistry and was reported to display potent antifungal activity. Motivated by its translational potential, we pursued the total synthesis of 1 to provide a reliable and efficient route enabling access to derivatives and chemical probes. Our synthesis adopted a modular approach to construct the guaianolide 5,7,5-tricyclic framework in a stepwise manner, allowing the installation of fragment-level handles for subsequent structure–activity relationship (SAR) studies. We evaluated two complementary routes that differed in the stage at which the tertiary hydroxyl group was installed, while the subsequent ring-construction sequence was conserved. In the epoxide-based route, poor regioselectivity in epoxide opening was observed, which prompted earlier introduction of the hydroxyl group in the alternative strategy. In place of allyl cuprate addition, tandem hydroallylation/cyclization was explored as a more direct approach to the β-allyl γ-lactone intermediate but was limited by issues of reactivity and selectivity. Completion of the synthesis provided access to compound 1 and allowed assignment of its absolute configuration by X-ray crystallography of a key intermediate.Biological evaluation of synthetic 1 showed no significant antifungal activity against Candida albicans under multiple assay conditions. In contrast, high-throughput screening using Profiling Relative Inhibition Simultaneously in Mixtures (PRISM) uncovered notable anticancer activity, including potent growth inhibition of BT12 atypical teratoid/rhabdoid tumor (ATRT) cells and additional activity across diverse cancer models. Taken together, these studies present a robust synthetic approach to the guaianolide scaffold, establish its previously unassigned absolute stereochemistry, and reveal the anticancer activity of 1. The results identify this scaffold as a promising entry point for the development of ATRT-directed therapeutics and provide a foundation for future structure–activity and mechanistic investigations.